Effect of Pretreatment of TaN Substrates on Atomic Layer Deposition Growth of Ru Thin Films

The polycrystalline ruthenium films are grown on TaN substrates by atomic layer deposition （ALD） using bis（cyclopentadienyl） ruthenium [RuCp2] and oxygen as ruthenium precursor and reactant respectively at a deposition temperature of 330℃. The low-energy Ar ion bombardment and Ru pre-deposition are performed to the underlying TaN substrates before ALD process in order to improve the Ru nucleation. X-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy are carried out to characterize the properties of ALD Ru films. The results show that the nucleation density of Ru films with Ar^＋ bombardment to the underlying TaN substrates is much higher than that of the ones without any pretreatment. The possible reasons are discussed.     

Effects of Substrate Temperature and Nitrogen Pressure on Growth of AIN Films by Pulsed Laser Deposition

Highly oriented aluminium nitride （AIN） films are grown on p-Si （100） substrates by pulsed laser deposition, and their characteristics of structure and composition are studied by x-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. The results show that the deposited films exhibit good crystalline properties with a sharp x-ray diffraction peak at 2θ= 33.15 ° corresponding to AIN h （100） crystalline orientation. The influences of substrate temperature and ambient nitrogen （N2） pressure on the crystallinity of A1N films are remarkable. At room temperature, when the ambient N2 pressure arises from 5 × 10^-6 Pa to 5 Pa, the crystallinity of the film becomes better. When the substrate temperature is 600℃, the film has the best crystallinity at 0.05 Pa. Furthermore, the effects of substrate temperature and ambient N2 pressure on the combination of A1-N bonds and surface morphology of AIN films are also studied.     

Temperature－Dependent Photoluminescence of ZnTe Films Grown on Si Substrates

ZnTe films have been prepared on Si substrates by metal-organic chemical vapour deposition (MOCVD), and the temperature-dependent photoluminescence (PL) properties were investigated. The near-band-edge (NBE) emission of the ZnTe sample at 83K shows an asymmetry line shape, which can be decomposed into two Gaus-siam lines labelled by FE and BE. Temperature-dependent PL intensity of the NBE peak shows two variation regions, and an expression with two dissociation channels fits well to the experimental data. The results of the temperature-dependent full width at half maximum (FWHM) and peak energy were well understood under the framework of the two-dissociation-channel model. That is, at low temperature, the emission from bound excitons governs the NBE peak, while above 157K, the free exciton emission becomes dominant gradually. A simple model with three energy levels was employed to describe the variation in emission intensity of BE and FE with temperature.     

Influences of Thalliation on the Morphology and Critical Temperature of Tl2Ba2CaCu2O8 Thin Films

Tl2Ba2CaCu2Ox(Tl-2212) thin films were prepared by the two-step technique.A precursor film was first prepared by the pulsed laser deposition method,and then experienced the incorporation of thalliation in a one-step or two-step annealing process.The experimental results show that the two-step annealing process produces dense and smooth films,and that the one-step annealing process produces a high critical temperature film of 101K,but the transition width is wide.Precursor films with homogeneous Ba2Ca1.3Cu2.1Ox composition are essential for producing high-quality Tl-2212 films.     

Effect of Substrates on CuInSe2 Nanoparticle Thin Films by Radio Frequency Reactive Sputtering

CuInSe2(CIS) nanoparticle thin films have been prepared by radio frequency reactive magnetron sputtering from compound ternary fan-shaped targets on low-temperature substrates with pure argon gas as the atmosphere.The stoichiometry of the ternary compound semiconductor quantum dots can easily be controlled by the ratios of the ternary elements and sputtering parameters.CIS nanoparticle thin films regularly shaped and distributed reasonably uniform in size on substrates of 7059 glass etc can be grown in this way.The average particle diameter can be varied between 40-80 nm by an appropriate choice of the substrate temperature,power density and total CIS coverage.the optical and electrical properties of the CIS films have also been studied.     

