Asymmetric Bipolar Pulsed Dc Magnetron Research Articles

Asymmetric Bipolar Pulsed dc Sputtered Nanocrystalline VN Coatings for Electrode Materials in Lithium Battery.

Nanocrystalline vanadium nitride (VN) coatings for electrode materials for lithium battery with various deposition parameters have been prepared using dc and asymmetric bipolar pulsed dc magnetron sputtering. The deposition parameters such as pulse frequency and the duty cycle were varied from 0 to 50 kHz and 100 to 75%, respectively. Microstructural, crystallographic and electrical characterizations were performed by FE-SEM, AFM, XRD and 4-point probe method. With an increase in pulse frequency, coating microstructure evolved from a porous columnar structure to a highly dense one. Single- phase cubic (FCC) VN coatings with different preferential orientations were obtained as a function of pulse frequency. Minimum resistivity of 108 μΩ-cm was obtained for the coatings deposited at pulse frequency of 25 kHz.

Measurement of deposition rate and ion energy distribution in a pulsed dc magnetron sputtering system using a retarding field analyzer with embedded quartz crystal microbalance.

A compact retarding field analyzer with embedded quartz crystal microbalance has been developed to measure deposition rate, ionized flux fraction, and ion energy distribution arriving at the substrate location. The sensor can be placed on grounded, electrically floating, or radio frequency (rf) biased electrodes. A calibration method is presented to compensate for temperature effects in the quartz crystal. The metal deposition rate, metal ionization fraction, and energy distribution of the ions arriving at the substrate location are investigated in an asymmetric bipolar pulsed dc magnetron sputtering reactor under grounded, floating, and rf biased conditions. The diagnostic presented in this research work does not suffer from complications caused by water cooling arrangements to maintain constant temperature and is an attractive technique for characterizing a thin film deposition system.

The Structure and Properties of Pulsed dc Sputtered Nanocrystalline NbN Coatings for Proton Exchange Membrane Fuel Cell.

Niobium nitride coatings for the surface modified proton exchange membrane fuel cells with various pulse parameters have been prepared using dc (direct current) and asymmetric-bipolar pulsed dc magnetron sputtering. The pulse frequency and the duty cycle were varied from 5 to 50 kHz and 50 to 95%, respectively. The deposition rate, grain size and resistivity of pulsed dc sputtered films were decreased when the pulse frequency increased, while the nano hardness of niobium nitride films increased. We present in detail coatings (e.g., deposition rate, grain size, prefer-orientation, resistivity and hardness). Our studies show that niobium nitride coatings with superior properties can be prepared using asymmetric-bipolar pulsed dc sputtering.

Omnidirectional photonic band gap in magnetron sputtered TiO2/SiO2 one dimensional photonic crystal

One dimensional photonic crystal (1DPC) of TiO2/SiO2 multilayer has been fabricated by sequential asymmetric bipolar pulsed dc magnetron sputtering of TiO2 and radio frequency magnetron sputtering of SiO2 to achieve wide omnidirectional photonic band in the visible region. The microstructure and optical response of the TiO2/SiO2 photonic crystal have been characterized by atomic force microscopy, scanning electron microscopy and spectrophotometry respectively. The surface of the photonic crystal is very smooth having surface roughness of 2.6nm. Reflection and transmission spectra have been measured in the wavelength range 300 to 1000nm for both transverse electric and transverse magnetic waves. Wide high reflection photonic band gap (∆λ=245nm) in the visible and near infrared regions (592–837nm) at normal incidence has been achieved. The measured photonic band gap (PBG) is found well matching with the calculated photonic band gap of an infinite 1DPC. The experimentally observed omnidirectional photonic band 592–668nm (∆λ=76nm) in the visible region with band to mid-band ratio ∆λ/λ=12% for reflectivity R>99% over the incident angle range of 0°–70° is found almost matching with the calculated omnidirectional PBG. The omnidirectional reflection band is found much wider as compared to the values reported in literature so far in the visible region for TiO2/SiO2 periodic photonic crystal.

