Silicon Foils Research Articles

Characterization of Magnetron Sputtered BiTe-Based Thermoelectric Thin Films.

Thermoelectric (TE) technology attracts much attention due to the fact it can convert thermal energy into electricity and vice versa. Thin-film TE materials can be synthesized on different kinds of substrates, which offer the possibility of the control of microstructure and composition to higher TE power, as well as the development of novel TE devices meeting flexible and miniature requirements. In this work, we use magnetron sputtering to deposit N-type and P-type BiTe-based thin films on silicon, glass, and Kapton HN polyimide foil. Their morphology, microstructure, and phase constituents are studied by SEM/EDX, XRD, and TEM. The electrical conductivity, thermal conductivity, and Seebeck coefficient of the thin film are measured by a special in-plane advanced test system. The output of electrical power (open-circuit voltage and electric current) of the thin film is measured by an in-house apparatus at different temperature gradient. The impact of deposition parameters and the thickness, width, and length of the thin film on the power output are also investigated for optimizing the thin-film flexible TE device to harvest thermal energy.

Investigation of Vacuum Arc-Deposited ta-C and ta-C:N Thin Films on Silicon and Stainless-Steel Foil Substrates Using Raman Spectroscopy

In this paper, we investigated the vacuum arc-deposited tetrahedral amorphous carbon (ta-C) and nitrogen-doped ta-C (ta-C:N) thin films grown on silicon and stainless-steel foil substrates by the visible Raman Spectroscopy. We found that carbon films grown on silicon surfaces prefer more sp3 hybridized carbon compared to the stainless-steel foil, which prefer more sp2 hybridized carbon even though the films are grown concurrently under the same conditions. The impact energy of plasma ions modifies the interfacial layer formation, giving a strong dependence of the sp2/sp3 ratio with the substrate bias, behaving differently for different substrates. However, nitrogen doping in amorphous carbon thin films helps to increase sp2 contents uniformly on both the surfaces for a fixed substrate bias. Understanding such interfaces are of interest for many electronic, optoelectronic, and energy storage devices as these interfaces get buried and can influence the properties significantly.

Determination of phases of complex scattering amplitudes and two-particle structure factors by investigating diffractograms of thin amorphous foils

Abstract In this study we analyse diffractograms of elastically filtered images of thin amorphous foils of carbon, silicon and germanium using the weak object approximation. The use of this approximation leads to a contrast transfer function containing a phase η(u) depending on the spatial frequency u. Furthermore, the derivative of this phase is included in the envelope function of the contrast transfer function. The phase can be attributed to the breakdown of the first-order Born approximation leading to complex scattering amplitudes characterized by this phase η(u). We analyse contrast transfer characteristics to determine the phase of complex scattering amplitudes of carbon, silicon and germanium as a function of spatial frequency and to measure the two-particle structure factor of the corresponding amorphous specimens. The contrast transfer characteristics were calculated from diffractograms of focal series of elastically filtered images. The phases measured show a decay with increasing spatial frequency and additional oscillations. The results for the two-particle structure factor also decay with increasing spatial frequency and contain low local maxima. Both can be attributed to voids or inhomogeneities within the amorphous structure.

Simulation of subpicosecond laser-plasma X-ray radiation source

The issue of optimizing laser-plasma X-ray sources is still relevant. In this context, numerical simulation methods are very effective. A series of 2d PIC calculations using the EPOCH code were carried out. The laser pulse duration was 0.7 ps, the peak intensity was 3· 1020 W/cm2, and silicon foil between 2 and 5 μm thick was used as a target. The conversion efficiency into the continuous X-ray spectrum was calculated. The results of comparison of numerical calculations with experimental measurements showed their satisfactory agreement. Keywords: laser plasma, petawatt laser, X-ray radiation, PIC simulation.

Моделирование рентгеновского излучения субпикосекундного лазерно-плазменного рентгеновского источника

The issue of optimizing laser-plasma X-ray sources is still relevant. In this context, numerical simulation methods are very effective. A series of 2d PIC calculations using the EPOCH code were carried out. The laser pulse duration was 0.7 ps, the peak intensity was 3x1e20 W/cm2, and silicon foil between 2 and 5 µm thick was used as a target. The conversion efficiency into the continuous X-ray spectrum was calculated. The results of comparison of numerical calculations with experimental measurements showed their satisfactory agreement.

