Crystallization characteristics of Li2O–Nb2O5 compound films on sapphire substrates and formation of crack-free and thick LiNbO3 epitaxial films

The formation of crystal phases in Li₂O–Nb₂O₅ compound films deposited on sapphire C-plane and A-plane substrates was studied by X-ray diffraction. Sufficiently oxidized samples with Li-deficient or stoichiometric compositions were prepared by co-sputtering from LiNbO₃ (LN) and Li₂O targets. Crystallization during deposition at elevated temperatures and solid-phase crystallization (SPC) of deposited amorphous films were investigated. For films on sapphire C-planes, nucleation into Li₃NbO₄(222) domains occurred at the onset temperature of crystallization. In the case of stoichiometric films, the LN(006) signal indicating epitaxial growth was the primary one for crystallization during deposition above 460 °C and SPC above 750 °C. Misoriented LN(104) domains tended to coexist with LN(006) domains. In the case of Li-deficient films, LiNb₃O₈(_602) domains coexisted with LN(006) at temperatures above 750 °C as a result of Li₂O loss. For films on sapphire A-planes, epitaxial LN(110) domains were predominant. Li₃NbO₄(222) domains were totally absent and the signal intensity of LiNb₃O₈(212) was less than 10% of that of LN(110) even for the Li-deficient films, which reflected fast crystallization of LN(110) domains. The SPC rate of stoichiometric film was considerably lower than that of Li-deficient film. As-crystallized LN film on the sapphire C-plane was strained with a narrow domain width. Thick film cracked as a result of stress caused by lattice mismatch with the substrate. In contrast, LN film processed by SPC was not strained and had large domains with flat film surface. Based on these results, crack-free 1-μm-thick LN epitaxial films on a sapphire C-plane were achieved. First, an amorphous LN buffer was subject to SPC to obtain a relaxed buffer layer. Subsequently, a stress-free thick LN overlayer was grown by co-sputtering from Li₂O and LN targets at 530 °C. The relaxed buffer layer effectively mitigated the strain caused by the lattice mismatch with the substrate.     

Preparation and characterization of TiO2 thin films by PECVD on Si substrate

Titanium oxide thin films were prepared on p-Si(l00) substrate by plasma enhanced chemical vapor deposition using high purity titanium isopropoxide and oxygen. The deposition rate was little affected by oxygen flow rate, but significantly affected by RF power, substrate temperature, carrier gas flow rate, and chamber pressure. Morphology of the film became coarser with increasing deposition time and chamber pressure, and the film showed less uniformity at high deposition rates. It was also found that the overall deposition process is controlled by heterogeneous surface reaction below 200°C., but controlled by mass transfer of reactants at higher temperatures. TiO₂ films deposited at temperatures lower than 400°C was amorphous, but showed the anatase crystalline structure upon 400°C deposition. The dielectric constant was about 47 for the films post-treated by rapid-thermal annealing (RTA) at 800°C. The leakage current was about 2×10⁻⁵ A/cm² for the films deposited at 400°C and RTA-treated at 600°C. However, it was decreased to less than 3×10⁻⁷ A/cm² for the film RTA-treated at 800°C.     

Mechanical Properties and Microstructural Characterization of Amorphous SiCxNy Thin Films After Annealing Beyond 1100°C

The effect of thermal annealing on structure and mechanical properties of amorphous SiC_xN_y (y ≥ 0) thin films was investigated up to 1500°C in air and Ar. The SiC_xN_y films (2.2–3.4 μm) were deposited by reactive DC magnetron sputtering on Si, Al₂O₃ and α‐SiC substrates without intentional heating and at 600°C. The SiC target with small excess of carbon was sputtered at various N₂/Ar gas flow ratios (0–0.48). The nitrogen content in the films changes in the range 0–43 at.%. Hardness and elastic modulus (nanoindentation), change in film thickness, film composition, and structure (Raman spectroscopy, XRD) were investigated in dependence on annealing temperature and nitrogen content. All SiC_xN_y films preserve their amorphous structure up to 1500°C. The hardness of all as‐deposited and both air‐ and Ar‐annealed SiC_xN_y films decreases with growth of nitrogen content. The annealing in Ar at temperatures of 1100°C–1300°C results in noticeable hardness growth despite the ordering of graphite‐like structure in carbon clusters in nitrogen free films. Unlike the SiC, this graphitization leads to hardness saturation of SiCN films starting above 900°C, especially for films with higher nitrogen content (deposited at higher N₂/Ar). This indicates the practical hardness limit achievable by thermal treatment for SiC_xN_y films deposited on unheated substrates. The ordering in carbon phase is facilitated by the presence of nitrogen in the films and its extent is controlled by the N/C atomic ratio. The suppression of graphitization was observed for N/C ranging between 0.5–0.7. Films deposited at 600°C show higher hardness and oxidation resistance after annealing in comparison with those deposited on unheated substrates. Hardness reaches 40 GPa for SiC and ~28 GPa for SiC_xN_y (35 at.% of nitrogen). Such a high hardness of SiC film stems from its partial crystallization. Annealing of SiC_xN_y film (35 at.% of N) in Ar at 1400°C is accompanied by formation of numerous hillocks (indicating heterogeneous structure of amorphous films) and redistribution of film material.     

