Structural and optical characterization of Ce-doped Gd2SiO5 films by sol-gel technique

Cerium-doped Gd₂SiO₅ (GSO:Ce) films have been prepared on (1 1 1) silicon substrates by the sol-gel technique. Annealing was performed in the temperature range from 400 to 1000 °C. X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the structure and morphology of GSO:Ce films. Results showed that GSO:Ce film starts to crystallize at about 600 °C, GSO:Ce films have a preferential (0 2 1) orientation, as the annealing temperature increase, the (0 2 1) peak intensity increases, the full width of half maximum (FWHM) decreases, and the grain size of GSO:Ce films increases. Emission spectra of GSO:Ce films were measured, results exhibit the characteristic blue emission peak at 427 nm.     

Formation of silicon nanodots from dysprosium-doped amorphous SiCxOy films grown by hot-filament assisted chemical vapor deposition of CH3SiH3 and Dy(DPM)3 gas jets

We report on Si nanodot formation by chemical vapor deposition (CVD) of ultrathin films and following oxidation. The film growth was carried out by hot-filament assisted CVD of CH₃SiH₃ and Dy(DPM)₃ gas jets at the substrate temperature of 600 °C. The transmission electron microscopy observation and X-ray photoelectron spectroscopy analysis indicated that ∼35 nm Dy-doped amorphous silicon oxycarbide (SiC_xO_y) films were grown on Si(1 0 0). The Dy concentration was 10-20% throughout the film. By further oxidation at 860 °C, the smooth amorphous film was changed to a rough structure composed of crystalline Si nanodots surrounded by heavily Dy-doped SiO₂.     

Effect of temperature on pulsed laser deposition of HgCdTe films

HgCdTe thin films have been deposited on Si(1 1 1) substrates at different substrate temperatures by pulsed laser deposition (PLD). An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the substrate temperature on the crystalline quality, surface morphology and composition of HgCdTe thin films were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). The results show that in our experimental conditions, the HgCdTe thin films deposited at 200 °C have the best quality. When the substrate temperature is over 250 °C, the HgCdTe film becomes thermodynamically unstable and the quality of the film is degraded.     

Influence of substrate temperature on the texture of barium ferrite film by magnetron sputtering

Barium ferrite thin films have been prepared by radio frequency magnetron sputtering on a sapphire (0 0 1) substrate at substrate temperature of 500 °C and 650 °C, respectively. The films were further annealed in air at 1000 °C for 5 h. X-ray diffraction shows that the films at the lower substrate temperatures have a good epitaxial relation with respect to the substrate, while the samples under the higher substrate temperatures have (1 0 9) planes parallel to the substrate. The remanence ratio decreases from 0.82 to 0.47 when the substrate temperature is increased. We attribute the variation of the growth direction to the enhanced vertical mobility of the deposited atoms when the substrate temperature is increased.     

Study of electronic structures for Fe thin films deposited on Si- and C-faces of 4H-SiC substrates by soft X-ray emission spectroscopy

Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system are fundamentally important from the viewpoint of device performance.We study interface electronic structure of iron thin film deposited on silicon (Si)- and carbon (C)-face of 4H-SiC(0 0 0 1) by using a soft X-ray emission spectroscopy (SXES). For specimens of Fe (50 nm)/4H-SiC (substrate) contact systems annealed at 700 and 900 °C, the Si L_2,3 emission spectra indicate different shapes and peak energies from the substrate depending on thermal-treated temperature. The product of materials such as silicides is suggested. Further, from comparison of Si L_2,3 emission spectra between Si- and C-face for the same annealing temperature at 700 °C, it is concluded that the similar silicides and/or ternary materials are formed on the two surfaces. However for those of 900 °C, the film on substrate is composed of the different silicide and/or ternary materials.     

Solid phase epitaxy of Ge films on CaF2/Si(1 1 1)

At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF₂/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 °C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 °C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.     

