Varying RF Power Research Articles

Studies on optoelectronic properties of magnetron Sputtered cadmium stannate (Cd2SnO4) thin films as alternative TCO materials for solar cell applications

Single phase cadmium stannate thin films were deposited on glass substrates through rf magnetron sputtering by varying rf power and keeping substrates at room temperature. The effect of rf power on physical properties of the films and the correlations were systematically investigated. It has been found from XRD that structural phase transition occurred from amorphous to spinel structure with increase of rf power. AFM images revealed that the deposited films show smooth surface with nano grains. High transmittance was retained by the films in visible region and the band gap was decreased from 3.05 to 2.49eV for increasing rf power by quantum confinement effect. The Mott-Davis model and drude model were used to evaluate the optical constants and free carrier absorption. The electrical resistivity of the films varied in three orders of magnitude as a function of rf power which could be explained by oxygen vacancies formation. From these results, the films deposited at 150 W has the low resistivity of the order of 10−3Ωcm with high optical transparency as 80% which could be the preferred conditions to deposit high quality films for future TCO layers for cadmium based CdTe/CdS solar cell devices.

Investigation of microstructural and electrical properties of composition dependent co-sputtered Hf1−xTaxO2 thin films

Tantalum doped HfO2 gate dielectric thin films were deposited on silicon substrates using RF reactive co-sputtering by varying RF power of Ta target from 15 W to 90 W. The morphological, compositional and electrical properties of Hf1−xTaxO2 films were systematically investigated. The Ta content was found to be increased up to 21% for a Ta target power of 90 W. The evolution of monoclinic phase of Hf1−xTaxO2 was seen from XRD study upto RF power of 60 W and afterwards, the amorphous like behaviour is appeared. The featureless smooth surface with the decrease in granular morphology has been observed from FESEM micrographs of the doped films at higher RF powers of Ta. The flatband voltage is found to be shifted towards negative voltage in the capacitance–voltage plot, which was attributed to the enhancement in positive oxide charge density with rise in RF power. The interface charge density has a minimum value of 7.85 × 1011 eV−1 cm−2 for the film deposited at Ta RF power of 75 W. The Hf1−xTaxO2 films deposited at Ta target RF power of 90 W has shown lower leakage current. The high on/off ratio of the current during the set process in Hf1−xTaxO2 based memristors is found suitable for bipolar resistive switching memory device applications.

Experimental benchmark of the NINJA code for application to the Linac4 H− ion source plasma

For a dedicated performance optimization of negative hydrogen ion sources applied at particle accelerators, a detailed assessment of the plasma processes is required. Due to the compact design of these sources, diagnostic access is typically limited to optical emission spectroscopy yielding only line-of-sight integrated results. In order to allow for a spatially resolved investigation, the electromagnetic particle-in-cell Monte Carlo collision code NINJA has been developed for the Linac4 ion source at CERN. This code considers the RF field generated by the ICP coil as well as the external static magnetic fields and calculates self-consistently the resulting discharge properties. NINJA is benchmarked at the diagnostically well accessible lab experiment CHARLIE (Concept studies for Helicon Assisted RF Low pressure Ion sourcEs) at varying RF power and gas pressure. A good general agreement is observed between experiment and simulation although the simulated electron density trends for varying pressure and power as well as the absolute electron temperature values deviate slightly from the measured ones. This can be explained by the assumption of strong inductive coupling in NINJA, whereas the CHARLIE discharges show the characteristics of loosely coupled plasmas. For the Linac4 plasma, this assumption is valid. Accordingly, both the absolute values of the accessible plasma parameters and their trends for varying RF power agree well in measurement and simulation. At varying RF power, the H− current extracted from the Linac4 source peaks at 40 kW. For volume operation, this is perfectly reflected by assessing the processes in front of the extraction aperture based on the simulation results where the highest H− density is obtained for the same power level. In surface operation, the production of negative hydrogen ions at the converter surface can only be considered by specialized beam formation codes, which require plasma parameters as input. It has been demonstrated that this input can be provided reliably by the NINJA code.

