Enhancement of porous silicon photoluminescence by chemical and electrochemical infiltration of conducting polymers

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Characterization of chromium thin films by sputter deposition

In this study, a systematic investigation on the deposition of Cr-CrO_x bi-layer film was performed by magnetron DC sputtering. The X-ray photoelectron spectrometer (XPS) examining the bare Cr film showed that the peaks of Cr 2P_3/2 and Cr 2P_1/2 appeared in the Cr thin film associated with the presence of a 12 nm oxide layer. The transmission was reduced to zero as the Cr film exceeded 100 nm in thickness. The reflection saturated at a value of ≈55% when the thickness of the Cr film reached 30 nm. The optical density exceeded 3.50 with a Cr film thickness over 150 nm. In order to reduce the reflection of the film to a level of ≤4%, a Cr-CrO_x bi-layer thin film was prepared. Overall, a Cr-CrO_x bi-layer film with the Cr layer 130 nm and the CrO_x layer 40 nm in thickness reported a transmission of zero, a reflection of 3.82% and an optical density of 4.04, all meeting the requirements of anti-reflection black matrix (BM) for display applications.     

Fabrication of porous lanthanum strontium manganite films by electrostatic spray deposition

In this work, electrostatic deposition was used to prepare porous lanthanum strontium manganite (LSM) films on a silicon substrate for cathode application in solid oxide fuel cells (SOFCs). The precursor solution was prepared by dissolving lanthanum nitrate hydrate, manganese nitrate hexahydrate and strontium chloride hexahydrate into a mixture of methanol and water. The morphology of the LSM film depended on process parameters such as substrate temperature, precursor flow rate, nozzle-substrate distance, and deposition time. The effect of heating temperature on the film’s crystal structure was investigated with X-ray diffraction in the heating temperature range of 700 °C to 900 °C. Porous LSM film was successfully prepared in the solution flow rate range of 2 l/min to 4.5 l/min, substrate temperatures of 127 °C to 330 °C, the nozzle-substrate distance range of 3 cm to 8 cm, and deposition times of 1 min to 16 min.     

Synthesis of GaN films on porous silicon substrates

A novel and simple method was employed to synthesize GaN films on porous silicon (PS) substrates. GaN films were obtained through the reaction between NH3 and Ga2O3 films deposited on the substrates with magnetron sputtering. Since GaN and PS are all good materials for luminescence, it is expected to obtain some new properties from GaN on PS. The samples were analyzed with X-ray diffraction (XRD) to identify crystalline structure. Fourier transmit infrared (FTIR) spectrum was used to analyze the chemical state of the samples. The films were observed with scanning electron microscopy (SEM) and were found to consist of many big crystal grains. Photoluminescence (PL) spectrum was used to illuminate the optical property of the GaN films.     

Evaluation of stress during and after sputter deposition of Cu and Ta films

The stress evolution of magnetron sputtered copper and tantalum films is presented for samples prepared at various sputtering pressures and powers. In-situ stress values were calculated using measurements from a Multi-beam Optical Stress Sensor (MOSS) system, while ex-situ stress values were calculated using measurements from a stylus profilometer. Extensive microstructural and surface analysis were performed by several techniques and related to the stress state of the film. The results demonstrate that during deposition, independent of the adatom mobility, the stress curves are initially compressive at low sputtering pressures, while at the highest sputtering pressure (1.4 Pa) the stress trend is always tensile. Meanwhile, the stress curves after deposition show a tensile trend for both materials at all sputtering pressures.     

Direct deposition of CeO2 films on Ni metal substrate by chemical vapor deposition

Cerium dioxide thin films have been grown in-situ directly on cube textured Ni substrate by metal-organic chemical vapor deposition (MOCVD). At a lower deposition temperature of 400°C, an amorphous film was formed. The texture of crystalline CeO₂ film was changed from (200) orientation to (111) orientation when the deposition temperature was increased from 450°C to 550°C. The growth rate was ~40 nm/min and the rms surface roughness was 50 nm for the CeO₂ film deposited at 450°C for 10 min. Surface roughness of the film was increased with the development of (111) orientation. Deposited CeO₂ film showed a mixed texture of (100)<001> and (100)<011> orientation. Depending on the deposition condition, the transition from (100)<001> texture to (100)<011> orientation was observed.     

