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In the present work, based on the density functional theory and crystal structure prediction algorithms, we found novel structures of alkali metal orthocarbonates Li4CO4-C2/c, Na4CO4-C2/c, and K4CO...

Based on ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of iron–nitrogen compounds in the pressure range of 100...

Here, we have thoroughly studied the effect of chemistry of graphene derivatives on the composition of N-species after N-doping with the help of core-level spectroscopy techniques. The modulation of the N-species by tailoring the functionalization and atomic structure of graphene derivatives prior to chemical N-doping is experimentally demonstrated for the first time. The large extent of non-terminated or phenol-functionalized graphene edges is found to facilitate the formation of pyridinic nitrogen with its relative content exceeding 72%. In turn, the predominant decoration by the pyrazolic moieties is shown for the perforated and carboxyl-derived graphene layers. The thermal annealing at moderate temperatures of ca.345 °C is shown to equally readjust the composition of N-species in graphene derivatives regardless of their chemistry, nanostructure, and the initial distribution of the N-species. Further examination of N K-edge X-ray absorption spectra (XAS) pointed out that the oxidation of the graphene layer governs the manifestation of the π∗ resonances and configuration of the σ∗ resonance. As a result, a set of facile methods to synthesize graphene derivatives with the desired type of the embedded nitrogen species for the optoelectronic and catalytic applications are proposed and crucial features of their identification using core-level spectroscopy techniques are emphasized.

The applicability of stationary liquid phases for gas–liquid chromatography was evaluated. The scale for quantitative one-parameter estimation of their polarity was chosen. Absorption and luminescence spectra of the five indicators coumarin 153, coumarin 314, coronene, 4-dicyanomethylene-2-methyl-6-[4-(dimethylamino)styryl]-4H-pyran (DCM), and 3-aminophthalimide in solvents of different polarity were obtained at room temperature. The dependence of the fluorescence and absorption maxima wavelengths on the medium polarity was evaluated. Various spectroscopic polarity scales were compared to show that the coronene fluorescence scale was most appropriate. This scale was used to assess the polarity of some widespread phases (squalane, polydimethylsiloxane PMS-100, 3,3′-oxydipropionitrile, 2-ethylhexylsebacate, etc.) for gas-liquid chromatography. This approach was shown to be promising for preliminary selection of chromatographic stationary phases.

The effect of anodic boriding modes on the structure of the modified layer and the tribological characteristics of the treated titanium alloy has been studied. The structure, phase, and elemental compositions of the layer have been studied by X-ray diffraction analysis and electron microscopy with energy dispersive X-ray spectroscopy analysis. Surface roughness and microhardness distribution have been measured by the standard methods. The tribological characteristics of the borided alloy have been studied under dry friction conditions using a counterbody made of bearing steel. It has been found that the modified layer contains titanium dioxide (rutile) and a solid solution of boron in titanium with precipitates of the beta phase. A fivefold increase in the wear resistance of the alloy due to an increase in hardness and a decrease in the roughness has been achieved owing to boriding in a solution of boric acid and ammonium chloride at temperatures of 850–900°C for 5 min.

Changes in the band structure of carbon nanotubes induced by twisting of the tubes around their axes are studied by quantum-chemical methods, namely, the symmetrized augmented cylindrical waves ab initio method. The effects of torsional modes on the electronic properties of achiral and chiral, semiconducting, metal, and quasi-metal nanotubes are calculated. It is found that, due to the intersection of dispersion curves, twisting of chiral tubes leads to complex dependences of the optical gap on the torsional mode amplitude. In zigzag-type achiral semiconductor tubes, the band structure and band gaps are stable toward torsional modes. In armchair tubes twisting leads to the rapid formation and increase of the band gap. In chiral and achiral, metallic and quasi-metallic nanotubes, the optical gap increases independently of the tube twisting direction, while in semiconductor nanotubes, it depends thereon. Our results can be used for the design of elements of nanoelectromechanical carbon nanotube systems.

