Features of the plasma sputtering of polycrystalline Pb1 − x Sn x S films

The processes of the sputtering and modification of surfaces of polycrystalline films of the ternary solid solution Pb_{1 ? x} Sn _x S (x = 0.9–1.0) in a high-density Ar plasma of high-frequency low-pressure inductive discharge are studied. Films with thicknesses of 1–4 μm are grown on glass substrates using the “hot-wall” method and consist of plate-like crystallites. It is established that the sputtering rate for lead-tin sulfide films does not exceed 2.0 nm/s, which is determined by the presence of oxygen-containing compounds on the surfaces. In the case of plate-like crystallites with nanodimensional thicknesses, the effect of smoothing of the developed surfaces of the polycrystalline Pb_{1 ? x} Sn _x S layers during plasma treatment is observed; this is important for fabricating multilayer device structures.     

Pb1−x Fe x films prepared by vapor condensation

ZF, LF and TF SR experiments with antiferromagnetic (AF) ceramical samples La_2–x Sr _x CuO_4–y have been performed in the temperature range 10–300 K. Zero field muon spin polarization functions obtained below the Neel temperature clearly show a nonzero initial precession phase-–0.35 rad. We propose an explanation based on existence of the dynamical magnetic fields on the muon.We thank Drs. A.G. Chistov and A.M. Brjazkalo from RSC Kurchatov Institute for the preparation the #2 La₂CuO_4–y sample.     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

Inhomogeneous state of the electron system in BaPb1 − x Sb x O3 superconducting perovskites: The 207Pb NMR study

Comprehensive measurements of the ²⁰⁷Pb NMR spectra, Knight shifts ²⁰⁷ K _s , spin-lattice relaxation rate ²⁰⁷ T ₁ ^?1 , and the Pb spin echo decay ²⁰⁷ E(2t) in BaPb_{1 ? x} Sb _x O₃ superconducting oxides (x ≤ 0.33) have been performed. A considerable increase in the shift distribution width when Sb is substituted for Pb indicates the formation of the inhomogeneous state of the electron system in the oxide conduction band. The shift magnitude proportional to the density of states near the Fermi energy, ²⁰⁷ K s ∝ N(E _F ), reaches its maximum in the compounds with x = 0.18–0.25 with the maximum temperatures T _c of the superconducting transition. In the BaPb_{1 ? x} Sb _x O₃ compounds, the Korringa relation is met, indicating that all of the samples are in the metal phase. The data on the Pb spin echo decay and the relevant estimates of the indirect coupling constants of the nuclei of the nearest neighbor Pb atoms clearly demonstrate the development of the electron system state in the oxide metal phase, which is microscopically inhomogeneous over the crystal.     

The metal-semiconductor transition in amorphous Si1−x Cr x films:T 0.19-contribution to the metallic conductivity

A detailed phenomenological re-analysis of previously published conductivity data, (T, x), is presented. It is based on the investigation of differences, (T, x ₁)–(T, x ₂). In this way, the cusp-like low-temperature term is amplified against the other temperature dependent contributions. This term can be described by wherep=0.19±0.03. It is present, if (4.2 K,x) exceeds 260 ^–1 cm^–1, at least up to (4.2 K,x)1350 ^–1 cm^–1 and forT60 K. But it is absent, if (4.2 K,x)180 ^–1 cm^–1. The disappearance of this contribution should be related to the metal-semiconductor transition, taking place atx _c 0.14. On the other hand, the presence of a term proportional toT ^1/2, as predicted by Altshuler and Aronov, seems unlikely.It is argued that the term should be related to the interplay of electron-electron interaction and disorder. The comparison with data from the literature shows that this contribution might also be present in heavily doped crystalline semiconductors.     

Phase transition and linear thermal expansion of (Pb1− x Ba x )ZrO3 ceramics

(Pb_{1? x} Ba _x )ZrO₃ ceramics for the composition range 0?≤?x?≤?0.30 were prepared by the mixed oxide solid state reaction method. Phase transition was studied by dielectric and dilatometric measurements. The ferroelectric to paraelectric phase transition temperature was progressively shifted to a lower temperature by replacing lead with barium. The x?=?0.20 sample showed the maximum dielectric constant of 16,300 at the transition temperature. For compositions 0?≤?x?≤?0.075, the antiferroelectric to ferroelectric phase transition exhibited a large linear thermal expansion. However, the antiferroelectric to ferroelectric phase transition did not exist for 0.10?≤?x?≤?0.30 samples. A phase diagram for PBZ ceramics prepared by the conventional mixed oxide method was also present.     

