Showing papers on "Van der Pauw method published in 2022"

A facile synthesis of novel polyaniline/graphene nanocomposite thin films for enzyme-free electrochemical sensing of hydrogen peroxide

Abstract: The electrochemical method is the most effective, facile, and economical approach for the detection of small molecules. The present article deals with the design and engineering of polymer–graphene-based thin films through an in situ facile synthesis technique for the development of high performance electrochemical sensors. We report a facile technique for preparing polyaniline (PANI) and polyaniline/graphene (PANI/G) nanocomposite thin films and their application as enzyme-free electrochemical sensors for hydrogen peroxide (H2O2). PANI and PANI/G films were deposited on a dopamine modified ITO substrate via spin coating and in situ deposition techniques. The in situ fabricated films, which exhibited better electrical properties and stability as compared to the spin coated films, were studied in detail. These thin films were characterized using UV-visible spectroscopy, FT-IR spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM) to study their optical, chemical, and surface textural properties. Results show a homogeneous distribution of the constituting materials. From the AFM results, it was found out that the PANI/G film showed increased surface roughness (∼20 nm) as compared to the PANI film (∼15 nm). The electrochemical properties of the films were determined using the van der Pauw method and cyclic voltammetry technique. The conductivity of the PANI and PANI/G films was estimated to be 5.38 × 103 and 6.84 × 103 S cm−1, respectively. Finally, the electrochemical sensing performances of the PANI and PANI/G films were investigated towards H2O2 reduction in a wide potential range of −0.6 to 0.6 V in 0.1 M PBS solution of pH 7.0. This work demonstrates the application of thin-film technology for the development of nanodevice sensors.

Double perovskite Cs2AgBiBr6 radiation sensor: synthesis and characterization of single crystals

Abstract: Abstract Single crystals of lead-free halide double perovskite Cs 2 AgBiBr 6 sensor material manifest a remarkable potential for application in radiation detection and imaging. In this study, the purity and crystallinity of solution-grown Cs 2 AgBiBr 6 single crystals with cubic Fm $$\overline{3}$$ 3 ¯ m symmetry have been corroborated by powder XRD measurements, while the single crystal XRD patterns reveal the dominant {111} lattice planes parallel to the sample surfaces. A wider range of lower resistivity values (10 6 –10 9 Ωcm) was obtained from the I-V measurements compared to the 1.55 × 10 9 –6.65 × 10 10 Ωcm values from the van der Pauw method, which is typically higher for the Ag than for the carbon paint electrodes. Charge-carrier mobility values estimated from the SCLC method for the carbon paint-Cs 2 AgBiBr 6 (1.90–4.82 cm 2 V −1 s −1 ) and the Ag-Cs 2 AgBiBr 6 (0.58–4.54 cm 2 V −1 s −1 ) including the density of trap states (10 9 –10 10 cm −3 ) are comparable. Similar values of 1.89 cm 2 V −1 s −1 and 2.36 cm 2 V −1 s −1 are derived from the Hall effect measurements for a sample with carbon and Ag electrodes, respectively. The key electrical parameters including the X-ray photoresponse measurements indicate that the Cs 2 AgBiBr 6 samples synthesized in this study satisfy requirements for radiation sensors. Graphical abstract

Electrical Resistivity of Fe and Fe‐3 wt%P at 5 GPa With Implications for the Moon's Core Conductivity and Dynamo

