High-pressure Deposition Research Articles

Atomic scale investigation of planar defects in 0.95Na0.5Bi0.5TiO3–0.05BaTiO3 thin films on SrTiO3 (001) substrates

Thin films of lead-free piezoelectric 0.95Na0.5Bi0.5TiO3–0.05BaTiO3 (0.95NBT–0.05BT) are epitaxially grown on single crystalline SrTiO3 (001) substrates at 800 °C, 850 °C and 900 °C, respectively, by a high-pressure sputtering deposition technique. The microstructure of the thin films is investigated by means of aberration-corrected scanning transmission electron microscopy. Planar defects are observed and the density of the defects increases with the increase of the film-growth temperature. Two types of planar defects in the films are studied at the atomic scale. One consists of groups of edge-sharing TiO6 octahedra with Bi atoms located between the TiO6 octahedral groups, and the other exists in the form of Na/Bi(Ba)O2Na/Bi(Ba) layer parallel to the (010) plane of the films. Based on the structure feature of the planar defects, the propagation of the planar defects related to edge-sharing TiO6 octahedra within the films and from the film-substrate interface is discussed. Furthermore, the ordering of the planar defects is expected to form new structures. In comparison with the microstructure of 0.95NBT–0.05BT bulk materials, the appearance of the high-density planar defects observed within the films could be considered to be responsible for the difference in the physical properties between the bulk materials and the films.

The influence of external magnetic field on the structural and optical properties of nanocrystalline ZnO thin films prepared by dip coating method

ZnO thin films were prepared by the sol gel dip coating method. Some samples were prepared under a DC magnetic field DC-MF (B); others were done without it. The sol gel was also continuously stirred. The field orientation in each case of deposition was chosen perpendicular as well as parallel to the growing ZnO-film substrate and the film depositions were carried out at a fixed B intensity value. The influences of magnetic field on the structural, morphological, and optical properties of ZnO thin films were investigated. In the perpendicular case, a cubic structure phase was observed at ambient conditions. It is noteworthy that this phase growth is only possible at high pressure deposition. In the parallel case, the films improved the crystal structure without creating a new phase. The structural properties of the ZnO films such as surface morphology and crystallinity were determined using scanning electron microscopy (SEM) and X-ray diffractometry (XRD), respectively. The optical properties of the ZnO films were characterized by the ultraviolet–visible (UV–Vis) spectroscopy.

Characterization of Sputtered CdTe Thin Films with Electron Backscatter Diffraction and Correlation with Device Performance.

The performance of polycrystalline CdTe photovoltaic thin films is expected to depend on the grain boundary density and corresponding grain size of the film microstructure. However, the electrical performance of grain boundaries within these films is not well understood, and can be beneficial, harmful, or neutral in terms of film performance. Electron backscatter diffraction has been used to characterize the grain size, grain boundary structure, and crystallographic texture of sputtered CdTe at varying deposition pressures before and after CdCl2 treatment in order to correlate performance with microstructure. Weak fiber textures were observed in the as-deposited films, with (111) textures present at lower deposition pressures and (110) textures observed at higher deposition pressures. The CdCl2-treated samples exhibited significant grain recrystallization with a high fraction of twin boundaries. Good correlation of solar cell efficiency was observed with twin-corrected grain size while poor correlation was found if the twin boundaries were considered as grain boundaries in the grain size determination. This implies that the twin boundaries are neutral with respect to recombination and carrier transport.

Preparation of iron cobaltite thin films by RF magnetron sputtering

Iron cobaltite thin films with spinel structure have been elaborated by radio-frequency (RF) magnetron sputtering from a Co1.75Fe1.25O4 target. Influence of argon pressure on structure, microstructure and physical properties of films has been examined. Iron–cobalt oxide thin films essentially consist of one spinel phase when deposited at low pressure (0.5 and 1.0Pa). At high pressure (2.0Pa), the global stoichiometry of the film is changed which results in the precipitation of a mixed monoxide of cobalt and iron beside the spinel phase. This in-situ reduction due to an oxygen loss occurring mainly at high deposition pressure has been revealed by X-ray diffraction and Raman spectroscopy. Microstructural evolution of thin film with argon pressure has been shown by microscopic observations (AFM and SEM). The evolution of magnetic and electrical properties, versus argon pressure, has been also studied by SQUID and 4 point probe measurements.

