RF-sputtered Films Research Articles

A role of oxygen vacancy on annealed ZnO film in the hydrogen atmosphere

RF-sputtered ZnO films were annealed in the ambient atmospheres of Ar or hydrogen gas. Hydrogen effects on oxygen vacancies of ZnO films were studied through the characterizations of physical and electrical properties after annealing at 300 °C. The carrier concentration was increased to ∼1017 cm−3 in both annealing ambient atmospheres. On the other hand, the mobility was distinctly decreased when the films were annealed in the ambient atmosphere of Ar gas. Even though the physical structure undergoes small changes regardless of annealing ambient atmospheres, the increase of oxygen vacancies was remarkably suppressed in the annealing ambient atmosphere of hydrogen gas. Two distinct band edge states, generated by oxygen vacancies, are correlated to the changes in carrier concentration and mobility as a function of energy level below the conduction band.

The Effect of Annealing in Controlled Vapor Pressure on the Thermoelectric Properties of RF-Sputtered Bi2Te3 Film

To investigate the effect of annealing in controlled atmosphere on the thermoelectric properties of Bi-Te film, Te-deficient Bi-Te film was deposited by sputtering, and then annealed with various Bi-Te alloy powders with different Te concentrations in a closed system at 250°C for 24 h. Bi-Te phases other than Bi2Te3 in the as-deposited film could be removed when the film was annealed with Bi-Te source powder containing 62 at.% or higher content of Te. At the same time, the values of Seebeck coefficient and carrier concentration of the films approach −105 μV/K and 3 × 1019 cm−3 to 6 × 1019 cm−3, respectively. This result indicates that mass transport of Te to the film takes place, resulting in the formation of Bi2Te3 phase and reduction of the amount of p-type carriers due to compositional change of the film from Te-deficient to stoichiometric. Annealing in controlled Te-vapor atmosphere is an effective method to improve the thermoelectric properties of Bi-Te film by changing the composition and phase of Te-deficient film to stoichiometric Bi2Te3 film.

Enhancement of the hall mobility in hydrogen-ion-irradiated ZnO films

RF-sputtered ZnO films were irradiated with hydrogen ions by using an ion accelerator at 110 keV. The physical and the electrical characteristics of the irradiated ZnO films were studied as functions of the hydrogen-ion irradiation dose. The Hall measurement indicated that the carrier concentration had small changes regardless of irradiated hydrogen amount, but the mobility was dramatically enhanced after irradiation of 1015 atoms/cm2. Even when the irradiated hydrogen dose was increased, the crystalline structure had no transformation and the composition was preserved. On the other hand, the electronic structure, measured by using X-ray absorption spectroscopy, exhibited a modification of the molecular orbital structure in the ZnO films irradiated at doses above 1015 atoms/cm2. These distortions of the molecular orbital in the conduction band could lead to a mobility enhancement without a structural transformation.

Microstructural and electrochemical properties of rf-sputtered LiMn2O4 thin film cathodes

Lithium transition metal oxides have received considerable attention in recent years as high voltage positive electrode materials in the fabrication of all solid state microbatteries. Among various lithium-based cathode materials, LiMn2O4 is one of the most promising cathode materials as it offers high energy density, high cell voltage, low cost, and low toxicity over the other electrode materials. Thin films of LiMn2O4 were prepared by radio frequency magnetron sputtering on gold-coated silicon substrates under various substrate temperatures ranging from 373 to 673 K in a partial pressure of 3 × 10−3 mbar with rf power 100 Watts. In the present investigation, the influence of substrate temperature on the growth and microstructural properties was studied. The films deposited at a substrate temperature less than 473 K was found to be X-ray amorphous. The initial crystallization has been observed at a substrate temperature of 523 K. The X-ray diffraction patterns of the films deposited in the substrate temperature range 523–673 K exhibited predominant (111) orientation representing cubic spinel structure with Fd3m symmetry. The grain size was found to be increased with the increase of substrate temperature as evidenced from SEM studies. However, additional impurity phases like Mn3O4 were observed for the films deposited at higher substrate temperatures (>673 K) because of re-evaporation of Li+ ions in the films. The electrochemical (EC) studies were carried for the films deposited at Ts = 673 K in aqueous media in the potential window of 0.0–1.2 V exhibited better electrochemical performance suggesting that the films are well suited as binder free thin film cathode material for commercially viable Li-ion secondary batteries.

