Nanocrystals

2023

MIPT scientists have determined the optimal set of tellurium sources for quantum dot synthesis

Researchers from MIPT and IONH RAS have proposed their own approach to selecting starting materials with optimal tellurium reactivity for nanoparticle synthesis. This will help experimental scientists choose the optimal reagents for colloidal quantum dots, which are used in the manufacture of solar panels, televisions and food quality control systems. The results of the study are published in the journal Nano-structures & Nano-objects. This was announced on August 31, 2023 by representatives of the Moscow Institute of Physics and Technology.

As reported, tellurium is a semimetal actively used in solar power and in the production of crystals, including nanoscale crystals, the so-called colloidal quantum dots, the physical properties of which (the frequency of absorbed or emitted electromagnetic waves) depend on their size. This extends the range of their use in application development. Quantum dots with absorption in the middle infrared range can be obtained for telluride nanocrystals, that is, tellurium compounds with metals, primarily mercury and lead tellurides. This opens up additional possibilities for applications of quantum dots in transport security systems, in security systems and thermography.

As a rule, the synthesis of colloidal quantum dots of tellurides is carried out by mixing two reagents containing tellurium and the desired metal. A common difficulty in carrying out synthesis is the temperature regime of interaction of starting materials. The synthesis temperature depends on the set of reagents used and the range is extremely small.

As of August 2023, one reagent dominates the synthesis of tellurium nanocrystals - this is a solution of tellurium in trioctylphosphine. It has been known for more than thirty years, but only research conducted by our laboratory made it possible to understand its nature. We obtained a series of phosphintellurides and examined them using NMR spectroscopy as well as quantum chemistry. The obtained data made it possible to determine their reactivity. spoke about the study Ivan Shuklov, Deputy Head of the Laboratory of Photonics of Quantum-Dimensional Structures of MIPT

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Knowledge of reactivity allowed scientists to obtain an optimal tellurium reagent, thanks to which it is possible to expand the list of metals for obtaining nanoparticles. Scientists synthesized telluride nanocrystals of cadmium, lead, mercury and zinc using a tellurium precursor that had never been used before.

In nanocrystal syntheses, it is important to have reagents with suitable reactivity and thus control the conditions of the syntheses in order to be able to carry out reactions at lower or higher temperatures for each particular metal. added Ivan Shuklov

Each metal has its own reactivity, which determines how easily it reacts with the precursor (starting material). For example, silver allows synthesis at room temperature, lead at 150 degrees, and cadmium may require over 300 degrees. Accordingly, the ability to manipulate the reactivity of the precursor is the ability to influence the synthesis temperature. If it is too high or low, the synthesis is unproductive. For example, at a low temperature, optimal crystalline points will not come out. Ideally, it is better to connect nanoparticles at a temperature of 100-200 degrees, and the correct selection of sources allows you to fit into this interval for any metal. Thus, depending on the reactivity of the sources, it is possible to select the combination "metal + precursor."

In our study, we developed a reagent - tricyclohexylphosphine telluride. It has no drawbacks to the standard trioctylphosphine-based starting material, as our reagent is free of secondary phosphine impurities. Thus, the results of syntheses with it are more predictable. In addition, the sources of Russian production, unlike trioctyl phosphine, which is especially important for modern industry. commented Alaa Alddin Mardini, Associate Researcher, MIPT Quantum Photosensorics Laboratory

The work was carried out with the support of the Ministry of Science and Higher Education of the Russian Federation.

In Russia, created a nanoscale fiber for photonic computers of the future

In Russia, created a nanoscale fiber for computers of the future. This project was told at the beginning of July 2023 at the Moscow Institute of Physics and Technology.

A group of scientists from Moscow and St. Petersburg investigated the optical properties of gallium phosphide nanowires and showed that complex optical elements for integrated circuits can be made from these crystals.