Stress Considerations in Thin Films for CMOS-Integrated Gas Sensors

The integration of gas sensor components into smart phones, tablets, and wrist watches will revolutionize the environmental health and safety industry by providing individuals the ability to detect harmful chemicals and pollutants in the environment using always-on hand-held devices. However, before this can be achieved, several challenges must be overcome. Until recently, available gas sensors relied on a bulky architecture whose manufacture was not compatible with that of a conventional CMOS process sequence. The integration with CMOS processing is essential in order to combine the sensor with MEMS and CMOS microelectronics. More recently, semiconducting metal oxides have been shown to exhibit very good conductometric sensing properties, when exposed to an ambient gas at high temperatures. The resistance of a metal oxide film is essentially comprised of two resistances occurring in parallel: one is influenced by the surface reaction and the other depends on the traditional idea of material conductivity. The resistance from the surface reaction is one which changes depending on the ambient temperature and exposure to a reacting gas in the ambient. Although many metal oxides have shown a gas response in their conductivity, tin oxide (SnO2) and tin-doped indium oxide (In2O3), known as indium-tin-oxide (ITO), have garnered particular attention. Due to the need for these films to be heated to temperatures between 300ºC and 550ºC during operation to increase the sensitivity, a considerable degradation of the film can result. In this study the post-processing stress through thin SnO2 and ITO films is analyzed in order to obtain more information about the reliability of these materials for operation in a gas sensor. The post-processing stress in a thin film is a result of two stress components: the intrinsic stress, which arises during the film deposition, and the thermo-mechanical stress, which is a result of the difference in the deposition temperature and the subsequent cooling to room temperature. The growth mode of thin films depends on the surface free energy of the deposit, the substrate, and the interface between the two materials. The stress evolution during sputter deposition of tin oxide and ITO films is analyzed here. The growth process during sputtering is characterized by the Volmer-Weber growth mode, where small islands of the depositing film form on the surface which, through expansion, impinge on each other, eventually forming a coalesced thin film. Due to the surface interaction between the materials and the impingement of the depositing islands, a stress forms in the thin film. The stress generation during a medium temperature (300ºC) deposition of SnO2 and low-temperature (50ºC) high pressure deposition of ITO is examined. The intrinsic stress is composed of a tensile and a compressive component; the tensile stress depends mainly on the Young modulus of the depositing material and the island geometries during the expansion and impingement of islands with each other. The compressive stress component depends on the geometry of a single island and the surface free energy, a material property which combines the grain boundary energy and the surface energy. Using published values for tin oxide, the average stress in the deposited thin film is simulated, with a result which matches measured values. Using a previously published intrinsic stress value for high-pressure deposited ITO, the appropriate surface free energy value for ITO was identified, enabling further understanding of this important material. The intrinsic stresses of sputtered SnO2 and ITO were found to be 200MPa and 300MPa, respectively. Upon subsequent cooling to room temperature, the stress in the SnO2 layer grew to 425MPa due to the different coefficients of thermal expansion (CTEs) between the tin oxide and the silicon dioxide films. In addition to the analysis of the stress generation during sputter deposition, an alternative efficient and economical deposition method is examined, namely spray pyrolysis. It has already been shown that tin oxide can be deposited using an efficient and economical technique known as spray pyrolysis. The details of this technique are discussed and a thin film with a thickness of 50nm is deposited on a SiO2 isolation layer in order to be used for a fully CMOS-integrated detector. Spray pyrolysis is a technique which involves three steps: the atomization of the precursor CnCl4 solution, the transport of the aerosol droplets towards the wafer, and the decomposition of precursor at or near the substrate resulting in film growth. A simulation methodology for spray pyrolysis is presented and the difference in the sensing response between sputtered and spray pyrolysis deposited SnO2 thin films for the detection of carbon monoxide (CO) in the environment is analyzed. Figure 1

