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Showing papers on "Van der Pauw method published in 2014"


Journal ArticleDOI
TL;DR: Two-probe and van der Pauw electrical measurements reveal bulk and surface conductivity values of 2 and 40 S·cm(-1), respectively, both records for MOFs and among the best for any coordination polymer.
Abstract: Reaction of 2,3,6,7,10,11-hexaaminotriphenylene with Ni2+ in aqueous NH3 solution under aerobic conditions produces Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm–1, respectively, both records for MOFs and among the best for any coordination polymer.

809 citations


Journal ArticleDOI
TL;DR: This work provides a foothold for the development of the first organic-based two-dimensional topological insulator, which will require the precise control of the oxidation state in the single-layer nickel bisdithiolene complex nanosheet.
Abstract: A bulk material comprising stacked nanosheets of nickel bis(dithiolene) complexes is investigated. The average oxidation number is −3/4 for each complex unit in the as-prepared sample; oxidation or reduction respectively can change this to 0 or −1. Refined electrical conductivity measurement, involving a single microflake sample being subjected to the van der Pauw method under scanning electron microscopy control, reveals a conductivity of 1.6 × 102 S cm–1, which is remarkably high for a coordination polymeric material. Conductivity is also noted to modulate with the change of oxidation state. Theoretical calculation and photoelectron emission spectroscopy reveal the stacked nanosheets to have a metallic nature. This work provides a foothold for the development of the first organic-based two-dimensional topological insulator, which will require the precise control of the oxidation state in the single-layer nickel bisdithiolene complex nanosheet (cf. Liu, F. et al. Nano Lett. 2013, 13, 2842).

355 citations


Journal ArticleDOI
TL;DR: In this article, the growth of GeTe thin films on a Si(111)-(√3 × √3)R30°-Sb surface is reported, and the formation of rotational domains in GeTe grown on Si(7 × 7) is explained by domain matched coincidence lattice formation with the Si(1 × 1) surface.
Abstract: The growth of GeTe thin films on a Si(111)-(√3 × √3)R30°-Sb surface is reported. At growth onset, the rapid formation of fully relaxed crystalline GeTe(0001)-(1 × 1) is observed. During growth, a GeTe(0001)-(√3 × √3)R30° surface reconstruction is also detected. Indeed, density functional theory (DFT) simulations indicate that the reconstructed GeTe(0001)-(√3 × √3)R30° structure is energetically competing with the GeTe(0001)-(1 × 1) reconstruction. The out-of-plane α-GeTe ||Si and in-plane α-GeTe ||Si epitaxial relationships are confirmed by X-ray diffraction (XRD). Suppression of rotational twist and reduction of twinned domains are achieved. The formation of rotational domains in GeTe grown on Si(111)-(7 × 7) is explained by domain matched coincidence lattice formation with the Si(111)-(1 × 1) surface. Atomic force microscopy (AFM) images show the coalescence of well-oriented islands with subnanometer roughness on their top part. van der Pauw measurements are performed to verify the...

59 citations


Journal ArticleDOI
TL;DR: A chemical rationale is provided for the NH3 n-doping based on the interaction of NH3 with intrinsic oxygen functionalities and defects of CVD graphene and of C-NH2 doping centers with acceptor species present in the air.
Abstract: Despite the large number of papers on the NH3 doping of graphene, the achievement of stable n-doped large area CVD (chemical vapor deposition) graphene, which is intrinsically p-doped, is still challenging. A control of the NH3 chemisorption and of the N-bond configuration is still needed. The feasibility of a room temperature high pressure NH3 treatment of CVD graphene to achieve n-type doping is shown here. We use and correlate data for (a) sheet resistance, Rsh, and the Hall coefficient, RH, in van der Pauw configuration, acquired in real time during the NH3 doping of CVD-graphene on a glass substrate, (b) optical measurements of the effect of doping on the graphene Van Hove singularity point at 4.6 eV in the dielectric function spectra by spectroscopic ellipsometry, and of (c) N-bond configuration by XPS to better understand and, finally, control the NH3 doping of graphene. The discussion is focused on the thermal and time stability of the n-doping after air exposure. A chemical rationale is provided for the NH3 n-doping based on the interaction of (i) NH3 with intrinsic oxygen functionalities and defects of CVD graphene and of (ii) C-NH2 doping centers with acceptor species present in the air.

