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In situ measurements of the resistance changes of carbon nanotube bundles irradiated by 60Co γ-quanta at room temperature are presented. The peculiarity of our study consists in providing the sample irradiation in a hermetic cell filled with different gases at atmosphere pressure. Here we demonstrate the results for irradiation in hydrogen, deuterium, helium and argon media. The obtained dependences of the resistance change versus irradiation dose in vacuum are presented, too. We have developed a novel two-stage mechanism, which implies defect introduction by energetic intermediate particles that are gas atoms. Preliminary calculations for Compton electrons (0.85 MeV) and atmospheric gas pressure show the high efficiency of this two-stage mechanism in comparison to conventional one-stage mechanism. It is shown that the defect introduction rate in the developed two-stage mechanism is strongly dependent on the gas atomic mass and coincides well with our experimental results.

The effect of radioactive irradiation on H2 sorption by bundles of single-wall carbon nanotubes (SWNTs) has been investigated in various gas media. The samples were irradiated with γ-quanta (1.2 MeV) of 60Co ((1.5–1.7) × 107 rad) radiation at room temperature in deuterium, nitrogen, and oxygen atmosphere (P = 1 atm), and in a vacuum. The processes of H2 sorption and desorption in the SWNT bundles were investigated before and after irradiation in the temperature interval 12–1270 K. It is found that irradiation in a gas environment has a significant effect both on the low-temperature H2 sorption induced by the weak physical interaction, and the chemical H2 sorption by the SWNT bundles. A phenomenological model has been proposed to explain the defect generation in carbon nanotubes irradiated in gas media.

Experimental data on the electroreflectance spectra of γ-irradiated epitaxial GaN films on sapphire are reported. The irradiation doses are 105−2 × 106 rad. The theoretical electroreflectance spectra calculated on the basis of a model of three types of transitions are in agreement with experimental data with reasonable accuracy. The energies and broadenings of the transitions derived in the context of the model give grounds to infer that, in the GaN films, there are internal stresses dependent on the γ-irradiation dose.

The role of hot carriers in enhancing the radiation resistance of GaAs solar cells has been investigated. The laser-pulse induced, short-circuit current response method was used to study solar cell degradation caused by radiation damage. Samples were subject to radiation doses in the range 1×10 14 –4×10 16 electron cm −2 and then probed with laser pulses with 7 ns duration and 3.7 eV energy. We have developed a non-stationary theory of minority carrier flow in the active region of the solar cell. The theory allows a description of the temporal evolution of the short-circuit current and the dependence on irradiation dose. The model agrees well with experimental results using a single fitting parameter. This parameter is the carrier capture cross-section of radiation center E5 in the p-region emitter of the solar cell. The value of the cross-section was determined to be 0.1×10 −12 cm 2 from the results under non-stationary condition. This is seven times lower than that deduced from the current–voltage characteristics in the dark for a similar solar cell. The difference can be explained by a strong reduction of capture cross-section with increased carrier energy. Our results suggest that the observed cross-section reduction is caused by carrier accumulation at energies comparable with the optical phonon energy.

The influence of radiation exposure in hydrogen atmosphere on the radial thermal expansion of single-walled carbon nanotubes and on their sorption of hydrogen is studied. The irradiation was carried out with cobalt-60 γ-rays (with an energy of 1.2 MeV and an irradiation dose of 1.5·107 rad) in the normal hydrogen atmosphere under pressure 1 atm and at temperature of 300 K. The sorption and desorption of hydrogen by samples of nanotubes were investigated over the temperature range 15–1170 K before and after irradiation. It was found that the irradiation of carbon nanotubes (CNTs) in hydrogen atmosphere leads to considerable increasing an amount of hydrogen sorbed by the sample. The irradiation in hydrogen atmosphere resulted in increasing absolute values of radial thermal expansion of CNTs bundles over the temperature range investigated (2–120 K). The effects of hydrogen physically and chemically sorbed in bundles of CNTs on the radial thermal expansion of the irradiated samples were distinguished.

