Radio-frequency Sputtering Method Research Articles

Synthesis and characterization of CdTe nanostructures grown by RF magnetron sputtering method

In this paper, we synthesize Cadmium Telluride nanostructures by radio frequency (RF) magnetron sputtering system on soda lime glass at various thicknesses. The effect of CdTe nanostructures thickness on crystalline, optical and morphological properties has been studied by means of X-ray diffraction (XRD), UV-VIS-NIR spectrophotometry, field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), respectively. The XRD parameters of CdTe nanostructures such as microstrain, dislocation density, and crystal size have been examined. From XRD analysis, it could be assumed that increasing deposition time caused the formation of the wurtzite hexagonal structure of the sputtered films. Optical properties of the grown nanostructures as a function of film thickness have been observed. All the films indicate more than 60% transmission over a wide range of wavelengths. The optical band gap values of the films have obtained in the range of 1.62–1.45 eV. The results indicate that an RF sputtering method succeeded in depositing of CdTe nanostructures with high purity and controllable physical properties, which is appropriate for photovoltaic and nuclear detector applications.

Surface and local electronic structure modification of MgO film using Zn and Fe ion implantation

Present work is motivated to investigate the surface and local electronic structure modifications of MgO films implanted with Zn and Fe ions. MgO film was deposited using radio frequency sputtering method. Atomic force microscopy measurements exhibit morphological changes associated with implantation. Implantation of Fe and Zn ions leads to the reduction of co-ordination geometry of Mg2+ ions in host lattice. The effect is dominant at bulk of film rather than surface as the large concentration of implanted ions resides inside bulk. Moreover, the evidences of interaction among implanted ions and oxygen are not being observed using near edge fine structure measurements.

Deposition of Titanium Aluminium Nitride Thin Layer on High Speed Steel Substrate by Radio Frequency Sputtering

High Speed Steel (HSS) has been widely used in manufacturing industry as one of cutting tool materials because of its good mechanical properties yet with a low price. However, since this material has a low thermal resistance property, it will limit its application when used in dry cutting process. Several methods have been used to improve the cutting performance of HSS in dry cutting. One of them was by growing a thin layer of hard coating on the contact surface of the cutting tool material. In this research, Titanium Aluminium Nitride layer were deposited on AISI M41 High Speed Steel substrate by using Radio Frequency (RF) Sputtering method. The aims of this study were to analyze the effect of variations of Aluminium surface area ratios (10, 20, 30, and 40 %) on the Titanium target and also to analyze the effect of deposition time (15, 30, and 45 minutes) on the composition, phase characterization and morphology of the thin layer that formed. The formation of TiAlN and AlN crystalline compounds were observed by X-Ray Diffraction method. A dense layer with a thickness range from 1.4 to 5.2 µm was observed by using a Scanning Electron Microscopy. It was known that the deposition time affect the thickness and also the roughness of the layer. The topography images by Atomic Force Microscopy showed that the deposition time of 45 minutes produce the finest layer with the surface roughness of 10.8 nm.

Nanofibrous Silver-Coated Polymeric Scaffolds with Tunable Electrical Properties.

Electrospun micro- and nanofibrous poly(glycerol sebacate)-poly(ε-caprolactone) (PGS-PCL) substrates have been extensively used as scaffolds for engineered tissues due to their desirable mechanical properties and their tunable degradability. In this study, we fabricated micro/nanofibrous scaffolds from a PGS-PCL composite using a standard electrospinning approach and then coated them with silver (Ag) using a custom radio frequency (RF) sputtering method. The Ag coating formed an electrically conductive layer around the fibers and decreased the pore size. The thickness of the Ag coating could be controlled, thereby tailoring the conductivity of the substrate. The flexible, stretchable patches formed excellent conformal contact with surrounding tissues and possessed excellent pattern-substrate fidelity. In vitro studies confirmed the platform’s biocompatibility and biodegradability. Finally, the potential controlled release of the Ag coating from the composite fibrous scaffolds could be beneficial for many clinical applications.

Resistive switching characteristics and conducting nanobits of polycrystalline NiO thin films

Thin films of NiO were deposited on Pt/Ta/glass sub-strates using a radio frequency (RF) sputtering method. The NiO thin films showed polycrystalline nature, indicating preferentially (111)-oriented structure. The resistive random access memory (RRAM) capacitor of a Pt/NiO/Pt structure exhibited unipolar switching characteristics and bistable resistivities for 200 repeated switching cycles. Furthermore, RRAM nanobits array was formed on the NiO thin films by applying a bias. The RRAM nanobits had a diameter of approximately 8 nm and were observed via a conducting atomic force microscope (CAFM). The density of the RRAM nanobits array was estimated to be approximately 0.64 Tbit/cm2.

