Transmission Mode Measurements Research Articles

Ultrafast charge separation dynamics in opaque, operational dye-sensitized solar cells revealed by femtosecond diffuse reflectance spectroscopy.

Efficient dye-sensitized solar cells are based on highly diffusive mesoscopic layers that render these devices opaque and unsuitable for ultrafast transient absorption spectroscopy measurements in transmission mode. We developed a novel sub-200 femtosecond time-resolved diffuse reflectance spectroscopy scheme combined with potentiostatic control to study various solar cells in fully operational condition. We studied performance optimized devices based on liquid redox electrolytes and opaque TiO2 films, as well as other morphologies, such as TiO2 fibers and nanotubes. Charge injection from the Z907 dye in all TiO2 morphologies was observed to take place in the sub-200 fs time scale. The kinetics of electron-hole back recombination has features in the picosecond to nanosecond time scale. This observation is significantly different from what was reported in the literature where the electron-hole back recombination for transparent films of small particles is generally accepted to occur on a longer time scale of microseconds. The kinetics of the ultrafast electron injection remained unchanged for voltages between +500 mV and –690 mV, where the injection yield eventually drops steeply. The primary charge separation in Y123 organic dye based devices was clearly slower occurring in two picoseconds and no kinetic component on the shorter femtosecond time scale was recorded.

J-NSE: Neutron spin echo spectrometer

Neutron Spin-Echo (NSE) spectroscopy is well known as the only neutron scattering technique that achieves energy resolution of several neV. By using the spin precession of polarized neutrons in magnetic field one can measure tiny velocity changes of the individual neutron during the scattering process. Contrary to other inelastic neutron scattering techniques, NSE measures the intermediate scattering function S(Q,t) in reciprocal space and time directly. The Neutron Spin-Echo spectrometer J-NSE, operated by JCNS, Forschungszentrum Jülich at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, covers a time range (2 ps to 200 ns) on length scales accessible by small angle scattering technique. Along with conventional NSE spectroscopy that allows bulk measurements in transmission mode, J-NSE offers a new possibility - gracing incidence spin echo spectroscopy (GINSENS), developed to be used as "push-button" option in order to resolve the depth dependent near surface dynamics.

Ce K edge XAS of ceria-based redox materials under realistic conditions for the two-step solar thermochemical dissociation of water and/or CO2.

X-ray absorption spectroscopy was used to characterise ceria-based materials under realistic conditions present in a reactor for solar thermochemical two-step water and carbon dioxide splitting. A setup suitable for in situ measurements in transmission mode at the cerium K edge from room temperature up to 1773 K is presented. Time-resolved X-ray absorption near-edge structure (XANES) data, collected for a 10 mol% hafnium-doped ceria sample (Ce0.9Hf0.1O2-δ) during reduction at 1773 K in a flow of inert gas and during re-oxidation by CO2 at 1073 K, enables the quantitative determination of the non-stoichiometry δ of the fluorite-type structure. XANES analysis suggests the formation of the hexagonal Ce2O3 phase upon reduction in 2% hydrogen/helium at 1773 K. We discuss the experimental limitations and possibilities of high-temperature in situ XAS at edges of lower energy as well as the importance of the technique for understanding and improving the properties of ceria-based oxygen storage materials for thermochemical solar energy conversion.

Detection of sub-micron lipid droplets using transmission-mode attenuation measurements in emulsion phantoms and liver

In liver transplantation, donor liver viability is assessed by the both the amount and type of fat present in the organ. General guidelines dictate that livers with more than 30% fat should not be transplanted; however, a lack of available donor organs has led to the consideration of livers with more fat. As a part of this process, it is desirable to distinguish micro-vesicular fat (< 1 µm droplets) from macro-vesicular fat (~10 µm droplets). A method of evaluating the relative amounts of micro- and macro-fat is proposed based on transmission-mode ultrasound attenuation measurements. For an emulsion of one liquid in another, attenuation comprises both intrinsic losses in each medium and excess attenuation associated with interactions between media. Using an established coupled-phase model, the excess attenuation associated with a monodisperse population of lipid droplets was calculated with physical properties representative of both liver tissue and dairy products. Calculations predict that excess attenuation can exceed intrinsic attenuation and that a well-defined peak in excess attenuation at 1 MHz should occur for droplets around 0.8 µm in diameter. Such predictions are consistent with preliminary transmission-mode measurements in dairy products. [Work supported by NIH grants EB017857, EB007643, EB016118, and T32 DK007779.]