Modulation of microstructure and interface properties of co-sputter derived Hf1−xTixO2 thin films with various Ti content

Hf1−xTixO2 dielectric thin films were deposited on Si (100) substrates by RF reactive co-sputtering with the variation in RF power of Ti target. The compositional, morphological, structural and optical properties of Hf1−xTixO2 films with various Ti concentration were systematically investigated by X-ray photoelectron spectroscopy (XPS), Field emmission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectroscopy techniques respectively. The electrical properties of the co-sputtered thin films were studied by capacitance–voltage and current density–voltage measurements. The XRD study has shown the enhancement in the the crystalline property of Hf1−xTixO2 film up to 60 W of Ti target power and amorphous like behaviour was observed for higher RF power. The Ti content in Hf1−xTixO2 was calculated from the XPS measurements, where the Ti content was found to be increased with rise in RF power. FESEM micrographs depict the increase in grain size upto the RF power 60 W. The Raman spectrum of the Hf1−xTixO2 film has shown that the major generated phase was titanium-substituted monoclinic phase of HfO2. The flatband voltage (Vfb) and oxide charge density (Qox) were extracted from the high frequency (1 MHz) C–V curve. The Dit has a minimum value for the film deposited at 60 W RF power of Ti target. The leakage current density of the Hf1−xTixO2 films was found to be minimum for the RF power 60 W.

Structural, surface morphology and optical properties of sputter-coated CaCu3Ti4O12 thin film: Influence of RF magnetron sputtering power

This study focusses on the investigation of RF power variations (100–300W) effects on structural, morphological and optical properties of CaCu3Ti4O12 thin film deposited on ITO/glass substrate in a non-reactive atmosphere (Ar). The increase of RF power from 100W to 300W led to evolution of (112), (022), (033), and (224) of CCTO XRD peaks. The results indicated that all the films were polycrystalline nature with cubic structure. The crystallite size increased from 20nm to 25nm with increasing RF power. FESEM revealed that the films deposited were uniform, porous with granular form, while the grain size increased from 30 to 50nm. AFM analysis confirmed the increment in surface roughness from 1.6 to 2.3nm with increasing film grain size. Besides, optical transmittance values decreased to minimum 70% with increasing RF power while optical energy bandgap increased from 3.20eV to 3.44eV. Therefore, favorable CCTO thin film properties can be possibly obtained for certain application by controlling RF magnetron sputtering power.

Effect of RF sputtering power on morphological and electrical properties of calcium copper titanate thin films

Calcium copper titanate (CCTO) thin films were deposited on p-type silicon substrate by RF magnetron sputtering at various RF powers. Post deposition annealing was carried out for all the samples at 950 °C for 1 h in air atmosphere. Various types of surface morphology have been observed for CCTO thin films with the variation of RF power. The evolution of polycrystalline structure of the CCTO thin films was confirmed by XRD studies. The FTIR characteristic absorption band of CCTO was observed in the range of 400–700 cm−1. The capacitance–voltage (C–V) and current–voltage (I–V) characteristics of the films were investigated employing Al/CCTO/Si MOS capacitors. CCTO films with higher dielectric constant, lower oxide and interface charge density were obtained at higher RF power. Leakage current was also found to be minimum for RF power of 105 W.

Influence of power and temperature on properties of sputtered AZO films

Aluminum-doped zinc oxide films (AZO) were deposited on glass substrates by magnetron sputtering. The effect of RF power and deposition temperature on wettability and optical properties of AZO films are studied in detail. The increase of RF power from 60W to 180W (power density from 1.54 to 4.62W/m2) leads to evolution of (100), (002) and (101) textures of zinc oxide. The XRD results shows increased preferred orientation of (002) plane along c-axis for deposited AZO films. The grain size increases from 14nm to 23nm with increase of RF power from 60W to 180W and from 17nm to 25nm with increase in deposition temperature from 200°C to 600°C. The static and dynamic contact angle formed by water and ethylene glycol varies as a function of RF power and deposition temperature. AZO films with an optical transmission 80% to 60%, refractive index 1.49 to 1.51 and band gap values from 3.29eV to 3.21eV were obtained in the wavelength range of 350–800nm. The electric resistivity varies from 3.9×10−2 to 1.1×10−2Ω·cm depending upon variation of RF power and deposition temperature.

Extracting dielectric spectroscopic properties from microwave-induced thermoacoustic signals.

Available data on the dielectric properties of biological tissue across a frequency range adds an extra degree of freedom of contrast besides the baseline structural information obtained by conventional imaging techniques. In this paper, we propose a new methodology to non-invasively extract the normalized effective conductivity of samples over a large frequency range using microwave-induced thermoacoustic (TA) signals. Additionally, a calibration approach has been adopted to remove the frequency dependency of the experimental setup errors as well as the RF power variation. The linear relationship between the TA signal amplitude on the absorbed microwave power is used to extract the properties of samples. Saline phantoms with various concentration are used to mimic different tissue materials in the proof-of-concept experiment. The extracted normalized effective conductivity by the proposed method matches the theoretical calculations as well as the direct contact measurements by a dielectric probe.

