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In this study, the influence of ceramic shield characteristics, including thickness and geometry, on the transmission spectrum and electron density measurements of a ceramic shield cutoff probe (CSC) was investigated to measure high-density or process plasma. Through electromagnetic simulations and circuit modeling, we examined the measurement characteristics of the CSC based on different ceramic shield geometries. When the ceramic shield is sufficiently thin, it does not affect the CSC wave transmission characteristics. However, for a thick ceramic shield, a cutoff frequency shift of up to 3% toward the lower side can occur. This shift is attributed to the electrical properties of the ceramic material, which can function as a parasitic capacitor. In addition, when fabricating a CSC, depending on the shape of the ceramic shield or the method used to couple it with the CSC body, a cutoff frequency shift can occur toward the lower side. The simulation results were validated through experiments, revealing a cutoff frequency shift toward the lower side of up to 18.0% in the simulations and up to 11.6% in the experiments. The findings of this study could assist in high-density or processing plasma measurements using cutoff probes. [ABSTRACT FROM AUTHOR]

We investigated the effect of the sheath around the probe tips on the transmission spectrum of a cutoff probe using an electromagnetic simulation and a circuit model. Our results show that the width of the sheath can change the transmission spectrum, which can affect the absolute value of the electron density. In a real-world cutoff probe structure, this effect may become apparent in a low-density plasma or when a high bias voltage is applied to the plasma. The key factor is capacitance, which contains the sheath component. In the case of a low-density plasma, the change in the sheath capacitance of the sheath region contributes to the shift in the resonant frequency. For thick sheath widths, at least a 5% discrepancy can occur between the actual plasma frequency and the measurement owing to variations in the capacitance, particularly the sheath components surrounding the probe. We expect that this study will facilitate reduction in the measurement error and uncertainty in microwave cutoff probe measurements, particularly when applied to low-density plasma measurements. [ABSTRACT FROM AUTHOR]

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect. [ABSTRACT FROM AUTHOR]

A flat-cutoff sensor installed on the chamber wall or chuck allows precise measurement of the plasma density in real time, even with a wafer placed on the sensor. However, a few studies have been conducted on the measurement characteristics in an environment where a wafer containing a metal layer is placed on a sensor. In this study, we investigated the effect of wafers containing metal layers on flat-cutoff sensor measurements using circuit models and experiments. The metal layer in the wafer shifts the cutoff frequency up to four times higher, and the degree of shift depends on the plasma density. The relationship between the shift in the cutoff frequency and plasma density can be interpreted as the ratio of the plasma inductance to that of the metal layer from the circuit model of the flat-cutoff sensor. The calculation results were verified experimentally using wafers containing Al and Ti metal layers. As a result, measurement was found to be possible even when a wafer containing a metal layer was placed on a flat-cutoff sensor, and these results can improve the measurement accuracy of the flat-cutoff sensor for the real-time plasma measurement. [ABSTRACT FROM AUTHOR]

A detailed consideration of the discrete mobility-spectrum analysis (DMSA) method and its application to transport studies in HgCdTe is given. First, a brief review of the methods of the analysis of field dependences of the Hall coefficient and conductivity in HgCdTe-based structures with a multi-carrier mobility spectrum is presented. The advantages and drawbacks of these methods, which include original mobility-spectrum analysis by Beck and Anderson, multi-carrier fitting and iterative approach by Dziuba and Górska, and the later developments of these techniques, are considered. The properties of the envelope of the mobility spectrum are analyzed, and the specifics of DMSA are presented. Analysis of some magnetic-field B dependences of conductivity tensor components σxx(B) and σxy(B) presented in the literature is performed with DMSA, and the results are compared to those obtained with other methods. [ABSTRACT FROM AUTHOR]

There is a growing concern within the surface science community that the massive increase in the number of XPS articles over the last few decades is accompanied by a decrease in work quality including in many cases meaningless chemical bond assignment. Should this trend continue, it would have disastrous consequences for scientific research. While there are many factors responsible for this situation, the lack of insight of physical principles combined with seeming ease of XPS operation and insufficient training are certainly the major ones. To counter that, we offer a comprehensive tutorial written in the form of a step-by-step guide starting from experimental planning, through sample selection and handling, instrument setup, data acquisition, spectra analysis, and results presentation. Six application examples highlight the broad range of research questions that can be answered by XPS. The topic selection and the discussion level are intended to be accessible for novices yet challenging possible preconceptions of experienced practitioners. The analyses of thin film samples are chosen for model cases as this is from where the bulk of XPS reports presently emanate and also where the author's key expertise lies. At the same time, the majority of discussed topics is applicable to surface science in general and is, thus, of relevance for the analyses of any type of sample and material class. The tutorial contains ca. 160 original spectra and over 290 references for further reading. Particular attention is paid to the correct workflow, development of good research practices, and solid knowledge of factors that impact the quality and reliability of the obtained information. What matters in the end is that the conclusions from the analysis can be trusted. Our aspiration is that after reading this tutorial each practitioner will be able to perform error-free data analysis and draw meaningful insights from the rich well of XPS. [ABSTRACT FROM AUTHOR]

Perovskite La2Ti2O7 nanocrystalline powder was obtained through the shock synthesis method. In the study, La2O3 and TiO2 powders were mixed through ball milling and, subsequently, shocked by a flyer at a velocity of 3.2 km/s. After shock treatment, the sample was recovered and characterized via various techniques, such as x-ray diffraction, Raman, scanning electron microscope, transmission electron microscope, and ultraviolet-visible diffuse reflection spectrum analysis, to find the presence of La2Ti2O7 nanocrystalline powder with an average grain size of approximately 30 nm in the recovered samples with different yields. Moreover, the results further confirm that the high shock temperature and long ball milling treatment induce higher activation of precursors to improve the La2Ti2O7 content in the recovered samples. By adjusting the relative density of precursor and the ball milling period, pure La2Ti2O7 nanocrystalline powder was obtained. The formation mechanism of La2Ti2O7 was carefully illustrated. This study presents a new method to synthesize La2Ti2O7 nanocrystalline powder by detonation-driven flyer impact. [ABSTRACT FROM AUTHOR]