Study the Microstructure of Rapidly Quenched Aluminum 30% Silicon Foils Produced By Using Conventional Method

A simple apparatus based on the hammer and anvil principle has been constructed and used to study the microstructure of aluminum 30% Silicon (Al-30% Si) foils with different thicknesses. Both (hammer and anvil) have been fabricated from oxygen free of high conductivity (OFHC) red copper. The cooling rate achieved or estimated was to be in the range of 1.67x104: 5x104 k sec-1. Microstructure studying of rapidly quenched Al-30% Si foils indicated that with decreasing the foil thickness the size of primarily Si crystalline decreases in the whole investigated range. However the volume fraction of the primarily silicon crystals in the structure remained constant down to thickness 0.3 mm; with further decreasing of the thickness the primarily silicon volume started to decreases.

Optimization of a laser plasma-based x-ray source according to WDM absorption spectroscopy requirements

X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter. It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest. In the present work, we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2 Å–6 Å (∼2 keV to 6 keV) by considering relatively low-Z elements. We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10 µm. An outer plastic layer can increase the emissivity even further.

Optimized shell thickness of NiSi/SiC core-shell nanowires grown by hot-wire chemical vapour deposition for supercapacitor applications

In this study, NiSi/SiC core-shell nanowires grown on crystal silicon and Ni foil substrates by hot-wire chemical vapour deposition were extensively investigated. These nanowires were grown by varying the CH4 flow-rate from 0.5 to 3.5 sccm. The nanowires were found to grow at CH4 flow-rates above 0.5 sccm. The structure of the nanowires consisted of a single crystalline NiSi as the core and polycrystalline SiC nanocolumn as the shell. The growth of the NiSi nanowires solely follows a limited nucleation silicide reaction, which is strongly dependent on the growth precursor vapour pressures of SiH4 and CH4 molecules. Increasing the CH4 flow-rate up to 2.0 sccm enhances the growth of high-density vertically aligned nanowires. The electrochemical properties of the NiSi/SiC core-shell nanowire electrodes were also investigated. The NiSi/SiC core-shell nanowire electrode prepared at 2.0 sccm demonstrated the highest electrochemical performance compared with other nanowire electrodes. This nanowire electrode had the highest specific capacitance (234.13 mF/cm2) at the highest scan rate and demonstrated good electrochemical stability (capacity retention of 80 %) at the highest applied current density after 2500 cycles.

Contrast modes in a 3D ion transmission approach at keV energies

We present options for visualizing contrast maps in 3D ion transmission experiments. Simultaneous measurement of angular distributions and flight time of ions transmitted through self-supporting, single-crystalline silicon foils allows for mapping of intensity and different energy loss moments. The transmitted projectiles were detected mainly for random beam-sample orientation using pulsed beams of He ions and protons with incident energies 50 and 200 keV. Differences in contrast, observed when varying the projectile type and energy, can be attributed to sample nuclear and electronic structure and bear witness to impact parameter dependent energy loss processes. Our results provide a base for interpretation of data obtained in prospective transmission studies when for example using a helium ion microscope.

Disparate Energy Scaling of Trajectory-Dependent Electronic Excitations for Slow Protons and He Ions.

We have simultaneously measured angular distributions and electronic energy loss of helium ions and protons directly transmitted through self-supporting, single-crystalline silicon foils. We have compared the energy loss along channeled and random trajectories for incident ion energies between 50 and 200keV. For all studied cases the energy loss in channeling geometry is found lower than in random geometry. In the case of protons, this difference increases with initial ion energy. This behavior can be explained by the increasing contribution of excitations of core electrons, which are more likely to happen at small impact parameters accessible only in random geometry. For helium ions we observe a reverse trend-a decrease of the difference between channeled and random energy loss for increasing ion energy. Because of the inefficiency of core-electron excitations even at small impact parameters at such low energies, another mechanism has to be the cause for the observed difference. We provide evidence that the observation originates from reionization events induced by close collisions of helium ions occurring only along random trajectories.

Joining of SiC, alumina, and mullite by the Refractory Metal—Wrap pressure‐less process

AbstractThe aim of this work was to discuss the suitability of the joining process called “RM‐Wrap” (RM = Refractory Metals, ie, Mo, Nb, Ta, Zr) as a pressure‐less and tailorable technique to join several different ceramics such as SiC, alumina, and mullite (3Al2O3.2SiO2). In the RM‐Wrap joining technique the refractory metal foil is used as a wrap containing one or more silicon foils. It is performed at 1450°C, under flowing argon, and the resulting joining materials are in situ formed composites made of refractory metal disilicides (MoSi2, NbSi2, TaSi2, or ZrSi2) embedded in a silicon‐rich matrix; their coefficient of thermal expansion has been calculated and the Laser Flash Method was used to measure the thermal diffusivity of one of them (MoSi2/Si) in 25°C‐1000°C range, then to calculate its thermal conductivity. All the obtained joints are uniform, continuous, and crack free. Some preliminary oxidation tests were carried out on all joints at 1100°C, 6 hours in air, giving unchanged morphology of the interface and the joining materials itself; the joint strength of RM‐Wrap joined SiC was measured at room temperature using three different mechanical tests: (a) single lap (SL), (b) single lap off‐set (SLO) and (c) torsion on hourglass‐shaped samples (THG) (on Mo‐wrap joined SiC).

