Planar Probe Research Articles

Effect of the Cu plasma density on ZnO:Cu thin films grown by PLD

ZnO:Cu thin films were deposited on Si (100) substrates at room temperature by the simultaneous laser ablation of Zn and Cu targets. The plasma parameters (mean kinetic energy (Ek) and density (Np)) were calculated using the time of flight curves obtained from Langmuir planar probe measurements and used as control parameters for the deposition process. In order to change the Cu content incorporated into the films, Np-Cu was varied while keeping Ek-Cu constant. On the other hand, Zinc plasma parameters were both kept constant. The main purpose of this research was to study the effect of combining Zn and Cu plasmas on the optical and structural properties of ZnO:Cu films. Additionally, the effect of a hydrothermal annealing using deionized water as a heterogeneous medium was investigated. XRD results showed a growth in the (101) orientation for all samples. Crystallinity in samples is influenced by plasma density from Cu target (Np-Cu), containing Cu+1 and Cu+2 ions. XRD and PL suggest a Cu+1 incorporation in films grown at intermediate plasma density.

Supersonic Shear Imaging Elastography in Skeletal Muscles: Relationship Between In Vivo and Synthetic Fiber Angles and Shear Modulus.

To verify a relationship between the pennation angle of synthetic fibers and muscle fibers with the shear modulus (μ) generated by Supersonic shear imaging (SSI) elastography and to compare the anisotropy of synthetic and in vivo pennate muscle fibers in the x2 -x3 plane (probe perpendicular to water surface or skin). First, the probe of Aixplorer ultrasound scanner (v.9, Supersonic Imagine, Aix-en-Provence, France) was placed in 2 positions (parallel [aligned] and transverse to the fibers) to test the anisotropy in the x2 -x3 plane. Subsequently, it was inclined (x1 -x3 plane) in relation to the fibers, forming 3 angles (18.25 °, 21.55 °, 36.86 °) for synthetic fibers and one (approximately 0 °) for muscle fibers. On the x2 -x3 plane, μ values of the synthetic and vastus lateralis fibers were significantly lower (P < .0001) at the transverse probe position than the longitudinal one. In the x1 -x3 plane, the μ values were significantly reduced (P < .0001) with the probe angle increasing, only for the synthetic fibers (approximately 0.90 kPa for each degree of pennation angle). The pennation angle was not related to the μ values generated by SSI elastography for the in vivo lateral head of the gastrocnemius and vastus lateralis muscles. However, a μ reduction with an angle increase in the synthetic fibers was observed. These findings contribute to increasing the applicability of SSI in distinct muscle architecture at normal or pathologic conditions.

Koch curve fractal geometry excitation probe for eddy current non-destructive testing

The sensitivity of eddy current (EC) nondestructive testing (NDT) probe is mainly related to the EC distribution in conductive specimens. To improve the sensitivity of this type of probes, a planar probe with a Koch curve excitation coil that can induce a multiradius EC distribution is proposed. FEM simulation was conducted to visualize the electromagnetic field distribution and understand the operating principle of the probe. A planar EC probe with a Koch curve excitation coil and an experimental measurement system was developed. A set of aluminum plates with different sizes of defects were tested to assess the improved sensitivity of the Koch curve-based probe.

High-Field Liquid-State Dynamic Nuclear Polarization in Microliter Samples.

Nuclear hyperpolarization in the liquid state by dynamic nuclear polarization (DNP) has been of great interest because of its potential use in NMR spectroscopy of small samples of biological and chemical compounds in aqueous media. Liquid state DNP generally requires microwave resonators in order to generate an alternating magnetic field strong enough to saturate electron spins in the solution. As a consequence, the sample size is limited to dimensions of the order of the wavelength, and this restricts the sample volume to less than 100 nL for DNP at 9 T (∼260 GHz). We show here a new approach that overcomes this sample size limitation. Large saturation of electron spins was obtained with a high-power (∼150 W) gyrotron without microwave resonators. Since high power microwaves can cause serious dielectric heating in polar solutions, we designed a planar probe which effectively alleviates dielectric heating. A thin liquid sample of 100 μm of thickness is placed on a block of high thermal conductivity aluminum nitride, with a gold coating that serves both as a ground plane and as a heat sink. A meander or a coil were used for NMR. We performed 1H DNP at 9.2 T (∼260 GHz) and at room temperature with 10 μL of water, a volume that is more than 100× larger than reported so far. The 1H NMR signal is enhanced by a factor of about -10 with 70 W of microwave power. We also demonstrated the liquid state of 31P DNP in fluorobenzene containing triphenylphosphine and obtained an enhancement of ∼200.