The results of experimental study of radiation resistance of GaAs-based solar cells are presented. The solar cells were irradiated by 1 MeV electrons at room temperature with the fluence up to 4 × 10 16 electrons cm - 2 . The radiation influence on the dark current and short-circuit current under illumination was investigated both experimentally and theoretically. It is shown that the radiation-produced electron traps E5 and hole traps H1 are responsible for irradiation-induced degradation of such solar cells. The radiation tolerance of the basic parameters (the short-circuit current, the output power) of GaAs solar cells is primarily determined by the radiation damage in p-regions.

Room temperature current–voltage and noise measurements have been made before and after gamma irradiation on AlGaN/GaN high electron mobility transistors (HEMTs) grown on sapphire. The saturation current due to radiation-induced defects shows a nonlinear dependence on radiation dose. The deviation of the device parameters does not exceed 20% at highest radiation dose 109 Rad and the devices with larger gate lengths demonstrate a higher radiation hardness to the 60Co gamma rays. The noise spectra of devices after gamma irradiation follow the flicker noise (1/fγ) dependence with the exponent γ close to one. The Hooge parameter estimated for the HEMTs after gamma irradiation dose does not show a gate-bias dependence and increases by approximately three to five times at radiation dose 2 × 108 Rad. The analysis of noise spectra allowed to identify the major sources of noise generation in the investigated HEMT heterostructures.

Radiation effects are investigated in thin epitaxial films of the high-Tc superconductor (HTSC) YBa2Cu3O7−x irradiated by low doses of 1-MeV electrons. The maximum radiation dose (4×1016 electrons/cm2) is chosen from the condition that the defects formed as a result of electron–nucleus collisions cause a negligible lowering of the critical temperature of YBa2Cu3O7−x. Under this condition the main source of radiation effects in HTSC films can be processes involving excitation of the electronic subsystem of YBa2Cu3O7−x. When YBa2Cu3O7−x films are irradiated by doses of (1–4)×1016 electrons/cm2 their critical temperature Tc is observed to increase (in contrast to published reports of a decrease in Tc at irradiation doses greater than 1018 electrons/cm2) and then, after the irradiation has stopped, to relax over time to its original value. These effects are similar to those observed in the photoexcitation of the electronic subsystem of YBa2Cu3O7−x (photostimulated superconductivity). A decrease of the critica...

In presented study we investigate the influence of electron irradiation, with energy of incident electrons 1 MeV, on the electrical resistance of single-walled carbon nanotube bundles. Irradiation was performed at liquid helium temperature for the first time. To determine radiationinduced damages accumulation and its further thermal recovering, the samples resistance was in situ measured in wide temperature range (5 – 300 K). The results reveal radiation damage annealing at temperature ~ 200 K that we associate with formation of inter-tube links in the bundles.

We report experimental results for the changes in conductivity of single-wall carbon nanotube bundles when irradiated by Co-60 gamma-rays in various environments. In the current study the samples investigated were irradiated in hermetic cells, either evacuated (0.1 Pa) or filled with hydrogen or deuterium at atmospheric pressure. In situ measurements of the resistance change as a function of irradiation dose at room temperature are presented. It was found that, for all irradiation conditions, the normalized resistance versus irradiation dose demonstrates a logarithmic behaviour. A phenomenological model for the observed dependence is derived. The current-voltage characteristics of the irradiated samples were measured in the temperature range from 4.5 to 300 K using short (10 ns) electric pulses, and the results demonstrate a scaling behaviour. This scaling occurs in the universal coordinates that correspond to the Tomonaga-Luttinger liquid concept. Our results confirm the existence of the Tomonaga-Luttinger liquid phase up to room temperature in carbon nanotubes after gamma-irradiation to a dose of 5 x10(7) rad in vacuum, 1 : 7 x 10(7) rad in hydrogen and 1 : 24 x 10(8) rad in deuterium.

