High Spatial Resolution Laser Research Articles

Nanoscale Photovoltaic Responses in 3D Radial Junction Solar Cells Revealed by High Spatial Resolution Laser Excitation Photoelectric Microscopy.

The actual light absorption photovoltaic responses realized in three-dimensional (3D) radial junction (RJ) units can be rather different from their planar counterparts and remain largely unexplored. We here adopt a laser excitation photoelectric microscope (LEPM) technology to probe the local light harvesting and photoelectric signals of 3D hydrogenated amorphous silicon (a-Si:H) RJ thin film solar cells constructed over a Si nanowire (SiNW) matrix, with a high spatial resolution of 600 nm thanks to the use of a high numerical aperture objective. The LEPM scan can help to resolve clearly the impacts of local structural damages, which are invisible to optical and SEM observations. More importantly, the high-resolution photoelectric mapping establishes a straightforward link between the local 3D geometry of RJ units and their light conversion performance. Surprisingly, it is found that the maximal photoelectric signals are usually recorded in the void locations among the standing SiNW RJs, instead of the overhead positions above the RJs. This phenomenon can be well explained and reproduced by finite element simulation analysis, which highlights unambiguously the dominant contribution of inter-RJ-unit scattering against direct mode incoupling in the 3D solar cell architecture. This LEPM mapping technology and the results help to achieve a straightforward and high-resolution evaluation of the local photovoltaic responses among the 3D RJ units, providing a solid basis for further structural optimization and performance improvement.

High resolution LDA measurements in transitional oblique shock wave boundary layer interaction

Spatial development of a transitional Oblique Shock Wave Interaction at Mach 1.68 is presented. This type of flow is characterised by very small length scales (boundary layer thickness is smaller than 1mm), high velocities, reverse flows and a wide range of velocity fluctuations along the transition process. Unsteady velocity fields have been obtained using a high spatial resolution Laser Doppler Anemometry system, allowing quantitative measurements of the velocity fluctuations down to $$y/\delta =0.1$$ . A model to take into account the finite size of the probe volume on the mean and RMS velocity measurements is used and applied to the present measurements. Finally, the amplification of the velocity fluctuations along the transitional separated shear layer is described.

Soot evolution and flame response to acoustic forcing of laminar non-premixed jet flames at varying amplitudes

New details regarding the soot evolution and its controlling parameters in steady and forced flames have been studied using high spatial resolution laser diagnostic techniques. Steady laminar non-premixed ethylene/nitrogen flames with three different diameters burners were acoustically forced using a loudspeaker. 10-Hz-sinusoidal signals of different amplitudes were transmitted to the loudspeaker to drive the flames. The results reveal that the spatial correlation between the soot field and the temperature profile is influenced by the burner diameter and forcing conditions. The soot field in steady laminar flames is confined to a relatively narrow temperature range, 1500–2000 K. In contradiction, the soot field in forced flames spread across a wider range of temperature, 1400–2100 K. Furthermore, the spatial correlation between the normalised soot concentration and primary particle size can be described with an exponential function. While it is observed that the exponential coefficients vary with burner diameter and forcing conditions, further study is necessary for a better understanding. In general, laminar flames forced at a lower amplitude (α=25%) tend to produce less soot than moderately forced (α=50%) flames. Further increasing the forcing amplitude to α=75% does not increase the soot production in laminar flames; conversely, lower peak and volume-integrated soot volume fraction are observed in the strongly forced flame (α=75%) as relative to the moderately forced counterpart. These findings shed new light on the seemingly contradictory results published in the literature regarding the effect of the forcing intensity on the soot production.

TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements.

High spatial resolution Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) determination of trace element concentrations is of great interest for geological and environmental studies. Data reduction is a very important aspect of LA-ICP-MS, and several commercial programs for handling LA-ICPMS trace element data are available. Each of these software packages has its specific advantages and disadvantages. Here we present TERMITE, an R script for the reduction of LA-ICPMS data, which can reduce both spot and line scan measurements. Several parameters can be adjusted by the user, who does not necessarily need prior knowledge in R. Currently, ten reference materials with different matrices for calibration of LA-ICPMS data are implemented, and additional reference materials can be added by the user. TERMITE also provides an optional outlier test, and the results are provided graphically (as a pdf file) as well as numerically (as a csv file). As an example, we apply TERMITE to a speleothem sample and compare the results with those obtained using the commercial software GLITTER. The two programs give similar results. TERMITE is particularly useful for samples that are homogeneous with respect to their major element composition (in particular for the element used as an internal standard) and when many measurements are performed using the same analytical parameters. In this case, data evaluation using TERMITE is much faster than with all other available software, and the concentrations of more than 100 single spot measurements can be calculated in less than a minute. TERMITE is an open-source software for the reduction of LA-ICPMS data, which is particularly useful for the fast, reproducible evaluation of large datasets of samples that are homogeneous with respect to their major element composition. Copyright © 2017 John Wiley & Sons, Ltd.