Broadband and tunable RF photonic phase shifter based on optical SSB modulation and FBG filtering

A broadband RF photonic phase shifter that can achieve the tunable phase shift with little RF power variation is presented. It is based on homodyne mixing technique. The beating between phase-modulated optical carrier and the first-order sideband can generate RF signal with desired phase shift. Results show the RF phase shifter can achieve a continuous 0–360° phase shift with low power variation at the frequency above 21.5GHz.

Determination of discharge parameters via OES at the Linac4 H− ion source

Optical emission spectroscopy (OES) measurements of the atomic Balmer series and the molecular Fulcher transition have been carried out at the Linac4 ion source in order to determine plasma parameters. As the spectroscopic system was only relatively calibrated, the data evaluation only yielded rough estimates of the plasma parameters (T(e) ≈ 1.2 eV, n(e) ≈ 1 × 10(19) m(-3), and n(H/)n(H2) ≈ 0.5 at standard operational parameters). The analysis of the Fulcher transition revealed a non-thermal "hockey-stick" rotational population of the hydrogen molecules. At varying RF power, the measurements at the on-axis line of sight (LOS) showed a peak in the rotational temperatures between 25 and 40 kW of RF power, whereas a steady decrease with power was observed at a tilted LOS, indicating the presence of strong plasma parameter gradients.

Automatic RF Input Power Level Control Methodology for SAR Measurement Validation

Evaluation of radiating radiofrequency fields from hand-held and body-mounted wireless communication devices to human bodies are conducted by measuring the specific absorption rate (SAR). The uncertainty of system validation and probe calibration in SAR measurement depend on the variation of RF power used for the validation and calibration. RF input power for system validation or probe calibration is controlled manually during the test process of the existing systems in the laboratories. Consequently, a long time is required to reach the stable power needed for testing that will cause less uncertainty. The standard uncertainty due to this power drift is typically 2.89%, which can be obtained by applying IEC 62209 in a normal operating condition. The principle of the Automatic Input Power Level Control System (AIPLC), which controls the equipment by a program that maintains a stable input power level, is suggested in this paper. The power drift is reduced to less than <TEX>${\pm}1.16dB$</TEX> by AIPLC, which reduces the standard uncertainty of power drift to 0.67%.

Study on Electrochemical Performance of Thin Film C60 As an Anode Material for Lithium Secondary Batteries

Lithium ion batteries are gaining more attention these days since it is being used in many application, ranging from portable devices to electric vehicles due to their superior energy density and cycleability over the other energy storage technologies. Among those applications, microrobotics is also getting more attention since it can be used for exploration in small and/or dangerous environment, finding survivor in the disaster site, and defense department needs. However, there is crucial shortage from these microrobotics, which are its power source limitation. In order to overcome this limitation, special attempts should be done by designing the energy storage cell as small as possible. In order to achieve this, carbon based thin film might be one of the plausible alternative. To this end, we made a carbon based thin film using the plasma enhanced thermal evaporation deposition. Since the available commercial graphite and graphene have extremely high melting point (ca. 3600 oC and ca. 3900 oC for graphite and graphene, respectively), these materials are not applicable when used as the precursor for thin film deposition process [1]. It has been already investigated that carbon with the structure of C70 and C60 has significantly low sublimation point of ca. 850 oC and 600 oC, respectively [2]. In our experiment scope, we made the carbon based thin film electrode using C60powder. The deposition of C60 thin films were deposited by plasma enhanced thermal evaporation. The samples were prepared under following conditions: a working pressure of 25 mTorr and deposition time of 1 min. The film thickness and RF power were varied. The film thickness was varied by introducing different amount of C60powder of 0.01 g, 0.02 g, and 0.04 g. The RF power variation was 100 W, 200 W, and 300 W. The results show that thicker C60 thin film would result in lower volumetric capacity. This might be related to the characteristic of C60 that intrinsically high resistance. Thus, increasing the thickness might increase the resistance of the film and might also lead to longer distance for lithium to diffuse into the C60electrode. Meanwhile, the investigation of plasma power variation shows that lower plasma power results in higher volumetric capacity. These phenomena would be the focus of our detail discussion. Reference 1. J. H. Los, K. V. Zakharchenko, M. I. Katsnelson, and A. Fasolino, Physical Review B 91, 045415 (2015). 2. Eiji Osawa (2002). Perspective of fullerene nanotechnology. Springer. pp. 275. Figure 1

