Role of oxygen in structural properties of annealed CuAlO2 films

CuAlO₂ films were sputtered on quartz substrates at different oxygen partial pressures (OPP) and carried out the annealing at 900 °C for 5 h in N₂ ambient. The structural properties of these films have been studied in detail by X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Annealed CuAlO₂ films are grown along the (0 0 1) preferential orientation. The film deposited at 20% OPP demonstrates the excellent crystalline behavior and the smallest electrical resistivity (41.8 Ω cm). At higher OPP, the crystalline behavior begins to degenerate up to the amorphous state at 60% OPP, and some micro-caves presented in the film surface become larger and deeper with the increase in OPP. We believe that the negative thermal expansion behavior associated with excess oxygen atoms is the primary responsibility for the change in structural properties.     

Incipient amorphous-to-crystalline transition in HfO2 as a function of thickness scaling and anneal temperature

A series of 1.4, 1.8, and 4.0 nm thick HfO₂ films deposited on Si(1 0 0) substrates have been measured by extended X-ray absorption fine-structure prior to anneal processing, following a standard post deposition anneal of 700 °C for 60 s in NH₃ ambient, and following an additional rapid thermal anneal cycle of 1000 °C for 10 s in N₂ ambient. Analysis of the second coordination shell gives clear evidence of increased ordering with increasing film thickness at each temperature. Similarly, increased ordering with increasing anneal temperature is evident for each film thickness. Although X-ray diffraction and high resolution transmission electron microscopy indicated the 1.4 nm HfO₂ samples to be amorphous, EXAFS has distinguished nanocrystalline from amorphous states for these films.     

Improving the performance of amorphous and crystalline silicon heterojunction solar cells by monitoring surface passivation

The influence of thermal annealing on the crystalline silicon surface passivating properties of selected amorphous silicon containing layer stacks (including intrinsic and doped films), as well as the correlation with silicon heterojunction solar cell performance has been investigated. All samples have been isochronally annealed for 1 h in an N₂ ambient at temperatures between 150 °C and 300 °C in incremental steps of 15 °C. For intrinsic films and intrinsic/n-type stacks, an improvement in passivation quality is observed up to 255 °C and 270 °C, respectively, and a deterioration at higher temperatures. For intrinsic/n-type a-Si:H layer stacks, a maximum minority carrier lifetime of 13.3 ms at an injection level of 10¹⁵ cm^? 3 has been measured. In contrast, for intrinsic/p-type a-Si:H layer stacks, a deterioration in passivation is observed upon annealing over the whole temperature range. Comparing the lifetime values and trends for the different layer stacks to the performance of the corresponding cells, it is inferred that the intrinsic/p-layer stack is limiting device performance. Furthermore, thermal annealing of p-type layers should be avoided entirely. We therefore propose an adapted processing sequence, leading to a substantial improvement in efficiency to 16.7%, well above the efficiency of 15.8% obtained with the ‘standard’ processing sequence.     

Synthesis of BaCeO3 powders by a fast aqueous citrate–nitrate process

A fast aqueous citrate–nitrate process has been successfully used to prepare the stoichiometric BaCeO₃ powders. It was found that an optimal amount of water added in the mixing process of barium nitrate, cerium nitrate, and citric acid is helpful on the formation of a clear gel that was subsequently formed by the condensation of added diethylene glycol monomers at room temperature. The gel was heated to an easily handled precursor in a powder form at 400 °C for 1 h. The precursors were characterized by X-ray powder diffraction (XRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA), Fourier transform infrared spectrometry (FTIR), and scanning electron microscopy (SEM). The phase evolution from the precursor to the desired BaCeO₃ powders by XRD and FTIR revealed that the presence of BaCO₃ is a complex problem in this process. A high-temperature trigonal BaCO₃ intermediate was found between 800 °C and 1000 °C by the in-situ X-ray powder diffraction experiments. The phase purity of the formed BaCeO₃ powders may be more properly identified by FTIR instead of XRD because of the amorphous feature of the carbonate phase. The TMA revealed that at 1100 °C part of the precursor crystallized to needle-shaped BaCeO₃ crystals accompanied by a small expansion, which is also related to the presence of BaCO₃ in the precursor, and this can be removed by a preheating treatment of the precursor at 900 °C for 4 h.     

Structural investigations of nitrided Nb2O5 and Nb2O5–SiO2 sol–gel derived films

Sol–gel derived xNb₂O₅–(100 ? x)SiO₂ films (where x = 100, 80, 60, 50, 40, 20, 0 mol%) were nitrided at various temperatures (800 °C, 900 °C, 1000 °C, 1100 °C and 1200 °C). The structural transformations occurring in the films as a result of ammonolysis were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The XRD results have shown that the temperatures below 1100 °C were too low to obtain a pure NbN phase in the samples. The AFM observations indicate that the formation of the NbN phase and the size of NbN grains are related to the silica content in the layer. NbN grains become more regular and larger as the niobium content increases. The maximum grain size of about 100 nm was observed for x = 100. Preparation of the Nb₂O₅–SiO₂ sol–gel derived layers and the subsequent nitridation is a promising method of inducing crystalline NbN in amorphous matrices. It follows from the XPS results that a small amount of Nb₂O₅ remains in the films after nitridation at 1200 °C and that nitrogen reacted not only with Nb₂O₅ but also with SiO₂.     