Stability control of elements of stone constructions of various structures is a prerequisite for their safe operation. The use of modern methods of non-destructive diagnostics of the stress-strain state of such constructions is an effective, and in many cases the only way to control it. Studies of thermal radiation accompanying the processes of solid bodies deformation allowed to justify and develop a method that allows to obtain non-contact information about changes in the stress-strain state in various types of geomaterials, including limestones. However, studies of the water saturation influence of rocks on the thermal radiation parameters recorded in this way are currently superficial. Taking into account the water saturation degree of rocks is necessary when monitoring the mechanical condition of stone structures that are in direct contact with water. The main purpose of this work is to study the dependences of changes in the intensity of thermal radiation from the surface of limestone samples with different humidity under conditions of uniaxial compression. The obtained results showed the expected significant decrease in the mechanical properties (uniaxial compressive strength and elastic modulus) of water-saturated samples in comparison with dry ones. At the same time, a significant increase in the intensity of thermal radiation of limestone samples subjected to compression with an increase in their water saturation was recorded, which makes it necessary to take into account the revealed regularity when identifying changes in the stress state of stone structures established according to non-contact IR diagnostics in real conditions.

Based on the ab initio calculations within the density functional theory and crystal structure prediction algorithms, the structure and stability of compounds in the Ni–S system at pressures of 100...

The behavior of binary composites (BC) containing polyvinyl alcohol (PVA‑1799) and various amounts of microcellulose (MC) in water and biochemical media (soil, compost, water-silt mixture) is studied. The results of the experiment emphasize the complex nature of the biodegradation of the studied composites under natural conditions. Introduction of microcellulose into the polymer matrix of PVA about 60 vol.% is accompanied by the formation of a porous structure that promotes the penetration of water and components of biochemical media into the volume of the material. At the same time, the uniform distribution of the MC fibers creates the effect of a reinforcing filler and allows you to maintain strength even with prolonged soaking of the BC. The achievement of «zero» strength at exposure in water is observed after 2 days, 14 days, 2 months. for BC with a content of MC 0, 80–60, 40–10 vol.%, respectively. After 6 months of incubation in the soil environment, the index of destruction of composites was 0.89, 0.87, 0.95, 0.96 with a degree of filling with microcellulose of 10, 20,40, 80 vol.%, respectively, while there was a lack of fragmentation of the samples. A method of computer colorometry in the dynamics of biodegradation of polysaccharide-filled thermoplastics is proposed to assess the degree of penetration of components of biochemical media into the volume of the material

The molecular-dynamics simulation of the formation of dimers for the case of the low-temperature (001) reconstruction of a GaAs surface terminated in Ga or As atoms is employed using the analytical potential, which takes into account σ- and π-bonds between atoms. The values of the decrease in the potential energy of atoms during the formation of the surface of an isolated dimer are found, and it is discovered that the potential energy of an atom in the As dimer is lower by several tenths of eV than that in the Ga dimer. In the temperature range of 25–40 K, the kinetics of the initial stages of the formation of Ga dimers is studied, and it is obtained that the characteristic energy of thermal activation of the formation of single isolated Ga dimers is ~29 meV and lower than the same value for As dimers (~38 meV). In the temperature range of 28–37 K, the time constants characterizing the average rate of the conversion of a single dimer into a chain of two dimers are estimated. For double Ga and As dimers, the reciprocal values of these times turn out to be in the ranges of 1011–1012 and 109–1010 s–1, while similar parameters for the formation of single dimers lie in the range of 4 × 106–108 and 1.4 × 106–7.4 × 107 s–1.

Here, the synthesis of holey carbonylated (C-ny) graphene derivative and its application for gas sensing is demonstrated. The carbonylation of graphene oxide leads to the 3-fold increase in the concentration of carbonyl groups’ up to 9 at.% with a substantial elimination of other oxygen functionalities. Such a chemical modification is accompanied by the perforation of the graphene layer with the appearance of matrices of nanoscale holes, leading to corrugation of the layer and its sectioning into localized domains of the π-conjugated network. Combined with the predominant presence of carbonyls, granting the specificity in gas molecules adsorption, these features result in the enhanced gas sensing properties of C-ny graphene at room temperature with a selective response to NH3. Opposite chemiresistive response towards ammonia when compared to other analytes, such as ethanol, acetone, CO2, is demonstrated for the C-ny graphene layer both in humid and dry air background. Moreover, a selective discrimination of all of the studied analytes is further approached by employing a vector signal generated by C-ny multielectrode chip. Comparing the experimental results with the calculations performed in framework of density functional theory, we clarify the effect of partial charge transfer caused by water and ammonia adsorption on the chemiresistive response.

