Polished Si Substrates Research Articles

Modeling of cracking behavior of CrAlN coatings on silicon during micro- and nanoindentation

The deformation and failure behavior of any coating governs the performance of the resulting coating system. In the present work, we numerically and experimentally examine the fundamental deformation mechanisms of CrAlN coating on Si substrate, particularly its cracking behavior under indentation processes. For this purpose, CrAlN coatings deposited on monocrystalline Si substrates by pulsed DC magnetron sputtering were subject to indentation procedures with different depths. Subsequent characterization of top surface and cross-sectional morphologies demonstrates a strong dependence of coating profile and microstructures on the initial surface condition of the substrate. Specifically, uniform CrAlN coatings with a thickness of 1.1 μm and densified columnar microstructures were prepared on a polished Si substrate. Berkovich nanoindentation test with an indentation depth of 530 nm derives the mechanical properties of the prepared CrAlN coating. The corresponding finite element simulation reveals the propensity of cracking initiation accompanied by the stress concentration at three edge corners of the dent. Subsequent microindentation test with an indentation depth of 1.09 μm demonstrates the coexistence of plastic deformation and brittle fracture of CrAlN coating. In particular, surface radial cracks within CrAlN coating are experimentally and theoretically observed, and the cracking processes are analyzed in detail by finite element simulations.

Arrayed and entangled silicon nanowires using Au nanoparticle catalysts prepared by pulsed laser-induced dewetting

The use of pulsed laser-induced dewetting (PLiD) is reported as a novel approach in the fabrication of Au nanoparticle (NP) catalytic arrays for the growth of Si nanowires (NWs) by chemical vapor deposition using SiCl4 in the presence of H2. On polished Si substrates, PLiD generates Au NP catalysts with long-range order and narrow size distributions. It has been shown that the monodispersed distribution of Au NPs provides consistent diameter control of the as-grown Si NWs. A systematic exploration of the Si NW synthesis time, temperature, and gas flow rates illustrates a level of tunability in terms of morphology, be it arrayed or entangled Si NWs, with varying experimental parameters. An investigation of the effect of growth temperature also showed that Si NWs can be synthesized at temperatures as low as 700 °C when using SiCl4 as the precursor. The use of porous Si substrates enabled direct observation of the diameter-dependent growth due to the simultaneous presence of three Au NP size distributions. Growth from the small- and medium-sized Au NP catalysts occurred first, followed by that from the large-sized Au NPs, which was only observed at extended times or high SiCl4 flow rates. The delayed onset of growth from the large-sized Au NPs is due to the longer time to achieve Si super-saturation of larger catalyst NPs. The morphology and diameter control of the as-grown Si NWs reported in this work makes this approach potentially useful toward applications such as nanoelectronics, sensors, and lithium ion battery electrodes depending on the desired morphology.

Study of silicon rich oxide light emitter capacitors using textured substrates by metal assisted chemical etching

Mono and multilayer silicon rich oxide light-emitting capacitors (SRO-LEC) were fabricated using both polished and textured Si substrates. The textured substrate surface was treated by metal-assisted chemical etching (MACE) for 10 s and 20 s forming nanoneedles. Monolayer devices fabricated using textured substrates required lower energy to emit light and present at least 40% higher emission intensity than non-textured substrates. On the other hand, multilayer devices fabricated on textured and polished substrates showed that both LECs required similar energy to start the emission, however, after the bias is increased up to 5.5 MV/cm the textured LECs presented 36% higher emission intensity. The evidence shows that the electric field is screened by the nanocrystals in the SRO with Ro = 10 at electric fields lower than 5.5 MV/cm.

