Electrical Probe Technique Research Articles

Optimization of a Diamond Nitrogen Vacancy Centre Magnetometer for Sensing of Biological Signals

Sensing of signals from biological processes, such as action potential propagation in nerves, are essential for clinical diagnosis and basic understanding of physiology. Sensing can be performed electrically by placing sensor probes near or inside a living specimen or dissected tissue using well established electrophysiology techniques. However, these electrical probe techniques have poor spatial resolution and cannot easily access tissue deep within a living subject, in particular within the brain. An alternative approach is to detect the magnetic field induced by the passage of the electrical signal, giving the equivalent readout without direct electrical contact. Such measurements are performed today using bulky and expensive superconducting sensors with poor spatial resolution. An alternative is to use nitrogen vacancy (NV) centres in diamond that promise biocompatibilty and high sensitivity without cryogenic cooling. In this work we present advances in biomagnetometry using NV centres, demonstrating magnetic field sensitivity of approximately 100 pT/$\sqrt{Hz}$ in the DC/low frequency range using a setup designed for biological measurements. Biocompatibility of the setup with a living sample (mouse brain slice) is studied and optimized, and we show work toward sensitivity improvements using a pulsed magnetometry scheme. In addition to the bulk magnetometry study, systematic artifacts in NV-ensemble widefield fluorescence imaging are investigated.

Electrical polarization phenomena, dielectric relaxations and structural transitions in a relaxor-ferroelectric terpolymer investigated with electrical probing techniques

Dielectric Relaxation Spectroscopy (DRS) and Thermally Stimulated Depolarization Current (TSDC) measurements were employed to study dielectric-relaxation processes, structural transitions and electric-polarization phenomena in poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer films. Results from DRS confirm the existence of two separate dispersion regions related to a para-to-ferroelectric phase transition and to the glass transition. The dipolar TSDC peak correlates with the loss peak of the α relaxation that represents the glass transition. The electric polarization calculated from the dipolar TSDC peak (glass transition) shows a non-linear electric-field dependence and saturates at high electric poling fields. As the observed behaviour is essentially the same as that of the electric polarization obtained from direct polarization-versus-electric-field hysteresis measurements, TSDC experiments are also suitable for studying the polarization in relaxor-ferroelectric polymers. A saturation polarization of 44 mC m−2 was found for an electric field of 190 MV m−1.

Revisiting the Buckling Metrology Method to Determine the Young's Modulus of 2D Materials.

Measuring the mechanical properties of 2D materials is a formidable task. While regular electrical and optical probing techniques are suitable even for atomically thin materials, conventional mechanical tests cannot be directly applied. Therefore, new mechanical testing techniques need to be developed. Up to now, the most widespread approaches require micro-fabrication to create freely suspended membranes, rendering their implementation complex and costly. Here, a simple yet powerful technique is revisited to measure the mechanical properties of thin films. The buckling metrology method, that does not require the fabrication of freely suspended structures, is used to determine the Young's modulus of several transition metal dichalcogenides (MoS2 , MoSe2 , WS2 , and WSe2 ) with thicknesses ranging from 2 to 10 layers. The obtained values for the Young's modulus and their uncertainty are critically compared with previously published results, finding that this simple technique provides results which are in good agreement with those reported using other highly sophisticated testing methods. By comparing the cost, complexity, and time required for the different methods reported in the literature, the buckling metrology method presents certain advantages that make it an interesting mechanical test tool for 2D materials.

