Unbalanced Magnetic Field Research Articles

Suppression of substrate temperature in DC magnetron sputtering deposition by magnetic mirror-type magnetron cathode

Magnetron sputtering generally increases the temperature of the substrate placed to face the sputtering target above 40 °C because the plasmas are transported through unbalanced magnetic field lines from the sputtering target to the substrate surface. However, by using a magnetic mirror-type magnetron cathode, we were able to suppress the temperature of the substrate temperature to the environmental temperature of less than 40 °C at a target–substrate distance of ≥50 mm with a DC input power of ≤30 W and an Ar gas pressure of ≤0.15 Pa. This was possible because the balanced magnetic field lines confined the plasmas near the sputtering target. By enabling film deposition on low heat-resistant substrates, this deposition technique for suppressing the substrate temperature may have uses in various application fields.

A facile strategy to synthesis nanocrystalline H-Diamond (H-D) phase in MoCx (H-D/a-C) composite coatings using a reactive sputtering system: The role of Mo content

In the magnetron sputtering system, using an unbalanced magnetic field configuration in the cathode is a privileged strategy for designing protective coatings on metal substrates for the specific application. In the present study, A105 carbon steel substrates coated with MoC x (H-D/a-C) composite films (H-D: hexagonal diamond, a-C: amorphous carbon) utilizing an unbalanced magnetron (UBM) sputtering technique. The effects of (Mo/C+H) ratio on microstructure, mechanical and tribological characteristics of MoC x (H-D/a-C) composite coatings were investigated. MoC x (H-D/a-C) coated A105 carbon steel substrates showed enhanced mechanical and tribological performance. The Mo content strongly affected the bonding structure of MoC x (H-D/a-C) composite coatings. The results from Raman spectroscopy showed that the coatings contain a high value of sp 2 carbon bonding, and its affluence increases with increasing (Mo/C+H) ratio. For the first time, the H-Diamond phase was successfully formed in all the UBM sputtered MoC x (H-D/a-C) composite coatings, while Mo acted as a catalyst for the nucleation and growth of H-Diamond phase. The MoC x (H-D/a-C) composite coatings with more H-Diamond phase and higher Mo content showed higher hardness and plasticity index, lower coefficient of friction (COF) and wear rate. The results confirmed that MoC x (H-D/a-C) coated A105 carbon steel substrates can be potentially applied to protect the surface of the perforated spherical ball of ball valves.

Effects of Boron Addition on the Structure and Properties of Cr–Al–Ti–N Coatings Obtained Using the CFUBMS System

The influence of boron on the structure and on the mechanical and tribological properties of protective coatings of the Cr–Al–Ti–N alloys obtained by magnetron sputtering in a closed unbalanced magnetic field using segmented planar ceramic SHS targets has been studied. The obtained coatings were examined using glow discharge optical emission spectroscopy, scanning electronic microscopy, X-ray diffraction phase analysis, nanoindentation, and tribological tests according to the pin-on-disk scheme. It has been shown that the introduction of B results in the suppression of the columnar structure and the reduction of the roughness of the coatings. Hardness, elasticity modulus, elastic recovery, wear resistance, and the coefficient of friction of coatings of the Cr–Al–Ti–B–N alloys have been determined. The introduction of 2.3 at % B leads to a high hardness (H = 15 GPa), stable friction coefficient (f = 0.65), and a decrease of the reduced wear (Vw = 7.5 × 10–6 mm3/(N m)). It has been shown that the hard Cr–Al–Ti–B–N coatings of the optimal composition in their mechanical and tribological properties exceed the coatings without boron addition.

Brilliant keV–MeV x-ray emission through weakly unbalanced quasi-static electric and magnetic fields

We proposed a new method to yield brilliant keV–MeV x-ray emission, inspired by Cao et al (2010 Phys. Plasma 17 043103). When a short femtosecond pulse is coupling into a microwire array target, due to the weakly unbalanced quasi-static electric and magnetic fields, the energetic electrons accelerated by the laser will emit a large amount of photons per shot, comparable to that from the laser-wake betatron radiation. It was found that the critical energy of the photons and the total photon yields are strongly dependent on the laser intensity and structure parameters of the target. The peak spectral brightness of the radiation in our scheme was estimated to be 4 × 1019 at the laser intensity 3 × 1020 W cm−2. More important, the photon energies can be extended to hundreds of keV to MeV readily if electron beam accelerated by the laser is in the range of MeV to GeV.