Mobility spectrum analysis (MSA) is a process of recovering the spectrum of carrier mobilities in an electronic material from a magnetic-field-dependent Hall measurement. This paper first presents a set of useful general properties of MSA that are true for all MSA methods. One such property is that Hall data can be classified as either "physical," with at least one spectrum of carrier mobilities that exactly fits the data, or "unphysical," where no mobility spectra exactly fit the data and the analysis must find approximate solutions. Almost all experimental Hall data collected at seven or more magnetic fields are slightly unphysical. The closest approximate solution for such unphysical data is always a set of discrete-carrier mobilities. A new method for multicarrier MSA is presented to display the likely properties of the discrete carriers as two-dimensional spectra vs both mobility and carrier density instead of one-dimensional spectra vs only mobility, as in previous methods. Measurement uncertainties are included as a fundamental part of the analysis so that the user can easily view the resultant uncertainty in the derived carrier properties. A separate method is also presented for reliably determining a smooth, high-entropy spectrum of carrier mobilities, which is constructed as the maximum-entropy linear combination of discrete-carrier solutions to the Hall data. An example using calculated Hall data corresponding to acoustic phonon scattering shows that the technique could potentially be used to measure the continuous mobility distributions that result from different scattering mechanisms. [ABSTRACT FROM AUTHOR]

Recent progress on (Si)GeSn optoelectronic devices holds great promise for photonic integration on Si substrates. In parallel to the development of bulk devices, (Si)GeSn-based quantum wells (QWs) have been investigated, aiming to improve device performance. While multiple QW structures are preferred for the device applications, a single quantum well (SQW) is more suitable for optical property studies. In this work, a comprehensive study of an SiGeSn/GeSn SQW was conducted. The calculated band diagram provided band alignment and energies of possible transitions. This SQW features a direct bandgap well with L–Γ valley energy separation of 50 meV, and barrier heights for both electron and hole are greater than 80 meV. Using two continuous-wave and two pulsed pumping lasers, the analysis of PL spectra allows for identifying different transitions and a better understanding of the SQW optical properties. This study could provide guidance for advancing the future QW design toward device applications. [ABSTRACT FROM AUTHOR]

A single-phase white light-emitting phosphor Ca3La3(BO3)5: Dy3+ (CLBD) was prepared via a solid-state reaction. The introduction of Dy3+ in Ca3La3(BO3)5 with a preferred location on La3+ was confirmed by x-ray diffraction and Rietveld structural refinement studies. The micrograph observed by scanning electron microscopy reveals an inhomogeneous and uneven dense morphology in the micrometer range. The optical spectra analysis shows that the CLBD can be efficiently excited by ultraviolet (UV) light and emitted intense white light due to the combination of blue 4F9/2 → 6H15/2 (∼485 nm) and yellow 4F9/2 → 6H13/2 (∼575 nm) emissions originated from 4f–4f transitions of Dy3+. The critical concentration is determined to be ∼12 mol. %, and the dipole–dipole (d–d) interaction is responsible for the quenching mechanism. In additional, the CLBD has high thermal stability. By incorporating the CLBD with a phosphor-capping method on AlInGaN LED, we obtain the white light that meets the spectral and efficiency requirements for high-efficacy solid-state white lighting lamps. The Commission Internationale de I'Eclairage chromaticity coordinates and color correlated temperature with optimal electroluminescence intensity are calculated to be ∼(0.338, 0.342) and 5950 K, respectively. All results indicate the CLBD could serve as a promising candidate for white UV-LEDs. [ABSTRACT FROM AUTHOR]

In the growing field of high-field terahertz (THz) spectroscopy, many ultrafast research labs are equipped to perform single-pulse (one-dimensional) THz measurements. We describe a simple and versatile method to modify one-dimensional THz experimental setups to generate two variably delayed THz pulses. This method optimizes the use of pump power to create two high-field THz pulses. Adding only a beam splitter and delay stage, research groups can access the wealth of information only available through two-dimensional (2D) measurements. We also provide useful guidance to those new to some challenges of 2D THz spectroscopy. [ABSTRACT FROM AUTHOR]

We report on the performance of Ar-filled hollow-core fibers (HCFs) capillary driven by long pulses (> --> 100 fs) of moderate energy (< 600 μ J) for coherent multidimensional spectroscopy in the visible range. The source is characterized by high overall transmission and excellent spatial mode. Broadening is achieved by self-phase modulation. Notably, the uncompressed visible output is shorter than the input pulse. This peculiar observation is explained by the structure of self-phase modulated pulses, coupled with spectral filtering. By virtue of its simplicity, low requirements, spectral stability, and the excellent properties of its spatial output, HCFs can provide an interesting alternative to achieve broadband visible pulses for broadband optical excitation and multidimensional spectroscopy applications. [ABSTRACT FROM AUTHOR]

We report on a simple method for the characterization of optical absorption in semiconductors at photon energies below the bandgap energy. Therefore, we perform spatially resolved and intensity dependent deflection spectroscopy to measure the local optical absorption. To separate the absorption mechanisms, we take advantage of different intensity scaling of these mechanisms and extract the material parameters by fitting intensity dependent absorption to a physical model. This model takes into account relevant optical absorption processes like linear absorption from defect states, two-photon absorption, and the Franz–Keldysh effect. The method is exemplarily carried out for GaAs, Si, and CdTe. The literature values of the two-photon absorption coefficient are reproduced and the strength of the Franz–Keldysh effect in CdTe is determined for the first time as C FK = [ 8.7 , ... , 16.9 ] × 10 13 m − 1 s − 1 / 2 . [ABSTRACT FROM AUTHOR]