Enhanced field emission from Si doped nanocrystalline AlN thin films

Si doped and undoped nanocrystalline aluminum nitride thin films were deposited on various substrates by direct current sputtering technique. X-ray diffraction analysis confirmed the formation of phase pure hexagonal aluminum nitride with a single peak corresponding to (1 0 0) reflection of AlN with lattice constants, a = 0.3114 nm and c = 0.4986 nm. Energy dispersive analysis of X-rays confirmed the presence of Si in the doped AlN films. Atomic force microscopic studies showed that the average particle size of the film prepared at substrate temperature 200 °C was 9.5 nm, but when 5 at.% Si was incorporated the average particle size increased to ∼21 nm. Field emission study indicated that, with increasing Si doping concentration, the emission characteristics have been improved. The turn-on field (E_to) was 15.0 (±0.7) V/μm, 8.0 (±0.4) V/μm and 7.8 (±0.5) V/μm for undoped, 3 at.% and 5 at.% Si doped AlN films respectively and the maximum current density of 0.27 μA/cm² has been observed for 5 at.% Si doped nanocrystalline AlN film. It was also found that the dielectric properties were highly dependent on Si doping.     

Thermal stability of Ag films in air prepared by thermal evaporation

The thermal stability of silver films in air has been studied. Pure Ag films, 250 nm in thickness, were prepared on glass substrates by thermal evaporation process, and subsequently annealed in air for 1 h at temperatures between 200 and 400 °C. The structure and morphology of the samples were investigated by X-ray diffraction, Raman spectra and atomic force microscopy. It is found that the crystallization enhances for the annealed films, and film surface becomes oxidized when annealing temperature is higher than 350 °C. The electrical and optical properties of the films were studied by van der Pauw method and spectrophotometer, respectively. Reflectance drops sharply as Ag films are annealed at temperatures above 250 °C. Film annealed at 250 °C has the maximum surface roughness and the minimum reflectance at 600 nm optical wavelength. Film annealed at 200 °C has the minimum resistivity, and resistivity increases with the increasing of the annealing temperature when temperature is above 200 °C. The results show that both oxidization on film surface and agglomeration of silver film result in infinite of electrical resistivity as the annealing temperature is above 350 °C.     

Epitaxially grown ZnO thin films on 6H-SiC(0 0 0 1) substrates prepared by spin coating-pyrolysis

Epitaxially grown ZnO thin film on 6H-SiC(0 0 0 1) substrate was prepared by using a spin coating-pyrolysis with a zinc naphthenate precursor. As-deposited film was pyrolyzed at 500 °C for 10 min in air and finally annealed at 800 °C for 30 min in air. In-plane alignment of the film was investigated by X-ray pole-figure analysis. Field emission-scanning electron microscope, scanning probe microscope, and He-Cd laser (325 nm) was used to analyze the surface morphology, the surface roughness and photoluminescence of the films. In the photoluminescence spectra, near-band-edge emission with a broad deep-level emission was observed. The position of the near-band-edge peak was around 3.27 eV.     

The effects of substrate temperature on the structure, morphology and photoluminescence properties of pulsed laser deposited SrAl2O4:Eu,Dy thin films

In this study, SrAl₂O₄:Eu²⁺,Dy³⁺ thin film phosphors were deposited on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique. The films were deposited at different substrate temperatures in the range of 40-700 °C. The structure, morphology and topography of the films were determined by using X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) data was collected in air at room temperature using a 325 nm He-Cd laser as an excitation source. The PL spectra of all the films were characterized by green phosphorescent photoluminescence at ∼530 nm. This emission was attributed to 4f⁶5d¹→4f⁷ transition of Eu²⁺. The highest PL intensity was observed from the films deposited at a substrate temperature of 400 °C. The effects of varying substrate temperature on the PL intensity were discussed.     

