Generalizations of Quantum Mechanics Induced by Classical Statistical Field Theory

No Heading We show that the Dirac-von Neumann formalism for quantum mechanics can be obtained as an approximation of classical statistical field theory. This approximation is based on the Taylor expansion (up to terms of the second order) of classical physical variables – maps f : Ω → R, where Ω is the infinite-dimensional Hilbert space. The space of classical statistical states consists of Gaussian measures ρ on Ω having zero mean value and dispersion σ²(ρ) ≈ h. This viewpoint to the conventional quantum formalism gives the possibility to create generalized quantum formalisms based on expansions of classical physical variables in the Taylor series up to terms of nth order and considering statistical states ρ having dispersion σ²(ρ) = hⁿ (for n = 2 we obtain the conventional quantum formalism).     

Isospin symmetry breaking in ρ→πγ decay

In terms of effective field theory and mixed-propagator approach, we show that there is a larger hidden effect of isospin breaking in ρ→πγ decay due to a ω exchange, ρ→ω→πγ. The branching ratio is predicted as B(ρ→πγ) = (11.67±2.0)×10^-4, which is much larger than Particle Data Group's datum (6.8±1.7)×10^-4 and one of charged mode, B(ρ^±→π^±γ) = (4.5±0.5)×10^-4. Received: 7 January 2002 / Accepted: 2 April 2002     

Double spin asymmetry in exclusive ρ0 muoproduction at COMPASS

The longitudinal double spin asymmetry A₁ ^ρ for exclusive leptoproduction of ρ⁰ mesons, μ+N→μ+N+ρ, is studied using the COMPASS 2002 and 2003 data. The measured reaction is incoherent exclusive ρ⁰ production on polarised deuterons. The Q² and x dependence of A₁ ^ρ is presented in a wide kinematical range, 3×10^-3<Q²< 7 (GeV/c)² and 5×10^-5<x<0.05. The results presented are the first measurements of A₁ ^ρ at small Q² (Q²< 0.1 (GeV/c)²) and small x (x<3×10^-3). The asymmetry is in general compatible with zero in the whole kinematical range. PACS 13.60.Le; 13.88.+e     

A size effect in the optical properties of powdered TiO2

The spectral reflectivity ρ in the region 0.36–2.1 μm and its change Δρ with irradiation by 30 keV electrons versus the average grain sizer _av in a TiO₂ (rutile) powder has been studied in the range 1–7.5 μm. It has been established that the dependence of ρ onr _av differs for different regions of the spectrum, but there is a common increase of ρ in the size range 2.5–4 μm. The value of Δρ after irradiation is also less in powders with this range of sizes. It has been shown that the dependence Δρ=f(r _av) with increasing electron fluence from 2·10¹⁵ to 4·10¹⁶ is strengthened for one band and weakened for another. Tomsk Polytechnic University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 41, No. 12, pp. 52–58, December, 1998.     

Concentration dependence of the intermediate frequency bandwidth of submillimeter heterodyne AlGaAs/GaAs nanostructures

The concentration dependence of the intermediate frequency bandwidth of heterodyne AlGaAs/GaAs detectors with 2D electron gas is measured using submillimeter spectroscopy with high time resolution at T= 4.2 K. The intermediate frequency bandwidth f_3dBfalls from 245 to 145 MHz with increasing concentration of 2D electrons n _s = (1.6-6.6) × 10[su11] cm^-2. The dependence f_3dB ≈ n _s ^- 0.04±is observed in the studied concentration range; this dependence is determined by electron scattering by the deformation potential of acoustic phonons and piezoelectric scattering.     

New perovskite oxides LaBa<Emphasis Type="Italic">M</Emphasis>CoO<Subscript>5 + δ</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Fe,Cu): Synthesis,structure, and properties

The electrical resistivity ρ and the thermopower S of ceramic materials LnBaCuFeO_{5 + δ} (Ln= La, Pr, Nd, Sm, Gd-Lu) are measured in air at temperatures in the range from 300 to 1100 K. All the studied ferrocuprates are p-type semiconductors. The electrical resistivity ρ and the thermopower S of these compounds increase with a decrease in the radius of the Ln ³⁺ cation (with an increase in the number of 4f electrons n in Ln ³⁺). The nonmonotonic behavior of the dependences ρ=f(n) and S=f(n) indicates that the electrical properties of the layered ferrocuprates LnBaCuFeO_{5 + δ} depend on the electronic configuration of the Ln ³⁺ cation. The power factors P calculated for the LnBaCuFeO_{5 + δ} ceramic materials from the experimental values of ρ and S increase with increasing temperature and, at T = 1000 K, reach the maximum values P = 102.0 and 54.1 μW m⁻¹ K⁻² for Ln = Pr(4f ²) and Sm(4f ⁵), respectively, and become close to each other and equal to 30–35 μW m⁻¹ K⁻² for Ln = Gd(4f ⁷), Dy(4f ⁹), and Ho(4f ¹⁰).     

