Chemical etching of p-type Si(lOO) by K2Cr2O7

Chemical etching of the (100) face of p-type Si by aqueous K₂Cr₂O₇ was investigated with a contactless transient photoconductivity method, i.e. the time-resolved microwave conductivity (TRMC) method, after ns laser pulse excitation and with XPS, UPS, and LEED. TRMC transients after etching show a much slower decay that is explained by a decrease of surface recombination velocity. XPS indicates the formation of a mixed oxide of Si^III and Cr^v. During heating to 600°C this layer first transforms to a Si^IV-Cr^III oxide. After heating to 1200°C the oxide and Cr at the surface have disappeared, as indicated by UPS (He I and He II) and LEED (sharp 2×1 LEED pattern). However, XPS still shows the presence of Cr^o which evidently is diffused into the bulk. This can also be deduced from the transient photoconductivity measurements as TRMC transients at this stage show a fast decay rate that must be due to an increased bulk decay rate of excess charge carriers.     

Defect properties of Ti-doped Cr2O3

The defects in Cr_2−xTi_xO₃ (x = 0, 0.2 and 0.3) were studied by a combination of X-ray diffraction, density and electrical conductivity measurements supported by atomistic simulation. The results are consistent with the Ti being dissolved as Ti⁴⁺ compensated by Cr vacancies which associate to form complex defects of lower energy. Ti doping gives n-type semiconductivity due to a small concentration of Ti³⁺ in equilibrium with the complexes.     

Electronic and magnetic properties of Ti(2)O(3), Cr(2)O(3), and Fe(2)O(3) calculated by the screened exchange hybrid density functional

The electronic and magnetic properties of the transition metal sesqui-oxides Cr(2)O(3), Ti(2)O(3), and Fe(2)O(3) have been calculated using the screened exchange (sX) hybrid density functional. This functional is found to give a band structure, bandgap, and magnetic moment in better agreement with experiment than the local density approximation (LDA) or the LDA+U methods. Ti(2)O(3) is found to be a spin-paired insulator with a bandgap of 0.22?eV in the Ti d orbitals. Cr(2)O(3) in its anti-ferromagnetic phase is an intermediate charge transfer Mott-Hubbard insulator with an indirect bandgap of 3.31?eV. Fe(2)O(3), with anti-ferromagnetic order, is found to be a wide bandgap charge transfer semiconductor with a 2.41?eV gap. Interestingly sX outperforms the HSE functional for the bandgaps of these oxides.     

Die Verschiebung der Absorptionsbanden des Cr2O3 durch Einbau in In2O3

The absorption spectrum of chromium oxyde as a solid solution in indium oxyde has been investigated. It consists of an absorption band with the peak at 11.5·10³ cm^?1 followed by a continuous absorption in the short wavelength region. From the experimental data conclusions are drawn how this spectrum should be interpreted.     

Lattice Location Studies of Indium in Cr2O3

The lattice sites of implanted In atoms in Cr₂O₃ were investigated by means of electron emission channeling (EC) measurements using ¹¹¹In probe atoms. EC spectra were recorded for several axes and compared to simulations. Indium atoms are most likely located at near-Cr sites. Small differences in the EC patterns for prompt and delayed electrons may be an indication for displacements of ¹¹¹Cd emitter atoms following the electron capture decay of In. This revised version was published online in September 2006 with corrections to the Cover Date.     

Magnetic-field-induced toroidal moment in the magnetoelectric Cr2O3

The appearance of a toroidal moment is observed in the magnetoelectric Cr₂O₃ in a strong magnetic field above the spin-flop transition field. This conclusion is based on the experimentally established fact that the off-diagonal components of the magnetoelectric susceptibility tensor of Cr₂O₃ contains an antisymmetric part that is dual to the toroidal moment. Therefore it has been shown that the magnetoelectric Cr₂O₃ in the spin-flop phase can be classified as a toroic. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 4, 302–306 (25 February 1999)     