A series of experiments are conducted for the study of time-dependent variations of major emission from the metastable excited He generated in various experimental conditions. Different Nd:YAG laser pulse widths and pulse energies, as well as purity of the He gas, are employed for studying quenching effects including the use of a Cu target in an experimental condition for spectrochemical analysis. It is found that in all cases investigated, the metastable excited He atom (He*) associated with the triplet He I 587.5 nm emission line has the unquestionable dominance over another triplet emission line of He I 388.8 nm and the singlet He I 667.8 nm emission. Further analysis of the present data combined with the results of previous studies suggested that the energy transfer between He atoms via the Penning-like collision-induced energy transfer process has so far remained less than appropriately addressed. It is strongly argued and demonstrated in this work that this underlying physical process is likely the moving force leading to the repeated He ionizations responsible for the self-propelled multiple amplification of the triplet He I 587.5 nm emission intensity particularly at the early stage of the shock wave formation. This study has convincingly demonstrated that the Penning-like collision-induced energy transfer process can also effectively take place between He* and the ablated atoms, implying its usefulness for spectrochemical laser-induced plasma spectroscopy analysis. [ABSTRACT FROM AUTHOR]

In this Tutorial, various methods of optical spectroscopy representing certain interest for magnetron discharge characterization are overviewed. The main principles, the implementation examples, and the selected results are given for each technique, accompanied by short discussions and suggestions for further reading. Both passive and active optical methods are covered, including optical absorption and laser-based techniques. The advantages and drawbacks of each diagnostic approach are critically analyzed. Special attention is devoted to the techniques extensively used by the authors in their own work, such as line ratio methods, absorption spectroscopy, interferometry, and laser-induced fluorescence. [ABSTRACT FROM AUTHOR]

In this article, we present high-pressure experimental investigations on EuNbO4, an interesting technologically important material, using synchrotron based x-ray powder diffraction, Raman spectroscopy, and europium photoluminescence measurements up to 39.2, 31.6, and 32.4 GPa, respectively. All three techniques show the stability of the ambient monoclinic phase until 20 GPa. Beyond that, a pressure-induced structural phase transition takes place with the coexistence of two phases over a wide pressure range. The structure of the high-pressure phase has been determined as orthorhombic (space group: Imma) with a volume discontinuity of nearly 9% at the transition indicating the nature of transition to be first order. The high-pressure phase remains stable up to ∼40 GPa. The equation of state data for both phases have been determined, and the modulus of incompressibility indicates that the high-pressure phase with bulk modulus as 246(29) GPa is less compressible compared to the low-pressure phase having bulk modulus as 138(4) GPa. The transition involves a change in the coordination polyhedron around europium, increasing the coordination number from 8 in the fergusonite to 12 in the orthorhombic phase, while the coordination around niobium remains 4 in both the phases. All the 18 expected Raman modes in the fergusonite structure have been observed, and their variation as a function of pressure has been reported. The mode Grüneisen parameters for the observed Raman frequencies for monoclinic and orthorhombic phases have been determined. Europium photoluminescence spectra show drastic changes near the transition pressure, which point toward changes in the local environment around the europium ion. [ABSTRACT FROM AUTHOR]

This study investigates element-specific atomic distances and strains in ferromagnetic (FM) nano-thin films deposited on a flexible substrate, which can be modulated by stretching the substrate. Extended x-ray absorption fine structure (EXAFS) spectroscopy was used for the experiments. Both in-plane tensile and out-of-plane compressive strains were investigated by applying %-order tensile strains to the substrate. The atomic distance changes induced by stretching the substrate were quantitatively discussed by considering the Poisson compression, crystalline orientations of the FM metals, and polarization in the EXAFS measurement. Consequently, the ratio of strain transfer from the flexible substrate to the FM layers was estimated to be about 30% and 60% in Co and Fe nano-thin films, respectively. The strain transfer in Co films with different Co or Pt underlayer thicknesses was also measured. The results are compared with the thickness dependence of the effective magnetoelastic coupling constant, which represents the magnitude of the inverse magnetostriction effect. Although the strain transfer partially contributes to the thickness dependence, the difference in the Co lattice constant is suggested to have a significant influence on the effective magnetoelastic coupling constant. [ABSTRACT FROM AUTHOR]

The ordered structure of the MgO–ZnO alloy system is a versatile tunable optical material, which is promising for diverse optoelectronic applications. However, isovalent and isostructural alloy compositions of MgO–ZnO are generally unstable at ambient conditions. Using state-of-the-art ab initio evolutionary simulations, we predict and study the properties of stable phases of MgO–ZnO. We establish the dynamical stability of the predicted crystal structures through phonon and Raman spectroscopy. Detailed analyses of two of the most stable structures reveal highly tunable properties that could be explored for photonic and optical applications. [ABSTRACT FROM AUTHOR]

A method to perform spectrum analysis on low power signals between 0.1 and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of an evanescent spin current. It is first shown that the ATJ oscillation frequency can be tuned linearly with time. Then, it is shown that the ATJ output is highly dependent on matching conditions that are highly dependent on the dimensions of the dielectric tunneling barrier. Spectrum analysis can be performed by using an appropriately designed ATJ, whose frequency is driven to increase linearly with time, a low pass filter, and a matched filter. This method of THz spectrum analysis, if realized in the experiment, will allow miniaturized electronics to rapidly analyze low power signals with a simple algorithm. It is also found by simulation and analytical theories that for an ATJ with a 0.09 μ m 2 footprint, spectrum analysis can be performed over a 0.25 THz bandwidth in just 25 ns on signals that are at the Johnson–Nyquist thermal noise floor. [ABSTRACT FROM AUTHOR]

A conductor-backed dielectric metasurface thermal emitter at mid-IR frequencies with narrowband emissivity is experimentally demonstrated. The metasurface emitter consists of a high permittivity silicon resonator on top of a ground plane, whose resonant mechanism is explained using image theory. The resonator, placed close to a copper ground plane, is designed to produce a magnetic resonance, resulting in a low-profile device with a single emission peak in its subwavelength frequency range. The thermal emitter is next fabricated using common CMOS processes. Frequency dependent optical constants of plasma-enhanced chemical vapor deposited films of Si, SiO 2 , and evaporated Cu are also reported in the mid-IR range. Narrowband thermal emission is successfully obtained at around 7.22 μ m (41.5 THz), which corresponds to the absorption band of SO 2. The Q-factor of about 37 is achieved with a peak emissivity of 0.65, which is significantly higher compared to the reported Q-factors of state-of-the-art plasmonic resonators. [ABSTRACT FROM AUTHOR]