Effects of Substrate Temperature on Helium Content and Microstructure of Nanocrystalline Titanium Films

Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition＇parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of （002） crystal planes of the He-charged Ti film shifts to a lower angle and that of （100） crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening.     

Microstructure of Epitaxial Er2O3 Thin Film on Oxidized Si （111） Substrate

Er2O3 thin films are grown on oxidized Si （111） substrates by molecular beam epitaxy. The sample grown under optimized condition is characterized in its microstructure, surface morphology and thickness using grazing incidence x-ray diffraction （GIXRD）, atomic force morphology and x-ray reflectivity. GIXRD measurements reveal that the Er2O3 thin film is a mosaic of single-crystal domains. The interplanar spacing d in-plane residual strain tensor ell and the strain relaxation degree ε are calculated. The Poisson ratio μ obtained by conventional x-ray diffraction is in good agreement with that of the bulk Er2O3. In-plane strains in three sets of planes, i.e. （440）, （404）, and （044）, are isotropic.     

Influence of Annealing Temperature on Structure, Optical Loss and Laser-Induced Damage Threshold of TiO2 Thin Films

TiO2 thin films are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for 4h, the spectra and XRD patterns of the TiO2 thin film are obtained. Weak absorption of coatings is measured by the surface thermal lensing technique, and laser-induced damage threshold （LIDT） is determined. It is found that with the increasing annealing temperature, the transmittance of TiO2 films decreases. Especially when coatings are annealed at high temperature over 1173K, the optical loss is very serious. Weak absorption detection indicates that the absorption of coatings decreases firstly and then increases, and the absorption and defects play major roles in the LIDT of TiO2 thin films.     

Optical Characterization of β-FeSi2 Thin Films Prepared by Femtosecond Laser Ablation

Iron disilicide thin films are prepared on fused quartz using femtosecond laser deposition （FsPLD） with a FeSi2 alloy target. X-ray diffraction results indicate the films are single-phase, orthorhombic, β-FeSi2. Field scanning electron microscopy, high resolution transmission electron microscopy, UV-VIS-NIR spectroscopy and Raman microscope are used to characterize the structure, composition, and optical properties of the β-FeSi2 films. Normal incidence spectral transmittance and reflectance data indicate a minimum, direct energy gap of 0.85 eV. The two most intense lines of Raman scattering peaked at 181.3 cm^-1 and 235.6cm^-1 for the film on fused quartz, and at 191.2cm^-1 and 243.8cm^-1 for the film on Si （100）, are observed.     

Giant Temperature Coefficient of Resistance in ZnO/Si （111） Thin Films

Giant negative temperature coefficient of resistance （TCR） was observed in ZnO/Si （111） thin films. The films were grown using the pulsed laser deposition （PLD） technique, taking Si （111） wafer as substrates, with a substrate at the temperature below 450°C in the PLD. It is found that both TCR-temperature behavior and TCR value are strongly affected by deposition temperature. The maximal TCR value over -10.9%K-1 can be observed at the deposition temperature from 20°C to 350°C and reaches to -13%K-1 at deposition temperature 20°C where the film shows X-ray diffraction amorphous. The results suggest that the ZnO/Si films demonstrate great potentials when used in a low-cost, high-performance, non-cooling and highly sensitive bolometer.     

Characterization of HfOxNy gate dielectrics using a hafnium oxide as target

Hafnium oxynitride (HfO_xN_y) gate dielectric has been deposited on Si (1 0 0) by means of radio frequency (rf) reactive sputtering using directly a HfO₂ target in N₂/Ar ambient. The thermal stability and microstructural characteristics for the HfO_xN_y films have been investigated. XPS results confirmed that nitrogen was successfully incorporated into the HfO₂ films. XRD analyses showed that the HfO_xN_y films remain amorphous after 800 °C annealing in N₂ ambient. Meanwhile the HfO_xN_y films can also effectively suppress oxygen diffusion during high temperature annealing and prevent interface layer from forming between HfO_xN_y films and Si substrates. AFM measurements demonstrated that surface roughness of the HfO_xN_y films increase slightly as compared to those pure HfO₂ films after post deposition annealing. By virtue of building reasonable model structure, the optical properties of the HfO_xN_y films have been discussed in detail.     