Noninvasive electrical plasma monitoring method using reactor substrates as alternative current-sensing electrodes

The authors propose a noninvasive electrical plasma monitoring method that uses two initially present metal reactor substrates, without the probe insertion. When a small sinusoidal voltage is applied between these two substrates, harmonic currents flow in a closed-loop circuit through the plasma. Assuming that the plasma exhibits nonlocal electron kinetics, the electron temperature and plasma density are determined based on an asymmetric double probe harmonic currents analysis. Experimental demonstrations were conducted in an inductively coupled plasma reactor, in which a grounded substrate and a bias electrode were used as the current-sensing electrodes. The electron temperature and plasma density measured with the proposed method agree well with measurements from a floating-type planar probe. This method can be applied to processing reactors that have no available port for electrical probe installation.

Investigation of new micromachined coplanar probe for near-field microwave microscopy

The near-field measurement is based generally on the use of purely passive miniature sensors, dedicated to the capture of a component of the electromagnetic field. The performances of probe are characterized by two quantities: the sensitivity and spatial resolution, related to the geometry of the probe. Improve the spatial resolution of a sensor is often at the expense of sensitivity. In this work, we have presented non-conventional planar microwave probe. We achieved These electrical probes, based on a combination of coplanar line and the point effect, using the clean room techniques. The motivation behind the choice of a coplanar line with a pointed end is the fact of having a quasi-TEM propagation mode in order to have the performances of the conventional coaxial probes and secondly to have a compatibility with the integrated circuits for future microwave integrated microscopy. To prevent the oxidation problem, we choose gold as the metal structure. We used an oxidized silicon substrate in order to reduce losses in the silicon. Simulations and measurements results on a micro-strip line have shown that the probe is mainly sensitive to the normal electric field. The estimated sensitivity is 30 µV/(V/m). Using this CPW probe on a precision X–Y scanning table, 2D images of micro-strip line have been successfully constructed, indicated that the ratio of the resolution to the wavelength $$R/\lambda$$ is around $$0.66\times 10^{-4}$$ at 1 GHz.

Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory.

The first seven coefficients of the expansion of the energy and angular distribution functions in Legendre polynomials for Hg+ ions in Hg vapor plasma with the parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and ions acquire on their mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of the calculation of the ion distribution function correctly describe the experimental data obtained from its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Is the Collecting Surface of a Flat One-Sided Probe Constant when Measuring the Ion Distribution Function?

The correctness of the known plane single-ended probe method for measuring the anisotropic ion distribution functions in a gas-discharge plasma has been considered. Analysis has been performed for positive probe potentials relative to the plasma with magnitudes on the order of the mean ion energy, which as a rule is much lower than the mean electron energy. We have analyzed the dependence of the collection surface area of a plane probe on its potential in this range. The structure of the near-probe layer has been determined for an isotropic electron distribution function of the Maxwellian or Druvestein type and an anisotropic ion distribution function. These results are used to derive analytic relations for the correction to the second derivative of the probe current with respect to the plane probe potential. It has been shown that, when the ion distribution function is measured in a wide range of conditions in the gas-discharge plasma, when the approximation of a collisionless probe layer is applicable, and the probe does not perturb the plasma, the dependence of the collection surface area of the probe on the potential can be disregarded in this range.