Phase development and crystallization of CuAlO2 thin films prepared by pulsed laser deposition

A polycrystalline CuAlO₂ single-phase target was fabricated by the conventional solid-state reaction route using Cu₂O and Al₂O₃. Thin films of CuAlO₂ were deposited by a pulsed laser deposition process on sapphire substrates at different temperatures. Then, post-annealing was followed at different conditions, and the phase development process of the films was examined. As grown thin films in the temperature range of 450–650 °C were amorphous. The c-axis oriented single phase of CuAlO₂ thin films were obtained when the films were post-annealed at 1100 °C in air after growing at 650 °C. Phi-scan of the film clearly showed 12 peaks, each of which are positioned at intervals of 30°. This is thought to be caused by the rhombohedral structured CuAlO₂ thin film growing in the states of 30° tilt during the annealing process. Hall effect analysis of the film was carried out.     

Characteristics of aluminum films prepared by metalorganic chemical vapor deposition using dimethylethylamine alane on the plasma-pretreated TiN surfaces

Aluminum films were prepared on H₂-plasma pretreated TiN substrates at deposition temperatures of 60-250 °C by metallorganic chemical vapor deposition using dimethylethylamine alane as a precursor. The films were highly pure and the growth rates were 3-50 nm/min, where the lowest deposition temperature was 60 °C. The resistivity was as low as 2.8 μΩcm. High substrate temperatures tended to favor a low resistivity and smooth surface morphology of the films, compared to films with a low temperature at a given thickness. Numerous empty pores appeared in the Al films deposited at a temperature below 150 °C when the film thickness exceeded 200 nm. The number of these pores tended to increase with decrease in temperature. However, in films deposited at temperatures above 200 °C, there were no pores and the large grains were interconnected to a high degree. Higher deposition temperatures yielded a greater preference of the (111) orientation of Al films.     

Polymeric semiconducting carbon from fullerene by pulsed laser ablation

The polymeric semiconducting carbon films are grown on silicon and quartz substrates by excimer (XeCl) pulsed laser deposition (PLD) technique using fullerene C₆₀ precursor. The substrate temperature is varied up to 300 °C. The structure and optical properties of the films strongly depend on the substrate temperature. The grain size is increased and uniform polymeric film with improved morphology at higher temperature is observed. The Tauc gap is about 1.35 eV for the film deposited at 100°C and with temperature the gap is decreased upto 1.1 eV for the film deposited at 250 °C and increased to about 1.4 eV for the film deposited at 300 °C. The optical absorption properties are improved with substrate temperature. Raman spectra show the presence of both G peak and D peak and are peaked at about 1590 cm^− 1 and 1360 cm^− 1, respectively for the film deposited at 100 °C. The G peak position remains almost unchanged while D peak has changed only a little with temperature might be due to its better crystalline structure compared to the typical amorphous carbon films and might show interesting in device such as, optoelectronic applications.     

Annealing Effect on the Properties of Cu(In0.7Ga0.3)Se2 Thin Films Grown by Femtosecond Pulsed Laser Deposition

This work reports the crystallization, microstructure, and surface composition of CuIn_0.7Ga_0.3Se₂ (CIGS) thin films grown by femtosecond pulsed laser deposition at different annealing temperatures. The structural and optical properties of the CIGS films were characterized by X‐ray diffraction, Raman scattering, UV‐visible spectroscopy, and Hall effect measurement. The results indicate that binary crystals of CuSe initially formed on the as‐deposited film, but then completely turned into a quaternary chalcopyrite structure after annealing at 400°C. Phase transformation significantly affects the surface morphology, Hall properties, and band gap. Transmission electron microscopy further revealed that an interface between the Mo substrate and CIGS crystallites contains an amorphous layer even at the high temperature of 500°C. For the application of photovoltaic devices, we also report on the photoresponse of both as‐deposited and annealed films as demonstrated by preliminary tests.     

