1 00:00:08,260 --> 00:00:17,530 Good afternoon, everybody. So this is Michelle Wright from Leiden, and he's the head of the single molecule optics group there. 2 00:00:18,730 --> 00:00:26,770 He's one of the pioneers of single molecule spectroscopy. And we have a joint project with him here at the Clarendon in the mid eighties. 3 00:00:27,010 --> 00:00:32,530 Michelle to the realisation that it should be possible to optically detect a single molecule. 4 00:00:33,040 --> 00:00:38,170 And a few years later, in 1990, he indeed began the first research to detect the first signal from one molecule. 5 00:00:39,550 --> 00:00:46,210 Last year, the Nobel Prize in Chemistry was awarded to Betzig her another for the development of super fluorescence signatures of 6 00:00:46,420 --> 00:00:52,810 fluorescence microscopy and the Nobel Committee description of the scientific background clearly underlined the groundbreaking, 7 00:00:52,860 --> 00:00:56,860 significant Michels experiment as the basis for the super resolution technique. 8 00:01:00,730 --> 00:01:06,730 Today, we should apply single molecule spectroscopy to molecular photo physics, and we are here to talk about that today. 9 00:01:07,390 --> 00:01:12,430 And he uses the technique to explore the spatial and temporal heterogeneity of complex, condensed matter. 10 00:01:13,210 --> 00:01:18,970 He has been honoured recently by the Netherlands National Scientists Society Physical Prize in 2016. 11 00:01:19,860 --> 00:01:28,990 So Michel, with you. Well, good afternoon, everyone, and thank you very much, Robert, for these kind words of introduction. 12 00:01:30,010 --> 00:01:35,770 It's a great pleasure and honour for me to be invited to the high places of physics, not for the first time. 13 00:01:35,770 --> 00:01:41,740 I actually realised it was almost 20 years ago here in Oxford for a golden conference at Queens College. 14 00:01:42,340 --> 00:01:45,520 And so I'm happy to be the advocate. All right. 15 00:01:45,520 --> 00:01:52,760 So this is my title is a bit complicated, but the main thing that you have to remember out of this is a world signal. 16 00:01:52,780 --> 00:01:57,700 So we'll work every single little thing, single molecule, single plasmonic gold. 17 00:01:57,700 --> 00:02:01,210 Nanoparticles, mostly gold. I will explain why in a moment. 18 00:02:01,870 --> 00:02:04,070 In the past, we also work with single nanocrystals. 19 00:02:04,210 --> 00:02:13,030 You can think of single conjugated polymer molecules, for example, etc. This is the current composition of the group six students. 20 00:02:13,030 --> 00:02:17,230 Three of them will finish this year. So it is much less big group than you might imagine. 21 00:02:17,590 --> 00:02:24,780 And two post-docs, mostly because they're all up and. But of course, more people have been involved in the results. 22 00:02:24,780 --> 00:02:28,260 I'm going to explain today and then as the talk proceeds. 23 00:02:29,490 --> 00:02:32,490 All right. So this is a brief outline of the different subjects. 24 00:02:32,820 --> 00:02:39,720 So the audience not so big. So please, I encourage you to stop me any time and ask your questions because of the number of subjects. 25 00:02:40,220 --> 00:02:43,920 I have little relation with one of those except the technique that we use. 26 00:02:44,400 --> 00:02:49,670 And so it's better to ask your questions as a subject just as been discussed. 27 00:02:49,680 --> 00:02:54,710 And if there is no timing of it, we skip all of all the other subjects. 28 00:02:54,960 --> 00:03:01,800 So we're going to look at, first of all, low temperature experiments, because several of you here are involved in interest in these results. 29 00:03:02,250 --> 00:03:08,250 We should use some examples that we can move to Plasmonic Plasmonic and see, first of all, 30 00:03:08,400 --> 00:03:15,930 how to detect little things not by the fluorescence but by other techniques, and then how to use plasmons for that. 31 00:03:16,440 --> 00:03:21,990 And you can have the sensing of just the refractive index of a molecule. 32 00:03:22,600 --> 00:03:25,440 Another small thing, all the fluorescence enhancement, 33 00:03:25,440 --> 00:03:34,070 which are slightly different ways of benefiting from this very high local field that you have around the metallic structure of supersonic structures. 34 00:03:34,730 --> 00:03:41,240 And then as a conclusion of the two of them, to explain a little bit about the nano bubbles that we have been studying recently 35 00:03:42,020 --> 00:03:46,790 around the heated nanoparticles and maybe on some possible applications of this. 36 00:03:48,360 --> 00:03:51,390 All right, so let me introduce our technique, single molecule spectroscopy. 37 00:03:51,410 --> 00:03:52,410 So how does it work? 38 00:03:52,860 --> 00:04:01,080 So what we want to do is look at single small things, single molecules with far field optics, not with scanning problem across copies. 39 00:04:01,440 --> 00:04:08,969 That's too difficult for us, not with near-field optics, which is very similar, but just with four filters. 40 00:04:08,970 --> 00:04:17,610 And then immediately the problem you encounter is the like diffraction limit light being to be focussed down to less than about Micron, 41 00:04:18,000 --> 00:04:22,469 which is you can at best select one cubic micron of sample and one cubic micron. 42 00:04:22,470 --> 00:04:28,980 You have one molecule that you have millions or billions of molecules depending on which molecule sizes you are interested in. 43 00:04:29,580 --> 00:04:33,809 So how to distinguish one molecule among a billion of other molecules? 44 00:04:33,810 --> 00:04:37,310 Well, the way to do that is to make this molecule particular, 45 00:04:37,350 --> 00:04:42,600 to make this molecule specific all to find the right signal that this molecule will give 46 00:04:42,600 --> 00:04:47,130 you and not the rest of the solvent or matrix molecules that you're not interested in. 47 00:04:47,970 --> 00:04:54,510 And one good way of and by no means the only way, but one very efficient way of doing that is to look at fluorescence. 48 00:04:54,510 --> 00:05:02,550 To work with a fluorescence. Confocal microscopy is a very old technique that has been used a lot in the biological sciences in biochemistry. 49 00:05:03,570 --> 00:05:10,899 The principle of this technique is very simple as just a fluorescent six like the same kind of fluorescence you have in this go way you will 50 00:05:10,900 --> 00:05:19,229 like your eye does not detect but excites luminescence of fluorescence from dyes that you will necrosis this and that you can see very, 51 00:05:19,230 --> 00:05:26,879 very well on a dark background. So basically you come with a laser and excitation laser that is focussed by suitable optics, 52 00:05:26,880 --> 00:05:29,400 sometimes used to different optics or excitation connection. 53 00:05:29,730 --> 00:05:40,350 It's much more convenient and easy to use the same optics to excite and collect your focus beam, excite all the molecules in full volume, 54 00:05:40,560 --> 00:05:50,250 and you collect the emitted fluorescence in the inverse pathway and send these fruit and filters to a photon counting detector. 55 00:05:50,910 --> 00:05:58,930 Usually an average photodiode beam is good enough. Photons deployed in the old days when the optics were was not that well advanced. 56 00:06:01,200 --> 00:06:04,680 So it's important at this point to realise how a particular fluorescence, 57 00:06:04,890 --> 00:06:11,130 I mean not every technique allow you to detect one molecule in about a million or billion other molecules. 58 00:06:12,000 --> 00:06:16,710 The reason why this works is that for us it's an electronic, resonant process. 59 00:06:16,740 --> 00:06:21,300 So the molecules that we absorb light will do this much more efficiently. 60 00:06:21,530 --> 00:06:30,270 The levels, its electronic levels are resonant with this light than if they are much shorter waves and much higher energies. 61 00:06:30,930 --> 00:06:39,840 And the rejection coefficient of the technique, that is how much background signal from the wrong molecule is going to reject, 62 00:06:40,320 --> 00:06:48,210 which in the case of fluorescence amounts to about 10 to 12 is so good because for us it is resonant. 63 00:06:48,420 --> 00:06:50,880 So basically you can reject, for instance, 64 00:06:52,320 --> 00:07:00,630 the romance cost of a single and filter out just random scattering to select one for the signal processing of one molecule. 65 00:07:00,990 --> 00:07:04,980 Because romance is not there isn't was for this resonant. 