Si Foil Research Articles

Arc plasma synthesized LaB6 nanocrystallite film on various substrates as a field emitter

Lanthanum hexaboride (LaB6) nanocrystallites/nanowires have been successfully synthesized using gas phase condensation in arc plasma. Our results show that the LaB6 nanowires have ~20 nm diameter and length of several micrometers. The as-synthesized LaB6 nanocrystallites and nanowires are crystalline in nature. Field emission studies were carried out on as synthesized LaB6 nano-powder deposited on W and Re tips and foils, and also on Si foil substrates under ultra high vacuum. The Fowler–Nordheim plots obtained from the current–voltage characteristics are found to be linear in accordance with the quantum mechanical tunneling phenomenon. High value of field enhancement factor (8177) is observed for LaB6 on Re substrate, indicating that the electron emission is from the nanometric features of the LaB6. Our results show that the arc plasma synthesized LaB6 nanocrystalline film exhibits good emission stability as emitter without severe deviations from the initial set value and also a strong ability to withstand the ion bombardment, which is useful for low operation voltage vacuum micro/nano electronic devices.

Recrystallization of twin-roll cast Al–Fe–Si foil stock processed without homogenization

Differential scanning calorimetry, hardness testing, electrical conductivity measurements and microstructural analysis were employed in the present work to investigate the response of twin-roll cast Al–0.8Fe–0.6Si strips to interannealing without prior homogenization. Recrystallization which occurs at 400 °C in sheet samples cold rolled only lightly ( ɛ ∼ 0.2) is gradually displaced to lower temperatures with increasing strain until ɛ ∼ 2.3. Precipitation occurs largely before a measurable recrystallization reaction at low strains, ɛ < 2.3, producing an acceptable grain structure across the section. The interaction of the two reactions at ɛ > 2.3 is believed to be responsible for a decreasing recrystallized fraction and for coarse grains at the surface where the interaction is likely to be most pronounced. Interannealing of the Al–0.8Fe–0.6Si alloy without a homogenization treatment produces acceptable grain structures across the section of the strip for much of the cold rolling strain range. It is thus concluded that Al–0.8Fe–0.6Si foil stock, intended for cosmetic foil applications where formability is not critical, could be processed without a high-temperature annealing treatment.

Residual stress in Ni-Mn-Ga thin films deposited on different substrates

Four series of Ni51.4Mn28.3Ga20.3/substrate thin film composites, where the substrate is either Si(100), MgO(100), alumina or Mo foil, and two series of Ni53.5Mn23.8Ga22.7/substrate composites where the substrate is either alumina or Mo foil, with different film thicknesses varying from 0.1 to 5 μm have been studied in the cubic phase by XRD stress measurements. The values of residual stresses are found to be dependent on both substrate and film thickness. In the submicron range, a correlation between thickness dependencies of residual stress and transformation temperatures is experimentally obtained. The temperature dependence of the d-spacing d220 is studied for the films deposited on Si(100).

Resonant diffusive radiation in random multilayered systems

-We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. The resonant condition can be satisfied for the wavelength region representing visible light as well as soft X rays. The intensity of diffusive soft X rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at a photon energy of 99.4 eV, the intensity of resonant diffusive radiation (RDR) generated by 5-MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453 eV and 13 MeV, electrons passing a Be/Ti multilayer generate RDR exceeding the Cherenkov radiation generated by electrons passing Ti foils by a factor =130.

Defect photoluminescence of ZnO nanorods synthesized by chemical methods

We investigated the morphology and properties of ZnO nanorods synthesized at 90 °C from the solutions of zinc nitrate hydrate and hexamethylenetetramine. Three different substrates were used: Si and Zn foil treated with ZnO nanoparticle seeds, and Si/polycrystalline ZnO film. The morphology of the samples was investigated by scanning electron microscopy, while their optical properties were characterized by photoluminescence spectroscopy. The substrate was found to affect the size uniformity and alignment of ZnO nanorods. The nanorods exhibited strong yellow defect emission. In order to investigate the possibility of improving the optical properties, the influence of annealing at different temperatures (200–600 °C) and in different atmospheres (Ar, air, N 2, forming gas) was investigated. While annealing in air improved UV-to-visible emission ratio, defect emission remained prominent. However, annealing in forming gas enhanced UV emission and suppressed defect emission.