Design and Optimization of Traction IPMSM With Asymmetrical Damper Bars for Integrated Charging Capability Using Evolutionary Algorithm

The 3-phase windings of interior permanent magnet synchronous machines (IPMSMs) used in electric vehicles (EVs) for traction can also be utilized for charging a battery. This integrated charging technology eliminates the on-board charger, leading to a significant reduction in the overall weight and cost of the EV. However, during integrated charging, the induced magnetic fields across the IPMSM windings are unbalanced, which could lead to addition of harmonic current components at the battery side, demagnetization, noise, and vibrations. This paper provides a novel design solution by implementing asymmetrical damper bars in the IPMSM rotor to mitigate unbalanced magnetic fields during integrated charging, and, thus, overcome the aforementioned issues. However, the bars introduced could affect the useful torque production of the machine during traction. Therefore, a magnetic equivalent circuit model based differential evolutionary algorithm is proposed and implemented to optimize the IPMSM rotor structure with dampers to achieve balanced magnetic fields during integrated charging operation and satisfactory traction performance. A comprehensive performance analysis of the optimally designed traction IPMSM equipped with integrated charging capability under both operating conditions is presented in this paper using finite element analysis.

The improvement of high power impulse magnetron sputtering performance by an external unbalanced magnetic field

High power impulse magnetron sputtering (HIPIMS) is an emerging technique that improves the ionization rate of magnetron-sputtered materials. However, HIPIMS often demands further improvement in the ionization rate in some applications. In this study, we applied an unbalanced magnetic field to enhance the HIPIMS discharge, using a conventional magnetron and a coaxial electro-solenoid coil. Vanadium target discharge currents and substrate ion currents were recorded using a digitizing oscilloscope at different coil currents. The elemental composition and temporal and spatial distributions of argon and vanadium atoms and ions in the high vacuum plasma were measured by optical emission spectroscopy. The results showed that the substrate ion current increased gradually with the coil current over the range 0–6 A, and that a high-density plasma beam was formed between the substrate and target. We explained this effect as the confinement of energetic electrons by the external magnetic field. Total ion production was also increased. Finally, we observed that the line intensities of Ar0, Ar1+, V0, and V1+ increased gradually to varying degrees under the external magnetic field.

High-rate magnetron sputtering with hot target

Chromium films were deposited by cooled and hot target magnetron sputtering techniques with unbalanced magnetic field configuration at equal target power density. The dependence of deposition rates of Cr films by the hot target magnetron sputtering on the power density was a non-linear at 27.5–31.5W/cm2. The optical emission studies indicated the enhancement of deposition rates due to the evaporation of the hot Cr target. The chromium film structure was strongly depended on the factor of «hot target» and the target power density. Cr films were structured to (110) direction in the case of the hot target sputtering, for cooled target configuration – the preferred orientation was changed from (110) to (200) with the power density. Cr+ to Cr ratio and heat flow from the cathode to the substrate influenced on the coating hardness and adhesion. The Cr films with 9.84–12.79GPa and the non-cracking behavior (up to 15N) were obtained.

Unstable force analysis for induction motor eccentricity

The increasing popularity of motors in machinery trains has led to an intensified interest in the forces they produce that may influence machinery vibration. Motor design typically assumes a uniform air gap, however in practice all motors operate with the rotor slightly displaced from the motor centerline in what is referred to as an eccentric position. Rotor center eccentricity can cause a radially unbalanced magnetic field when the motor is operating. This will results in both a radial force pulling the motor further away from the center, and a tangential force which can induce a vibration stability problem. In this paper, a magnetic equivalent circuit MEC modeling method is proposed to calculate both the radial and tangential motor eccentric force. The treatment of tangential force determination is rarely addressed, but it is very important for rotordynamic vibration stability evaluation. The proposed model is also coupled with the motor electric circuit model to provide capability for transient vibration simulations. FEM is used to verify the MEC model. A parametric study is performed on the motor radial and tangential eccentric forces. Also a Jeffcott rotor model is used to study the influence of the motor eccentric force on mechanical vibration stability and nonlinear behavior. Furthermore, a stability criteria for the bearing damping is provided. The motor radial and tangential eccentric forces are both curved fitted to include their nonlinearity in time domain transient simulation for both a Jeffcott rotor model and a geared machinery train with coupled torsional-lateral motion. Nonlinear motions are observed, including limit cycles and bifurcation induced vibration amplitude jumps.

Highly c-axis oriented AlN film grown by unbalanced magnetron reactive sputtering and its electrical properties

Highly c-axis oriented aluminum nitride films have been successfully grown by DC magnetron reactive sputtering with unbalanced magnetic fields at room temperature. It is shown that the application of unbalanced magnetic fields can improve the extent of preferential growth along the c-axis, and form AlN films with denser, larger grains and smaller surface roughness, compared to that grown with balanced magnetic fields. The AlN films prepared under optimized growth conditions have a dielectric constant of approximately 10.5 and a dielectric loss of 0.02 in the frequency range of 103–106 Hz, and a leakage current of <1 × 10−7 A/cm2 at 5 V bias voltage, all the dielectric and insulating properties being superior to the films synthesized with balanced magnetic fields. In this work, the unbalanced magnetic fields are induced by adding an electromagnetic coil on the magnetron cathode.