The mid-infrared (IR)-sensitive n/p-junction was fabricated on a p-doped silicon (Si) wafer via ultrashort laser n-type surface hyperdoping and high-temperature annealing. First, the n-type sulfur ...

Based on density functional theory and the crystal structure prediction methods, USPEX and AIRSS, stable intermediate compounds in the Ni–X (X = B, C, and N) systems and their structures were determined in the pressure range of 0–400 GPa. It was found that in the Ni–B system, in addition to the known ambient-pressure phases, the new nickel boride, Ni2B3-Immm, stabilizes above 202 GPa. In the Ni–C system, Ni3C-Pnma was shown to be the only stable nickel carbide which stabilizes above 53 GPa. In the Ni–N system, four new phases, Ni6N-R, Ni3N-Cmcm, Ni7N3-Pbca, and NiN2-Pa, were predicted. For the new predicted phases enriched by a light-element, Ni2B3-Immm and NiN2-Pa, mechanical and electronic properties have been studied.

Using molecular dynamics simulation and evolutionary metadynamic calculations, a series of structures were revealed that possessed enthalpies and Gibbs energies lower than those of aragonite but hi...

We have studied the growth of GaN layers by the metalorganic vapor phase epitaxy (MOVPE) on sapphire substrates at various reactor pressures, including ones above the atmospheric level. It is established that the epitaxial growth at higher pressures does not affect the crystalline perfection of epilayers, their electron mobility, and background impurity level, but leads to the formation of GaN surface with lower lateral scale of inhomogeneities. In addition, the reactor pressure influences the ratio of edge and impurity lines in the photoluminescence spectra and leakage current level in reversely biased Schottky barriers.

Phases of CaCO3 stabilized at high pressures and temperatures are the potential agents of the global carbon cycle, transferring oxidized carbon in deep Earth’s interiors and thus are of special int...

The new composite chiral stationary phase for high-performance liquid chromatography was prepared and characterized. Poly(styrene-divinylbenzene) microspherical particles with diameter of 3.3 micron were used as a matrix and coated with layer of 10 nm gold nanoparticles. Immobilized gold nanoparticles increased specific surface area of adsorbent and simplify covalent attachment of sulfur-containing compounds. In this work l-lysine conjugate with lipoic acid was synthesized, characterized and used for modification of gold nanoparticles. The prepared chiral selector was immobilized by the reaction of sulfur-containing groups from lipoic acid residue with gold surface of nanoparticles with formation of self-assembled monolayer. The prepared chiral stationary phase was characterized by nitrogen adsorption at low temperatures, diffuse reflection spectroscopy, scanning electron microscopy. The chromatographic retention of beta-blockers and profens was studied under conditions of reversed-phase HPLC. The possibility of enantiomers separation was demonstrated for flurbiprofen and ketoprofen racemates using 100 × 4.6 mm ID chromatographic column.