Effect of substrate temperature and annealing temperature on the structural, electrical and microstructural properties of thin Pt films by rf magnetron sputtering

Influence of both substrate temperature, T_s, and annealing temperature, T_a, on the structural, electrical and microstructural properties of sputtered deposited Pt thin films have been investigated. X-ray diffraction results show that as deposited Pt films (T_s = 300, 400 °C) are preferentially oriented along (1 1 1) direction. A little growth both along (2 0 0) and (3 1 1) directions are also noticed in the as deposited Pt films. After annealing in air (T_a = 500-700 °C), films become strongly oriented along (1 1 1) plane. With annealing temperature, average crystallite size, D, of the Pt films increases and micro-strain, e, and lattice constant, a₀, decreases. Residual strain observed in the as deposited Pt films is found to be compressive in nature while that in the annealed films is tensile. This change in the strain from compressive to tensile upon annealing is explained in the light of mismatch between the thermal expansion coefficients of the film material and substrate. Room temperature resistivity of Pt films is dependant on both the T_s and T_a of the films. Observed decrease in the film resistivity with T_a is discussed in terms of annihilation of film defects and grain-boundary. Scanning electron microscopic study reveals that as the annealing temperature increases film densification improves. But at an annealing temperature of ∼600 °C, pinholes appear on the film surface and the size of pinhole increases with further increase in the annealing temperature. From X-ray photoelectron spectroscopic analysis, existence of a thin layer of chemisorbed atomic oxygen is detected on the surfaces of the as deposited Pt films. Upon annealing, coverage of this surface oxygen increases.     

Crystallization and surface morphology evolution of erbium fluoride films on different substrates

Erbium fluoride (ErF₃) films were thermally deposited on Ge(1 1 1), Si(0 0 1) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(1 1 1) at 200 °C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100 °C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200 °C. The crystallization temperature (T_c) of ErF₃ films on the three substrates has the relation which is which is induced by the wetting angle of ErF₃ films on different substrates.     

Investigation of thin TiO2 films cosputtered with Si species

Titanium dioxide (TiO₂) films were fabricated by cosputtering titanium (Ti) target and SiO₂ or Si slice with ion-beam-sputtering deposition (IBSD) technique and were postannealed at 450 °C for 6 h. The variations of oxygen bonding, which included high-binding-energy oxygen (HBO), bridging oxygen (BO), low-binding-energy oxygen (LBO), and three chemical states of titanium (Ti⁴⁺, Ti³⁺ and Ti²⁺) were analyzed by X-ray photoelectron spectroscopy (XPS). The enhancement of HBO and reduction of BO in O 1s spectra as functions of SiO₂ or Si amount in cosputtered film imply the formation of Si-O-Ti linkage. Corresponding increase of Ti³⁺ in Ti 2p spectra further confirmed the property modification of the cosputtered film resulting from the variation of the chemical bonding. An observed correlation between the chemical structure and optical properties, refractive index and extinction coefficient, of the SiO₂ or Si cosputtered films demonstrated that the change of chemical bonding in the film results in the modification of optical properties. Furthermore, it was found that the optical properties of the cosputtered films were strongly depended on the cosputtering targets. In case of the Si cosputtered films both the refractive indices and extinction coefficients were reduced after postannealing, however, the opposite trend was observed in SiO₂ cosputtered films.     

The influence of substrate on the properties of Er2O3 films grown by magnetron sputtering

The structural properties and the room temperature luminescence of Er₂O₃ thin films deposited by RF magnetron sputtering have been studied. Films characterized by good morphological properties have been obtained by using a SiO₂ interlayer between the film and the Si substrate. The evolution of the properties of the Er₂O₃ films due to rapid thermal annealing processes in O₂ ambient performed at temperatures in the range 800-1200 °C has been investigated in details. The existence of well-defined annealing conditions (temperature of 1100 °C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. The same annealing processes are less effective when Er₂O₃ is deposited on Si. In this latter case interfacial reactions and pit formation occur, leading to a material characterized by stronger non-radiative phenomena that limit the PL efficiency.     

Structural characterization of β-V2O5 films prepared by DC reactive magnetron sputtering

β-V₂O₅ films were successfully prepared on silicon substrates by direct current (DC) reactive magnetron sputtering. X-ray diffraction (XRD), Raman spectra and field emission scan electron spectroscopy (SEM) were used to characterize the samples. Results revealed that the deposition temperature significantly influenced on the crystal structure of V₂O₅ films in the growth process. When the deposition temperature was below 500 °C, the sputtered film exhibited the α-V₂O₅ structure. However, β-V₂O₅ film was successfully obtained at 550 °C. High deposition temperature might provide V and O ions high mobility and energy in the reactive sputtering process, which induced the metastable β-V₂O₅ phase formed. The thermal stability of β-V₂O₅ film was studied by micro-Raman spectroscopy. The structure of sputtered β-V₂O₅ film was unstable under high temperature conditions (beyond 500 °C).     

