Vibrational-mechanical properties of the highly-mismatched Cd1-xBexTe semiconductor alloy: experiment and ab initio calculations.

The emerging CdTe-BeTe semiconductor alloy that exhibits a dramatic mismatch in bond covalency and bond stiffness clarifying its vibrational-mechanical properties is used as a benchmark to test the limits of the percolation model (PM) worked out to explain the complex Raman spectra of the related but less contrasted Zn1-xBex-chalcogenides. The test is done by way of experiment ([Formula: see text]), combining Raman scattering with X-ray diffraction at high pressure, and ab initio calculations ([Formula: see text] ~ 0-0.5; [Formula: see text]~1). The (macroscopic) bulk modulus [Formula: see text] drops below the CdTe value on minor Be incorporation, at variance with a linear [Formula: see text] versus [Formula: see text] increase predicted ab initio, thus hinting at large anharmonic effects in the real crystal. Yet, no anomaly occurs at the (microscopic) bond scale as the regular bimodal PM-type Raman signal predicted ab initio for Be-Te in minority ([Formula: see text]~0, 0.5) is barely detected experimentally. At large Be content ([Formula: see text]~1), the same bimodal signal relaxes all the way down to inversion, an unprecedented case. However, specific pressure dependencies of the regular ([Formula: see text]~0, 0.5) and inverted ([Formula: see text]~1) Be-Te Raman doublets are in line with the predictions of the PM. Hence, the PM applies as such to Cd1-xBexTe without further refinement, albeit in a "relaxed" form. This enhances the model's validity as a generic descriptor of phonons in alloys.

Quantitative phase-amplitude surface determination in reflection differential interference contrast profilometry.

An approach for measuring the surface profile of the samples with reflection variations using the Nomarski differential interference method is presented. The system is analyzed with Jones's matrices tool, and polarization effects of a non-polarizing beam splitter are taken into account. Equations are also developed to allow the determination of the surface profile from interference intensity when the sample reflectively is not uniform. The validity and accuracy of the measurement are verified by measuring the adhered silicon cantilever on a substrate with high reflectivity. This method is expected to be a valuable tool to inspect elements of micromechanics and microsystems.

Interferometric technique with a reference scale.

A double interferometer technique is presented. One interferometer generates a reference scale, while the other one is used as a measuring tool. The presented apparatus makes it possible to overcome 2π ambiguity by monitoring the phase difference at short time or space intervals. The phase unwrapping procedure is very simple due to a homodyne reference scale time interval method. The accuracy of the method is of 1 nm. The drift of the laser power and unequal gain of the photodetectors do not affect the system performance. The precision of the technique can be improved significantly by using a high-resolution time interval analyzer. The application of the method for determining the profile of a curved surface is demonstrated.

Exceptional phonon point versus free phonon coupling in Zn1-xBexTe under pressure: an experimental and ab initio Raman study.

Raman scattering and ab initio Raman/phonon calculations, supported by X-ray diffraction, are combined to study the vibrational properties of Zn1-xBexTe under pressure. The dependence of the Be-Te (distinct) and Zn-Te (compact) Raman doublets that distinguish between Be- and Zn-like environments is examined within the percolation model with special attention to x ~ (0,1). The Be-like environment hardens faster than the Zn-like one under pressure, resulting in the two sub-modes per doublet getting closer and mechanically coupled. When a bond is so dominant that it forms a matrix-like continuum, its two submodes freely couple on crossing at the resonance, with an effective transfer of oscillator strength. Post resonance the two submodes stabilize into an inverted doublet shifted in block under pressure. When a bond achieves lower content and merely self-connects via (finite/infinite) treelike chains, the coupling is undermined by overdamping of the in-chain stretching until a «phonon exceptional point¼ is reached at the resonance. Only the out-of-chain vibrations «survive¼ the resonance, the in-chain ones are «killed¼. This picture is not bond-related, and hence presumably generic to mixed crystals of the closing-type under pressure (dominant over the opening-type), indicating a key role of the mesostructure in the pressure dependence of phonons in mixed crystals.

Defect-induced ultimately fast volume phonon-polaritons in the wurtzite Zn0.74Mg0.26Se mixed crystal.