New Possibilities of Probe Detection of Anisotropic Charged-Particle Distribution Functions in an Arbitrary-Symmetry Plasma

We have analyzed the precision and systematic errors of the familiar method of a plane single-ended probe for measuring the anisotropic distribution functions for electrons and ions in plasma. Analytic relations that connect the plasma parameters and the required number of terms in a series are obtained under the conditions when anisotropy is due to the presence of an electric field in the plasma. It has been shown that ten terms of the series are usually sufficient to adequately describe the ion distribution function, except for the case of strong fields. For strongly anisotropic charged particle distribution functions, the spline interpolation technique for experimental data is proposed and tested, which substantially reduces the systematic error for a preset number of terms in the series. It has been shown for abundant actual plasma objects with the mirror symmetry that the number of required orientations of a plane probe for the experimental distribution function can be reduced by half compared to the most general case of the absence of any symmetry for a fixed number of terms in the Legendre series, while for the same number of orientations, the number of terms in the series, which are determined from these measurements, doubled accordingly.

Ion current density distribution in a pulsed non-self-sustained glow discharge with a large hollow cathode

The paper reports on azimuthal and radial distributions of the ion saturation current density measured with a single cylindrical and a plane probe in the plasma of a low-pressure (≈1 Pa) pulsed non-self-sustained glow discharge with a large (0.21 m3) hollow cathode at discharge currents higher than 100 A. It is shown that increasing the discharge operating voltage and decreasing the operating pressure in the range 0.4–1 Pa improves the uniformity of the ion current density distribution.

Al-Si-N thin films deposited by laser ablation: Effect of plasma parameters on mechanical and optical properties

Al-Si-N thin films were deposited using simultaneous laser ablation of silicon and aluminum targets in a nitrogen atmosphere at a substrate temperature of 200°C. The silicon content of the films was studied as a function of the plasma parameters (mean ion kinetic energy and plasma density), produced by the ablation of the silicon target. The plasma parameters were measured by means of a planar Langmuir probe and optical emission spectroscopy. The chemical composition of the films was determined by X-ray photoelectron spectroscopy. The results showed a dependence between the silicon content and the silicon plasma density. Optical emission spectroscopy measurements showed that variations of the working pressure produced changes in the intensity of excited species (N2+, Si2+, Al+ and Al0), and in the incorporation of these elements into the films. For a working pressure of 0.6Pa, hardness measurements gave a maximum of 30±1.5GPa for a silicon content of 4at.%. The optical constants (refractive index and extinction coefficient) and direct band gap were evaluated as a function of the silicon content in the films.

Observation of transverse coherent backscattering in disordered photonic structures

Coherent backscattering, also referred to as weak localization, is an exciting multidisciplinary phenomenon that appears in disordered systems of multiple coherent-wave scattering. Providing proper scattering conditions in (2 + 1) dimensional randomized photonic systems, we optically implement, observe, and analyse transverse coherent backscattering. Ensembles of disordered wave-guide structures are prepared by random-intensity nondiffracting writing entities according to the beam’s intensity distribution. The structure size of the induced potentials naturally define an effective mobility edge, and thus, we identify a crucial impact of the plane probe waves’ spatial frequency on the strength and shape of the spectral coherent backscattering signal. We additionally observe transverse elastic scattering as a precursor of weak localization. To testify the coherent character as a fundamental condition for coherent backscattering, we propose a scheme to continuously reduce the spatial coherence of the probe beam which directly reduces the degree of localization and coherent backscattering. With our experiments, we propose a testing platform that allows comprehensive examination of coherent backscattering with a broad set of preparation parameters and under uncritical laboratory conditions. Our results are directly transferable to more complex systems of disordered wave potentials, not being restricted to photonic systems.