듀티 싸이클 및 펄스 주파수가 TiAlN 코팅막의 미세구조와 기계적 특성에 미치는 영향에 관한 연구

This paper presents the effects of pulse plasma parameters such as duty cycle and pulse frequency on the properties of TiAlN coatings deposited by asymmetric bipolar pulsed DC magnetron sputtering systems. The results show that, with decreasing duty cycle and increasing pulse frequency, the coating morphology changes from a columnar structure to a dense structure with finer grains. Pulsed sputtered TiAlN coatings showed higher hardness, higher residual stress, and smaller grain sizes than did DC prepared TiAlN coatings. Moreover, residual stress and nanoindentation hardness of pulsed sputtered TiAlN coatings increased with increasing pulse frequency. Meanwhile, the surface roughness decreased continuously with increasing pulsed DC frequency up to 50 kHz.

The Structure and Properties of Pulsed dc Magnetron Sputtered Nanocrystalline TiN Films for Electrodes of Alkali Metal Thermal-to-Electric Conversion Systems

Titanium nitride films used as an important electrode material for the design of alkali metal thermal-to-electric conversion (AMTEC) system have been prepared using dc (direct current) and asymmetric-bipolar pulsed dc magnetron sputtering. The pulse frequency and the duty cycle were varied from 5 to 50 kHz and 50 to 95%, respectively. The deposition rate, grain size and resistivity of pulsed dc sputtered films were decreased when the pulse frequency increased, while the nano hardness of titanium nitride films increased. We present in detail coatings (e.g., deposition rate, grain size, prefer-orientation, resistivity and hardness). Our studies show that titanium nitride coatings with superior properties can be prepared using asymmetric-bipolar pulsed dc sputtering.

Preparation of Thin Films by a Bipolar Pulsed-DC Magnetron Sputtering System Using Ca<sub>3</sub>Co<sub>4</sub>O<sub>9</sub> and CaMnO<sub>3</sub> Targets

The thin films were deposited on the glass substrates by an asymmetric bipolar pulsed-dc magnetron sputtering system using the Ca3Co4O9 and CaMnO3 Targets (n-type) targets of 60 mm diameter and 2.5 mm thickness. The targets were prepared from powder precursors, which obtained by a solid state reaction. Optical emissions from plasmas during sputter depositions of films were detected using a high resolution spectrometer. Thickness of thin film was estimated by Tolansky’s Fizeau fringe method and ellipsometic measurement. Crystal structures were studied from X-ray diffraction. The thermoelectric properties were assessed from Seebeck coefficient and electrical resistivity measurements at room temperature. The power factors were calculated. It was found that the optical emission spectrums showed that the Ca, Mn, Co and O atoms were sputtered from the targets onto glass substrates. As-deposited Ca-Co-O and Ca-Mn-O films thickness values were 0.435 ?m and 0.449 ?m, respectively. The X-ray diffraction patterns clearly showed amorphous nature of the as-deposited films. Determining thermoelectric properties of Ca-Co-O film gave Seebeck coefficient of 0.146 mV/K, electrical resistivity of 0.473Ω.cm, and power factor of 4.531 μW/m?K at room temperature. Ca-Mn-O film baring a high resistance was not the experimental determination of thermoelectric properties.

Ion flux-film structure relationship during magnetron sputtering of WO3

In this work, we have investigated the influence of the magnetic field configuration during magnetron sputtering of WO 3 in order to establish the ion flux-film structure relationship. An asymmetric bipolar pulsed DC magnetron sputtering (PDMS) was used with two magnetic field configurations: balanced (BM) and unbalanced (UMB) magnetic configurations. Ion Energy Distribution Functions (IEDFs) of the main ion populations (Ar + , O + ) were recorded. The IEDFs are broad with, in addition of the thermalized distribution around 2 eV, two peaks with available ion kinetic energy up to 40–100 eV associated with the positive part of the pulse. Comparing the BM and UBM data, we calculated an increase by a factor of 5 of the ionic current while the average energy per ion was kept constant (~44 eV). X-ray diffraction demonstrates the influence of the magnetic configuration on the coating phase constitution. The films are crystallized in the WO 3 monoclinic phase with preferential orientations along the c axis using the BM configuration and along the a axis using the UBM one’s. On the other hand, it has been demonstrated that the grain size increases with the thickness using the BM configuration (up to 18 nm) while it remains constant using the UBM one’s (~7 nm).