Hydrodynamic study of two phase flow of column flotation using electrical resistance tomography and pressure probe techniques

Gas dispersion characteristics are very important to design and selection of flotation process for the fine particle separation. Although the separation of flotation process heavily depends on hydrophobicity of given solid particles, but their rate of attachment and detachment depends on local gas dispersion characteristics. In this work, gas dispersion characteristics in a 100 mm laboratory column flotation have been investigated by exploring the flow behavior in terms of the local and mean gas hold-up, bubble rise velocity and bubble size distribution across the column. This experimental data has been used to demonstrate the validation of the two-fluid CFD model predictions in the column flotation. The column hydrodynamics are estimated by using high speed dual planar Electrical Resistance Tomography (ERT) system and pressure transducers. In all the experiments, water is used as the liquid phase and air (bubbles) as the disperse phase. Using the ERT system, measurement of two phase distributions are examined for a wide range of design and operating conditions of the column including different spargers and frother dosage, where the flow changes from homogenous to transition bubbly flow. It is confirmed by ERT that the gas-holdup increases with an increase in the sparger porosity, air superficial velocity, liquid height and liquid feed flow rate. To test the reliability of ERT measurements, simultaneously a set of pressure transducers is used to obtain the sectional average gas holdup and validated. It is observed that bubble density occupancy is more at center region of the column and gas holdup value increases with the increase of gas superficial velocity. Dynamic gas disengagement technique is utilized to measure bubble rise velocity and sauter mean bubble diameter. At end this ERT data has been used to validate two-fluid CFD model (modified with suitable drag and lift forces via user defined functions) predictions in the column and found a close agreement.

Self-sensing cantilevers with integrated conductive coaxial tips for high-resolution electrical scanning probe metrology

The lateral resolution of many electrical scanning probe techniques is limited by the spatial extent of the electrostatic potential profiles produced by their probes. Conventional unshielded conductive atomic force microscopy probes produce broad potential profiles. Shielded probes could offer higher resolution and easier data interpretation in the study of nanostructures. Electrical scanning probe techniques require a method of locating structures of interest, often by mapping surface topography. As the samples studied with these techniques are often photosensitive, the typical laser measurement of cantilever deflection can excite the sample, causing undesirable changes electrical properties. In this work, we present the design, fabrication, and characterization of probes that integrate coaxial tips for spatially sharp potential profiles with piezoresistors for self-contained, electrical displacement sensing. With the apex 100 nm above the sample surface, the electrostatic potential profile produced by our coaxial tips is more than 2 times narrower than that of unshielded tips with no long tails. In a scan bandwidth of 1 Hz–10 kHz, our probes have a displacement resolution of 2.9 Å at 293 K and 79 Å at 2 K, where the low-temperature performance is limited by amplifier noise. We show scanning gate microscopy images of a quantum point contact obtained with our probes, highlighting the improvement to lateral resolution resulting from the coaxial tip.

An appraisal of viscous oil–water two-phase flow through an undulated pipeline in peak configuration

Experimental results on flow patterns and pressure drop characteristics of viscous oil–water flow through undulated pipeline in peak configuration have been studied in this work. Undulated pipeline consists of two inclined sections (uphill and downhill) connected between two horizontal pipes (upstream and downstream) at peak configuration. Experiments have been conducted over a wide range of superficial velocities of oil (USO=0.015–1.3m/s) and water (USW=0.1–1.2m/s). Seven different flow patterns (viz., plug, slug, wavy stratified, stratified mixed, wispy annular, dispersion of oil in water and dispersion of water in oil) are identified by visual, imaging and electrical conductance probe techniques at all the four sections. Our results shows that present undulation (5°) has a marginal effect on the flow behavior of viscous oil–water mixture and the range of fluid velocity differs for a particular flow pattern. The pressure gradient characteristics across the peak experiences relatively more pressure gradient as compared to upstream and downstream at USW⩾0.6m/s, which is attributed to the combined effect of undulation (viz., peak configuration) along the pipeline, flow pattern, and effective viscosity and density of the fluid mixture.

Mixing Characteristics and Bubble Behavior in an Airlift Internal Loop Reactor with Low Aspect Ratio

The present study summarizes the results of macro- and micro-mixing characteristics in an airlift internal loop reactor with low aspect ratio (H/D≤5) using the electrolytic tracer response technique and the method of parallel competing reactions respectively. The micro-mixing has never been investigated in airlift loop reactors. The dual-tip electrical conductivity probe technique is used for measurement of local bubble behavior in the reactor. The effects of several operating parameters and geometric variables are investigated. It is found that the increase in superficial gas velocity corresponds to the increase in energy input, liquid circulation velocity and shear rate, decreasing the macro-mixing time and segregation index. Moreover, it is shown that top clearance and draft diameter affect flow resistance. However, the bubble redistribution with a screen mesh on the perforated plate distributor for macro-mixing is insignificant. The top region with a high energy dissipation rate is a suitable location for feeding reactants. The analysis of present experimental data provides a valuable insight into the interaction between gas and liquid phases for mixing and improves the understanding of intrinsic roles of hydrodynamics upon the reactor design and operating parameter selection.