Surface characterization and properties of silicon nitride films prepared by ion-assisted deposition

Silicon nitride (SiN) films had been prepared at low substrate temperature (100 °C) using the ion-assisted deposition (IAD) process. The films had been analyzed by the measurement of X-ray diffraction, atomic force microscopy, Fourier transform infrared spectrometry, nano indenter, and ellipsometry. The effects of N-ion current density on the surface morphology, compositional, mechanical, and infrared optical properties of SiN thin films were investigated. The results showed that the stoichiometric Si₃N₄ thin film with desirable properties, such as continuous and smooth surface morphology, extremely low hydrogen content, mechanical strong, and low extinction coefficient, could be obtained by using the IAD technique.     

Relative photoluminescence of ZnO nanorods size-controlled by changing the precursor ratio in metal organic chemical vapor deposition

The photoluminescent (PL) properties of vertically and laterally well-oriented ZnO nanorod arrays (NRAs) synthesized by metalorganic chemical vapor deposition on Al₂O₃ (0001) substrates were investigated. The size of the NRAs was controlled by systematic tuning of the precursor ratio. Regardless of the size of the NRAs, the PL properties were the same when measured at room temperature and at low temperatures. This observation suggests that changing the precursor ratio is a good way of controlling the size of ZnO NRAs while maintaining consistent PL properties.     

Relationship between mechanical properties and chemical groups in a-C:F films prepared by RF unbalanced magnetron sputter deposition

a-C:F films were prepared by RF unbalanced magnetron sputter deposition on Si substrates. The modulus and hardness of the films and their relationship with chemical groups in the films were investigated. The results show that the modulus and hardness of the deposited films are not only determined by the nature of cross-link C-C network, but also affected by the fluorocarbon groups. The C-C network of the films is composed of sp² cluster, thus the modulus and hardness of films are close to those of polycrystalline graphite. Compared with other fluorocarbon groups existing in the films, the effect of -(CF-CF)_n- group on the modulus and hardness of the films is much higher. With increasing of -(CF-CF)_n- group proportion, modulus and hardness of the films linearly decrease.     

Low temperature sputter deposition of SnOx:Sb films for transparent conducting oxide applications

SnO_x:Sb films have been prepared by reactive dc magnetron sputtering from a metallic target, with the aim of evaluating the potential of SnO_x:Sb as an attractive low-cost alternative to In₂O₃:Sn (ITO) for TCO applications. The deposition was performed without any additional heating of the substrates. The films were subsequently analysed regarding their optical, electrical and structural properties. Our results show that there is only a narrow process window for the sputter deposition of transparent and conducting tin oxide films at low temperature. A sharp minimum in resistivity of 4.9 mΩ cm is observed at an oxygen content of approximately 17% in the sputtering gas. Under these deposition conditions, the SnO₂:Sb films turn out to be both highly transparent and crystalline. At lower oxygen content (10-15%) the SnO_x:Sb films are substoichiometric, as revealed by Rutherford backscattering, and show a low transmission and high resistivity due to numerous defects and the presence of the SnO phase. At higher oxygen content (> 17%) excess oxygen is incorporated into the films, which is attributed to an increase of oxygen ion bombardment. This leads to a degradation of the electrical properties and a decrease of the density of the films, whilst the optical transmittance slightly improves.     

Applications of porous silicon thin films in solar cells and biosensors

An overview of the applications of porous silicon (PS) thin films, as antireflection coatings (ARC) in silicon solar cells and transducers in biosensors, is presented. The reflectance spectra of PS films have been compared with other conventional ARCs (such as SiN_x TiO₂/MgF₂ and ZnS), and optimal PS ARC with minimum reflectance has been obtained. The implementation of PS into an industrially compatible screen-printed (SP) solar cell by both the electrochemical etching (ECE) and chemical etching (CE) methods are reviewed. Porous silicon films, formed via ECE for short anodization times, on textured n⁺ emitter ofc-Si solar cell having SP front and back contacts, lead to improvements in the performance of solar cells and demonstrate their viability in industrial applications.     