A Comparison of Terahertz Pulsed Spectroscopy and Backward-Wave Oscillator Spectroscopy

This paper presents new experimental and theoretical results for the material parameter reconstruction utilizing the terahertz (THz) pulsed spectroscopy (TPS). The material parameter reconstruction algorithm was realized and experimentally implemented to study the test sample. The algorithm takes into account multiple reflections of THz pulse within the flat sample during the transmission mode measurements. Therefore the samples with small thickness or low refractive index could be studied utilizing the proposed method. In order to estimate the reconstruction accuracy, test sample material parameters, obtained with the TPS, were compared with the results of the same sample studying by the use of the backward-wave oscillator (BWO) spectroscopy. Thus, high reconstruction accuracy was demonstrated.

It's in your blood: spectral biomarker candidates for urinary bladder cancer from automated FTIR spectroscopy

Blood samples of urinary bladder cancer (UBC) patients and patients with urinary tract infection were analysed with advanced automated high throughput Fourier transform infrared (HT-FTIR)-spectroscopy. Thin dried film samples were robotically prepared on multi-well titer plates (MTP) for absorbance measurements in transmission mode. Within the absorbance, 1st and 2nd derivative spectra of serum and two plasma preparations, discriminative patterns were identified and validated using bioinformatic tools. The optimal spectral resolution for data acquisition was determined. An accurate discrimination of the patient groups was achieved with three different independent spectral variable sets. The HT-FTIR blood test may support future clinical diagnostics.

Integrated transmission-reflection quantitative ultrasound noninvasive prediction of trabecular bone principal structural orientation validated with mechanical testing

Quantitative ultrasound (QUS) measurement was shown to have the ability to predict the principal structural orientation (PSO) with a spherical bone model. It is hypothesized that with a cubic bone model, integrated transmission-reflection QUS measurement can predict the PSO and therefore improved the correlation with the mechanical and structural parameters. Twelve trabecular bone cubes were harvested from bovine distal femur. Compression testing and µCT of 30 µm resolution were performed to obtain the mechanical and structural parameters. QUS measurement was performed on the transverse plane in a range of angles, from -30̊ to 30̊ to medial-lateral orientation at 5̊ increment. For each angle, reflection mode was used to measure the thickness of the sample in the specific scanning angle. Then, the sample thickness was used to normalize the transmission mode measurement in the same angle. The thickness measured by reflection mode QUS was highly correlated to the results measured by caliber (slope = 0.99, R2 = 0.85). Compared to the traditional transmission mode, the correlation coefficients (R2) between transmission-reflection mode ultrasound velocity versus mechanical and structural parameters were improved (elastic modulus, 0.62 to 0.73; SMI, 0.74 to 0.90; BV/TV, 0.75 to 0.85; Tb.N, 0.60 to 0.75; Tb.Sp, 0.66 to 0.73).

About molybdenum behaviour during U(Mo)/Al(Si) interaction processes

U(Mo)/Al(Si) diffusion couples are studied to provide a better understanding of the interaction processes between the U(Mo) fuel and the Al(Si) matrix and, more specifically, to determine the molybdenum behaviour in the interaction product, close to the U(Mo) alloy. Micro-computed tomography and micro-X-ray diffraction measurements in transmission mode, coupled with scanning transmission electron microscopy and energy dispersive X-ray spectroscopy analysis show that molybdenum is present in the interaction layer, close to the U(Mo) interface, in an U4Mo(MoxSi1−x)Si2 ternary intermediate phase, mixed with the U3Si5 phase. The formation of this Mo-containing phase is accompanied by a Mo depletion process, in the underlying U(Mo) alloy, this depletion leading to a γ-U(Mo) phase local destabilisation.A strong correlation between the Si and the Mo behaviours, in the U(Mo)/Al(Si) system, is thus evidenced.