Characterization of rf-sputtered HfMgZnO thin films

ABSTRACTMgZnO becomes amorphous or short-range-ordered with the addition of hafnium oxide. The films are rf-sputter deposited onto glass substrates (Eagle 2000, Corning Inc.) from Mg0.05HfxZn0.95-xO targets (x=0, 0.025, 0.05, 0.075, 0.1) in pure Ar ambient at room temperature. The sputtered Mg0.05Zn0.95O exhibits strong (002) preferred orientation with XRD peak located at 2θ=34.16o. The XRD peak intensity is also greatly reduced, indicating the material amorphorization proceeds with the addition of Hf. The grain size, estimated from the full-width-at-half-maximum (FWHM) of the (002) XRD peak, decreases from 24.1 to 3.3 nm as the Hf content x increases from 0 to 0.025 in Mg0.05HfxZn0.95-xO. No sharp XRD peaks are detected in the as-sputtered films when more than 5.0 at.% Hf are added into the materials. The films remain in amorphous or short-range-ordered states after annealing at 600 oC for 30 mins. All Mg0.05HfxZn0.95-xO films (100 nm in thickness) are highly transparent (> 80 %) in the visible region from 400 to 800 nm and have sharp absorption edges in the UV region. The tauc bandgap ΔE (eV), as a function of hafnium composition x, is fitted as ΔE=3.336+6.08x for room temperature as-deposited films, and ΔE=3.302+2.60x for films after 30 min 600 oC annealing. The annealing process decreases the bandgap shift caused by the incorporation of Hf in the materials.

The anodized crystalline WO3 nanoporous network with enhanced electrochromic properties

We demonstrate that a three dimensional (3D) crystalline tungsten trioxide (WO(3)) nanoporous network, directly grown on a transparent conductive oxide (TCO) substrate, is a suitable working electrode material for high performance electrochromic devices. This nanostructure, with achievable thicknesses of up to 2 μm, is prepared at room temperature by the electrochemical anodization of a RF-sputtered tungsten film deposited on a fluoride doped tin oxide (FTO) conductive glass, under low applied anodic voltages and mild chemical dissolution conditions. For the crystalline nanoporous network with thicknesses ranging from 0.6 to 1 μm, impressive coloration efficiencies of up to 141.5 cm(2) C(-1) are achieved by applying a low coloration voltage of -0.25 V. It is also observed that there is no significant degradation of the electrochromic properties of the porous film after 2000 continuous coloration-bleaching cycles. The remarkable electrochromic characteristics of this crystalline and nanoporous WO(3) are mainly ascribed to the combination of a large surface area, facilitating increased intercalation of protons, as well as excellent continuous and directional paths for charge transfer and proton migration in the highly crystalline material.

Thermal Evolution of Band Edge States in ZnO Film as a Function of Annealing Ambient Atmosphere

RF-sputtered ZnO films were annealed under various annealing ambient atmospheres, including a vacuum, air, and water vapor. The physical and electrical properties of ZnO films annealed in various ambient atmospheres, were studied as a function of annealing temperature. The carrier concentration was dramatically increased, and the mobility was decreased when the films were annealed in a vacuum or water vapor. Even though the annealing ambient atmosphere and temperature were different, the preferred orientation and crystallization of the annealed ZnO films are maintained. However, two distinct band edge states below the conduction band, observed by spectroscopic ellipsometry measurement, undergo a thermal change as a function of annealing ambient atmosphere and these changes are correlated to changes in carrier concentration and mobility.