AlGaN-based deep-ultraviolet light-emitting diodes (LEDs) incorporating uneven multiple quantum wells (MQWs) with inclined and terrace zones, which were fabricated on an AlN template with dense macrosteps, have exhibited a high internal quantum efficiency (IQE). To investigate the microscopic structure of uneven MQWs, cathodoluminescence (CL) mapping characterization was carried out, and the maps of the CL intensity at 300 K relative to that at 38 K were obtained for uneven MQWs that targeted 265 and 285 nm LEDs. At an electron beam current of less than 1.0 nA, the signals from inclined and terrace zones of the uneven MQWs were confirmed to satisfy the nonsaturated excitation condition at 300 K. Nonradiative recombination (NR) was insufficiently frozen even at 38 K, specifically on the terraces in the 265 nm MQW, suggesting high concentrations of NR centers due to point defects (PDs). In contrast, NR in the 285 nm MQW at 38 K was closer to freeze-out. The concentration of PDs in the 285 nm MQW was likely to be lower than that in the 265 nm MQW. Finally, the ratios of the CL intensity at 300 K to those at 38 K were mapped, demonstrating an approach to creating an approximate map of IQE. The values in the CL intensity ratio maps are discussed by considering the analytical error factors. The results support the model of localized current injection through Ga-rich stripe zones in the n-AlGaN cladding layer. [ABSTRACT FROM AUTHOR]

A realization of the force-induced remnant magnetization spectroscopy technique of specific biomolecular binding is presented, where detection is accomplished with wide-field optical and diamond-based magnetometry using an ensemble of nitrogen-vacancy color centers. This diamond-based technique that has both optical and magnetic detection modalities may be adapted for massively parallel screening of arrays of nanoscale samples. [ABSTRACT FROM AUTHOR]

Pure hydroxyapatite (HAp) semiconducting microrods with very low dielectric loss have been synthesized in aqueous media of pH values 6, 8, and 10 by the hydrothermal method. Samples are characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectra analyses. The optical bandgap energies of these samples are found to be within the semiconducting range (∼3–4 eV). FESEM and TEM image analyses reveal the formation of microrods and reduction of the average length of the rods with increasing pH values. A core-shell-like microrod structure has been observed in the sample with pH value 6. The charge carrier follows an adiabatic small polaron hopping mechanism. The dielectric loss values are very small compared to that of other ceramic oxides which is very advantageous for electronic applications. Correlated barrier hopping model is the dominant charge transport mechanism within the samples with maximum barrier heights of 0.25 eV, 0.26 eV, and 0.27 eV for samples with pH values 6, 8, and 10, respectively. Nonideal Debye type relaxation appears within the material when the AC field is applied for temperatures above 100 °C. [ABSTRACT FROM AUTHOR]

We carry out the surface potential (SP) measurements of Si-doped InN nanorods (NRs) grown by plasma-assisted molecular beam epitaxy. Photoluminescence and photoemission spectroscopic studies reveal that the Si-doped InN nanorods possess surface electron accumulation. To estimate the SP value of the InN nanorods, a contact potential difference is measured using Kelvin probe force microscopy (KPFM). In order to avoid the influence of the surface adsorbed species, KPFM measurements were carried out at a high vacuum condition of ∼7.5 × 10−7 mbar. The SP value of the Si-doped InN nanorods is found to depend on the size of nanorods. The size-dependent SP value of the Si-doped InN nanorods is attributed to the variation in the downward surface band bending caused by the change in the sheet carrier density of surface electron accumulation. The change in surface band bending is the result of the variation in the free-electron distribution with a size of the NRs. [ABSTRACT FROM AUTHOR]

Terahertz (THz) quantum-cascade lasers (QCLs) are currently unparalleled for high-resolution spectroscopy of very sharp absorption lines (linewidths below 100 MHz) in the range between 2 and 5.4 THz. Since the frequency range accessible by a single QCL is determined by its typically very limited tuning range, a particular QCL has to be fabricated for each specific application. We quantitatively analyze the frequencies of the modes in THz QCLs with a Fabry–Pérot resonator as a function of its length taking into account waveguide dispersion. Based on these results, we develop a process based on mechanical polishing of the front facet to adjust the emission frequency with a precision of 1 GHz. The demonstrated process makes it possible to reliably fabricate THz QCLs for the spectroscopy of very sharp absorption lines. [ABSTRACT FROM AUTHOR]

Spectroscopic techniques, including photoelectron spectroscopy, diffuse reflectance, and x-ray absorption, are used to investigate the electronic structure and the local structure of LaOBiS 2 − x Se x thermoelectric material. It is found that Se substitution effectively suppresses local distortion that can be responsible for the increased carrier mobility together with a change in the electronic structure. The results suggest a possible way to control thermoelectric properties by tuning of the local crystal structure of these materials. [ABSTRACT FROM AUTHOR]

Most of our current understanding of mechanisms of photosynthesis comes from spectroscopy. However, the classical definition of a radio antenna can be extended to the optical regime to discuss the function of light-harvesting antennae. Further to our previously proposed model of a loop antenna, we provide several more physical explanations in considering the nonreciprocal properties of light harvesters of bacteria. We explain the function of the nonheme iron at the reaction center and present reasons for each module of the light harvester being composed of one carotenoid, two short α -helical polypeptides, and three bacteriochlorophylls; we also explained the toroidal shape of the light harvester, the upper bound of the characteristic length of the light harvester, the functional role played by the observed long-lasting spectrometric signal, and the observed photon antibunching. Based on these analyses, two mechanisms that might be used by radiation-durable bacteria, Deinococcus radiodurans; and the nonreciprocity of an archaeon, Haloquadratum walsbyi, are analyzed. The physical lessons involved are useful for designing artificial light harvesters, optical sensors, wireless power chargers, passive superPlanckian heat radiators, photocatalytic hydrogen generators, and radiation protective cloaks. In particular, it can predict what kind of particles should be used to separate sunlight into a photovoltaically and thermally useful range to enhance the efficiency of solar cells. [ABSTRACT FROM AUTHOR]

