Transmission Mode Measurements Research Articles

Nucleation and quantum confinement of nano-platelet Bi2–Bi2Se3

The nucleation, nano-platelet growth, and optical properties under quantum confinement are investigated in the topological semimetal superlattice Bi2–Bi2Se3 as a function of thickness and Ar + ion pressure in sputtered growths. Quantum confinement and evolution of the band structure with a series of reduced dimensionality and surface terminations are studied by density functional theory corroborating the observed optical properties. An initial Volmer–Weber growth mode of nano-platelets is observed until a pressure-dependent critical thickness, where a transition to Frank–van der Merwe growth occurs. Nucleation statistics characterized using atomic force microscopy find the nearest-neighbor ordering of nano-platelets. Optical properties using ultraviolet to visible light spectroscopy measurements in transmission mode reveal a marked increase in optical bandgap below a nano-platelet critical volume reaching a maximum of 2.21 eV. Raman vibrational spectroscopy is performed, revealing softening of vibrational modes as the nano-platelet volume decreases.

Non-Linear Conductivity Response of Graphene on Thin-Film PET Characterized by Transmission and Reflection Air-Plasma THz-TDS.

We demonstrate that the conductivity of graphene on thin-film polymer substrates can be accurately determined by reflection-mode air-plasma-based THz time-domain spectroscopy (THz-TDS). The phase uncertainty issue associated with reflection measurements is discussed, and our implementation is validated by convincing agreement with graphene electrical properties extracted from more conventional transmission-mode measurements. Both the reflection and transmission THz-TDS measurements reveal strong non-linear and instantaneous conductivity depletion across an ultra-broad bandwidth (1-9 THz) under relatively high incident THz electrical field strengths (up to 1050 kV/cm).

Diffraction-limited mid-infrared microspectroscopy to reveal a micron-thick interfacial water layer signature.

Mid-infrared microspectroscopy is a non-invasive tool for identifying the molecular structure and chemical composition at the scale of the probe, i.e. at the scale of the beam. Consequently, investigating small objects or domains (commensurable to the wavelength) requires high-resolution measurements, even down to the diffraction limit. Herein, different protocols and machines allowing high-resolution measurements in transmission mode (aperture size (i.e., beam size) from 15 × 15 μm to 3 × 3 μm) are tested using the same sample. The model sample is a closed cavity containing a water-air assemblage buried in a quartz fragment (fluid inclusion). The spectral range covers the water stretching band (3000-3800 cm-1), whose variations are followed as a function of the distance to the cavity wall. The experiments compare the performance of one focal plane array (FPA) detector associated with a Globar source with respect to a single-element mercury cadmium telluride (MCT) detector associated with a supercontinuum laser (SCL) or a synchrotron radiation source (SRS). This work also outlines the importance of post-experimental data processing, including interference fringe removal and Mie scattering correction, to ensure that the observed spectral signatures are not related to optical aberrations. We show that the SCL and the SRS-based setups detect specific spectral features along the quartz boundary (solid surface), invisible to the FPA imaging microscope. Additionally, the broadband SCL thus has the potential to substitute at the laboratory scale the SRS for conducting diffraction-limited high-resolution measurements.

A quantitative study of thermal cycling along the build direction of Ti-6Al-4V produced by laser powder bed fusion

During laser-powder bed fusion (l-PBF) the printed material is subjected to multiple fast heating and cooling cycles when the laser interacts with neighboring tracks or layers above. The complex thermal history influences the final microstructure and the macroscopic properties of the printed part. In this work, we demonstrate how high-speed in situ X-ray diffraction in transmission mode can be used to measure temperature profiles and cooling rates in a Ti-6Al-4V single-track wall. During the laser remelting of the top layer, a temperature exceeding the β transus temperature (Tβ ∼ 1252 K) is measured up to 150 µm below the surface. The maximum observed cooling rates vary from 106 K/s at the top surface, to 105 K/s at a depth of 135 µm and 104 K/s at a depth of 255 µm. Based on the temporal evolution of the various crystallographic phases, the dimensions of the melt pool and the high-temperature β zone surrounding the melt pool are estimated. It is anticipated that the data obtained from in situ measurements in transmission mode on a thin wall combined with in situ measurements in reflection mode on a bulk sample will allow verification and validation of finite element models used in l-PBF processing.

Optimization of terahertz fingerprint and identification capabilities by using PSO algorithm

In the terahertz range, materials are often characterized by a specific spectral response that contains unique resonant frequencies, which allows to detect and identify them very precisely. In this work, we have developed a new efficient calculating model that can be applied to identify the resonance frequencies of the material using terahertz time-domaine spectroscopy measurements in transmission mode. Furthermore, the PSO optimization algorithm is an extremely powerful tool that, once associated with our model, allowed us to quickly and accurately extract the optical characteristics of the material such as the absorption and the refractive index of the material. The performances of the proposed technique are very relevant particularly in the case of important noise.

