Breaking the Optical Resolution Limit by Near-field Microscopy

Gaining spectroscopic information of a sample by optical image devices (spectrometers, fourier transform spectroscopy) is a daily and important task in science. But it encounters a fundamental problem when used in nanotechnology where sample structures can have dimensions of a few nanometers. Then the optical resolution is limited by diffraction to about half the used wavelength. For the visible spectrum this means a possible resolution of around 300nm but for the infrared (1-50µm) or terahertz (50 - 500µm) regime this allows only µm resolution, far too bad for nanotechnology. Different techniques like AFM, SEM or TEM exist to examine nanoscaled samples but all of them lack to gain directly spectroscopic information. This gap can be closed by near-field microscopy.
The most advanced near-field technique, called s-SNOM for scattering scanning near-field optical microscope, is based onto an AFM in tapping mode. Additionally to an ordinary AFM, a laser is focused onto the cantilever tip apex generating a nano-focus locally illuminating the sample surface. The interaction between the nano-focus and the sample scatters the light which will be modified in amplitude and/ or phase. Scanning the sample and recording for every pixel the scattered light allows obtaining an optical image. Thereby the optical resolution is only determined by the tip apex radius and independent of the illuminating wavelength! This has been demonstrated from the visible to the THz [1]. Routinely, 20nm is achieved but sub 10nm has been demonstrated too. For gaining spectral information the wavelength has to be changed and a new picture to be taken. Comparing the different pictures enables to gain the desired spectral information of the material properties, like the chemical composition, crystal structure or mobile carrier density which is very interesting for the semiconductor industry [2,3]. But also applications in biology are possible as demonstrated with a tobacco virus [4]. Thereby s-SNOM benefits from the advantage that its sample hasn’t to be labeled as it often necessary in biology. Currently, different approaches are underway to replace the tunable laser source by a broadband source to record the spectral information in one measurement attempt. Today, s-SNOM starts to enter several labs of research groups completing their analysis tools for nanotechnology. Hence, keep your eyes open, especially on the nanoscale!

University Groups:
Nanogune, San Sebastian
University of Washington
University of Rochester
ICFO, Barcelona

Company:
Neaspec GmbH

References:
[1] Terahertz Near-Field Nanoscopy of Mobile Carriers in Single Semiconductor Nanodevices, A.J. Huber, Nano Lett., 2008, 8 (11), pp 3766–3770

[2] Simultaneous IR Material Recognition and Conductivity Mapping by Nanoscale Near-Field Microscopy, A.J. Huber, Volume 19 Issue 17, Pages 2209 - 2212

[3] Controlling the near-field oscillations of loaded plasmonic nanoantennas, M. Schnell, Nature Photonics 3, 287 - 291 (2009)

[4] Infrared Spectroscopic Mapping of Single Nanoparticles and Viruses at Nanoscale Resolution, M.Brehm, Nano Lett., 2006, 6 (7), pp 1307–1310

World's fastest camera

The technique, called Serial Time-Encoded Amplified imaging (STEAM), is based on supercontinuum laser pulses (ie., ultrabroad bandwidth pulses). The pulses are propagated to a bidimensional colour matrix by two optical elements. Then, the beam lights the samples: a part of it is reflected by the sample, depending on the dark and light areas of the illuminated point, and the reflections come back through the same way. Since the propagation of the different colours of the pulse is so regular, the range of reflected colours have detailed spatial information about the sample.

According to Bahram Jalali, professor of the University of California and director of this research, "the light points reflects their assigned wavelength, but the dark ones do not, so when the bidimensional rainbow is reflected in the object, the image is copied over the pulse spectrum". The pulse goes back through the optical dispersive system and is converted once more in a single spot, with the image saved in a serie of distributed colours; then, the beam goes through a dispersive fiber (ie., an optical fiber with different velocity limits for each colour). As result, the red part of the spectrum travels at different from the blue, they get separated and finally they arrived at different moments. The signal is then detected by a photodiode and the image is reconstructed. As a result of this technique, an improvement of the speed of images recording is improved (it is the same as the laser repetition rate) with a very high spatial resolution. This could find a wide variety of applications, such as pictures of blood or even the internal structure of the cells.