Effect of substrate roughness and material selection on the microstructure of sputtering deposited boron carbide thin films

Amorphous boron carbide (B4C) thin films are by far the most popular form for the neutron converting layers in the 10B-based neutron detectors, which are a rising trend in detector technologies in response to the increasing scarcity and price of 3He, the standard material for neutron detection. The microstructure of the B4C films is closely related to the important properties, e.g. density and adhesion, for the converting layers, which eventually affect the detection efficiency and the long-term stability of the detectors. To study the influence from substrates of different roughness and materials, the B4C films were deposited on polished Si substrates with Al, Ti, and Cu buffer layers and unpolished Si, Al, Ti, and Cu substrates by direct current magnetron sputtering at a substrate temperature of 623 K. The tapered columnar grains and nodular defects, generally observed in SEM images, indicated a strong shadowing effect where voids were introduced around the grains. The change in the grain size did not show a direct dependence to the substrate roughness, acquired from the surface profile, nor to the mass density of the films, obtained from reflectivity patterns. However, films with non-uniform size of columnar grains were deposited on substrates with high skewness, leading to a drop of mass density from ~95% down to ~70% of tabulated bulk density. On the other hand, similar microstructures and mass density were obtained from the films deposited on Al, Ti, and Cu of different roughness and good adhesion were observed from cross-cut adhesion tests, showing the reliability of sputtering deposited B4C films on common structural materials in neutron detectors.

Pyro-phototronic effect enhanced broadband photodetection based on CdS nanorod arrays by magnetron sputtering.

In this work, self-powered photodetectors (PDs) based on RF magnetron sputtering-fabricated CdS nanorod arrays and polished Si substrates were prepared for the first time. By introducing the pyro-phototronic effect of wurtzite CdS, the self-powered PDs exhibit a broadband response range from UV (365 nm) to IR (1310 nm) at zero bias, even beyond the bandgap limit of the material. Both the photoresponsivity and specific detectivity are also enhanced by 23.3 times compared with those only based on the photovoltaic effect. In addition, the rise and fall times of self-powered PDs are 70 μs and 90 μs under 980 nm laser illumination. This research not only expands the application of CdS nanostructures in the field of pyro-phototronics, but also greatly enriches the preparation methods of CdS based pyro-phototronics materials.

FORMATION OF TRIANGULAR Cu MICROCRYSTALS IN Ti/Cu/Si THIN FILMS DURING ANNEALING

Sandwich stacked Ti/Cu/Si thin films were deposited on a single-side polished Si(111) substrate using DC magnetron sputtering system and annealed using a rapid thermal annealing (RTA) system. Complex dendritic patterns, whose branches are composed of Cu rods and triangular Cu microcrystals were obtained on Ti/Cu thin film annealed at 700[Formula: see text]C. The shape of one triangular Cu microcrystal is a truncated equilateral triangular pyramid with a flat top. Triangular Cu microcrystals grow in the number when Ti/Cu thin films are annealed at 800[Formula: see text]C. Experimental results show that anisotropy affects the growth of surface patterns and the top Ti capping layer works as a protection for the underlying Cu layer from oxidation.

Evaluation of lattice dynamics, infrared optical properties and visible emissions of hexagonal GeO2 films prepared by liquid phase deposition

GeO2 films with thicknesses from 10 to 22 μm have been deposited on polished Si(100) substrates using liquid phase deposition.

Characteristics of Carrier Collection of Nanopillar-Patterned Silicon Solar Cells.

Nanopillar-patterned Si solar cells were investigated. Ag nanoparticles were coated on a polished Si substrate as an etching mask. Reactive ion etching caused Si nanopillars to replicate in a reverse fashion on the Ag nanoparticles over a large area. The nanopillar structures efficiently reduced the light reflection on the surface and effectively drove the incident light into a Si absorber. This induced a significant enhancement of the photogenerated-current with an improved solar cell efficiency of 16.07%. The Si nanopillar-patterned solar cells showed improved carrier collection for long wavelengths; however, the surface-defect induced recombination degraded the quantum efficiency at short wavelengths. We suggest that the reduction of recombination loss should be considered for efficient nanostructure solar cells.