Effects of nickel doping on structural and optical properties of spinel lithium manganate thin films

Spinel LiNi_xMn_2−xO₄ (x≤0.9) thin films were synthesized by a sol-gel method employing spin-coating. The Ni-doped films were found to maintain cubic structure at low x but to exhibit a phase transition to tetragonal structure for x≥0.6. Such cubic-tetragonal phase transition can be explained in terms of Ni³⁺(d⁷) ions with low-spin (t_2g⁶,e_g¹) configuration occupying the octahedral sites of the compound, thus being subject to the Jahn-Teller effect. By X-ray photoelectron spectroscopy both Ni³⁺ and Ni²⁺ ions were detected where Ni²⁺ is more populated than Ni³⁺. Optical properties of the LiNi_xMn_2−xO₄ films were investigated by spectroscopic ellipsometry in the visible-ultraviolet range. The measured dielectric function spectra mainly consist of broad absorption structures attributed to charge-transfer transitions, O²⁻(2p)→Mn⁴⁺(3d) for 1.9 (t_2g) and 2.8-3.0 eV (e_g) structures and O²⁻(2p)→Mn³⁺(3d) for 2.3 (t_2g) and 3.4-3.6 eV (e_g) structures. Also, sharp absorption structures were observed at about 1.6, 1.7, and 1.9 eV, interpreted as being due to d-d crystal-field transitions within the octahedral Mn³⁺ ion. In terms of these transitions, the evolution of the optical absorption spectrum of LiMn₂O₄ by Ni doping could be explained and the related electronic structure parameters were obtained.     

Phase diagram and dielectric behavior of Ba0.6Sr0.4TiO3 thin films grown on orthorhombic substrates

Using Landau-Devonshire (LD)-type phenomenological model, we investigate the phase diagrams and dielectric behaviors of single-domain single-crystal Ba_0.6Sr_0.4TiO₃ films deposited on orthorhombic substrates. An anisotropic strain factor is introduced to quantitatively calculate the effects of anisotropic in-plane misfit strains. Investigation indicates that anisotropic strains play a crucial role on formation of stable ferroelectric phases and dielectric properties. The anisotropic strains induce tetragonal phases which only contain one in-plane spontaneous polarization component. These phases do not exist in BST films of the same composition under isotropic strains. Moreover, permittivity and tunability of films can reach to maximum when the corresponding spontaneous polarization component disappears at the boundaries of structural phase transition.     

Strain and Size Effects on Ferroelectric Properties of BaTiO3 Nanofilms

The strain and size effects on the ferroelectric properties of BaTiO3 films are studied using the molecular dynamics method based on a shell model. It is found that from microscopic view, these two effects share the same physical nature, i.e., the resulting crystal cell distortions lead to the separation of negative and positive charge eentres. The strain and size effects are therefore coupled, and the critical thicknesses of films would depend on the in-plane strains, which provides a possible interpretation on the discrepancies among the experimental measurements of the critical thicknesses. A polarization map is given to clearly reflect the relations among the size, strain and polarization of the nano films.     

Electrical Properties of La-Doped Al2O3 Films on Si （100） Substrates as a High-Dielectric-Constant Gate Material

Amorphous La-doped Al2O3 （La： Al2O3） thin films are deposited on n-type （100） Si substrates by rf magnetron co-sputterlng. The composition of the deposited films is measured by energy dispersive x-ray spectroscopy： Capacitance-voltage measurement shows that the dielectric constant k of La-doped Al2O3 films ranges from 8.5 to 11.6 with the increasing La content, and the highest k value of 11.6 is obtained for the 20.14% La content film. In the structure of the Al/La：Al2O3/Si metal oxide semiconductor, the dominant conduction stems from the space- charge-limited current at different temperatures. In addition, the wavelength dependence of the transmittance is studied by ultraviolet spectroscopy and the band gap of all the deposited films is above 5.5eV. The results demonstrate that La-doped Al2O3 can meet the requirement of next-generation gate materials.     