66 00:07:05,640 --> 00:07:10,950 If you would like to do a signal through the detection of signal spectroscopy with infrared absorption, for example, 67 00:07:11,400 --> 00:07:14,670 this would be much more difficult because the bigger the signal to pick on ratio, 68 00:07:14,670 --> 00:07:20,610 the resonance ratio you having infrared absorption is almost a thousand on maybe 10,000 doing the best case. 69 00:07:21,120 --> 00:07:28,349 And this kind of coefficients will never enable you to go to the ten to a nine or 10 to 12, 70 00:07:28,350 --> 00:07:33,090 which is necessary to see a single molecule among a billion of longer markers. 71 00:07:34,020 --> 00:07:38,540 All right. So with this very simple introduction, then we look at the results later in the program, 72 00:07:38,550 --> 00:07:48,510 see other techniques that are either related to fluorescence or completely different from the from that, but all rely on optical resonance. 73 00:07:50,260 --> 00:07:55,839 Okay. So now you have yo your one molecule among a million other molecules and that means you have 74 00:07:55,840 --> 00:08:00,040 to dilute yourself or your first molecules are diluted are extremely low concentration, 75 00:08:00,130 --> 00:08:06,760 familial, nonporous and simple. What you can do to distinguish molecules, just scan your excitation samples and move it around. 76 00:08:07,300 --> 00:08:15,220 Russell Scale. And every time you hit the process of molecule or single process, you go up and see a single and this is coded as a colour. 77 00:08:16,060 --> 00:08:24,490 You see examples of single molecules, you see the size of this box is Diffraction Limited. 78 00:08:24,490 --> 00:08:27,850 That goes to the perspective of your microscope. 79 00:08:28,510 --> 00:08:33,469 And you also can distinguish that several of these spots are not actually homogeneous spots, 80 00:08:33,470 --> 00:08:37,600 but they are lines and that means that the molecules are blinking them is a signal, 81 00:08:37,600 --> 00:08:42,130 even though the laser excitation is continuous, continuous wave looks like continuously. 82 00:08:42,730 --> 00:08:49,330 The first and second wave is not coming. Continuous you can focus on for a while, then it goes off and goes on again because of. 83 00:08:49,810 --> 00:08:55,480 And this on one hand is annoying because of course during the black doc intervals we have no signal. 84 00:08:55,630 --> 00:09:02,470 So we use information on the Morgan. On the other hand, this is very useful and powerful way of identifying seal molecules. 85 00:09:02,470 --> 00:09:10,330 You see, for example, this very bright spot is probably a group of the moon dust, impurity with many, many molecules that all meet at the same time. 86 00:09:10,810 --> 00:09:14,060 And then you have this very, very bright and stable spot, no blinking. 87 00:09:14,060 --> 00:09:18,040 No. On the other hand, on this molecule, for example, this is why can we know? 88 00:09:18,040 --> 00:09:24,660 Because the signal, if we put our laser on the spot, the signal will go on and off in one step, one step blinking. 89 00:09:25,750 --> 00:09:30,820 And that allows this allows us to be sure that this is a single molecule because 90 00:09:31,180 --> 00:09:35,230 two or more molecules contribute to the signal will give intermediate steps. 91 00:09:36,040 --> 00:09:43,149 And also this allows you to get additional information, for example, super resolution, by identifying these such really spots, 92 00:09:43,150 --> 00:09:50,620 being sources, you may find the central spot with much higher accuracy that you can have on the on the points function. 93 00:09:50,620 --> 00:10:02,409 And so this allows you to locate the centroid of the spot much better and to do super resolution because we think that was the Nobel Prize of 2014, 94 00:10:02,410 --> 00:10:05,920 which we wanted to bet to have another for the developing. 95 00:10:05,920 --> 00:10:09,280 This imaging technique is extremely powerful in biological sites. 96 00:10:10,240 --> 00:10:15,610 All right. So remember, this is bringing us up the at the same time, of course, and a blessing. 97 00:10:18,250 --> 00:10:25,329 All right. And there is another way you can distinguish molecules if you can have at your disposal of an additional dimension. 98 00:10:25,330 --> 00:10:32,230 So X, Y, Z, the two components of position in space are obvious ways of distinguishing different molecules. 99 00:10:32,620 --> 00:10:41,080 Another one is frequency, if by any, because we can assign different frequencies, optical frequencies in this case to different molecules. 100 00:10:41,620 --> 00:10:46,990 You just need to scan your excitation frequency to distinguish what the molecules in the spectrum. 101 00:10:47,320 --> 00:10:50,710 That is what is done here. That's actually your original work from 1990. 102 00:10:51,430 --> 00:10:58,690 Well, you have this molecule, fantasy red absorbing molecule in a transparent matrix, part of it in actually absorbing the EUV. 103 00:10:58,710 --> 00:11:05,530 That is completely irrelevant for these experiments. When we scanned the frequency of our laser, we find enhancements. 104 00:11:05,770 --> 00:11:09,070 So this is sort of a frequency image of our sample. 105 00:11:09,340 --> 00:11:12,400 And so a distinguishing molecule of the focus of position X, Y, Z. 106 00:11:12,730 --> 00:11:17,230 We distinguish discrete distinguish them are the function of excitation frequency. 107 00:11:17,230 --> 00:11:21,340 And the line you see here is a lifetime limited line. 108 00:11:21,350 --> 00:11:29,590 Is this an X from at a very low temperature took and the lifetime is actually to the line which is actually lifetime limited. 109 00:11:29,830 --> 00:11:36,540 So that means that the photons which are delivered by these single molecules on the single photon line are absolutely indistinguishable, 110 00:11:36,550 --> 00:11:41,890 you know, just a language just determined by the lifetime of the emission. 111 00:11:43,470 --> 00:11:48,100 All right. So let's discuss some recent expenses we did with these short lines. 112 00:11:48,100 --> 00:11:56,100 And this will probably sound familiar to many of you here, but this would be the first part of the audit. 113 00:11:57,340 --> 00:12:05,560 All right. So one of the first things we we decided to do was to try to use the same molecules to probe how charges are moving and material. 114 00:12:05,920 --> 00:12:10,720 And in order to do that, we decided to take a more eco crystal policy, because at that time, 115 00:12:11,290 --> 00:12:15,880 we could have published very fascinating results, which turn out to be fraud, to be fake. 116 00:12:16,420 --> 00:12:23,530 Later on this, we didn't know the time. And so we wanted to have sort of a local probe of these fascinating facts we've seen on Michael's. 117 00:12:24,880 --> 00:12:35,080 So this child transport that was started actually in 2000, two or three, more recently, the work has been pursued by Nicole for heart. 118 00:12:35,980 --> 00:12:38,500 We're going to finish this later on this year. 119 00:12:38,890 --> 00:12:45,370 And it just shows you an example of the recent results of Nicole on this molecule that some of you know very well is called. 120 00:12:45,380 --> 00:12:55,030 Nobody saw their name, Michael, that resulted in earnings right at around 800 nanometre in this matrix product called benzene. 121 00:12:55,540 --> 00:13:00,550 And what you see here is a single molecule line are very stable, very stable and narrow. 122 00:13:01,000 --> 00:13:07,579 These are the lifetime unit. As for us as well as we can determine and cannot be 100% sure that there is actually 123 00:13:07,580 --> 00:13:13,090 a new spectrum if you look at living in less than 10% or 20% of disclosure. 124 00:13:13,690 --> 00:13:19,510 So it's mostly like the individual least. And what you hear is the saturation examples of these. 125 00:13:19,530 --> 00:13:24,180 It's like it was really very, very nice and stable. And the symbols are easy to manufacture. 126 00:13:25,170 --> 00:13:34,140 Actually, I have to go back a few years now to go to the experiments by these few people who later on move to think of an economy. 127 00:13:34,830 --> 00:13:39,720 And it was hoped by two post-doc Klemens Hoffmann, who was not working for us, 128 00:13:39,730 --> 00:13:45,300 I mean Regensburg in Germany and he was working for some time in in Moscow. 129 00:13:46,140 --> 00:13:53,880 And all this work was done in collaboration with Stockhausen, give it from the Institute of Physics of the Polish Academy of Sciences in Warsaw. 