Photon Emission Spectroscopy Research Articles

Physical mechanisms of contact-electrification induced photon emission spectroscopy from interfaces

Physical mechanisms of contact-electrification induced photon emission spectroscopy from interfaces

Radiation necrosis or tumor progression? A review of the radiographic modalities used in the diagnosis of cerebral radiation necrosis

Cerebral radiation necrosis is a complication of radiation therapy that can be seen months to years following radiation treatment. Differentiating radiation necrosis from tumor progression on standard magnetic resonance imaging (MRI) is often difficult and advanced imaging techniques may be needed to make an accurate diagnosis. The purpose of this article is to review the imaging modalities used in differentiating radiation necrosis from tumor progression following radiation therapy for brain metastases. We performed a review of the literature addressing the radiographic modalities used in the diagnosis of radiation necrosis. Differentiating radiation necrosis from tumor progression remains a diagnostic challenge and advanced imaging modalities are often required to make a definitive diagnosis. If diagnostic uncertainty remains following conventional imaging, a multi-modality diagnostic approach with perfusion MRI, magnetic resonance spectroscopy (MRS), positron emission tomography (PET), single photon emission spectroscopy (SPECT), and radiomics may be used to improve diagnosis. Several imaging modalities exist to aid in the diagnosis of radiation necrosis. Future studies developing advanced imaging techniques are needed.

Why Does Pt Shell Bearing Tensile Strain Still Have Superior Activity for the Oxygen Reduction Reaction?

Nanoparticles with a 55 nm Au core and a few monolayers of Pt shell (denoted as Au@Ptx ML, x = 1–4) are found to have superior activity toward the oxygen reduction reaction (ORR) compared to commercial Pt nanoparticles and polycrystalline Pt (pc-Pt) electrodes in 0.1 M HClO4. The half-wave potential for ORR at Au@Pt1 ML is ca. 20 mV positively shifted. With the decrease of the Pt shell thickness from 4 to 1 monolayer, both the extent of enhancement of the ORR activity and the adsorption strength of oxygen-containing species increase; the latter is confirmed by results from surface-enhanced Raman spectroscopy (SERS) and X-ray photon emission spectroscopy (XPS). Furthermore, SERS results also reveal that adsorbed CO on such catalysts displays a blue shift in Pt–CO and a red shift in C–O stretching frequencies compared to that at pc-Pt under otherwise identical conditions. Positive double layer effects induced by diminishing surface charge density, which leads to the less rigid first layer of water, are suggested to be the origin of the superior ORR performance of Au@Ptx ML to that of commercial Pt/C catalysts.

Interface inter-atomic electron-transition induced photon emission in contact-electrification.

Contact electrification (CE) (or triboelectrification) is the phenomena where charges are produced through physical contact between two materials. Here we report the atomic featured photon emission spectra during CE between two solid materials. Photon emission provides the evidence that electron transfer takes place at the interface from an atom in one material to another atom in the other material during CE. This process is the contact electrification induced interface photon emission spectroscopy (CEIIPES). It naturally paves a way to a spectroscopy corresponding to the CE at an interface, which might impact our understanding of the interaction between solids, liquids, and gases. The physics presented here could be expanded to Auger electron excitation, x-ray emission, and electron emission in CE for general cases, which remain to be explored. This could lead to a general field that may be termed as contact electrification induced interface spectroscopy (CEIIS).

Synthesis and Characterization of Er3+-Doped SrNb2O6 Phosphor for FIR Based Thermometer

A new optical thermometer material—Er3+-doped SrNb2O6—based on the fluorescence intensity ratio was synthesized and investigated by both theoretical calculation and experimental measurement, combining X-ray diffractometry (XRD), XRD Rietveld refinement, scanning electron microscopy, X-ray photon emission spectroscopy, photoluminescence (PL) and PL excitation of qualitative and quantitative analysis, to develop a novel green-emitting phosphor with excellent thermometry sensitivity. The Er3+ ions occupied 4e sites of SrNb2O6, and the stable activator occupation induces luminescence properties of emissions at 525, 531, and 550 nm. The SrNb2O6: Er3+ phosphor possesses an outstanding thermal sensitivity in the measurement region of 298–523 K, where Sa and Sr can achieve 6.15 × 10−3 K−1 and 1093.2711/T2, respectively, at 323 K. The optical thermal properties originated from the thermal excitation and formation of quashing thermal equilibrium between 2H11/2 and 4S3/2 levels, leading to photons on 4S3/2 → 4I15/2 transfer process thermally populate onto 2H11/2 → 4I15/2 transfer process. This work will lay a foundation for further exploration of activator suitability in columbite phosphors, making it practicable to foreseeably improve thermal sensitivity and PL for emergent applications in optical thermometer.