We describe the performance of a superconductor–insulator–superconductor (SIS) mixer operating in the frequency range of 780–950 GHz. Unlike most SIS mixers, the tunnel junction employs two different superconductors, a niobium nitride top and a niobium bottom electrode sandwiching an aluminum nitride barrier layer, fabricated on a niobium titanium nitride ground plane. The mixer was tested in a pulse tube cryostat, with all the optical components, in the signal path, mounted inside the vacuum environment to avoid attenuation of the RF signal as it propagates from the hot/cold loads to the mixer. With this setup, we have measured an RF-corrected noise temperature of $\sim$ 220 K. In this article, we focus on investigating the influence of local oscillator (LO) power heating on the performance of the terahertz mixer. The increase in the junction's physical temperature can be observed experimentally by noting the suppression of the gap voltage in the pumped current–voltage ( $I\text{--}V$ ) curve as the LO pumping level is increased. Similar observation has already been reported, and attempts were made to estimate the effective temperature of the device using equations of heat transfer between the mixer chip layers. Here, we present an experimental method of quantifying this effect by recovering the effective temperature of the junction through comparing the pumped $I\text{--}V$ curves at different pumping levels and fixed bath temperature, with the unpumped $I\text{--}V$ curves obtained at varying bath temperatures. We also estimate, for the first time, the effect of heating on the noise temperature as a function of bath temperature and frequency. We show that for typical experimental parameters, the LO heating can increase the double-sideband receiver noise temperature by as much as 20%, and that in the frequency range of the measurements, the effective temperature of the junction at fixed LO power increases linearly with frequency at a rate of 0.5 K/100 GHz.

In chiral gold nanotubes, alternating electric current generates an electromagnetic field; under these conditions, the nanotubes become emitting solenoid nanoantennas. With the use of the Maxwell equations and taking into account the geometry of nanotubes, their band structure, and the ballistic model of electron transfer, we have calculated the alternating axial magnetic and azimuthal electric fields generated by helical currents in chiral gold nanotubes. The calculations demonstrate that large alternating magnetic and electric fields can be generated in nanoscale volumes of gold nanotubes and that the eigenfrequencies of the field components are in the X-ray range.

The fluorescence-based methods of single-molecule optical detection have opened up unprecedented possibilities for imaging, monitoring, and sensing at a single-molecule level. However, single-molecule detection methods are very slow, making them practically inapplicable. In this paper, we show how to overcome this key limitation using the expanded laser spot, laser excitation in a nonfluorescent spectral window of biomolecules, and more binding fluorescent molecules on a biomolecule that increases the detection volume and the number of collected photons. We demonstrate advantages of the developed approach unreachable by any other technique using detection of single cardiac troponin-T molecules: (i) 1000-fold faster than by known approaches, (ii) real-time imaging of single troponin-T molecules dissolved in human blood serum, (iii) measurement of troponin-T concentration with a clinically important sensitivity of about 1 pg/mL. The developed approach can be used for ultrafast, ultrasensitive detection, monitoring, and real-time imaging of other biomolecules as well as of larger objects including pathogenic viruses and bacteria.

Phosphorus is one of the potential light elements of the core of the Earth and other planets. The high-pressure behavior of phosphorus compounds with nickel and iron attracts considerable attention...

A set of structures of homomolecular organic crystals with information on the solvent utilized for crystallization was extracted from the Cambridge Structural Database in order to identify possible...

The results of experiments aimed at fabricating and studying the properties of photodetector structures based on single-layer graphene produced by chemical vapor deposition are presented. The configuration of a Ta2O5 vertical microcavity with a resonance wavelength of about 850 nm and a lower dielectric SiO2/Ta2O5 distributed Bragg reflector is taken as the base structure. The conditions for the transfer and fabrication of mesas in the graphene layer on the microcavity surface are optimized. The diagnostics by Raman spectroscopy of the structural quality of graphene after fabrication of the mesas in the graphene layer and contact pads are indicative of the single-layer structure of graphene with a low intensity of features in its spectrum, responsible for imperfection of the structure. The photocurrent is measured under local optical pumping.

Low-carbon steel (Type 20) is subjected to cathodic carburizing followed by quenching and anodic plasma electrolytic polishing. The structure of the surface layer and its elemental composition are established, and the microhardness distribution within the surface layer, as well as its surface roughness, are measured. The microhardness of the surface layer exceeds 900 HV after carburizing at 900°C for 20 min in a solution containing ammonium chloride and glycerol. It is established that an increase in the surface roughness Ra to 9 μm after cathodic carburizing is related to the formation and destruction of an outer oxide layer. It is shown that the surface roughness can be reduced to 3.5 μm by anodic polishing in a 3% solution of ammonium chloride for 180 s.