High Spatial Resolution Laser Desorption/Ionization Mass Spectrometry Imaging of Organic Layers in an Organic Light-Emitting Diode.

To improve the durability of organic materials in electronic devices, an analytical method that can obtain information about the molecular structure directly from specific areas on a device is desired. For this purpose, laser desorption/ionization mass spectrometry imaging (LDI-MSI) is one of the most promising methods. The high spatial resolution stigmatic LDI-MSI with MULTUM-IMG2 in the direct analysis of organic light-emitting diodes was shown to obtain a detailed mass image of organic material in the degraded area after air exposure. The mass image was observed to have a noticeably improved spatial resolution over typical X-ray photoelectron spectroscopy, generally used technique in analysis of electronic devices. A prospective m/z was successfully deduced from the high spatial resolution MSI data. Additionally, mass resolution and accuracy using a spiral-orbit TOF mass spectrometer, SpiralTOF, were also investigated. The monoisotopic mass for the main component, N,N'-di-1-naphthalenyl-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (m/z 588), was measured with a mass resolution of approximately 80,000 and a mass error of about 5 mDa using an external calibrant. This high mass resolution and accuracy data successfully deduced a possible elemental composition of partially remained material in the degraded area, C36H24, which was determined as anthracene, 9-[1,1'-biphenyl]-4-yl-10-(2-naphthalenyl) by combining structural information with high-energy CID data. The high spatial resolution of 1 μm in LDI-MSI along with high mass resolution and accuracy could be useful in obtaining molecular structure information directly from specific areas on a device, and is expected to contribute to the evolution of electrical device durability.

High spatial resolution laser cavity extinction and laser-induced incandescence in low-soot-producing flames

Abstract Accurate measurement techniques for in situ determination of soot are necessary to understand and monitor the process of soot particle production. One of these techniques is line-of-sight extinction, which is a fast, low-cost and quantitative method to investigate the soot volume fraction in flames. However, the extinction-based technique suffers from relatively high measurement uncertainty due to low signal-to-noise ratio, as the single-pass attenuation of the laser beam intensity is often insufficient. Multi-pass techniques can increase the sensitivity, but may suffer from low spatial resolution. To overcome this problem, we have developed a high spatial resolution laser cavity extinction technique to measure the soot volume fraction from low-soot-producing flames. A laser beam cavity is realised by placing two partially reflective concave mirrors on either side of the laminar diffusion flame under investigation. This configuration makes the beam convergent inside the cavity, allowing a spatial resolution within 200 μm, whilst increasing the absorption by an order of magnitude. Three different hydrocarbon fuels are tested: methane, propane and ethylene. The measurements of soot distribution across the flame show good agreement with results using laser-induced incandescence (LII) in the range from around 20 ppb to 15 ppm.

Features of oxide layer formation in high-aspect slot structures by means of MOCVD

Processes were studied concerning the deposition of Hf and Mg oxide layers in the slot structures with the aspect ratio values from 30 to 500 by means of a pulsed MOCVD technique with a discrete components dosing. For assembling the slot structures, different combinations of materials have been used such as Si/Si, Si/glass, glass/chromium patterned glass, and Si/chromium patterned glass. The layers were characterized by means of XRD, XPS, and SEM methods. The thickness profiles of deposited films were measured using a high spatial resolution laser ellipsometry. It has been demonstrated that the radial distribution profiles of the thickness are determined by the process temperature, the aspect ratio value and the type of precursor. In contrast to HfO2 the layers of MgO with decreasing process temperature demonstrate change in the shape of layer profile distribution from a bowl-like shape to a dome-like one, with an increase of the film thickness at the center of the substrate. An image transfer process in the slot structure wherein one of the glass substrates is chromium-patterned has been studied within a wide range of experimental parameters. In order to describe these effects there has been a hybrid model proposed involving a combination of molecular dynamics and Monte Carlo methods. All the results obtained are discussed in detail.

Parallel laser micromachining based on diffractive optical elements with dispersion compensated femtosecond pulses

We experimentally demonstrate multi-beam high spatial resolution laser micromachining with femtosecond pulses. The effects of chromatic aberrations as well as pulse stretching on the material processed due to diffraction were significantly mitigated by using a suited dispersion compensated module (DCM). This permits to increase the area of processing in a factor 3 in comparison with a conventional setup. Specifically, 52 blind holes have been drilled simultaneously onto a stainless steel sample with a 30 fs laser pulse in a parallel processing configuration.