High efficiency of photon-to-heat conversion with a 6-layered metal/dielectric film structure in the 250-1200 nm wavelength region.

The optical properties and thermal stability of a 6-layered metal/dielectric film structure are investigated in this work. A high optical absorption average of > 98% is achieved in the broad spectral range of 250-1200 nm with experiment results, in good agreement with our simulated results. The samples have a typical layered structure of: SiO(2)(57.3 nm)/Ti(5.7 nm)/SiO(2) (67.1 nm)/Ti(11.6 nm)/SiO(2)(51.4 nm)/Cu(>100 nm), deposited on optically polished Si or K9-glass substrates by magnetron sputtering. The sample of the 6-layered metal/dielectric film structure has an AM1.5G solar absorptance of 95.5% with the features of low thermal emittance of 0.136 at 700K and good thermal stability, and will be potentially suitable for practical application in high-efficiency solar absorber devices in many fields.

Conditioning of Si-interfaces by wet-chemical oxidation: Electronic interface properties study by surface photovoltage measurements

The field-modulated surface photovoltage (SPV) method, a very surface sensitive technique, was utilized to determine electronic interface properties on wet-chemically oxidized and etched silicon (Si) interfaces. The influence of preparation-induced surface micro-roughness and un-stoichiometric oxides on the resulting the surface charge, energetic distribution Dit(E), and density Dit,min of rechargeable states was studied by simultaneous, spectroscopic ellipsometry (SE) measurements on polished Si(111) and Si(100) substrates.

Sub-terahertz sound excitation and detection by a long Josephson junction

The paper reports on experimental observations of sub-terahertz sound wave generation and detection by a long Josephson junction. This effect was discovered in spectral measurements of sub-terahertz electromagnetic emission from a flux-flow oscillator (FFO) deposited on an optically polished Si substrate. The ‘back action’ of the acoustic waves generated by the FFO and reflected by the bottom surface of the Si substrate results in the appearance of resonant steps in the FFO IVCs with spacings as small as 29 nV for a 0.3 mm substrate thickness; these steps manifest themselves in a pronounced resonant structure in the emission spectra, with spacings of about 14 MHz, precisely according to the Josephson relation. The mechanism of acoustic wave generation and detection by the FFO is discussed; a possibility for employing the discovered effect for FFO frequency stabilization has been demonstrated. A simple and reliable way to suppress the superfine resonant structure has been developed and proved; this invention allows continuous frequency tuning and FFO phase locking at any desired frequency, all of which are vitally important for most applications.

Initial stages of ITO/Si interface formation: In situ x-ray photoelectron spectroscopy measurements upon magnetron sputtering and atomistic modelling using density functional theory

Initial stages of indium tin oxide (ITO) growth on a polished Si substrate upon magnetron sputtering were studied experimentally using in-situ x-ray photoelectron spectroscopy measurements. The presence of pure indium and tin, as well as Si bonded to oxygen at the ITO/Si interface were observed. The experimental observations were compared with several atomistic models of ITO/Si interfaces. A periodic model of the ITO/Si interface was constructed, giving detailed information about the local environment at the interface. Molecular dynamics based on density functional theory was performed, showing how metal-oxygen bonds are broken on behalf of silicon-oxygen bonds. These theoretical results support and provide an explanation for the present as well as previous ex-situ and in-situ experimental observations pointing to the creation of metallic In and Sn along with the growth of SiOx at the ITO/Si interface.

Formation of artificial opals viewed in situ by X-ray grazing insidence diffraction

Formation of artificial opal films by a vertical deposition method was in situ studied using the grazing incidence X-ray diffraction technique. Monodisperse spherical polymethyl methacrylate particles (200 nm in diameter) were deposited on the polished Si substrate from an aqueous suspension. The ordering of particles on a fixed area of the substrate located in turn in the bulk suspension under the meniscus and in the air was continuously monitored by the X-ray scattering upon moving the meniscus down owing to evaporation of the solvent. The triple air-liquid-solid phase boundary, i.e. the top line of the meniscus, is identified as the most probable location of the crystallization process. The analysis of observed Bragg reflections and the particle form-factor indicates that the obtained artificial opal-like structures are composed of the spheres arranged in a close-packed hexagonal layers parallel to the substrate. The characteristic correlation length along the normal to the substrate of 550 ± 100 nm is obtained from the half full width of Bragg peaks.