Yttria stabilized zirconia pellets with different crystallite sizes were irradiated with 80 MeV Ag6+ ions at room temperature and 1000 K to understand the effect of crystallite size/material microstructure and irradiation temperature on the radiation tolerance against high energy heavy ions [where electronic energy loss (Se) dominates]. XRD and Raman spectroscopy measurements reveal that, irrespective of the irradiation temperature, the nano-crystalline samples suffered more damage when compared with the bulk-like sample. A reduction in the irradiation damage, i.e., improvement in the radiation tolerance, was observed for all the samples irradiated at 1000 K. The reduction in the damage, however, was remarkably higher for the nano-crystalline samples compared with the bulk-like sample, and hence the difference in the damage between the bulk-like and nano-crystalline samples was also significantly lower at 1000 K than that at room temperature. The irradiation damage, against Se, was thus found to be critically dependent on the interplay between the irradiation temperature and the crystallite size. These results are explained on the basis of the "in-elastic thermal spike" model by taking into consideration the combined effects of crystallite size and environmental (irradiation) temperature on the electron-phonon coupling strength and the lattice thermal conductivity and hence on the resulting thermal spike. These results, besides being crucial from the fundamental prospect of comprehending the size and temperature dependent radiation damage against Se, may also be important from the perspective of designing highly nano-crystalline materials for applications in various radiation environments. [ABSTRACT FROM AUTHOR]

In this study, we produced self-assembly structures (desiccation patterns) in the drying sessile drops of SnO2-R6G colloidal suspension that have functional applications. Colloidal suspensions of SnO2 nanoparticles were synthesized using the sol-gel method and, subsequently, R6G molecules were added into the suspension. Centimeter-sized honeycomb- or tree-like self-assembled structures of the nanoparticle-dye composite are formed from the evaporating droplets on a flat glass surface. The usual "coffee ring" effect observed in the case of drying of a sessile drop of dye solution is inhibited this way, which is desirable in many applications. The structures were investigated using optical microscopy and spectroscopy. The resemblance between transmission and fluorescence images illustrates the feasibility of organizing dye molecules in a specific way using self-assembled nanoparticles as a template. However, dye fluorescence from the self-assembly is very weak, which might be due to photoinduced interfacial electron transfer from the excited dye molecules to the nanoparticles. [ABSTRACT FROM AUTHOR]

Thermally stimulated techniques—thermally stimulated current (TSC) spectroscopy and thermally stimulated depolarization current (TSDC) spectroscopy—were used to comparatively study the electrical properties and deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk crystals. It was found that the samples are highly resistive and each sample may have different dark current activation energy. Deep level defects revealed by the thermally stimulated techniques vary from sample to sample. In addition to the common traps E1 (∼0.56 eV), E2 (∼0.84 eV), and E3 (∼0.99 eV), reported in the literature and revealed by DLTS studies of Ga2O3 bulk crystals, that were also found in our samples by the thermally stimulated techniques, a trap at ∼110 meV and several other traps are revealed specifically by TSDC between 105 and 225 K. [ABSTRACT FROM AUTHOR]

We are developing a proximal noncontact detection technique for trace amounts of hazardous materials using diffuse reflectance infrared spectral signatures. Spectroscopy is performed at a distance by tuning a quantum cascade laser system through its wavelength range (6-11 μm) as the active illumination source and collecting a portion of the diffusely reflected light from the target onto an MCT focal plane array. The signals from each collected frame are binned and processed into an image hypercube that contains spectral and spatial information. The primary motivation of this work is to protect the loss of life by detecting trace explosives on contaminated surfaces before attacks occur. Here, we present results from backscatter experiments on trace samples with low loading and fill factors on glass substrates and compare them with a conventional benchtop analysis technique, FTIR diffuse reflectance. The backscatter results illustrate the ability to detect explosives at 1 m distance at the nanogram level, which is beyond the capability of the benchtop FTIR diffuse reflectance measurement. [ABSTRACT FROM AUTHOR]

The localization of deep traps in normally-off AlGaN/GaN metal-oxide-semiconductor channel high-electron mobility transistors has been established by means of capacitance and current deep level transient spectroscopies (DLTS). Electrical simulations of the total current density between the drain and source contacts, the electron density, and the equipotential line distribution helped to understand the transport mechanisms into the device and to determine the zone probed by DLTS measurements. By changing the drain-source voltage in current DLTS or the reverse bias in capacitance DLTS, we demonstrated that we can choose to probe either the region below the gate or the region between the gate and drain electrodes. We could then see that defects related to reactive ion etching induced surface damage, expected to be formed during the gate recess process, were located only under the gate contact whereas native defects were found everywhere in the GaN layer. Thanks to this method of localization, we assigned a trap with an EC – 0.5 eV to ion etching induced damage. [ABSTRACT FROM AUTHOR]

Among the small cation sized rare earth sesquioxides, the reported transition pressure of cubic Tm2O3 is ambiguous. Pressure induced structural phase transition in cubic Tm2O3 has been reinvestigated using the synchrotron X-ray diffraction, Raman spectroscopy, and ab initio density functional theory (DFT) calculations up to a pressure of 25 GPa. Both the X-ray diffraction and Raman spectroscopic measurements revealed an irreversible polymorphic structural phase transition from type-C cubic to type-B monoclinic at around 12 GPa, whereas the same is predicted to be 8 GPa from the density functional theory. The phase transition observed at 12 GPa is in contrast to the literature and the reasoning has been established by other studies, viz., Raman spectroscopy and DFT. A third order Birch-Murnaghan equation of state fit to the experimental compressibility curve yielded a zero pressure bulk modulus of 149(2) GPa with the pressure derivatives 4.8(5) for the parent cubic phase and 169(2) GPa with the pressure derivative 4 for the high pressure monoclinic phase, respectively. These values are in good agreement with the calculated bulk modulus of 146 and 151 GPa for the cubic and monoclinic phases, respectively. Raman modes for the monoclinic phase of Tm2O3 are measured and reported for the first time. The mode Grüneisen parameter of different Raman modes for both cubic and monoclinic phases of Tm2O3 has also been determined. The experimental results are correlated with changes in the density of states near the Fermi level, which are indicative of structural instabilities in the parent cubic structure. [ABSTRACT FROM AUTHOR]