Design of planar microcoil-based NMR probe ensuring high SNR

A microNMR probe for ex vivo applications may consist of at least one microcoil, which can be used as the oscillating magnetic field (MF) generator as well as receiver coil, and a sample holder, with a volume in the range of nanoliters to micro-liters, placed near the microcoil. The Signal-to-Noise ratio (SNR) of such a probe is, however, dependent not only on its design but also on the measurement setup, and the measured sample. This paper introduces a performance factor P independent of both the proton spin density in the sample and the external DC magnetic field, and which can thus assess the performance of the probe alone. First, two of the components of the P factor (inhomogeneity factor K and filling factor η) are defined and an approach to calculate their values for different probe variants from electromagnetic simulations is devised. A criterion based on dominant component of the magnetic field is then formulated to help designers optimize the sample volume which also affects the performance of the probe, in order to obtain the best SNR for a given planar microcoil. Finally, the P factor values are compared between different planar microcoils with different number of turns and conductor aspect ratios, and planar microcoils are also compared with conventional solenoids. These comparisons highlight which microcoil geometry-sample volume combination will ensure a high SNR under any external setup.

Efficient Rectangular Waveguide-to-Stripline Transition in $D$ -Band

We present a waveguide-to-stripline transition for full ${D}$ -band operation from 110 to 170 GHz. An $E$ -plane probe in parallel with the waveguide main axis is configured to effectively couple the signal in the primary TE10 mode from the waveguide into the quasi-TEM mode on the chip. Stripline is chosen to minimize the propagation loss, which in turn facilitates efficient power transmission. The probe in conjunction with the stripline is fabricated on a narrow and thin quartz substrate in order to eliminate possible leakage due to dielectric-loaded waveguide modes. The entire structure is optimized by the use of finite element simulation software and is validated with experiments. Measurements on a back-to-back waveguide component showed good coupling efficiency with an insertion loss of about 1 dB or better across the entire band.

Ionospheric Langmuir Probe Electron Temperature Asymmetry and Magnetic Field Connectivity

Simulation results are presented, which demonstrate the effect of magnetic field orientation on electron temperature inferred from a planar Langmuir probe (PLP) near a physical object. PLP characteristics are calculated with two orientations of the magnetic field corresponding to: 1) magnetic field lines intersecting the PLP, also intersecting a physical object, and 2) field lines intersecting the PLP not intersecting any other physical object. In the first case, the PLP is referred to as being “magnetically connected” to another object, while in the second case it is “magnetically disconnected”. Characteristics computed for the PLP in these two cases are used to infer the electron temperature obtained using otherwise identical plasma parameters (electron and ion density and temperature, plasma flow velocity). Applying the same equation to fit the characteristics as derived by Rother et al. for the CHAMP PLP, the fitted electron temperature is found to be significantly lower when the magnetic field is oriented so as to magnetically connect both the probe and a physical object. This in turn is consistent qualitatively with the reported asymmetry in the electron temperature inferred from CHAMP’s PLP between the northbound and southbound legs of the orbit at midlatitudes [1] .

Conducting wall Hall thrusters in magnetic shielding and standard configurations

Traditional Hall thrusters are fitted with boron nitride dielectric discharge channels that confine the plasma discharge. Wall properties have significant effects on the performances and stability of the thrusters. In magnetically shielded thrusters, interactions between the plasma and the walls are greatly reduced, and the potential drop responsible for ion acceleration is situated outside the channel. This opens the way to the utilization of alternative materials for the discharge channel. In this work, graphite walls are compared to BN-SiO2 walls in the 200 W magnetically shielded ISCT200-MS and the unshielded ISCT200-US Hall thrusters. The magnetically shielded thruster shows no significant change in the discharge current mean value and oscillations, while the unshielded thruster's discharge current increases by 25% and becomes noticeably less stable. The electric field profile is also investigated through laser spectroscopy, and no significant difference is recorded between the ceramic and graphite cases for the shielded thruster. The unshielded thruster, on the other hand, has its acceleration region shifted 15% of the channel length downstream. Lastly, the plume profile is measured with planar probes fitted with guard rings. Once again the material wall has little influence on the plume characteristics in the shielded thruster, while the unshielded one is significantly affected.