Atomic layer deposition of TiO2 from tetrakis-dimethylamido-titanium and ozone

Ozone (O₃) was employed as an oxygen source for the atomic layer deposition (ALD) of titanium dioxide (TiO₂) based on tetrakis-dimethyl-amido titanium (TDMAT). The effects of deposition temperature and O₃ feeding time on the film growth kinetics and physical/chemical properties of the TiO₂ films were investigated. Film growth was possible at as low as 75 °C, and the growth rate (thickness/cycles) of TiO₂ was minimally affected by varying the temperatures at 150–225 °C. Moreover, saturated growth behavior on the O₃ feeding time was observed at longer than 0.5 s. Higher temperatures tend to provide films with lower levels of carbon impurities. The film thickness increased linearly as the number of cycles increased. With thicker films and at higher deposition temperatures, surface roughening tended to increase. The as-deposited films were amorphous regardless of the substrate temperatures and there was no change of crystal phase even after annealing at temperatures of 400–600 °C. The films deposited in 0.5 mm holes with an aspect ratio of 3: 1 showed an excellent conformality.     

Influence of deposition parameters on the structure and microstructure of Bi12TiO20 films obtained by pulsed laser deposition

The structure, morphology and surface roughness of Bi₁₂TiO₂₀ (BTO) thin films grown on R-sapphire by pulsed laser deposition (PLD) were studied at different substrate temperatures, target-substrate distances, oxygen pressures and laser-pulse repetition rates. Although the substrate temperature seems to be the most important experimental parameter, the gas pressure and the target–substrate distance played important role on the phase formed and film thickness, with a significant effect of the laser-pulse repetition rate on the films thickness and preferred orientation of the deposited film. Single-phase γ-Bi₁₂TiO₂₀ was obtained on substrates at 650?°C, while several BTO metastable phases were observed in films deposited on substrates at temperatures between 500 and 600?°C. By the first time, thin films of pure and textured δ-Bi₁₂TiO₂₀ were successfully growth on substrates at 450?°C. When annealed, all the films deposited at lower temperatures resulted in the thermodynamically stable γ-Bi₁₂TiO₂₀.     

Low surface temperature synthesis and characterization of diamond thin films

Polycrystalline diamond films are deposited on p-type Si(100) and n-type SiC(6H) substrates at low surface deposition temperatures of 370–530 °C using a microwave plasma enhanced chemical vapor deposition (MPECVD) system. The surface temperature during deposition is monitored by an IR pyrometer capable of measuring temperature between 250 and 600 °C in a microwave environment. The lower deposition temperature is achieved by using an especially designed cooling stage. The influence of the deposition conditions on the growth rate and structure of the diamond film is investigated. A very high growth rate up to 1.3 μm/h on SiC substrate at 530 °C surface temperature is attributed to an optimized Ar-rich Ar/H₂/CH₄ gas composition, deposition pressure, and microwave power. The structure and microstructure of the films are characterized by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. A detailed stress analysis of the deposited diamond films of grain sizes between 2 and 7 μm showed a net tensile residual stress and predominantly sp³-bonded carbon in the deposited films.     

Temperature influence on the interlayer and surface morphology of diamond coating on 3D porous titanium substrates

Nanocrystalline (NCD) and/or microcrystalline (MCD) diamond films grown on three-dimensional porous titanium (Ti) substrate were obtained by hot filament chemical vapor deposition (HFCVD) technique. The morphology variation of diamond films grown on porous three-dimensional titanium substrate was studied at four different deposition temperatures to investigate their influence on nucleation density. Scanning electron microscopy images depicted the continuous change from microcrystalline diamond grains with a random crystallographic orientation, at 500 °C and 600 °C, to a cauliflower-like structure for deposits at 700 °C and 800 °C. Visible Raman spectroscopy confirmed the good quality of diamond films and revealed that the amount of amorphous carbon increased associated to the film morphology changes from MCD to NCD. X-ray diffraction analyses, performed both through θ–2θ scans and at grazing incidence angle, allowed the investigation of the crystallographic properties and structural evolution of the different film/substrate interface phases, such as TiC(111), TiC(200) and TiH₂. The results revealed that the temperature enhanced the nucleation sites for diamond growth.     