Abstract: A high-magnetic field once existed in the early history of the Moon, suggesting the core once possessed a thermally driven dynamo. The thermal conductivity of core materials is a significant parameter of the dynamo. The lunar core composition is thought to be iron or iron-alloyed with some light elements (e.g., S, P, Si, and C), but its transport properties remain uncertain. We measured the electrical resistivity of iron and Fe-3 wt%P alloys at 5 GPa and high temperatures. Apart from the quasi four-point technique, the four-probe van der Pauw technique was also employed to measure the resistivity of pure iron. Adding ∼3 wt% phosphorus to iron slightly increases the resistivity at 5 GPa and 1000–1500 K due to the impurity effect. The resistivity of Fe-3 wt%P alloys increases at the onset of melting. Via the Wiedemann-Franz law, the thermal conductivity at the lunar core-mantle boundary (CMB) is estimated to be 28.6–34.2 Wm−1K−1 for a light-element free core and 31.5 ± 1.9 Wm−1K−1 for a phosphorus-bearing (∼3 wt% P) core. Therefore, small amounts of phosphorus in the lunar core slightly impact its thermal conductivity. The estimated conductive heat flow across the lunar CMB varies from 4.5 to 5.7 GW, and the adiabatic heat flux varies from 3.3 to 4.2 mW/m2, depending on the core's composition (Fe or Fe-3 wt%P). Integrating our results with previous lunar core evolution models, we suggest that a thermally driven dynamo persisted until 3.63–3.88 Ga ago.

Charge. transport, conductivity and Seebeck coefficient in pristine and TCNQ loaded preferentially grown metal-organic framework films

Abstract: Abstract This investigation on metal-organic framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport and p -type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current–voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF thin films are grown using quasi-liquid phase epitaxy (LPE) on specially functionalized silicon or borosilicate glass substrates. In addition to the pristine SURMOF films also the effect of loading these porous thin films with TCNQ has been investigated. Positive charge carrier conduction and a strong anisotropy in electrical conduction was observed for highly oriented SURMOF films and corroborated with Seebeck coefficient measurements. Van der Pauw four-point Hall sample measurements provide important insight into the electrical behavior of such porous and hybrid organic–inorganic crystalline materials, which renders them attractive for potential use in microelectronic and optoelectronic devices and thermoelectric applications.

Resistivity study of inkjet-printed structures and electrical interfacing on flexible substrates

Abstract: Development and evaluation of electronics with printing techniques such as inkjet printing is currently an active subject of research with various outstanding results in sensing applications. Printing technologies have shown high efficiency and compatibility with various types of inks and substrates, enhancing the opportunity for scientific innovation and research in this field. The present work reports on the evaluation of the resistivity and the sheet resistance of inkjet-printed conductive commercial Ag-nanoparticle ink, graphene ink and a custom functionalized reduced graphene oxide (f-rGO) ink on Kapton substrate using the Van-der-Pauw method. Two different approximations have been used to determine the sheet resistance (Rs) and the corresponding resistivity (ρ). The results showed differences in the extracted sheet resistance value, which emphasizes the importance of the adopted calculation method. Furthermore, in order to demonstrate the ability to fabricate printed structures with efficient electrical connection to external devices, we have evaluated standard methods for interfacing two inkjet-printed materials on Kapton substrate, namely: commercial Ag-nanoparticle ink and graphene ink. Two standard connection techniques implementing a 4-pin Flexible Printed Circuit (FPC) connector and an Amphenol Clincher connector were evaluated, along with a custom direct interconnection approach. Direct interconnection between Cu patterned tracks and printed structures attracts special interest because it addresses one of the main problems in printed electronics, which is the interfacing of the printed structure with other electronic or read-out components. Thus, the printed Ag-Graphene/Cu direct interconnection case was further investigated. Two-point [2p] and four-point [4p] measurements were performed in order to study the effect of the various probe locations of engagement to the extracted resistance. The results acquired for this interconnection method revealed the importance of the measurement probe location. To support these experimental results, FEA simulations were performed and the outcomes were consistent with the experimental findings.

Nanoscale Conductive Sheets in Ferroelectric BaTiO3: Large Hall Electron Mobilities at Head-to-Head Domain Walls

Abstract: Strongly charged head-to-head domain walls that are purposely engineered along the [110] crystallographic orientation into ferroelectric BaTiO3 single crystals have been proposed as intrinsically nanoscaled two-dimensional electron gases (2DEGs) because of their significant conductivity. Here, we quantify these 2DEG properties through dedicated Hall transport measurements in van der Pauw 4-point geometry, finding the electron mobility to reach around 400 cm2 (V s)−1, while the two-dimensional charge density amounts to 7 × 103 cm–2. We underline the necessity to take into account the thermal and geometrical misalignment offset voltages by evaluating the Hall resistance under magnetic field sweeps; otherwise, errors of several hundred percent in the derived transport parameters can occur.