Influence of heat treatment on physical properties of In–Ga–Zn–O thin films

For unstable In–Ga–Zn–O (IGZO) thin films, electron-beam irradiation during transmission electron microscopy or heat treatment is reported to change the film structure and enhance its crystallization. Using IGZO films formed under two conditions, we study how the physical properties of IGZO films correlate with the electron-beam irradiation dose or heat-treatment temperature. IGZO films deposited under high deposition pressure contain many voids, have a relatively high impurity concentration, and are crystallized by electron-beam irradiation or heat treatment. In contrast, IGZO films formed under low deposition pressure are dense and the crystal size in the film does not change under electron-beam irradiation or heat treatment. In addition, heat treatment further increases the density of an originally dense film and reduces the defect density.

Microplasma-Based Growth of Biphasic NiFe2O4/NiO Nanogranular Films for Exchange Bias Applications

Biphasic, nanostructured NiFe2O4/NiO films exhibiting exchange bias were synthesized using high-pressure microplasma-based deposition. Organometallic Ni and Fe precursors were dissociated via electron impact in the hollow cathode region of a supersonic plasma jet with oxygen to form a directed flux of Ni and Fe oxide species that were subsequently spray-deposited on SiO2/Si substrates to form nanostructured thin films. Exchange bias (HE) and coercivity (HC) enhancement were observed for all films containing NiO after field cooling, indicating an exchange interaction between NiFe2O4 and NiO. HE and HC increased with NiO content, which may be explained by a concomitant increase in NiFe2O4/NiO interfacial density. Large HE (∼250 Oe) and HC (∼700 Oe) were measured at 20 K, and exchange bias persisted at high temperatures (305 K) where an HE and HC of 80 and 400 Oe were observed, respectively.

Structure and magnetic properties of highly textured nanocrystalline Mn–Zn ferrite thin film

Nanoparticles of Mn0.2Zn0.8Fe2O4 were chemically synthesized by co-precipitating the metal ions in aqueous solutions in a suitable alkaline medium. The identified XRD peaks confirm single phase spinal formation. The nanoparticle size authentication is carried out from XRD data using Debye Scherrer equation. Thin film fabricated from this nanomaterial by pulse laser deposition technique on quartz substrate was characterized using XRD and Raman spectroscopic techniques. XRD results revealed the formation of high degree of texture in the film. AFM analysis confirms nanogranular morphology and preferred directional growth. A high deposition pressure and the use of a laser plume confined to a small area for transportation of the target species created certain level of porosity in the deposited thin film. Magnetic property measurement of this highly textured nanocrystalline Mn–Zn ferrite thin film revealed enhancement in properties, which are explained on the basis of texture and surface features originated from film growth mechanism.

Photoluminescence and structural properties of Si/SiC core–shell nanowires growth by HWCVD

Si/SiC core–shell nanowires grown by hot-wire chemical vapor deposition were studied. Ni nanoparticles act as metal nano-templates to catalyze the growth of these core–shell nanowires. These nanowires were grown at different deposition pressures of 0.5 and 1mbar. The nanowires showed a tapered-like morphology at deposition pressure 0.5mbar. Increase in pressure to 1mbar leads to a formation of agglomerated grains at the root of the nanowires. The results show that these nanowires consisted of crystalline Si core and amorphous SiC shell nanowires. Increase in pressure enhanced the formation of SiC phase in the shell of the nanowires. On the other hand, the formation of the agglomerated grains attributed to an increasing of the SiC phase at higher deposition pressure. The presence of Si and SiC nano-crystallites embedded within an amorphous matrix exhibited a room temperature PL emission in the range of 400–1000nm. The effects of the deposition pressure on the optical and structural properties of the nanowires are also discussed.