Teleportation –from Fiction to Reality?

“Beam me up, Scotty”, who hasn’t yet heard this phrase from Star-Trek? Beaming – alias teleportation –is a favored part of many science fiction stories and thus well-known by publics. Probably most of us would like to have a teleportation tool, for saving stressful traveling time, or to experience famous adventures on alien planets… During the last ten years you may have heard that scientists have successfully entered the field of teleportation. But, is it the same teleportation as in Stark Trek? Let us find out what fiction is and what to reality belongs.

In Star Trek, humans and materials are teleported with superluminal speed from one place to another – empty - place. Thereby, teleported is the matter (atoms) or energy and the information in which state the matter is. Mostly, the teleportation process is controlled by a station which can act as receiver or sender. In Science things are a bit more complicated as usual, but the good news is that there exists no physical law which prohibits the teleportation of humans – it is only quite complex to do so. Today, mostly single photons are teleported. Contrary to Star Trek and similar, in reality you can teleport only the information of a state and not its matter or energy. As a consequence, you need at the receiver place already the same type of matter/ energy onto which you can overwrite the state of the particle which you want to teleport. Furthermore, you can´t do it with superluminal velocity, hence no causality violation. The reason is that the particle at the sender and the one at the receiver´s place have to be specially prepared, namely to be entangled together. The entanglement allows the teleportation of the state of a particle with superluminal velocity (Einstein called it “spooky action at a distance”) but to read out this information for further processing, the receiver needs some special information from the sender -after he performed a special action to the particle- which he can get only with not superluminal velocity (by phone etc). Another point is the entanglement process for more complex systems. Photons and ions are routinely entangled, but even simple molecules are very hard to do so. To my knowledge, single Buckminsterfullerene (C60, 60 carbon atoms) are the biggest systems which have been entangled (diameter around 0.7nm). But they haven’t yet been teleported, because as larger an entangled system is, as shorter the duration of the entanglement state. Now, imagine a human body and you will understand why it is quite difficult to teleport us. Hence, “beam me up, Scotty” has to stay for longer time in fiction.

These days, teleportation in the lab with photons is already routinely done. The teleported distance increases continuous and is over 100km for teleportation in free space as in fibers. Furthermore, teleportation using ions (spin) have been demonstrated too. In future, scientists are planning to teleport larger atom complexes (fullerene) up to small bacteria. But until this time has arrived, new techniques have to be developed.

Nevertheless, theoretically humans could be teleported but the question arises, if our body is teleported, will our spirit, our soul be teleported too? Nobody knows.

Video from the teleportation group in Geneva (in french):

Links to teleportation groups:
Geneva, Prof. Gisin
Munich, Prof. Weinfurter
Vienna, Prof. Zeilinger

Pink is not a colour

Have a look at the visible spectrum; you can see many colours: red, blue, green, yellow... but what about pink?

You can not find it in the spectrum... but then, why do we see it? Basically, we could say that the reason is just the difference between wavelength (property of waves) and colour (asigned by the brain).

When the eye perceives just one wavelength (for example 600 nm), our brain identifies the colour of that wavelength (in this example, red).

But, what happens if the eye receives light of more than one wavelength? In this case, the colour interpreted by the brain is usually the sum of the input responses on the retina, i.e. the colour halfway between them... except when the wavelengths come from both ends of the light spectrum at once (i.e. red and violet light).

In this case, the colour halfway would be green (not very representative of the mixture), so the brain simply invents a new colour halfway between them: pink (or magenta, according to its official name).

This post has been adapted from http://www.biotele.com/magenta.html. You can find there a extended version.

Ultra-Fast Dynamics Imaging

Hi, my name is Camilo Ruiz and i am special correspondent sent to the island of Ischia close to Naples Italy for the conference Ultra-Fast Dynamics Imaging celebrated from 30/04 - 03/05 in 2009.

This small workshop was organized by the local group at University of Naples and many of the most important players in the attosecond science were invited to participate. While attosecond is all about precious stability only achieved in well equipped and rich labs, everybody was happy to be invited to the southest part of Europe, where the sun is always there and there is not much of a rush, so we had a perfect combination.