Zinc oxide flakes-corolla lobes like nano combined structure for SAW applications

Novel ZnO combined structures were obtained using the radio frequency (RF) sputtering method. The effects of two different substrates, Si and 128° YX LiNbO3, on the structural, morphological, and optical properties of ZnO films were investigated. Field emission scanning electron microscopy clearly revealed the formation of a mixed flake-corolla lobe-like structure. The grain size of the obtained structure depended on the substrate type. Two different X-ray diffraction peaks were obtained for ZnO growth on LiNbO3, at the (200) and (201) diffraction planes, respectively.

Thin film solar cell based on p-CuSbS2 together with Cd-free GaN/InGaN bilayer

CuSbS2 thin film solar cell with 2.99 % efficiency has been demonstrated by using the Cd-free GaN and In0.15Ga0.85N as n-type semiconductor bilayer. CuSbS2 films on the TiN-coated Mo/glass substrates were made by co-sputtering technique at 300 °C with a cermet target of (Cu + Sb2S3) operated at 50–60 W and a metal target of Cu at 2 W, followed by thermal annealing at 350–450 °C for 1 h. The effects of processing conditions on the growth behavior, microstructural characteristics, and electrical properties of CuSbS2 films had been investigated. Solar cell devices were fabricated by depositing ~50 nm GaN and ~300 nm In0.15Ga0.85N layers with low temperature radio-frequency (RF) sputtering method, followed by RF sputtering 300–400 nm indium-tin oxide for front contact and pasting silver glue for electric contacts. The CuSbS2 thin film sputtered at 55 W had a [Cu]/[Sb] ratio of 0.80 with co-exists of the Sb2S3, and had a hole concentration of 1.41 × 1018 cm−3, an electrical conductivity 0.1 S cm−1, and mobility of 13 cm2 V−1 s−1. The efficiency of the solar cell device had a 3.83-fold increase if the p-CuSbS2/CdS/n-ZnO system had its conventionally designed CdS/n-type ZnO layer replaced by n-type GaN/In0.15Ga0.85N bilayer.

Fabrication and characterization of nitrogen doped p-ZnO on n-Si heterojunctions

Metal oxide semiconductors are promising materials for fabricating p-n heterojunctions which are technologically important for many electronic devices. The reason is their unique characteristics of tuneable electrical properties that can be controlled by doping. In the present work, a p-n heterojunction was fabricated by depositing nitrogen doped zinc oxide (ZnO:N) thin films on an n-type Si substrate using the radio frequency (RF) sputtering method. X-ray diffraction patterns shows the preferred orientation (002) peak of ZnO, which deteriorated with increasing N concentration. The crystallite size varied from 35 to 20nm for different N concentration. The morphology of the ZnO:N thin films were highly dense and smooth. The optical band gap of the heterojunctions increased from 3.2 to 3.3eV as the flow rate increased from 5 to 9 SCCM N2. The current-voltage (I–V) characteristics confirm the p-n junction behaviour of the ZnO:N/Si heterojunctions. The I–V characteristics were also measured at different temperatures in the dark. The photoelectric response on the I–V characteristics of the heterojunctions was also measured. The stability of the ZnO:N/Si heterojunction with respect to time duration was assessed. The results demonstrate that such physical processed novel thin films are promising for potential applications in electro-optic devices.

Morphology, composition, structure and optical properties of CuO/Cu2O thin films prepared by RF sputtering method

In this paper, copper oxide (CuO/Cu2O) nanocrystalline thin films were deposited by radio frequency (RF) magnetron sputtering system at 75 W and 100 W. The surface, optical, composition and structural properties of obtaining samples were characterized by using atomic force microscopy (AFM), UV–Vis spectrophotometer, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The optical band gaps of produced films were calculated as 2.05 eV and 1.83 eV for 75 W and 100 W. The layer’s thicknesses were measured as 20 nm and 50 nm using a Filmetrics F20. FESEM images of the samples prove the AFM images change and also show homogeneity of thin films and variation relative to power change, thus revealed the surface of samples disturb in homogen mode. EDX results denote presence of Cu and O elements inside the deposited samples.