The Fe1−xCoxS system (x < 0.25); transition and the high temperature phase

The α-transition in Fe_1−xCo_xS materials is examined based on electrical, magnetic and structural properties. A decrease of the transition temperature is observed with increasing alloying rate up to x_co = 0.24, where the transition is completely cancelled. Beyond this critical concentration the materials exhibit a high-temperature FeS type behavior.The existence of hk0 reflections, with h and/or k = 2n + 1 in the cobalt-stabilized superstructure, the high-temperature phase of FeS, establishes that the structure is hexagonal, space group P6₃mc, with two independent metal positions, in contrast to the previously proposed tri-twinned MnP type model.The physical and structural results are discussed within the framework of conductivity by polarons. The α-transition occurs when the polaron concentration, thermally created or introduced by impurities, reaches the critical value x_p ≅ 0.08. The driving mechanism for the α-transition is a reduction of the polaron dissociation energy by a temperature increase or by cobalt alloying.     

Temperature and composition dependence of the energy band gap of Pb1−x Mn x S solid solution

Photovoltaicp-n junctions inn-type Pb_1–xMn _x Sx0.04, have been made by sulphur diffusion. Current-voltage and resistance-voltage characteristics have been examined at various temperatures. The spectral responses of the diodes have been measured within the temperature range from 5 to 300 K at a zero bias. From these measurements the energy band gap of Pb_1–x Mn _x S solid solution has been determined as a function of temperature and manganese content. A phenomenological expression describing the variation of the energy gap of Pb_1–x Mn _x S with temperature and alloy composition has been proposed.     

Negatron effects in CdSe1 − x Te x and ZnS1−x Se x films

Various negatron effects in films of alloys of II–VI compounds deposited from solutions as a function of the deposition mode and heat treatment are studied. It is found that the negative photocapacitance effect, which was first discovered in ZnS_1?x Se _x films, and the slowly relaxing negative photoelectric effects, which are caused by the transition of electrons located in a nanoscale surface layer from the shallow energy levels of trapping centers to deeper levels with a lower polarizability and by the presence of nanoscale clusters in these materials, which play the role of a “reservoir” for minority charge carriers, occur according to a single mechanism. A model to explain the basic laws of negative photoconductivity in CdSe_{1 ? x} Te _x films deposited from a solution is proposed. Negative residual conductivity is explained in terms of double-barrier relief model, while negative differential photoconductivity is attributed to the presence of nanoscale electric domains.     

Optical properties of ternary ZnS x Se1−x polycrystalline thin films

Ternary ZnS_xSe_1–x polycrystalline thin films were prepared by evaporation in vacuum of 10^–5 Torr. The molecular fractionx varied in the region ox1. The optical constants (the refractive indexn, the absorption indexk, and the absorption coefficient) were determined in the wavelength range 300–1600nm. A plot representing ₂=f(hv) shows that the ZnS_xSe_1–x polycrystalline thin films of different compositions have two direct transitions corresponding to the energy gapsE andE+. The variation in eitherE orE+ withx indicates that this system belongs to the amalgamation type. Such variation follows a quadratic equation. The bowing parameter was found to be 0.456 eV, roughly equal to the calculated value 0.60 eV using the empirical pseudopotential method based on the virtual-crystal approximation, in which the disorder effect has not been taken into account.     

A study of Ba x Mg1 − x F2 optical films

Ba _x Me_{1 ? x} F₂ binary fluoride films (“Me” denotes calcium or magnesium fluoride) are studied. A method of processing the reflection and transmission spectra is proposed to determine the optical constants. The dispersion dependences of the refractive indices and absorption coefficients of films in the range of 1.3–12 μm are found. Dispersion in films in the regions of additional absorption bands, which are absent in single crystals, is observed for the first time. It is shown that the films of binary fluorides have a higher packing density, a lower absorption, and better operating characteristics than do films of pure fluorides. The films are promising for application as optical interference coatings in the mid-IR spectral region.     

In-plane and out-of-plane anisotropic magnetoresistances in La1 − x Pb x MnO3 thin films

The temperature and field dependences of in-plane (IP) and out-of-plane (OP) anisotropic magnetoresistances (AMRs) have been measured in La_{1 ? x} Pb _x MnO₃ (LPMO) thin films having different microstructures, namely the single-crystal (SC), nanocrystalline (NC) and polycrystalline (PC) microstructures. The OP AMR, irrespective of the microstructure, is found to be considerably larger than the IP AMR. The magnetization data show that the larger OP AMR arises because magnetization is favoured in the film plane owing to strain anisotropy. In addition, the temperature and field dependences of both IP and OP AMRs are governed by the crystallinity of the films, indicating that the AMRs are strongly influenced by the magnetization process.     

High-Moment-Low-Moment Description of Magnetovolume Effects in Y(Mn x Al 1− x ) 2 and Y x Sc 1− x Mn 2

Based on the assumption of a high-moment-low-moment instability of the Mn atom, we construct a simple spin model with coupled magnetic and spatial degrees of freedom to describe the Laves phase systems Y(Mn x Al 1 m x ) 2 and Y x Sc 1 m x Mn 2 . Monte Carlo simulations of this model qualitatively reproduce anomalies observed in these materials like a discontinuous giant volume change and anomalous thermal expansion behavior.     

