Structural comparison of GdF3 films grown on CaF2 (111) and SiO2 substrates

Wide bandgap metal fluorides are the materials of choice for optical coating applications at 193 nm. Low loss and environmentally stable optics requires a mitigating fluoride film structure on a nanometer scale. To understand the growth mechanism of fluoride materials, GdF(3) films grown on CaF(2) (111) and SiO(2) substrates were investigated. Film inhomogeneity and surface roughness were modeled by fitting ellipsometric data with an effective medium approximation, indicating a correlation between film inhomogeneity and surface roughness. The modeled surface roughness was compared with the atomic force microscope measurement. Film inhomogeneity was correlated to the cone-shaped columnar structure revealed by cross-sectional images from a scanning electron microscope. The film crystalline structure was determined by x-ray diffraction measurement, suggesting a different growth mechanism of GdF(3) films on crystalline and amorphous substrates.     

Structural and textural characterization of LiFePO4 thin films prepared by pulsed laser deposition on Si substrates

LiFePO₄ thin films were grown on silicon (100) substrates by pulsed laser deposition using Traditional Geometry (TG) and Off-Axis Geometry (OAG) deposition chambers. We examined and compared the structure and composition of the so formed thin films. The nails observed on the OAG-film present an amorphous “body” and a crystallized “head”. The Fe/P ratio determined using energy dispersive spectrometry combined with high angle annular dark field images reveals a metallic iron heart surrounded by LiFePO₄ shell. On the other hand, the protuberances on TG-film are pure iron. The focused ion beam prepared cross-section of the film suggests the presence of iron particles and iron dendritic like filaments inside the LiFePO₄ layer.     

Hetero-epitaxy and structure characterization of Si films on 6H-SiC substrates

In order to realize the non-ultraviolet application of SiC optoelectronic devices, Si/6H-SiC heterojunctions were prepared by the low-pressure chemical vapour deposition at 850 °C. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) results indicate that Si thin films have a monocrystalline structure and were grown along the (111) crystal plane. The rationality of the (111) growth plane was also analyzed by the theoretical calculation. High-density structural defects such as stacking faults and twins were observed on Si films by the high-resolution transmission electron microscopy. This phenomenon was also validated by the SAED patterns of defect-rich regions on Si films.     

Structural characterization of thin amorphous Si films

We present a study of structural changes occurring in thin amorphous silicon (a-Si). The a-Si films were deposited on single-crystalline Si substrates held at room temperature or 200 °C by magnetron sputtering of a Si target in pure Ar atmosphere, and therefore the films were hydrogen-free. All samples were annealed in vacuum and subsequently studied by EPR and GISAXS. A strong decrease in the dangling bonds content at lower annealing temperatures, and then an increase of it at around 550 °C, suggested significant structural changes. In parallel the samples were studied by GISAXS which confirmed changes at the nanometric scale attributed to voids in the material. A nice correlation of the results of the two techniques shows advantages of this approach in the analysis of structural changes in a-Si material.     

Structural and dielectric properties of Ba0.7Sr0.3TiO3 thin films grown on thin Bi layer-coated Pt(111)/Ti/SiO2/Si substrates

In this work, the growth and study of dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) thin films grown on thin Bi layer coated Pt(111)/Ti/SiO₂/Si substrates, depending on thin Bi layer thickness is reported. The BST thin film (thickness 180 nm) grown on 10-nm-thick Bi layer exhibited more improved structural and dielectric properties than that grown on bare Pt(111)/Ti/SiO₂/Si substrate. The 10-nm-thick Bi layer in optimum configuration was effective for the grain growth of BST phase and suppressed the formation of the oxygen-deficient layer at the interface between the BST thin film and bottom electrode, which resulted in an increase in dielectric constant and a decrease in leakage current density of the Pt/BST thin film/Pt capacitor.     