Local stress modification during in situ transmission electron microscopy straining experiments

The stress distribution in a foil strained in situ in a transmission electron microscope is strongly affected by the polished depression and the hole. In the present study, this effect has been investigated in detail on a Fe–Si foil plastically deformed under uniaxial straining in transmission electron microscopy. The slip-trace direction varied considerably around the hole, indicating local changes of the macroscopic slip plane. Since non-crystallographic slip occurs in Fe–Si under conditions used in the experiment and the crystallographic relation between the macroscopic slip plane and the tensile stress direction is known, the local tensile axes could be established. It was found that the deviations of the local tensile stress axis from the external stress axis may be as large as ±60°. The stress distribution determined experimentally is compared with an analytical solution as well as a finite element analysis of the problem.

Resonant diffusive radiation in random multilayered systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. Resonant condition can be satisfied for the wavelength region representing visible light as well as soft X-rays. The intensity of diffusive soft X-rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at photon energy of 99.4eV, the intensity of resonant diffusive radiation (RDR) generated by 5MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453eV and 13MeV electrons passing Be/Ti multilayer generate RDR exceeding Cherenkov radiation generated by electrons passing a Ti foils by a factor ≈130.

Transient observation of extended x-ray absorption fine structure in laser-melted Si by using femtosecond laser-produced-plasma soft x ray

We have demonstrated the time-resolved measurement of the extended x-ray absorption fine structure (EXAFS) in laser-melted Si foil by using a pump-probe absorption spectroscopy system that utilizes a femtosecond laser-produced-plasma soft x-ray source. By using 100-fs laser irradiation, we observed the transient change in the Si L-edge EXAFS, that is, a slight shortening of its oscillation period and a decrease in its oscillation amplitude. This result suggests that the Si-Si atomic distance expanded and structural disordering occurred as a result of the production of liquid Si.

Spectroscopic Diagnostics of DBD in Ar/Fluorocarbon Mixtures – Correlation between Plasma Parameters and Properties of Deposited Polymer Films

AbstractSummary: Spectroscopic diagnostics of a pulse‐modulated dielectric barrier discharge (DBD) in fluorocarbon mixtures at atmospheric pressure are reported. Plasma diagnostics was performed by FTIR‐absorption spectroscopy as well as by emission/absorption spectroscopy in the UV‐vis range. The following fluorocarbon molecules have been studied: CF4, C2F6, C3F8, C2H2F4, C3HF7 and c‐C4F8. Emission and absorption spectroscopy were performed simultaneously in combination with the measurement of the electric parameters (current, voltage and phase). Surface tension measurement, FTIR‐absorption spectroscopy and XPS were applied to get information on the surface tension, chemical composition and structure of the fluorocarbon polymer films in dependence on the fluorocarbon gas applied. Substrates used were Si wafers, foils and textiles. Analysis of XPS spectra indicates that polymer films can be deposited if the F/C ratio of precursor molecule is smaller than or close to 3. FTIR‐absorption spectra of the films on Si wafers indicated an “amorphous” film structure with the main absorption peak of CF2‐groups at 1 200 cm−1. F/C ratio of precursor molecule is strongly correlated with the appearance of an “amorphous” PTFE absorption peak at 740 cm−1 in the discharge volume. XPS‐analysis and FTIR‐absorption spectroscopy show the influence of H atom content in fluorocarbon molecule or admixture of H2 molecules on the cross linking effect in the films. Depending on the experimental conditions and gas mixture, films with a smallest surface tension of about 11 mN/m could be deposited.Dependence of surface tension (total, polar and dispersive components) on effective deposition time and substrate material (PP, PET) (Ar/c‐C4F8 discharge).magnified imageDependence of surface tension (total, polar and dispersive components) on effective deposition time and substrate material (PP, PET) (Ar/c‐C4F8 discharge).