Room temperature deposition of amorphous p-type CuFeO2 and fabrication of CuFeO2/n-Si heterojunction by RF sputtering method

Transparent conducting amorphous p-type CuFeO2 (CFO) thin film was prepared by radio-frequency (RF) magnetron sputtering method at room temperature using polycrystalline CuFeO2 target. Amorphous structure of as-deposited film was confirmed by XRD. XPS analysis convinced that the chemical state of Cu+ and Fe3+ in the film, and the chemical composition of the thin films is close to the stoichiometry of CuFeO2. Surface morphology of the film was analysed by SEM studies. p-type nature and concentration of carriers was investigated by Hall effect measurement. The p–n heterojunction in the structure of Al/n-Si/p-CuFeO2/Al showed good rectifying behaviour with a forward and reverse currents ratio of 555 at 2 V. The turn-on voltage and reverse leakage current values were found to be 0.9 V and 4 μA at −2 V. Further, the conduction mechanism of forward bias voltage was controlled by thermionic emission (TE) and trap-space charge limited current (TCLC) mechanisms.

Thermoelectric characterization and fabrication of nanostructured p-type Bi0.5Sb1.5Te3 and n-type Bi2Te3 thin film thermoelectric energy generator with an in-plane planar structure

This paper presents in-plane bismuth-telluride-based thermoelectric (TE) energy generators fabricated using metal-shadow and radio-frequency sputtering methods at room temperature. The TE energy generators consist of four couples of 300-nm-thick nanostructured Bi2Te3 (n-BT) and Bi0.5Sb1.5Te3 (p-BST) thin films used as n-type and p-type materials, respectively, on a Si substrate for the p/n junctions of the TE energy generators. Furthermore, the effect of annealing treatment of both n-BT and p-BST thin films on the electrical and TE properties as well as the TE performance of the TE energy generators is discussed. By varying the temperature between the hot and cold junction legs of the n-BT/p-BST in-plane TE energy generators annealed at 200 °C, the maximum output voltage and power are determined to be ∼3.6 mV and ∼1.1 nW, respectively, at a temperature difference of 50 K. The output powers increased by ∼590% compared to that of the as-grown TE generator at a temperature difference of 90 K. This improvement in the TE performance is attributed to the enhancement of the electrical conductivity after heat treatment. From a numerical simulation conducted using a commercial software (COMSOL), we are confident that it plays a crucial role in determining the dimension (i.e., thickness of each leg) and material properties of both n-BT and p-BST materials of the in-plane TE energy generators.

Morphology of TiAlN Thin Film onto HSS as Cutting Tools by Using Mosaic-Styled Target RF Sputtering Method

High Speed Steel (HSS) has been widely used in manufacturing industry as cutting tools. Several methods have been used to improve the cutting performance of HSS in dry cutting. One of them was by growing a thin layer of hard coating on the contact surface of the cutting tool material. In this research, Titanium Aluminum Nitride (TiAlN) layer were deposited on AISI M41 HSS substrate by using Radio Frequency (RF) sputtering method with mosaic styled of target materials. The aluminum surface area ratios on the Titanium target are 10, 20, 30, and 40 % respectively. The deposition time are 15, 30, and 45 minutes respectively. The formation of TiAlN and AlN crystalline compounds were observed by X-Ray Diffraction method. The morphology of thin film layer with a thickness range from 1.4 to 5.2 µm was observed by using a Scanning Electron Microscopy. It was known that the deposition time affect to the thickness and also the roughness of the layer. The topography images by Atomic Force Microscopy showed that the deposition time of 45 minutes produce the finest layer with the surface roughness of 10.8 nm.

Oxygen-doped zirconium nitride based transparent resistive random access memory devices fabricated by radio frequency sputtering method

In this work, we present a feasibility of bipolar resistive switching (RS) characteristics for Oxygen-doped zirconium nitride (O-doped ZrNx) films, produced by sputtering method, which shows a high optical transmittance of approximately 78% in the visible region as well as near ultra-violet region. In addition, in a RS test, the device has a large current ratio of 5 × 103 in positive bias region and 5 × 105 in negative bias region. Then, to evaluate an ability of data storage for the proposed memory devices, we measured a retention time for 104 s at room temperature (RT) and 85 °C as well. As a result, the set and reset states were stably maintained with a current ratio of ∼102 at 85 °C to ∼103 at RT. This result means that the transparent memory by controlling the working pressure during sputtering process to deposit the ZrNx films could be a milestone for future see-through electronic devices.