Anti-reflection coatings for silicon solar cells from hydrogenated diamond like carbon

Aiming towards a specific application as antireflection coatings (ARC) in Si solar cells, the growth of hydrogenated diamond like carbon (HDLC) films, by RF magnetron sputtering, has been optimized through comprehensive optical and structural studies. Various physical properties of the films e.g., (ID/IG) ratio in the Raman spectra, percentage of sp3 hybridization in XPS spectra, H-content in the network, etc., have been correlated with different ARC application properties e.g., transmittance, reflectance, optical band gap, refractive index, surface roughness, etc. The ARC properties have been optimized on unheated substrates, through systematic variations of RF power, gas flow rate, gas pressure and finally controlled introduction of hydrogen to the DLC network at its most favorable plasma parameters. The optimum HDLC films possess (T700)max∼95.8%, (R700)min∼3.87%, (n700)min∼1.62 along with simultaneous (Eg)max∼2.53eV and ∼75.6% of sp3 hybridization in the C-network, corresponding to a bonded H-content of ∼23at.%. Encouraging improvements in the ARC properties over the optimized DLC film were obtained with the controlled addition of hydrogen, and the optimum HDLC films appear quite promising for applications in Si solar cells. Systematic materials development has been performed through comprehensive understanding of the parameter space and its optimization, as elaborately discussed.

Synthesis, Characteristics, and Material Properties Dataset of Bi:DyIG‐Oxide Garnet‐Type Nanocomposites

The fabrication, annealing crystallization processes, and material properties of (Bi,Dy)3(Fe,Ga)5O12:Bi2O3 nanocomposites are investigated and summarized. The stoichiometry of these nanocomposites is optimized for magnetooptic applications using the approach of stoichiometry adjustment (implemented by means of varying RF power densities applied to the sputtering targets used to prepare the nanocomposite thin films). The crystallization processes for all developed batches of as‐deposited films are carried out by annealing runs at different temperatures and process durations. This paper describes the methodologies used to optimize the compositions (by calculating the volumetric fractions of excess bismuth oxide to be mixed with the garnet‐stoichiometry species during cosputtering processes) and to obtain the optical and magnetooptical properties data and presents the materials properties summary of garnet‐bismuth oxide thin film composites as well.

Physical properties of rf magnetron sputter deposited NiO:WO3 thin films

The present study describes various physical properties of mixed nickel–tungsten oxide (NiO:WO3) (95:5) thin films prepared on glass substrate by rf magnetron sputtering due to the variation in rf power (100, 150, and 200 W). X-ray diffraction study shows that all the deposited films are amorphous in nature. The maximum transmittance of 97% in the infrared region was observed for the film deposited at 100 W rf power. A systematic reduction in the optical band gap is observed with increasing rf power, which is associated with the rf power induced effect leading to the production of localized states near the band edges of NiO:WO3. The Urbach energy (EU) value was found to increase with rf power, which may be due to the increased defects in the NiO matrix. From the optical study, we have evaluated various parameters such as refractive index, packing density, lattice dielectric constant, ratio between free carrier density and free carrier effective mass, plasma frequency, and dispersion energy parameters, etc. These results are discussed and correlated well with the light of possible mechanisms underlying the phenomena. The compositional purity of the film was confirmed by energy dispersive x-ray analysis (EDAX) and Auger electron spectroscopic (AES) measurements. The Raman spectra of NiO:WO3 films show two peaks corresponding to one-phonon LO mode at 560 cm−1 and two-phonon LO mode at 1100 cm−1 due to the vibrations of Ni–O bonds and a strong peak at 860 cm−1 corresponds to the stretching vibration of W–O pair in the WO6 group. The band edge emission at 369 nm was observed in photoluminescence spectra.

High-Speed Visualization of Filament Instabilities and Self-Organization Effect in RF Argon Plasma Jet at Atmospheric Pressure

An RF argon plasma jet has been explored using high-speed camera imaging at 10000 frames/s. Small variations of gas flow and/or RF power lead to instabilities of the filament movement. Two types of instabilities have been observed depending on the interrelated azimuthal velocities of filaments. In the case of antiparallel filament velocities, one filament is collapsing and fuses with the other filament, while the collapsing filament exhibits a striated structure. In the case of parallel velocities, both filaments establish a symmetric configuration and rotate with constant velocity in the jet. Spatially and temporally resolved features are visualized with a time-colored stroboscopic image.