130 00:13:55,610 --> 00:14:00,679 So this is another example of the kind of images you can get in the frequency spectrum. 131 00:14:00,680 --> 00:14:08,989 You see when scanning the laser is working on the delays or you see lines and when you have many lines of code, you can't distinguish them very well. 132 00:14:08,990 --> 00:14:15,650 You can go to the wings or change your sample and take a more diluted sample and the cumulative result of a single molecule. 133 00:14:16,250 --> 00:14:19,729 And we have also done with collaboration with colleagues in France, 134 00:14:19,730 --> 00:14:27,110 some dynamic simulation to understand how this DVT they've been so carrying molecule is embedded in the interesting crystal 135 00:14:27,470 --> 00:14:34,459 and we find these two special embedding sites that we assigned to the spectroscopic sites that you see in the spectrum, 136 00:14:34,460 --> 00:14:38,200 the red side and the main side, their orientations. 137 00:14:38,210 --> 00:14:43,370 Energies Well, good agreement between simulations and experiments. 138 00:14:44,430 --> 00:14:51,030 All right. This just to show the kind of system we are working with, keep in mind that in these experiments, everything is very stable. 139 00:14:51,360 --> 00:14:56,130 The molecule is not wiggling too much. It is a good fit between the molecule shape and the whole. 140 00:14:56,820 --> 00:15:00,540 The work has to live in the to go forward. So we move in the lattice. 141 00:15:01,260 --> 00:15:08,819 And actually, in this case, this DVT is replacing three host molecules with three interesting molecules in most cases, 142 00:15:08,820 --> 00:15:11,420 but it's not the same three for the two sides. 143 00:15:13,230 --> 00:15:21,060 Right now you have to to to to know that interesting is a conjugate molecule and interesting crystals you can propagate you can 144 00:15:21,300 --> 00:15:29,760 conduct electricity by host so you can double this material from gold with the holes and these holes can move in the letters, 145 00:15:30,690 --> 00:15:37,530 even at low temperature by tunnelling. And so what we try to do here is see, well, I assume you can see a single charge. 146 00:15:37,560 --> 00:15:46,560 They don't know who is it w the result and we are not able to see single charges yet, but this is a project we want to continue in the next few years. 147 00:15:47,490 --> 00:15:55,980 All right. So we made such a 3D structure and this field of action, this type structure in which we inject holes of a source, 148 00:15:56,220 --> 00:16:07,020 which is a gold electrode, and we collect the charge with the drain and we can choose from the potential with with a gate record. 149 00:16:09,190 --> 00:16:15,519 And you see an example here. The first thing you see when you're playing affixes to a such a symbol is that we have a dog effect. 150 00:16:15,520 --> 00:16:18,970 So what you see here is the spectrum so far that is your voltage. 151 00:16:19,210 --> 00:16:24,640 You see strikingly different single molecule lines when you vary the voltage either positively or negatively. 152 00:16:24,910 --> 00:16:31,840 You said there is a shift and the shift is roughly quadratic. The reason for that is that this molecule and the site around it are central symmetric. 153 00:16:32,080 --> 00:16:36,730 So it doesn't matter for the frequency whether you blow feeling one other direction, 154 00:16:37,150 --> 00:16:43,000 it should be symmetrical and that's what you see in most cases, or on very small deviations. 155 00:16:43,000 --> 00:16:52,000 But it's a weak perturbation. But in some cases, these molecule for that molecule is my point is not working very well, but it's working. 156 00:16:52,450 --> 00:16:55,750 So this molecule has a very strong slope. This one is even larger. 157 00:16:56,260 --> 00:17:02,920 Some molecules somehow have a minor dog effect that shouldn't be really with the profile Y 158 00:17:03,010 --> 00:17:09,370 because the central symmetry is broken and we're seeing this breaking of symmetry to the charge. 159 00:17:09,370 --> 00:17:17,190 Injection is inside the material. So building holds, injecting the material back in the vicinity of the molecule break the symmetry. 160 00:17:17,230 --> 00:17:20,320 We create a very extremely strong electric field look and feel. 161 00:17:20,770 --> 00:17:25,590 And then our added electric field has a linear component that we observe here. 162 00:17:26,730 --> 00:17:37,139 So this allows us to probe into the way Chelsea's objective was very indirect and difficult compared to Probe Microscopist Kelvin from Microscope, 163 00:17:37,140 --> 00:17:42,450 for example. But it's a very different way of contrasting these films. 164 00:17:44,870 --> 00:17:49,560 Even more interesting to look at the dynamics. And this is a complicated plot. 165 00:17:49,580 --> 00:17:56,000 I didn't want to take this week to complete it. But what I can stress is this is a time at which we stopped. 166 00:17:56,510 --> 00:18:05,389 We went for associate voltage of 50 volt to zero and we saw some molecules feel this change of feel of a very long time. 167 00:18:05,390 --> 00:18:13,580 So the time is minutes. So this about one hour. And what you see is of these molecules relaxing up cells very quickly and then more and more slowly. 168 00:18:13,580 --> 00:18:19,820 So what's happening here, we think, is that the charge distribution is now relaxing then into a new equilibrium. 169 00:18:20,030 --> 00:18:23,839 And there are first processes which are behaving as well as very slow process. 170 00:18:23,840 --> 00:18:28,100 And if we wait even longer, we see that this line is still relaxing very slowly. 171 00:18:28,100 --> 00:18:34,249 So a very non-accidental relaxation, which for us is the reflection of the distribution of turning barriers, 172 00:18:34,250 --> 00:18:37,340 because this is not the material in which holes, 173 00:18:37,730 --> 00:18:45,680 tunnels or barriers, and you have small barriers, first relaxation as well as very broad and high barriers and therefore longer excitation. 174 00:18:46,910 --> 00:18:49,930 You also see some noise. So this is another example. 175 00:18:49,970 --> 00:18:53,990 And here it is not photon noise. It's completely it is correlated. 176 00:18:54,380 --> 00:19:02,330 And you see this noise which tells us something about the way the characteristic in which this the discrete character of this, the distribution. 177 00:19:02,600 --> 00:19:09,710 So by looking more closely of this whole and maybe changing the geometrical symbol, what we hope is to go to see more charges in the future. 178 00:19:11,800 --> 00:19:15,850 Okay. But you can also this is because you see some dynamics. 179 00:19:16,180 --> 00:19:24,730 We ask ourselves the question, what happens if instead of applying a step size to the voltage, we apply a an AC voltage and oscillating voltage. 180 00:19:25,060 --> 00:19:29,920 So how will this slowly selection system of charge respond to an AC field? 181 00:19:31,270 --> 00:19:36,040 And you should do this experiment with changing the density of the voltage. 182 00:19:36,040 --> 00:19:40,180 Would you expect this of the line is just shifting the spectrum with the spectrum 183 00:19:40,420 --> 00:19:43,270 so that it is shifting and you get more intensity of the turning points. 184 00:19:43,270 --> 00:19:48,130 But there is not oscillating dependence of the frequency of the switch of time. 185 00:19:48,520 --> 00:19:54,970 Well, the molecule stays long at the turning points. On the second little curve you get more intensity and you have a split of intensity. 186 00:19:55,240 --> 00:19:57,850 That's the real measurement, exactly as you would expect. 187 00:19:58,420 --> 00:20:03,670 The surprise, however, came when we scanned not the intensity of the voltage, but the frequency of the voltage. 188 00:20:03,670 --> 00:20:10,480 So AC voltage, low frequency typically from some tens of hertz to some hundreds of kilohertz. 189 00:20:11,320 --> 00:20:14,710 And what we saw is this, and most of them expect everything to be very fast. 190 00:20:15,220 --> 00:20:18,460 But what's happened is that in some cases you find these resonances. 191 00:20:18,940 --> 00:20:26,020 So something resonates with the frequency of the voltage and you find resonance is all over the place from that's a megahertz, which is. 192 00:20:26,430 --> 00:20:32,590 But what we could apply with our voltage source all the way down to a few tens of those extremely low frequencies. 