Direct calculation of transition intensities in LiYF<Subscript>4</Subscript>: Nd<Superscript>3+</Superscript>

Duan’s simple model is extended to analyze the mixing of the 4f ^{N − 1}5d configuration with the 4f ^N states. The explicit static coupling and traditional dynamic coupling are considered, and the parameters are fitted according to the absorption spectrum in LiYF₄: Nd³⁺. The parameter values obtained are as follows: T ₃₂ = −28i × 10⁻⁷, T ₅₂ = −1151i × 10⁻⁷, A ₃₂² = 192i × 10⁻¹² cm, A ₅₂⁴ = i × 10⁻¹² cm, A ₇₂⁶ = 54i × 10⁻¹² cm, and A ₇₆⁶ = −680i × 10⁻¹² cm. Compared to the experimental measurements, the present model yields better results than those obtained from the Judd-Ofelt theory. The text was submitted by the authors in English.     

Ion conduction and space-charge polarization processes in Li<Subscript>2</Subscript>Ge<Subscript>7</Subscript>O<Subscript>15</Subscript> crystals

The electrical properties of a lithium heptagermanate (Li₂Ge₇O₁₅) crystal have been studied in DC and AC measuring fields at temperatures from 500 to 700 K. In a DC field, a substantial decrease of electrical conductivity σ with time has been detected. On the basis of kinetic dependences σ(t), estimates of the charge carrier diffusion coefficient D have been obtained. In the frequency range 10¹–10⁵ Hz, the spectra of complex impedance ρ*(f) have been measured. The analysis of diagrams in the complex plane (ρ″–ρ′) has been performed within the equivalent circuit approach. It has been shown that, in the considered temperature and frequency intervals, the electrical properties of Li₂Ge₇O₁₅ crystals have been determined by the hopping conduction of interstitial lithium ions A _Li and accumulation of charge carriers near the blocking Pt electrodes.     

Frequency dependence of junction capacitance of BPW34 and BPW41 p-i-n photodiodes

This article investigates the frequency dependence of small-signal capacitance of silicon BPW34 and BPW41 (Vishay) p-i-n photodiodes. We show that the capacitance-frequency characteristics of these photodiodes are well-described by the Schibli and Milnes model. The activation energy and the concentration of the dominant trap levels detected in BPW34 and BPW41 are 280–330 meV and 1.1×10¹²−1.2×10¹² cm⁻³, respectively. According to the high-frequency C-V measurements, the impurity concentrations are determined to be about 5.3×10¹² and 1.9×10¹³ cm⁻³ in BPW41 and BPW34, respectively using the method of ΔV/Δ(C ⁻²) vs. C.      

Size effect in zinc whiskers

The effect of size on the zero field resistivity in zinc whiskers was measured. The results are in agreement withAleksandrov's value ofϱ·λ=1.8×10⁻¹¹ Ωcm². The dependence on temperature and on transverse and longitudinal magnetic field was also investigated.     

Leakage current and capacitance characteristics of Si/SiO2/Si single-barrier varactor

We investigate, both experimentally and theoretically, current and capacitance (I–V/C–V) characteristics and the device performance of Si/SiO₂/Si single-barrier varactor diodes (SBVs). Two diodes were fabricated with different SiO₂ layer thicknesses using the state-of-the-art wafer bonding technique. The devices have very low leakage currents (about 5×10^-2 and 1.8×10^-2 mA/mm²) and intrinsic capacitance levels of typically 1.5 and 50 nF/mm² for diodes with 5-nm and 20-nm oxide layers, respectively. With the present device physical parameters (25-mm² device area, 760-μm modulation layer thickness and ≈10¹⁵-cm^-3 doping level), the estimated cut-off frequency is about 5×10⁷ Hz. With the physical parameters of the present existing III–V triplers, the cut-off frequency of our Si-based SBV can be as high as 0.5 THz. Received: 9 February 2001 / Accepted: 9 February 2001 / Published online: 23 March 2001     

