Sample Plane Research Articles

Admittance spectroscopy of dopants implanted in silicon and impurity state-induced AC magnetoresistance effect

A silicon structure doped with Ga using ion implantation has been investigated by admittance spectroscopy. It has been established that the presence of the Ga impurity, along with the B one, in the silicon structure leads to the appearance of the second peak in the temperature dependence of the real part of the impedance (admittance). Moreover, switching-on a magnetic field parallel to the sample plane shifts the singularities in the temperature curve to the high-temperature region. This results in the manifestation of both the positive and negative magnetoresistance effect upon temperature and magnetic field variation. It has been found by the standard admittance spectroscopy analysis of the impedance data that the energy structure of the investigated sample includes two interfacial energy levels ES1(0) = 42 meV and ES2(0) = 69.4 meV. As expected, these energies are consistent with the energies of B and Ga dopants. In a magnetic field, these levels increase by 3 meV for B and 2 meV for Ga, which induces the magnetoresistance effect. It has been demonstrated that the interfacial state-induced magnetoresistance effect can be tuned by ion implantation and dopant selection.

A perpendicular field electromagnet with a 250 mm access bore.

We present a laboratory electromagnet capable of generating magnetic fields up to ±0.48 T, specifically designed as a perpendicular flux source for thin film samples in an ambient environment. The magnet features a 250 mm diameter clear access bore above the sample plane, thus offering compatibility with a wide variety of experimental apparatus. Despite its generous size, the magnet thermally dissipates less than 1 kW at maximum field. A shaped ferromagnetic core is used to amplify and homogenize the field B, leading to an estimated uniformity of ±1.5 mT (≲0.3%) in B within a 28 mm2 zone at maximum field. The sample stage is thermally regulated and isolated from the magnet, enabling temperature control with ±5 mK precision even at elevated magnetic fields.

Methodical errors in measuring the specular reflection coefficient from a planar sample of material for two types of measuring facilities

This paper is discussed two methods for measuring the bistatic scattering characteristics of flat samples of the material. The experimental studies and numerical simulations of the dependence of the specular reflection coefficient on the incident angle of wave on a flat material sample carried out in the bistatic scheme of the experiment (rotation of the receiving and transmitting antennas) and in the monostatic scheme using a dihedral corner reflector (rotation of the object). Measurements for the magnetodielectric flat sample were carried out in ITAE RAS on two test facilities with the corresponding scheme of the experiment. To identify the errors of the methods used, we carried out numerical simulations of the measurement of the specular reflection coefficient of the sample under test by the method of integral equations (method of moments) in the FEKO program in the formulation of two experimental schemes. The obtained results were compared with each other and with the results of analytical calculations of the specular reflection coefficient carried out using the Fresnel formulas when considering an infinite flat layer of material. These calculations make it possible to compare the methodical errors in measuring the reflection coefficient in the two considered experimental schemes. It was shown that the results of the measurements using the corner reflector give methodical errors (deviations from the analytical calculation) by 1–2 dB more than the measurements on the bistatic facility. The results of experiments and numerical simulations are in agreement with each other. The conclusions obtained in this work are applicable to any experimental facilities for the study of planar materials.

Composite materials based on polyacrylamide and gelatin reinforced with polypropylene microfiber

The conditions for preparation of a composite hydrogel based on polyacrylamide and gelatin, which is reinforced with polypropylene microfiber, were determined to increase its strength. The conditions of modification of polypropylene microfiber were established under which its surface is hydrophilized, which was confirmed by a significant increase in the water retention of microfiber by 11.0–15.2 times. Under the same conditions, an increase in the values of the hydrogen component of free surface energy on planar samples of polypropylene was observed (from 2.81.0 mN m–1 to 29.81.0 mN m–1). Optimal conditions (minimum limits of component concentrations, temperature range, and pH of a medium) were determined, under which a hydrogel based on polyacrylamide and gelatin with satisfactory physicochemical and mechanical properties can be formed. A composite hydrogel, based on polyacrylamide and gelatin reinforced with modified polypropylene microfiber, was prepared. It was found that the introduction of modified microfiber increases the limits of the beginning of destruction from 20–30 to 130 kPa. The results of the investigation of the drug release from the hydrogel indicated that the obtained composites can be used as matrices to create a hydrogel therapeutic bandages with the function of prolonged drug delivery.