Magnetic fields generated by nanosolenoids based on gold nanotubes have been calculated. The electron energy levels in nanotubes have been calculated by the linearized augmented cylindrical wave method with cyclic Born–Von Karman boundary conditions and with taking into account helical symmetry of the tubes. The numbers of conducting channels, low-temperature ballistic electron currents, and magnetic fields in nanosolenoids based on gold nanotubes of various length and structure have been determined. The data obtained demonstrate that chiral gold nanotubes are promising materials for creation of nanosolenoids with strong magnetic fields and can be used for more realistic design of nanosolenoids.

The effect of gamma irradiation and doping with silicon dioxide on the first-order solid-state phase transition in polytetrafluoroethylene is studied by the differential scanning calorimetry method. A quantitative analysis of the profiles of the heat capacity peaks is carried out on the basis of the theory of diffuse phase transitions. It is shown that the elementary volume of the phase transformation depends on the γ irradiation and the concentration of silicon dioxide.

Spaser nanoparticles, with ultranarrow spectral line width, small size and good biocompatibility, offer a bright prospect as potential biological probes. Sadly, over ten years since the first demon...

Unique sulfur- and carbon- doped silicon nanoparticles, as well as partially oxidized, are obtained by nanosecond laser ablation of silicon in liquid carbon disulfide. Detailed structural, chemical, and optical characterization of these particles was performed by scanning and transmission electron microscopy, IR spectroscopy, energy dispersive X-ray spectroscopy, and Raman scattering spectroscopy. It is shown that the sulfur concentration in particles is on the order of 1 at %, owing to which they demonstrate a considerable absorption in the mid-IR region.

An orthorhombic modification of (Fe,Ni)2P, allabogdanite, found in iron meteorites was considered to be thermodynamically stable at pressures above 8 GPa and temperatures of 1673 K according to the results of recent static high-pressure and high-temperature experiments. A hexagonal polymorphic modification of (Fe,Ni)2P, barringerite, was considered to be stable at ambient conditions. Experimental investigation through the solid-state synthesis supported by ab initio calculations was carried out to clarify the stability fields of (Fe,Ni)2P polymorphs. Both experimental and theoretical studies show that Fe2P-allabogdanite is a low-temperature phase stable at ambient conditions up to a temperature of at least 773 K and, therefore, is not necessarily associated with high pressures. This is consistent with the textural relationships of allabogdanite in iron meteorites.

Design of cathodic protection systems of the trunk pipeline is regulated by current standards, based on the condition of uniformity and constancy of the electric conductivity of the multilayered half-space surrounding the pipeline. The current mathematical models of such systems also use an average value of the medium electric conductivity, which does not fully reflect the actual characteristics of the soil, in which the pipeline is laid. The authors present a method that accounts for the thickness and electrical conductivity of individual beds in a vertically-inhomogeneous, horizontally layered medium (the most practically appropriate case). Using method of computational experiment, the authors showed the importance of accounting for the effect of the medium layers structure and electrical resistivity on the protective voltage of the electric current in the cathodic protection system for underground trunk pipeline and studied the magnetic field sensitivity dependence on the insulation resistance of the pipeline defect-containing segments and on the altitude of data acquisition.

Based on the first-principles calculations within the density functional theory and crystal structure prediction algorithms iron phosphide phases stable under pressure of the Earth’s core and tempe...

Magnetic fields generated by the nanosolenoids based on the (5, 3) and (10,7) gold nanotubes (AuNTs) 12–600 Å long with numbers of Au atoms 20–2000 are calculated. The electron energy levels of the finite length tubules were determined using the linearized augmented cylindrical waves method with Born–von Karman cyclic boundary conditions and on account of a helical symmetry of the AuNTs. Using these data, the numbers of conducting channels NF and the low-temperature ballistic electron currents in the finite AuNTs are determined, and finally, the magnetic fields B of the gold nanosolenoids are obtained. Due to the increase in the number of conduction channels with the increase in the length of the tubes, the internal magnetic field gradually increases from 1.6 T/V in a tubule with L = 12 Å up to 12 T/V in a tube with L = 600 Å, slowly approaching the magnetic field of 14 T/V of the infinite (5, 3) AuNT. At a distance of 5 Å from the ends of the tubes (near z = L/2 – 5 Å), this field decreases rapidly, halving at z = L/2 and almost zeroing near z = L/2 + 5 Å. The field from the outside of the tubes is weak but not zero as in the infinite tubule. It is minimal at z = 0 and reaches a maximum at the edge of the AuNTs, where it is about 3–4 times less than the internal field. These results pave the way for a more realistic design of the nanosolenoids.