Research Progress in Diamond Cutting Tool Materials and Preparation Technology

High temperature and high pressure (HTHP) and chemical vapor deposition (CVD) are two important methods of preparing diamond. This article briefly introduced the kinds of diamond cutting tool materials and the two technologies of synthesizing diamond. And in the end, the developing trends of diamond cutting tool materials and the preparation technologies were forecasted.

Hot-wire chemical vapor deposition prepared aluminum doped p-type microcrystalline silicon carbide window layers for thin film silicon solar cells

Al-doped p-type microcrystalline silicon carbide (µc-SiC:H) thin films were deposited by hot-wire chemical vapor deposition at substrate temperatures below 400 °C. Monomethylsilane (MMS) highly diluted in hydrogen was used as the SiC source in favor of SiC deposition in a stoichiometric form. Aluminum (Al) introduced from trimethylaluminum (TMAl) was used as the p-type dopant. The material property of Al-doped p-type µc-SiC:H thin films deposited with different deposition pressure and filament temperature was investigated in this work. Such µc-SiC:H material is of mainly cubic (3C) SiC polytype. For certain conditions, like high deposition pressure and high filament temperature, additional hexagonal phase and/or stacking faults can be observed. P-type µc-SiC:H thin films with optical band gap E04 ranging from 2.0 to 2.8 eV and dark conductivity ranging from 10−5 to 0.1 S/cm can be prepared. Such transparent and conductive p-type µc-SiC:H thin films were applied in thin film silicon solar cells as the window layer, resulting in an improved quantum efficiency at wavelengths below 480 nm.

Study of Ar + O2 deposition pressures on properties of pulsed laser deposited CdTe thin films at high substrate temperature

Cadmium telluride (CdTe) thin films deposited by pulsed laser deposition (PLD) on fluorine–tin–oxide substrates under different pressures of argon (Ar) + oxygen (O2) at high substrate temperature (Ts = 500 °C) was reported in this paper. In our work, the CdTe thin films were prepared successfully at high Ts by inputting Ar + O2. As reported, PLD-CdTe thin films were almost prepared at low substrate temperatures (<300 °C) under vacuum conditions. The deposition of CdTe thin films at high Ts by PLD is rarely reported. The influence of the Ar + O2 gas pressure on thickness, structural performance, surface morphology, optical property and band gap (Eg) had been investigated respectively by Ambios probe level meter, X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectrometer. Strong dependence of properties on the deposition pressures was revealed. In the range of Ar + O2 gas pressure from 5 to 12 Torr, the deposition rate and the Eg of CdTe films vary in the range of 41.9–57.66 nm/min then to 35.26 nm/min and 1.51–1.54 eV then to 1.47 eV, respectively. The XRD diagrams showed that the as-deposited films were polycrystalline, and the main phase was cubic phase. However, the preferred orientation peak disappeared when the deposition pressure was higher. SEM images indicated that the CdTe film deposited at a higher deposition pressure was more uniform and had a higher compactness and a lower pinhole density. Furthermore, based on this thorough study, FTO/PLD-CdS (100 nm)/PLD-CdTe (~1.5 μm)/HgTe:Cu/Ag solar cells with an efficiency of 6.68 % and an area of 0.64 mm2 were prepared successfully.

Effect of total gas pressure and O2/N2 flow rate on the nanostructure of N-doped TiO2 thin films deposited by reactive sputtering

N-doped TiO2 thin films have been deposited by reactive RF magnetron sputtering at different total gas pressures and varying O2/N2 gas flow rates at 300°C. The thin film nanostructure has been studied by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Increasing the deposition pressure leads to reduced crystallinity of the thin films and a higher N2 flow rate was required to incorporate N into the growing film. This is attributed to the lower energy ion bombardment of the surface and N adatom chemical reactivity being reduced at higher total gas pressures. Ar+ ion sputtering of the deposited N-doped TiO2 thin films has enabled a detailed XPS investigation of the surface and bulk N species to be performed. Adsorbed N species have been identified on all the deposited thin film surfaces, with the most prevalent adsorbed N species occurring at a binding energy of approximately 400eV, shown to originate from atmospheric contamination, most probably N containing organic species. The bulk N content varies between 0.6 and 6.0 at.% and N is located predominantly at substitutional sites in the TiO2. The presence of interstitial N, in the form of NO species, has been identified by XPS in some thin films deposited at higher deposition pressures. Hence, varying the total gas pressure may provide a route for tailoring the location of N in the bulk structure. At higher N contents (>3at.%), TiN is found as a secondary phase within the bulk structure and the presence of TiN leads to a sharp reduction in the band gap. Post-deposition annealing of low N containing films results in an N-doped TiO2 single phase anatase structure.