Direct spectroscopic observation of Berry-phase interference in the Ni4 single-molecule magnet

Berry phase effects in spin systems lead to the suppression of tunneling effects when different tunneling paths interfere destructively. Such effects have been seen in several single-molecule magnets (SMMs) through measurements of magnetization dynamics, where the experimental signal may arise from the contributions of numerous energy levels. Here we present experimental measurements of Berry phase interference effects that are determined through electron-spin resonance on a four-fold symmetric SMM. Specifically, we measure transitions between tunnel-split excited states in the Ni$_4$ SMM in the presence of a transverse field in the hard plane of the crystalline sample. By using a home-built rotation apparatus, the direction of the sample can be changed \textit{in situ} so that that the field direction can be swept through the entire hard plane of the sample. When the field is in certain directions in the plane, we observe a splitting of the transition, a hallmark of Berry phase interference. The experimental results are well reproduced by theoretical predictions, and fitting of the data provides information about the effects of dipolar interactions and sample misalignment.

Optimization of Adsorbent Layer Type and Developing Solvent in Coccidiostats Sample Preparation with Procedure of Solvent Front Position Extraction.

Coccidiostats are drugs used against coccidiosis, a common disease among breeding animals. Their widespread application leads to the appearance of their residues in food, which is potentially harmful for human health and life. The European Union has established limits of concentrations of these drugs in premixtures and food. Nowadays, there are many methods for monitoring coccidiostats’ presence in market products, but their frequent weakness is sample preparation. Solvent Front Position Extraction is a planar chromatography-based sample preparation method that allows for effective assay of samples with coccidiostats when coupled with LC-MS/MS. The purpose of this research was to find common conditions for the effective isolation of eight coccidiostats from biological sample components with both lower and higher retention than the substances of interest. The acquired results were used for effective isolation of monensin and salinomycin from the premixture samples and allowed for their quantitative determination. The application of a semi-automatic device for the development of chromatograms positively impacted the results, confirming the effectiveness of the method for determining coccidiostats in biological samples.

Long-time drift induced changes in electrical characteristics of graphene–metal contacts

Chemical vapour deposition (CVD) graphene is commonly recognized as promising 2D material for development of electronic devices. However, the long-term drift of electrical parameters still requires deeper understanding before the technological means can be selected for an individual type of the devices. In this work, the changes in the electrical resistance were investigated over long time in the planar samples based on the CVD graphene with Au and Ni contacts. The samples were arranged as arrays of the resistors on a silicon substrate covered with a 250 nm layer of thermally grown silicon dioxide. The annealing in pure argon gas flow at 573 K was used to return the electrical properties of samples to the initial state. The effects of drift and annealing were compared for the three parts of structures, namely the electrical contact, the graphene sheet and the edge of the metal film with a hanging graphene sheet. For these parts, the resistance changes were related to the strain and doping of supported and hanged parts of the graphene sheet. Raman spectroscopy and Kelvin force probe microscopy were used to characterize charge doping, strain and work function in the graphene. The drift was explained in terms of the most prominent changes in the doping, strain and work function detected within the edge zone of the contact. It was proved that the annealing significantly changed the p-type doping and work function in the graphene layer in this edge zone. The properties were almost independent of test conditions in the SiO2 supported graphene. The changes in the contact parameters produced by drift mechanisms were proved being reversible under proper annealing conditions.

Cathodoluminescence of Ultrathin Twisted Ge1- x Snx S van der Waals Nanoribbon Waveguides.

Ultrathin van der Waals semiconductors have shown extraordinary optoelectronic and photonic properties. Propagating photonic modes make layered crystal waveguides attractive for photonic circuitry and for studying hybrid light-matter states. Accessing guided modes by conventional optics is challenging due to the limited spatial resolution and poor out-of-plane far-field coupling. Scanning near-field optical microscopy can overcome these issues and can characterize waveguide modes down to a resolution of tens of nanometers, albeit for planar samples or nanostructures with moderate height variations. Electron microscopy provides atomic-scale localization also for more complex geometries, and recent advances have extended the accessible excitations from interband transitions to phonons. Here, bottom-up synthesized layered semiconductor (Ge1- x Snx S) nanoribbons with an axial twist and deep subwavelength thickness are demonstrated as a platform for realizing waveguide modes, and cathodoluminescence spectroscopy is introduced as a tool to characterize them. Combined experiments and simulations show the excitation of guided modes by the electron beam and their efficient detection via photons emitted in the ribbon plane, which enables the measurement of key properties such as the evanescent field into the vacuum cladding with nanometer resolution. The results identify van der Waals waveguides operating in the infrared and highlight an electron-microscopy-based approach for probing complex-shaped nanophotonic structures.