Utilizing TiO2 amorphous precursors for polymorph selection: An in situ TEM study of phase formation and kinetics

Selective synthesis of metastable polymorphs requires a fundamental understanding of the complex energy landscapes in which these phases form. Recently, the development of in situ high temperature and controlled atmosphere transmission electron microscopy has enabled the direct observation of nucleation, growth, and phase transformations with near atomic resolution. In this work, we directly observe the crystallization behavior of amorphous TiO₂ thin films grown under different pulsed laser deposition conditions and quantify the mechanisms behind metastable crystalline polymorph stabilization. Films deposited at 10 mTorr chamber oxygen pressure crystallize into nanocrystalline Anatase at 325°C, whereas films deposited at 2 mTorr crystallize into significantly larger needle-like grains of Brookite and Anatase at 270°C. Increasing film deposition rate by a factor of 4 results in a 10× increase in the crystalline growth front velocity as well as a decrease in crystallization temperature from 270°C to 225°C. Engineering the amorphous precursor state through deposition conditions therefore provides routes to microstructure control and the accessibility of higher energy metastable phases.     

Epitaxial growth of LaMnO3 thin films on different single crystal substrates by polymer assisted deposition

Structure of epitaxial LaMnO₃ thin films grown on different single crystal substrates by unconventional polymer assisted deposition (PAD) method was investigated. Epitaxial films were prepared from lanthanum manganite water based solutions deposited by spin coating on single crystal MgO (001), SrTiO₃ (001) and SrTiO₃ (110) substrates, and the influence of substrate type on the film structure was analysed. Better uniformity of the epitaxial LaMnO₃ films on SrTiO₃ substrates was obtained, but a non-stoichiometric La_1-xMnO₃ phase was formed after the heat treatment at 750 °C. In addition, the prepared thin films were multiple annealed at different temperatures up to 900 °C, in order to investigate importance of post-annealing treatment. Epitaxial nature of the prepared films was preserved after annealing at up to 900 °C and the structure rearrangement through formation of cell closer to bulk stochiometric LaMnO₃ phase was observed.     

Substrate temperature dependent bolometric properties of TiO2−x films for infrared image sensor applications

In this study, we investigated the substrate temperature (T_S) dependent bolometric properties on TiO_2−x films for infrared image sensor applications. The film crystallinity was changed from amorphous to rutile phase with increasing the T_S. The decrement of resistivity with temperature in TiO_2−x test-devices confirms the typical semiconducting property. All the test pattern devices have linear I-V characteristic performance which infers that the ohmic contact was well formed at the interface between the TiO_2−x and the Ti electrode. The resistivity, activation energy (E_a) and the temperature coefficient of resistance (TCR) values of the device samples were decreased up to 200 °C of T_S. The sample deposited at 200 °C had a significantly low 1/f noise parameter and a high universal bolometric parameter (β). However, at the substrate temperature of 250 °C, the E_a, TCR and the 1/f noise values were increased due to increase of the resistivity. The TCR and the 1/f noise values are proportional to the resistivity of TiO_2−x films. As a result, the low resistivity of TiO_2−x sample deposited at 200 °C is a viable bolometric material for uncooled IR image sensors.     

Atomic layer deposition of pure In2O3 films for a temperature range of 200–300 °C using heteroleptic liquid In(DMAMP)2(OiPr) precursor

In₂O₃ films were deposited by atomic layer deposition (ALD) using a newly synthesized heteroleptic In precursor, In(DMAMP)₂(OⁱPr), and O₃ at 150–300 °C. Self-limiting growth characteristics were exhibited for a wide ALD temperature range of 200–300 °C and growth rate of 0.029–0.033 nm/cycle. At a low temperature of 150 °C, the amorphous In₂O₃ film was deposited, while polycrystalline In₂O₃ films were achieved at 200–300 °C. The In₂O₃ films grown in this ALD temperature range had high densities of 7.0–7.2 g/cm³, which are comparable to those of bulk In₂O₃. At all growth temperatures (150–300 °C), no carbon or nitrogen impurities were detected, suggesting high reactivity of the In(DMAMP)₂(OⁱPr) precursor. The ALD In₂O₃ films showed n-type electronic property with high electron concentrations of 1.6 × 10²⁰–3.6 × 10²⁰/cm³ and a Hall mobility of 31–39 cm²/V·s.     

TaCx Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

TaC_x films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH₂C(CH₃)₃]₃Cl₂) and H₂ plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200°C to 400°C. The ALD–TaC_x films with the formation of nanocrystalline structures and a rock‐salt phase were confirmed by X‐ray and electron diffraction. The ALD temperature window was found to be 225°C–300°C with a growth rate of ~0.11 nm per cycle. The resistivity of the ALD–TaC_x films was dependent on the microstructural features, such as the grain size and crystallinity, as well as their composition (C/Ta ratio), and the presence of impurities in the films, which could be controlled by varying the deposition parameters, such as the deposition temperature and reactant pulse conditions. With increasing deposition temperature and reactant pulse time, Ta‐rich films with a low Cl impurity concentration and larger grain size were obtained. The film with a resistivity less than 400 μΩ cm was obtained at 300°C, which was within the ALD temperature window, by optimizing the H₂ plasma pulse time. The step coverage of the film deposited at 300°C was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of ~4.5. The performance of the ALD–TaC_x films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD–TaC_x (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600°C for 30 min.     