Nanoscale TiO2 and Ta2O5 as efficient antireflection coatings on commercial monocrystalline silicon solar cell

In this paper, we report the enhancement of photon to electron conversion efficiency of commercial monocrystalline silicon solar cells after deposition of nanoscale TiO2 and Ta2O5 as an antireflection coating. The nanoscale TiO2 and Ta2O5 ARC’s remarkably enhanced PEC efficiency of m-Si solar cells from 17.18% to 17.87% and 18.8% respectably. The enhancement in PEC efficiency is predominantly attributed to the increase in fill factor from 36.8% to 36.9% and 37.2% after deposition of nanoscale TiO2 and Ta2O5 as ARCs respectively. The reflectance of nanoscale TiO2 ARCs increased from 27% to 43% within the wavelength range from to 530 nm and decreases to 34% with increasing wavelength. However, for Ta2O5 the reflectance was 11% at 370 nm and increased up to 29% in the studied wavelength range. The reduced magnitude of reflectance for Ta2O5 throughout the studied wavelength resulted in notable improvement of PEC efficiency compared to TiO2. The phase formation of nanoscale TiO2 characterized by x-ray diffraction reviles the presence of both anatase and rutile phase TiO2 whereas Ta2O5 displays amorphous nature. The oxidation state of titanium (Ti) and tantalum (Ta) was evaluated from x-ray photon emission spectroscopy and observed to be in the form of Ti4+ and Ta5+ chemical state. The nanoscale thickness of both TiO2 and Ta2O5 ARCs was acquired by variable angle spectroscopic ellipsometry and found to be 55.2 nm and 70.8 nm respectively, and the same was confirmed by measuring cross-section thickness of ARCs using a scanning electron microscope.

Sample dependence studies of the Kondo Weyl semimetal YbPtBi

Materials with non-trivial band topology have attracted enormous attention in recent years due to their unique physical properties and potential applications in quantum computation. After the discovery of topological insulators, many semimetals were also found to possess non-trivial band topology, such as Dirac and Weyl semimetals. To date, most of the discovered topological semimetals are materials with weak electronic correlations, so it is desirable to find topological semimetals with strong electronic correlations. In our previous work, we found that YbPtBi is a promising Kondo Weyl semimetal candidate. At high temperature, electronic structure calculations show that pairs of triply degenerate points can be found, which is supported by angle resolved photonemission spectroscopy (ARPES) measurements. In an external magnetic field, these points are split into pairs of Weyl nodes, and the presence of Weyl fermions is revealed by the angle dependent magnetotransport measurements. However, at low temperatures when the electronic structure are strongly influenced by band hybridization, the results of heat capacity measurements suggest a nodal thermal excitation, which is evidence for the presence of Weyl Kondo semimetal phase in YbPtBi. This is further supported by the observation of a topological Hall effect in Hall resistivity measurements. Here we present a study of the sample dependence of the properties of YbPtBi. The relationship between the carrier density and negative longitudinal magnetoresistance (MR) clearly suggests the presence of the chiral anomaly and can be consistently explained based on the band structure. The analysis of the Hall resistivity reveals a strong signal of an anomalous Hall effect at low temperature, which may arise from the complex Berry curvature in momentum space. These results further suggest that YbPtBi is a potential platform for studying the properties of Weyl fermions in the presence of strong electronic correlations.

Microstructural characterization of nanostructured supersonic sprayed Ni–Sn coatings after wear tests at elevated temperature

Abstract The paper presents results of the wear behavior, as well as the microstructural (scanning and transmission electron microscopy) and compositional (microanalysis with using energy dispersive and X-ray photon emission spectroscopy) characterization of nanostructured Ni-20Sn (wt.%) coatings, deposited on an Inconel 718 substrate by supersonic cold gas spraying at different spraying parameters. Coatings were examined in the as-deposited state and after testing in a linearly reciprocating sliding wear test at room temperature, 200, 400 and 550 °C. It was found that the Ni–Sn coatings exhibit superior wear resistance compared to benchmark materials. This is attributed to an appropriate balance of soft (Ni) and to hard (Ni3Sn – intermetallic) phases and to the nanostructure of the matrix, as well as to the presence of an NiO oxide tribo-layer, as revealed by the microanalysis and electron microscopy.

