Single Crystal Si Substrates Research Articles

Study of surface morphology and optical properties of Nb2O5 thin films with annealing

Nb2O5 films have been deposited on variety of substrates using the sol-gel dip coating technique. As-deposited films on all substrates are amorphous. Films were annealed under controlled ambience at 300, 400 and 600°C for 5 h. As-deposited films on glass substrate show uniform surface structure. The crystal structure and surface topography are found to depend strongly on the annealing temperature and nature of the substrates. The average grain size of 40 nm is observed in films annealed at 300°C. On annealing at 400°C increasing grain size and resulting fusing of them, enhanced surface roughness. Films deposited on NaCl substrates crystallized into a stable monoclinic phase and those deposited on single crystal Si substrates crystallized into hexagonal phase after annealing at 600°C. The as-deposited films show very high transmittance (>90%) in the visible region. The optical band gap is observed to increase from 4.35 eV when the films are in amorphous state to 4.87 eV on crystallization.

Structural, optical and electrical properties of ZnO films grown by pulsed laser deposition (PLD)

ZnO thin films were grown on single-crystal Si(1 0 0) and quartz glass substrates by pulsed laser deposition (PLD) technique using a KrF excimer laser with wavelength of 248 nm. The structural, optical and electrical properties of the as-grown films were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electronic microscopy (FE-SEM), transmittance spectrometry, and Hall-effect measurement. The films show c-axis oriented hexagonal wurtize crystal structure even at low substrate temperature of 200 °C. With the increase of substrate temperature and oxygen pressure, the crystallinity is enhanced and the film presents smooth, dense and uniformed microstructure, and strong interface bonding with substrate. The films grown at higher substrate temperature and oxygen pressure exhibit high average transmittance about 90% in the visible region and very sharp absorption edge at 378 nm. The energy band gap calculated from the transmittance spectra is about 3.25∼3.27 eV. Hall measurement indicates that the resistivity of films increases with substrate temperature and oxygen pressure.

Fabrication of polycrystalline La 0.7Sr 0.3MnO 3 thin films on Si (1 0 0) substrates by chemical solution deposition

Polycrystalline La 0.7Sr 0.3MnO 3 (LSMO) thin films with nanometer scale grains were fabricated on Si (1 0 0) single crystal substrates by the chemical solution deposition (CSD) method. The LSMO film exhibits typical transport properties of the polycrystalline film of manganites. The low-field magnetoresistance (MR) as high as 2.54% is obtained at H = 0.05 T and 300 K. The enhanced MR effect for LSMO film is attributed to the suppression of the spin-dependent scattering of polarized electrons at the grain boundaries (GBs).

Thermal Oxidation of Thin Films of Fe–Ni Solid Solutions

The oxidation kinetics of thin films of dilute Fe-Ni solid solutions (0.17, 0.54, 0.65, 0.91, and 1.87 at % Ni) on single-crystal Si substrates are studied. The oxidation rate of the films is found to decrease with increasing Ni concentration. The predominant phase in all of the oxide layers is Fe 2 O 3 , independent of the oxidation conditions. It is shown that, at an Ni content of about 1 at %, the composition dependences of the oxide thickness, refractive index, extinction coefficient, and apparent activation energy for oxidation show extrema. The mechanism of film oxidation is discussed.

Nanopores in Macroporous Silicon

Macroporous silicon is studied by IR absorption spectroscopy, x-ray diffraction, and the electron–positron annihilation method in comparison with single-crystal Si (substrate), polycrystalline Si (powder), anda-SiO2 (silica glass). According to IR absorption data, as-prepared macroporous silicon contains a significant amount of oxidized material. Annihilation spectra of macroporous silicon attest to the presence of a system of nanopores, in which positronium atoms are likely to localize. Diffraction patterns reveal considerable amounts of silicon particles oriented at random. Both the polycrystalline phase and nanopores reside on the surface of macropores.

Dependence of Ba(Zr0.1Ti0.9)O3 films growth on substrate temperature upon radio-frequency plasma enhanced pulsed laser deposition

The high-crystallization perovskite Ba(Zr0.1Ti0.9)O3 (BZT) films were deposited on the surface of a polished single crystal Si (111) substrate by radio-frequency plasma enhanced pulsed laser deposition (RF-PEPLD). X-ray diffraction (XRD), Raman scattering spectra, and scanning electric microscopy were used to characterize the crystal structure, phonon mode, and surface morphology of the deposited BZT films. The dependence of the crystallinity of the prepared BZT films on the substrate temperature was traced by XRD in detail. The experimental results showed that the crystallinity of the BZT films was improved gradually with increasing substrate temperature when it was below 720°C. Above 720°C, the crystallinity of the BZT films gradually worsened with increasing substrate temperature. Accordingly, we have determined the threshold value of 720°C of the substrate temperature for the high-crystallization of BZT films upon RE-PEPLD. The mechanism concerning the dependence of the crystallinity of the BZT films on the growth temperature is discussed in the paper.