Effect of Mg doping in ZnO buffer layer on ZnO thin film devices for electronic applications

Zinc Oxide (ZnO) thin films have been grown on p-silicon (Si) substrate using magnesium doped ZnO (Mg: ZnO) buffer layer by radio-frequency (RF) sputtering method. In this paper, we have optimized the concentration of Mg (0–5 atomic percent (at. %)) ZnO buffer layer to examine its effect on ZnO thin film based devices for electronic and optoelectronic applications. The crystalline nature, morphology and topography of the surface of the thin film have been characterized. The optical as well as electrical properties of the active ZnO film can be tailored by varying the concentration of Mg in the buffer layer. The crystallite size in the active ZnO thin film was found to increase with the Mg concentration in the buffer layer in the range of 0–3 at. % and subsequently decrease with increasing Mg atom concentration in the ZnO. The same was verified by the surface morphology and topography studies carried out with scanning electron microscope (SEM) and atomic electron microscopy (AFM) respectively. The reflectance in the visible region was measured to be less than 80% and found to decrease with increase in Mg concentration from 0 to 3 at. % in the buffer region. The optical bandgap was initially found to increase from 3.02 eV to 3.74 eV by increasing the Mg content from 0 to 3 at. % but subsequently decreases and drops down to 3.43 eV for a concentration of 5 at. %. The study of an Au:Pd/ZnO Schottky diode reveals that for optimum doping of the buffer layer the device exhibits superior rectifying behavior. The barrier height, ideality factor, rectification ratio, reverse saturation current and series resistance of the Schottky diode were extracted from the measured current voltage (I–V) characteristics.

Microstructure and micromorphology of ZnO thin films: Case study on Al doping and annealing effects

The aim of this work is to investigate the three-dimensional (3-D) surface texture of Aliminium doped Zinc Oxide (AZO) thin films deposited by Radio Frequency sputtering method on the quartz substrates. Deposited samples were annealed under argon flux at three different temperatures: 400 °C, 500 °C, and 600 °C, followed by gradual cooling down to room temperature. To characterize the structure of samples X-ray diffraction (XRD) patterns and Rutherford Back Scattering (RBS) spectra were applied. The Scanning electron microscope (SEM) and the atomic force microscope (AFM) were applied to study the samples' surface morphology. Then statistical, fractal and functional surface characteristics were computed. The analysis of 3-D surface texture of AZO thin films is crucial to control the 3-D surface topography features and to correct interpretate the surface topographic parameters. It also allows understanding the relationship between 3-D the surface topography and the functional (physical, chemical and mechanical) properties of AZO thin films.

Transparent Conductive and Wide Band Gap Characteristics of Quaternary Mg and Al Co-Doped ZnO Thin Films Prepared by Radio Frequency Sputtering Method

Transparent Conductive and Wide Band Gap Characteristics of Quaternary Mg and Al Co-Doped ZnO Thin Films Prepared by Radio Frequency Sputtering Method

Optical Study of Cuprous Oxide and Ferric Oxide Based Materials for Applications in Low Cost Solar Cells

One of the interesting forms of cuprous oxide and ferric oxide based materials is CuFeO2 which can be a delafossite-type compound and is a well known p-type semiconductor. This compound makes up an interesting family of materials for technological applications. CuFeO2 thin films recently gained renewed interest for potential applications in solar cell devices especially as absorption layers. One of the interesting facts is that CuFeO2 is made from cheap materials such as copper and iron. In this study, CuFeO2 thin films are intentionally deposited on corning glass and silicon substrates by the radio-frequency and direct current sputtering method with complicated and well developed co-sputtering recipes. The deposition was performed at room temperature which leads to an amorphous phase with extremely low roughness and high density. The films also were annealed at 500°C in 5% H2 in Ar for the passivation. A detailed optical study was performed on these thin films by spectroscopic ellipsometry and by ultra-violet visible near infrared spectroscopy. Depending on sputtering conditions, the direct band gap was extrapolated to be from 1.96 eV to 2.2 eV and 2.92 eV to 2.96 eV and the indirect band gap is about 1.22 eV to 1.42 eV. A good electrical conduction is also observed which is suitable␣for solar cell applications. In future more study on the structural properties will be carried out in order to fully understand these materials.