Growth of Bi1.5MgNb1.5O7 thin films on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering

In this letter, bismuth magnesium niobate (Bi_1.5MgNb_1.5O₇, BMN) thin films were deposited on Pt/Ti/SiO₂/Si substrates by using radio-frequency magnetron sputtering at various substrate temperatures. Based on the phase compositions and microstructures of these samples, we discussed the nucleation and growth of the BMN thin films and how the substrate temperature influenced these processes. The thin film begins to crystallize at 450 °C, and the annealed films were all composed of the cubic pyrochlore phase with a strong (222)-preferred orientation. The film deposited at 450 °C exhibited a large dielectric constant of 173, and a tunability of 26.6 % was obtained at a max dc bias field of 0.8 MV/cm.     

Structural characterization of TiN coatings on Si substrates irradiated with Ar ions

The present study deals with TiN/Si bilayers irradiated at room temperature (RT) with 120 keV Ar ions. The TiN layers were deposited by d.c. reactive sputtering on Si(100) wafers to a thickness of ～ 240 nm. After deposition the TiN/Si bilayers were irradiated to the fluences of 1 × 10¹⁵ ions/cm² and 1 × 10¹⁶ ions/cm². Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), grazing angle X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that the variation of the lattice constants, mean grain size and micro-strain can be attributed to the formation of the high density damage region in the TiN film structure. It has been found that this damage region is mainly distributed within ～ 100 nm at surface of the TiN layers.     

AlN/Si衬底上ZnO薄膜的择优取向生长

当ZnO薄膜直接沉积在Si衬底上时,由于ZnO与Si的晶格失配度大,不易于获得高质量的ZnO薄膜.因此,选择合适的衬底材料沉积ZnO薄膜,对提高其质量非常重要.本文采用射频磁控溅射法,通过在Si(100)衬底上预沉积AlN作为ZnO薄膜生长的缓冲层,获得了择优取向的ZnO薄膜.我们还讨论了ZnO薄膜在AlN/Si衬底上的取向生长机理.     

Selective growth of ZnO nanorods on SiO2/Si substrates using a graphene buffer layer

A promising strategy for the selective growth of ZnO nanorods on SiO₂/Si substrates using a graphene buffer layer in a low temperature solution process is described. High densities of ZnO nanorods were grown over a large area and most ZnO nanorods were vertically well-aligned on graphene. Furthermore, selective growth of ZnO nanorods on graphene was realized by applying a simple mechanical treatment, since ZnO nanorods formed on graphene are mechanically stable on an atomic level. These results were confirmed by first principles calculations which showed that the ZnO-graphene binding has a low destabilization energy. In addition, it was found that ZnO nanorods grown on SiO₂/Si with a graphene buffer layer have better optical properties than ZnO nanorods grown on bare SiO₂/Si. The nanostructured ZnO-graphene materials have promising applications in future flexible electronic and optical devices.     

Synthesis of sequentially-deposited Cu/BaF2/Y films on SrTiO3 and buffered Si substrates

Sequentially-deposited layers of Cu/BaF₂/Y on buffered Si and SrTiO₃ substrates have been synthesised to produce YBa₂Cu₃O_7−δ thin film. An attempt has been made to see the effect of the ZrO₂ and Al buffer layers on Si of the annealing of the layered structure. X-ray diffraction studies reveal that on ZrO₂-buffered Si the annealing of the layered structure leads to formation of 211 phase while on Al-buffer layer 123 phase is obtained. Noticeable effect in annealed-layered structure of oblique deposition of BaF₂ from a Knudson Cell is seen in X-ray diffraction.     

Growth and characterisation of SiC films deposited on a-SiO2/Si (100) substrates

Abstract

The growth of polycrystalline SiC films has been carried out by low pressure chemical vapour deposition in a horizontal quartz reaction chamber using tetramethylsilane and H2 as the precursor gas mixture. Silicon (100) wafers were used as substrates. A thin Si O₂ amorphous layer of ~6 nm was formed before SiC deposition to reduce the strain induced by the 8% difference in thermal expansion coefficients between SiC and Si. Samples were. analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared reflectivity. The structure of films grown at temperatures between 950 and 1150°C varies from amorphous to polycrystalline SiC. Preferential [111] orientation and columnar growth of polycrystalline films develops with increasing temperature.