193 00:20:33,460 --> 00:20:36,280 So what is the charge injection? That's what we saw. The beam. 194 00:20:37,390 --> 00:20:46,570 This kept us busy several years until we understood that what we see actually here is just all just local oscillator motors, mechanical ventilation. 195 00:20:46,930 --> 00:20:53,140 And when we just happen to have an electrical excitation, which is in resonance with this mechanical mode, 196 00:20:53,320 --> 00:20:58,840 is to localise filaments which are defects on the crystal that we don't really know. 197 00:20:59,680 --> 00:21:04,450 Then we have these resonances and there are many interesting features of the time to go into that. 198 00:21:05,200 --> 00:21:11,019 But this gave us the idea of because we couldn't control these local modes, let us try to simulate them. 199 00:21:11,020 --> 00:21:15,820 So let's try to replace this vocal mode by something that we know how to make and how to control. 200 00:21:16,270 --> 00:21:21,190 And we did this with with a device that many of us know that's just a tuning for. 201 00:21:21,250 --> 00:21:26,229 That's an oscillator which you can drive with an AC voltage in exactly which frequency. 202 00:21:26,230 --> 00:21:33,640 That is how it regulates tune, the amplitude of the oscillation of the problems with the voltage intensity. 203 00:21:34,060 --> 00:21:38,350 And this was published two years ago in physical review letters. 204 00:21:38,830 --> 00:21:42,790 So the work was done by Peter Navarro, that sort of, you know, 205 00:21:43,480 --> 00:21:49,930 and the postdoc you should chance of fiddle is now back in Mexico at the University of Mexico City. 206 00:21:50,530 --> 00:21:54,400 And you she's back in China and an assistant professor position. 207 00:21:56,570 --> 00:22:01,550 Okay. So what they did is just take it during fall that you can drive with an applied voltage 208 00:22:01,670 --> 00:22:07,310 and pasted or attached to it in a single and try to increase always DVT molecules. 209 00:22:08,060 --> 00:22:13,430 And what you expect to see is this when the doing oscillating, there is stress in the crystal. 210 00:22:13,970 --> 00:22:21,230 If the stress is extensive, you get the four level of an increase of frequency, a blue shift of the resonance. 211 00:22:21,230 --> 00:22:22,840 When you press an increase or decrease, 212 00:22:22,970 --> 00:22:29,720 ratchet that you get and you expect therefore the line of the molecule to accompany the tuning forks oscillations in the spectrum. 213 00:22:30,300 --> 00:22:31,520 That's actually what they found. 214 00:22:32,420 --> 00:22:39,380 These are the kind of resonances that you see are very similar to the ones that you observe with localised systems that we didn't know what they were. 215 00:22:39,740 --> 00:22:47,090 So these comparisons are very close. You also see an harmonicity just we saw in the case of these natural two level systems. 216 00:22:47,600 --> 00:22:58,129 And so what we were after in this case is to try to demonstrate how sensitive this nano microphone we call it is not on microphone, 217 00:22:58,130 --> 00:23:04,820 because a micro so small how sensitive it is. So on the numbers we we obtain. 218 00:23:04,820 --> 00:23:08,210 So it's on the off peak or metal based world of hertz. 219 00:23:09,260 --> 00:23:13,860 There's not and it's nothing compared to the to the legal detection sensitivity. 220 00:23:14,210 --> 00:23:22,540 But the big advantage is legal is four km large on like all but our molecules is only a fraction of another rather larger. 221 00:23:23,120 --> 00:23:28,009 And that means we have a detector which is extremely sensitive but also extremely small. 222 00:23:28,010 --> 00:23:35,510 So we can place very close to an acoustic source and still be able to measure very small displacements with a significant accuracy. 223 00:23:36,110 --> 00:23:44,840 So this is, of course, of high relevance to electro optical mechanical devices, when to push them into the quantum limb. 224 00:23:45,230 --> 00:23:50,810 What you see here in this case is a trace of the applied voltage, plus some background. 225 00:23:51,320 --> 00:23:55,630 So this is what unfortunately not the thermal background that you could expect, of course, is there. 226 00:23:55,660 --> 00:23:59,209 But we are still always amazed with the somewhat background which is here is just a 227 00:23:59,210 --> 00:24:03,830 noise from our Christ that is just with both that keeps the vacuum ones increases. 228 00:24:04,160 --> 00:24:07,700 So we are not after that when we expose what do you want to do it better? 229 00:24:07,700 --> 00:24:10,760 And then of course you have to switch off the beam and do better measurements. 230 00:24:12,760 --> 00:24:19,780 All right. So this is for the first priority and seemingly just pixels could go to all any questions or remarks 231 00:24:19,840 --> 00:24:25,720 or about this part before I'll switch to the rest because I would not go back to load material. 232 00:24:26,890 --> 00:24:34,960 So let me switch now. So so far just to stress fluorescence and for good reason too. 233 00:24:35,440 --> 00:24:39,850 But of course it's also very interesting to see other signals and fluorescence and 234 00:24:40,090 --> 00:24:44,260 this is one technique that we have proposed actually is a very old technique, 235 00:24:44,260 --> 00:24:53,739 actually, but we just translated it into a microscopic version back in 2002 already in my cooking module from a group in Moldova, 236 00:24:53,740 --> 00:24:57,550 and this was later improved by Muniz and colleagues. 237 00:24:59,470 --> 00:25:08,680 This technique is just relying on the change of index or refraction around the heated particles of so-called thermo lens. 238 00:25:09,010 --> 00:25:13,390 So if you have if you have a homogeneous medium, you know, there is regular scattering. 239 00:25:13,870 --> 00:25:24,220 But this is very weak effect. If you introduce a small index or a fraction, there will be scattering that was responsible for the for the blue sky. 240 00:25:25,450 --> 00:25:28,840 If you make now this index, that fraction change. 241 00:25:30,650 --> 00:25:35,990 A consequence of a change of temperature. And this you can do by looking at absorbing materials. 242 00:25:36,470 --> 00:25:39,920 You can have something similar to the to the Mirage effect. 243 00:25:40,430 --> 00:25:48,380 If you heat the black surface and a blocking surface in some other, it would be a and phoenix of pressure. 244 00:25:48,710 --> 00:25:55,300 And this will modify the propagation of light rays in the parallel direction to the surface. 245 00:25:55,310 --> 00:26:00,990 Very, very sensitive. So this is basically the technique we use and we use that with these set up. 246 00:26:01,010 --> 00:26:04,040 So the work was done in our group recently by these two people. 247 00:26:05,630 --> 00:26:12,860 And I was working for a field station, you know, in Germany and most of I almost was who was post-doc research before linking 248 00:26:13,070 --> 00:26:19,610 as Rice University and now he's back in Turkey on non scientific position. 249 00:26:21,080 --> 00:26:24,110 So the technique we do is as follows We have two beams. 250 00:26:24,110 --> 00:26:29,540 So this is a crosstalk between two beams that we are exploiting so that Jesus Christ we effect. 251 00:26:29,540 --> 00:26:35,149 It's an equal effect in which we have one beam which is there to be absorbed to heat the particle. 252 00:26:35,150 --> 00:26:40,459 So the particles to the focus of this will be and then we have a probing, 253 00:26:40,460 --> 00:26:45,230 which is the the red beam in this case that we focus almost on the same point experimentally. 254 00:26:45,230 --> 00:26:53,150 It's very hard to achieve exactly the same point. And you should achieve a slightly different focus for the red beam and the for the green, actually. 255 00:26:53,930 --> 00:26:56,120 But this is, you know, just an experimental detail. 256 00:26:56,990 --> 00:27:04,800 And what happens is that the the green beam by hitting the particle is going to modulate through moderate intensity of the agreement, 257 00:27:04,830 --> 00:27:08,040 modulate the index of pressure, and therefore the scatter intensity. 258 00:27:08,060 --> 00:27:18,830 And we bear the signature of this because of scattering in the frames of a scattered field by this index of refraction lens and incoming field. 