High-quality silicon/insulator heteroepitaxial structures formed by molecular beam epitaxy using Al2O3 and Si

Heteroepitaxial growth of γ-Al₂O₃ films on a Si substrate and the growth of Si films on the γ-Al₂O₃/Si structures by molecular beam epitaxy have been investigated. It has been found from AFM and RHEED observations that, γ-Al₂O₃ films with an atomically smooth surface with an RMS values of ∼3 Å and high crystalline quality can be grown on Si (1 1 1) substrates at substrate temperatures of 650–750°C. Al₂O₃ films grown at higher temperatures above 800°C, did not show good surface morphology due to etching of a Si surface by N₂O gas in the initial growth stage. It has also been found that it is possible to grow high-quality Si layers by the predeposition of Al layer followed by thermal treatment prior to the Si molecular beam epitaxy. Cross-sectional TEM observations have shown that the epitaxial Si had significantly improved crystalline quality and surface morphology when the Al predeposition layer thickness was 10 Å and the thermal treatment temperature was 900°C. The resulting improved crystalline quality of Si films grown on Al₂O₃ is believed to be due to the Al₂O₃ surface modification.     

Structural and optical properties of TiO2 thin films derived by sol–gel dip coating process

Nanocrystalline thin films of titanium dioxide have been fabricated on glass and silica substrates from partially hydrolyzed precursor solution. These films were subjected to heat treatment for 1 h at temperatures 100, 200, 300, 400, 500, 600, 700, 800 and 900 °C and characterized by XRD, SEM, XPS and optical techniques. As deposited films are found to be amorphous and also contain hydroxyl and organic functional groups. Films heat treated above 100 °C do not contain hydroxyl and organic functional groups. Microcrystalline behavior is observed in the films heat treated above 300 °C. Crystallite size increases from ∼5 to 50 nm as sintering temperature is increased from 300 to 700 °C. Formation of anatase phase with c-axis length 7.03 Å is observed in the films annealed up to 700 °C. These films peel off from the substrate beyond 700 °C annealing temperature. Density as well as refractive index of the films increases with increase in annealing temperature up to 700 °C. Refractive index is found to show Cauchys behavior. Transmission better than 70% is observed in the visible range. There is a strong absorption around 370 nm, which is attributed to band gap absorption of the material.     

Plastic deformation behavior of amorphous Fe78Si9B13 alloy at elevated temperature

The plastic deformation behavior of amorphous Fe₇₈Si₉B₁₃ alloy was investigated under uniaxial tension and gas pressure bulging. The deformed specimens were studied by means of XRD and SEM. It is shown that amorphous Fe₇₈Si₉B₁₃ ribbon has good deformation ability in the temperature range from 450 °C to 500 °C. The elongation of 36.3% and the relative bulging height (RBH) of 0.45 were obtained at 500 °C. In the uniaxial tension test, the amount of the crystalline α-Fe phase increases with deformation temperature below the crystallization temperature, which also suggests that the tensile stress promotes the crystallization of amorphous Fe₇₈Si₉B₁₃ ribbon. The suitable gas pressure bulging conditions for the specimens are 500 °C, 3.4 MPa and 30 min.     

Microstructure and properties of spark plasma sintered Fe–Cr–Mo–Y–B–C bulk metallic glass

Fabrication of Fe-based amorphous alloy using spark plasma sintering (SPS) process has been reported. Fully amorphous compacts with ～95% relative density were successfully sintered at temperature about 100 °C lower than glass transition temperature (T_g: 575 °C). Formation of crystalline Fe₂₃(C, B)₆ phases within near-fully dense (～99%) amorphous matrix is observed at sintering temperatures (>550 °C) close to glass transition temperature. Microstructure evolution in sintered compacts indicated that density, degree of crystallinity, and mechanical properties can be effectively controlled by optimizing SPS parameters.     