It is shown that applying isotropic quantitative mobility analysis to anisotropic materials can lead to drastic qualitative errors, even in the case of modest anisotropy. The procedure may provide not only wrong values for carrier mobilities and concentrations but even a wrong number of carrier species. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is a well-established method for detecting mechanical defects in materials and structures activated by piezoelectric resonance. However, the detection sensitivity is not always satisfactory for very small defects, such as those that are of great importance for high-field insulation. In this study, an enhanced defect detection method is developed to solve this problem. A high-voltage (1 kV) time-domain resonance analysis is used in combination with conventional impedance spectrum analysis. The resonant frequencies and damping factors of the characteristic high-voltage piezoelectric resonances are extracted from time-domain data, and the damping factors are found to be more sensitive to the defect geometry. The results suggest that the time-domain method used here may have potential for applications where a high sensitivity of defect detection is required. [ABSTRACT FROM AUTHOR]

The divacancy (V2) is one of the fundamental defects in silicon. However, the interaction of V2 with hydrogen is still not fully understood. In the present work, deep level transient spectroscopy (DLTS) results on hydrogen-assisted annealing of V2 are presented. H+ ions were implanted with multiple energies into n-type Czochralski-grown samples, yielding uniform (box-like) concentration-versus-depth profiles of V2 and hydrogen in the region probed by the DLTS measurements. The evolution kinetics of V2 reveals two distinct processes: (i) a fast one attributed to dissociation of phosphorus-hydrogen pairs and reaction with highly mobile atomic Hi and (ii) a slow one whose origin is not identified yet. During the slow process, we observe the formation of a hydrogen-related electronic state, labeled E5* and positioned ∼0.42 eV below the conduction band edge. The growth of E5* displays a close one-to-one proportionality with the loss of a V2-related DLTS peak, presumably due to V2H, overlapping with that of the single negatively charged V2. [ABSTRACT FROM AUTHOR]

This paper determines all the 13 elastic constants Cij of monoclinic β-Ga2O3, which has never been achieved since the discovery of this crystal about 100 years ago. We used resonant ultrasound spectroscopy with laser-Doppler interferometry, where the resonant-mode identification was unambiguously made by comparing measured and calculated displacement distributions on the vibrating specimen surface. Using more than 110 resonance frequencies, we inversely determined the Cij: C11 = 242.8 ± 2.9, C22 = 343.8 ± 3.8, C33 = 347.4 ± 2.5, C44 = 47.8 ± 0.2, C55 = 88.6 ± 0.5, C66 = 104.0 ± 0.5, C12 = 128 ± 0.1, C13 = 160 ± 1.5, C23 = 70.9 ± 2.1, C15 = –1.62 ± 0.05, C25 = 0.36 ± 0.01, C35 = 0.97 ± 0.03, and C46 = 5.59 ± 0.69 GPa. We also performed a density-functional-theory calculation and found that the local density approximation yields both the lattice parameters and Cij closer to the measurements than the generalized gradient approximation. Strong elastic-stiffness anisotropy is found in the diagonal elastic constants: C11 is smaller than C22 and C33 by ∼30%, and the difference between C44 and C66 exceeds 50%. Our measurements also reveal anomalous Poisson's ratios: ν21 and ν31 exceed 0.5, and ν23 and ν32 are almost zero. We explain these unusual elastic properties with the truss-like deformation of the tetrahedra-octahedra network and confirm this view with the ab- initio calculation. [ABSTRACT FROM AUTHOR]

We used photoluminescence (PL) spectroscopy combined with scanning near-field optical microscopy to directly observe the potential barriers in InGaN/GaN multiple quantum wells (MQWs) on a GaN layer grown under moderate temperatures (MT-GaN) as the V-pit expansion layer. Area-averaged PL spectra revealed shoulders on the higher-energy side of the InGaN/GaN MQW emission (HE emission) even at room temperature (RT), as well as at low temperature. These HE emission regions, which possessed island-like shapes in the PL intensity maps at RT, corresponded to the dark regions in the PL intensity maps of GaN emission. Low-temperature local PL spectra acquired at the measurement points where HE emissions were observed revealed multiple HE emission peaks at two distinct energies. Most of the regions where the HE emission occurred corresponded to the dark regions of GaN emission and their outer circumference. These experimental observations demonstrate the formation of potential barriers around threading dislocations in the InGaN/GaN MQWs on an MT-GaN layer as the pit expansion layer. The energy difference between the HE emissions and the MQW emissions on the MT-GaN layer tended to increase with increasing V-pit diameter and was much larger than the energy difference for an InGaN/GaN superlattice structure. This was rationalized by the greater change in transition energy for thinner MQWs on V-pits than for planar MQWs, when the thickness in the MQWs on MT-GaN decreases owing to strain effects. [ABSTRACT FROM AUTHOR]

Using Brillouin light scattering spectroscopy and dynamical matrix method calculations, we study collective spin waves in dense arrays of periodically double-side width-modulated Permalloy nanowires. Width modulation is achieved by creating a sequence of triangular notches on the two parallel nanowire sides, with a periodicity of p = 1000 nm and a tunable relative displacement (Δ) of the notch sequence on the two lateral sides. Both symmetric (Δ = 0) and asymmetric (Δ = 250 and 500 nm) width-modulated nanowires were investigated. We have found that the detected modes have Bloch-type character and belong to a doublet derived from the splitting of the mode characteristics of the nanowire with the homogeneous width. Interestingly, the amplitude of the magnonic band, the frequency difference of the doublet, and their relative scattering intensity can be efficiently controlled by increasing Δ rather than having single- or symmetric (Δ = 0) double-side width-modulation. [ABSTRACT FROM AUTHOR]