Photoconductivity and electrical properties of epitaxial Pb1 − xCdxSe films

Photosensitive monocrystalline films Pb_{1 − x}Cd_xSe (x⩽ 0.03) of low carrier concentration (n = 0.3 ÷ 4 × 10¹⁷ cm⁻³ have been grown by hot wall epitaxy method on cleaved (111)BaF₂ or (100)KCl substrates.Photoconductive thresholds determined by spectral response measurements (at temperatures 4.2, 77 and 300 K) were in good agreement with the fundamental absorption edges and showed a large increase in the energy gap E_g with Cd content. Photoconductivity in the impurity range (hv < E_g) was observed.The temperature dependence of the Hall coefficient and the mobility between 4.2 and 300 K have been studied. Temperature freeze out of the free carriers was observed.Discussion of the carrier scattering mechanisms and impurity photoconductivity phenomena is presented.     

Anomalies of the static dielectric constant of Pb1−x Ge x Te

The static dielectric constant of Pb_1–x Ge _x Te (0x0.05) has been determined from differential capacitance measurements on Schottky-barriers in the temperature range of 4.2–300 K. A comparison with data deduced from the phonon frequencies via the Lyddane-Sachs-Teller relation shows substantial discrepancies which are attributed to lattice defects.Work supported by Jubiläumsfonds der Österreichischen Nationalbank     

Optical and electrical properties of flash-evaporated Pb1−xHgxSe films

Results of optical and electrical properties of flash-evaporated Pb_1−xHg_xSe films, in the composition range 0.07 ⩽ x ⩽ 0.93, show that the alloy films are formed by alloying of PbSe and HgSe. The optical band gaps of films grown on substrates at 25 and 100°C decrease linearly from 0.20 to 0.09 eV and from 0.15 to 0.065 eV, respectively, as the Hg concentration in the films is increased from 0.07 to 0.93. Activation energy values, as obtained from conductivity measurements, suggest that between 225 and 400 K the conduction results mainly from thermally-generated charge carriers, whereas at the lower temperatures (<225 K) impurity conduction dominates. Irreversible changes in the properties of the films are observed at > 400 K.     

The ferromagnetic to antiferromagnetic transition in La1−x Y x Mn2Si2(57Fe) compounds

A set of La_1–xY_xMn₂Si₂(⁵⁷Fe) samples withx=0, 0.1, 0.15, 0.2, 0.25, 0.3, 0.5 and 1.0 have been prepared with the tetragonal ThCr₂Si₂ structure.⁵⁷Fe Mössbauer spectra have been collected at 4.2 K for all samples. The spectra can be well fitted by two sextets, the predominant one (90% of the spectral area) being associated with⁵⁷Fe atoms in the Mn 4d site, with the remainder located in the Si 4e site. The analysis shows that there are distinct changes in the hyperfine interaction parameters for samples above and below the critical concentrationx _c 0.15, at which a transition from ferromagnetism to antiferromagnetism occurs. This transition is a result of a change in the exchange interactions linked with changes in the interatomic distances, due to the smaller atomic volume of Y compared to that of La.On leave from Applied Acoustics Institute, Shaanxi Teachers University, Xian, PR China.     

Surface nanostructure effects on optical properties of Pb(Zr x Ti1−x )O3 thin films

Optical scattering properties of nanostructured matter have crucial impact on performance efficiency of various photonic components, such as waveguides, display elements, and solar cells. In this paper, diffuse transmission properties of nanocrystalline Pb(Zr _x Ti_1?x )O₃ thin films with a high refractive index of ~2.5 and optical transmittance are presented. Thin films with a thicknesses ranging from 50 to 500 nm were studied using integrating sphere technique and results were compared to simulations performed by a scalar scattering theory. Thin films were deposited by pulsed laser deposition at room temperature on MgO(100) substrates and post-annealed at a temperature of 800 °C. Structural phase evolution-induced surface effects, which introduced periodicity on the film surface, cause the definite diffuse elements in transmission spectra of the films. Low and evenly distributed scattering amplitudes in k-space were seen for highly tetragonal- or trigonal-oriented films with non-textured surfaces, which led to low diffuse transmission values (T _D ≈ 5 %), while confined and increased scattering amplitudes in k-space were seen for tetragonal–trigonal-oriented films, with phase co-existence, which led to microstructure-induced textured surfaces and increased diffuse transmission values (T _D ≈ 50 %). For highly textured surfaces, scattering amplitudes distributed in tilted ellipsoid shape in k-space was observed. Difference between modeled and measured values was 3.8 % in maximum.