47 citations


Journal ArticleDOI
TL;DR: It was found that the conducting Pt/C volume fraction does not change with RH, which suggests that effective medium theory models that depend on volume fraction alone cannot explain the reduction in conductivity with RH.
Abstract: A method is described for measuring the effective electronic conductivity of porous fuel cell catalyst layers (CLs) as a function of relative humidity (RH). Four formulations of CLs with different carbon black (CB) contents and ionomer equivalent weights (EWs) were tested. The van der Pauw method was used to measure the sheet resistance (RS), which increased with RH for all samples. The increase was attributed to ionomer swelling upon water uptake, which affects the connectivity of CB aggregates. Greater increases in RS were observed for samples with lower EW, which uptake more water on a mass basis per mass ionomer. Transient RS measurements were taken during absorption and desorption, and the resistance kinetics were fit using a double exponential decay model. No hysteresis was observed, and the absorption and desorption kinetics were virtually symmetric. Thickness measurements were attempted at different RHs, but no discernible changes were observed. This finding led to the conclusion that the conducti...

41 citations


Journal ArticleDOI
TL;DR: In this article, the influence of microstructure on the gas sensing characteristics of ZnO thin films was investigated using MOCVD growth technique using diethyl zinc and tert-butanol as zinc and oxygen precursors.
Abstract: The present work is aimed to investigate the influence of microstructure on the gas sensing characteristics of ZnO thin films. By controlling the deposition parameters we have successfully grown ZnO thin films of different microstructures on quartz substrates by MOCVD growth technique using diethyl zinc and tert-butanol as zinc and oxygen precursors, respectively. X-ray diffraction pattern shows that the films are textured along (0 0 2) plane. FESEM images reveal the uniform deposition of fine grains with varying microstructures. Growth mode dependent microstructure formation is explained on the basis of a simple model. The optical characterization reveals that the films are transparent in the visible range with band gap energy in the range 3.234–3.217 eV. The effect of microstructure on the electrical parameters of the ZnO such as carrier concentration, resistivity and Hall mobility is understood through Hall effect measurement using standard Van der Pauw geometry. The gas sensing characteristics of the grown films is investigated as a function of temperature and gas concentration in CO test gas environment. The observed results are analyzed on the basis of the variation of microstructures of the grown films.

32 citations


Journal ArticleDOI
TL;DR: Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3)q(CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.
Abstract: An apparatus for measuring the Seebeck coefficient and electrical conductivity is presented and characterized. The device can be used in a wide temperature range from room temperature to 1050 °C and in all common atmospheres, including oxidizing, reducing, humid, and inert. The apparatus is suitable for samples with different geometries (disk-, bar-shaped), allowing a complete thermoelectric characterization (including thermal conductivity) on a single sample. The Seebeck coefficient α can be measured in both sample directions (in-plane and cross-plane) simultaneously. Electrical conductivity is measured via the van der Pauw method. Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3)q(CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.