Physicists have created nanoscale fiber for computers of the future

According to the company, the performance of computers and smartphones directly depends on the number of transistors that can be fitted to their chip. For example, modern laptops contain several tens of billions of transistors. Every year the size of the electronic components decreases, but the developers are already close to the limit when quantum effects will interfere with the operation of processors. In addition, the use of electrons to transmit and process information inevitably leads to the release of heat in metal buses. Therefore, scientists are looking for alternative ways to improve computer performance. One of these directions is optical integrated circuits, in which information is transmitted using light. Photons interact much weaker with the conductor, excluding the heating of devices. Optical signals have already proven themselves to transmit data in fiber, but on nanoscales, otherwise on a chip, there are no ready-made solutions yet. Scientists from MIPT select optimal materials suitable for creating optical nanodevices. Such materials should transmit visible light (or even better ultraviolet light) and have low optical losses.

As one of such promising materials of physics from the Center for Photonics and Two-Dimensional Materials, MIPT and colleagues studied gallium phosphide. Scientists made waveguides from its nanocrystals, determined the minimum allowable diameter at which they would transmit light, and created a splitter from two crystals.

For the experiment, scientists grew filiform nanocrystals of gallium phosphide of different diameters on a silicon substrate. Such "threads" can be used as a waveguide - the channel of the light transmitting, in fact, the simplest optical element.

We show that using filiform nanocrystals, it is possible to make 100 nanometer waveguides - this is an important step to reduce the size of optical elements. By changing the geometry of the crystals, you can filter the light that the waveguide transmits, and by varying their chemical composition, you can create nanoscale light sources for systems on the chip. told Alexey Bolshakov, head of the laboratory of functional nanomaterials MIPT

In the first part of the experiment, physicists investigated the effect of the diameter of the waveguide on its light-conducting properties. A laser beam was focused on one end of a nanocrystal of known diameter and looked through an optical microscope whether light was illuminated at the other end. The minimum crystal diameter at which light passed through the waveguide was dependent on the wavelength of the laser. The longer the wavelength, the wider the waveguide must be.

The scientists then investigated the transmittance of the waveguide in more detail. To do this, they injected broad-band laser radiation (from visible to near infrared) into one end of the nanowire and measured the spectrum on the other. The output spectrum was dependent on its diameter. Certain wires showed the occurrence of peaks in the transmission spectra. This means that gallium phosphide waveguides exhibit resonant properties - with their help it is possible to amplify light of a certain frequency, achieving signal filtration or laser radiation generation at the nanoscale.

In the last part of the work, the researchers created another element of the optical circuit - a splitter. They curved two nanowires and connected to each other in the form of the letter "X." By illuminating the tip of one of them, physicists received a light signal at the ends of both nanocrystals, however, of different frequencies, that is, light flowed from one waveguide to the other. By connecting several such nanowires to each other, more complex optical elements necessary for optical circuitry can be created. Elasticity and retention of bending on the substrate is a special characteristic of gallium phosphide nanocrystals. Scientists have shown that even with a strong bend, the material does not collapse, retains its shape and transmits light.

During the experiments, the material demonstrated excellent optical characteristics: low losses, visible and infrared light transmission, as well as mechanical elasticity, which make gallium phosphide a promising material for nanooptic devices, physicists said. Scientists at the Center for Photonics and 2D Materials at MIPT have shown that it can be used to create not only the simplest waveguides, but also filters, resonators and complex elements for optical microcircuits.

We experimentally showed and theoretically explained what sizes a gallium phosphide waveguide must have to support light transmission. Next, we will direct efforts to the manufacture of more complex optical elements: filters, interferometers. We can spectrally separate optical signals using circuits of several nanostructures, which is important for creating logic elements. We also create waveguides from other materials that will work at different wavelengths of light. shared plans Alexey Bolshakov

In addition to the employees of the laboratory of functional nanomaterials of the Center for Photonics and Two-Dimensional Materials of MIPT, their colleagues from Alfer University, HSE, ITMO, St. Petersburg State University, Polytechnic University (all - St. Petersburg) and Yerevan State University took part in the work.