Rapid prototyping of microfluidic devices for integrating with FT-IR spectroscopic imaging

A versatile approach for the rapid prototyping of microfluidic devices suitable for use with FT-IR spectroscopic imaging is introduced. Device manufacture is based on the direct printing of paraffin onto the surface of an infrared transparent substrate, followed by encapsulation. Key features of this approach are low running costs, rapid production times, simplicity of design modifications and suitability for integration with FT-IR spectroscopic measurements. In the current experiments, the minimum width of channel walls was found to be approximately 120 mum and approximately 200 when a 25 mum and 12 mum spacer is used, respectively. Water and poly(ethylene glycol) are used as model fluids in a laminar flow regime, and are imaged in both transmission and attenuated total reflection (ATR) modes. It is established that adoption of transmission mode measurements yields superior sensitivity whilst the ATR mode is more suitable for quantitative analysis using strong spectral absorption bands. Results indicate that devices manufactured using this approach are suitable for use with in situ FT-IR spectroscopic imaging.

Development of a liquid flow cell to measure soft X-ray absorption in transmission mode: A test for liquid water

A liquid flow cell has been developed for the transmission-mode measurement of soft X-ray absorption spectra of liquid samples, and applied to bulk liquid water at the O K-edge region. Soft X-rays pass through the region filled by helium gas and then through the liquid sample, and finally reaches the detector in a helium atmosphere. Each region is separated by a 100 nm-thick SiN x membrane window, which is thin enough to transmit soft X-rays. The artifact of the higher order X-rays at the O K-edge region is evaluated by varying the sample thickness for 100–800 nm, and is removed successfully to obtain consistent soft X-ray absorbance for the liquid water. The sample thickness is estimated from the edge jump in absorbance. In the present cell, fresh liquid samples can be supplied to avoid the radiation damage. By changing the pressure of helium gas and the continuous flow speed of liquids, it is possible to control the thickness of liquid samples.

A maximum likelihood method for obtaining integrated attenuation from ultrasound transmission mode measurements

In photoacoustic imaging applications an image is reconstructed of the optical absorption distribution the imaged object. The photoacoustic measurements however are also dependent on acoustic properties of the imaged object. By estimating the acoustic properties from photoacoustic measurements, we can improve the performance of the optical absorption reconstruction and allow for the imaging of separate acoustic modalities. We derive and evaluate a maximum likelihood estimator for the measurements of integrated acoustic attenuation. This estimator is applicable to media like soft tissue. In this kind of media, the attenuation due to dissipative effects obeys a frequency power law. By measuring the propagation of ultrasound signals through such a medium, the parameters that describe the attenuation can be estimated. In this paper a new method is introduced for estimating the attenuation of ultrasound media by means of transmission mode measurements. The method is based on analyzing the noise characteristics of the received signals and the formulation of a maximum likelihood estimator. The new estimator is compared to existing methods and was found to be a better estimator in terms of the RMS error than previous methods.

Commissioning and performance of X-ray absorption spectroscopy beamline at the Siam Photon Laboratory

We report commissioning results and performance of X-ray absorption spectroscopy (XAS) beamline, BL-8, at the Siam Photon Laboratory. BL-8 has been opened for users since the year 2006. It is tunable by a fixed-exit double crystal monochromator equipped with InSb(1 1 1), Si(1 1 1), and Ge(2 2 0) crystals covering photon energy from 1830 to 9000 eV. Thus elemental absorption K-edges of silicon up to copper can be investigated. Other heavier elements may be studied via their L or M edges. The front end is windowless and the beamline is terminated with a Kapton window followed by the XAS station equipped with ionization chambers for transmission-mode measurements. The measured photon flux at sample is approximately 10 8–10 10 photons/s/100 mA for the 1 mm×10 mm beam size. The commissioning XANES spectra of sulfur standards and EXAFS spectra of copper are presented.

In situ infrared spectroscopic and scanning Kelvin probe measurements of water and ion transport at polymer/metal interfaces

Scanning ATR-spectroscopy and scanning Kelvin probe studies are introduced as new analysis techniques for the study of water and ion transport at polymer/metal interfaces. The new approach of scanning ATR spectroscopic analysis of water transport at the adhesive/metal interface is combined with scanning measurements in transmission mode of water transport along adhesive joints and non-scanning ATR-measurements of the water transport in a vertical direction through the adhesive. D2O was chosen in some cases instead of water due to its excellent traceability in the infrared spectra. A scanning Kelvin probe was chosen for the detection of the transport kinetics of hydrated alkali ions along the adhesive/metal interface based on the local measurement of interfacial electrode potentials. The complimentary FT-IR techniques showed that the interfacial diffusion of water, in the case of epoxy adhesives on iron, is about two orders of magnitude faster that the transport through the adhesive itself. Similar transport kinetics at the interface is also shown by hydrated ions. Moreover, the here presented FT-IR–ATR and SKP results reveal more information on how adhesion promoting organosilane layers and organosilanes as additives act at polymer/metal interfaces in the presence of water incorporated in the interphase zone.