30 citations


Journal ArticleDOI
TL;DR: In this paper, the surface potential of c-Si is controlled by the shallow Cat-doping and the surface recombination velocity of minority carriers is greatly reduced by this potential control.
Abstract: Phosphorus (P) or boron (B) atoms can be doped at temperatures as low as 80 to 350 °C, when crystalline silicon (c-Si) is exposed only for a few minutes to species generated by catalytic cracking reaction of phosphine (PH3) or diborane (B2H6) with heated tungsten (W) catalyzer. This paper is to investigate systematically this novel doping method, “Cat-doping”, in detail. The electrical properties of P or B doped layers are studied by the Van der Pauw method based on the Hall effects measurement. The profiles of P or B atoms in c-Si are observed by secondary ion mass spectrometry mainly from back side of samples to eliminate knock-on effects. It is confirmed that the surface of p-type c-Si is converted to n-type by P Cat-doping at 80 °C, and similarly, that of n-type c-Si is to p-type by B Cat-doping. The doping depth is as shallow as 5 nm or less and the electrically activated doping concentration is 1018 to 1019 cm-3 for both P and B doping. It is also found that the surface potential of c-Si is controlled by the shallow Cat-doping and that the surface recombination velocity of minority carriers in c-Si can be enormously lowered by this potential control.

26 citations


Journal ArticleDOI
Lan Liu1, Ruisong Guo1, Shanshan Wang1, Yuexia Yang1, Dongsheng Yin1 
TL;DR: In this paper, the authors used a combined EDTA-citrate complexing sol-gel method to synthesize a solid oxide fuel cell (PBSCN) with various proportions of nickel.

22 citations


Journal ArticleDOI
TL;DR: In this article, a DC magnetron sputtering in a reactive atmosphere of Ar and CH4 at 800 1C was used to create Titanium carbide abstract Epitaxial TiC films.

16 citations


Journal ArticleDOI
TL;DR: In this paper, the authors derived exact analytic expressions for the sensitivity of sheet resistance and Hall sheet resistance measurements to local inhomogeneities for the cases of nonzero magnetic fields, strong perturbations, and perturbation over a finite area.
Abstract: We derive exact, analytic expressions for the sensitivity of sheet resistance and Hall sheet resistance measurements to local inhomogeneities for the cases of nonzero magnetic fields, strong perturbations, and perturbations over a finite area, extending our earlier results on weak perturbations. We express these sensitivities for conductance tensor components and for other charge transport quantities. Both resistive and Hall sensitivities, for a van der Pauw specimen in a finite magnetic field, are a superposition of the zero-field sensitivities to both sheet resistance and Hall sheet resistance. Strong perturbations produce a nonlinear correction term that depends on the strength of the inhomogeneity. Solution of the specific case of a finite-sized circular inhomogeneity coaxial with a circular specimen suggests a first-order correction for the general case. Our results are confirmed by computer simulations on both a linear four-point probe array on a large circular disc and a van der Pauw square geometry. Furthermore, the results also agree well with Nahlik et al. published experimental results for physical holes in a circular copper foil disc.

Journal ArticleDOI
TL;DR: In this article, the van der Pauw method for two-dimensional samples of arbitrary shape with an isolated hole is considered, and the relationship between extreme values of the resistances allow one to determine the specific resistivity of the sample and the dimensionless parameter related to the geometry of the isolated hole, known as the Riemann modulus.
Abstract: The van der Pauw method for two-dimensional samples of arbitrary shape with an isolated hole is considered. Correlations between extreme values of the resistances allow one to determine the specific resistivity of the sample and the dimensionless parameter related to the geometry of the isolated hole, known as the Riemann modulus. The parameter is invariant under conformal mappings. Experimental verification of the method is presented.