The full program of the conference as well as the book of abstract can be found in the conference web page , i will instead point out some of the topics that i liked more together with some references.

On wednesday 29th, we had several good results. From the University of Frankfurt, Reinhard Dörner presented a paper on "Inteference and electron entanglement in photoionization of H2 and N2", this work is published in Science recently and explore the question of electron localization: When a diatomic molecule absorb a big photon a hole is produce because a k-shell electron is ionized, but then the question is weather the hole created is localized or not. In the case of the hole being localized, the electron hole should hope in 20 fs, later in time an Auger electron should be emitted to fill the hole. If this electron is emitted from one electron only, it should be diffracted but if it is not localized, probably the diffraction will be vanished.

Quotimg the reference: "Whether the core hole is better thought of as being localized or delocalized depends on the direction in which the photoelectron or Auger electron is emitted. Detecting the direction of the photoelectron in the experiment selects between cases in which the transient core hole is best described by a delocalized state of g or u symmetry, and other cases for which it is more appropriate to think of a localized hole. This situation can be described by a coherent superposition of gerade and ungerade states, or alternatively by a superposition of states corresponding to a hole on the left and one on the right."

Certainly there is more to it, as the enviroment breaks this description, but as expected the answer is very quantum like. These are beautiful experiments which don't even need a fast pulse, these are synchrton radiation only. Will time might play a role? Lets find a 419 eV photons in a short pulse to answer that.

The gropu of Garching talked about the new set of experiments in solid interfaces, these are very interesting results, more interesting is the new rout of this leading lab which will concentrate on multiple streaking. As this is something i am also doing i will not mention anything more about it. But try this paper.

These are just two talks, so you can imagine the number of things happening. The next message might be about the new XFELs around the globe.

First light from world's first hard X-ray laser

A couple of days ago, it was published that the the world's first X-ray laser (LCLS) has achieved "first light".

When fine tuning is complete, the LCLS will provide the world's brightest, shortest pulses of laser X-rays for scientific study. As tool for studying the arrangement of atoms in materials, this source will find a wide range of applications in science.

(I love this video, you can really feel the passion of these scientists for their work)

But do you know how it works?

Imagine an accelerated electron bunch which goes through a sinusoidal transverse magnetic field. It will experience a force given by F=q(E+vxB) (Lorentz's force) and thus the trajectory will be sinusoidal too; if the trajectory is a curve, the electrons suffer centripetal acceleration. As it is well known, a charged accelerated particle emits radiation (Lienard-Wiechert). In the Spring-8 website, you can download a program to simulate the radiation emitted by an electron in different magnetic fields.

Due to the electron-radiation interaction, the electrons form electron bunches which emit coherently and the intensity is increased.

These systems are called free electron lasers (FEL); they consist on an accelerator (formed by klystrons which deliver microwave radiation to accelerate the electron and a resonator) and a ondulator (a periodic structure of magnets to produce the sinusoidal transverse magnetic field).

The main problem of these facilities is the size and cost.
Another approach to get X-rays is based on high power lasers: instead of the accelerator, a high-power laser accelerates the electrons which go later through the ondulator. This implementation leads to a reduction of energy and size (in fact, these systems are called Table-Top XFEL).

Prof. Sánchez Ramos awarded Best Invention of the Year

Spanish researcher Professor Celia Sánchez Ramos, has been awarded in Geneva with a prize for the Best Invention of the Year given by the World Intellectual Property Organisation.
Prof. Sánchez Ramos, who is a researcher at the Complutense University in Madrid (UCM), invented a light filter for contact lenses to protect the retina and prevent blindness.
Between 15% and 20% of the light spectrum consists of harmful colours for us (blue and violet), which destroy the retina neurons leading to a degeneration into the macula (DMAE); the fovea, a part of the retina structure, protects us from these colours. Prof. Sánchez Ramos proved that this part of the spectrum could be blocked by inserting a yellow filter into the lenses.
In spite of being yellow, the lens does not vary the perception of the person.
To test the efficiency of the lens, the researcher carried out a experiment with rats exposed to different light types and rabbits which had been previously operated for cataracs.
Nowadays, the UCM is carrying out a clinic trial in 23 hospitals with people operated for cataracs.