Investigation of nature of excitons in PPDT2FBT and effect of optical interference

Electroabsorption (EA) measurements can be used to identify the type of excitons contributing to the absorption spectra of semiconductors. However, the shape of the EA spectrum may vary depending on the mode of measurement due to the optical interference effects. Analysis without considering these effects may lead to erroneous conclusions. In this work, we present EA measurements and analysis for reflection mode measurements considering optical interference effects. We compared the inferences with transmission mode measurements and discuss the limitations. We identified the nature of excitons associated with each transition in the absorption spectrum of poly[(2,5-bis(2-hexyldecyloxy)-phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]-thiadiazole)] thin film from EA measurements. The bands at 1.89, 2.05, and 2.27 eV had a mixed nature consisting of charge transfer and Frenkel characteristics. Of these, the band at 2.05 eV showed the strongest charge transfer characteristic. From thickness dependent measurements, we showed that the interference effects increase with the thickness of the semiconductor layer. The nature of excitons, however, could still be deduced qualitatively from reflection mode EA measurements.

X-ray absorption fine structure measurements on Ru–Zn/ZSM-5 during heterogeneous catalysis using an in situ spectroscopic cell

We introduce a design of a portable, multi-functional spectroscopic cell for in situ structural probe of materials using hard x-rays. This versatile reaction cell allows x-ray absorption fine structure (XAFS) and x-ray diffraction measurements in transmission mode on solids at a controlled temperature, pressure, and gas environment. A model heterogeneous catalysis system, co-aromatization of octane with methane catalyzed by Ru–Zn/ZSM-5, was employed to demonstrate the performance of the spectroscopic cell. Quick XAFS measurement at the Ru K-edge was performed during the catalyst activation and catalysis reaction. The chemical reduction of Ru from RuO2 to metallic-like Ru is found to occur rapidly once the temperature is above a threshold, and the reduction is completed in ∼75 s. Prolonged heating during catalysis reaction at constant operating temperature has a minimum effect on the electronic structure of the Ru species.

Two-dimensional solid-state array detectors: A technique for in vivo dose verification in a variable effective area.

PurposeWe introduce a technique that employs a 2D detector in transmission mode (TM) to verify dose maps at a depth of dmax in Solid Water. TM measurements, when taken at a different surface‐to‐detector distance (SDD), allow for the area at dmax (in which the dose map is calculated) to be adjusted.MethodsWe considered the detector prototype “MP512” (an array of 512 diode‐sensitive volumes, 2 mm spatial resolution). Measurements in transmission mode were taken at SDDs in the range from 0.3 to 24 cm. Dose mode (DM) measurements were made at dmax in Solid Water. We considered radiation fields in the range from 2 × 2 cm2 to 10 × 10 cm2, produced by 6 MV flattened photon beams; we derived a relationship between DM and TM measurements as a function of SDD and field size. The relationship was used to calculate, from TM measurements at 4 and 24 cm SDD, dose maps at dmax in fields of 1 × 1 cm2 and 4 × 4 cm2, and in IMRT fields. Calculations were cross‐checked (gamma analysis) with the treatment planning system and with measurements (MP512, films, ionization chamber).ResultsIn the square fields, calculations agreed with measurements to within ±2.36%. In the IMRT fields, using acceptance criteria of 3%/3 mm, 2%/2 mm, 1%/1 mm, calculations had respective gamma passing rates greater than 96.89%, 90.50%, 62.20% (for a 4 cm SSD); and greater than 97.22%, 93.80%, 59.00% (for a 24 cm SSD). Lower rates (1%/1 mm criterion) can be explained by submillimeter misalignments, dose averaging in calculations, noise artifacts in film dosimetry.ConclusionsIt is possible to perform TM measurements at the SSD which produces the best fit between the area at dmax in which the dose map is calculated and the size of the monitored target.

Examination of Natural and Standard Fe<sub>3</sub>O<sub>4</sub> Powders Using X-Ray Absorption Near-Edge Spectroscopy (XANES)