An investigation on the role of low temperature annealing on the structural, morphological, optical, and electrical properties of DC magnetron sputtered Zn(1-x)Sn(x)O thin films

Abstract: This study reveals the effect of low-temperature air annealing on various physical properties of Zn (1-x) Sn (x) O (x = 0.14) (TZO) thin films. The thin films were grown on glass substrates by co-sputtering techniques and the grown films were subjected to low temperature air -annealing. X-ray diffraction studies on the grown samples reveal a polycrystalline nature with a hexagonal wurtzite structure. A Change in orientation from (002) to (100) followed by an increase in crystallinity was observed in 100 °C annealed samples. A variation in the optical band gap from 3.17 to 3.44 eV after annealing was noticed. Changes in the defect density of Zn interstitials and Oxygen vacancies are clearly noticeable from PL analysis. X-ray Photoelectron Spectroscopy (XPS) elucidate an enhanced oxygen vacancies after doping. The van der Pauw resistivity measurement revealed a decrement in the resistivity after doping and annealing.

Modifications of Epitaxial Graphene on SiC for the Electrochemical Detection and Identification of Heavy Metal Salts in Seawater

Abstract: The electrochemical detection of heavy metal ions is reported using an inexpensive portable in-house built potentiostat and epitaxial graphene. Monolayer, hydrogen-intercalated quasi-freestanding bilayer, and multilayer epitaxial graphene were each tested as working electrodes before and after modification with an oxygen plasma etch to introduce oxygen chemical groups to the surface. The graphene samples were characterized using X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy, and van der Pauw Hall measurements. Dose–response curves in seawater were evaluated with added trace levels of four heavy metal salts (CdCl2, CuSO4, HgCl2, and PbCl2), along with detection algorithms based on machine learning and library development for each form of graphene and its oxygen plasma modification. Oxygen plasma-modified, hydrogen-intercalated quasi-freestanding bilayer epitaxial graphene was found to perform best for correctly identifying heavy metals in seawater.

Large Hall electron mobilities in head-to-head BaTiO$_3$-domain walls

Abstract: Strongly charged head-to-head (H2H) domain walls (DWs) that are purposely engineered along the [110] crystallographic orientation into ferroelectric BaTiO 3 single crystals have been proposed as novel 2-dimensional electron gases (2DEGs) due to their significant domain wall conductivity (DWC). Here, we quantify these 2DEG properties through dedicated Hall-transport measurements in van-der-Pauw 4-point geometry at room temperature, finding the electron mobility to reach around 400 cm 2 (Vs) − 1 , while the 2-dimensional charge density amounts to 7 × 10 3 cm − 2 . We un-derline the necessity to take account of thermal and geometrical-misalignment offset voltages by evaluating the Hall resistance under magnetic-field sweeps, since otherwise dramatic errors of several hundred percent in the derived mobility and charge density values can occur. Apart from the specific characterization of the conducting BaTiO 3 DW, we pro-pose the method as an easy and fast way to quantitatively characterize ferroic conducting DWs, complementary to previously proposed scanning-probe-based Hall-potential analyses.