Electron-electron scattering in three-dimensional amorphous IGZO films

Electron dephasing process is important and interesting in disordered conductors. In general three-dimensional (3D) disordered metals, the electron-electron (e-e) scattering is negligibly weak compared with the electron-phonon (e-ph) scattering. Thus, the theoretical prediction concerning the e-e scattering rate 1/τee as a function of temperature T in 3D disordered conductor has not been fully tested so far, though it was proposed four decades ago. In the frame of free-electron-like model, the e-ph relaxation rate 1/τep is proportional to carrier concentration n, while the small-and large-energy-transfer e-e scattering rate obey the laws 1/τeeS ∝ n-4/3 and 1/τeeL ∝ n-2/3, respectively. In other words, e-e scattering may dominate the dephasing processes in 3D disordered metals with sufficient low carrier concentrations. In the present work, we systematically investigate the electronic transport properties of amorphous indium gallium zinc oxide (a-IGZO) prepared by the radio frequency sputtering method. The carrier concentrations of the highly degenerate IGZO films are all ～ 5×1019 cm-3, which are 3-4 orders of magnitude lower than those of typical metals. Our thick films (～ 800 nm) are 3D systems with respect to weak-localization (WL) effect and e-e scattering. X-ray diffraction patterns of the films indicate that our films are all amorphous. For each film, the resistivity increases with the increase of the temperature in the high temperature region (T ≥ 200 K) and the carrier concentration is almost invariable in the whole measured temperature range. This indicates that the films possess metal-like transport properties. By comparing the low-field magnetoconductivity versus magnetic field data σ (B) with that from the 3D WL theory, we extract the electron dephasing rate 1/τφ at different temperatures in the low temperature region. It is found that 1/τφ varies linearly with T3/2 for each film. The T3/2 behavior of 1/τφ can be quantitatively described by the 3D small-energy-transfer e-e scattering theory. The e-ph scattering rate 1/τep and large-energy-transfer e-e scattering rate 1/τeeL are negligibly weak in this low-carrier-concentration conductor. Thus, we can observe the T3/2 behavior of 1/τφ.

Nickel titanate (NiTiO3) thin films: RF-sputtering synthesis and investigation of related features for photocatalysis

Polycrystalline nickel titanate thin films were deposited on silicon substrates by the radio-frequency (rf) sputtering method using NiTiO3 targets, which in turn were sintered from powders obtained by solid state reaction. The deposition parameters such as rf-powers, partial pressures of argon and oxygen, as well as substrate temperatures were optimized to ensure the homogeneous and stoichiometric composition of NiTiO3 thin films. Post-synthesis annealing at suitable temperatures and time durations was realized to stabilize the ilmenite structure with improved crystalline features deduced from structural and vibrational investigations by using XRD and Raman spectroscopy. The surface roughness and thin film microstructure were characterized by AFM which points out the organisation of the film surface. Representative films with ilmenite structure and defined surface microstructure and optical absorbance were tested as visible light driven heterogeneous photocatalysts for the degradation of organic dyes.

Interface and electrical properties of ultra-thin HfO2 film grown by radio frequency sputtering

Interfacial composition and electrical properties of ultra-thin hafnium oxide (HfO2) films on p-type <100> Si substrate are reported. Hafnium oxide (HfO2) thin films are prepared using radio-frequency sputtering method and subsequently annealed at different temperature. The effect of post-deposition annealing on the interfacial and chemical state of HfO2/Si gate stack has been characterised by means of X-ray reflectivity and X-ray photoelectron spectroscopy studies. Peaks of X-ray photoelectron spectroscopy spectra at 530.50 and 532.25eV originate from Hf–O–Si bond illustrated the creation of Hf-silicate based interfacial layer at the high-k/Si interface. X-ray reflectivity fitting result also corroborated the formation of Hf silicate interfacial layer. Capacitance-voltage measurements revealed insignificant hysteresis in case of film annealed at 600°C. Interface trap density has been extracted using Terman method and is found to be 3.18×10−11cm−2eV−1 at −1.0V. Minimum equivalent oxide thickness (EOT) of 1.3nm was obtained for the film annealed at 600°C. The gate leakage current density of the HfO2 film annealed at 600°C is 1.5×10−5A/cm2 at a bias voltage of −2V.