Sputtered Silicon Nitride Thin Films for Non-Volatile Memory Applications

The present work reports the preparation, as well as the optical and electrical characterization of silicon nitride reactive RF-sputtered thin films. Argon and nitrogen mixtures have been used in different concentrations to optimize the film electrical proprieties. The thickness and the refractive index of the films were measured by spectral ellipsometry and current-voltage measurements were performed. Furthermore, the films also presented a high degree of amorphization, as indicated by qualitative measurements of its crystallinity. Complete memory structures were fabricated and a program/erase voltage shift window of 10V was measured.

The effect of electrochemical lithiation on physicochemical properties of RF-sputtered Sn thin films

Thin films of Sn were deposited on Pt/Si substrates by sputtering technique and subjected to electrochemical lithiation studies. Electrochemical lithiation of Sn resulted in the formation of Sn–Li alloys of different compositions. Charging of Sn-coated Pt/Si electrodes was terminated at different potentials and the electrodes were examined for physicochemical properties. The scanning electron microscopy and atomic force microscopy images suggested that the Sn films expanded on lithiation. Roughness of the film increased with an increase in the quantity of Li present in Sn–Li alloy. Electrochemical impedance data suggested that the kinetics of charging became sluggish with an increase in the quantity of Li in Sn–Li alloy.

Damp heat stability of Al-doped zinc oxide films on smooth and rough substrates

Properly encapsulated chalcopyrite-based solar modules from a number of manufacturers have passed the accelerated ageing tests in damp heat. Non-encapsulated modules after damp heat exposure show an increased series resistance which is contributed significantly from the increase in lateral sheet resistance of the transparent Al-doped zinc oxide (ZAO) front contact. We have shown previously, that a rough substrate morphology (on a μm-scale) is a major influence in the ZAO degradation mechanism, due to local perturbations of the ZAO growth ( extended grain boundaries). To further model and examine the extended grain boundaries we present a study of the electrical properties of RF-sputtered ZAO films before and after damp heat, grown on rough quartz glass as well as on polished, texture-etched and patterned silicon. The pattern consisted of equidistant trenches and have a periodical two-dimensional geometry. The strongest decrease of ZAO conductivity occurs on the patterned silicon substrate perpendicular to the trenches. The conductivity parallel to the trenches, however, had the same trend as the conductivity of ZAO on smooth silicon. Measured activation energies of the conductivity of 40 meV or less after damp heat are not sufficient to explain the drastic decrease of conductivity in terms of a grain-boundary-barrier theory (as described, e.g., by Seto). We will summarise our current understanding of the extended grain boundaries and present a refined barrier model to explain our experimental observations.

고주파 마그네트론 스퍼터링 방법을 사용하여 Al 기판위에 증착된 PTFE 박막의 초-발수에 관한 특성 연구

Super-hydrophobic properties have been achieved on the rf-sputtered polytetrafluoroethylene(PTFE) films deposited on etched aluminum surfaces. The microstructural evolution created after etching has been investigated by FESEM. The water contact angle over can be achieved on the rf-sputtered ultra-tihn PTFE film less than 10 nm coated on aluminum surface etched with 7 wt.%, 12.5 wt.%, and 15 wt.% HCl concentration for 12 min. XPS analysis have revealed the presence of a large quantity of and groups in the rf-sputtered PTFE films that effectively can reduce the surface energy of etched aluminum. The presence of patterned morphology along with the low surface energy at the rf-sputtered PTFE coating makes the aluminum surface with high super-hydrophobic property.

Enhanced response characteristics of SnO2 thin film loaded with nanoscale catalytic clusters for Methane gas

ABSTRACTIn recent years, an increase in usage of methane gas in household and automobile industry has been observed. Detection of methane is always a great cause of concern for safety at home or automobile industries, productions in mines and chemical factories. This paper reports the response characteristics of rf-sputtered SnO2 thin films (90 nm thin) loaded with nanoscale catalytic clusters for detection of methane. Ultrathin (8 nm) metal and metal-oxide catalysts (Pt, Ag, Ni, Pd, Au, NiO, Au2O3) clusters are loaded over the surface SnO2 thin film. The SnO2-Pd cluster structure is found to exhibit an enhanced response (97.2%) for 200 ppm of methane at a relatively low operating temperature (220oC). The enhanced response is shown to be primarily due to the dominant roles played by both Fermi level energy control mechanism and spillover mechanism.