The piezoelectric properties of lead zirconate titanate (PZT) ceramics can be improved by low-temperature cyclic treatment. It is established that the conditions of ceramics storage predetermine whether a series of high-gradient thermal shock processing will improve or degrade the material properties.

The stability of Fe4H, Fe2H, FeH, Fe3H5, FeH2, FeH3, FeH4, Fe3H13, FeH5, and FeH6 iron hydrides at temperatures of 0–5000 K and pressures of 100–400 GPa has been analyzed for the first time in the density functional theory using the lattice dynamics method in the quasiharmonic approximation, and the corresponding PT phase diagrams have been obtained. It has been found that heating expands a set of stable stoichiometric compounds, so that a number of structures metastable at room temperature are stabilized at temperatures above 1000 K. The topological analysis of structures of iron hydrides indicates that most of them belong to rare or unique topological types. An increase in the amount of hydrogen in a structure is accompanied by the reduction of the length of an H-H bond, which results in the formation of dumbbell-like hydrogen molecules H2 in FeHx structures with x > 6. However, these structures are thermodynamically unstable and decay into a mixture of FeH6 and solid H.

This study considers some aspects of electrolytic plasma in the process of anodic carburising of steel, including the nature of the glow in a vapour gaseous envelope, its thickness under various hydrodynamic conditions; it also examines the formation patterns of a hardened layer after carburising along with quenching in the same electrolyte. The glow in a vapour gaseous envelope was examined with a spectrometer; its profile and thickness were determined by solving energy and mass balance equations in a pre-anode area. The structure of the carburised layer and hardness distribution were explored with an optical microscope and a microhardness tester. Carbon concentration in the carburised layer was determined by means of optical emission spectroscopy. The investigation has revealed that the glow in a vapour gaseous envelope under carburising is a continuous emission from heated bodies—vapour gaseous phase and the sample without any electric discharges. It has been theoretically derived, that in laminar approximation the layer has maximal thickness under certain hydrodynamic conditions. This conclusion has been confirmed by homogeneous distribution of current density throughout the surface of the sample during its carburising under condition of force hydrodynamics, i.e. the sample being flowed round with cooled electrolyte. Aerated stirring in electrolyte does not provide homogeneous current density distribution, which falls in vertical direction. Anodic carburising of steel in a glycerol electrolyte followed by quenching results in the formation of a martensitic layer up to 200 μm in thickness, within 5-min treatment, with maximal microhardness 1000 HV.

The article describes the research for improvement of properties of low-carbon steel 20 by anodic nitroboriding in the electrolyte containing boric acid in the quantity necessary for ensuring sufficient boron potential in the saturating medium—vapor-gaseous envelope. Current–voltage and temperature–voltage characteristics of plasma-electrolytic treatment in the suggested electrolyte; the influence of oxidation and anodic dissolution processes on weight balance, structure and phase composition of the modified layer, its microhardness, roughness and wear resistance were considered. There was a significant (up to 1180 HV) increase in microhardness and a fivefold decrease in wear and corrosion. The data of tests showed that the operational resource increases more than 45 times for threaded fastening pair subjected to nitroboriding.

It was shown that the nanoindentation treatment of the atomically flat GaAs surface with the tip of atomic-force microscope in contact mode allows to produce small size pits with the depth in the range from a few tenths of nm up to a 1.5 nm. The experimental data can be qualitatively described on the base of kinetic concept of fracture of solid state developed by Zhurkov, which suppose the generation of defects and subsequent destruction of the GaAs surface. The molecular dynamics modelling confirmed thermally activated destruction of a few top atomic layers under indentation. The presented technology could be used to form the shape of solid state surfaces with subnanometer resolution in depth without wet etching processes.