Floating and flying ferrofluid bridges induced by external magnetic fields

A ferrofluid is a mixture that exhibits both magnetism and fluidity. This merit enables the ferrofluid to be used in a wide variety of areas. Here we show that a floating ferrofluid bridge can be induced between two separated boards under a balanced external magnetic field generated by two magnets, while a flying ferrofluid bridge can be induced under an unbalanced external magnetic field generated by only one magnet. The mechanisms of the ferrofluid bridges were discussed and the corresponding mathematical equations were also established to describe the interacting magnetic force between the ferro particles inside the ferrofluid. This work answered a basic question that, except for the well-known floating water bridges that are related to electricity, one can also build up a liquid bridge that is related to magnetism.

Spatial Distribution of a High-Power Impulse Magnetron Sputtering Glow Plasma by a Controlled Unbalanced Magnetic Field

Spatial distribution of a high-power impulse magnetron sputtering carbon-glow plasma was investigated using a controlled unbalanced magnetic field, where a number of the inner magnets were varied. The magnets were arranged in a concentric circle and their number affected the production-zone of the plasma on the target, which simultaneously changed the instantaneous power consumed in the plasma. The plasma was produced at the region with the peak magnetic-field density and extended outward radially on the target with an increased number of the inner magnets.

Effect of Metal Pad Instabilities on Current Efficiency in Aluminium Electrolysis

Uncompensated residual magnetic field in aluminium electrolysis cells leads to metal instability which is reflected as voltage instability referred to as voltage noise. The latter affects current efficiency and power consumption and has, therefore, a significant effect on the economy of the electrolysis operation. The characteristics of metal instability are studied in detail in this investigation by carrying out measurements related to voltage, magnetic flux, thermal energy loss and thickness of the frozen electrolyte (ledge). Current sinking method is employed to calculate counter electromotive force from which values for current efficiency are derived. These values are compared with those obtained from the copper dilution experiments. The studies indicate that unstable cell operation resulting from significant metal instability effect, due to unbalanced magnetic fields, leads to deterioration in ledge thickness, more heat loss and reduced current efficiency.

IR emission from the target during plasma magnetron sputter deposition

In this article, energy flux measurements at the substrate location are reported. In particular, the energy flux related to IR radiation emanating from the titanium (10cm in diam.) target surface is quantified during magnetron sputter deposition processes. In order to modulate the plasma–target surface interaction and the radiative energy flux thereof, the working conditions were varied systematically. The experiments were performed in balanced and unbalanced magnetic field configurations with direct current (DC), pulsed DC and high power impulse magnetron sputtering (HiPIMS) discharges. The power delivered to the plasma was varied too, typically from 100 to 800W. Our data show that the IR contribution to the total energy flux at the substrate increases with the supplied sputter power and as the discharge is driven in a pulse regime. In the case of HiPIMS discharge generated with a balanced magnetic field, the energy flux associated to the IR radiation produced by the target becomes comparable to the energy flux originating from collisional processes (interaction of plasma particles such as ions, electron, sputtered atoms etc. with the substrate). From IR contribution, it was possible to estimate the rise of the target surface temperature during the sputtering process. Typical values found for a titanium target are in the range 210°C to 870°C.

Measuring the energy flux at the substrate position during magnetron sputter deposition processes

In this work, the energetic conditions at the substrate were investigated in dc magnetron sputtering (DCMS), pulsed dc magnetron sputtering (pDCMS), and high power impulse magnetron sputtering (HiPIMS) discharges by means of an energy flux diagnostic based on a thermopile sensor, the probe being set at the substrate position. Measurements were performed in front of a titanium target for a highly unbalanced magnetic field configuration. The average power was always kept to 400 W and the probe was at the floating potential. Variation of the energy flux against the pulse peak power in HiPIMS was first investigated. It was demonstrated that the energy per deposited titanium atom is the highest for short pulses (5 μs) high pulse peak power (39 kW), as in this case, the ion production is efficient and the deposition rate is reduced by self-sputtering. As the argon pressure is increased, the energy deposition is reduced as the probability of scattering in the gas phase is increased. In the case of the HiPIMS discharge run at moderate peak power density (10 kW), the energy per deposited atom was found to be lower than the one measured for DCMS and pDCMS discharges. In these conditions, the HiPIMS discharge could be characterized as soft and close to a pulsed DCMS discharge run at very low duty cycle. For the sake of comparison, measurements were also carried out in DCMS mode with a balanced magnetron cathode, in the same working conditions of pressure and power. The energy flux at the substrate is significantly increased as the discharge is generated in an unbalanced field.