Correction: Corrigendum: Porous Carbon Nanoparticle Networks with Tunable Absorbability

Porous carbon materials with high specific surface areas and superhydrophobicity have attracted much research interest due to their potential application in the areas of water filtration, water/oil separation, and oil-spill cleanup. Most reported superhydrophobic porous carbon materials are fabricated by complex processes involving the use of catalysts and high temperatures but with low throughput. Here, we present a facile single-step method for fabricating porous carbon nanoparticle (CNP) networks with selective absorbability for water and oils via the glow discharge of hydrocarbon plasma without a catalyst at room temperature. Porous CNP networks were grown by the continuous deposition of CNPs at a relatively high deposition pressure. By varying the fluorine content, the porous CNP networks exhibited tunable repellence against liquids with various degrees of surface tension. These porous CNP networks could be applied for the separation of not only water/oil mixtures but also mixtures of liquids with different surface tension levels.

Porous Carbon Nanoparticle Networks with Tunable Absorbability

Porous carbon materials with high specific surface areas and superhydrophobicity have attracted much research interest due to their potential application in the areas of water filtration, water/oil separation, and oil-spill cleanup. Most reported superhydrophobic porous carbon materials are fabricated by complex processes involving the use of catalysts and high temperatures but with low throughput. Here, we present a facile single-step method for fabricating porous carbon nanoparticle (CNP) networks with selective absorbability for water and oils via the glow discharge of hydrocarbon plasma without a catalyst at room temperature. Porous CNP networks were grown by the continuous deposition of CNPs at a relatively high deposition pressure. By varying the fluorine content, the porous CNP networks exhibited tunable repellence against liquids with various degrees of surface tension. These porous CNP networks could be applied for the separation of not only water/oil mixtures but also mixtures of liquids with different surface tension levels.

Influence of structural disorder on magnetic domain formation in perpendicular anisotropy thin films

Using a combination of resonant soft x-ray scattering, magnetometry, x-ray reflectivity and microscopy techniques we have investigated the magnetic properties and microstructure of a series of perpendicular anisotropy Co/Pt multilayer films with respect to structural disorder tuned by varying the sputtering deposition pressure. The observed magnetic changes in domain size, shape and correlation length originate from structural and chemical variations in the samples, such as chemical segregation and grain formation as well as roughness at the surface and interfaces, which are all impacted by the deposition pressure. For low pressure samples we find evidence of a random "gas-like" distribution of magnetic domains, while in the higher pressure samples the domain structure exhibits only short range "liquid-like" positional ordering. The structural and chemical disorder induced by the higher deposition pressure first leads to an increase in the number of magnetic point defects that limit free domain wall propagation. Then, as the sputtering pressure is further increased, the domain wall energy density is lowered due to the formation of local regions with reduced magnetic moment, and finally magnetically void regions appear that confine the magnetic domains and clusters, similar to segregated granular magnetic recording media.

Process Control of Reactive Sputter Deposition of AlO $_{x}$ and Improved Surface Passivation of Crystalline Silicon

In this paper, we investigate the relationship between the deposition-process parameters of reactively sputtered aluminium oxide films and the passivation of silicon surfaces. A method of tuning the deposition process has been established that results in a reduced level of surface recombination, where surface recombination velocities as low as 8.5 cm/s have been achieved on 1 Ω·cm n-type monocrystalline silicon. We find that in order to achieve good surface passivation, the deposition need to be conducted at low power density and at high deposition pressure. We have found that effective passivation is achieved when a sputtering target is close to being fully oxidized-indicated by deposition rate - likely resulting in films that are less aluminium rich. Additionally, Fourier-transform-infrared spectroscopy measurements were used for film characterization; the correlation between effective lifetime and the integrated absorption of all Al and O related bonds shows that films with lower absorption in the wavenumber range 500-1060 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> result in better passivation.