GeO2 based high k dielectric material synthesized by sol–gel process

Recently, there has been lot of research on new high dielectric constant (high k) materials for use in future generations of ultra-large scale integrated circuits (ULSI). There are number of requirements for the new high k materials, such as high dielectric constant, thermal stability (400 °C or higher), high mechanical strength, and good adhesion to neighboring layers. Keeping in view the properties required for the replacement of existing SiO₂ dielectrics, new high k dielectric material based on GeO₂ has been synthesized. Polycrystalline GeO₂ thin films have been deposited by simple, and cost effective sol–gel spin coating process. The obtained xerogel films of germanium oxide have been annealed at 400 °C, 600 °C and 800 °C for 3 h in argon atmosphere. Elemental composition, morphology, and phase analysis have been measured by employing X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction techniques, respectively. The formation of the hexagonal GeO₂ phase at and above 400 °C has been reported. The composition of the annealed films have been measured and found to be 68 at.% of O, 32 at.% of Ge for GeO₂, which are close to the stoichiometry of the GeO₂.     

Phase evolution on heat treatment of sodium silicate water glass

Heat treatment of sodium silicate water glass of the nominal composition Na₂O/SiO₂ = 1:3 was carried out from 100 °C up to 800 °C and the advancement of the resulting phases was followed up by powder X-ray diffraction, scanning electron microscopy and thermogravimetry along with differential thermal analysis. The water glass, initially being an amorphous solid, starts to form crystals of β-Na₂Si₂O₅ at about 400 °C and crystallizes the SiO₂ modification cristobalite at about 600 °C that coexists along with β-Na₂Si₂O₅ up to 700 °C. At 750 °C Na₆Si₈O₁₉ appears as a separate phase and beyond 800 °C, the system turns into a liquid.     

Structural and magnetic properties of nanocrystalline particles in an amorphous Fe73.5Nb3CuSi13.5B9 matrix

We report structural and magnetic properties of fine particles embedded in an amorphous magnetic matrix. As-quenched amorphous Fe_73.5Nb₃CuSi_13.5B₉ ribbons (FINEMET) were submitted to the thermal treatments of several times (1 ? t ? 240 min) at 570 °C using a conventional furnace. The analyses of the X-ray diffraction patterns at room temperature reveal that our samples consist of single phase Fe₃Si nanocrystals embedded in a residual amorphous phase. Magnetic measurements show that the saturation moment at T = 450 °C increases as a function of annealing time. This behavior is attributed to an increase of the fraction of nanocrystallites in the residual amorphous phase.     

Surface morphology of spin-coated As–S–Se chalcogenide thin films

Surface morphology and roughness of amorphous spin-coated As–S–Se chalcogenide thin films were determined using atomic force microscopy. Prepared films were coated from butylamine solutions with thicknesses d ∼ 100 nm and then annealed in a vacuum furnace at 45 °C and 90 °C for 1 h for their stabilization. The root mean square surface roughness analysis of surfaces of as-deposited spin-coated As–S–Se films indicated a very smooth film surface (with R_q values 0.42–0.45 ± 0.2 nm depending on composition). The nanoscale images of as-deposited films confirmed that surface of the films is created by domains with dimensions 20–40 nm, which corresponds to diameters of clusters found in solutions. The domain character of film surfaces gradually disappeared with increasing annealing temperature while the solvent was removed from the films. Middle-infrared transmission spectra recorded a decrease of intensities of vibration bands connected to N–H (at 3367 and 3292 cm⁻¹) and C–H (at 2965, 2935 and 2880 cm⁻¹) stretching vibrations. Temperature regions of solvent evaporation T = 60–90 °C and glass transformation temperatures T_g = 135–150 °C of spin-coated As–S–Se thin films were determined using a modulated differential scanning calorimetry.     

Enhancement of photoluminescence in SiCxNy nanoparticle films by addition of a Ni buffer layer

This work reports the effect of the presence of a Ni buffer layer on the photoluminescence (PL) of SiC_xN_y nanoparticle films prepared by RF plasma magnetron sputtering process in a reactive N₂ + Ar + H₂ gas mixture. An introduction of a Ni buffer of 80 nm or thicker remarkably improves the PL of the films. Annealing in a temperature range of 400–1100 °C is found to significantly affect the PL intensity. Optimal PL is achievable at 600 °C. X-ray photoelectron and Fourier-transform infrared spectroscopy suggest that the strong PL is directly related to the composition of the SiC_xN_y nanoparticle and the concentration of Si–O, and Si–N bonds. The results are relevant to the development of wide bandgap optoelectronic devices.     

Correlation between the method of preparation and the properties of the sol–gel HfO2 thin films

This work describes the preparation of HfO₂ thin films by the sol–gel method, starting with different precursors such as hafnium ethoxide, hafnium 2,4-pentadionate and hafnium chloride. From the solution prepared as mentioned above, thin films on silicon wafer substrates have been realized by ‘dip-coating’ with a pulling out speed of 5 cm min^?1. The films densification was achieved by thermal treatment for 10 min at 100 °C and 30 min at 450 °C or 600 °C, with a heating rate of 1 °C min^?1. The structural and optical properties of the films are determined employing spectroellipsometric (SE) measurements in the visible range (0.4–0.7 μm), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The main objective of this paper was to establish a correlation between the method of preparation (precursor, annealing temperature) and the properties of the obtained films. The samples prepared from pentadionate and ethoxide precursors are homogenous and uniform in thickness. The samples prepared starting from chloride precursor are thicker and proved to be less uniform in thickness. Higher non-uniformity develops in multi-deposition films or in crystallized films. A nano-porosity is present in the quasi-amorphous films as well in the crystallized one. For the samples deposited on silicon wafer, the thermal treatment induced the formation of a SiO₂ layer at the coating–substrate interface.     