Метод и реализация высокоэффективной диагностики формы электронного зонда растрового электронного микроскопа

An important unit of an electron microscope is the system controlling the electron beam, responsible for raster forming on the specimen and the electron probe focusing, which provides an achievement of minimum of aberrations and the maximum of resolving capacity of formed electron image. During using electron microscope the image quality gradually deteriorates, manifesting the resolving capacity reduction and the astigmatism appearance. An attachment developed for the raster electron microscope, permitting to perform the highly effective diagnostics of the configuration of the scanning electron beam, controlled by a precision magneto-optical system, has been offered. It has been shown that the direct visual observing the scanning electron probe, in particular the evaluation of the ellipticity of its cross-section using the WEB camera matrix, combined with the sample plane, as a result, provides more efficient tuning and repair of the scanning electron microscope.

The X-Ray Fundamental Plane of the Platinum Sample, the Kilonovae, and the SNe Ib/c Associated with GRBs

Abstract A large fraction of gamma-ray burst (GRB) lightcurves (LCs) show X-ray plateaus. We analyze all GRBs with known redshifts presenting plateaus observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. The fundamental plane relation between the rest-frame time and X-ray luminosity at the end of the plateau emission and the peak prompt luminosity holds for all the GRB classes when selection biases and cosmological evolutions are applied. We have discovered two important findings: (1) a new class of long GRBs with good data coverage: the platinum sample; and (2) the platinum, the SNe-LGRB, and the KN-SGRB samples, yield the smallest intrinsic scatter with σ platinum,GRB−SNe = 0.22 ± 0.10 and σ KN−SGRB = 0.24 ± 0.12. The SNe-LGRBs are composed of GRBs associated spectroscopically with the SNe Ib,c, the KN-SGRBs are composed by eight GRBs associated with kilonovae or where there could have been such an association. The highest correlation coefficients are yielded for the SN-LGRB-ABC sample, which includes GRBs spectroscopically associated with SNe Ib/c or with a clear optical bump in the LC resembling the SNe Ib/c, ( ), the SN-LGRBs ( ), and the KN-SGRBs ( ) when the redshift evolution is considered. These category planes are reliable candidates to use as cosmological tools. Furthermore, the distance from the gold fundamental plane is a crucial discriminant among classes. In fact, we find that the distributions of the distances of the SNe-LGRB, SNe-LGRB-ABC, KN-SGRB, and SGRB samples from the gold fundamental plane are statistically different from the distribution of the gold GRBs’ distances from the gold fundamental plane with and without considering evolution cases.

Electrodeposition of Cuprous Oxide on a Free-Standing Porous Cu Framework for Photoelectrochemical Water Splitting

The use of hydrogen as a chemical fuel is an attractive and promising method as an alternative sustainable green energy carrier. The combination of direct sunlight and semiconductor photoelectrodes in a photo-electrochemical (PEC) cell can generate hydrogen by splitting water molecules into H2 and O2 1. Copper(I) oxide or Cuprous oxide (Cu2O) is a p-type semiconductor with a bandgap of ~2 eV which makes it suitable for solar visible light absorption and it possesses a suitable band position for water reduction to hydrogen in the PEC cell2. The focus here is to increase the surface area of Cu2O photocathode to improve the PEC water splitting performance. Using dynamic hydrogen-bubble assisted electrochemical deposition method, a highly porous Cu substrate was synthesized in an acid copper sulfate bath at current densities above -1 A/cm2. To obtain a free-standing porous copper framework the structure must be reinforced at a lower current density using the same acidic bath and was separated from the substrate via ultrasonication The Cu2O crystal was then deposited on the free-standing porous Cu framework from an alkaline copper bath. The photoelectrochemical analysis of Cu2O was performed using a solar simulator at 1.5 AM and it shows a significant improvement of the photocurrent in comparison to the planar sample. M. Grätzel, Nature, 414, 338–344 (2001).A. Paracchino, V. Laporte, K. Sivula, M. Grätzel, and E. Thimsen, Nat. Mater., 10, 456–461 (2011). Figure 1

Influence of planes of anisotropy on physical and mechanical properties of freshwater limestone (Mudstone)