Density Measurements in Low Pressure, Weakly Magnetized, RF Plasmas: Experimental Verification of the Sheath Expansion Effect

This experimental study shows the validity of Sheridan's method in determining plasma density in low pressure, weakly magnetized, RF plasmas using ion saturation current data measured by a planar Langmuir probe. The ion density derived from Sheridan's method which takes into account the sheath expansion around the negatively biased probe tip, presents a good consistency with the electron density measured by a cylindrical RF-compensated Langmuir probe using the Druyvesteyn theory. The ion density obtained from the simplified method which neglects the sheath expansion effect, overestimates the true density magnitude, e.g., by a factor of 3 to 12 for the present experiment.

Regenerative trapping: How Pd improves the durability of Pt diesel oxidation catalysts

Pt is an active component in diesel oxidation catalysts (DOCs) but it ripens to form large particles at elevated temperatures due to significant vapor phase transport of PtO2. Adding Pd improves the durability of the catalyst but there is no clear consensus in the literature for the responsible mechanism. In this study, we examined the role of PtO2 vapor pressure on sintering. The vapor pressure of PtO2 was determined by measuring the emission of Pt using planar model catalysts and electron probe microanalysis (EPMA). Significant emission of Pt to the vapor phase was observed in a Pt/SiO2 model catalyst that was aged in flowing air at 800°C. Adding Pd lowered the rate of emission, and so did decreasing the oxygen concentration. Lowering of the vapor pressure of PtO2 led to a decreased rate of sintering. However, the most significant decrease in sintering rate was observed in the presence of excess PdO. The excess PdO serves to trap mobile Pt species, resulting in significantly smaller Pt-Pd particles after aging in air at 800°C for 10h. When PtO2 is emitted from a metallic Pt-Pd particle it can result in the formation of a separate PdO phase. Hence, in these catalysts the PdO is regenerated in the course of catalyst sintering. We propose that regenerative trapping of mobile Pt species by PdO plays an important role in improving the durability of Pt-Pd bimetallic catalysts.

A flow microslot NMR probe coupled with a capillary isotachophoresis system exhibits improved properties compared to solenoid designs.

We report on the hyphenation of capillary isotachophoresis (cITP) separations with online nuclear magnetic resonance (NMR) detection using a planar microslot waveguide probe design. While cITP is commonly coupled with a solenoidal microcoil NMR probe, the structural information provided is limited by broad resonances and poor spectral resolution due to the magnetic field created by the separation current. The microslot probe design described herein allows the separation capillary to be oriented parallel to the static magnetic field, B 0, eliminating the spectral broadening produced by the secondary magnetic field induced by the separation current. This allows high-resolution nuclear magnetic resonance spectra of the charged analytes to be obtained in online mode, whereas conventional solenoidal capillary NMR designs must resort to the stopped flow mode. The potential of the microslot probe for hyphenated electrophoretic separations is demonstrated by performing cITP focusing and online NMR detection of the 1H NMR spectrum of a system containing spermine and aniline. Graphical Abstract High resolution NMR spectra in flow capillarelectrophoretic separations with microslot NMR probe.

Determination of plasma density from data on the ion current to cylindrical and planar probes

To improve probe methods of plasma diagnostics, special probe measurements were performed and numerical models describing ion transport to a probe with allowance for collisions were developed. The current–voltage characteristics of cylindrical and planar probes were measured in an RF capacitive discharge in argon at a frequency of 81 MHz and plasma densities of 1010–1011 cm–3, typical of modern RF reactors. 1D and 2D numerical models based on the particle-in-cell method with Monte Carlo collisions for simulating ion motion and the Boltzmann equilibrium for electrons are developed to describe current collection by a probe. The models were used to find the plasma density from the ion part of the current–voltage characteristic, study the effect of ion collisions, and verify simplified approaches to determining the plasma density. A 1D hydrodynamic model of the ion current to a cylindrical probe with allowance for ion collisions is proposed. For a planar probe, a method to determine the plasma density from the averaged numerical results is developed. A comparative analysis of different approaches to calculating the plasma density from the ion current to a probe is performed.