Resonant two-photon absorption in the Cr2O3 antiferromagnet

Two-photon absorption (TPA) spectra of the Cr₂O₃ model antiferromagnet have been studied for two polarization configurations at energies ranging from 2.5 to 3.55 eV. Several strong TPA peaks with the maximum coefficient β ～ 0.08 cm/MW are observed in the 2.7–3.1-eV range characterized by the ⁴ A ₂(F) → ⁴ T ₁(F) d-d one-photon transition of the Cr³⁺ ion. An analysis of the results obtained suggests that the general form of the TPA spectrum in this range is primarily determined by the resonance at the ² E(G) and ² T ₁(G) intermediate levels. At energies above 3.44 eV, the TPA coefficient sharply increases up to β ～ 0.1 cm/MW due to transitions between the valence and conduction bands.     

External quadrupole magnetic field of antiferromagnetic Cr2O3

We report the results of an experimental study of the external magnetic field of an antiferromagnetic Cr₂O₃ single-crystal. They confirm reliably that this field corresponds to a magnetic quadrupole field, as predicted by Dzyaloshinskii [Solid State Comm. 82, 570 (1992)] and observed by D. N. Astrov and N. B. Ermakov [JETP Lett. 59, 297 (1994)]. The quadrupole moment of the sample was found to be several times smaller than the value predicted by calculations. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 9, 713–718 (10 May 1996)     

Negligible magnetism in excellent structural quality Cr(x)Ti(1-x)O(2) anatase: contrast with high-T(C) ferromagnetism in structurally defective Cr(x)Ti(1-x)O(2)

We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective Cr:TiO(2) (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). We show for the first time that charge-compensating oxygen vacancies alone, as predicted by F-center mediated exchange, are not sufficient to activate ferromagnetism. Instead, the onset of ferromagnetism correlates with the presence of structural defects.     

紫外可见光谱法测定Cr3+电化学氧化过程中的Cr2O2-7

应用紫外可见光谱法对以二氧化铅为阳极,硫酸介质中Cr~(3 )电化学氧化过程中反应生成的Cr_2O_7~(2-)进行了分析测定,并测定了该反应过程的现场光谱。实验结果表明,以350nm作为Cr_2O_7~(2-)的定量吸收波长,可以测定Cr~(3 )电化学氧化过程中的Cr_2O_7~(2-)浓度,其摩尔吸光系数为1.98×10~3L·mol~(-1)·cm~(-1),体系中Pb~(2 )的存在对测定没有干扰。该反应过程的现场光谱测定表明,在以硫酸为介质、二氧化铅为阳极的Cr~(3 )电化学氧化反应生成Cr_2O_7~(2-)过程中,没有检测到中间体。     

K2O-ZnO-Al2O3-B2O3-SiO2系掺Cr3+透明莫来石微晶玻璃的研究

采用了X射线衍射、透射电镜和吸收光谱及荧光光谱技术研究了K2O－ZnO-Al2O3-B2O3－SiO2系掺Cr^3 玻璃的析晶性能和光谱。研究结果表明：在K2O－Al2O3-B2O3-SiO2系掺Cr^3 玻璃的基础上引入ZnO后，析晶性能明显改善；析晶温度降低，析出的纳米莫来石微晶均匀、规则；微晶玻璃的发光强度明显增强。     

Hyperfine interactions of111Cd impurities in Cr2O3

The electric and (antiferro-)magnetic hyperfine interaction of¹¹¹Cd in α-Cr₂O₃ after¹¹¹In implantation was studied via PAC. Two fractions with axially symmetric electric field gradients were observed having antishielding factors of V_zz/V_zz ^pc=79(12) and 106(16), respectively. From the line broadening of the Fourier components of the first fraction its supertransferred magnetic field was estimated as B_loc (20 K)≤0.41 T, about two orders of magnitude smaller than for substitutional¹¹¹Cd in NiO and CoO.     

Critical dynamics of models of the antiferromagnet Cr2O3

The critical dynamics of models of the real antiferromagnet Cr₂O₃ is investigated by the Monte Carlo method. The relaxation times of systems with N = 256, 500, 864, 2048, and 2916 spins are determined using the autocorrelation functions formalism. The values of the dynamic critical index z are calculated based on them.