FTIR Spectroscopic Study of Biogenic Mn-Oxide Formation by Pseudomonas putida GB-1

Biomineralization in heterogeneous aqueous systems results from a complex association between pre-existing surfaces, bacterial cells, extracellular biomacromolecules, and neoformed precipitates. Fourier transform infrared (FTIR) spectroscopy was used in several complementary sample introduction modes (attenuated total reflectance [ATR], diffuse reflectance [DRIFT], and transmission) to investigate the processes of cell adhesion, biofilm growth, and biological Mn-oxidation by Pseudomonas putida strain GB-1. Distinct differences in the adhesive properties of GB-1 were observed upon Mn oxidation. No adhesion to the ZnSe crystal surface was observed for planktonic GB-1 cells coated with biogenic MnO x , whereas cell adhesion was extensive and a GB-1 biofilm was readily grown on ZnSe, CdTe, and Ge crystals prior to Mn-oxidation. IR peak intensity ratios reveal changes in biomolecular (carbohydrate, phosphate, and protein) composition during biologically catalyzed Mn-oxidation. In situ monitoring via ATR-FTIR of an active GB-1 biofilm and DRIFT data revealed an increase in extracellular protein (amide I and II) during Mn(II) oxidation, whereas transmission mode measurements suggest an overall increase in carbohydrate and phosphate moieties. The FTIR spectrum of biogenic Mn oxide comprises Mn-O stretching vibrations characteristic of various known Mn oxides (e.g., “acid” birnessite, romanechite, todorokite), but it is not identical to known synthetic solids, possibly because of solid-phase incorporation of biomolecular constituents. The results suggest that, when biogenic MnO x accumulates on the surfaces of planktonic cells, adhesion of the bacteria to other negatively charged surfaces is hindered via blocking of surficial proteins.

Transmission Measurements on Intact Apples Moving at High Speed

Two different near infared spectrometric systems, both based on readily available optical components, were investigated for direct transmission mode measurements on intact apples ( Malus domestica Borkh.) moving at high speed (500 mm s−1). One system was based on the principle of time-delayed integration spectroscopy(TDIS) in which light emanating from a moving object was electronically tracked as it moved through the field of view of the spectrometer. The other system, a large aperture spectrometer (LAS), was a more conventional design in which the light from the object is accumulated in a series of one-shot measurements as the fruit progresses through the field of view. The systems were each optimally configured, using the same core optic components, to detect the low levels of light diffusely transmitted through apples between 650 and 950 nm. Performance comparisons were made in the context of dry-matter predictions; an important metric for apple quality. Modelling and validation statistics ( R2, RMSEP) for dry-matter predictions were (0.87, 0.43%) and (0.81, 0.48%) for the LAS and TDIS systems, respectively. These accuracies are excellent and similar to what is normally achievable on the more common but slower interactance-type NIR fruit measurement systems. Hence, the results have demonstrated that use of a direct transmission mode is a viable option for high-speed fruit measurement, even for a very opaque fruit like apples.

Terahertz surface plasmon polariton coupling on metallic gratings

Terahertz time-domain spectroscopy is used to study the nature and efficiency of coupling between surface plasmon polaritons and free-space terahertz radiation by metallic gratings made from brass rods and a grooved aluminum plate. Reflection and transmission mode measurements indicate very rapid coupling and decoupling with > 70% efficiency after accounting for scattering. Results indicate a good match to theoretical coupling frequencies within the accuracy of the experimental setup.