Production and characterization of thin, self-supporting Si foils for use as targets in radioactive beam experiments

Development of thin, self-supporting silicon foils (both natural and isotopically-enriched) for use as targets in reaction studies with radioactive beams is detailed. Foils with a thickness of ∼220μg/cm2 were produced using vapor deposition and were floated onto aluminum frames with 10–15 mm diameter holes. During their production, the foil thickness was measured using a quartz crystal monitor. Subsequently, the foil thickness was characterized by α particle energy loss measurements and Rutherford backscattering (RBS). These measurements demonstrated that the thickness could be determined to within a 0.5% uncertainty. The elemental purity of the foils was assessed using RBS and X-ray photoelectron spectroscopy. This analysis demonstrated that the foils have 87%–90% silicon abundance.

Silicon foil patching for blast tympanic membrane perforation: a retrospective study

AimTo establish whether covering the tympanic membrane perforation after war blast injury with silicon foil can enhance the ear drum healing rate and to determine the appropriate timing of silicon patching.MethodsWe retrospectively analyzed the charts of 210 patients wounded during the Homeland War in Croatia 1991-1995, with 315 blast tympanic membrane perforations. In 44 patients (61 perforations), the eardrum perforation was covered by silicon foil, whereas in 166 patients (254 perforations) it was left to heal spontaneously. The patients who underwent the patching procedure were divided in two groups according to the time period between the blast injury and the procedure: 38 perforations were treated within 3 days and 23 perforations were treated 4 to 6 days after the blast injury.ResultsThe rate of tympanic membrane healing in the silicon foil patching group was significantly higher (91.8%) than that in the group of perforations left to heal spontaneously (79.9%, P = 0.029). The healing rate was significantly higher in the group treated within 3 days after the blast injury (97.4%) than in the group treated 4 to 6 days after the injury (82.6%, P = 0.042).ConclusionCovering the perforation after the war blast injury with silicon foil significantly improves the rate of tympanic membrane healing. To obtain the best healing outcome, the procedure should be performed within the first 72 hours after the trauma.

Selection of Optimum Binder for Silicon Powder Anode in Lithium-Ion Batteries Based on the Impact of Its Molecular Structure on Charge–Discharge Behavior

The high-capacity and optimal cycle characteristics of the silicon powder anode render it essential in lithium-ion batteries. The authors attempted to obtain a composite material by coating individual silicon particles of µm-order diameter with conductive carbon additive and resin to serve as a binder of an anode in a lithium-ion battery and thus improve its charge–discharge characteristics. Structural strain and hardness due to stress on the binder resin were alleviated by the adhesion between silicon or copper foil as a collector and the binder resin, preventing the systematic deterioration of the anode composite matrix immersed in electrolyte compositions including Li salt and fluoride. Moreover, the binder resin itself was confirmed to play a role of active material with occlusion and release of Li-ion. Furthermore, charge–discharge characteristics of the silicon powder anode active material strongly depend on the type of binder resin used; therefore, the binder resin used as composite material in rechargeable batteries should be carefully selected. Some resins for binding silicon particles were investigated for their mechanical and electrochemical properties, and a carbonized polyimide obtained a good charge–discharge cyclic property in a lithium-ion battery.

Measurement of Dielectrics From 20 to 50 GHz With a Fabry–Pérot Open Resonator

A novel approach to the measurement of complex permittivity of low-loss dielectric materials with the aid of an open Fabry–Perot resonator with concave Gaussian mirrors is presented in this paper. For that purpose, a new scalar 1-D layered electromagnetic (EM) model of the resonator is proposed. The model takes the advantage of Cartesian-to-Gaussian coordinate transformation and axisymmetrical properties of the TEM modes of interest. There are several advantages of the proposed approach. The first is the use of Gaussian mirrors instead of spherical ones, which better fit to the shape of Gaussian wavefronts. Second, the model more accurately accounts for oblique incidence of the wave onto the surface of the sample, which is one of the major challenges in case of alternative models based on a characteristic equation. An automated measurement setup operating in the 20–50-GHz range has been designed and manufactured to experimentally validate the proposed measurement method. A real part of permittivity of a few well-known materials, such as silicon, quartz, polystyrene, or polyethylene terephthalate (PET) foil, has been measured with the accuracy better than 0.5%, which means a significant improvement as compared to the state of the art in this area.