Two-color laser desorption of nanostructured MgO thin films

Neutral magnesium atom emission from nanostructured MgO thin films is induced using two-color nanosecond laser excitation. We find that combined vis/UV excitation, for single-color pulse energies below the desorption threshold, induces neutral Mg-atom emission with hyperthermal kinetic energies in the range of 0.1-0.2 eV. The observed metal atom emission is consistent with a mechanism involving rapid electron transfer to three-coordinated Mg surface sites. The two-color Mg-atom signal is significant only for parallel laser polarizations and temporally overlapped laser pulses indicating that intermediate excited states are short-lived compared to the 5 ns laser pulse duration.     

Preparation and characterisation of compositionally graded BaxSr1-xTiO3 thin films

Ba_xSr_1-xTiO₃ thin films with a compositional gradient of x=0.3 to 1 (in 0.1 mole fraction increments) were fabricated on Pt/Ti/SiO₂/Si substrates using a modified sol–gel technique. The graded film crystallised in a perovskite structure and consists of a uniform microstructure with comparatively larger grains. The room-temperature relative dielectric constant (ε_r) and dielectric loss (cosδ) at 100 kHz were found to be 305 and 0.03 respectively. Dielectric peaks were not observed in the temperature range from -20 °C to 120 °C. The dielectric constant and dielectric loss were almost independent of temperature. Polarisation–electric field measurements at room temperature revealed a saturated but slim hysteresis loop with a remanent polarisation (P_r) of 0.6 μC/cm² and a coercive field (E_c) of 2.4 kV/mm. The graded film behaves as a stack of Ba_xSr_1-xTiO₃ capacitors connected in series and hence the dielectric Curie peaks are removed. Received: 4 October 2001 / Accepted: 17 October 2001 / Published online: 23 January 2002     

Ultraviolet Photoelectric Effect in ZrO2 Single Crystals

Nanosecond photoelectric effect is observed in a ZrO2 single crystal at ambient temperature for the first time. The rise time is 20ns and the full width at half maximum is about 30ns for the photovoltaic pulse when the wafer surface of the ZrO2 single crystal is irradiated by 248 nm KrF laser pulses. The experimental results show that ZrO2 single crystals may be a potential candidate in UV photodetectors.     

Dependence of excess bismuth content in precursor sols on ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films fabricated by chemical solution deposition

Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were fabricated on Pt/Ti/SiO₂/Si(1 0 0) substrates by chemical solution deposition (CSD), and the dependence of ferroelectric and dielectric properties of the as-deposited BLT thin films on excess Bi content in precursor sols was studied. It is found that the prepared BLT thin film shows the best polarization-electric field, capacitance-voltage and dielectric constant (?_r)-frequency characteristics, when the value of excess Bi content in precursor sols is 10%. In detail, its remnant polarization (2P_r) value is 40 μC/cm², the capacitance tunability is 21% measured at room temperature under conditions of an applied voltage of 8 V and measurement frequency of 10 kHz, and the ?_r is 696 at 100 kHz frequency.     

Band bending measurement of HfO2/SiO2/Si capacitor with ultra-thin La2O3 insertion by XPS

The flat band voltage shifts of HfO₂/SiO₂/nSi capacitors with ultra-thin La₂O₃ insertion at HfO₂/SiO₂ interface have been confirmed using hard X-ray photoelectron spectroscopy (HX-PES). By increasing the amount of La₂O₃ insertion, the binding energy of Si 1s core spectra increases, which means that the surface potential of Si substrate also increases. A voltage drop difference of HfO₂ and La₂O₃ at SiO₂ interface can be estimated to be 0.40 V.