Dependence of surface tension and deposition rate of fluorocarbon polymer films on plasma parameters in a dielectric barrier discharge (DBD)

Fluorocarbon polymer films were deposited on Si, PP and PET foils in a dielectric barrier discharge (DBD) at atmospheric pressure. The deposition rate and surface tension were measured with dependence on external (gas composition, discharge power, discharge gap, pre- and post-treatment procedure) and internal plasma parameter (gas temperature and composition of the plasma). Experiments were performed using as starting molecules the following fluorocarbons: CF4, C2F6, C3HF7 and c-C4F8. Also the influence of additional hydrogen and oxygen on deposition rate and surface tension was investigated. By contact angle measurements with three liquids the polar as well as the dispersive component of surface tension were measured. The results of tension surface measurements correlate to results obtained by FTIR and XPS measurements of the films. It is shown that the amount of CF2- and CF3-bindings in the film is the dominant correlation factor between XPS and surface tension.

Microchip laser-induced breakdown spectroscopy: a preliminary feasibility investigation.

A commercial, 7 microJ/pulse, 550 ps microchip laser is used to induce plasma on Pb, Si, Cu, Fe, Ni, Ti, Zn, Ta, and Mo foils and a Si wafer. The measured plasma lifetime is comparable with the duration of the laser pulse (a few ns). The plasma continuum radiation is low, while some of the strong resonance lines (e.g., Zn 213.86 nm) show self-reversal. Quantitative analysis is possible using non-gated detectors but analytical lines should be chosen with care to avoid reduction in the linear dynamic range. The mass removed (0.5-20 ng/pulse) is sufficient to yield spectra that are detectable with portable grating spectrometers equipped with non-gated, non-intensified detector arrays. The spectrum of Cd is detected with a broadband portable spectrometer (200-950 nm). The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications.

Properties of liquid silicon observed by time-resolved x-ray absorption spectroscopy.

Time-resolved x-ray spectroscopy at the Si L edges is used to probe the electronic structure of an amorphous Si foil as it melts following absorption of an ultrafast laser pulse. Picosecond temporal resolution allows observation of the transient liquid phase before vaporization and before the liquid breaks up into droplets. The melting causes changes in the spectrum that match predictions of molecular dynamics and ab initio x-ray absorption codes.

Portevin–Le Chatelier effect in biaxially strained Al–Fe–Si foils

Instability patterns linked to negative strain rate sensitivity of the flow stress are observed in Al–Fe–Si foils during biaxial bulge testing. They are interpreted as resulting from the Portevin–Le Chatelier effect. A linear stability analysis supporting this interpretation is provided.

Measurements of Si ion stopping in amorphous silicon

The stopping of 28 Si ions in polycrystalline Si foils has been measured over the energy range 0.1–3.3 MeV per nucleon. For the low energy interval (0.1–0.5 MeV per nucleon), time of flight-energy elastic recoil detection analysis method was used, whilst for the high energy region (1.2–3.3 MeV per nucleon) the energy loss in the same foil was measured using a Si p–i–n diode with the 28 Si ions directly incident on the foil following acceleration. Below the stopping maximum the results are in good agreement with literature data based on Doppler shift measurements of short nuclear lifetimes but are about 20% smaller than the SRIM prediction. Above the stopping maximum the data are in agreement with SRIM within the limits of statistical uncertainty.

Capture from random flux to channeling for protons transmitted through a Si foil

Flux redistribution and formation of channeling peaks have been observed in the geometry of initially wide-angle incidence for protons transmitted through monocrystalline Si membranes. The channeling peaks are generated by the crystalline medium as a result of multiple charge-exchange events due to the impact-parameter dependence of the electron capture and loss cross-sections. This explains successfully the detection of channeling peaks only at a low enough residual proton energy: Epf⩽0.6 MeV, after the transmission.