The work was carried out with the support of the Ministry of Science and Higher Education of the Russian Federation and the Russian Science Foundation. Published in the scientific journal Small.

2022: Physical effect discovered that could form the basis of quantum devices

Scientists from NUST MISIS and MIPT discovered the physical effect of resonant oscillations of superconducting critical current in a Josephson device based on a nanocrystal of a topological insulator created by a scientific team. This was announced on October 31, 2022 by representatives of NUST MISIS.

A physical effect has been discovered that could form the basis of promising quantum devices

As reported, mesoscopic devices based on topological insulators are a real scientific klondike, where scientists are looking for and still find many fundamental and applied effects. As can be understood from the name, materials of this type are usually referred to as insulators, or otherwise as dielectrics or semiconductors that do not pass electric current through themselves. But with one very exception: in its thinnest surface layer, this material conducts current like a metal.

Roughly speaking, one can imagine a topological insulator as something like a fragment of a tree covered on both sides with copper. However, in this case, we are not talking about two substances, but about a homogeneous sample of the same material. Moreover, the material is such that the special quantum state of electrons in the surface layer makes them not just current carriers, but "topologically protected" carriers.

This property is due to the fact that these quantum states of electrons are extremely stable - unlike ordinary electronic states in metal, here they are more stable when interacting with atomic defects, steps or other imperfections of the material.

At the Center for Advanced Methods of Mesophysics and Nanotechnology

We found the physical effect of oscillations of the critical current of the Josephson contact, consisting of two superconducting niobium electrodes, between which there is a nanocrystal of a topological insulator Bi2Te2.3Se0.7 hexagonal shape. Oscillations appear in the temperature range from 400 to 20 mK (-272.7 ° C) and have a very unusual pointed shape. The period of these oscillations is only 1 oersted, which corresponds to an extremely small energy scale, approximately 1 mkeV. We have found that the observed effect can be due to the resonant tunneling of Andreev quasiparticles between the energy levels formed near the superconductor/topological insulator boundaries. told Vasily Stolyarov, study leader, senior researcher at the Laboratory of Superconducting Metamaterials NUST MISIS, director of the Center for Advanced Methods of Mesophysics and Nanotechnology MIPT

Experiments were performed on a BlueFors LD250 dissolution refrigerator. To conduct such precision studies, the method of filtering electronic and thermal noise developed by one of the co-authors was used.

According to the developers, the wide range of temperatures at which the picoidal form of oscillations and their ultra-small period appear are direct experimental evidence that the material studied can serve as a platform for the implementation of quantum devices of the future.

The topological security of the electronic subsystem of this class of materials can lead to optimal stability of such devices to sources of decoherence, and therefore higher accuracy of calculations compared to the physical principles used for October 2022 in "classical" qubits.

The next stage of the study, according to the co-authors of the work, will be the improvement of the technology for the synthesis of nanocrystals, the technology for the manufacture of direct superconducting devices, as well as the study of how to effectively control quasi-partial Andreev levels and how to implement a quantum logical device based on them.

Our result is fundamental since previously the presence of Andreev levels in systems with superconductor/topological insulator boundaries was not predicted. Also, due to the small energy scale of the system of such levels, it was impossible to think about a visual electronic transport experiment. In this case, the coincidence of circumstances allowed us to do this. concluded Vasily Stolyarov

The work was carried out with the support of the Russian Science Foundation (project 21-72-00140).

In addition to scientists from the Center for Advanced Methods of Mesophysics and Nanotechnology, MIPT and the Laboratory of Superconducting Metamaterials, NITU MISIS, their colleagues from the Sorbonne University (Paris), the Institute of Microelectronics Technologies of the Russian Academy of Sciences, the Institute of Solid State Physics of the Russian Academy of Sciences and the University of Twente (Netherlands) took part in the work.

The results of the work are presented in the international scientific journal Advanced Quantum Technologies.

See also

• Nanotubes
• Nanosprings
• Nanolattices
• Nanophotonics
• Nanoparticles in medicine
• Nanofibers in medicine
• Nano-films of boron nitride