Nonconventional approaches to ultrasonic assessment of skeletal system

Conventional bone ultrasonometry is based on the transmission mode measurement of the linear acoustic parameters of bone (speed of sound and broadband attenuation). It is a well-established technique specifically for osteoporosis diagnostics though it is highly limited in its applications. It cannot be used for the assessment of the hip bone which is the most important area in characterization of the skeletal system and can hardly be used in pediatric applications, particularly in neonatology, for the assessment of newborns and premature and low-birth-weight infants skeletal systems, which became especially vital during the last few decades. There are several new ideas on acoustic assessment of the skeletal sites hardly accessible by the conventional bone ultrasonometry and on principles of the acoustic characterization of bone quality, fracture risk evaluation, and monitoring of therapeutic interventions. New approaches are based on the use of the ultrasound radiation pressure for the remote generation of acoustic waves in bones, on the use of various modes of guided acoustic waves having a propagation speed dependent on both the elasticity modulus and the bone thickness, on the use of geometrical dispersion of sound velocity for bone characterization, and the use of principles of nonlinear acoustic spectroscopy for remote bone testing. [Work supported by NIH.]

Arterial audiophotoplethysmography

SummaryBackground: Digital blood pressure is an important prognostic parameter in peripheral arterial disease. However, it is rarely determined in clinical routine because the methods available are too cumbersome. Patients and methods: Arterial audiophotoplethysmography (APPG) uses an in-built audio output. The systolic pressure corresponds to the reappearance of a pulssynchrone beep during deflation of the pressure cuff (25 mm wide on fingers and toes) after suprasystolic inflation. Measurements can be performed either in transmission or reflection mode. 50 healthy volunteers (age: 23-75 years) were examined in supine position. Blood pressure was taken at the A. brachialis, A. ulnaris, A. radialis, A. poplitea, A. tibialis anterior and posterior using ultrasound Doppler (USD), at the A. brachialis, fingers 1-5, A. poplitea and toes 1-3 using APPG. Results: Regarding the A. brachialis and poplitea, we found an excellent correlation between values obtained by USD and APPG in transmission mode (r: 0.92-0.99), the correlation with the reflection mode-values was slightly lower (r: 0.81- 0.93). The values obtained in reflection mode were significantly lower than in transmission mode (average 5.2 mmHg on the arms, 12.9 mmHg on the legs). Finger pressure was identical with A. brachialis-pressure. Toe/- brachial index was 0.81-0.86 (transmission) and 0.72- 0.78 (reflection). No significant difference was found between any of the fingers, respectively the toes. Conclusions: APPG is a reliable method for determination of digital blood pressure, which can be easily performed. Measurements in transmission mode should be preferred.

A cell for combined UV-visible and x-ray absorption spectroscopy studies under low-temperature and air exclusion conditions

A measuring system that integrates a low-temperature optical cell UV-visible (UV-Vis) for air exclusion experiments with a liquid x-ray absorption spectroscopy (XAS) cell (x-ray absorption near-edge spectroscopy and extended x-ray absorption fine structure) is reported here together with its application in studies of organometallic complexes. UV-Vis measurements are performed in a three-compartment glass vessel, fitted with an external fiber optics probe. This UV-Vis cell is suitable for the measurement of oxygen- and air-sensitive compounds at variable temperatures (RT to −78 °C). The liquid XAS cell is filled with the UV-Vis solution at low temperature and can be used in both fluorescence- or transmission-mode measurements with (frozen) solutions. The complete measuring system is reusable and easy to clean and handle. To test the performance of these cells the oxygenation behavior of a dinuclear organometallic copper(I) complex was studied in acetone by UV-Vis and XAS. It is shown that direct correlation of low-temperature UV-Vis and XAS data is possible in organic solvents.

Exafs studies of LiYF 4 -LiREF 4 solid solutions

In this work we are investigating dopant environments in LiYF 4 -LiREF 4 (RE=rare-earth cations) solid solutions, via EXAFS. The main aims are to identify the local environmental symmetry and the average lattice distortion as a function of the concentration and the type of the RE ion. LiY 1 m x RE x F 4 (RE=Gd or Lu) (0< x <1) single crystals were grown by the Czochralski technique under argon or CF 4 atmosphere, crystal-pulling rates were 0.6-1 v mm/h for <100>-oriented boules, with 8-25 v rpm rotation rates. Most of the crystals were also codoped with 2.7 v mol% of neodymium in the melt. EXAFS measurements were performed in transmission and fluorescence modes in the synchrotron XAS line of the LNLS, Campinas, Brazil, in and above the L III absorption edges of the RE ions. The samples were prepared as powder films, for the transmission mode measurements, and as powder or single crystals for fluorescence mode measurements. The WINXAS program was used for data reduction and fitting, and the FEFF6 package was used for the simulations of the spectra. The EXAFS oscillation curves were obtained by standard procedure.