Volume-phonon-polaritons (VPP's) propagating at a light-in-vacuum-like speed are identified in the wurtzite-type Zn0.74Mg0.26Se mixed crystal by near-forward Raman scattering. Their detection is selective to both the laser energy and the laser polarization, depending on whether the ordinary (n0) or extraordinary (ne) refractive index is addressed. Yet, no significant linear birefringence (n0 [Formula: see text] ne) is observed by ellipsometry. The current access to ultrafast VPP's is attributed to the quasi-resonant Raman probing of an anomalous dispersion of n0 due to impurity levels created deep in the optical band gap by oriented structural defects. The resonance conditions are evidenced by a dramatic enhancement of the Raman signals due to the polar modes. Hence, this work reveals a capacity for the lattice defects' engineering to "accelerate" the VPP's of a mixed crystal up to light-in-vacuum-like speeds. This is attractive for ultrafast signal processing in the terahertz range. On the fundamental side we provide an insight into the VPP's created by alloying ultimately close to the center of the Brillouin zone.

Suggested design of gold-nanoobjects-based terahertz radiation source for biomedical research.

Gold nanoparticles (GNPs) may serve as devices to emit electromagnetic radiation in the terahertz (THz) range, whereby the energy is delivered by radio frequency or microwave photons which will not by themselves induce transitions between sparse confinement-shaped electron levels of a GNP, but may borrow the energy from longitudinal acoustic (LA) phonons to overcome the confinement gap. Upon excitation, the Fermi electron cannot relax otherwise than via emitting a THz photon, the other relaxation channels being blocked by force of shape and size considerations. Within this general scope that has already been outlined earlier, the present work specifically discusses two-phonon processes, namely (i) a combined absorption-emission of two phonons from the top of the LA branch, and (ii) an absorption of two such phonons with nearly identical wavevectors. The case (i) may serve as a source of soft THz radiation (at ≃0.54 THz), the case (ii) the hard THz radiation at 8.7 THz. Numerical estimates are done for crystalline particles in the shape of rhombicuboctahedra, of 5-7 nm size. A technical realisation of this idea is briefly discussed, assuming the deposition of GNPs onto/within the substrate of Teflon®, the material sustaining high temperatures and transparent in the THz range.

Highly energetic phenomena in water electrolysis.

Water electrolysis performed in microsystems with a fast change of voltage polarity produces optically invisible nanobubbles containing H2 and O2 gases. In this form the gases are able to the reverse reaction of water formation. Here we report extreme phenomena observed in a millimeter-sized open system. Under a frequency of driving pulses above 100 kHz the process is accompanied by clicking sounds repeated every 50 ms or so. Fast video reveals that synchronously with the click a bubble is growing between the electrodes which reaches a size of 300 µm in 50 µs. Detailed dynamics of the system is monitored by means of a vibrometer by observing a piece of silicon floating above the electrodes. The energy of a single event is estimated as 0.3 µJ and a significant part of this energy is transformed into mechanical work moving the piece. The observations are explained by the combustion of hydrogen and oxygen mixture in the initial bubble with a diameter of about 40 µm. Unusual combustion mechanism supporting spontaneous ignition at room temperature is responsible for the process. The observed effect demonstrates a principal possibility to build a microscopic internal combustion engine.

Pressure-induced phonon freezing in the ZnSeS II-VI mixed crystal: phonon-polaritons and ab initio calculations.

Near-forward Raman scattering combined with ab initio phonon and bond length calculations is used to study the 'phonon-polariton' transverse optical modes (with mixed electrical-mechanical character) of the II-VI ZnSe1-x S x mixed crystal under pressure. The goal of the study is to determine the pressure dependence of the poorly-resolved percolation-type Zn-S Raman doublet of the three oscillator [1 × (Zn-Se), 2 × (Zn-S)] ZnSe0.68S0.32 mixed crystal, which exhibits a phase transition at approximately the same pressure as its two end compounds (~14 GPa, zincblende → rocksalt), as determined by high-pressure x-ray diffraction. We find that the intensity of the lower Zn-S sub-mode of ZnSe0.68S0.32, due to Zn-S bonds vibrating in their own (S-like) environment, decreases under pressure (Raman scattering), whereas its frequency progressively converges onto that of the upper Zn-S sub-mode, due to Zn-S vibrations in the foreign (Se-like) environment (ab initio calculations). Ultimately, only the latter sub-mode survives. A similar 'phonon freezing' was earlier evidenced with the well-resolved percolation-type Be-Se doublet of Zn1-x Be x Se (Pradhan et al 2010 Phys. Rev. B 81 115207), that exhibits a large contrast in the pressure-induced structural transitions of its end compounds. We deduce that the above collapse/convergence process is intrinsic to the percolation doublet of a short bond under pressure, at least in a ZnSe-based mixed crystal, and not due to any pressure-induced structural transition.