Suppression of Ni agglomeration in PLD fabricated Ni-YSZ composite for surface modification of SOFC anode

The suppression of Ni agglomeration in Ni-yttria stabilized zirconia (Ni-YSZ) nano-composite thin films deposited by pulsed laser deposition (PLD) has been investigated by varying post-annealing temperatures at a range of 800–1200 °C. Grain growth to a certain extent appears to be necessary to obtain a stable Ni-YSZ composite microstructure by suppressing massive Ni agglomeration. The microstructurally stable and uniform nano-porous Ni-YSZ thin film was obtained by 1200 °C post-annealing and reduction of the NiO–YSZ thin film, and it was applied as the surface modification layer of the bulk anode support used in conventional solid oxide fuel cells (SOFCs). By this approach, we were able to successfully realize a thin film electrolyte SOFC exhibiting the open cell voltage (OCV) higher than 1 V with a 1-μm thick film electrolyte on the porous anode support.     

Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO₂ films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO₂ films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO₂ film growth. The TiO₂ films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO₂ surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO₂ film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO₂ could not be deposited on the substrate and a cloudy TiO₂ film was formed due to the increase of surface roughness, respectively.     

Piezo-ferroelectric response of bismuth ferrite based thin films and their related photo/piezocatalytic performance

Bismuth ferrite based thin films were grown by RF magnetron sputtering under different experimental conditions. The effects of substrate temperature, Ar:O₂ mass flow ratio and gas mixture pressure on the films’ microstructure, phase evolution, optic, ferroelectric and magnetic properties were systematically investigated. The structural analysis results revealed an amorphous phase for the films deposited at a substrate temperature below 500 °C, while for the thin films deposited at 700 °C, a ε-Fe₂O₃ secondary phase was detected. The diffraction lines of the samples deposited at 600 °C were associated with Bi₂Fe₄O₉ and Bi₂₅FeO₄₀ phases. The increase in the mixture gas pressure up to 1 Pa showed an improved crystallinity of the deposited films, while, at higher working gas pressures, the films were found to be amorphous. The use of low O₂ to Ar mass flow ratio during the deposition led to a phase transformation process. EDX and RBS measurements exposed a uniform distribution of the main elements, revealing some stoichiometry changes induced by the pressure variation. The optical band gap values were influenced by the substrate temperature and pressure of the Ar:O₂ gas. The magnetic properties were correlated with the structural features, the highest magnetic response being observed for the sample deposited at 600 °C, 1 Pa and 3:1 Ar:O₂ gas pressure. According to the PFM results, the film deposited at 700 °C, Ar:O₂ ratio 3:1 and total gas pressure 1 Pa clearly outperformed the others due to their excellent ferroelectric properties and outstanding piezo-response. The sample deposited at 700 °C showed both visible light-driven degradation and piezodegradation activities. The piezocatalytic and photocatalytic activities were ascribed to the high piezoresponse and to a more efficient separation of electrons and holes induced by a built-in electric field that is caused by the larger remnant polarization of Bi₂Fe₄O₉ and Bi₂Fe₄O₉/ε-Fe₂O₃ hetero-junction.     

Plasma polymerized tetramethyl germanium films deposited at elevated substrate temperatures

Thin plasma polymerized films of tetramethyl germanium are deposited at various substrate temperatures. The influence of substrate temperature on the deposition rate, composition, structure, and electrical properties of the films is discussed. With an increase in the substrate temperature from 25°C to 150°C under similar plasma deposition conditions, the conductivity of the film increased by four orders of magnitude. Films of plasma polymerized tetramethyl germanium deposited at 150°C show typical semiconducting behavior (increasing conductivity with increasing temperature) and have a sheet conductivity of 1.0 × 10^?6 S cm^?1 at 25°C. There is a direct correlation between the conductivity and the composition of the films, i.e., the higher the conductivity the higher the ratio of germanium to carbon at the surface. At deposition temperatures of 25 and 75°C the germanium to carbon ratio was essentially the same, but at a deposition temperature of 150°C, this ratio was considerably higher.