Effect of thickness of thin film SnO2 based LPG sensors

ABSTRACTThis paper reports the response characteristics of rf-sputtered SnO2 thin films (of varying thickness) for LPG detection. To monitor and precisely measure leakages, the development of a reliable LPG sensor with improved sensitivity is crucial in preventing fatal accidents. In the present study, thin film of SnO2 is used as the sensing element for LPG sensor. The thickness of a thin film is a very important parameter and determines their main operating characteristics, such as sensor response, rate of response, and working temperature. In the present study, thickness of SnO2 film is varied between 30 nm to 180 nm. The structure, composition and optical properties of SnO2 thin films have been examined by XRD, SEM, AFM and UV-Vis. The crystallite size for 90 nm thin film (for (110) plane) is found to be the smallest ~4-5 nm. Sensor response $(S = \left( {{{R_a - R_g } \over {R_a }}} \right) \times 100\% )$ increases with thickness of the sensing film, with a highest sensor response (~67%) observed for 90 nm thin film and thereafter it decreases. The structural and optical properties clearly support the observed enhanced sensor response for 90 nm thin film.

Transformation from [formula omitted]-FeSi to [formula omitted]- FeSi2 in RF-sputtered FeSix films

FeSix films were deposited on Si (100) substrates using RF sputtering at room temperature and at 300 °C. After deposition, FeSix films were annealed at 400–900 °C in Ar ambient. XRD measurements revealed that the FeSix films deposited at R. T. for 30 min were completely transformed to β-phase due to annealing at 900 °C for 1 h. On the contrary, the FeSix films deposited at 300 °C for 30 min contained both ε-FeSi and β- FeSi2 after annealing at 900 °C for 1 h. The FeSix films deposited at 300 °C for 3 min were completely transformed to β-phase due to annealing at 800 °C for 1 h. For the FeSix films deposited at 300 °C for 30 min, ε-FeSi transformed to β- FeSi2 in RF-sputtered films due to long time annealing of 10 h. It can be concluded that high-temperature and long-time annealing is necessary for the ε-FeSi bonds in the FeSix films to decompose and for the Fe atoms to be diffused into Si substrates leaving only β-phase FeSi2 in the films.

Control of defect-mediated tunneling barrier heights in ultrathin MgO films

The impact of oxygen vacancies on local tunneling properties across rf-sputtered MgO thin films was investigated by optical absorption spectroscopy and conducting atomic force microscopy. Adding O2 to the Ar plasma during MgO growth alters the oxygen defect populations, leading to improved local tunneling characteristics such as a lower density of current hotspots and a lower tunnel current amplitude. We discuss a defect-based potential landscape across ultrathin MgO barriers.

Structural Characterization of Sputtered Silicon Thin Films after Rapid Thermal Annealing for Active-Matrix Organic Light Emitting Diode

The microcrystalline phase obtained by adopting a two-step rapid thermal annealing (RTA) process for rf-sputtered silicon films deposited on thermally durable glass was characterized. The optical properties, surface morphology, and internal stress of the annealed Si films are investigated. As the thermally durable glass substrate allows heating of the deposited films at high temperatures, micro-polycrystalline silicon (micro-poly-Si) films of uniform grain size with a smooth surface and a low internal stress could be obtained after annealing at 750 °C. The thermal stress in the Si films was 100 times lower than that found in the films deposited on conventional glass. Uniform grains with an average grain size of 30 nm were observed by transmission electron microscopy (TEM) in the films annealed at 800 °C. These micro-poly-Si films have potential application for fabrication of uniform and reliable thin film transistors (TFTs) for large scale active-matrix organic light emitting diode (AMOLED) displays.