Preparation of Hot Water-Resistant Silica Thin Films from Polysilazane Solution at Room Temperature

Perhydropolysilazane (PHPS) films were deposited on single-crystal Si substrates by spin-coating using a xylene solution of PHPS, and then suspended over 1 mol L−1 ammonia water at room temperature. The PHPS-to-silica conversion occurring on the exposure to the ammonia water vapor was studied by infrared absorption spectroscopy. Si--H and N--H infrared absorption peaks decreased and Si--O--Si bands increased, showing PHPS-to-silica conversion; the conversion was almost completed in 6 h. The exposed films were soaked in 80°C water for 24 h, and the reduction in thickness on soaking was evaluated. The PHPS-derived films suspended over the ammonia water for 6 h exhibited only 2% reduction in thickness on soaking in 80°C water. Alkoxide-derived silica gel films dried in the ambient atmosphere or suspended over the ammonia water, on the other hand, exhibited significant reduction in thickness on soaking in 80°C water.

Green’s-function method for modeling surface acoustic wave dispersion in anisotropic material systems and determination of material parameters

A Green’s-function method for modeling propagation of surface acoustic waves in anisotropic nanolayered materials is reviewed. The mathematical model, developed at NIST, provides a computationally efficient inversion algorithm for determination of the material parameters of the film, such as its elastic constants and density, from observed dispersion of the surface acoustic waves. The application of the method to a 306 nm thick TiN film having transverse isotropy on a single crystal Si substrate is discussed as an example. The errors in the values of the parameters determined by using the inversion algorithm and the question of uniqueness of the values of the parameters are discussed in detail. It is suggested that, at least in the example considered in this paper, the SAW dispersion can be used to determine any two parameters of the film, provided other parameters are known by independent measurements. In particular, the values of c 11 and the density of the film, obtained from the measured SAW dispersion, are the most reliable and the value of c 44 is the least reliable. The method is extended to account for defective bonding between the film and the interface and the effect of an intermediate layer of silica between the film and the substrate.

Preparation, characterization and mechanical properties of Y2O3 thin film deposited on sulfonated self-assembled monolayer of 3-mercaptopropyl trimethoxysilane

Abstract Silane coupling reagent (3-mercaptopropyl)trimethoxysilane was self-assembled on a single-crystal Si substrate to form a two-dimensional organic monoalyer (MPTS-SAM) and the terminal –SH group in the film was in-situ oxidized to –SO3H group to endow the film with good chemisorption ability. Thus Y2O3 thin film were deposited on the oxidized MPTS-SAM, by enhanced hydrolysis of yttrium nitrate (Y(NO3)3 · 6H2O) solution in the presence of urea (CO(NH2)2) at 80 °C, making use of the chemisorption ability of the –SO3H group. The thickness and refractive index of the films were determined with an ellipsometer. The morphologies of the films were observed on an atomic force microscope. The adhesion strength and friction behavior of the films on the silicon substrate sliding against a steel ball was examined on a UMT-2MT friction and wear test system. It was found that the Y2O3-600 thin film was well adhered to the substrate with a critical load (Lc) of 2.8 N and had excellent antiwear and friction-reduction performance under a low load of 0.2 N. Thus the Y2O3 film might find promising application in the surface-protection of single crystal Si and SiC in microelectromechanical systems (MEMS).

Demonstration of all in situ magnesium diboride superconductor thin-film tunnel junctions

High-quality planar tunnel junctions of MgB2 superconductor have been fabricated, all in situ, on Si single crystal substrates with Al2O3 as well as MgO barriers. Two superconducting energy gaps due to the σ and π bands of MgB2 have been unambiguously determined from superconductor-insulator-superconductor tunneling conductance measurements, showing good agreement with the theoretical predictions. Phonon structures have also been observed in tunneling. Our junction fabrication technique and well defined tunneling characteristics show a distinct possibility for the development of superconductive electronics based on MgB2 junctions.

Self-assembling growth of (Ba,Sr)TiO3 epitaxial thin films

Ferroelectric thin films of SrTiO3, BaTiO3, and (Ba,Sr)TiO3 were fabricated epitaxially on SrTiO3(100) and Si(111) single crystal substrates in an ultrahigh vacuum (10−5 Pa) by laser molecular beam epitaxy. The lowest crystallization temperatures of homoepitaxial thin films of SrTiO3 and heteroepitaxial thin films of BaTiO3 and (Ba,Sr)TiO3 on SrTiO3(100) substrates obtained were as low as 280, 330, and 340 °C, respectively. With the growth rate lower than 0.17 Å/s, it was discovered that the thickness of each layer of BTO film was an integral of the BTO unit cell height. When the growth rate was decreased from 0.17 to 0.05 Å/s, the thickness of each layer varied from nine unit cells to one unit cell. It is very important to construct a nanometer structure of inorganic ABO3 perovskite oxides by this kind of self-assembly.