Studies of synthesizing behaviors and superconductivity of sol-gel YBa2Cu3O7-x samples in flowing oxygen atmosphere

Systematic studies of synthesizing behaviors of sol-gel YBa₂Cu₃O_7−x samples in flowing oxygen atmosphere and their superconductivity have been performed. A set of high temperature ρ-T curves has been obtained for the whole synthesizing process. After four rounds of synthesizing, the resistivity of the sample was around ρ=1.00×10⁻³Ω · cm at room temperature. The ρ-T curve of the fourth round shows that the orthorhombic to tetragonal phase transformation of the sample occurs around 600 °C, which is lower than that of the YBa₂Cu₃O_7−x sample prepared by conventional solid-state reaction method. Other measurements, such as X-ray diffraction, SEM measurement and low temperature R-T and M-T measurement, were also performed. And the R-T and M-T measurement results suggest that during the synthesizing process, there exist some state at which the sample has better superconductivity than the other states. Moreover, we found screw dislocations presenting on the sample broken surface from the SEM images. This will change the concept that the screw dislocations can only grow on the surface of the YBCO thin films and single crystals.      

Magnetoresistivity and acoustoelectronic effects in a tilted magnetic field in <Emphasis Type="Italic">p</Emphasis>-Si/SiGe/Si structures with an anisotropic <Emphasis Type="Italic">g</Emphasis> factor

Magnetoresistivity ρ _xx and ρ _xy and the acoustoelectronic effects are measured in p-Si/SiGe/Si with an impurity concentration p = 1.99 × 10¹¹ cm⁻² in the temperature range 0.3–2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt θ to the normal to the plane of a two-dimensional p-Si/SiGe/Si channel is determined. A first-order ferromagnet-paramagnet phase transition is observed in the magnetic fields corresponding to a filling factor ν = 2 at θ ≈ 59°–60°.     

Positron lifetime measurements inn- andp-type silicon

Positron lifetime measurements were carried out in four different samples of silicon, namelyn-type (P-doped) 75 Ωcm,n-type (Sb-doped) 0.018 Ωcm,p-type (B-doped) 60 Ωcm andp-type (B-doped) 0.02 Ωcm. The measurements were made at room temperature and at 77K. A positron lifetime of τ₁=(230±2) psec was found for all samples, independant of dopant or temperature. Paper A 17 presented at 3 rd Internat'l Conf. Positron Annihilation. Otaniemi, Finland (August 1973).     

Magnetoresistance of the semiconducting spinelide Cu0.625Ga0.375Cr2Se4 having a low-temperature long-range magnetic order-spin glass transition

A study is reported of the dependence of magnetoresistance Δρ/ρ on the square of magnetization σ ² of the semiconducting spinelide Cu_0.625Ga_0.375Cr₂Se₄, which exhibits a low-temperature transition from long-range magnetic order (LRMO) to the spin glass (SG) state in strong magnetic fields. It is shown that at the freezing temperature T _f the Δρ/ρ(σ ²) relations change their slope, and that below T _f this slope is about one half that for T>T f. This finding, together with the earlier observation that the freezing temperature does not depend on the frequency of the ac magnetic field in which it was measured, suggests that the spin-glass phase consists of spins of individual Cr³⁺ ions, and that the SG-LRMO crossover is a phase transition. Fiz. Tverd. Tela (St. Petersburg) 40, 315–317 (February 1998)     

A wet chemical preparation of transparent conducting thin films of Al-doped ZnO nanoparticles

A wet chemical deposition method for preparing transparent conductive thin films on the base of Al-doped ZnO (AZO) nanoparticles has been demonstrated. AZO nanoparticles with a size of 7 nm have been synthesised by a simple precipitation method in refluxed conditions in ethanol using zinc acetate and Al-isopropylate. The presence of Al in ZnO was revealed by the EDX elemental analysis (1.8 at.%) and UV–Vis spectroscopy (a blue shift due to Burstein–Moss effect). The obtained colloid solution with the AZO nanoparticles was used for preparing by spin-coating thin films on glass substrates. The film demonstrated excellent homogeneity and transparency (T > 90%) in the visible spectrum after heating at 400 °C. Its resistivity turned to be excessively high (ρ = 2.6 Ω cm) that we ascribe to a poor charge percolation due to a high film porosity revealed by SEM observations. To improve the percolation via reducing the porosity, a sol–gel solution was deposited “layer-by-layer” in alternation with layers derived from the AZO colloid followed by heating. As it was shown by optical spectroscopy measurements, the density of thus prepared film was increased more than twice leading to a significant decrease in resistivity to 1.3 × 10⁻² Ω cm.     