Journal ArticleDOI
TL;DR: In this paper, the structural, optical and electrical properties of aluminum doped zinc oxide (AZO) films were examined after annealing in air and hydrogen atmosphere, and the observed phenomena result in an increase of the resistivity, the reduction of the transmittance, and a ca. 0.4 eV drop in optical band gap.
Abstract: Aluminum doped zinc oxide (AZO) films deposited by ion beam co-sputtering system were investigated after annealing. Films with ca. 200 nm thickness and 0.7 at.% Al were examined after 100, 200, 300, and 400 °C annealing in air and hydrogen atmosphere. The structural, optical and electrical properties of the films were measured ex situ by XRD, optical microscope, XPS, spectrometer, and Hall measurement with the Van der Pauw method, respectively. Our previous studies found that the resistivity of the film was closely related to the intensity of the (002) XRD peak, d-spacing, grain size, mean free path of the charge carrier, concentration of the carrier, and compressive stress which was released after 400 °C annealing in air. Moreover, the optical band gap was clearly correlated to the concentration of the charge carrier. Films after being annealed in air show that the release of the compressive stress decreased the grain size. After 400 °C annealing, surface cracks and the reduction of the oxygen vacancy and zinc interstitial were observed. All the observed phenomena result in the increase of the resistivity, the reduction of the transmittance, and a ca. 0.4 eV drop in optical band gap. However, films after being annealed in hydrogen atmosphere show not much change in the structure which attributed to the little variation of the optical transmittance and optical band gap, and the resistivity of the films. It clearly shows that the annealing in hydrogen is a much better way than in air to anneal the AZO films.

Journal ArticleDOI
TL;DR: A criterion was developed, making it possible to decide whether the electroconductive properties of the woven fabric specimen can be evaluated with the Van der Pauw method, and the Monte Carlo method was applied to evaluate the uncertainty.
Abstract: This paper presents a method for evaluating measurement uncertainty in the situation when the function of the measurement model occurring in an implicit mathematical form. The Van der Pauw equation used for determining the surface resistance of an electroconductive specimen was selected as a sample measurement model. With the use of the Mathematica program, it is possible to quickly determine the value of the specimen resistance. The evaluation of the uncertainty of measurement result of the surface resistance that is implied by the Van der Pauw equation is more complicated. The Monte Carlo method was applied to evaluate the uncertainty. The Monte Carlo method, including the iterative Newton algorithm, was described and realized with the use of the STATISTICA program. The effectiveness of the selected methods and developed tools was confirmed by the studies and analysis of the result of the surface resistance measurement of a specially selected woven fabric. In particular, a criterion was developed, making it possible to decide whether the electroconductive properties of the woven fabric specimen can be evaluated with the Van der Pauw method. It was shown that the selected electroconductive fabric had all characteristics typical for a Van der Pauw structure.

Journal ArticleDOI
01 Oct 2014-Vacuum
TL;DR: In this article, the effects of carrier concentration on the dielectric function of indium tin oxide (ITO) films were investigated by spectroscopic ellipsometry using Tauc-Lorentz and Drude oscillator terms.

Journal ArticleDOI
TL;DR: In this paper, the authors performed a cAPCVD study of a TiO2/SnO2 system using a range of techniques such as X-ray diffraction (XRD), wavelength dispersive x-ray (WDX) spectroscopy, XPS, scanning electron microscopy (SEM), and ultra violet-visible (UV-vis) spectrographs.
Abstract: Combinatorial atmospheric pressure (cAP)CVD is used to deposit a film of graded composition from mainly TiO2 to TiO2/SnO2 to mainly SnO2. This is the first cAPCVD study of a TiO2/SnO2 system. The thin film is characterized using a range of techniques such as X-ray diffraction (XRD), wavelength dispersive X-ray (WDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and ultra violet-visible (UV-vis) spectroscopy. It is found that, at various positions on the film, there are intimate compositions of TiO2 and SnO2. The photocatalytic activity is examined via the degradation of a Resazurin-based ‘intelligent ink’ under 365 nm wavelength irradiation. The change in the concentration of the dye can be monitored by digital imaging alone. The results show how TiO2-rich regions are photocatalytically active, producing a maximum formal quantum yield of 3.32 × 10−4 molecules per absorbed photon. The sheet resistance is determined using a four-point probe via the van der Pauw method. The conductivity is highest in the SnO2-rich and thicker regions of the film, however some of the intimate composite regions of TiO2/SnO2 show both conductivity and photocatalytic activity.

Journal ArticleDOI
TL;DR: In this paper, the growth of ZnO layers deposited by spray pyrolysis on polymeric substrate was studied, and structural, morphological, optical and electrical properties of the layers were measured by X-ray diffraction, scanning electron microscopy, optical spectroscopy and van der Pauw and Hall method.

