In this paper, we explore the possibility of using free-standing thin films from single-walled carbon nanotube (SWCNT) material in optics of the extreme ultraviolet (EUV) range. Test samples were ...fabricated using an aerosol chemical vapor deposition method. Synchrotron radiation was used to record the transmittance spectra of samples in the EUV range. The measured transmittance for a film 40 nm thick almost monotonously increases from 76% at a wavelength of 20 nm–99% at a wavelength of 1 nm. The measured stress-strain curve for the test samples shows that the SWCNT-based thin films have rather high ductility as opposite to fragile films made of conventional solid state materials. We use numerical simulations to demonstrate that the film strain occurs mainly by straightening and sliding of the nanotubes past each other without forming of strain localization responsible for fragile behavior. The combination of high radiation transmittance and unique mechanical properties makes the SWCNT-based thin films very promising for use in the EUV optics. In particular, such films can be used to protect delicate optical elements for EUV lithography from their contamination with debris particles.
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•High quality Bi1.1Sb0.9Te2S crystals were grown by the Bridgman technique.•Optical parameters were determined from far infrared reflectivity spectra.•ARPES spectra revealed a wide direct bandgap ...topological insulator phase.•The Dirac point is positioned well away from the valence and conduction bands.
Successful applications of a topological insulator (TI) in spintronics require its bandgap to be wider then in a typical TI and the energy position of the Dirac point in the dispersion relations to be away from the valence and conduction bands. In this study we grew Bi1.1Sb0.9Te2S crystals and examined their elemental composition, structural, optical and electronic properties as well as the electronic band structure. The high structural quality of the grown crystals was established by X-ray diffraction and Raman spectroscopy. Angular resolved photoelectron spectroscopy demonstrated a near parabolic character of the valence and conduction bands and a direct bandgap of 0.36 eV. The dispersion relations also revealed a Dirac cone, confirming the topological insulator nature of this material, with the position of the Dirac point being 100 meV above the valence band maximum. Far infrared reflectivity spectra revealed a plasma edge and two phonon dips. Fitting these spectra with theoretical functions based on the Drude-Lorentz model allows determination of the high frequency dielectric constant (41.3), plasma frequency (936 cm−1) and the frequencies of two infrared phonons (177.7 cm−1 and 77.4 cm−1).
The DANSS detector is located directly under the nuclear reactor at the Kalinin nuclear power plant. Such a position ensures about 50 m.w.e. shielding from cosmic rays in the vertical direction; as a ...result, the detector occupies an intermediate position between surface and underground detectors in the shielding from cosmic rays. The sensitive volume of the detector consisting of a 1-m
3
plastic scintillator is surrounded by the multilayer passive shielding and muon veto. The main aim of the DANSS experiment is to measure the antineutrino spectrum at various distances from the source. To this end, the detector is placed on a lifting platform in order to record data at three positions of 10.9, 11.9, and 12.9 m from the reactor core. The detector can reconstruct muon tracks passing through its sensitive volume. The pressure, temperature, and decay coefficients for muons in various regions of the zenith angle
have been determined from the muon data collected during four years using the effective generation level method.
Shape recovery in conventional shape memory alloys is typically a relatively slow process showing low heating rate sensitivity. In contrast to that, some shape memory alloys such as Ni–Fe–Ga–Co, ...Cu–Al–Ni, Cu–Al–Fe–Mn can exhibit the effect of burst-like shape recovery when the original shape is restored almost instantaneously in a very narrow temperature range. Here we report on an abnormal stress-strain behavior of Ni49Fe18Ga27Co6 single crystals upon uniaxial compression along the 110 axis and caloric effects during burst-like recovery of shape memory strain in the samples. Differential scanning calorimetry (DSC) study revealed that DSC peak shifts to lower temperatures with increasing heating rate.
•Ni49Fe18Ga27Co6 single crystals exhibit an anomalous stress-strain behavior when compressed along the 110 axis.•Ni49Fe18Ga27Co6 single crystals compressed along the 110 axis manifest a burst-like shape recovery.•The burst-like shape recovery is accompanied with an anomalous heat intake.•The transition temperature of the burst-like shape recovery is decreasing with increasing heating rate.
Results of the Hall-effect studies of surface properties of n–type HgCdTe films modified with arsenic ion implantation and thermal annealing are reported on. A complete annihilation of ...implantation-induced extended defects (dislocation loops), quasi-point defects and related donor centers was observed as a result of a two-stage arsenic activation annealing. A high degree of activation of implanted arsenic was achieved with the annealing. In some cases, the annealing was found to lead to the modification of the properties of the ‘base’ layers not affected by implantation due to activation of uncontrolled acceptor defects and resulting changes in the degree of electrical compensation.
•Modification of the surface of HgCdTe films with arsenic implantation and annealing was studied.•Annealing was shown to annihilate structural defects induced by implantation.•High degree of activation of arsenic as a result of post-implantation annealing was achieved.•Activation of residual acceptor impurities by post-implantation annealing was discovered.