Enhanced electrochemical properties of as grown LiCoO2 film cathodes: Influence of silicon substrate surface texturing

Influence of Si substrate texturing on growth, microstuctural and electrochemical properties of lithium cobalt oxide (LiCoO2) cathode films was investigated. A batch of rf magnetron sputtered LiCoO2 films were prepared on both Au/Ti/SiO2/(polished) Si and Au/Ti/SiO2/(textured) Si substrates and the film properties were studied, systematically. As-grown films on polished Si substrates were exhibited partially ordered rock-salt structure with a very poor electrochemical performance. However, the as-grown films on textured Si substrates exhibited relatively predominant (0 0 3) orientation with R 3¯ m symmetry and exhibited an initial discharge capacity of 57.5 μAhcm−2 μm−1 with an appreciable capacity fade rate of 0.07%, even after 50 cycles. Electrochemical performance of these films was in close comparison with the annealed (650 °C) LiCoO2 films of Au/Ti/SiO2/(polished) Si substrates. The experimental observations were thoroughly demonstrated and suggested that the as-grown LiCoO2 films on textured Si substrates can be useful for all types of 2D solid state Li+-ion microbattery applications.

In-situ study of magnetic thin films on nanorippled Si (1 0 0) substrates

Magnetic properties of ultrathin Co film on nanorippled Si substrate have been studied. Low energy ion beam erosion of Si (100) substrate has been used to produce nanoripples with the wavelength and amplitude of modulations being 32nm and 1.2nm, respectively. In-situ magneto-optical Kerr effect measurements have been used to study the evolution of the hysteresis loop with film thickness. The results are compared with those of Co film deposited on polished Si substrate. Co films on nanorippled surface exhibit a strong uniaxial magnetic anisotropy with its easy axis along a direction normal to the ripple wave vector. The magnetic anisotropy exhibits a monotonous decrease with increasing film thickness. Co film on nanorippled Si surface exhibits a magnetic dead layer of 0.8nm because of possible intermixing of Co with Si to form non-magnetic silicide.

Influence of growth temperature on the optical and structural properties of ultrathin ZnO films

This study investigates the effect of growth temperature on the optical and structural properties of ultrathin ZnO films on the polished Si substrate. Thickness of the ultrathin ZnO films deposited by atomic layer deposition (ALD) method was about 10 nm. Photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques were used to measure the properties of ultrathin ZnO films. Experimental results showed that the ultrathin ZnO film deposited at 200 °C had excellent ultraviolet emission intensity, and the average roughness of the film surface was about 0.26 nm.

A single target RF magnetron co-sputtered iron doped tin oxide films with pillars

The SnO 2 gas sensors and catalytic surfaces are produced by different techniques with a wide range of dopants improving their selectivity and sensitivities. The surface topology is important because the active surface area can be enlarged dramatically by employing nanostructures. Many reported techniques for the tin oxide nanostructures preparation require fine powders or liquid precursors together with high temperatures above 500 °C. But the nanostructures can be formed by the RF off-axis magnetron sputtering technique at room temperature from a bulk target. The single target co-sputtering of SnO 2 target with Fe inset was used to deposit SnO 2 film doped by iron. The 400 nm diameter pillars were successfully deposited in controllable density on polished Si substrates at low pressure 0.3 Pa of argon and oxygen gas mixture. The pillars were not formatted at the beginning of deposition process but certain SnO 2 film was required. The surface around the pillars was flat without any significant texture. The iron in form of the iron oxide was found to be the doping in deposited coatings when the stannic oxide was sub-stoichiometry with oxygen vacancies.