Characterizing the Conductivity of Aerosol Jet Printed Silver Traces on Glass Using Intense Pulsed Light (IPL)

Abstract: Aerosol Jet Printing is a novel micron-scale printing technology capable of handling a variety of materials due to a large print material viscosity range and high substrate standoff distance of 3–5 mm. To finalize the properties of printed materials, a form of post-processing is often required. A current widely applicable post-processing technique exists in traditional oven curing. However, oven curing greatly restricts the viable substrates as well as curing time. Intense Pulsed Light (IPL) offers the chance to greatly expand this substrate variety and decrease curing time. However, limited models currently exist to relate the finished material properties to the unique settings of current IPL technology. In this paper, an experiment is developed through a General Full Factorial Design of Experiments (DOE) model to characterize conductivity of Ag ink using IPL as a post processing technique. This is conducted through Novacentrix Ag ink (JSA426) by 3 × 3 mm Van der Pauw sensor pads cured using IPL. Sample pads were generated in triplicate over a range of Energy Levels, Counts and Durations for IPL and the resulting conductivity measured. The collected conductivity data was then analyzed using ANOVA to determine the significant interactions. From this, a regression model is developed to predict the conductivity for any Energy-Count-Duration value. The methods employed are applicable to any post-processing technique, and further optimization of the model is proposed for future work.

Optical and Electrical Properties of ZnMgO with High Mg Content Elaborated by Ultrasonic Spray Pyrolysis Using Water‐Based Solutions

Abstract: ZnMgO thin films are elaborated by ultrasonic spray pyrolysis using water‐based solutions only, for an Mg composition as high as 70 mol%. The elaboration conditions are optimized and the structural, optical, and electrical properties of the ZnMgO films are investigated with respect to the Mg concentration using X‐Ray fluorescence, X‐Ray diffraction, atomic force microscopy, Raman and transmission spectroscopies, and van der Pauw/Hall effect electrical measurements. The obtained properties are correlated to analyze the miscibility and, for single‐phase material, the optoelectronic, optical, and transport properties with respect to the composition. The elaborated thin films exhibit a monotonous increase in the bandgap, a high transparency above 90% in the visible region, and a dramatic decrease in the n‐type carrier concentration, for Mg compositions lower than 30 mol% where wurtzite single‐phase structure is evidenced. A compensation mechanism of the n‐type dopants in ZnO, attributed to interstitial Zn which acts as a shallow donor, is given as an explanation of this variation of the carrier concentration. These optoelectronic properties show that ZnMgO can be efficiently used in applications such as UV detectors and solar cells.

Ion implantation effects on the microstructure, electrical resistivity and thermal conductivity of amorphous CrSi2 thin films

Abstract: The microstructural changes induced by ion implantation may lead to advantageous modifications of chromium disilicide's (CrSi2) electrical and thermal properties. As a potential thermoelectric material, CrSi2 has attracted attention due to its semiconductor properties and high thermal stability. This contribution investigates the influence of different ion species and implantation conditions on the microstructure, electrical resistivity ρ and thermal conductivity κ behaviors in amorphous CrSi2 thin films. ~ 260-nm-thick CrSi2 films were produced by magnetron sputtering and deposited onto a SiO2/Si substrate. Samples were implanted at room temperature either with Ne or Al ions to form a concentration–depth plateau reaching a concentration of ≈ 1.0 at.% (Ne), or ≈ 0.008 at.% (Al). Ne and Al implantations were also performed with the targets heated at 250 °C. The microstructural modifications were characterized via TEM and STEM-EDX. The electrical resistivity ρ was measured by the van der Pauw method, and the thermal conductivity κ measurements were obtained with SThM. The results obtained show that room temperature Al and Ne implantations cause the reduction of ρ as compared to the pristine film. In contrast, the ρ values are significantly higher for Ne and Al implantations in heated substrates. The microstructure evolution, electrical and thermal behaviors are discussed considering the effects of radiation damage and the formation of dense nanocrystallite arrays during the implantation process.