The formation of the freshwater lakes and travertine limestone was caused by the tectonic depression, which occurred in the Dinarides during the Miocene. This stone has been exploited and used since far back on the territory of Bosnia and Herzegovina as a building stone and for different architectural purposes. Most of the investigations were concentrated on the “tenelija” stone due to its massive use and construction of the famous Stari Most (Old Bridge) in Mostar. Not much investigation was devoted to “miljevina” (mudstone) which belongs to the same petrographic type. This is a soft carbonate rock that is highly porous, has small density, relatively low strengths, poor wear resistance, and low resistance to frost. In this paper, the influence of layers (planes of anisotropy - foliation) of the mudstone was investigated. Within an experimental campaign, numerous sets of tests were performed on different samples. Tests include uniaxial compressive strength (UCS) on cube and cylinder specimens, flexural strength under concentrated load and constant moment, tensile strength based on Brazilian tests, determination of Young’s modulus, modulus of deformations, and Poisson ratio. Prediction of UCS and Young’s modulus, as elastic mechanical characteristics, represent the main goal in engineering projects. Additionally, the influence of sample conditions and planes of anisotropy was investigated. Results have been compared and correlations are established. As a result, a new relation between uniaxial compressive strength obtained on cube and cylinder samples for a stone of low compressive strength is proposed.

Laser scanning reflection-matrix microscopy for aberration-free imaging through intact mouse skull

A mouse skull is a barrier for high-resolution optical imaging because its thick and inhomogeneous internal structures induce complex aberrations varying drastically from position to position. Invasive procedures creating either thinned-skull or open-skull windows are often required for the microscopic imaging of brain tissues underneath. Here, we propose a label-free imaging modality termed laser scanning reflection-matrix microscopy for recording the amplitude and phase maps of reflected waves at non-confocal points as well as confocal points. The proposed method enables us to find and computationally correct up to 10,000 angular modes of aberrations varying at every 10 × 10 µm2 patch in the sample plane. We realized reflectance imaging of myelinated axons in vivo underneath an intact mouse skull, with an ideal diffraction-limited spatial resolution of 450 nm. Furthermore, we demonstrated through-skull two-photon fluorescence imaging of neuronal dendrites and their spines by physically correcting the aberrations identified from the reflection matrix.

Optical Trapping of Photosoftened Solid Polymers

We present evidence of optical trapping of solid polymer films by a tightly focused near-infrared (NIR) laser beam (785 nm) when the polymer is softened by green laser (532 nm) irradiation, which is uniformly distributed over the film surface. While the whole film is softened by the green laser, only the part which is subjected to the NIR laser is trapped. The film, which is transparent in the NIR range and strongly absorbs the visible light, is deposited on a glass substrate. The NIR laser is focused at the sample plane and attracts the polymer to the laser focus, by the optical gradient force, during the green light irradiation, indicating that molecular mobility is strongly reduced and the optical gradient force of the NIR laser is inefficient in moving the polymer below the glass-transition temperature of the polymer without photosoftening. The observations are consistent with the theory of photochemical tweezing, which rests on the assumption that photosensitive polymers, containing azo dyes, are softened, i.e., molecular mobility is enhanced, by photoisomerization of the azo dyes during green light irradiation, and are moved in gradients of light fields. We also found that this two-color laser tweezing scheme is sensitive to light polarization, owing to the polarization sensitivity of the azo dye chromophores.

Anisotropy of magnetoelectric effects in an amorphous ferromagnet-piezoelectric heterostructure

In-plane anisotropy of linear and nonlinear magnetoelectric (ME) effects in a heterostructure composed of mechanically coupled layers of amorphous iron-based ferromagnet and piezoelectric lead zirconate-titanate ceramics has been investigated. The measurements were performed on a disk-shaped sample subjected to a low-frequency excitation magnetic field h oriented either parallel or perpendicular to a bias magnetic field H0. The first harmonic of the voltage response was recorded in the case of the linear ME effect, which was excited at frequencies of acoustic resonances of the sample, and the second harmonic in the case of the nonlinear ME effect excited in the non-resonance regime. Strong uniaxial or biaxial anisotropy for different directions of the bias field within the sample plane was observed. The uniaxial anisotropy of the ME effect occurs due to the uniaxial magnetic and magnetostrictive anisotropy of the amorphous ferromagnetic layer that is a result of its fabrication by the ultrafast cooling method. The biaxial anisotropy at resonant frequencies is the manifestation of the spatial structure of the excited acoustic modes. The anisotropy of ME effects should be taken into account when developing magnetoelectric devices based on composite heterostructures.

