Here are presented investigations of powder and glass-like samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co. The neutron diffraction study reveals an amorphous structure of the samples doped with Au and Co, as well as the magnetic scattering due to a long-range FM order in the Co-doped sample. The composition and molecular structure of the sample doped with Au is clarified with the NMR investigations. The temperature dependence of the magnetization, M (T), exhibits large irreversibility in low fields of B=1–7mT. M (B) saturates already above 2T at high temperatures, but deviates from the saturation behavior below ~50 (150K). Magnetic hysteresis is observed already at 300K and exhibits a power-law temperature decay of the coercive field, Bc (T). The macroscopic behavior above is typical of an assembly of partially blocked magnetic nanoparticles. The values of the saturation magnetization, Ms, and the blocking temperature, Tb, are obtained as well. However, the hysteresis loop in the Co-doped sample differs from that in other samples, and the values of Bc and Ms are noticeably increased.

The objects of investigations are germanium nanocrystallites formed inside a SiO2 layer by ion implantation followed by high-temperature annealing. Germanium nanocrystallites inside a thin (30 nm) layer of thermal SiO2 oxide are charged by means of scanning probe microscopy, and the resulting charged zones are visualized and analyzed. It is shown that stable charge regions up to 30 nm in diameter that consist of several charged germanium nanocrystallites can be formed under the probe of an atomic-force microscope. It turns out that the ability of the germanium nanocrystallites to keep the induced charge is extremely sensitive to the intercrystallite distance and the presence of defect centers in the SiO2 layer. This is explained by the fact that the charge escapes from the germanium nanocrystallites by tunneling either between adjacent crystallites or through defect centers in the SiO2.

Novel scanning probe microscopy method of near field imaging of laser radiation is proposed. The method providing a submicron spatial resolution is based on detection of a shift of the probe resonance related to its heating by absorbed radiation. The method has been realized with a conventional silicon probe and has been employed for visualization of infrared emission from a half-disk semiconductor whispering gallery mode laser.

The charge carrier accumulation and relaxation effects in the active region of polymer field-effect transistor structures based on the semiconducting polymer poly(9-epoxypropylcarbazole) have been studied by means of Kelvin probe microscopy. It has been shown that the introduction of gold nanoparticles into the polymer noticeably accelerates the processes considered. The characteristic times of charge accumulation and dissipation upon the application and removal of the potential at the transistor gate in this case are of a few minutes.

The behavior of charges locally injected from the probe of an atomic force microscope into nanothin films of high- k SmScO 3 dielectric deposited on a silicon substrate is studied by the method of Kelvin probe force microscopy. Prior to examination, the films were annealed at different temperatures. At temperatures above 900°C, the amorphous as-prepared films exhibit polycrystalline inclusions. In the films annealed at 900°C, the injected charge persists for a long time that several tens of times exceeds the charge retention time observed when conventional dielectrics, such as SiO 2 and Si 3 N 4 , are used. In addition, the diffusion of carriers in the plane of the dielectric layers sharply slows down.

A charge leakage in LaScO3 nanolayers on a Si substrate has been investigated by Kelvin probe microscopy. A charge leakage from the LaScO3 layer to the LaScO3/Si interface layer with a subsequent lateral charge spreading in the interface layer and simultaneous leakage to the Si substrate has been revealed in this system. A lateral charge spreading has not been directly observed in the LaScO3 layer.

The distribution of external potential along GaAs nanowires with electric contacts formed at the ends has been studied by the method of Kelvin probe force gradient microscopy (KPFGM). It is established that, in the case of Schottky contact formation, the application of external blocking voltage leads to charge accumulation in the surface layer of natural oxide near the contact, which significantly modifies the potential profile along the GaAs nanowire. The accumulation of charge and its dissipation upon removal of the blocking voltage proceed with characteristic times on the order of several minutes.

We propose an experimental method of near field optical imaging by scanning probe microscopy in which the probe itself serves as an infrared photodetector. The method providing a submicron spatial resolution is based on detection of a shift of the probe resonance related to its heating by absorbed IR radiation. The method does not require an apertured probe and can be realized with a conventional silicon probe used in atomic force microscopy. The method has been employed for visualization of infrared emission from a half-disk semiconductor whispering gallery mode laser.