Effect of Varying Doping Level on Structural, Electrical and Optical Properties of Al Doped ZnO Spin Coated Films

Abstract: The synthesis and characterization of spin-coated Al-doped ZnO (AZO) thin films with varying Al concentrations (0%, 5%, 10%, 15% and 20%) onto glass substrates have been demonstrated in this paper. The structural, electrical and optical properties of the spin-coated thin films have been investigated by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) analysis, Van Der Pauw method and UV-visible spectroscopy. The EDX study shows well-defined peaks which confirm the presence of only Zn, O and Al and no other impurities in the films. The increase of Al and decrease of Zn weight percentages with increasing doping level confirms the effective substitution of Zn by Al. SEM of the surfaces of the films shows that undoped ZnO films contain particle agglomeration which is reduced with Al doping and the surfaces of the films gradually became more uniform. The thickness of the AZO films varied from 86 to 699 nm with increasing Al doping concentration. The electrical conductivity of the films increased up to ~ 7 × 10-2 (Ω.cm)-1 due to doping with 5% Al concentration. The optical transmittance highly increased above 95% in the visible range with the introduction of Al dopant and it kept rising with the increase of Al concentration. The optical energy band gap of undoped ZnO increased from 3.275eV to 3.342 eV with 5% Al doping.

Mathematical analysis of Van der Pauw’s method for measuring resistivity

Abstract: The Van der Pauw method has tremendous significance in measuring material resistivity in arbitrary shapes. The extended Van der Pauw method can be used to measure the resistivity of anisotropic materials or even materials with holes without enormous measurements or calculations. However, the method requires that the material be thin enough to be considered quasi-two-dimension, and the measurement of equivalent resistance is largely influenced by contact resistance. This paper aims to find the factors that influence the measurement’s accuracy by formula analyzing, trying to improve the precision of Van der Pauw’s measurement.

In situ measurements of electrical resistivity of metals in a cubic multi-anvil apparatus by van der Pauw method.

Abstract: On the basis of the van der Pauw method, we developed a new technique for measuring the electrical resistivity of metals in a cubic multi-anvil high-pressure apparatus. Four electrode wires were introduced into the sample chamber and in contact with the pre-pressed metal disk on the periphery. The sample temperature was measured with a NiCr-NiSi (K-type) thermocouple, which was separated from the sample by a thin hexagonal boron nitride layer. The electrodes and thermocouple were electrically insulated from each other and from the heater by an alumina tube as well. Their leads were in connection with cables through the gap between the tungsten carbide anvils. We performed experiments to determine the temperature dependence of electrical resistivity of pure iron at 3 and 5 GPa. The experiments produce reproducible measurements and the results provide an independent check on electrical resistivity data produced by other methods. The new technique provides reliable electrical resistivity measurements of metallic alloys and compounds at high pressure and temperature.

Easy and computer-time-saving implementation of the van der Pauw method including anisotropy and probe positioning correction factors using approximate closed-form analytical functions.

Abstract: Measurements in a van der Pauw configuration often require the use of complicated mathematical expressions or implicit relations, which may be computer-time-consuming or tedious to implement in a given software. Thus, a closed-form expression is often desirable. We propose to approximate these relations by closed-form analytical functions using only basic operators that can be easily implemented. We present explicitly the functions and the numerical values of their parameters for the cases of standard van der Pauw measurement, anisotropic resistivities, and the probe position correction factor. The discrepancy with the exact values is smaller than 10-5, which is sufficient for practical purposes.

A novel resistivity measurement method for a homogeneous cylinder shape based on the vdP configuration

Abstract: The electrical resistivity method for a cylinder shape is an essential method for reflecting physical properties. However, the use of a nondestructive resistivity method with the circumferential cross-section arrangement for working components remains challenging. This paper provides a simple novel resistivity method for a cylinder shape based on the van der Pauw configuration, with four electrodes placed near the middle cross-section layer of shape. First, the theoretical solution formulae for the electrostatic potential function in the cylindrical coordinate system are derived. Then, the effect of the electrode and shape size is analysed. The results show that the electrode height is less than 1% of the cylinder height and the radian angle is less than 10°, where the electrode size effect on the correction factor (CF) can be ignored, and CF rarely depends on the cylinder shape. Finally, a prototype is designed, and the proposed method is verified in laboratory tests using geomaterials. The performance of the proposed method for fine soil at high moisture contents is found to be better than that at low moisture contents.