We present a comprehensive study on the influence of Ti doping on K+ migration in the K1–xFe1–xTixO2 solid electrolyte. A novel approach is proposed which is based on modeling of configurational spaces (CSs) and full sets of inequivalent migration pathways by means of density functional theory (DFT) calculations and machine learning (ML) techniques. A 2 × 1 × 1 supercell (32 formula units) of a low-temperature polymorph of the KFeO2 compound with space group symmetry Pbca was used. For the three lowest Ti contents (x = 0.03, 0.06, and 0.09), all symmetrically inequivalent configurations of atomic arrangements (CSs) and K+ migration pathways (total numbers: 128, 59520, and 8630400) were generated. With the DFT-derived energetics of K+ migration at the lowest doping level (x = 0.03), the ML models were trained to predict ionic transport properties by using geometrical descriptors for the pathway-dopant arrangement. The trained ML models were then used to evaluate the K+ migration properties for pathways at ...

It is important to be able to control the physical and chemical integrity of carbon-based porous monolith structures while being tailored for targeted analytical, energy and catalytic based applications. A set up using a CO2 laser in continuous mode (CW CO2 laser) was implemented to cut fragile and porous carbon monolithic (CM) and nanotemplated carbon monolithic (NTCM) rods into discs with a prescribed thickness and dimensional integrity (denoted as LCM and LNTCM, or LCMs). Changes in structure, porosity and composition of LCMs were induced by the efficient thermal energy afforded by the CW CO2 laser irradiation under tightly controlled process conditions. The main effects observed before and after laser cutting were studied in comparison with traditional scalpel blade cutting of carbon monolithic (SCM). FE-SEM images confirmed that the resulting LCMs exhibited a more open, interconnected macroporous structure and smoothed mesopores to a depth of approximately 5 μm, while the structure of the bulk section remained intact. Minimal changes in chemical compositions were confirmed by XPS. Raman spectroscopy revealed a modest increase in the graphitic content on the cross sections of LCM discs. Phenol and Bisphenol A (BPA) was used as a model analyte for demonstration of resulting discs adsorption performance.

We present the design and results of characterization of a new sideband separating (2SB) mixer for 800-950GHz, based on superconductor-insulator-superconductor (SIS) junctions. This is the first waveguide 2SB SIS mixer demonstrated at such a high frequency. The design is following the classical quadrature hybrid architecture, meanwhile additional attention was put on the reduction of reflections in the RF structure in order to minimize the RF imbalance, to achieve a high image rejection ratio (IRR). The RF waveguide block was manufactured by micromilling and populated by single-ended SIS mixers developed earlier for upgrade of the CHAMP+ high-band array on the APEX telescope. These SIS mixers have double-sideband (DSB) noise temperatures from 210 to 400K. The assembled 2SB mixer yields a SSB noise temperature from 450 to 900K, with an IRR above 15dB in 95 of the band. Comparing the DSB and the SSB sensitivities, we find that the waveguide losses are as low as expected and do not exceed 0.6dB. The presented mixer is a prototype for use in a 2SB dual polarization receiver planned for deployment on the APEX telescope.

We report the results of systematic Raman spectroscopy studies of AlxGa1 –xN (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric conditions and growth fluxes. The high-intensity asymmetric low-frequency peak obeying Bose statistics is discovered in Raman spectra of the layers grown by temperature-modulated epitaxy at strongly Ga-enriched conditions. Theoretical model is developed to explain the origin and the high intensity of the observed low-frequency peak, which is attributed to the presence of excessive metallic gallium in AlGaN layers and can be explained by vibrations of gallium clusters with a diameter of ~1 nm. The nature of the low-frequency peak is similar to that of the boson peak in glasses, which occupies the same frequency range in Raman spectra. We demonstrate the capabilities of Raman spectroscopy as an express and non-destructive technique for optimization of growth conditions of AlGaN layers to achieve simultaneously the atomically-smooth droplet-free surface morphology and the high structural quality.