Using the traveling heater method, we have developed commercial CdZnTe (CZT) crystal growth, fabrication, and in-house test technologies for both, photon-starved gamma spectroscopic sensors and high-flux x-ray photon-counting for medical imaging and other applications. We compare the performance of different CZT material types for gamma spectroscopy and for high-flux x-ray imaging. We demonstrate single-threshold photon counting and basic imaging capability of pixelated CZT detectors at the highest x-ray fluxes we could generate in-house, i.e., ∼250 × 106 photons/(mm2 s). We show that the test system can be used for universal, absolute flux calibration of x-ray beams based on an accurate pile-up fitting algorithm. The detectors also perform spectroscopically under high-flux, when tested with energy discriminating electronics. A brief investigation on the effects of leakage, photo, and excess currents including their temporal behavior is also presented. Sub 1% uncorrected single-pixel resolution of the 662 keV 137Cs full energy peak was achieved with the gamma spectroscopy optimized material, fabricated into pixelated sensors. [ABSTRACT FROM AUTHOR]

We report on the performance and inherent artifacts of k-space optical microscopy for the study of periodic arrays of nanoparticles under the various illumination configurations available on an inverted optical microscope. We focus on the origin of these artifacts and the ways to overcome or even benefit from them. In particular, a recently reported artifact, called the “condenser effect,” is demonstrated here in a new way. The consequences of this artifact (which is due to spurious reflections in the objective) on Fourier-space imaging and spectroscopic measurements are analyzed in detail. The advantages of using k-space optical microscopy to determine the optical band structure of plasmonic arrays and to perform surface plasmon resonance experiments are demonstrated. Potential applications of k-space imaging for the accurate lateral and axial positioning of the sample in optical microscopy are investigated. [ABSTRACT FROM AUTHOR]

Organic semiconductor crystals exhibit unique optoelectronic characteristics such as high carrier mobility and laser oscillation. Nonetheless, it remains difficult thus far to achieve such potential activities on an optical device configuration mainly because of lack of knowledge of optical parameters such as refractive indices and their dispersion. Here, we demonstrate a simple but powerful design principle of high-performance organic single-crystal light-emitting devices. The method is based upon observation of emission-angle dependent spectra produced from an organic slab single crystal equipped with a one-dimensional diffraction grating. The emission spectra are characterized by sharply resolved lines whose locations are blueshifted or redshifted as a function of the emission angles. Detailed analysis of these emission lines has enabled us to solve equations of electromagnetic wave motion within and outside the slab crystal and to get solutions under appropriate boundary conditions. The design principle also allows us to relate crystal thicknesses and orders of both longitudinal and transverse modes of emission. Thus, we have been able to optimize the geometry of a slab organic crystal in an organic light-emitting device configuration. The relevant knowledge can directly be used for designing an organic laser either optically excited or electrically excited. [ABSTRACT FROM AUTHOR]

Compared to conventional plasma nitrocarburizing the active screen plasma nitrocarburizing technology reduces significantly the risk of soot production and cementite precipitation in the compound layer of nitrocarburized materials. However, in long-time treatments, the uncontrollable contamination even up to full saturation of the metallic active screen and of the walls of the used plasma reactor with carbon compounds is still a remaining factor of uncertainty. It may result in an increased carbon concentration or even in an appearance of the cementite phase in the compound layer of the treated steel surface, as in the case of 42CrMo4 (AISI 4140). The absolute concentration of hydrogen cyanide (HCN), in situ monitored by tunable diode laser absorption spectroscopy, and the emission intensity of the CN (0–0) band of the violet system at a wavelength of λ = 388 nm, recorded by optical emission spectroscopy, were found to be reliable parameters to control the carburizing potential of the nitrocarburizing plasma. A close relationship was found between (i) the concentration of HCN and the CN band emission intensity with (ii) the level of the methane admixture in the feed gas and the time-dependent contamination effects of the active screen and other inner reactor surfaces with carbon compounds. Therefore, this relation could serve as a basis for an in-line control of the carburizing activity in plasma nitrocarburizing processes with methane admixture using an active screen. [ABSTRACT FROM AUTHOR]

Saturable absorption is a key technology for shaping the waveform of light such as in passive mode-locking. The combination of high-Q optical microcavities with a saturable absorber allows stable lasing and soliton formation. This work describes saturable absorption by carbon nanotubes (CNTs) on silica microtoroids. CNTs, which are saturable absorbers capable of a fast response time and broadband absorption, were grown on silica microtoroids by chemical vapor deposition (CVD). Raman spectroscopy revealed that the CNTs are in good quality (G/D ratio ∼ 7) and about 1.0 nm in diameter, thus confirming that a sample for use in the telecommunication band can be prepared by CVD. A counter-propagating pump-probe experiment enabled us to investigate the characteristics of CNTs as saturable absorbers while suppressing thermo-optic bistability in a microcavity system. The results revealed a saturable absorption coefficient of 0.042 cm−1, a saturable intensity of 25.9 MW/cm2, and a modulation depth of 28%. This is the first step toward the demonstration of the robust mode-locking in a silica microtoroid consisting of CNTs. [ABSTRACT FROM AUTHOR]

The quality of graphene can be strongly modified during the transfer process following chemical vapor deposition (CVD) growth. Here, we transferred CVD-grown graphene from a copper foil to a SiO2/Si substrate using wet etching with four different etchants: HNO3, FeCl3, (NH4)2S2O8, and a commercial copper etchant. We then compared the quality of graphene after the transfer process in terms of surface modifications, pollutions (residues and contaminations), and electrical properties (mobility and density). Our tests and analyses showed that the commercial copper etchant provides the best structural integrity, the least amount of residues, and the smallest doping carrier concentration. [ABSTRACT FROM AUTHOR]

