Peculiarities of the density of states in SN junctions

We study the density of states (DoS) $\nu(E)$ in a normal-metallic (N) film contacted by a bulk superconductor (S). We assume that the system is diffusive and the SN interface is transparent. In the limit of thin N layer (compared to the coherence length), we analytically find three different types of the DoS peculiarity at energy equal to the bulk superconducting order parameter $\Delta_0$. (i) In the absence of the inverse proximity effect, the peculiarity has the check-mark form with $\nu(\Delta_0)=0$ as long as the thickness of the N layer is smaller than a critical value. (ii) When the inverse proximity effect comes into play, the check-mark is immediately elevated so that $\nu(\Delta_0)>0$. (iii) Upon further increasing of the inverse proximity effect, $\nu(E)$ gradually evolves to the vertical peculiarity (with an infinite-derivative inflection point at $E=\Delta_0$). This crossover is controlled by a materials-matching parameter which depends on the relative degree of disorder in the S and N materials.Comment: 20 pages, 8 figures. Version 2: updated Introduction and Conclusions, added Discussion section (on experimental relevance) and references. Final version as published in Annals of Physic

Micro-Raman Investigation of Hydrogen Localized in Cone-Shaped Defects Formed on the Silicon Wafer Surface

The goal of this work is the micro-Raman study of molecular hydrogen localized in cone-shaped defects, which are formed on the surface of previously helium implanted and annealed Czochralski Si wafers as a result of hydrogen plasma treatment. The line at ≈ 4158 cm corresponding to molecular hydrogen is observed in the Raman spectra when the laser beam is focused both on cone-shaped defects or defect-free regions of the surface. The laser irradiation of cone-shaped defects during micro-Raman experiments leads to intensity increase of this line when the irradiation time is increasing, with subsequent appearance of lines at ≈ 3621 and ≈ 3698 cm–1 and simultaneous disappearance of 4158 cm–1 line. No such effect was observed when the laser beam was focused on defect-free regions. The experiments have shown that heat treatment of the samples studied causes the appearance in the Raman spectra of lines at ≈ 3468, ≈ 3621, and ≈ 3812 cm–1, which can be associated with molecular hydrogen

Magnetotransport in Nanostructured Ni Films Electrodeposited on Si Substrate

The study of electrical resistivity  and magnetoresistance MR in nanogranular Ni films was performed over the temperature range 2 - 300 K and at the magnetic field induction B up to 8 T. The Ni layers having a thickness of about 500 nm were prepared by electrodeposition on n-Si wafers. According to an X-ray diffraction study, a strongly textured face-centered cubic structure was formed in the as-deposited films with an average grain sizes of about 10 - 70 nm. Experiments have demonstrated that the magnetic field and temperature dependences of the MR effect in Ni films shown two main peculiarities: (1) dependencies on the mutual orientations of vectors B, current and the film plane; (2) two contributions to the MR - negative anisotropic magnetoresistance and positive Lorentz-like MR

Gigantic Magnetoresistive Effect in n-SiSiO2Ni Nanostructures Fabricated by the Template-Assisted Electrochemical Deposition

The study of the carrier transport and magnetotransport in n-Si/SiO2/Ni nanostructures with granular Ni nanorods embedded into the pores in SiO2 was performed over the temperature range 2 – 300 K and at the magnetic field induction up to 8 T. In n-Si/SiO2/Ni nanostructures at temperatures of about 25 K a huge positive MR effect is observed. Possible mechanisms of the effect is discussed

Influence of wide band gap oxide substrates on the photoelectrochemical properties and structural disorder of CdS nanoparticles grown by the successive ionic layer adsorption and reaction (SILAR) method

The photoelectrochemical properties of nanoheterostructures based on the wide band gap oxide substrates (ZnO, TiO2, In2O3) and CdS nanoparticles deposited by the successive ionic layer adsorption and reaction (SILAR) method have been studied as a function of the CdS deposition cycle number (N). The incident photon-to-current conversion efficiency (IPCE) passes through a maximum with the increase of N, which is ascribed to the competition between the increase in optical absorption and photocarrier recombination. The maximal IPCE values for the In2O3/CdS and ZnO/CdS heterostructures are attained at N ≈ 20, whereas for TiO2/CdS, the appropriate N value is an order of magnitude higher. The photocurrent and Raman spectroscopy studies of CdS nanoparticles revealed the occurrence of the quantum confinement effect, demonstrating the most rapid weakening with the increase of N in ZnO/CdS heterostructures. The structural disorder of CdS nanoparticles was characterized by the Urbach energy (EU), spectral width of the CdS longitudinal optical (LO) phonon band and the relative intensity of the surface optical (SO) phonon band in the Raman spectra. Maximal values of EU (100–120 meV) correspond to СdS nanoparticles on a In2O3 surface, correlating with the fact that the CdS LO band spectral width and intensity ratio for the CdS SO and LO bands are maximal for In2O3/CdS films. A notable variation in the degree of disorder of CdS nanoparticles is observed only in the initial stages of CdS growth (several tens of deposition cycles), indicating the preservation of the nanocrystalline state of CdS over a wide range of SILAR cycles

Optical and photoelectrical properties of CdSxSe1–x films produced by screen-printing technology

In this paper the optical and photoelectrical properties of CdSxSe1–x films prepared using the screenprinting and sintering technique, were studied. CdCl2 was used both as a sintering flux and as a doping agent. CuCl was also used as a doping agent. The temperatures and times of preparation varied in the range of 500–600 °С and 5–60 min, respectively. The as-prepared films were characterized by the scanning electron microscopy, micro-probe X-Ray analysis, photoluminescence and photoconductance methods. Our investigations have shown that photoresponse of the CdSxSe1–x films prepared by a screenprinting method can be suitable for the production of large-area photosensitive devices

Mechanisms of carrier transport in Cux(SiO2)1-x nanocomposites manufactured by ion-beam sputtering with Ar ions

The present paper investigates the temperature/frequency dependences of admittance Z in the granular Cux(SiO2)1x nanocomposite lms around the percolation threshold xC in the temperature range of 4 30 K and frequencies of 20 MHz. The behavior of low-frequency ReZ(T) dependences displayed the predominance of electrons hopping between the closest Cu-based nanoparticles for the samples below the percolation threshold xC = 0:59 and nearly metallic behaviour beyond the xC. The high-frequency curves ReZ(f) at temperatures T > 10 K for the samples with x < xC exhibited behavior close to ReZ(f) fs with s 1:0 which is very similar to the known Mott law for electron hopping mechanism. For the samples beyond the percolation threshold (x > xC), the frequency dependences of ReZ(f) displayed inductive-like (not capacitive) behaviour with positive values of the phase shift angles

Electronic properties of Bi-Sn diluted alloys

The dependences of resistivity, magnetoresistance, Hall effect and thermoEMF in the 4 – 300 K temperature range and in magnetic fields up to 8 T were studied for the Bi1-xSnx (0 ≤ x ≤ 0.006) diluted alloys produced by the melt spinning method. The observed decrease of conductivity and magnetoresistance with doping is explained in terms of charge carriers scattering on tin atoms, whereas the shift of the Hall and Seebeck coefficients to the range of positive values is connected with enhanced contribution of holes in the charge transport