Reconstructing the life-time lead exposure in children using dentine in deciduous teeth

Data are presented to demonstrate that the circumpulpal dentine of deciduous teeth can be used to reconstruct a detailed record of childhood exposure to lead. By combining high spatial resolution laser ablation ICP-MS with dental histology, information was acquired on the concentration of lead in dentine from in utero to several years after birth, using a true time template of dentine growth. Time corrected lead analyses for pairs of deciduous molars confirmed that between-tooth variation for the same child was negligible and that meaningful exposure histories can be obtained from a single, multi-point ablation transect on longitudinal sections of individual teeth. For a laser beam of 100μm diameter, the lead signal for each ablation point represented a time span of 42days. Simultaneous analyses for Sr, Zn and Mg suggest that the incorporation of Pb into dentine (carbonated apatite) is most likely controlled by nanocrystal growth mechanisms. The study also highlights the importance of discriminating between primary and secondary dentine and the dangers of translating lead analyses into blood lead estimates without determining the age or duration of dentine sampled. Further work is in progress to validate deciduous teeth as blood lead biomarkers.

Calibration of a high spatial resolution laser two-color heterodyne interferometer for density profile measurements in the TJ-II stellarator

A high spatial resolution two-color (CO(2), lambda=10.6 microm, He-Ne, lambda=633 nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4-5 mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in approximately 2 mm lateral resolution in the reconstruction of the interferometric wavefront.

Application of High Spatial Resolution Laser Ablation ICP‐MS to Crystal‐Melt Trace Element Partition Coefficient Determination

In this contribution we evaluate the capabilities of laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) using a 12 μm spot size. Precision, accuracy and detection limits were assessed on the USGS BCR‐2G reference material. We demonstrate that the 12 μm LA‐ICP‐MS analyses of experimentally‐grown amphibole and garnet are in excellent agreement with secondary ion mass spectrometry (SIMS) trace element determinations on the same crystals. The 12 μm spot size configuration was subsequently used to determine trace element crystal‐melt partition coefficients (Dc/m) for a wide range of trace elements in amphibole in equilibrium with a basanitic melt. The following strategy to determine accurately and evaluate Dc/m is proposed. One or more major elements determined previously by electron probe microanalysis (EPMA) was used to ensure consistency between EPMA and the composition of the aerosol produced by the laser ablation. Measured Dc/m values were successively evaluated using the lattice strain model. The use of this strategy significantly improved the precision and accuracy of Dc/m determination when a LA‐ICP‐MS configuration with a high spatial resolution was employed.

Laser ablation 40 Ar/ 39 Ar dating of metamorphic fabrics in the Caledonides of north Ireland

In situ 40 Ar/ 39 Ar dating of two texturally distinct biotite generations within a phyllite from the Caledonian orogen of Ireland was performed using a high spatial resolution laser microprobe. In this sample, an older generation of biotite (Bt 1 ) is aligned subparallel to a steeply dipping crenulation foliation, which itself is overprinted by a regionally developed shallow-dipping foliation. The second biotite generation (Bt 2 ) occurs as randomly oriented porphyroblasts that overprint and therefore postdate both foliations. A dataset of 89 ages from a single thick section was acquired for six Bt 1 and eight Bt 2 crystals. The two biotite generations yielded two statistically distinct age distributions with Bt 1 maxima at c . 433 Ma and Bt 2 maxima at c . 417 Ma. A small number of analyses (11% Bt 1 and 26% Bt 2 ) from within crystals yielded ‘main population’ ages that conflict with the dominant age populations and relative chronology established by field relationships. Discordant analyses from the earlier Bt 1 crystals are younger (than the Bt 2 population) and probably reflect intracrystalline partial resetting during a later thermal perturbation. The discordant Bt 2 analyses are predominantly older (than the Bt 2 population) and are interpreted as indicating localized excess 40 Ar. Such dis cordant analyses indicate intracrystalline variation reflecting both excess 40 Ar (Bt 2 population) and 40 Ar loss (Bt 1 population), and were therefore discarded when determining geologically meaningful ages.

An automatic scanning algorithm for high spatial resolution laser vibrometer measurements

Many structural problems, as for instance the prediction of the radiated acoustic noise from vibration data, require measurements with a high spatial resolution. An adapted instrument to perform this kind of measurements is the scanning laser Doppler vibrometer. Since the spatial complexity of the vibration patterns is usually unknown in advance, the number of scanned locations is often taken ad hoc. This implies that the amount of measurement locations can be over- or under-estimated. In this article, a method is presented to automatically determine the number and the location of the grid points to be scanned in order to model the vibration behaviour accurately enough. In particular, the method can be used to successfully find delaminated areas in composite plates (which typically exhibit local vibration behaviour).