Pressure dependent structural and optical properties of silicon carbide thin films deposited by hot wire chemical vapor deposition from pure silane and methane gases

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition technique from silane (SiH4) and methane (CH4) gas precursors. The effect of deposition pressure on structural and optical properties of SiC films was investigated. Various spectroscopic methods including Fourier transform infrared spectroscopy, Raman scattering spectroscopy, Auger electron spectroscopy, and UV–Vis–NIR spectroscopy were used to study these properties. Films deposited at low deposition pressure were Si-rich, and were embedded with nano-crystals of silicon. These films showed strong absorption in the visible region and had low energy band gaps. Near stoichiometric SiC film, were formed at intermediate deposition pressure and these films were transparent in the visible region and exhibited a wide optical band gap. High deposition pressures caused inhomogeneity in the film as reflected by the increase in disorder parameter and low refractive index of the films. This was shown to be due to formation of sp 2 carbon clusters in the film structure.

Low temperature selective epitaxial growth of SiCP on Si(110) oriented surfaces

We demonstrate growth of SiCP film on Si(110) substrates with excellent structural quality, based on X-Ray Diffraction, Cross-sectional Transmission Electron Microscopy and Secondary Ion Mass Spectrometry analysis. This (110) surface orientation is very important since it represents the sidewall of recessed Source/Drain (S/D) areas when the film is used as an embedded stressor to induce uniaxial tensile strain in a planar transistor. An optimized (110) SiCP growth process can also be used to thicken the S/D regions of non-planar multi-gate device structures (e.g. Fin Field Effect Transistors, Tri-gate FETs) with a highly doped epitaxial film in order to enable good electrical contacts and/or induce strain. The films have been grown using Si3H8, SiH3CH3 and PH3 for growth and Cl2 as the etchant gas, all in inert carrier gas. H2 has been eliminated, preventing Cl2 from reacting with H2 yielding HCl, since Cl2 is needed to establish selectivity. We present trends on temperature, total pressure, SiH3CH3, PH3 and Cl2 etch flow. We studied selective epitaxial growth (SEG) in the 525–575°C range. Thanks to the use of Si3H8 we can obtain high SEG rates even at 525°C in conjunction with a high deposition pressure of 20 kPa (~150Torr). It is observed that the growth rate, carbon concentration, phosphorous concentration and etch rate of SiCP on Si (110) differs greatly from that on Si (100). A process optimized specifically for Si(100) surfaces may yield no growth on Si(110) surfaces. However, optimizing a process on Si(110) is assured to result in growth on Si(100). Comparing one process optimized on Si(110) with the results on Si(100), we found a substantially lower SEG rate, higher [P] incorporation and lower [C] incorporation on Si(110). One key criterion for growth on patterned substrates with Si(110) sidewalls is that the SEG rate on the sidewall must be≥0; otherwise the vertical sidewall will be etched and undercut of the spacer will occur, degrading the structural quality of the transistor and potentially impacting the electrical performance of the device.

Asphaltene Deposition Measurement and Modeling for Flow Assurance of Tubings and Flow Lines

A recently developed asphaltene deposition model is tuned with some experimental data obtained in RealView, a high pressure deposition cell. The tuned model is validated with further experimental data. The lab-scale model is then extended to field-scale tubings and flow lines, and the predicted deposition profile is qualitatively compared with field observations. Finally, an experimental protocol is developed for asphaltene deposition measurement and modeling for flow assurance of tubings and flow lines. The successful applications of RealView in investigating the impacts of shear, run time, residence time, pressure, chemical inhibitor, and surface roughness on the deposition of asphaltenes from five fluids from the Gulf of Mexico are also discussed.