Synthesis and characterization of two-layer-structured ZnO p-n homojunctions by ultrasonic spray pyrolysis

The two-layer-structured ZnO p-n homojunctions were prepared on single-crystal Si (100) substrate by depositing undoped n-type ZnO film on N–In codoped p-type ZnO film using ultrasonic spray pyrolysis. The crystal structure and morphology of the obtained ZnO homojunctions were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The two-layer structure was confirmed by secondary ion mass spectroscopy depth profile analysis. The current–voltage (I–V) characteristics derived from the undoped ZnO/N–In codoped ZnO two-layer structure clearly show the rectifying characteristics of typical p-n junctions.

Interaction of Pb and Sn with Thin Films of Their Oxides on Single-Crystal Silicon

Experimental data are presented on the interactions between Pb and thin SnO and SnO2 films and between Sn and thin PbO films during vacuum annealing and subsequent heat treatment in flowing oxygen. The Pb and Sn films were deposited by magnetron sputtering onto single-crystal Si substrates; the SnO and SnO2 films were produced by heat-treating Sn in flowing oxygen at 470 and 870 K, respectively; and the PbO films were obtained by heat-treating Pb films at 520 K. During annealing of Pb/SnO2 /Si heterostructures at 870 K in a vacuum of 0.33 × 10–2 Pa, Pb reacts with lead oxides to form PbSnO3 , whereas vacuum annealing of Sn/PbO/Si heterostructures leads to the formation of SnO and Pb metal. The lead stannates forming in vacuum persist during subsequent heat treatment in flowing oxygen at atmospheric pressure at temperatures of up to 1120 K.

Study of silica–titania films doped with Er and Ag by RBS and ERDA

The photoluminescence (PL) efficiency of Er-doped silica–titania planar waveguides, prepared by sol–gel processing, may be enhanced through the incorporation of neutral Ag metal particles. However, the presence of residual Si–OH groups and the limited reproducibility of the doping process limit the optical activity of the Er 3+ ions. We have used Rutherford backscattering spectrometry (RBS) combined with elastic recoil detection analysis (ERDA) to study the incorporation behaviour of Ag and H atoms during the heat treatments used to densify the films. These were deposited by sol–gel spin-coating on single crystal Si or silica-buffered Si substrates (∼5 μm thick silica buffer layer). The results indicate a homogeneous distribution of Er in the as-deposited films. On the contrary, Ag displays a bimodal in-depth profile centred at the film surface and at the film/substrate interface. Annealing up to 700 °C leads to in-diffusion and concentration of all the Ag species at the latter interface. The H concentration maintains nearly the same values after annealing at 500 and 900 °C, with larger values for temperatures in between. During heat treatment the Er profile remains stable.

Structural properties of Fe ion implanted and ruby laser annealed Si layers

The processes in the synthesis of iron silicide thin films (FeSi and FeSi2) on a single-crystal Si substrate implanted with different doses of Fe+ ions (D = 1015–2 × 1017 cm−2) and subjected to pulsed laser annealing (λ = 0.69 µm, τ = 80 ns, W = 0.6–1.4 J cm−2) are investigated. Using x-ray diffraction, transmission electron microscopy and Rutherford backscattering spectrometry, the structure and phase composition of the synthesized films and the depth profile of Fe atoms in the Si are studied. It is shown that laser annealing (W = 0.6–1.1 J cm−2) of high-dose implanted Si (D > 1017 cm−2) results in the formation of epitaxial iron monosilicide (FeSi) layers. Increasing the pulse energy up to 1.4 J cm−2 leads to a redistribution of Fe atoms in the Si and formation of a mixture of silicide phases (FeSi+FeSi2) with the cellular structure of a synthesized layer. In the case of low-dose implanted Si (D ∼ 1016 cm−2), the formation of cellular structures takes place at lower energy densities (W ∼ 0.8 J cm−2), with segregation of Fe atoms to the Si surface.

ＤＣマグネトロンスパッタリング法によるＦｅ‐Ｇａ合金薄膜の作製

The magnetostrictive properties of Fe-Ga (Ga: 8 at%-21 at%) alloy films prepared by DC magnetron sputtering system were investigated. Base pressure was less than 1.0×10-4 Pa and Fe-Ga films were deposited onto Single crystal Si(100) and polyimide substrate at room temperature with DC 200 W in an Ar atmosphere of 2.5×10-1 Pa. The lattice parameter of Fe-Ga films with a bcc structure increased with the increasing Ga concentration. The Fe-Ga films showed columnar grains with a crystalline orientation for ‹110› perpendicular to the film plane. The magnetostriction of Fe-Ga films increased with the increasing Ga concentration. Fe-21 at%Ga film showed a maximum magnetostriction of 180 ppm at an applied magnetic field of 1200 kA/m.