Fabrication of superhydrophobic nanostructured surface on aluminum alloy

A superhydrophobic surface was prepared by consecutive immersion in boiling water and sputtering of polytetrafluoroethylene (PTFE or Teflon®) on the surface of an aluminum alloy substrate. Immersion in boiling water was used to create a micro-nanostructure on the alloy substrate. Then, the rough surface was coated with RF-sputtered Teflon film. The immersion time in boiling water plays an important role in surface morphology and water repellency of the deposited Teflon coating. Scanning electron microscopy images showed a “flower-like” structure in first few minutes of immersion. And as the immersion time lengthened, a “cornflake” structure appeared. FTIR analyses of Teflon-like coating deposited on water treated aluminum alloy surfaces showed fluorinated groups, which effectively reduce surface energy. The Teflon-like coating deposited on a rough surface achieved with five-minute immersion in boiling water provided a high static contact angle (∼164°) and low contact angle hysteresis (∼4°).

Super-hydrophobicity of PTFE Films Coated on an Etched Al Surface by Using a RF-magnetron Sputtering Method

Super-hydrophobic properties were achieved for RF-sputtered ultra-thin polytetrafluoroethylene(PTFE) films deposited on etched aluminum surfaces. The microstructural evolution created after etching was investigated by using field emission scanning electron microscopy (FE-SEM). In our investigation, super-hydrophobic surfaces with water contact angles higher than 150 were achieved on RF-sputtered ultra-thin PTFE films of less than 10 nm coated on aluminum(Al) surfaces etched for ten minutes with hydrochloric acid (HCl, 7 wt.% in H2O). X-ray photoelectron spectroscopy (XPS) analysis revealed the presence of a large quantity of -CF3 and -CF2 groups in the RF-sputtered PTFE films, which effectively reduced the surface energy of the etched aluminum. We concluded that the presence of a patterned morphology, along with the low surface energy on ultra-thin RF-sputtered PTFE coating, made the Al surface highly super-hydrophobic.

Differentiation of mesenchymal stem cells onto highly adherent radio frequency‐sputtered carbonated hydroxylapatite thin films

In this work, an improved version of the radio frequency magnetron sputtering (RF-MS) technique was used to prepare highly adherent B-type carbonated hydroxylapatite (B-CHA) thin films. Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction studies proved that the coatings maintained the composition and revealed the polycrystalline structure of HA. Scanning electron microscopy analysis showed that the CHA films are rough and exhibit a homogeneous microstructure. Energy-dispersive X-ray spectroscopy (EDX) mapping demonstrated a uniform distribution of the Ca and P cations while a Ca/P ratio of 1.8 was found. In addition, the FTIR experiments showed a remarkable reproducibility of the nanostructures. Human mesenchymal stem cells (hMSCs), in vitro differentiated osteoblasts, and explanted bone cells were grown over the surface of CHA coatings for periods between a few hours and 21 days. Osteoprogenitor cells maintained viability and characteristic morphology after adhesion on CHA coatings. Ki67-positive osteoblasts were the evidence of cell proliferation events. Cells showed positive staining for markers of osteoblast phenotype such as collagen type I, bone sialoprotein and osteonectin. Our data showed the formation of mineralized foci by differentiation of hMSCs to human primary osteoblasts after cultivation in osteogenic media on RF-sputtered films. The results demonstrate the capacity of B-type CHA coating to support MSCs adhesion and osteogenic differentiation ability.

Sensing mechanism of hydrogen gas sensor based on RF-sputtered ZnO thin films

The mechanism of hydrogen (H 2) gas sensing in the range of 200–1000 ppm of RF-sputtered ZnO films was studied. The I–V characteristics as a function of operating temperature proved the ohmic behaviour of the contacts to the sensor. The complex impedance spectrum (IS) of the ZnO films showed a single semicircle with shrinkage in the diameter as the temperature increased. The best fitting of these data proved that the device structure can be modelled as a single resistance-capacitance equivalent circuit. It was suggested that the conductivity mechanism in the ZnO sensor is controlled by surface reaction. The impedance spectrum also exhibited a decreased in semicircle radius as the hydrogen concentration was increased in the range from 200 ppm to 1000 ppm.