A time-resolved optical pump-probe technique has been applied for studying the ultrafast dynamics in the magnetic semiconductor EuTe near the absorption band gap. We show that application of external magnetic field up to 6 T results in crossover from the inverse Faraday effect taking place on the femtosecond time scale to the optical orientation phenomenon with an evolution in the picosecond time domain. We propose a model which includes both these processes, possessing different spectral and temporal properties. The circularly polarized optical pumping induces the electronic transition 4 f 7 5 d 0 → 4 f 6 5 d 1 forming the absorption band gap in EuTe. The observed crossover is related to a strong magnetic-field shift of the band gap in EuTe at low temperatures. It was found that manipulation of spin states on intrinsic defect levels takes place on a time scale of 19 ps in the applied magnetic field of 6 T. [ABSTRACT FROM AUTHOR]

In red phosphor CaAlSiN3:Eu2+, unintentional blue emission occurs with increasing intensity at low Eu2+ concentrations and also at low measurement temperatures. Time-resolved photoluminescence measurements were used to confirm the decrease in red emission and increase in blue emission with the decreasing Eu2+ concentration. The peak timing of blue emission occurred faster than that of red emission, and long lasting luminescence of red emission was observed as well as that of blue emission. The Eu2+ concentration dependences of the red and blue emissions were similar to those of the g values 4.75 (Eu2+) and 2.0025 (nitrogen vacancies), respectively, which were observed from electron spin resonance (ESR) measurements. The origin of the blue emission is proposed to be nitrogen vacancy defects, which had about the same ESR signal intensity as that of Eu2+ ions in CaAlSiN3:Eu2+ containing 0.01 at. % Eu2+. The possibility of red emission also arising from excited electron tunneling or thermal pathways via nitrogen vacancies is discussed. Long lasting red emission was observed, which is proposed to involve trapped electrons remaining at nitrogen vacancies, yielding blue emission and inducing red emission from Eu2+ ions. [ABSTRACT FROM AUTHOR]

We investigate the effect of mass disorder, temperature, and pressure on the spectral thermal conductivity of multicomponent crystalline solid solutions via molecular dynamics simulations. The thermal conductivities of Lennard-Jones based solid solutions with one to five different atomic components in the crystalline lattice are simulated at a range of uniaxial strain levels and temperatures. Our results show that for multicomponent alloys, increasing only the mass impurity scattering by adding atoms with different masses in the solid solution does not lead to significant changes in the spectral contributions to thermal conductivity. However, increasing the impurity concentration or changing the local force-field of the impurity atoms in the solid solution has a relatively significant impact on the spectral contributions to thermal conductivity. The effect of chemical order in these alloys is shown to drastically alter the temperature dependence due to the different scattering mechanisms dictating thermal conductivities in the ordered and disordered states. Furthermore, in comparison to a homogeneous solid, crystalline solid solutions (especially the disordered states) show a reduced pressure dependence on thermal conductivity, which becomes more prominent as the number of components is increased. This is attributed to the fact that while anharmonic effects in homogeneous solids lead to the large temperature and pressure dependencies in their thermal conductivities, impurity scattering in solid solutions leads to a largely reduced dependence on pressure and temperature. [ABSTRACT FROM AUTHOR]

A dielectric spectroscopic study and an ac conductivity analysis in the 100 Hz–1MHz frequency and 30–450°C temperature ranges are presented for the piezoceramic compound (K0.44Na0.52Li0.04)0.97 La0.01Nb0.9Ta0.103, synthesized by the traditional ceramic method using NaNbO3 as a precursor obtained by the reactive templated grain growth method technique. La doping of KxNa1-xNbO3 (KNN) produces a shift of the phase transition temperatures (orthorhombic-tetragonal and tetragonal-cubic) toward lower temperatures. The measured relative permittivity maximum and the relative permittivity at room temperature are remarkably high. Conductivity behaves according to Jonscher’s law in the 400 Hz–1500 Hz frequency range at temperatures between 75 and 300°C, with values of n1 ≤ 0.70, lower than those reported in the literature for similar compounds. The activation energy in the case of dc (long range) conductivity, 1.72 eV, points out to double ionized oxygen vacancies. This value is higher than the 1.46 eV of undoped KNN, evincing the influence of Li and La in the conduction processes of KNN. [ABSTRACT FROM AUTHOR]

A series of experiments on tungsten spectroscopy has been carried out in a Large Helical Device with tungsten pellet injection to study the tungsten spectra. In particular, understanding of an unresolved transition array (UTA) is still insufficient, whereas the UTA is very important for the diagnostics and transport study of tungsten ions in edge plasmas of International Thermonuclear Experimental Reactor. For the purpose, extreme-ultra violet (EUV) spectra of UTA observed in the wavelength range of 15Å –70Å are analyzed at two different wavelength intervals of 15–45Å and 45–70Å, which mainly consist of Δn=1, 2 and Δn=0 transitions for n=4 partially ionized tungsten ions, respectively. At first, the UTA line intensity is analyzed against central electron temperature at the temperature recovery phase after the pellet injection to examine the presence of blended lines. Next, vertical profiles measured with two space-resolved EUV spectrometers are analyzed against electron temperature profiles for further precise investigation of the UTA spectra. For the analysis, local emissivity profiles are obtained from the measured vertical intensity profiles with the Abel inversion method based on magnetic surface structures calculated by the VMEC code. It is then possible to investigate the ionization stage of tungsten ions comprising the UTA. As a result, it is found that the wavelength intervals of 49.24Å ≤λ≤ 49.46Å, 48.81Å ≤λ≤ 49.03Å, and 47.94Å ≤λ≤ 48.15Å, which are identified as W27+, W26+, and W24+, respectively, are applicable to the tungsten diagnostics. The result of the line component analysis on the tungsten UTA is summarized in tables. [ABSTRACT FROM AUTHOR]