(111)Si thin layers detachment by stress-induced spallation

In this work, results of controlled detachment of (111) silicon by stress induced spalling (SIS) process, which is based on a gluing on a metallic stressor layer by an epoxy adhesive on top of a silicon substrate, are presented. It is shown that silicon foils mainly (1 × 1) cm2 with different thicknesses (~50–170 µm) can be successfully detached using different materials (steel, copper, aluminum, nickel and titanium) as stressor layers with thicknesses ~50–500 µm. Such detachment can be realized by dipping of a stressor/glue/silicon wafer based structure into liquid nitrogen. As a result, Si foils with different thicknesses from ~50 µm to ~170 µm can be detached. An analytical and numerical approaches based on principles of linear elastic fracture mechanics is developed and they are shown that such approaches can predict general trends and conditions for the detachment of silicon foils with desired thicknesses using a stressor layer. Raman spectroscopy analysis of the residual stresses in detached silicon foils shows, that tensile stresses (up to −36 MPa) as well as higher value compressive stresses (up to ~444 MPa) are present in such foils. Moreover, optical and scanning electron microscopy (SEM) measurements show that surface of the detached foils exhibits some periodic lines originated by stresses.

A setup for micro-structured silicon targets by femtosecond laser irradiation

We present a process to fabricate micro-structured thin silicon foils with highly light absorbing properties over a broad wavelength region based on short-pulse laser treatment. We employ this fascinating technique to the fabrication of targets for high-intensity laser-plasma experiments. A polished silicon wafer is processed with high-intensity femtosecond laser pulses resulting in conical spikes within the irradiated region. Height, distance, and shape of these spikes depend primarily on the number, energy, central wavelength and duration of the incident laser pulses, as well as the ambient medium. This method is of great value for the future development of target fabrication. The broad parameter base offers a huge selection regarding shape and dimensions of the resulting structure. It can be included in existing laser operations within the manufacturing chain while offering a high degree of customisability. Within the reach of higher repetition rates of high-power laser systems and an increased number of requested targets, this manufacturing method can be scaled while being cost efficient and easily adaptable.

X-ray absorption spectroscopy study of energy transport in foil targets heated by petawatt laser pulses

X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5×1020 and 2.5×1020 W/cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.

Silicon foil solar cells on low cost supports

In this work, we report recent results of solar cells fabricated on silicon foils obtained by the Stress induced LIft-off Method (SLIM)-cut technique using an epoxy stress-inducing layer. Indeed, the use of silicon foils for the production of solar cells offers the ability to reduce material costs while allowing potentially a higher conversion efficiency. We show experimentally that silicon foil thicknesses between 40 and 140 μm can be tuned by changing the thickness of the epoxy. Standalone silicon foil based solar cells have been realized, and conversion efficiencies of 12.5% and 13.8% have been measured using 55 μm and 120 μm thick foils, respectively. In view of potential industrialization, mechanical support must be used during solar cells and module fabrication to avoid silicon foil breakage. Two different supporting substrates were therefore tested: an aluminum sheet and a sintered silicon substrate. Conversion efficiencies of 10.9% and 12.1% were obtained using 40 μm and 90 μm thick silicon foils on a polished Al substrate. Finally, a promising result of 13.1% was obtained after mini-module fabrication from 6 SLIM-cut solar cells (100 μm thick silicon foils) on the sintered silicon substrate using the i-cell concept.

Fabricating 40 µm-thin silicon solar cells with different orientations by using SLiM-cut method

Thin silicon foils with different crystal orientations were fabricated using the stress induced lift-off (SLiM-cut) method. The thickness of the silicon foils was approximately 40 µm. The foil had a smoother surface than the foil. With surface passivation, the minority carrier lifetimes of the and silicon foil were 1.0 µs and 1.6 µs, respectively. In this study, 4 cm2-thin silicon solar cells with heterojunction structures were fabricated. The energy conversion efficiencies were determined to be 10.74% and 14.74% for the and solar cells, respectively. The surface quality of the silicon foils was determined to affect the solar cell character. This study demonstrated that fabricating the solar cell by using silicon foil obtained from the SLiM-cut method is feasible.