The structural and optical properties of ZnO/Si thin films by RTA treatments

ZnO/Si thin films were prepared by rf magnetron sputtering method and some of the samples were treated by rapid thermal annealing (RTA) process at different temperatures ranging from 400 to 800 °C. The effects of RTA treatment on the structural properties were studied by using X-ray diffraction and atomic force microscopy while optical properties were studied by the photoluminescence measurements. It is observed that the ZnO film annealed at 600 °C reveals the strongest UV emission intensity and narrowest full width at half maximum among the temperature ranges studied. The enhanced UV emission from the film annealed at 600 °C is attributed to the improved crystalline quality of ZnO film due to the effective relaxation of residual compressive stress and achieving maximum grain size.     

Rapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates

The structural and optical properties of ZnO films deposited on Si substrate following rapid thermal annealing (RTA) have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and photoluminescence (PL) measurements. After RTA treatment, the XRD spectra have shown an effective relaxation of the residual compressive stress, an increase of the intensity and narrowing of the full-width at half-maximum (FWHM) of the (0 0 2) diffraction peak of the as-grown ZnO film. AFM images show roughening of the film surface due to increase of grain size after RTA. The PL spectrum reveals a significant improvement in the UV luminescence of ZnO films following RTA at 800 °C for 1 min.     

Surface characterization and microstructure of ITO thin films at different annealing temperatures

In this study, the electron beam evaporation method is used to generate an indium tin oxide (ITO) thin film on a glass substrate at room temperature. The surface characteristics of this ITO thin film are then investigated by means of an AFM (atomic force microscopy) method. The influence of postgrowth thermal annealing on the microstructure and surface morphology of ITO thin films are also examined. The results demonstrate that the film annealed at higher annealing temperature (300 °C) has higher surface roughness, which is due to the aggregation of the native grains into larger clusters upon annealing. The fractal analysis reveals that the value of fractal dimension D_f falls within the range 2.16-2.20 depending upon the annealing temperatures and is calculated by the height-height correlation function.     

Room temperature photoluminescence mechanism of SiOx film after annealing at different temperatures

SiO_x films were deposited on Si(1 0 0) substrates by evaporation of SiO powder. The samples were annealed from room-temperature (RT) to 1100 °C. After the samples were cooled down to RT, photoluminescence (PL) spectra from these samples were measured. It was found that when the annealing temperature Ta is not higher than 1000 °C, there is a PL centered at 620 nm, and with Ta increasing the intensity increases at first and then decreases when Ta is higher than 500 °C. When Ta is no less than 1000 °C another PL peak located at 720 nm appears. Combined with Raman and XRD spectra, we confirm that the latter PL is from Si nanocrystals that start to form when Ta is higher than 1000 °C. PL spectra for Ta<900 °C were discussed in detail and was attributed to defects in the matrix rather than from Si clusters.     

Electrostatic spray deposited zinc oxide films for gas sensor applications

In this work, thin films of zinc oxide (ZnO) for gas-sensor applications were deposited on platinum coated alumina substrate, using electrostatic spray deposition (ESD) technique. As precursor solution zinc acetate in ethanol was used. Scanning electron microscopy (SEM) evaluation showed a porous and homogeneous film morphology and the energy dispersive X-ray analysis (EDX) confirmed the composition of the films with no presence of other impurities. The microstructure studied with X-ray diffraction (XRD) and Raman spectroscopy indicated that the ZnO oxide films are crystallized in a hexagonal wurtzite phase. The films showed good sensitivity to 1 ppm nitrogen dioxide (NO₂) at 300 °C while a much lower sensitivity to 12 ppm hydrogen sulphide (H₂S).