Mode coupling and resonance instabilities in quasi-two-dimensional dust clusters in complex plasmas.

Small quasi-two-dimensional dust clusters consisting of three to eleven particles are formed in an argon plasma under varying rf power. Their normal modes are investigated through their mode spectra obtained from tracking the particles' thermal motion. Detailed coupling patterns between their horizontal and vertical modes are detected for particle numbers up to 7 and discrete instabilities are found for dust clusters with particle number ⩾9, as predicted in previous theory on ion-flow induced mode coupling in small clusters. The instabilities are proven to be induced by resonance between coupled horizontal and vertical normal modes.

English

Diamond like carbon (DLC) films are deposited on glass substrates by using radio frequency plasma enhanced chemical vapour deposition technique with the variation of RF power. DLC films are deposited by using argon and acetylene plasma, at pressure 5×10-2 mbar for 60 minutes. Various properties like surface morphology, hydrophobicity, nanohardness, and structural properties are studied by using atomic force microscope, contact angle measurement setup, nano-hardness tester and Raman spectrometer, respectively. Systematic variation in surface morphology with RF power has been observed. It has been observed that the morphology of the films is correlated with the hardness, sp3 content, roughness, and contact angle. Observed results have been explained using Raman spectra.

Structural and optical properties of nc-Si:H thin films deposited by layer-by-layer technique

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited on c-Si and quartz substrates by layer-by-layer (LBL) technique using radio-frequency plasma enhanced chemical vapour deposition system. The effects of rf power on the interlayer elemental profiling, structural and optical properties of the films were investigated by Auger electron spectroscopy, Fourier transform infrared spectroscopy, Raman scattering spectroscopy, X-ray diffraction and optical transmission and reflection spectroscopy. The results revealed that the LBL deposition leads to a formation of different ranges of crystallite sizes of nc-Si corresponds 3–6 and 8–26 nm respectively. LBL deposition also demonstrated a capability to increase the crystalline volume fraction of nc-Si up to 65.3 % with the crystallite size in between 5 and 6 nm, at the rf power in between 80 and 100 W. However, the crystalline volume fraction decreased for the rf power above 100 W due to the growth of nc-Si was suppressed by the formation of SiO2. In addition, the onset of crystallization of the films deposited on c-Si and quartz substrates are different with increase in the rf power. The effects of rf power on the growth of nc-Si, and the hydrogen content, structural disorder, crystallite size of nc-Si and oxygen diffusion into the LBL layer with the change of optical energy gap under the variation of rf power are also discussed.

A reactive magnetron sputtering route for attaining a controlled core-rim phase partitioning in Cu2O/CuO thin films with resistive switching potential

The achievement of a reproducible and controlled deposition of partitioned Cu2O/CuO thin films by techniques compatible with ULSI processing like reactive magnetron sputtering has been reported as an outstanding challenge in the literature. This phase partitioning underlies their performance as reversible resistive memory switching devices in advanced microelectronic applications of the future. They are currently fabricated by thermal oxidation and chemical methods. We have used a combination of an understanding from plasma chemistry, thermo-kinetics of ions, and rf power variation during deposition to successfully identify a processing window for preparing partitioned Cu2O/CuO films. The production of a core rich Cu2O and surface rich Cu2O/CuO mixture necessary for oxygen migration during resistive switching is confirmed by XRD peaks, Fourier transform infra red Cu (I)-O vibrational modes, XPS Cu 2P3/2 and O 1S peak fitting, and a comparison of satellite peak ratio's in Cu 2P3/2 fitted peaks. We are proposing based on the findings reported in this paper that an XPS satellite peak intensity(Is) to main peak intensity ratio (Im) ≤ 0.45 as an indicator of a core rich Cu2O and surface rich Cu2O/CuO formation in our prepared films. CuO is solely responsible for the satellite peaks. This is explained on the basis that plasma dissociation of oxygen will be limited to the predominant formation of Cu2O under certain plasma deposition conditions we have identified in this paper, which also results in a core-rim phase partitioning. The deposited films also followed a Volmer-Weber columnar growth mode, which could facilitate oxygen vacancy migration and conductive filaments at the columnar interfaces. This is further confirmed by optical transmittance and band-gap measurements using spectrophotometry. This development is expected to impact on the early adoption of copper oxide based resistive memory electronic switching devices in advanced electronic devices of the future. The relative abundance of copper is another major complementary driver for the interest in copper oxide films.