The rapid thermal processing chemical vapor deposition of silicon epitaxial films

The future of ultralarge-scale integration technology is tending toward reduced thermal processing to realize devices with higher integration densities and better performance. Rapid thermal processing chemical vapor deposition (RTPCVD) is a promising technology that can preserve the advantages of high-temperature processing without degrading the fidelity of junction profiles. Defect free, thin silicon epilayers with extremely abrupt dopant-transition profiles can be re-producibly grown by RTPCVD. Very high quality n-type and p-type heavily doped epilayers, using boron, arsenic, and phosphorus as dopants, have been grown by RTPCVD. Through superior process control and reduced thermal exposure, RTPCVD is expected to play an important part in the next generation of fabrication technology and in the development of novel silicon-based materials.     

High-strength superelastic Ti–Ni microtubes fabricated by sputter deposition

Ti–Ni microtubes are attractive materials for biomedical devices, such as micro-catheters and micro-stents, but it is difficult to fabricate them with dimensions of less than 100 μm by conventional tube-drawing. In this study, Ti–Ni microtubes with 50 μm inner diameter and a tube wall thickness of 6 μm was successfully fabricated using a novel method in which Ti–Ni was sputter-deposited on a Cu wire with a diameter of 50 μm. All the microtubes exhibited shape memory behavior after crystallization at 873 K for 3.6 ks. Microtubes fabricated without rotating the Cu wire during deposition have low fracture strength due to the columnar grains and non-uniform tube wall thickness. Microtubes fabricated by depositing Ti–Ni on a rotating wire have a uniform wall thickness and the fracture strength increased with increasing rotation speed. Microtubes made by the rotating-wire method exhibited superelasticity of 3% strain at room temperature with high fracture stress of 950 MPa, suggesting that they are suitable for practical applications.     

Structural and mechanical properties of amorphous silicon carbonitride films prepared by vapor-transport chemical vapor deposition

The deposition of amorphous silicon carbonitride (a-SiCN:H) films has been successfully achieved through an in-house developed vapor-transport chemical vapor deposition (VT-CVD) technique in a nitrogenated atmosphere. Polydimethylsilane (PDMS) was used as a single-source precursor for both silicon and carbon, while NH₃ was mixed with argon to ensure the in-situ nitrogenation of the films. The chemical bonding and the atomic composition of the a-SiCN:H films were systematically investigated, as a function of their N content, by means of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). AFM was used to obtain 2-D and 3-D views of the films. The mechanical properties [(hardness (H) and Young's modulus (E)] of the freshly prepared films were investigated by the nanoindentation technique. It is shown that by controlling the NH₃/Ar gas flow ratio in the reactor, a-SiCN:H films with various N contents [(0-27) at.% range] are achieved. On the microstructural level, the increase incorporation of N in the a-SiCN:H films is found not only to lead to C atom substitution by N atoms in the local Si-C-N environment but also to an enhanced incorporation of hydrogen bonded to both Si and N. Furthermore, the increase incorporation of N in the a-SiCN:H films resulted in an increase of the average R_rms surface roughness from 4 to 12 nm. Moreover, the films became porous with pore size and density increase as a result of increasing N at.%. Ultimately, both H and E of the a-SiCN:H films were found to be sensitive to their N content, as they decrease (from ~ 17 GPa and 160 GPa to ~ 13 GPa and 136 GPa, respectively) when the N content is increased from 0 to 27 at.%. The formation of Si-N, Si-H, and N-H bonds at the detriment of the more stiff Si-C bonds is thought to account for the observed lowering of the mechanical properties of the a-SiCN:H films as their N content increased.     