Investigation of Fe K-edge X-Ray Absorption Near Edge Spectroscopy (XANES) spectra of Fe3O4 (FeO.Fe2O3) from natural source compared with the Fe3O4 standard is presented. The natural Fe3O4 powder was prepared from ironstone of Tanah Laut, Kalimantan Selatan by co-precipitation method. XANES measurements in transmission mode were performed at the Synchrotron Light Research Institute (SLRI), Nakhon Ratchasima, Thailand. XRD phase analysis confirms that the synthesized Fe3O4 powder is a single phase, but it cannot determine the proportion of Fe2O3 and FeO in the structure. TEM measurement confirms that the particle size of natural Fe3O4 about 10 nm. Qualitative analysis of the pre-edge XANES data revealed that the absorbing atom in the XAS measurement is Fe3+. Meanwhile, the absorption edge (E0) values of natural and standard Fe3O4 powders were 7126.44 eV and 7125.02 eV, respectively. The proportion was then acquired using XANES data analysis through Linear Combination Fitting (LCF). It was found that the natural Fe3O4 sample consisted of 98 wt. % Fe2O3 and 2 wt.% FeO, while the standard Fe3O4 powder consisted of 96 wt. % Fe2O3 and 4 wt. % FeO. The mechanism of the absorption in both samples is also described and compared.

Laser Inscription of Microfluidic Devices for Biological Assays.

A rapid and direct CO2 laser ablation method was developed to create superhydrophilic surfaces and arrays of hydrophobic-superhydrophilic patterns for application in bioassays. Here, a combination of superhydrophilic and hemiwicking wetting characteristics was exploited to create microfluidic slides that were used as biological assays that prevented cell aggregation. This feature allowed microscopic analyses to be carried out at the individual cell level. This bioassay enabled control of cell population in localized areas (15 cells cm-2). The device had 84% transparency, allowing direct fluorescence microscopy measurements in transmission mode. High adhesion of aqueous fluids on superhydrophilic areas surrounded by superhydrophobic boundaries provided selective retention and confinement. The adhered droplets maintained retention under 180° substrate tilt. These architectures provided rapid self-partitioning of the liquid into an array of droplets. The hydrophobic-superhydrophilic patterned arrays may have applications in microfluidic bioassays, high-throughput screening, and medical diagnostics.

Novel optical biosensor method to identify human blood types using free-space frequency-modulated wave of NIR photon technology.

BackgroundThe free-space broadband frequency-modulated near-infrared (NIR) photon transmission and backscattering mode technique has been used in this paper as an optical biosensor method.PurposeThe purpose is to measure, identify, and extract the optical properties of different blood types.Patients and methodsThe method depends on the measurements of broadband frequencies ranging from 30 up to 1,000 MHz to predict two important parameters related to the incident-modulated signal. Blind samples collected from 30 patients were examined using the optical NIR transmission mode system, and an additional 40 blood samples from random patients were examined using the optical NIR reflection mode system. The study is divided into two stages: The first stage is dedicated to measuring the insertion loss and insertion phase over 30–1,000 MHz in a transmission mode to characterize the behavior of modulated photons as they interact with the blood samples. The second stage is dedicated to performing noninvasive backscattering measurements using the optical band developed to match the first stage results.ResultsIn this paper, we have created an indexed database using optical transmission mode measurements, and then mapped it to a reflection noninvasive measurement to identify the blood types. Then for the purpose of device accuracy, we randomly selected 480 new human subjects to measure the false-negative error percentage. This method is novel in terms of using an optical system to measure and identify blood types without collecting blood samples.ConclusionThe novel approach shows a highly accurate method in identifying different blood types instantaneously using optical sensing for both in vitro and in vivo procedures, thereby saving time and effort.

Non-destructive DRIFT spectroscopy measurement of the degree of curing of industrial epoxy/silica composite buildup layers

The degree of curing of epoxy composites and coatings is one key parameter to control the reliability of manufacturing processes, particularly in printed circuit board (PCB) manufacturing where epoxy buildup composites are partially cured before processing. We show that the reaction of curing of an industrially relevant buildup composite (epoxy-phenol reinforced with silica fillers) can be monitored by diffuse reflectance infrared Fourier transform (DRIFT) in the near-infrared range. The accuracy of DRIFT measurements is confirmed by comparison with measurements in transmission mode on reference composite samples. DRIFT is demonstrated to offer an easy and reliable measurement of the epoxy degree of curing on PCB coupons.

Synthesis, structural and X-ray absorption spectroscopy of (PbxBi1-x).TiO3 borosilicate glass and glass ceramics

Two series of glasses were synthesized by conventional rapid melt-quench method for different glass systems 55[(PbxBi1-x).TiO3]-44[2SiO2B2O3] and 65[(PbxBi1-x).TiO3]-34[2SiO2B2O3] doped with 1 mole percent of La2O3. X-ray diffraction study of synthesized glass sample shows amorphous nature while the glass ceramic sample revealed a cubic crystal structure due to devitrification of the glass as major crystalline phase of bismuth titanium oxide. X-ray absorption spectroscopy measurements in transmission mode were carried out and confirm the maximum value of absorption coefficient, 3.05 at energy 13450 eV for lead free glass ceramic sample. Scanning electron microscopy and contact angle measurements were also performed to explain the surface morphology. Energy dispersive X-ray analysis confirmed the presence of grains of bismuth titanium oxide and its elemental analysis with O, Ti, Si, Bi nanoparticles. The inclusions of La2O3 results in development of well interconnected crystallites were formed as major phase of bismuth titanium oxide.