Pyrolytic conversion studies of blended polycarbosilane and polyaluminasilazane

Multinuclear solid-state NMR spectroscopy, FTIR and Raman experiments are employed to investigate the pyrolytic conversion of blended polycarbosilane and polyaluminasilazane (denoted CA) up to 800 °C, with the aim of studying structural evolutions and interactions between polycarbosilane and polyaluminasilazane during the pyrolysis process. Vinyl and SiCH₃ units can react with Si–H, SiCH₃ and Si–CH₂–Si groups below 400 °C. These crosslinking reactions can increase the ceramic yield of the blended precursors. At 500 °C aromatic carbon is formed, and N–H and Si–H groups vanish at 600 °C and 700 °C, respectively. At 600 °C, SiCH₃ and Si–H units can further react with SiCN₃, SiC₂N₂, N–H and C–H units. An amount of amorphous carbon and CSi₄ and CSi₃H groups are detectable at 800 °C. Even at this temperature there are still many aromatic protons. In addition, there are also SiC₄, SiC₃N, SiCN₃ and SiN₄ units. Silicon forms SiN₄ more readily than SiC₄. Many AlN₅ groups transform into AlN₆ groups. The D and G bands of graphite are observed in CA pyrolyzed at 1400 °C. According to the XRD patterns, the reflection of crystalline β-Si₃N₄ vanishes at 1700 °C, and the residue pyrolyzed at 1800 °C mainly contains a large number of 2H-SiC/AlN solid solution crystals and a few β-SiC crystals.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.     

Selection of post-growth treatment parameters for atomic layer deposition of structurally disordered TiO2 thin films

Routes to atomic layer-deposited TiO₂ films with decreased leakage have been studied by using electrical characterization techniques. The combination of post-deposition annealing parameters, time and temperature, which provides measurable aluminum–titanium oxide–silicon structures – i.e., having capacitance–voltage curves which show accumulation behavior – are 625 °C, 10 min for p-type substrates, and 550 °C, 10 min for n-type substrates. The best annealing conditions for p-type substrates are 625 °C with the length extended to 30 min, which produces an interfacial state density of about 5–6 × 10¹¹ cm^?2 eV^?1, and disordered-induced gap state density below our experimental limits. We have also proved that a post-deposition annealing must be applied to TiO₂/HfO₂ and HfO₂/TiO₂/HfO₂ stacked structures to obtain adequate measurability conditions.     

MOCVD and characterization of Hf-silicate thin films using HTB and TEMAS

Hafnium silicate (HfSi_xO_y) films were deposited by metal-organic chemical vapor deposition (MOCVD) using a combination of precursors: hafnium tetra-tert-butoxide [Hf(OC(CH₃)₃)₄, HTB] and tetrakis-ethylmethylamino silane [Si(N(C₂H₅)(CH₃))₄, TEMAS]. The activation energy was independent on the ratio of precursor amounts in the surface reaction regime. The grown films showed Hf-rich characteristics and the impurity concentrations were less than 1 at.% (below detection limits). Hafnium silicate films were amorphous up to 700 °C annealing. Hf/(Hf + Si) composition ratio and dielectric constant (k) of the Hf-silicate films decreased by increasing the growth temperature above 270 °C.     

Low-temperature metal-induced crystallization of Mn-containing amorphous Ge thin films

This work focuses on the crystallization of amorphous germanium (a-Ge) thin films induced by manganese species. A series of Mn-containing a-Ge films ([Mn] ~ 0?3.7 at.% range) was deposited at 150 °C by the cosputtering technique. After deposition, all films were submitted to isochronal thermal annealing treatments up to 600 °C and analyzed by Raman scattering, optical transmission spectroscopy and electrical resistivity measurements. The experimental results indicate that: (a) Mn impurity lowers the crystallization temperature of a-Ge in ~ 100 °C, as confirmed by the Raman analyses, (b) the optical properties of the films are affected by both the insertion of Mn and the temperature of thermal treatment, with the optical bandgap staying in the range of ~ 0.7?1 eV, and (c) the electrical resistivity of the samples is also influenced by the Mn concentration and by the temperature of annealing, varying between ~ 1.0×10¹ and 1.6×10⁴ Ω cm. These experimental observations were systematically studied and the possible reasons associated to them are presented and discussed.