Deposition and characterization of titania–silica optical multilayers by asymmetric bipolar pulsed dc sputtering of oxide targets

Titania–silica (TiO2/SiO2) optical multilayer structures have been conventionally deposited by reactive sputtering of metallic targets. In order to overcome the problems of arcing, target poisoning and low deposition rates encountered there, the application of oxide targets was investigated in this work with asymmetric bipolar pulsed dc magnetron sputtering. In order to evaluate the usefulness of this deposition methodology, an electric field optimized Fabry Perot mirror for He–Cd laser (λ = 441.6 nm) spectroscopy was deposited and characterized. For comparison, this mirror was also deposited by the reactive electron beam (EB) evaporation technique. The mirrors developed by the two complementary techniques were investigated for their microstructural and optical reflection properties invoking atomic force microscopy, ellipsometry, grazing incidence reflectometry and spectrophotometry. From these measurements the layer geometry, optical constants, mass density, topography, surface and interface roughness and disorder parameters were evaluated. The microstructural properties and spectral functional characteristics of the pulsed dc sputtered multilayer mirror were found to be distinctively superior to the EB deposited mirror. The knowledge gathered during this study has been utilized to develop a 21-layer high-pass edge filter for radio photoluminescence dosimetry.

Pulsed dc Magnetron Discharges and their Utilization in Plasma Surface Engineering

AbstractFundamental aspects of magnetron operation in two types of practically interesting discharges, i.e. in highpower unipolar pulsed dc magnetron discharges for ionized high‐rate sputtering and in asymmetric bipolar pulsed dc magnetron discharges for reactive sputtering, were investigated on the basis of time‐resolved plasma diagnostics. We present the results obtained using time‐resolved optical emission spectroscopy and time‐ and energy‐resolved mass spectroscopy in high‐power unipolar pulsed dc magnetron discharges at a repetition frequency of 1 kHz, an argon pressure of 1 Pa and an average target power loading in a pulse up to 500 W/cm2. The main aim was to study complex ionization mechanisms of sputtered Cu atoms and working gas (Ar) atoms, and to characterize energy distributions of Cu+ and Ar+ ions and their fractions in ion fluxes to a substrate during pulses. Some results achieved with a grooved target at the frequencies up to 50 kHz are discussed. We report also on the results obtained using energy‐resolved mass spectroscopy and time‐resolved Langmuir probe measurements in asymmetric bipolar pulsed dc magnetron discharges at repetition frequencies of 100 kHz and 350 kHz, an argon pressure of 0.53 Pa and a mean discharge power of 300W. They explain a complex correlation between the pulsed plasma dynamics and the enhanced ion bombardment of growing films in these discharges. Some new development trends in the field of the dual pulsed dc magnetron sputtering are outlined. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The distribution of ion energies at the substrate in an asymmetric bi-polar pulsed DC magnetron discharge

Using an energy-resolved mass spectrometer and a time-resolved Langmuir probe, the distribution of bombarding ion energies, their fluxes and energy fluxes at a substrate in an asymmetric bi-polar pulsed DC magnetron have been determined. The discharge was operated in Ar at a pressure of 0.53 Pa with a Ti target and pulsed DC frequencies of 100 and 350 kHz with a range of duty cycles (from 50 to 96%). At 100 kHz, the Ar+and Ti+ time-averaged ion energy distribution functions (IEDFs) reveal three peaks, which are at low energy (<10 eV), in a mid-range (20-50 eV) and at high energy (60-100 eV). We correlate these peaks with distinct phases of the discharge voltage. At 350 kHz the IEDFs show four peaks reflecting a more complex voltage waveform. The low-energy ions are generated in the `on' phase when the plasma potential is typically a few volts above ground. The Ti+ energy spectra show a remnant of the original sputter-neutral energy distribution function. The mid-range ions are produced in the quiescent region of the voltage reverse phase, when the plasma potential is raised globally a few volts above the cathode potential, typically 10-30 V. The high-energy ions are generated in a period of ~0.3 µs, during the discharge voltage overshoot, when the target potential rises to typically over +140 V. However, given the time resolution of the Langmuir probe (0.5 µs), it is not possible to determine if plasma potential is lifted globally to this high potential or only close to the cathode. At 350 kHz, these `fast' ions make up to about a quarter of the total ion flux at the substrate and an upper bound transient power flux of about 2.5 times the maximum delivered in the `on' phase. The total power flux to a substrate in the sustained phase of the discharge is found to increase with frequency and reverse time.