Structure and properties of phosphorus-carbide thin solid films

Phosphorus-carbide (CPx) thin solid films have been deposited by unbalanced reactive magnetron sputtering from a compound C-P target and investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, elastic recoil detection analysis, Raman scattering spectroscopy, nanoindentation, and four-point electrical probe techniques. CPx films with x=0.1 deposited at 300°C exhibit a structure with elements of short-range ordering in the form of curved and inter-locked fullerene-like fragments. The films have a hardness of 34.4GPa, elastic recovery of 72% and surface roughness of 0.5nm. Higher deposition temperatures yield CPx films with an increasingly amorphous structure, and reduced hardness.

Shock Compression of the New 47Zr45Ti5Al3V Alloys up to 200 GPa

Shock compression experiments on a new kind of 47Zr45Ti5Al3V alloys at pressures between 28 and 200 GPa are performed using a two-stage light gas gun. The Hugoniot data are obtained by combining the impedance-match method and the electrical probe technique. The relationship between the shock wave velocity Us and particle velocity up can be described linearly by Us = 4.324(±0.035) + 1.177(±0.012)up. No obvious evidence of phase transition is found in the shock compression pressure range. The calculated Us − up relationship obtained from the additive principle is different from the experimental data, indicating that the α → β phase transition occurs below 28 GPa. The Grüneisen parameter γ obtained from the experimental data can be expressed by γ = 1.277(ρ0/ρ). The zero-pressure bulk modulus B0s = 97.96 GPa and its pressure derivative B′0s = 3.68. The P—V—T equation of state for 47Zr45Ti5Al3V is given using the Vinet equation of state to describe the cold curve and the Debye model for the thermal contributions.

(Invited) Scanning Probe Analysis of Dielectrics on High Mobility Substrates

In this work we employ electrical scanning probe techniques to evaluate on a nanoscale the influence of semiconductor surface morphology on the electrical properties of dielectrics. Gate leakage, reliability and oxide thickness uniformity are assessed by conductive atomic force microscopy (C-AFM). Interface traps are analyzed by scanning capacitance microscopy (SCM). A correlation between nanoscale and macroscale trends is established following reverse processing of the devices. The impact of surface morphology on localized dielectric properties is evaluated by studying MOSFETs having the same silicon channel strain but different dielectric/substrate interface roughness. The correlation between surface morphology, leakage and SCM signal suggests that for dielectrics on high mobility substrates prone to surface roughening, the morphology as well as the dielectric itself play a role in the final dielectric quality. Optimized epitaxial growth will therefore enable improved device performance, reliability and variability. The results have implications for all technologies which employ relaxed SiGe templates.

Direct Probing of Schottky Barriers in Si Nanowire Schottky Barrier Field Effect Transistors

This work elucidates the role of the Schottky junction in the electronic transport of nanometer-scale transistors. In the example of Schottky barrier silicon nanowire field effect transistors, an electrical scanning probe technique is applied to examine the charge transport effects of a nanometer-scale local top gate during operation. The results prove experimentally that Schottky barriers control the charge carrier transport in these devices. In addition, a proof of concept for a reprogrammable nonvolatile memory device based on band bending at the Schottky barriers will be shown.