Journal ArticleDOI
TL;DR: In this article, the authors used maximum entropy-mobility spectrum analysis (ME-MSA) and Bryan's algorithm mobility spectrum (BAMS) analysis to determine hole gas drift mobility at low and room temperature.

Journal ArticleDOI
TL;DR: In this article, the crystal structure at room temperature of GdBa 1 − x Sr x Co 2 O 5+ δ ( x ǫ = 0.0, 0.25,0.5 and 1.0) was investigated.

Journal ArticleDOI
TL;DR: In this article, the transverse output of rotationally symmetric four-contact van der Pauw (VDP) stress sensors depends upon only the inplane shear stress or the difference of the in-plane normal stresses on (100) silicon.
Abstract: Under the proper orientations and excitations, the transverse output of rotationally symmetric four-contact van der Pauw (VDP) stress sensors depends upon only the in-plane shear stress or the difference of the in-plane normal stresses on (100) silicon. In bridgemode, each sensor requires only one four-wire measurement and produces an output voltage with a sensitivity that is 3.16 times that of the equivalent resistor rosettes or bridges, just as in the normal VDP sensor mode that requires two separate measurements. Both numerical and experimental results are presented to validate the conjectured behavior of the sensor. Similar results apply to sensors on (111) silicon. The output voltage results provide a simple mathematical expression for the offset voltage in Hall effect devices or the response of pseudo Hall-effect sensors. Bridge operation facilitates use of the VDP structure in embedded stress sensors in integrated circuits. [DOI: 10.1115/1.4028333]

Journal ArticleDOI
TL;DR: In this article, the surface resistance measurement of thin film electrodes formed on flexible substrates with using vacuum deposition technology -PVD was analyzed and the adequacy of the use of the measurement methods to the different shapes of electrodes was analyzed.
Abstract: The following article presents methods of surface resistance measurement of thin film electrodes formed on flexible substrates with using vacuum deposition technology - PVD. The adequacy of the use of the measurement methods to the different shapes of electrodes was analyzed. (Measurement of surface resistance of thin layers of different shapes produced on flexible substrates).

Journal ArticleDOI
TL;DR: In this paper, the development and fabrication of extended short-wavelength infrared (SWIR) HgCdTe (MCT) sensors grown on CdTe/Si substrates by molecular beam epitaxy (MBE) was reported.
Abstract: The development and fabrication of extended short-wavelength infrared (SWIR) HgCdTe (MCT) sensors grown on CdTe/Si substrates is reported. The MCT epilayers were grown on CdTe/Si substrates by molecular beam epitaxy (MBE). The epilayers were evaluated using Fourier transform infrared spectroscopy (FTIR), X-ray double crystal rocking curve (DCRC), Van der Pauw Hall measurements, dislocation defect–decoration etching and Nomarski microscopy. The FTIR analysis revealed a cutoff wavelength of 2.25 μm at 300 K which corresponds to a cadmium composition of 47%. As-grown epilayers have void defect densities less than 10 3 cm −2 and etch pit densities of ∼1 × 10 7 cm −2 . The Hall mobilities of annealed MCT samples are on the order of 1500 cm 2 /Vs and have carrier concentrations of ∼1 × 10 16 cm −3 at 300 K. Samples were doped in situ with indium (donor) and ion-implanted with arsenic (acceptor) to fabricate p–n diodes with sizes ranging from 15 μm to 250 μm diameter. We present the results and analysis of temperature dependent current–voltage ( I – V ) and quantum efficiency/responsivity measurements on the p–n diodes. In our analysis, we found that the I – V characteristics of small devices were dominated by shunt currents and quantum efficiency is limited by Shockley–Read–Hall (SRH) mechanisms.