MST/3317     

Characterization of lead zirconate titanate thin film deposition onto Pt/Ti/SiO2/Si substrates

Lead zirconate titanate, (Pb(Zr_0.52Ti_0.48)O₃PZT) thin films were deposited onto a Pt/Ti/SiO_2/Si substrate using radio frequency (r.f.) planar magnetron sputtering in this study. The deposited PZT thin films were almost amorphous before the annealing processes and developed a perovskite structure after the annealing process. If the annealing temperature was too low or annealing time too short, pyrochlore would form. However, if the annealing temperature was too high or annealing time too long, the thin film structure would degrade due to the volatilization of PbO. The significant finding in this experiment is that high quality perovskite PZT thin films on Pt/Ti/SiO_2/Si substrates can be obtained by adjusting the annealing temperature to a range of 650 °C to 850 °C and annealing time to a range from 5 to 80 min. In this experiment, the optimal annealing condition was an annealing temperature of 650 °C and time of 20 min. The properties of PZT thin film annealed at 650 °C for 20 min were dielectric constant _r = 869 free dielectric constant ^T ₃₃ = 893 piezoelectric constant d₃₃ = 2.03p m V^-1 piezoelectric constant g₃₃ = 2.57 x 10^-4 V m N^-1, remanent polarization P₁ = 112.5 nC cm^-2 and coercive field E_c= 0.061 kV cm^-1.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Emission properties of DLC films on Si substrates

DLC films were deposited on polished both n-type and p-type silicon substrates. The silicon resistivity was ～0.02 Θ cm. Some of the DLC films 20 nm thick were deposited on the n-type Si surface with the submicron cones. SEM and Raman spectroscopy were used for structural investigations. Field electron emission occurs after dielectric breakdown, except for the samples with Si cones for which the emission seems to originate from SiC formed during the first stage of electron emission. It seems that too much sp² graphite phase may give rise to the observed increase in the turn-on field from 50 V/μm up to 150 V/μm.     

Characteristics of PbTiO3 thin films on Pt/Ti/SiO2/Si by continuous cooling process

In order to introduce a new deposition process for ferroelectric thin film, the deposition temperature was continuously cooled down from 580°C to 400°C during the deposition which we call continuous cooling process (CCP). X-ray diffraction patterns showed that the PbTiO₃ thin films deposited by the CCP and at 480°C had polycrystallinity, but at substrate temperatures of 400°C and 580°C had poor crystallinity. Scanning electron microscopy of the CCP-deposited film surface showed larger granular-like micrograins than that of the film deposited at 480°C and smaller than that of the film at 580°C. While there was no other phase formation at the PbTiO₃-Pt interface in the CCP-deposited film, resulting in a sharp interface, there was severe interface reaction at the PbTiO₃-Pt and the Pt-Si in the film deposited at 580°C, resulting in an abrupt interface. Atomic force microscopy under ambient conditions showed smoother surface of the film by the CCP than that of the films at 580°C. Furthermore, the film by the CCP had higher packing density than that of the film at 480°C. Besides enhancement of the structural properties, the CCP deposition appeared to have improved the electrical properties such as dielectric constant, dissipation factor, leak current density and polarization. In the case of the film by the CCP, polarization-electrical field measurement showed the saturation polarization of 27 Ccm^–2, remanent of 14 Ccm^–2 and coercive of 150 kV. These results indicate that the CCP in metalorganic chemical vapour deposition has a possibility for fabrication of PbTiO₃ ferroelectric thin films.     

Structure and internal stress in ultra-thin silver films deposited on MgF2 and SiO substrates

A substantially improved bending-beam technique combined with the capacitance method was used for the continuous determination of the internal stress during vacuum deposition of ultra-thin silver films. With this method a sensitivity improvement of about two orders of magnitude was achieved compared with results reported previously. By proper experimental design all radiation interference on the stress-measuring appratus except the unavoidable direct heat radiated from the evaporators was eliminated. With this improved method it was possible to determine continuously the internal stress of silver films deposited onto fresh MgF₂ or SiO substrate films under varying experimental conditions (i.e. evaporation rate, residual gas pressure). Based on correlations between internal stress and the structure of the films observed using an electron microscope a model is proposed that explains the origin of the alternately compressive and tensile stress in such ultra-thin films.