Fabrication and photoluminescence of Er-doped ZnO thin films on SiO2/Si substrate by pulsed laser deposition

Er doped ZnO thin films were grown on Si substrates using SiO2 buffer layer by pulsed laser deposition (PLD) method.The obtained films crystallize well and show high c-axis orientation.The Er content was evidently detected by the energy dispersive X-ray spectroscopy (EDS).Upon annealing in O2 ambience at different temperatures, the films show different photoluminescence properties at 1.54 μm.The samples annealed at 700 and 850 ℃ show intense photoluminescence peaks which enhance with the annealing temperature, while no obvious luminescence peaks are observed for the as-grown samples or annealed at 500 ℃.The possible mechanism was discussed.     

Composite electrodes for current sources based on graphene-like films in porous silicon

In this work, the results of formation of composite membranes with a thickness of about 200 μm with a high electric conduction based on porous silicon and graphene-like films have been presented. A method of CVD film synthesis that makes it possible to form a graphene-like coating on the inner surface of gradient-porous silicon with variable pore morphology across the thickness has been proposed. The pore sizes vary gradually from units of nanometers on the upper surface to several micrometers deep in silicon.     

Coating the inner walls of metal tubes with carbon films by physical vapor deposition at low temperature

Tubes are often required to exhibit better performance in corrosion and wear behavior than the material the tube is made of can offer. The situation can be improved when the tube is coated with a protective film. This can be achieved by sputter coating with an ion beam. A sputter target is located inside the tube. Energetic ions are accelerated into the tube and impinge onto the target. Thus, material is sputtered from the target onto the inner walls of the tube. Two apparatus for coating tubes of different lengths and diameters are described. Aluminum and stainless steel tubes were coated with amorphous carbon films. Results on adhesion, corrosion performance in aqueous media and thickness uniformity are shown.     

Two novel rolling processes of porous metal preforms prepared by spray deposition technique using conventional rolling mill

For the spray deposited preforms with the porosity up to 10–15%, densification processing is necessary to produce fully dense products. In this paper, two novel processes named as “Frame-Confined Rolling” and “Ceramic Rolling” are presented. The experimental results show that these two methods can improve the workability of the porous preforms without forming cracks on surface and edge during rolling.     

Controlling the deposition rate during target erosion in reactive pulsed DC magnetron sputter deposition of alumina

Alumina coatings were synthesized by reactive pulsed DC magnetron sputtering in an industrial-scale deposition system. The aim of this study was to investigate the influence of target erosion (racetrack depth) on the deposition rate. Hysteresis curves, showing the cathode voltage as a function of oxygen flow, were mapped out for different target erosion depths and temperatures, revealing significant variations, e.g. in the metallic mode voltage level. Each deposition was made with a fixed cathode voltage and the cathode current was controlled by adjusting the oxygen flow in a feedback loop by means of which a constant power was maintained. Keeping the power constant, this procedure was repeated for various cathode voltages within the hysteresis transition region and at different racetrack depths and deposition temperatures. The corresponding deposition rates were observed to depend mainly on the relative cathode voltage set-point in-between the oxide and metallic voltage levels in the hysteresis region. This result enables control of the deposition rate by maintaining a constant relative cathode voltage as the target erodes.     

Composite TiN–Ni thin films deposited by reactive magnetron sputter ion-plating

Composite TiN–Ni thin films were deposited by direct-current (DC) magnetron sputter ion-plating from an alloy Ti–48 at% Ni target in a mixture of argon and nitrogen gases at a total pressure of 0.1 Pa onto glass and stainless steel substrates heated to temperatures higher than 250 °C. The films deposited at the nitrogen flow Q_N2≥6.4 sccm consisted of a mixture of δ-TiN and fcc nickel phases. The effects of negative substrate bias and substrate temperature on the crystal structure of the films were studied. The substrate bias of −200 V resulted in improved crystallization of films and a smaller difference in size between the TiN and nickel grains, as compared with films deposited onto substrates at floating potential. It was possible to vary the crystal grain size of both phases by varying the substrate temperature in the range 270–430 °C. The maximum hardness measured in the films was 10.5 GPa. It is expected that the hardness can be increased by decreasing the content of nickel.