Введение В настоящее время большой интерес исследо-вателей вызывают так называемые нитевидные нанокристаллы (ННК) полупроводников [1, 2]. Эти объекты представляют собой кристалличе-ские стержни диаметром от 30 до 200 нм и длиной до 3  5 мкм. Для их получения чаще всего ис-пользуются методы молекулярно-лучевой эпитак-сии (МЛЭ) и газофазной эпитаксии (ГФЭ) на под-ложках, активированных наноразмерными капля-ми металла (Au, Ga и др.) [3]. Рост ННК происхо-дит, как правило, по механизму пар–жидкость–кристалл (ПЖК) [4]. К настоящему времени полу-чены ННК на основе GaAs, AlGaAs, InP, InAs, GaN, Si, Ge, ZnO и др. [5]. Широкие возможности управления геометрическими параметрами, леги-рованием и составом ННК открывают перспекти-вы для реализации на базе массивов ННК широ-кого спектра приборов нано- и оптоэлектроники: наноразмерных транзисторов с малыми времена-ми переключения [6], биосенсоров [7], гибких и прозрачных дисплеев [8] и др. В частности, были реализованы фотоприемники и светодиоды на основе ННК из различных материалов [9]. Значи-тельным достижением стала демонстрация лазер-ной генерации в одиночных ННК при оптической накачке [10, 11]. Характерной особенностью ННК является малость типичных значений их радиуса R

A convenient and fast method for measuring Young’s modulus of semiconductor nanowires obliquely standing on the growth substrate is presented. In this method, the nanowire is elastically bent under the force exerted by the probe of an atomic-force microscope, and the load-unload dependences for the bending of the probe cantilever are recorded. Next, these curves are used to find the bending stiffness of the tilted nanowires, after which, taking into account the nanowire dimensions, Young’s modulus is obtained. The implementation of this method is demonstrated for tilted GaAs nanowires growing on a GaAs (111) substrate. Young’s modulus is determined by applying finite-element analysis to the problem of the stationary elastic bending of a nanowire taking into account the actual nanowire shape and faceting. It proves that a fairly accurate estimate of Young’s modulus can be obtained even if the nanowire shape is approximated by a circular cylinder with a single cross-sectional area. The values of Young’s modulus obtained for GaAs nanowires of cubic lattice symmetry are 2 to 3 times smaller than its value for bulk GaAs. This difference is attributed to the presence of stacking faults in the central part of the nanowires.

Magnetization M (T, B) of powder and glassy samples containing carbon nanoparticles is investigated in the interval of temperatures T between similar to 3 - 300 K and magnetic fields B up to 5 T. Low-field magnetization, M (T), exhibits a strong magnetic irreversibility, which is suppressed above the field of similar to 1 T. The dependence of M (B) saturates at high temperatures above B similar to 2 T, magnetic hysteresis is observed already at 300 K. The values of the saturation magnetization, the coercivity field and the maximum blocking temperature are obtained. Analysis of the experimental data gives evidence for concentration of the magnetization close to the surface of the particles, which is consistent with the origin of magnetism in nanocarbon presumably due to intrinsic disorder and surface defects.

Magnetic properties of powder and glassy samples with carbon nanoparticles. not intentionally doped and doped with Ag, Au and Co, are investigated at temperatures T ~ 3 — 300 K in magnetic fields B up to 5 T. Magnetization M (T) exhibits in low fields of B = 1 — 50 mT a strong irreversibility, which is suppressed above B ~ 1 T. The high-temperature (T ~ 200 — 300 K) dependence of M on B demonstrates a saturation above B ~ 2 T. Magnetic hysteresis is observed already at 300 K. exhibiting a power-law temperature decay of the coercive field. Analysis of the experimental data suggests a concentration of the magnetization close to the surface of the carbon nanoparticles. This is consistent with the origin of magnetism in nanocarbon due to intrinsic surface defects. Deviations of macroscopic and microscopic parameters in the Co-doped sample from those in the other samples imply an influence of the Co ions and/or clusters.