Microconical surface structuring of aluminium tubes by femtosecond laser processing

Femtosecond laser microstructuring is a convenient technology for the targeted surface functionalization of various materials. Commonly, the structuring process is performed on planar surfaces. Here, we investigated femtosecond laser structuring of aluminium tubes. Process parameters, i.e. the number of pulses per spot on the surface and the line distance, have been transformed from a line-by-line process on planar samples towards a helical process. The process is based on laser treating the rotating tube while the laser beam is moved along the axis of the tube. A significant difference of the surface structure obtained on a cylinder in comparison to the planar geometry is revealed. With exactly matching process parameters, a strong increase of the dimensions of the surface structures on aluminium tubes has been observed. With a typical parameter set to achieve microconically structured aluminium, the cone height increases from 5 to 24 μm and the cone-to-cone distance from 13 to 59 μm. The structure sizes were found to be unaffected from the diameter of the tube within a range from 12 to 40 mm. A possible explanation for the increased structure size is given by altered particle redeposition. Two different parameter sets have been transformed from a planar geometry to the cylindrical geometry. Deep black aluminium tubes providing hydrophobicity with a water contact angle up to 148° and a thermal emissivity up to 87% are demonstrated.

Magnetic Resonance Force Spectroscopy of Magnetic Vortex Oscillations

Forced oscillations of magnetization of NiFe circular disk in the presence of external longitudinal magnetic field are studied with the aid of micromagnetic simulation and experiments using magnetic resonance force spectroscopy. Main attention is paid to low-frequency resonance related to gyrotropic motion of the core of magnetic vortex. The resonance frequency of the gyromode is significantly shifted when the external magnetic field is applied in the sample plane. Effect of nonuniform magnetic field of the probe on the oscillations of magnetization is discussed.

Investigation of Stress State in Plane Truss Nodes

Stress state in a plane truss node was studied in two ways: numerically using the finite element method and experimentally using the photoelasticity method. The finite element method was used to calculate plane truss model. Photoelasticityor polarization-optical method was used to research stresses of piezo-optical materials. The picture of interference fringe patterns in the model of a plane truss was obtained by the method of photoelasticity. Stresses were calculated with their help. The purpose of the work was to compare both methods. Fields of maximum tangent stresses were obtained in the sample plane using both methods. This work is a continuation of [1]. So, we obtained picture of interference fringe patterns and isocline fields in the node of the farm model, using the photoelasticity method. The field of maximum tangent stresses in the truss node was obtained by the photoelasticity method. The stress fields in the truss node were obtained by the finite element method in the software package “SCAD”. A comparative analysis of the numerical and physical experiments results was carried out and it was found that the nature of the stress distribution in both numerical and physical experiments coincides.

Study of stresses in plane truss nodes

in this paper, the stress state in a plane truss node was studied in two ways: numerically using the finite element method and experimentally using the photoelasticity method. The finite element method was used to calculate plane truss model. Photoelasticity or polarization-optical method was used to research stresses of piezo-optical materials. The picture of interference fringe patterns in the model of a planetruss was obtained by the method of photoelasticity. Stresses were calculated with their help. The purpose of the work was compared with both methods. Fields of maximum tangent stresses were obtained in the sample plane using both methods.

An investigation of the possibility of estimating the residual shear strength of rough joints using planar small joint in limestone rocks

Determining the residual frictional properties of rock discontinuities in detail is crucial for the design of safe rock structures. In this paper, direct shear experiments were conducted on two types of artificial limestone joint samples (rough standard tensile joints and grinded planar small joints). The primary goal of this study is to compare the shear behavior of the two above-mentioned types of rock joints during the residual state of shear. The result of roughness analysis shows that during the shearing of rough joints, the increase in normal stress resulted from reduction in contact area which is caused by the mismatch between two surfaces in residual state, will lead to the stress concentration, asperity degradation and plastic deformations. Therefore, several CNL direct shear tests under different normal stresses were carried out on planar joint samples having small contact area (10 × 10 mm2) and it was found that when approximately similar normal stress acts on contact areas during residual state, the residual shear strength measured from those ground surfaces show a good accordance with the residual friction of standard rough joint samples.