Novel test structures fabricated on the basis of Si nanowires are the ultimate building blocks for future nanoelectronics and biological sensor applications. These structures have to be stable in operation. However, a great many factors influence stability, especially in a nanowire channel. In this contribution, we report on the transport and noise properties of nanowires with different channel lengths. We applied small-dose gamma irradiation treatment of the samples to obtain more stable operation of the test device structures. The structures under study were fabricated on the basis of SOI wafers using nanoimprint technology. High-quality nanowires were obtained by chemical wet etching with low defect density. In spite of relatively large lengths of the channels from 2µm to 22 µm, we found that normalized current noise spectral density decreases as a function of 1/(L2 ) in the samples with lengths below 7µm. Such dependence is characteristic of the contact contribution to the noise properties.At the same time, in relatively long samples the behavior was changed to 1/L dependence, demonstrating the priority of channel noise. The latter dependence was also registered for samples with small lengths after gamma irradiation, reflecting the improvement effect of the irradiation due to stress relaxation in the contact regions as well as increased stability of the structures and decreased scattering in the structure characteristics (Figure 1).An analysis of the random telegraph signal noise component, recorded for samples with small length before gamma treatment and reduced level after this treatment, confirms the obtained results. This demonstrates the positive effect of irradiation on the stability and reliability of the structure parameters.

In presented experimental study, the single-walled carbon nanotube bundles were irradiated by 60Co γ - quanta with energies 1.2 MeV in hydrogen and deuterium media at room temperature. Investigation of hydrogen sorption/desorption was carried out for irradiated and unirradiated samples in wide temperature range from 12 to 1273 K. Comparison of obtained results denotes that hydrogen adsorption capacity depends on gas environment used during γ - irradiation treatment. Moreover, this dependence is different in various temperature ranges. Irradiation in deuterium improves physisorption (below 65 K) up to 3.6 times. While irradiation in hydrogen medium improves chemsorption (above 673 K) up to 12.8 times in comparison with unirradiated sample. Single-walled carbon nanotubes are able to store hydrogen in temperatures from 70 to 500 K. Also, γ - irradiation in hydrogen and deuterium media enhance the amount of chemisorbed hydrogen even at gas loading pressure of 1 bar.

The effect of a small dose of gamma irradiation on transport characteristics of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures was investigated. It is shown that the carrier concentration remains practically unchanged after an irradiation dose of 10(6) rad, while the 2DEG mobility exhibits a considerable increase. The results are explained within a model that takes into account the relaxation of elastic strains and structural-impurity ordering occurring in the barrier layer under irradiation. (C) 2008 American Institute of Physics.

Effect of small dose gamma-irradiation on electrical characteristics of AlGaN/GaN high electron mobility transistors has been investigated. Decreasing of the leakage current and its noise has been registered after dose of 1×106 Rad. As-grown heterostructures used in further for the device fabrication have been examined after the same radiation treatment. The small dose radiation results are explained within a model that takes into account relaxation of elastic strains and structural-impurity ordering occurring in the barrier layer under irradiation.

Currently, there is a great interest in in situ superconducting materials in which the dispersive superconducting current paths in a normal matrix are created by physical-chemical processes that occur naturally in certain alloys, rather than by the more common “forced” method, which is used in multifilamentary composite materials.

In this work we present steady-state characteristics and low-frequency noise spectra of AlGaN/GaN based high electron mobility transistors (HEMTs) exposed to gamma ray radiation. The devices with a variety of gate length (150-350 nm) and width (100-400 νm) were irradiated by 60Co gamma rays with doses in the range of 104-109 Rad and flux of 102 Rad/s. Dose dependencies of basic operating parameters of the transistors, such as saturation current (Isat), transconductance (gm), channel conductance (gc), and threshold voltage (VT) are analysed. Our study show that visible changes of above mentioned parameters are observed under relatively small doses (105 Rad) and strongly depend on the HEMT's topology. The transconductance decreases and threshold voltage becomes more negative for all devices while deviation of these parameters from its initial values does not exceed 20% at highest irradiation dose. At the same time variation of the channel conductance as well as saturation current depends to a high extent on the gate voltage (Vg). At |Vg| < |Vcr|, both Isat and gc show a reversal proportional to the cumulative dosage of radiation. However, at |Vg| > |Vcr|, drain saturation current and channel conductance increase with the cumulative dosage of radiation. The effect is more pronounced in short-length-gate devices.