Active Millimeter-Wave Radiometry for Nondestructive Testing/Evaluation of Composites—Glass Fiber Reinforced Polymer

Manufacture and in-service assessment of composite materials can be challenging since there is, yet, no standard method for testing them. Nevertheless, regular inspection is necessary to maintain the structural integrity. This paper describes a nondestructive, broadband noise mapping method that uses a millimeter-wave radiometer to detect defects in composite materials. The $W$ -band system is configured for transmission mode measurement in which an amplified photonic source illuminates a glass fiber reinforced polymer containing machined defects. A high sensitivity radiometer is used for imaging the sample. The radiometer consists of a Schottky diode-based frequency tripler and a fundamental mixer.

What is fluidity? Designing an experimental system to probe stress and velocity fluctuations in flowing suspensions

We develop a method to investigate the microscopic origin of granular fluidity. We design a Couette cell in which we can probe the flow of soft hydrogel suspensions. As we drive the suspension with a rheometer, we have access to global flow characteristics. In addition, the Couette cell has been modified to have a transparent bottom and lid, allowing for imaging of suspension characteristics in transmission, for example flow fields. We can also use transmission imaging to probe local stresses in the suspension: we use hydrogel particles composed of gelatin, which through its photoelastic properties gives access to local stress fluctuations. We thus have access to all local microscopic variables that are relevant in the understanding of granular suspensions. We show here that our setup can indeed visualize stress fields inside the suspensions and perform flow field measurements in transmission mode. We compare the profiles of the gelatin suspension to that of a polyacrylamide hydrogel suspension, to assess robustness of observed phenomenology. We find that the flow profiles for both types of hydrogels are different; gelatin suspensions feature narrower and less rate-dependent flow profiles. We speculate on the origin of the observed difference by considering the frictional properties of the suspended particles.

单端面透射模式长周期光栅的设计和测试

单端面透射模式长周期光栅的设计和测试

单端面长周期光栅透射模式测量技术

单端面长周期光栅透射模式测量技术

Two-Dimensional Nanogranularity of the Oxygen Chains in the YBa2Cu3O6.33 Superconductor

The organization of dopants in high temperature superconductors provides complex topological geometries that controls superconducting properties. This makes the study of dopants spatial distribution of fundamental importance. The mobile oxygen ions, y, in the CuO2 plane of YBa2Cu3O6+y (0.33<y<0.67) form ordered chains which greatly affect the transport properties of the material. Here we visualize and characterize the 2D spatial organization of these oxygen chains using scanning micro X-ray diffraction measurements in transmission mode on a thin single crystal slab with y=0.33 (Tc=7 K) near the critical doping for the insulator-to-metal transition. We show the typical landscape of percolation made of a granular spatial pattern due the oxygen chains segregating in quasi-one-dimensional needles of Ortho II (O-II) phase embedded in an insulating matrix with low density of disordered oxygen interstitials

Design of transmission-mode measurements for estimating ultrasound attenuation and nonlinearity in liver

Previously, it has been shown that ultrasound measurements of sound speed and nonlinearity can be used to quantify the fatty and non-fatty components of liver tissue. In addition, it has been proposed that ultrasound attenuation measurements can be used to distinguish fatty components comprising either sub-micron lipid droplets (microsteatosis) or much larger cell-sized droplets (macrosteatosis). To perform all of these measurements, a caliper device is being developed based on a transmission-mode approach. Design challenges are posed by competing requirements: sub-megahertz frequencies for optimal detection of microsteatosis and nonlinearity estimation based on waveform distortion over relatively short distances. To meet these challenges, a design is proposed in which ultrasound at 667 kHz is generated by a 50 mm piezoceramic disk and all measurements are made in the plane-wave regime. Given geometrical and physical constraints, all analysis was performed in the time domain. The nonlinearity coefficient ...

Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge.

The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D2O spectrum is found to be blue shifted with respect to H2O, and the D2O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D2O and H2O, while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero-point energies and vibrational zero-point distributions in the ground-states of the liquids. The influence of the shape of the final-state potential, inclusion of the Franck-Condon structure, and differences between liquid H2O and D2O resulting from different hydrogen-bond environments in the liquids are addressed. The differences between the O K-edge absorption spectra of water from our transmission-mode measurements and from the state-of-the-art x-ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground-state zero-point energies and vibrational zero-point distributions in liquid H2O and D2O. This clearly motivates the need for new calculations of the O K-edge x-ray absorption spectrum of liquid water.