Effects of O2 on the {113} defect formation in Si observed by in situ ultrahigh vacuum transmission electron microscopy

The nucleation and growth of the {113} defects in floating zone Si have been observed in situ in a ultrahigh vacuum (UHV) transmission electron microscopy. After the surfaces of a Si foil are controlled, intense irradiation of 200 keV electrons proceeds at 400 or 500 °C in the base pressure of 1.0×10−7 Pa. We have found that the defect development changes prominently after O2 is injected in a specimen chamber. While O2 flows, the pressure is kept at about 5.0×10−5 Pa. This result has brought direct evidence for the effect of O2 on formation of the defects, since no other impurities are involved in the UHV environment.

Extreme ultraviolet probing of laser imprint in a thin foil using an x-ray laser backlighter

For direct drive inertial confinement fusion, a capsule is imploded by directly illuminating the surface with laser light. Beam smoothing and uniformity of illumination affect the seeding of instabilities at the ablation front. We have developed a technique for studying the imprint of a laser beam on a thin foil using an x-ray laser as an extreme ultraviolet (XUV) backlighter. We use multilayer XUV optics to relay the x-ray laser onto the directly driven foil, and then to image the foil modulation onto a charged coupled device camera. This technique allows us to measure small fractional variations in the foil thickness. We have measured the modulation due to imprint from a low intensity 0.35 μm drive beam incident on a 3 μm Si foil using an yttrium x-ray laser on Nova. We present results from a similar technique to measure the imprinted modulation due to a low intensity 0.53 μm drive beam incident on a 2 μm Al foil using a germanium x-ray laser at the Vulcan facility.

Measurement of 0.35 microm laser imprint in a thin Si foil using an x-ray laser backlighter.

Imprinted modulations in optical depth of a thin Si foil due to 0.35 \ensuremath{\mu}m laser irradiation at about $3\ifmmode\times\else\texttimes\fi{}{10}^{12}$ W/c${\mathrm{m}}^{2}$ have been measured at shock breakout. These measurements were made by high resolution face-on radiography using a gain saturated yttrium x-ray laser backlighter operating at a wavelength of 15.5 nm with a multilayer optics imaging system. The imprinted modulation due to a static speckle pattern and a 0.29 and a 0.33 THz spectral dispersion smoothed speckle pattern were studied. Comparison of the imprinted modulation is made with simulations.

X-ray laser radiography of perturbations due to imprint of laser speckle in 0.35 μm laser irradiation of a thin Si foil

A gain saturated yttrium x-ray laser operating at a wavelength of 15.5 nm has been used as an extreme ultraviolet probe to measure optical depth modulations in a thin Si foil by face-on radiography. The high brightness of this Ne-like x-ray laser allows probing of a sample with a high opacity. This technique is sensitive to very small modulations in the optical depth of the foil, corresponding to thickness variations of a few 10 nm of cold material. This technique is used to measure the effect of direct drive laser imprint on a thin Si foil by face-on radiography using multilayer optics to image the foil with 26× magnification. We have recorded modulations in a thin Si foil that was irradiated by a 400 ps, 0.35 μm beam at an intensity of about 3×1012 W/cm2.

Silicon stencil masks for masked ion beam lithography proximity printing

Silicon membranes with 2 μm to 6 μm thickness and ≈ 10×10 mm2 mask field have been fabricated with the help of electrochemical etch stop techniques. The Si foil was coated with 0.3 μm thick PECVD Si3N4. Shaped electron beam lithography was done in ARCH (OCG) positive resist. RIE etching into the nitride layer was done with CHF3/Ar/SF6. Silicon trench etching was based on Cl2/Ar/BCl3 plasma chemistry implementing gas chopping. Ion beam proximity printing of the Silicon stencil mask structures was done with 55 keV Helium ions into 0.4 μm thick AZ PN114 negative resist using the Alpha ion projector of the Society for the Advancements of Microelectronics in Austria in the MIBL (Masked Ion Beam Lithography) mode. Pattern transfer of a mask feature of less than 100 nm diameter (25:1 aspect ratio in the stencil mask) could be demonstrated even for a mask to wafer gap of 1 mm. The prospects of fabricating large area (> 100×100 mm2) Silicon stencil masks for MIBL printing of gate levels for FieldEmitterDisplays (FEDs) andMicro-Electro-Mechanical-Systems (MEMS) is discussed.