Simple and versatile modifications allowing time gated spectral acquisition, imaging and lifetime profiling on conventional wide-field microscopes

An inverted microscope has been adapted to allow time-gated imaging and spectroscopy to be carried out on samples containing responsive lanthanide probes. The adaptation employs readily available components, including a pulsed light source, time-gated camera, spectrometer and photon counting detector, allowing imaging, emission spectroscopy and lifetime measurements. Each component is controlled by a suite of software written in LabVIEW and is powered via conventional USB ports.

Investigation of a Ge nanoparticle film by means of electron stimulated photon emission spectroscopy

Electron stimulated photon emission spectroscopy was used for the study of the electronic structure of Ge nanoparticles. A nanoparticle film was prepared by thermal deposition on a quartz substrate. Photon emission was stimulated by electron bombardment at energies of several hundred electron volts. Electron field emission from a W-tip was used at tip voltage Ut=100–600eV. A spectrometer in combination with a liquid nitrogen cooled charge-coupled device (CCD) camera was used for light detection. Light emission spectra were measured in the energy range 1.18–4.2eV. They are characterized by features at ∼1.6 and ∼3.1eV. A comparison with light emission spectra obtained with another excitation, i.e. by applying a voltage of Uf=2V to the Ge nanoparticle film gives further insight into the mechanism of photon emission.

Magnetic properties of mechanically activated SmMnO3 powders

Magnetic properties of the initial (pre-milling) and mechanically activated SmMnO3 polycrystalline powders were studied. Magnetization measurements were carried out in the temperature range of T = 4–300 K and the magnetic fields up to ±20 kOe. The powders were subjected to both high-energy and low-energy ball milling. The samples studied were analyzed by X-ray diffraction method and X-ray photon-emission spectroscopy. It was found that all the mechanically activated powders SmMnO3 have significantly different magnetic characteristics (transition temperatures, coercive forces, remanent magnetizations) in comparison with initial samarium manganite. The inversion of field cooled (FC) and zero-field cooled magnetizations was observed for the initial sample only. Mechanically activated samples demonstrate positive FC magnetizations in the whole measured temperature range. It is established that the magnetic properties of the samples are strongly dependent on the mode of mechanical activation. Much noticeably, modifications in magnetic characteristics of powder studied were obtained in the case of low-energy mechanical treatment.

Low temperature synthesis and electrical characterization of germanium doped Ti-based nanocrystals for nonvolatile memory

Chemical and electrical characteristics of Ti-based nanocrystals containing germanium, fabricated by annealing the co-sputtered thin film with titanium silicide and germanium targets, were demonstrated for low temperature applications of nonvolatile memory. Formation and composition characteristics of nanocrystals (NCs) at various annealing temperatures were examined by transmission electron microscopy and X-ray photon-emission spectroscopy, respectively. It was observed that the addition of germanium (Ge) significantly reduces the proposed thermal budget necessary for Ti-based NC formation due to the rise of morphological instability and agglomeration properties during annealing. NC structures formed after annealing at 500 °C, and separated well at 600 °C annealing. However, it was also observed that significant thermal desorption of Ge atoms occurs at 600 °C due to the sublimation of formatted GeO phase and results in a serious decrease of memory window. Therefore, an approach to effectively restrain Ge thermal desorption is proposed by encapsulating the Ti-based trapping layer with a thick silicon oxide layer before 600 °C annealing. The electrical characteristics of data retention in the sample with the 600 °C annealing exhibited better performance than the 500 °C-annealed sample, a result associated with the better separation and better crystallization of the NC structures.

Role of germanium in the reduced temperature dependence of Ti-based nanocrystals formation for nonvolatile memory applications

We investigated the physical and electrical characteristics of Ti-based nanocrystals (NCs) with composition of germanium fabricated by cosputtering titanium silicide and germanium targets for low temperature applications of nonvolatile memory. The addition of Ge significantly reduces the thermal budget necessary for Ti-based NCs formation to 500 °C in 2 min due to the rise of its morphological instability and agglomeration properties. Compositions characteristics were analyzed by x-ray photon-emission spectroscopy and formations of NCs were observed by transmission electron microscopy. Additionally, capacitance-voltage characteristics, data retention, and endurance properties are characterized to demonstrate its advantages for nonvolatile memory device applications.