259 00:27:19,340 --> 00:27:27,379 And this diffraction will give you a signal, which, of course we scale now, like the volume, like the poor rigidity of this. 260 00:27:27,380 --> 00:27:34,160 So it's not like a normal scattering smoke engulfing the square of the the volume, which is important like in radio scattering, 261 00:27:34,520 --> 00:27:43,790 but it's the definitive because there is interference in the frames, accommodating the effect between the incoming field and the sky that we want. 262 00:27:43,790 --> 00:27:48,320 So I don't want to discuss the signal to noise ratio. And this is very interesting that we have no time. 263 00:27:49,070 --> 00:27:54,840 And what you find with this technique is that it's a dark background technique because it's very is not 264 00:27:54,840 --> 00:28:00,950 soft and there is no thermal of scattering because you do modulate the frequency of the motivation. 265 00:28:00,950 --> 00:28:06,290 But it has a very high dynamics. It is a large scale of sensitivity, then in 2 to 3 in the same scale. 266 00:28:06,710 --> 00:28:10,670 And for example, here what we see are 20 nanometre gold on the volumes, 267 00:28:11,000 --> 00:28:16,550 which are the big dots and the same type of five nanometre, which are about 200, 2000 times weaker. 268 00:28:16,880 --> 00:28:22,460 We see them on the on the same scale. So that means that there is a very, very high dynamic range for this technique. 269 00:28:22,790 --> 00:28:32,869 It is not very sensitive. I should stress that the the best sensitivity that you can detect with this technique was in the one house band, 270 00:28:32,870 --> 00:28:41,450 which is about, let's say, another world. So this is nothing compared to the presence which would be distant because it's much less sensitive. 271 00:28:42,020 --> 00:28:45,139 But the bigger the edges that works for anything that absorbs. 272 00:28:45,140 --> 00:28:53,390 So you need anything that emits that caresses, any absorber will give you photons almost because with just the heat and the heat is down. 273 00:28:55,480 --> 00:28:59,809 It's even possible to apply this technique to single molecules, although it was very difficult. 274 00:28:59,810 --> 00:29:08,920 So this was a big achievement. I must offer five years ago or six, and what you see is a single molecules of these, so very special. 275 00:29:08,920 --> 00:29:16,840 They were very photosensitive photo resistant. So we can actually it was very hard to bleach this destroy these molecules. 276 00:29:16,840 --> 00:29:19,870 These were the signals that to use oxygen. 277 00:29:19,870 --> 00:29:23,200 So if you use nitrogen, they are basically for forever. 278 00:29:25,100 --> 00:29:29,810 You can also compare for us and see if you can measure them to appropriate signals. 279 00:29:30,050 --> 00:29:33,770 What you see as the measurements for gold nanoparticles in those fields. 280 00:29:34,190 --> 00:29:40,429 And what you see here is the the ratio of the absorption of the luminescence signal to the appropriate signal. 281 00:29:40,430 --> 00:29:44,450 You can deduce the quantum use of luminescence for the spot, which is extremely small number. 282 00:29:45,020 --> 00:29:47,300 Then to my system to 1027, 283 00:29:47,780 --> 00:29:56,870 but it's independent of size that something that was been known before they examined the York and Feldman in Munich Bay and several measurements. 284 00:29:56,870 --> 00:30:04,070 But this is done on single particles and you see that this quantum is almost not dependent on the size of the particles. 285 00:30:07,160 --> 00:30:12,550 Okay. Though more recently we moved from spherical gold nanoparticles to gold. 286 00:30:12,560 --> 00:30:16,000 None of us. So now this is this. 287 00:30:16,010 --> 00:30:19,700 This appears small to the plasmonic aspect. So we'll have to introduce this. 288 00:30:20,120 --> 00:30:27,109 The subject was introduced in the group. I mentioned them before, so let me first discuss the plasmonic aspect. 289 00:30:27,110 --> 00:30:36,499 So a plasma normally is a magnetic wave that propagates at the interface between it's a metal on an absorbing material and a dielectric. 290 00:30:36,500 --> 00:30:40,850 So typically a wave property at the metal vacuum interface. 291 00:30:42,080 --> 00:30:44,510 However, in the case of a smooth, very small particle, 292 00:30:44,840 --> 00:30:54,170 the plasma is even simpler than this because of course you have to to satisfy this boundary condition the wave is propagating around the particle. 293 00:30:54,710 --> 00:31:01,640 And if the size of the particle is much less than the wavelength of the plasma, then what you expect is that you have a dipole excitation, 294 00:31:01,640 --> 00:31:06,620 so you have positive charge on one side and negative charge on the other side. 295 00:31:06,620 --> 00:31:11,170 So just a dipole excitation, these charges division, 296 00:31:11,180 --> 00:31:16,000 the particle just resembles dipole where you shift the positive charges or rather the 297 00:31:16,010 --> 00:31:20,809 negative charge of the electrons with respect to the immobile ions at optical frequencies, 298 00:31:20,810 --> 00:31:25,700 the ions are much heavier being much heavier than the electrons won't respond. 299 00:31:26,330 --> 00:31:39,350 And therefore we have a dipole. So clearly the frequency will be in the optical domain because the mass of the electrons is set to low. 300 00:31:39,590 --> 00:31:45,890 And basically it's just the frequency of resonance would be a ratio of racial frequencies, 301 00:31:45,910 --> 00:31:51,590 which depends on the Coulomb field within positive and negative charges and the mass the effectiveness of the electrons. 302 00:31:53,780 --> 00:31:59,929 You can also see that this frequency is actually not depending on the number of electrons that are provided. 303 00:31:59,930 --> 00:32:04,880 You can suppose the particles will be small enough to be able to have this dipole excitation. 304 00:32:05,780 --> 00:32:09,020 The size of the particle is not really of any matter. 305 00:32:10,450 --> 00:32:14,500 However, the shape of the particle is if you take known an elongated particle, 306 00:32:15,040 --> 00:32:20,050 you'll see that for a given number of charges of or given mass of the electrons, 307 00:32:20,860 --> 00:32:26,829 the Coulomb field between positive and negative charge can be made arbitrarily weaker and weaker by thinking more and more in 308 00:32:26,830 --> 00:32:34,720 obligated particle to take another way and extremely low becomes negligible before the shock value becomes extremely small. 309 00:32:34,990 --> 00:32:39,130 And that means that you shift the frequency down to more to the right of the need for it. 310 00:32:39,880 --> 00:32:46,150 So these are very nice feature because it allows us now you to consider this by tuning the aspect ratio of the 311 00:32:46,150 --> 00:32:54,190 particles to tune the frequency and to that this frequency to any source or emitter that we care to observe. 312 00:32:54,190 --> 00:33:01,020 So these are a very nice degree of freedom for us to observe plasmonic effects of the frequency that we are interested in. 313 00:33:02,870 --> 00:33:10,189 Okay. Some are very few words of description of of these particles that these team images recalled because they 314 00:33:10,190 --> 00:33:16,250 saw it with the moment in Australia where you see that they are of extremely high lattice qualities, 315 00:33:16,490 --> 00:33:22,620 single crystals and basically can have in two different shapes so that these are the shape we are most interested in. 316 00:33:22,640 --> 00:33:31,120 Single crystals with long axis along one of the one z was your direction of the gold can be 317 00:33:31,130 --> 00:33:37,160 crystal on this other multi twin between the crystals all grown under different conditions. 318 00:33:37,160 --> 00:33:49,340 We usually don't use them. That is important because first of all, the way that the shape of the appearance of this vessel is very well defined. 319 00:33:49,340 --> 00:33:53,150 And also, as you see, that the crystal is of very high quality. 320 00:33:53,690 --> 00:33:58,340 You have very little scattering of the electrons by defects or impurities. 321 00:33:58,790 --> 00:34:03,020 So it means that the plasma installation is of the best possible quality. 322 00:34:03,080 --> 00:34:07,430 It's only four months that will limit the lifetime of the Plasmonic solution. 323 00:34:11,000 --> 00:34:16,670 Okay. So this is an example of the optical spectra of this of these nanorods. 324 00:34:16,670 --> 00:34:22,460 So this is an example you see here, three different nanorods in a T in the image. 325 00:34:22,940 --> 00:34:26,299 And here we see the same area in the optical image. 