Theoretical description and experimental observation of aerosol transport processes in laser ablation inductively coupled plasma mass spectrometry

The transport efficiency of laser-induced aerosols mainly influences the detection capabilities for high spatial resolution laser ablation microanalysis. Therefore, the volume of the ablation cell, the geometry, the gas flow pattern and the transfer tube to carry the aerosol into the ICP are important influences on the transport process and the signal structure. Four different ablation cell volumes, ranging from 0.25 to 63 cm3, in combination with various transfer tubes of different diameters and lengths were investigated. The signal structure was significantly modified by reducing the volume of the sample chamber by a factor of approximately 250. The peak height of single laser shot (aerosol density) was increased by a factor of 6, the signal width (aerosol dispersion) was reduced by a factor of 7 and the rinse time of the sample chamber was consequently shortened to approximately 1 s, thereby eliminating processes of sample recirculation within the cell. The gas flow pattern inside the cell was experimentally traced by introducing powder of different sizes (grain size <1 µm and <65 µm) inside the cell. An angle of 40° at the apex of the gas injection cone was observed at the tip of the inlet nozzle, for a 0.5 mm id nozzle and 1 L min−1 gas flow. The gas inlet nozzle ensured a steady, high efficiency flow, influencing the precision of the measurements. The amount of transported material was constant within the precision of the ablation process for optimized transport and ionization conditions in all ablation cells. The ablation in a sample cell of volume of 0.25 cm3 showed slightly reduced sample transport and a slightly longer rinse time than for a 1.5 cm3 cell, which could be an indication that with extremely reduced cell volumes aerosol–wall interaction might limit the transport efficiency. The variation of the transport tube diameter (4–7 mm) and length (1.5–6 m) showed an influence on the signal structure, but the total amount of sample transferred was not influenced. Nevertheless, the variation of the dispersion as a function of the total volume of the transport system (cell and tube) showed that cell volume more significantly influenced the signal structure. A mathematical model was developed to describe the structure of the signal in relation to the parameters of the ablation set-up and its scope is discussed.

Temperature measurements of metal lines under current stress by high-resolution laser probing

Accelerated reliability tests of aluminum interconnections with respect to electromigration are often performed by high current density stressing of particular structures designed to promote failures of this kind. In order to derive predictions of the interconnect lifetime under normal operating conditions, it is essential to know the temperature of the test structure when high current-density stressing conditions are applied. In this paper, we present the first experimental temperature measurements with two high spatial resolution laser probes of metal lines. The two optical probes provide an indirect access to the temperature of the metal line. The calibration of the probes for temperature measurements is performed by comparison to electrical temperature measurements. The probes have a lateral resolution of 1 /spl mu/m. Two types of test structures, used in accelerated electromigration analysis, are studied. The measurements are compared with two theoretical simulations. Good agreement is obtained only when a particular value of the thermal conductivity of the submicrometer oxide insulation layer of the metal line is used. This is not surprising, since the thermal properties of submicrometer layers are size dependant. Our experimental method provides an elegant way to determine these parameters.

Submicron Optical Spectroscopic Surface Characterisation Using Near-Field Probes.

Abstract The development of scanning near-field optical microscopy has provided a submicron optical tool which has important applications in both fundamental studies and in device fabrication and analysis. The strength of the technique lies not only in its resolution of approximately 50nm, which is an order of magnitude improvement on diffractive optical techniques, but also in its ability to allow highly developed optical spectroscopies to be used for chemical analysis at this resolution. We have particular interest in the application of near-field probes to high spatial resolution laser spectroscopy in a range of organic, biological and inorganic systems. In this paper we shall describe the development of instrumentation for luminescence, Raman and time resolved spectroscopy in air and under fluids and will present the results of studies of phase separated polymer mixtures, organic crystals and semiconductor materials. The current scanning near-field optical microscope is based around a tapered optical fibre, at the end of which a submicron aperture has been defined by a metal coating.

Sintering of silver interlayers in polyimide films

Annealing at 220–420 °C and exposure to laser light were used to induce sintering of silver metal interlayers in polyimide films. The sintering process was followed by transmission electron microscopy, electrical conductivity, optical reflectivity measurements, and x-ray scattering. We find that upon sintering at temperatures below Tg≂380 °C of the polymide film, sintering of the silver interlayer is induced. A dramatic increase in both the optical reflectivity (from 32% to 95%) and a hundredfold increase in electrical conductivity are observed upon sintering. Both the average size and the connectivity of the silver particles in the interlayer are increased in the process; however, there is no apparent change in the polymer. High-speed (∼100 ns) high spatial resolution laser writing (∼1 μm) is feasible by a selective sintering process. It is, therefore, of potential interest as a basis for write-once, high-density optical information storage. It is suggested that a surface diffusion mechanism is responsible for the observed sintering process.