Electrical-optical analysis of a GaN/sapphire LED chip by considering the resistivity of the current-spreading layer

The effects of current distribution in LED chips on the electrical potential and optical light extraction efficiency are investigated by a numerical simulation. The results show that when the resistivity of the current-spreading layer is decreased there is current-crowding near the n-contact. On the other hand, when the resistivity in the current-spreading layer increases, there is current-crowding near the p-contact. When the current is crowded near the n-contact due to less resistivity of the current-spreading layer, the input power is lower because of the smaller series resistance in the chip, and the light extraction efficiency is higher since the shadowing effect of the p-contact can be avoided. For L _p = 50 μm in this study, the light extraction efficiency at ρ _ITO = 0.1 × 10⁻³ Ω·cm is 1.4 times better than that when L _p = 100 μm, even though the driving voltage is raised 1.02 times.     

Trap-centers of self-interstitials in silicon

Deep-level profiles were measured radially acrossn-type FZ silicon wafers containing A-swirl defects by applying DLTS to an array of Schottky contacts. The trapparameters were obtained very accurately using a computer-fit procedure for the full DLTS peaks. Two acceptor levels atE _c −0.49 eV (σ _n =6.6×10⁻¹⁶cm²) andE _c −0.07 eV (σ _n =4.6×10⁻¹⁶cm²) were observed, which varied oppositely to the A-swirl defect density. At short ranges (1–2mm) the trap concentration-profile was smeared out and did not follow the strong fluctuations in the etch pattern. Both levels were measured together with the same concentration. The profiles indicate outdiffusion. A level atE _c −0.14 eV (σ _n =1.1×10⁻¹⁶cm²) was not related to A-swirl defects. A level atE _c −0.11 eV (σ _n =1.1×10⁻¹⁵cm²) was only detected in one ingot. The properties of the deep level atE _c −0.49 eV are discussed in the light of published DLTS results reported for γ-irradiation, laser annealing after self-implantation, annealing under pressure and oxidation of silicon samples. It is concluded, that this level is related to interstitial silicon rather than to an impurity.     

Kinetics of radiation-induced segregation in 12Cr-MoWSiVNbB steel after Ni<Superscript>++</Superscript> and He<Superscript>+</Superscript> ion irradiation

Ferritic-martensitic 12Cr-MoWSiVNbB (EP-823) steel was irradiated with 7 MeV Ni⁺⁺ ions within fluence interval 5 × 10¹⁸−5.4 × 10¹⁹ ions/m² and with 30 and 70 keV He⁺ ions within fluence interval 10²⁰–10²¹ ions/m² at 500°C. Results from a comparative analysis of Cr and Si radiation-induced segregation profiles near the surface are presented. Dependence of the amount of surface segregation on damage dose, displacement generation rate, and radiation-induced point defects concentration is established.     

Formation of high-conductivity NiSi2 layers on Si at zero-mismatch temperature by high-current Ni-ion implantation

2 and Si lattices at 380 °C, which was defined as zero-mismatch temperature. The implantation was conducted with a metal vapor vacuum arc (MEVVA) ion implanter at an extraction voltage of 45 kV. Based on a thermal conduction estimation, a temperature rise of 380 °C required the Ni-ion current density to be 35 μA/cm². For the Si(111) wafers, the high conducting NiSi₂ layers were indeed directly formed after Ni-ion implantation with this specific current density to a normal dose of 2×10¹⁷ ions/cm² and the resistivity was as low as 9 μΩ cm. For the Si(111) wafers pre-covered with a 10-nm Ni overlayer, the resistivity of the NiSi₂ layers obtained under the same conditions decreased down to about 6 μΩ cm. The superior electrical property of the NiSi₂ was thought to be related to its formation temperature, i.e. at a zero-mismatch temperature of 380 °C, which resulted in minimizing the stress and stress-induced defects involved in its formation as well as cooling process. Received: 27 April 1998 / Accepted: 26 October 1998