Multigraphene films grown by sublimation on the surface of a semi-insulating 6H-SiC substrate have been studied. It is shown that pregrowth annealing of the substrate in a quasiclosed growth cell improves the structural quality of a multigraphene film. Ohmic contacts to the film have been fabricated, and the Hall effect has been studied at low temperatures. It is found that a 2D electron gas exists in the films. It is concluded that the conductivity of the film is determined by defects existing within the graphene layer or at the interface between the graphene film and a SiC substrate.

Application of Kelvin probe force gradient microscopy (KPFGM) to visualize the local charge dissipation in thin dielectric layers is considered. By this method, the local charge behavior in nano thin SiO2, Si3N4, and LaScO3 dielectric layers has been studied. Local charging of the layers has been performed at the point contact with a conductive probe. KPFGM potential images reveal variations of the surface potential in the locally charged areas, which makes it possible to detect the injected charge and to study its behavior. Special experiments on the SiO2 layers with embedded Si-nanocrystals, when lateral spreading of injected charge had been suppressed, permitted to demonstrate high (better than 20 nm) lateral resolution of KPFGM observations. A simple electrostatic model has been developed to estimate the total amount of injected charge. The obtained estimations made it possible to control charge retention in the dielectric layer and possible leaks into the substrate. The studied dielectric layers demonstrate a broadening of the charged area with time t, proportionally to t1/2, what indicates the domination of the diffusion mechanism in charge lateral spreading on the large time scale. These observations permitted to determine the diffusion coefficients, mobilities, and diffusion activation energies for charges in the studied dielectric layers. To obtain the correct information on the injected charge behavior, the parasitic charge dissipation through the surface film of adsorbed water should be reduced to a negligible level. It was achieved by working in moderate vacuum conditions with an additional sample heating.

Influence of high-vacuum annealing at temperatures in the range 1300-1400°C and residual pressure of ~10-6 Torr on the surface of 6H-SiC (0001) wafers has been studied. Auger spectroscopy and RHEED data show that the annealing conditions do not lead to any surface reconstruction of the wafers. Atomic force microscopy reveals atomically flat surface terraces separated by steps of unit-cell height (h = 1.5 nm).

A technique for measurement of longitudinal current-voltage characteristics of semiconductor nanowhiskers remaining in contact with the growth surface is suggested. The technique is based on setting up a stable conductive contact between the top of a nanowhisker and the probe of an atomic-force microscope. It is demonstrated that, as the force pressing the probe against the top of the nanowhisker increases, the natural oxide layer covering the top is punctured and a direct contact between the probe and the nanowhisker body is established. In order to prevent nanowhiskers from bending and, ultimately, breaking, they need to be somehow fixed in space. In this study, GaAs nanowhiskers were kept fixed by partially overgrowing them with a GaAs layer. To isolate nanowhiskers from the matrix they were embedded in, they were coated by a nanometer layer of AlGaAs. Doping of GaAs nanowhiskers with silicon was investigated. The shape of the current-voltage characteristics obtained indicates that introduction of silicon leads to p-type conduction in nanowhiskers, in contrast to n-type conduction in bulk GaAs crystals grown by molecular-beam epitaxy. This difference is attributed to the fact that the vapor-liquid-solid process used to obtain nanowhiskers includes a final stage of liquid-phase epitaxy, a characteristic of the latter being p-type conduction obtained in bulk GaAs(Si) crystals.

The method of scanning Kelvin probe force microscopy has been used to study the electric field distribution in GaAs-based p +-π-n-n + detector structures. In the active layer volume, two maxima in the field strength profiles have been found, which are localized in the regions of p +-π and π-n junctions. A volt-age drop on the π-n junction expands the region of collection of nonequilibrium holes, thus increasing the charge collection efficiency for the absorption of γ photons with an energy of 59.5 keV.

Atomic-force microscopy and scanning tunnel electron microscopy have been used to study the surface of single-crystal 6H-SiC (0001) substrates subjected to step-by-step high-temperature annealing in vacuum. An annealing procedure leading to surface structuring by atomically smooth steps with heights of 0.75 and 1.5 nm has been found. It is suggested to use the structured surfaces as test objects for z-calibration of scanning probe microscopes.

The possibility of forming nanocarbon films on the SiC surface with the use of the technology employed in sublimation epitaxy of silicon carbide has been demonstrated. The temperature range for synthesis of nanocarbon films has been found. The presence in films of two-dimensional graphite crystals has been revealed.