Journal ArticleDOI
TL;DR: In this article, the origins of low resistivity in H ion-implanted ZnO bulk single crystals are studied by Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) photoluminescence (PL), and Van der Pauw methods.
Abstract: The origins of low resistivity in H ion-implanted ZnO bulk single crystals are studied by Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) photoluminescence (PL), and Van der Pauw methods. The H-ion implantation (peak concentration: 1.45 × 1020 cm−3) into ZnO is performed using a 500 keV implanter. The resistivity decreases from 2.5 × 103 Ω cm for unimplanted ZnO to 6.5 Ω cm for as-implanted one. RBS measurements show that Zn interstitial as a shallow donor is not recognized in as-implanted samples. From photoluminescence measurements, the broad green band emission is observed in as-implanted samples. NRA measurements for as-implanted ZnO suggest the existence of the oxygen interstitial. The origins of the low resistivity in the as-implanted sample are attributed to both the H interstitial as a shallow donor and complex donor between H and disordered O. The activation energy of H related donors estimated from the temperature dependence of carrier concentration is 29 meV.

Journal ArticleDOI
TL;DR: In this paper, the effect of deposition temperature on the structural, optical, and electrical properties of the ZnO thin films was characterized using scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL), ultraviolet-visible (UV-Vis) spectrograph and reflectance accessory, and van der Pauw method.
Abstract: Sol-gel dip-coating was used to prepare ZnO thin films with relaxed residual stress by lowering the deposition temperature from room temperature (25°C) to −25°C. The effect of deposition temperature on the structural, optical, and electrical properties of the films was characterized using scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL), ultraviolet-visible (UV-Vis) spectroscopy and reflectance accessory, and the van der Pauw method. All the thin films were deposited successfully onto quartz substrates and exhibited fibrous root morphology. At low temperature, the deposition rate was higher than at room temperature (RT) because of enhanced viscosity of the films. Further, lowering the deposition temperature affected the structural, optical, and electrical properties of the ZnO thin films. The surface morphology, residual stress, PL properties, and optical transmittance and reflectance of the films were measured, and this information was used to determine the absorption coefficient, optical band gap, Urbach energy, refractive index, refractive index at infinite wavelength, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator wavelength, moments M −1 and M −3, dielectric constant, optical conductivity, and electrical resistivity of the ZnO thin films.


Journal ArticleDOI
TL;DR: In this article, the physical vapour deposition (PVD) method has been employed to yield gallium telluride (GaTe) platelets, and the morphology and growth mechanism of these platelets were investigated with the aid of scanning electron micrographs.
Abstract: The physical vapour deposition (PVD) method has been employed to yield gallium telluride (GaTe) platelets. The morphology and growth mechanism of these platelets were investigated with the aid of scanning electron micrographs. The stoichiometry and homogeneity of the grown samples were confirmed by chemical analysis. The X-ray diffraction (XRD) technique has been used to explore the structure and phase of the compound. On the basis of the Archimedes principle, the density of crystals was estimated to be 5.442 kg mm−3. The resistivity and conductivity type were determined by the van der Pauw method. UV–vis–NIR studies revealed a direct transition with an energy gap of 1.69 eV. Mechanical properties such as microhardness, toughness, Young's modulus and elastic stiffness constant of GaTe crystals in response to the stress field due to an external load were studied to realize their suitability for radiation detector applications. The present observations provide an insight into the physical properties of the vapour-grown GaTe platelets, which are found to be superior over their melt counterparts.

Journal ArticleDOI
Bing Zhang1, Zhen Lin, Xiao Zhang, Xiang Yu1, Jiali Wei1, Xiaoping Wang1 
TL;DR: In this article, a four-electrode system with an axial-radial two-dimensional adjustment structure coupled to an ac voltage excitation source and signal collecting circuit was developed for the absolute measurement of electrolytic conductivity in aqueous solutions.
Abstract: Based on an innovative application of van der Pauw's theory, a system was developed for the absolute measurement of electrolytic conductivity in aqueous solutions. An electrolytic conductivity meter was designed that uses a four-electrode system with an axial–radial two-dimensional adjustment structure coupled to an ac voltage excitation source and signal collecting circuit. The measurement accuracy, resolution and repeatability of the measurement system were examined through a series of experiments. Moreover, the measurement system and a high-precision electrolytic conductivity meter were compared using some actual water samples.