326 00:34:26,300 --> 00:34:32,300 And those are two spectra, two example spectra. So this spectral and of course strongly polarised along axes. 327 00:34:32,300 --> 00:34:37,610 Remember the two charges of the Ellipse, which of course is strongly polarised on the long axis? 328 00:34:37,610 --> 00:34:44,419 Overall, the perpendicular transverse plasmon is a completely different frequency of the integrity here. 329 00:34:44,420 --> 00:34:48,979 It's much, much weaker and you see that this resonance is also extreme shock. 330 00:34:48,980 --> 00:34:52,639 That means that you will have enhanced interaction with the local field. 331 00:34:52,640 --> 00:34:59,930 So you have very good interaction with the local field, the tip of the rods where the well the charge is. 332 00:35:00,110 --> 00:35:04,429 So it is concentrated charge area is where the field will be. 333 00:35:04,430 --> 00:35:08,120 So the two ends of the lot will be the place where the new field is strongest. 334 00:35:10,490 --> 00:35:13,970 So what to do with that? So one example, this is the work of Peter Islam. 335 00:35:14,930 --> 00:35:22,610 One example is this Plasmonic Plasmonic sensing plus one is sensing that we want to be able to detect a single protein molecule. 336 00:35:23,120 --> 00:35:28,490 And of course there is a trade off too to, to, to strike between having a very small, 337 00:35:29,090 --> 00:35:32,600 very large particle, whereas particle can be measured with a high signal to noise ratio. 338 00:35:32,960 --> 00:35:36,020 However, a molecule will be very small compared to this particle. 339 00:35:36,020 --> 00:35:40,340 So the effect we expect is going to be small together, large, single, with a small variation. 340 00:35:40,550 --> 00:35:44,450 On the other hand, you can go to very small particles, then you have a better ratio. 341 00:35:44,450 --> 00:35:47,990 But the micro is a very big for the basis you can hope to see something. 342 00:35:48,020 --> 00:35:57,079 So we could find a good optimum with these kind of rods which are rather inundated with of about ten nanometre length, about 14 on the metal too. 343 00:35:57,080 --> 00:36:02,090 This gave us a good a good compromise between the two demands. 344 00:36:02,990 --> 00:36:08,960 So what has been done by Peter? This is now assistant professor in the Technical University. 345 00:36:09,380 --> 00:36:16,390 I would mention some of his work at the end and the calculations have been done by a middle fellow who is assistant professor in Elizabeth in both of. 346 00:36:18,090 --> 00:36:26,600 So the idea is very similar to the one you saw before with this acoustic detect of of acoustic waves at low temperature. 347 00:36:26,610 --> 00:36:29,830 But now we're doing that at room temperature with the plasma. 348 00:36:30,330 --> 00:36:35,910 So what we do is put the laser on the length of the plasma frequency. 349 00:36:36,450 --> 00:36:41,129 If a molecule comes and sticks to the plasma and to the to the plasmonic particles, 350 00:36:41,130 --> 00:36:45,750 and we have a shift of the plasma from the dust down to the solid like him. 351 00:36:46,230 --> 00:36:50,670 And if you can measure the, for example, the absorption density, 352 00:36:50,670 --> 00:36:56,940 the force almost equal or the scattering intensity with high accuracy, we see a change of the signal when the particle comes. 353 00:36:58,390 --> 00:37:01,900 And. He's the example of this. 354 00:37:02,140 --> 00:37:10,780 This is the example of a trace that that pit acquired with no protein in the solution so nothing happens is very stable. 355 00:37:11,140 --> 00:37:12,130 Plasmonic trace. 356 00:37:12,760 --> 00:37:20,980 If you have low concentrations, one event, one one group comes in binds and these are traceable several molecules by and sometimes even unbind. 357 00:37:21,610 --> 00:37:24,969 And eventually you get more and more molecules at the end of the world and you can follow this. 358 00:37:24,970 --> 00:37:29,680 So what Peter now is doing is doing the same experiment, not with one rod, 359 00:37:29,680 --> 00:37:36,910 but with several tens of rods, an example of one of these maps with arrays of minerals. 360 00:37:37,570 --> 00:37:43,570 This published in nano letters this year and you can now do these six were not looking one bit in the many tens of 361 00:37:43,570 --> 00:37:52,120 different worlds and see at the same time of many parallel events of binding of protein molecules on these plus one. 362 00:37:54,490 --> 00:37:56,590 Another thing you can do is fluorescence enhancement, 363 00:37:57,730 --> 00:38:04,840 and it's also a nice combination of a medical property for residence with plasmonic enhancement for another world. 364 00:38:05,680 --> 00:38:09,130 This work was done essentially by these two gentlemen. 365 00:38:09,490 --> 00:38:15,080 So I suppose looking good and knowing the group of your conference in Belgium and some 366 00:38:15,120 --> 00:38:21,730 others is back in India and is looking at DeNardo and I think has a very good start there. 367 00:38:23,890 --> 00:38:30,820 All right, so what is done now? We try to adapt our goals down the road to the two day and the day we took this one, 368 00:38:30,820 --> 00:38:35,229 which normally is not a good choice to look at because this molecule does not reverse very efficiently. 369 00:38:35,230 --> 00:38:44,500 The quantum is about a few percent, 2%. So it would be possible to see single molecules, but it's very, very difficult if mean definitely not. 370 00:38:44,860 --> 00:38:47,889 And the other conditions that we you'll see very simple. 371 00:38:47,890 --> 00:38:53,920 But if you use a single nothing wrong that has a spectrum here, that's the yellow shaded spectrum. 372 00:38:54,340 --> 00:39:02,620 Both has the spectrum which overlaps significantly the visitations because of the light and the fluorescent spectrum of the then you see very 373 00:39:02,620 --> 00:39:11,530 strong signals and is shown here you see an example or trace where you see your signal and then suddenly there is a burst of resonance. 374 00:39:11,590 --> 00:39:17,770 So what happens there is we could imagine this diffusing and molecule diffusing entering the near 375 00:39:17,770 --> 00:39:22,530 field and giving this not actually what happens is much too fast on this timescale these seconds you. 376 00:39:22,870 --> 00:39:26,400 So what happens is that molecules come bind to the glass or face. 377 00:39:26,410 --> 00:39:31,870 I should show you the sample. So these molecules are swimming in solution diffusion through the near field. 378 00:39:31,870 --> 00:39:36,280 This is only a few tenths of none of this is very, very small. The different time is extremely short. 379 00:39:36,670 --> 00:39:42,280 But what happens is the more scum stick to the glass and eventually reach or detach sometimes. 380 00:39:42,610 --> 00:39:48,310 And was that molecules are fixed here. There are enough for us as photons for us to observe these bursts. 381 00:39:49,030 --> 00:39:54,610 And this gives us some information on the molecules and which is here for this correlation function. 382 00:39:55,390 --> 00:40:00,700 So we have continued to investigating these kind of signals more and more recently, 383 00:40:00,700 --> 00:40:05,380 this theoretical consideration of what's happened, what's happening there. 384 00:40:05,830 --> 00:40:11,709 So the for instance enhancement photon actually comprises of two components. 385 00:40:11,710 --> 00:40:16,780 There is an excitation enhancement factor and radiative enhancement factors plus 386 00:40:16,780 --> 00:40:20,870 some factors corresponding to the molecule photo physics inside the molecule. 387 00:40:20,870 --> 00:40:22,450 But we have no time to go into. 388 00:40:22,480 --> 00:40:30,790 So in the proper conditions, the enhancements that we can expect for low quantum those is just a product of the excitation enhancement. 389 00:40:30,790 --> 00:40:34,839 Yes, because of course, if you are in a new field, there is a stronger field. 390 00:40:34,840 --> 00:40:38,620 It's more likely to excite the molecule in the near field of your far field. 391 00:40:39,430 --> 00:40:42,700 Not only that, the non world also acts as an antenna. 392 00:40:42,910 --> 00:40:45,610 So it's an antenna for reception but also for emission. 393 00:40:46,030 --> 00:40:52,510 And because the plasma is not too far from the spectrum of light, there is also the radiative enhancement and these two factors encoded. 394 00:40:52,570 --> 00:40:56,560 Not all can sum up or multiply up to something thousand. 