Diagnostics of plasma plume produced by laser ablation using ICCD imaging and transient electrical probe technique

The dynamics of transient plasmas generated by high-fluence nanosecond laser ablation has been investigated by means of fast ICCD imaging and electrical probes in transient regime. Measurements have been carried out on plasmas produced in vacuum (5× 10−6 Torr residual pressure) by a pulsed Excimer laser (20 ns, XeCl, λ= 308 nm) irradiating stainless steel targets. Two plasma expansion velocities were estimated, one from probe measurements and another from recorded ICCD images. Electron plasma temperature (0.1 − 0.3 eV) and density (1 − 5×1011 cm−3) were measured by electrical probes for a laser radiation power density of 6×108 W/cm2.

Direct measurement of nonlinear ferromagnetic damping via the intrinsic foldover effect

An approach to measure precisely nonlinear ferromagnetic damping is demonstrated by using spin dynamos in combination with sensitive electrical probing techniques. The directly measured intrinsic foldover effect unravels a 50-year-old mystery of ferromagnetic metals. Pivotal importance of nonlinear ferromagnetic damping is uncovered via its distinct dependence on the frequency, amplitude, and initial conditions. The experimental results are in excellent agreement with a nonlinear oscillator model, which revises the pioneer work of Anderson and Suhl for nonlinear magnetization dynamics.

Characterisation of trapped electric charge carriers behaviour at nanometer scale by electrostatic force microscopy

Atomic force microscopy (AFM) and related electrical probe techniques such as electrostatic force microscopy (EFM) can be used to perform injection and detection of electric charge carriers in nanostructures or oxide layer at the nanometer scale. In this paper the control and the deposition of both positive and negative local charges are described and discussed. A basic introduction to both the theoretical and experimental techniques of EFM is also presented. In addition a review of the analytical calculation of tip–surface capacitance interaction is described and then utilised to estimate charge storage in oxide layers and nanostructures from EFM images or spectroscopy curves. The charge resolution of EFM at room temperature and a controlled atmosphere is estimated to be about 20 charge carriers. The EFM technique is also used to inject charges and to study their behaviour in confined silicon nanostructures covered by a thin layer of oxide and separated from the Si substrate by a SiO 2 layer. The total injected charge is found to depend on the thickness of the oxide layer. The electric field has emerged to be a key parameter in the injection mechanism. The dynamics and propagation of the deposited charge carriers have been studied and a homogenous distribution of the charge in the nanostructure has been observed. Thanks to these studies and observation, the localisation of the trapped charges has been determined: it occurs mainly in the silicon pattern rather than on the thin covering oxide layer. This charge localisation together with charge energy calculation leads to a better understanding of the origin of the charge dissipation.

Radio frequency pulse response of an in-plane-gate field effect transistor

We report radio frequency responses of an in-plane-gate field effect transistor (IPGFET) using an electrical pulse and probe technique. A series of high frequency pulses with the frequency up to 3 GHz were superimposed on the DC gate bias, and the time-averaged drain current was measured. The frequency and amplitude dependence of the time-averaged current depended on both the intrinsic gate response time of the IPGFET and the charging/discharging time of the traps at the etched surface.

Cell Membranes Suspended Across Nanoaperture Arrays

We present a method for spreading large (>100 microm(2)) cell membrane fragments across nanoapertures in planar supports. Electron-beam and focused-ion-beam lithography were used to fabricate arrays of 50-600 nm diameter holes in free-standing silicon nitride (SiN) solid films 100-500 nm thick. By pressing adhering live cells onto the nanostructured SiN surface and then removing them, planar cell membrane sheets (CMSs) were transferred in a well-defined orientation onto the SiN support. We demonstrate the accessibility to both extracellular and intracellular surfaces of CMSs by targeting membrane constituents side-specifically with fluorescent markers. Our approach is of interest for studying ligand-receptor interactions using optical, electrical, and scanning probe techniques at the single-molecule level.