Journal ArticleDOI
TL;DR: In this article, the structural and electronic properties of TaxSiyNz thin films were investigated as a function of the N and Si contents, and the optical properties were investigated by ellipsometric measurements, while the DC. electrical resistivity was measured using the van der Pauw configuration at 300 K.

Patent
23 Apr 2014
TL;DR: In this paper, a tri-axial testing device for testing the water content distribution of a soil sample is presented, which comprises a constant current alternating current source, a dynamic voltage tester, a computer and a plurality of groups of sheet electrodes, wherein the sheet electrodes correspond to the layers of the columnar triaxial soil sample.
Abstract: The invention discloses a tri-axial testing device for testing the water content distribution of a soil sample. The device comprises a constant current alternating current source, a dynamic voltage tester, a computer and a plurality of groups of sheet electrodes, wherein the sheet electrodes correspond to the layers of the columnar tri-axial soil sample; each group comprises four sheet electrodes which are sequentially adhered to the corresponding layer of the soil sample and a tri-axial membrane at an interval of 45 degrees along the circumferential direction of the corresponding layer of the soil sample; the farthest two sheet electrodes and the middle two sheet electrodes in each group are alternately connected with the two electrodes of the constant current alternating current source and the two input ends of the dynamic voltage tester; the output end of the dynamic voltage tester is connected with the computer. According to the device, the van der Pauw principle is used for dynamically measuring the water content of the soil sample in real time; due to the adoption of the flexible sheet electrodes, the influence on the mechanical properties of the soil sample is avoided, and the testing accuracy of the water content of the soil sample is greatly improved.

Proceedings ArticleDOI
27 May 2014
TL;DR: A non-destructive pad resistance method based on the well known van der Pauw method is introduced in this article that indicates bond aging more conveniently than previously reported bond resistance methods, which can indicate the beginning of a late stage of bond deterioration of the Au/Al system and effectively serve as a nondestructive reliability indicator.
Abstract: In microelectronic wire bonding, a reliable electrical connection is of utmost importance. With the advent of advanced bonding wire materials such as Cu, Pd coated Cu, and Ag alloys, there are substantial ongoing efforts in process development and reliability characterization with these materials. To measure bond quality and especially bond reliability is limited with respect to sample size and number of different conditions that can be covered with available resources. Methods that apply non-destructive bond quality measurements during thermal aging could be useful to increase characterization throughput while keeping the need for resources under control. A non-destructive pad resistance method based on the well known van der Pauw method is introduced that indicates bond aging more conveniently than previously reported bond resistance methods. With four connection lines designed at each corner of a standard square bonding pad, the pad resistance was monitored at various stages during reliability testing by high temperature storage at 250 °C of a Au ball bond ≈50 μm in diameter and ≈15 μm high on a standard Al pad. The pad resistance increased during aging up to 30.8 h due to intermetallics (IMCs) formation, then dropped ≈5 % during 14 h down to 50.1 mΩ, and then rose again to reach a plateau above 55 mΩ after 76 h that remain unchanged for the remainder of the aging which lasted 150 h. To explain the unexpected resistance drop a number of finite element (FE) models was developed to simulate various IMC distributions in the bond zone and their effect on the pad resistance. It was found that the resistance drop can be explained by the occurrence of Al-rich IMCs at the periphery of the bond in later stages of bond aging. Compared to the earlier Au-rich IMCs, Al-rich IMCs have lower resistivity. Therefore, the time of the pad resistance drop can indicate the beginning of a late stage of bond deterioration of the Au/Al system and effectively serve as a non-destructive reliability indicator.