395 00:40:57,100 --> 00:41:03,460 That's what we measured, or even 10,000 called. Into theory, we have the proper overlap of spectrum. 396 00:41:04,790 --> 00:41:09,260 So this is something that we think is potentially very interesting in chemistry, 397 00:41:10,370 --> 00:41:15,590 not only to detect dyes with low quantum yields and those that do normally don't see to the single molecule level, 398 00:41:16,310 --> 00:41:22,639 but also some emitters that you normally don't expect to be able to detect at all, like, 399 00:41:22,640 --> 00:41:28,220 for example, bentonite complexes, which may be extremely interesting because of the high stability. 400 00:41:28,610 --> 00:41:32,450 So this is something that we are exploring at the moment in our group. 401 00:41:34,260 --> 00:41:38,559 So let me skip this. No. And I like to finish. 402 00:41:38,560 --> 00:41:41,770 I think I have first you taught me, then this is for you. 403 00:41:42,250 --> 00:41:45,280 So let me try to finish with this new subject. 404 00:41:45,280 --> 00:41:47,800 Actually, we we started two years ago. 405 00:41:49,120 --> 00:41:56,709 I mentioned already in this photo thermal experiments that there is heating and heating and normally you try to avoid it, 406 00:41:56,710 --> 00:42:00,040 especially when we did the optical trapping experiments. 407 00:42:00,880 --> 00:42:04,390 The heating may be a large one. On the other hand, this may be useful. 408 00:42:04,480 --> 00:42:15,879 And what we have been exploring in here is what are the conditions under which a steam bubble or nano bubble can form around the heated part? 409 00:42:15,880 --> 00:42:25,270 But if you really heat seriously the fluid around the particle, if it is in the food may change phase and this has potentially, 410 00:42:25,450 --> 00:42:28,659 you know, to two sides, first of all, a very fundamental side. 411 00:42:28,660 --> 00:42:34,800 So one is how does a phase transition change when you go to smaller and smaller size? 412 00:42:34,810 --> 00:42:38,560 I mean, at some point you hit the somewhat dynamic limit and. 413 00:42:40,040 --> 00:42:43,250 How do you approach it? So this is the face of resistance. 414 00:42:43,820 --> 00:42:49,219 It's a smoother, more continuous when you go to small size. How small the size have to be. 415 00:42:49,220 --> 00:42:53,570 And of course, we are still in the range of sometimes development as opposed to very microscopic. 416 00:42:54,980 --> 00:43:03,560 But it's a first step in the direction that you want to go further, to explore further, to move to this very fundamental question. 417 00:43:04,220 --> 00:43:11,120 On the other hand, there is a very applied side to this problem, and this is in the foot of some of cancer therapy. 418 00:43:11,120 --> 00:43:17,030 There has been a recent publication in Nature Nanotechnology of some some weeks ago, I think, 419 00:43:17,930 --> 00:43:24,740 in which people have measured or proven that by creating another bubbles you can kill cancer cells. 420 00:43:24,810 --> 00:43:33,770 Not only that, you know, but on the metastasising cells that are only by targeting the cancer cells with golden particles. 421 00:43:34,190 --> 00:43:41,510 And this effect can be, as you would expect, I mean, hitting maybe a problem, but hitting with a very few particles is not sufficient. 422 00:43:42,080 --> 00:43:49,100 But you can also use some waves, acoustic shock waves that can be produced by your laser by post later. 423 00:43:49,640 --> 00:43:58,219 So that's the applied site. So so we we are, you know, fundamental physicists also in this and we are interested in in the basic side. 424 00:43:58,220 --> 00:44:02,340 But it's also nice if it can be useful for possibly. All right. 425 00:44:03,000 --> 00:44:06,330 So this this one has been published here a few weeks ago, last year. 426 00:44:07,470 --> 00:44:15,330 It's mostly the work of the how so lady is finishing his thesis now and most of his work has been on this plus one against the wolves. 427 00:44:15,330 --> 00:44:22,890 But he has a successor, Thomas Newlands, who actually was a this of centre here in Oxford and the group of curious companies. 428 00:44:25,300 --> 00:44:28,810 So what happens if you try to boil water in a really small town? 429 00:44:28,810 --> 00:44:33,070 So you know what happens in a normal pen at room pressure when you bury what? 430 00:44:33,070 --> 00:44:38,120 I have to go through 100 stations in order to get bubbles and water, boys. 431 00:44:38,770 --> 00:44:45,430 But if you will. So I think that we have a very small container, actually, that you have to create a bubble which and closes the particle. 432 00:44:46,150 --> 00:44:53,290 And if you look at this picture this you realise that there is such a thing as plus one pressure inside the bubble. 433 00:44:53,950 --> 00:44:59,800 And because the radius of the boat was very small is le plus pressure, which is like one of the radius is very large. 434 00:45:00,220 --> 00:45:04,780 It can easily amount to zero atmospheres and it also know what happens if you 435 00:45:04,780 --> 00:45:09,190 increase the pressure of your boiling water when the body temperature goes up. 436 00:45:09,250 --> 00:45:15,070 That's a pressure cooker. That's what we cook food faster at, high pressure and that room pressure. 437 00:45:15,790 --> 00:45:19,869 That's why you can cook at the top of Mount Everest. All right. 438 00:45:19,870 --> 00:45:27,880 So this is what you expect. And this calculation is drawn from the list tables of the the water properties. 439 00:45:29,110 --> 00:45:32,890 What you see here is that in order to boil water, a smaller and smaller case, 440 00:45:33,130 --> 00:45:39,340 this is the radius of particle 20 down with the foil you go all the way in Stokes 373 up to room pressure. 441 00:45:39,820 --> 00:45:46,930 Now you have to go all the way to 530 or so Kelvin, which is something a 200 something degree. 442 00:45:46,930 --> 00:45:52,750 And if you go small enough, you go above the critical temperature of water, which means that you cannot boiling one. 443 00:45:53,060 --> 00:45:59,560 You go from liquid to gas without any water under normal conditions. 444 00:46:00,310 --> 00:46:10,020 So this is actually a problem I would show you in any minute. This temperature already to about 300 searchers is very high for the surface go that and 445 00:46:10,030 --> 00:46:14,679 so what happens then you go to this temperature goal that I was already able to migrate 446 00:46:14,680 --> 00:46:19,659 on the surface of a particle that's especially bad in the area and the contact between 447 00:46:19,660 --> 00:46:25,570 the particle in the glass because that means that the gold atoms in prone to move, 448 00:46:25,960 --> 00:46:30,040 the particles changing. So the experiments you're going to do are not real reproducible. 449 00:46:30,460 --> 00:46:37,540 That's why we prefer to do these experiments with at least to understand what was going on at least 20 years ago. 450 00:46:38,110 --> 00:46:43,930 So what you see here is the same covers which contain contain both at about 50 degrees Celsius. 451 00:46:44,380 --> 00:46:47,980 And that means that the temperature has much lower. 452 00:46:48,220 --> 00:46:53,230 And in case of water, that means that we can neglect this rearrangement of cold atoms. 453 00:46:53,650 --> 00:47:01,150 And we go to if we look at the the heating power, we can keep the particle for a long, long time without any changes of its properties. 454 00:47:01,720 --> 00:47:07,790 And this is a temperature dependence of the finish of distance. While we are expecting, but also at low power, 455 00:47:07,810 --> 00:47:14,800 you see that the particle temperature is constant inside because the quality of all heat connectivity is very high. 456 00:47:15,370 --> 00:47:26,590 And then you have the standard one of our so we do this on day one of our dependence outside the particle which follows from the Brussels law. 457 00:47:27,630 --> 00:47:34,080 And at some point you hit this curve. And that's the last time when you have a stable water, 458 00:47:34,380 --> 00:47:41,190 liquid water or liquid containing these guys or the particle when you go higher and create a vapour show 459 00:47:41,520 --> 00:47:46,620 in the steady state conditions and you have this jump of temperature and you see that in from this point, 460 00:47:46,800 --> 00:47:53,640 the temperature increases very quickly. This is because the heat conductivity of the steam is very low because it's a gas. 461 00:47:54,840 --> 00:48:01,389 So it also explains, you know, if you hit a bit too much higher than the threshold, you should hit too much lower the temperature. 