Electrical Scanning Probe Microscopy: Investigating the Inner Workings of Electronic and Optoelectronic Devices

Semiconductor electronic and optoelectronic devices such as transistors, lasers, modulators, and detectors are critical to the contemporary computing and communications infrastructure. These devices have been optimized for efficiency in power consumption and speed of response. There are gaps in the detailed understanding of the internal operation of these devices. Experimental electrical and optical methods have allowed comprehensive elaboration of input–output characteristics, but do not give spatially resolved information about currents, carriers, and potentials on the nanometer scale relevant to quantum heterostructure device operation. In response, electrical scanning probe techniques have been developed and deployed to observe experimentally, with nanometric spatial resolution, two-dimensional profiles of the electrical resistance, capacitance, potential, and free carrier distribution, within actively driven devices. Experimental configurations for the most prevalent electrical probing techniques based on atomic force microscopy are illustrated with considerations for practical implementation. Interpretation of the measured quantities are presented and calibrated, demonstrating that internal quantities of device operation can be uncovered. Several application areas are examined: spreading resistance and capacitance characterization of free carriers in III-V device structures; acquisition of electric potential and field distributions of semiconductor lasers, nanocrystals, and thin films; scanning voltage analysis on diode lasers—the direct observation of the internal manifestations of current blocking breakdown in a buried heterostructure laser, the effect of current spreading inside actively biased ridge waveguide lasers, anomalously high series resistance encountered in ridge lasers—as well as in CMOS transistors; and free-carrier measurement of working lasers with scanning differential spreading techniques. Applications to emerging fields of nanotechnology and nanoelectronics are suggested.

Experimental study of discharge with liquid non-metallic (tap-water) electrodes in air at atmospheric pressure

The discharge with liquid non-metallic electrodes (DLNME) was investigated. The discharge burnt steadily with a DC power supply between two streams of weakly conducting liquid (tap water) in open air at atmospheric pressure. The metallic current leads were inserted into the streams and were covered by a 5 mm thick water layer. The discharge burnt in volumetric (diffuse) form with fairly high voltage (~3 kV between leads) and low current density (~0.2-0.25 A cm-2). The plasma state in the inter-electrode gap was studied by spectroscopy, microwave sounding and electrical probe technique. The rotational and vibrational temperatures of N2 electronically excited molecules were measured. The absolute radiation values of different species were obtained as a function of position in the gap. The electric field E and the concentration of charged particles were obtained. The value of parameter E/Ng was estimated (Ng being the gas concentration). The density of water vapour in the discharge column was estimated. The results obtained show that DLNME generate molecular plasma at high pressure but out of thermal equilibrium. The properties of DLNME make it promising for various engineering applications, including those in plasma chemistry.

Spectroscopic and electric probe measurements of plasma parameters in the negative glow region of helium discharge plasma

The essential plasma parameters, i.e., electron temperature, T e electron density, n e and ion temperature, T i, have been measured in the negative glow (NG) region of a helium cold-cathode discharge plasma as a function of the filler gas pressure. For the determination of these parameters two different techniques have been used throughout this work. Spectroscopic technique depending on the line intensity ratio of He(I) resonance line at 3888.65 Å and He(II) ionized line at 4686 Å, besides the width and profile of the working heluim gas, is the first one, while electrical single probe technique depending on the voltage–current characteristics of the plasma is the second one. By this second technique the experimental data of the floating potential, V f, and the plasma potential, V s, were used to define the negative glow region. Comparison between the results of both techniques revealed a strong agreement of the measured values of T e, besides a fairly good agreement of the measured values of n e.

Optical Monitoring of Capacitance in Hemispherical Grain Polycrystalline Silicon for Advanced Dynamic Random Access Memory Application

A novel approach for monitoring the capacitance using optical data from the material characteristics of hemispherical grain (HSG) polycrystalline silicon film is reported. This noncontact optical method provides indirect measurement of electrical capacitance for advanced dynamic random access memory (DRAM) applications using HSG material. By a simple statistical analysis of the microscopic HSG structure, the actual electrical capacitance is estimated to better than 90% confidence level through correlation of the optically measured thickness and the void content of the HSG film. Data from broad band spectrophotometry (190–750 nm) with beam profile reflectometry are fitted in the context of the Bruggeman effective medium approximation (EMA) model to give HSG thickness and void content. The actual capacitance obtained from the electrical probe technique using an intrusive electrode on finished DRAM devices indicates good agreement with our approach.