Observation of electron tunneling induced photon emission in gallium (Ga) doped (1%) zinc oxide (ZnO) sample using scanning tunneling microscopy

Electron tunneling induced photon emission in gallium doped (1%) zinc oxide was detected by scanning tunneling microscope in ambient condition. Simultaneously acquired topography and photon maps reveal interesting correlation. Photon maps depict few intense emission spots. Existence of a threshold tunneling current (6 nA) and applied bias (1.8 V), for detectable photon emission was observed. Further analysis of the results suggests Fowler-type photon emission which is ascribed to radiative electron-hole recombination. Localized photon emission spectroscopy exhibits prominent peaks at hν=2.96, 3.43, and 3.80 eV, which match well with the results obtained from photoluminescence studies.

Photon emission spectroscopy of thin MgO films with the STM: from a tip-mediated to an intrinsic emission characteristic

Electron injection from the tip of a scanning tunnelling microscope (STM) has been used to stimulate local photon emission from the surface of a thin MgO film grown on Mo(001). Depending on the excitation energy, several emission regimes have been identified on the basis of the energy and the spatial distribution of the emitted photons. At low excitation bias, tip-induced plasmons are excited in the tip–sample gap, carrying little information on the oxide film. With increasing tip bias, radiative electron transitions between field-emission resonances dominate the photon response from the MgO surface. Intrinsic optical modes of the oxide material, such as radiative decays of electron–hole pairs, are only observed when operating the STM in the field emission regime, where the direct correlation between the photon signal and the local surface morphology gets partially lost due to the increased tip–sample distance.

Electron capture in collisions betweenO6+ions andH2Omolecules

By means of photon emission spectroscopy, state selective electron capture cross section for low energy (0.1-7.5 keV/amu) collisions of O6+ on H2O molecules have been measured. Over the range of interaction energies the state selective cross sections change strongly, i.e., by factors up to 5, while the total one-electron capture cross section turns out to increase by approximately 40%. Possibilities of using O VI line emission ratios as a remote diagnostics of astrophysical plasma are indicated.

Charge Exchange Emission from Solar Wind Helium Ions

Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisions between fully ionized helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s-1). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observations of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.

Light emission spectroscopy of self-assembled arrays of silver nano-crystals with the STM

The optical properties of ordered and disordered assemblies of Ag nano-crystals on HOPG have been characterized by photon emission spectroscopy with the STM. The spectra reveal two emission maxima, which are attributed to plasmon modes oscillating parallel and perpendicular to the substrate plane. The interpretation of the emission mechanism is supported by polarization measurements and model calculations. The effect of long-range order in the particle layer on the optical properties is discussed.

Photon Emission Spectroscopy of Single Oxide-Supported Ag-Au Alloy Clusters

The alloying of Ag and Au has been investigated on the level of individual clusters by analyzing the light emission excited by electron injection from an STM tip. Different Ag-Au alloy and shell-core clusters have been prepared at room temperature on a thin ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ film on NiAl(110) by simultaneous and successive deposition of both noble metals. For simultaneous deposition, one Mie-plasmon resonance has been detected with a wavelength position shifting from the pure Au to the Ag value with increasing Ag content. The results are in agreement with calculations based on Mie theory indicating a complete mixing of both materials. For successive deposition, two Mie resonances have been observed, attributed to plasmon excitations in the shell and core of the clusters. Comparing these results to model calculations, a considerable intermixing of the core and shell materials is concluded, which is especially strong in Au shell-Ag core clusters.

Charge exchange and dissociative processes in collisions of slowHe2+ions withH2Omolecules

Experimental and theoretical studies of one-electron capture in collisions of He2+ ions with H2O molecules have been carried out in the range 0.025-12 keV amu(-1) corresponding to typical solar wind velocities of 70-1523 km s(-1). Translational energy spectroscopy (TES), photon emission spectroscopy (PES), and fragment ion spectroscopy were employed to identify and quantify the collision mechanisms involved. Cross sections for selective single electron capture into n=1, 2, and 3 states of the He+ ion were obtained using TES while PES provided cross sections for capture into the He+(2p) and He+(3p) states. Our model calculations show that He+(n=2) and He+(n=3) formation proceeds via a single-electron process governed by the nucleus-electron interaction. In contrast, the He+(1s) formation mechanism involves an exothermic two-electron process driven by the electron-electron interaction, where the potential energy released by the electron capture is used to remove a second electron thereby resulting in fragmentation of the H2O molecule. This process is found to become increasingly important as the collision energy decreases. The experimental cross sections are found to be in reasonable agreement with cross sections calculated using the Demkov and Landau-Zener models.