Electronic structure study by means of x-ray spectroscopy and theoretical calculations of the "ferric star" single molecule magnet.

The electronic structure of the single molecule magnet system {M[Fe(L(1))(2)](3)}4CHCl(3) [M=Fe,Cr;L(1)=CH(3)N(CH(2)CH(2)O)(2) (2-)] has been studied using x-ray photoelectron spectroscopy, x-ray-absorption spectroscopy, soft-x-ray emission spectroscopy, as well as theoretical density-functional-based methods. There is a good agreement between theoretical calculations and experimental data. The valence band mainly consists of three bands between 2 and 30 eV. Both theory and experiments show that the top of the valence band is dominated by the hybridization between Fe 3d and O 2p bands. From the shape of the Fe 2p spectra it is argued that Fe in the molecule is most likely in the 2+ charge state. Its neighboring atoms (O,N) exhibit a magnetic polarization yielding effective spin S=52 per iron atom, giving a high-spin state molecule with a total S=5 effective spin for the case of M=Fe.

An x-ray emission and density functional theory study of the electronic structure of Zn(1-x)Mn(x)S.

Mn 3d electronic states in the dilute magnetic semiconductor Zn(1-x)Mn(x)S (x = 0.1-0.3) are studied using soft x-ray emission (XES) measurements and density functional theory (DFT). Mn L(2,3) emission spectra of Zn(1-x)Mn(x)S (x = 0.1-0.3) suggest that the Mn impurities do not form clusters in the host ZnS lattice, in agreement with previous models. A shift in the position of a Mn L(3) XES feature suggests a change in the nature of the hybridization between the Mn 3d(3/2) and S 3p states as a function of x. Our DFT calculations reproduce the weak interatomic exchange interaction, as well as the strong intra-atomic exchange splitting that is expected from observations of Zeeman splitting in such materials.

Differential amplitude scanning optical microscope computer aided for linewidth measurements.

A computer-aided differential amplitude scanning optical microscope for accurate linewidth measurements is described. The operation of the system includes an experimental data treatment based on the correspondent image formation theory. Experimental results for a three-track structure are presented. The developed technique is shown to be capable of measuring submicrometer linewidths with nanometer accuracy.

[Teratoblastoma of the lung in a child]. / Teratoblastoma legkogo u rebenka.

A rare case of teratoblastoma located in the lungs is described. Pleural fluid was examined; its principal morphologic component was vascular tissue, which permitted a tentative diagnosis of a vascular tumor (possibly perithelioma); the presence of connective tissue and oxyphilic interstitial substance elements necessitated a differential diagnosis to rule out chemodectoma. The final diagnosis of teratoblastoma was made in pathohistologic examination.

[Intestinal metaplasia and stomach cancer]. / Kishechnaia metaplazia i rak zheludka.

Foci of intestinal metaplasia of gastric mucosa are known to be heterogeneous both morphologically and functionally, and several types of such metaplasia are now recognized. However, different authors use different criteria for their identification and, moreover, evaluate the signs of metaplasia in different ways. Also, the relationship of different types of intestinal metaplasia to one another and to dysplastic changes in the epithelium and to gastric cancer is a matter of controversy. Variants of intestinal metaplasia with sulfomucin secretion are considered as precancerous states that may give rise to gastric cancer of an intestinal type.

[Unithiol in the treatment of secondary amyloidosis patients]. / Unitiol v lechenii bol'nykh vtorichnym amiloidozom.

Seventy-five patients with secondary amyloidosis were treated with unithiol. Good objective results were obtained in 19 patients, who demonstrated considerable improvement of the general well-being, reduction in proteinuria, edemas, appreciable elevation of the levels of total protein. albumins and sulfhydryl groups in blood serum. Satisfactory results were obtained in 18 patients who showed a certain improvement of the general well-being, moderate drop of proteinuria, elevation of the levels of albumins and sulfhydryl groups in blood serum. Twenty-four patients noted only subjective improvement. Fourteen patients did not respond or showed deterioration of the health status. Three patients developed allergic rash which disappeared after drug discontinuation and administration of the common desensitization agents.