Analysis on the roundness of bulb turbine generator based on the unbalanced magnetic

Because of design, manufacture, installation and operation, there are some relatively eccentric in bulb tubular turbine units under operating condition. It easily caused uneven air gap, unbalanced magnetic field, unbalanced magnetic pull and torque. It could also increase the bending and torsion vibration of generator,at the same time, the roundness of stator and rotor would be aggravated which often caused by accidents such as generator sweep chamber. In this paper, basing on the design, installation and operation experience, the reasons of the unbalanced magnetic pull, mechanism and operation research were analyzed by theoretical calculation and the prototype test.

Voluminous high-density plasma generator based on high-current pulsed magnetron discharge

Results of investigations into the spatial and temporal parameters of the voluminous plasma generated by two high-current pulsed magnetron sputtering systems operating in balanced and unbalanced regimes are presented. It is demonstrated that the plasma filling the vacuum chamber comprises two components: the plasma drifting from the region of magnetron magnetic traps and the plasma generated by oscillating electrons directly in the chamber volume. For the balanced magnetron magnetic field configuration, the plasma in the centre of the vacuum chamber with volume of ~10 L has concentration of (1–2)⋅1013 cm−3 for magnetron discharge current amplitude of 350 A. The application of the unbalanced magnetic field configuration allows the plasma concentration in the central part of the vacuum chamber to be increased to ~6⋅1013 cm−3.

Practical Optimum Design Based on Magnetic Balance and Copper Loss Minimization for a Single-Phase Line Start PM Motor

This paper introduces the condition of balanced operation to solve problems caused by an unbalanced magnetic field when a single-phase line start permanent magnet motor operates in steady-state. Using an equivalent circuit on the basis of symmetric field theory, conditions are found for balanced operation at rated conditions and for copper loss minimization in the stator. The initial model is modified applying these two conditions from commercial model. In addition, an optimum design is implemented in order to improve starting characteristic. In an optimum design process, the sampling points are chosen by latin hypercube sampling and from the results, an approximation model is made by the radial basis function. Then the optimization results are obtained by a genetic algorithm. The validity of the proposed design is verified by confirming the efficiency, torque ripple, ohmic loss of the rotor, and starting characteristic through time step FE-analysis and experimental results.

Design and Analysis of Enhanced Chromium Nitride Film Performance by Tuning Sputtering Magnetic Systems

This paper presents the optimal chromium nitride (CrN) deposited performance by tuning magnetic systems on die steel in PVD. The strength of magnetic fields was controlled by adjusting the gap distance between magnet sets and target surfaces of the unbalanced magnetic field of sputtering systems. In L18 orthogonal experiments, the effect of control factors were explored such as gap distance between magnet set and target surface (GDMT), target current, argon and nitrogen flow rate, DC pulse frequency, and work distance. Hardness and wear behavior of the CrN films were analyzed using a statistical method. The wear rate was estimated by Pappus’s theorem. Among the results, the Cr2N phase with the mixture crystallographic orientations of (111) and (002) exhibited better wear resistance than CrN(200) with a single preferential orientation. In addition, variance analysis exhibited the largest percentage contribution to friction coefficient in comparison with the other two properties of friction coefficient and GDMT, which showed that GDMT is extremely sensitive to friction coefficient.

Depth profile analyses of nc-TiC/a-C:H coating prepared by balanced magnetron sputtering

Nanocrystalline titanium carbide embedded in an hydrogenated amorphous carbon matrix (nc-TiC/a-C:H) shows high hardness and Young's modulus together with low wear and low friction coefficient. In this paper, we report on the preparation of well adherent nc-TiC/a-C:H coatings ~5μm thick on stainless steel substrates using a well balanced magnetic field configuration and only very low power RF bias on the substrate. Hardness and Young's modulus of these coatings are 43GPa and 380GPa, respectively. The mechanical properties – hardness and Young's modulus – measured from the coating's top reach the values obtained at optimized experiments where the unbalanced magnetic field configuration was used. A simple method of depth profiling suitable for evaluation of mechanical properties of several micrometers thick coatings is developed and employed. The paper reports on the depth profile analyses of the coating hardness, Young's modulus, composition and morphology.

Gas Adsorption Properties of Fluorocarbon Thin Films Prepared Using Three Different Types of RF Magnetron Sputtering Systems

Fluorocarbon thin films were deposited onto a quartz crystal with a poly(tetrafluoroethylene) target using three different types of RF magnetron sputtering systems with strong, weak, and unbalanced magnetic fields. The adsorption properties of these thin films for water, ethanol, acetone, acetaldehyde, toluene, and methyl salicylate were evaluated using the quartz crystal microbalance (QCM) method in order to characterize the surface properties of these thin films. These thin films have low sensitivities to non-polar solvents that contain methyl and aromatic groups, and high sensitivities to polar solvents that contain carbonyl and hydroxyl groups. Chemical structures, especially, polar moieties in these fluorocarbon thin films would affect the gas adsorption properties.