462 00:48:01,390 --> 00:48:09,870 But it will go up to this point where the particle is prone to change and to change shape and and the contact area is going to evolve. 463 00:48:11,480 --> 00:48:18,530 So we we need to we need to learn how to control the power of the of the beam well enough so that we don't go to this regime. 464 00:48:19,820 --> 00:48:27,140 So this is what an experiment was for to small detection gives users as just a foot or something on the function of of hitting power. 465 00:48:27,350 --> 00:48:31,430 So increase specific and then suddenly something happens. 466 00:48:31,820 --> 00:48:35,810 This is welcome. But this thing is not very political for the reasons I mentioned. 467 00:48:36,170 --> 00:48:42,139 So when we moved pertained we expected to see the same and actually what we did that was not detected with rocking 468 00:48:42,140 --> 00:48:48,890 liquidity for to someone we just Darity plugged in the photodiode signal into the acquisition electronics. 469 00:48:49,490 --> 00:48:55,640 And what we saw is this this is the signal to this the detector current as a function of time. 470 00:48:56,630 --> 00:48:59,810 And the time timescale is very, very short. 471 00:48:59,810 --> 00:49:03,469 This 100 microsecond. And you see this noise is actually not noise. 472 00:49:03,470 --> 00:49:09,380 If you expend blood on the screen, you see this is a succession of very brief pulses. 473 00:49:10,280 --> 00:49:17,180 So what happens there is exactly what you can do in your kitchen when you put your bed of the fire. 474 00:49:17,570 --> 00:49:26,720 We have bubbles, bump, bump, bump up. This explosion of bubbles is explosive boiling, except that this exploding building is extremely fast, 475 00:49:27,080 --> 00:49:32,390 typically one microsecond between two different explosions. The explosion is a very brief event. 476 00:49:32,770 --> 00:49:37,190 You have an integration here. This lasts about some tens of nanoseconds. 477 00:49:37,550 --> 00:49:46,490 That's nearly the resolution of our detector. It's a little bit longer so we can deconstruct somehow and get some information. 478 00:49:46,850 --> 00:49:52,190 But actually, we need a better detector to really see this profile. So this is a very, very first event. 479 00:49:52,940 --> 00:49:54,440 How do we understand that? 480 00:49:54,440 --> 00:50:02,419 So roughly our models, although we need to of course a better surgical modelling that this qualitative explanation I'm going to give you. 481 00:50:02,420 --> 00:50:14,450 So what happens is that when the particle is heating, we get a layer of hot water around the heated particle and with it is first of presentation. 482 00:50:14,450 --> 00:50:18,350 So we go immediately to the gas phase without the nucleation of it. 483 00:50:19,040 --> 00:50:27,700 And as in many first order transitions, you have to go across the transition line before this nucleation event happens. 484 00:50:27,710 --> 00:50:31,430 You have to wait on the thermal fluctuation for this nucleation to happen. 485 00:50:31,790 --> 00:50:38,299 And when this happens, then you have this excess energy stored in hot water that will be able to be restored to the system. 486 00:50:38,300 --> 00:50:45,530 And this is a reduction of very quickly to then to the steady state that it should have accepted. 487 00:50:45,530 --> 00:50:47,299 And you see this, these are unstable. 488 00:50:47,300 --> 00:50:54,379 So this instability is actually not something that that happens as a run away, but it is very actually very periodic. 489 00:50:54,380 --> 00:51:03,250 This a histogram of the times between events. So in this case, very close to half of microseconds with a very small, let's say, a deviation. 490 00:51:03,290 --> 00:51:07,849 So another variation of form from this one, and there is no memory. 491 00:51:07,850 --> 00:51:13,159 So it seems that the system really forgets about the performance problem when you prepare the next one. 492 00:51:13,160 --> 00:51:18,120 So it's completely run it. This, we really have to understand better. 493 00:51:19,530 --> 00:51:24,300 That's the the first to see the first few facts that you can see. 494 00:51:25,290 --> 00:51:31,080 Even more interesting. You can also see that in some cases, especially when you go to lower power, 495 00:51:31,200 --> 00:51:35,370 when the time between experience rather one microsecond instead of half of microsecond, 496 00:51:35,670 --> 00:51:41,640 in some case you see an additional peak that comes in the other and very remarkably if you integrate the signal. 497 00:51:41,850 --> 00:51:49,590 So the second peak is very sharp to them is that the second peak has a very well-defined delay with the original explosion. 498 00:51:51,280 --> 00:51:58,359 So this was really a puzzle for us until we realised, we realised that of course there are some ways released on these explosions. 499 00:51:58,360 --> 00:52:01,330 It is a very violent process and there risk transfer. 500 00:52:02,740 --> 00:52:11,110 It's a dynamic transfer to a shock wave of your presidential waggle or an acoustic wave that propagates around the particle. 501 00:52:11,110 --> 00:52:19,750 As soon as the explosion takes rates and the sound waves can reflect, reflect on this interface, actually, that's the small structure you see there. 502 00:52:20,830 --> 00:52:26,379 You see this little bump here that's exactly at the distance of the time delay that 503 00:52:26,380 --> 00:52:31,600 you expect for propagation through the glass slide in which the focus is resting. 504 00:52:31,870 --> 00:52:39,430 But the addition blast slider is this emotion oil. And we know the thickness because this is just a built in property of the objective. 505 00:52:39,730 --> 00:52:47,730 And then the other from this which is a heavy glass, which is a massive plus and this there can be reflections here. 506 00:52:48,250 --> 00:52:50,319 And what you see here is just the reflection. 507 00:52:50,320 --> 00:52:57,520 This red arrow is just a reflection of some weight on this area, on this interface between the oil and the glass. 508 00:52:57,940 --> 00:53:05,080 And sometimes you can even see the second reflection, which corresponds to a double reflection in this oil. 509 00:53:05,440 --> 00:53:12,820 And so, again, this shows that it is possible in this way to release film, which is the material. 510 00:53:13,180 --> 00:53:17,860 And the next thing we like to do is not only to release on the waves, but also to detect them. 511 00:53:18,370 --> 00:53:24,520 So you can imagine this bubble, if we can maintain these bubbles, can disturb the bubble in a steady state, not exploding, but stable. 512 00:53:25,060 --> 00:53:31,299 And we can do that. Then this compressible system will be very sensitive to changes of the external pressure. 513 00:53:31,300 --> 00:53:39,880 So we can use this as a game, as a micro or nano microphone or able to translate or to to try and use an optical signal. 514 00:53:40,780 --> 00:53:48,559 So in the acoustic signal into an optical signal. And so you can hope I mean, dream that you could do, for example, 515 00:53:48,560 --> 00:53:58,030 an experiment by using these particles of small microphones and detecting this way, you know, the sun, but could provide to a body, for example. 516 00:54:00,090 --> 00:54:07,470 All right. So with this, I think I came to my conclusion and in a very nutshell, so we've seen it's one of the low temperature. 517 00:54:07,500 --> 00:54:11,760 We benefit from this very narrow, very sharp rise. 518 00:54:12,120 --> 00:54:20,040 And this we want to continue in the future. And Plasmonic properties are extremely interesting for a whole range of experiments I just mentioned here, 519 00:54:20,040 --> 00:54:23,059 the experiments we did with the Nanorods, they have the advantage of that. 520 00:54:23,060 --> 00:54:25,440 We can make ourselves the Nanorods. Of course, 521 00:54:25,440 --> 00:54:31,740 the variety of plasmonic particles is huge and you can even imagine much larger enhancements with different 522 00:54:32,100 --> 00:54:39,360 assemblies of nanorods or even more sophisticated structures like my husband in London or many other colleagues. 523 00:54:39,750 --> 00:54:45,510 So there is indeed a lot to do with combining plasmonic structure of metal particles, 524 00:54:45,960 --> 00:54:52,500 and these are graphically made structures with molecules and small emitters. 525 00:54:53,100 --> 00:54:55,290 So with this would like to thank you for your attention.