Exciton emission in tetrahedral carbon self‐organized and ring‐shaped quantum dots

AbstractAFM topography, TEM data, spectra of radiative annihilation of excitons in tetrahedral nano carbon quantum dots (QDs) and quantum rings (QRs) were studied in detail. Anti‐Stokes exciton emission (ASEE) spectra in 6.3–4.7 eV energy interval at 4.2–200 K were induced via cascade Urbach tail states transitions under femtosecond laser radiation (λ=266 nm) pumping. Near diamond in composition nano carbon layers (nt‐C) on cleaved KCl and polished Si substrates with high density of self‐organized surface QDs, isolated, aggregated QRs and fractal bulk networks were grown using carbon ion beam of low energy and fluence. Regular networks of QDs 3–20 nm in diameter less than 1 nm in height and up to 3×1011 cm‐2density were obtained. In ASEE spectra fine–structured via 5–6 meV narrow and week 6.0596 eV, 6.0557 eV and 6.0032 eV lines have been resolved at low level of excitation.The strong, fine‐structured via 3.0–4.5 meV lines and bands above and below the energy of indirect exciton transition in diamond have been found in two types of nt‐C layers as well. The parameter dependences of lines and bands upon the level of laser pumping were studied. We suppose that above mentioned components of ASEE spectra are originated from radiative annihilation of excitons in surface and bulk QDs and ring‐like quantum networks. At strong excitation level fine‐structured with 3.5–4.0 meV energy period new 4.8394 eV and 4.7925 eV exciton lines were induced and dominated in emission spectra. These lines are result of exciton annihilation in bulk quantum confined fractal features. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication, structural and electrical properties of compressively strained Ge-on-insulator substrates

Compressively strained germanium-on-insulator (c-GeOI) substrates with a definitely reduced defect density are expected to yield superior hole mobilities together with low off-state currents in p-type metal oxide semiconductor field effect transistors (MOSFETs). In order to fabricate c-GeOI wafers, we started with double-side polished Si(0 0 1) substrates and grew, by reduced pressure-chemical vapour deposition, Si0.15Ge0.85 virtual substrates (VS) on the front side. The wafer curvature was compensated thanks to the deposition of a thick Ge layer on the backside. We then grew, after a chemical mechanical polishing, various thickness (37–148 nm) Ge layers. They stayed smooth (root-mean-square roughness <5 Å) and pseudomorphically strained on the VS underneath (perpendicular lattice parameter: 5.681 Å ⇔ bulk Ge lattice parameter: 5.658 Å) up to a 74 nm thickness. These c-Ge layers were then bonded on oxidized Si substrates using the SmartCut™ process. The resulting c-GeOI substrates were of high crystalline quality, compressively strained and smooth. The threading dislocations density (8 × 105 cm−2 ⇔ 1.7 × 105 cm−2 for the SiGe VS template used to strain the c-Ge layers) was indeed 20 times less than the one associated with conventional GeOI substrates obtained from thick Ge epilayers. Pseudo-MOSFET measurements were performed to quantify the hole mobility gain in those c-GeOI substrates. A +150% enhancement compared to conventional silicon-on-insulator substrates was evidenced, validating the interest of these stacks.

The effect of ion sputtering of silicon substrates on the catalyst morphology and growth of carbon nanotube arrays

Polished Si substrates are sputtered by He + ions, and carbon nanotube arrays are prepared on the Fe-coated substrates by heat chemical vapor deposition from acetylene. Scanning electron microscopy and atomic force microscopy are employed to examine the morphologies of sputtered substrates, catalyst and carbon nanotube arrays. It is found that ion sputtering is effective in increasing the roughness of Si substrates, and helpful in obtaining higher density Fe catalyst particles and better-aligned carbon nanotube arrays.