Dielectric Properties of Mn-Doped BST Thin Films for Microwave Application

In this letter, we report on the effect of Mn doping on the tunability and dielectric loss of Ba0.6Sr0.4TiO3 thin films at low frequency (100 kHz) and at microwave frequency (3.5 GHz), respectively. Perovskite Ba0.6Sr0.4TiO3 thin films were deposited on Pt/TiO2/SiO2/Si and MgO single crystal substrates by pulsed laser deposition. At an applied electric field of 150 kV/cm, the BST films (0, 1, 3, 5 mol% Mn doped) grown on Pt/TiO2/SiO2/Si substrate showed the tunability value within the range from 46% to 49%. With 3% Mn doped BST thin films, results gave a tunability of 49% and a loss tangent as low as 0.0158 and the highest figure of merit of about 31. The microwave properties of BST films grown on MgO substrate were measured using interdigital capacitors (IDC) structure at 3.5 GHz. 3 mol% Mn doped BST also showed better tunability (27.4%) compared to that (11.6%) of undoped BST film. It is suggested that 3 mol% Mn doped BST film is effective candidate for high performance tunable device applications.

Effect of aluminium ion implantation on the oxidation resistance of DC magnetron sputter-deposited TiB2 thin films

This paper presents a novel approach to providing high-temperature oxidation protection for titanium diboride thin films via aluminium ion implantation . Through ion beam modification, it was anticipated that metastable phases, not otherwise observed in stoichiometric TiB 2 , would form, giving rise to a stable oxidation barrier layer upon oxidation. Films, deposited onto single-crystal Si (1 0 0) substrates, were subjected to metal vapour vacuum arc aluminium ion implantation to doses of between 1×10 16 and 3×10 17 ions/cm 2 using extraction voltages of up to 35 kV, vacuum annealed at 1100 °C, then oxidised in air at 650 °C for durations between 1 and 60 min. Analysis was performed using Rutherford backscattering spectroscopy , heavy ion elastic recoil detection analysis, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. Aluminium ion implantation resulted in the formation of various Ti–Al and Al–B phases. Upon oxidation, the preferential oxidation of aluminium was observed, giving rise to a protective Al 2 O 3 barrier layer. Aluminium ion implantation was thus observed to reduce the oxidation rate of titanium diboride thin films.

Effect of aluminium ion implantation on the oxidation resistance of DC magnetron sputter-deposited TiB 2 thin films

This paper presents a novel approach to providing high-temperature oxidation protection for titanium diboride thin films via aluminium ion implantation. Through ion beam modification, it was anticipated that metastable phases, not otherwise observed in stoichiometric TiB 2, would form, giving rise to a stable oxidation barrier layer upon oxidation. Films, deposited onto single-crystal Si (1 0 0) substrates, were subjected to metal vapour vacuum arc aluminium ion implantation to doses of between 1×10 16 and 3×10 17 ions/cm 2 using extraction voltages of up to 35 kV, vacuum annealed at 1100 °C, then oxidised in air at 650 °C for durations between 1 and 60 min. Analysis was performed using Rutherford backscattering spectroscopy, heavy ion elastic recoil detection analysis, X-ray photoelectron spectroscopy, X-ray diffraction and scanning electron microscopy. Aluminium ion implantation resulted in the formation of various Ti–Al and Al–B phases. Upon oxidation, the preferential oxidation of aluminium was observed, giving rise to a protective Al 2O 3 barrier layer. Aluminium ion implantation was thus observed to reduce the oxidation rate of titanium diboride thin films.

Effect of deposition parameters on different stages of diamond deposition in HFCVD technique

The effect of applied bias and system pressure on different stages in the deposition process occurring during diamond deposition on mirror polished Si single crystal substrates in the HFCVD technique has been investigated. For characterization of the deposit, Fourier Transform Infrared Spectroscopy and Laser Raman spectroscopy have been used as the primary techniques while X-ray diffraction and scanning electron microscopy served as supplementary techniques. The findings are that the use of an overall low system pressure ∼1.3 mbar and application of an appropriate bias to the substrate during the initial stages facilitates the growth of highly oriented cubic silicon carbide film on mirror polished Si single crystal substrates under conditions conventionally used to grow diamond in HFCVD technique. A critical pressure ‘regime’ ∼26 mbar has been found to exist during the growth stage for the concurrent growth of SiC and diamond such that only SiC grows below this pressure and diamond starts growing at or above this value. It is suggested that around this transition region, SiC gets partly converted to nanocrystalline diamond structured carbon, which then grows into bigger crystals under appropriate growth conditions.