We present an optical spectroscopy study of Cu2ZnSnSe4 (CZTSe) thin films deposited on Mo/glass substrates. The Cu/Zn+Sn ratio in these films varies from nearly stoichiometric to strongly Cu ...deficient and Zn rich. Increasing Cu deficiency and Zn excess widens the bandgap Eg, determined using photoluminescence excitation (PLE) at 4.2K, from 0.99eV to 1.03eV and blue shifts the dominant band in the photoluminescence (PL) spectra from 0.83eV to 0.95eV. The PL spectra of the near stoichiometric film reveal two bands: a dominant band centred at 0.83eV and a lower intensity one at 0.93eV. The temperature and excitation intensity dependence of the PL spectra help to identify the recombination mechanisms of the observed emission bands as free-to-bound: recombination of free electrons with holes localised at acceptors affected by randomly distributed potential fluctuations. Both the mean depth of such fluctuations, determined by analysing the shape of the dominant bands, and the broadening energy, estimated from the PLE spectra, become smaller with increasing Cu deficiency and Zn excess which also widens Eg due to an improved ordering of the Cu/Zn atoms. These changes in the elemental composition induce a significant blue shift of the PL bands exceeding the Eg widening. This is attributed to a change of the dominant acceptor for a shallow one, and is beneficial for the solar cell performance. Film regions with a higher degree of Cu/Zn ordering are present in the near stoichiometric film generating the second PL band at 0.93eV.
•CZTSe thin films with different Cu/Zn+Sn ratios are fabricated on Mo/glass substrates.•PL temperature and excitation intensity dependence are analysed.•The band gaps are determined using PLE.•PL bands are identified as band-to-impurity transitions.•Optical spectroscopy parameters are correlated with solar cell performance.
In this paper the electronic structure of the valence states in CuInSe2, CuGaSe2 and CuIn0.5Ga0.5Se2 is considered in details in a wide energy range up to 20 eV from the Fermi level. Examining the ...electronic structure within the LDA + U method we focus on the deep, occupied 4d indium and 3d gallium electronic states. The calculated electronic structure is compared with high-resolution experimental photoemission (PE) spectra measured for high structural quality single crystals of these compounds at a photon energy of 600 eV. The comparison helped us to understand the nature of the observed spectral features associated with electronic states near the Fermi level. The calculated energies of the Ga-3d and In-4d states exhibited a good agreement with the experimentally determined spectral positions of these states in the PE spectra. The significance of these states for the application in quantum optics is discussed.
•The electronic structure of Cu(In,Ga)Se2 is studied within LDA + U method.•The calculations are found to be in a good agreement with the photoemission spectra.•We explore the effect of spin-orbit coupling of the deep 4d In and 3d Ga states.•We discuss the influence of deep states on applications in quantum optics.
Thin films of p-type Cu3BiS3 with an orthorhombic wittichenite structure, a semiconductor with high potential for thin film solar cell absorber layers, were synthesised by thermal annealing of Cu and ...Bi precursors, magnetron sputtered on Mo/glass substrate, with a layer of thermo-evaporated S. The elemental composition, structural and electronic properties are studied. The Raman spectrum shows four modes with the dominant peak at 292cm−1. Photoreflectance spectra demonstrate two band gaps EgX and EgY, associated with the X and Y valence sub-bands, and their evolution with temperature. Fitting the temperature dependencies of the band-gaps gives values of 1.24 and 1.53eV for EgX and EgY at 0K as well as the average phonon energy. Photoluminescence spectra at 5K reveal two bright and broad emission bands at 0.84 and 0.99eV, which quench with an activation energy of 40meV. The photocurrent excitation measurements demonstrate a photoresponse and suggest a direct allowed nature of the band gap.
•Report Raman and PL spectra•Determine two band gaps using photo-reflectivity analysis•Analyse their temperature dependence and find average phonon temperature•Clarify the nature of defects from temperature and excitation power analysis of PL spectra•Propose a model of radiative recombination
Metal–insulator–semiconductor (MIS) structures based on HgCdTe were fabricated after various stages of pn junction formation using As+ implantation and activation annealing. The energy of As+ ions ...was 200 keV with the fluence of 1014 cm−2. Heteroepitaxial HgCdTe films with near-surface graded-gap layers were grown by molecular beam epitaxy (MBE) on silicon substrates. It was shown that the electron concentration in the near-surface semiconductor layer increases after implantation to values of about 1017 cm−3, and after implantation and annealing in the near-surface semiconductor layer, a p+ layer appears with a hole concentration of more than 1.5 × 1018 cm−3. The generation rate of minority charge carriers in the space charge region after implantation is low, which indicates a low defectiveness of the thin near-surface MBE HgCdTe layer. After implantation and annealing, the generation rate increases significantly, which may be due to high defectiveness near the interface between Al2O3 and MBE HgCdTe. Dopant profiles were constructed in the near-surface HgCdTe layers after various technological procedures. It was shown that after implantation in films, the dopant concentration increases with distance from the interface to the depth of 0.1 μm.
•Surface HgCdTe properties were modified by As implantation and thermal annealing.•Metal–insulator–semiconductor structures were created and their admittance studied.•Concentration profiles in HgCdTe after various procedures were determined.•After As implantation, a low-defect layer appears near the interface HgCdTe-Al2O3.•Activation annealing leads to a decrease in the density of slow states.
Dark currents in medium-wave
nBn
structures based on HgCdTe grown with the aid of molecular beam epitaxy on the (013) GaAs substrates are studied. The passivation of the surface of the side walls of ...the mesastructures is performed using Al
2
O
3
films formed by plasma atomic layer deposition. It is shown that the volume component of the dark current dominates in the
nBn
structures with a composition in the barrier layer of 0.84. The activation energy of the current is close to the band gap of the absorbing layer. Comparison of the experimental results with the results of the Rule07 empirical model shows that the diffusion limitation of the dark current takes place in the fabricated structures in a temperature interval of 180–300 K. The results indicate that the molecular beam epitaxy of HgCdTe on alternative substrates is a promising method for fabrication of unipolar barrier detectors for a spectral interval of 3–5 µm.
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