Groundwater Salinity Monitoring Using a New Fiber Optic Sensor

Abstract: This column reviews the general features of PHT3D Version 2, a reactive multicomponent transport model that couples the geochemical modeling software PHREEQC-2 (Parkhurst and Appelo 1999) with three-dimensional groundwater flow and transport simulators MODFLOW-2000 and MT3DMS (Zheng and Wang 1999). The original version of PHT3D was developed by Henning Prommer and Version 2 by Henning Prommer and Vincent Post (Prommer and Post 2010). More detailed information about PHT3D is available at the website http://www.pht3d.org.Thereviewwasconducted separately by two review-ers. This column is presented in two parts. and charge Monitoring of freshening and salinization is indispens-able in coastal groundwater management. Here we present insights into a recently developed fiber optic (FO) sensor to monitor water salinity. This sensor has potential advantages over conventional direct and indirect (geophysical) monitoring techniques (Nienhuis et al. 2010; Pezard et al. 2012; Folch et al. 2020), like costs (especially for deeper applica-tions), measurement frequency, and insensitivity to electric and electromagnetic fields. The sensor is based on fiber bragg grating (FBG) technology and a salt-responsive coating. Each sensor consists of a coated and an uncoated FBG. The uncoated FBG is used for temperature compensation. The coating expands and contracts as a function of water activity. In saturated coastal aquifers containing mixtures of meteoric water and sea water, water activity can readily be converted to water salinity, especially at higher solute concentrations. Upon transmission of light through the fiber, a specific wavelength of the reflected light at the FBG is occurs, which is used to determine the water salinity. We compared FO sensors with commercial conductiv-ity-temperature-depth (CTD) sensors at two locations below an intertidal area at the coast of the Western Netherlands in the winter of 2020–2021. The results of one of the locations (“North”) are shown in Figure 1. Although the general response of the FO sensor to salinity changes related to rela-tively short-term (hourly) variations shows a good resem-blance with the CTD response, some important differences can be observed, which are

Simple Proofs of Upper and Lower Envelopes of Van Der Pauw’s Equation for Hall-Plates with an Insulated Hole and Four Peripheral Point-Contacts

Abstract: For plane singly-connected domains with insulating boundary and four point-sized contacts,  , van der Pauw derived a famous equation re-lating the two R with the sheet resistance without any other parameters. If the domain has one hole van der Pauw’s equation becomes an inequality with upper and lower bounds, the envelopes. This was conjectured by Szymański et al. in 2013, and only recently it was proven by Miyoshi et al. with elaborate mathematical tools. The present article gives new proofs closer to physical intuition and partly with simpler mathematics. It relies heavily on conformal transformation and it expresses for the first time the trans-resistances and the lower envelope in terms of Jacobi functions, elliptic integrals, and the modular lambda elliptic function. New simple formulae for the asymptotic limit of a very large hole are also

Electrical Characterization of II-VI Thin Films for Solar Cells Application

Abstract: Cds and CdTe both are effective absorber semiconductors for thin-film solar cells. It is a naturally n-type material, which has a direct bandgap value of 2.42 eV at room temperature It has great importance in light detectors in this work, CdS thin films (TF) were synthesized on glass substrates by RF Magnetron sputtering technique in an inert gas atmosphere. The electrical properties of CdS were characterized by the Van Der Pauw method. The films showed p-type conductivity, while the films deposited at different annealed times exhibited n-type conductivity. The resistivity of the CdTe films decrease as the conductivity increased. As the source rate was increased, the hole concentration in the as-grown p-type CdTe films increased. It was also reported annealing process affects the electrical properties. Al doping CdS the value of resistivity becomes minimum as the resistivity becomes maximum although mobility has maximum value after an increase in Al doping the mobility value. As a result, the CdS/CdTe thin-film showed enhanced electrical properties for solar cell applications.

Conductive n-type gallium nitride thin films prepared by sputter deposition

Abstract: Given the recent increase in the demand for gallium nitride (GaN) in different markets like optoelectronics and power devices, the request for epitaxially grown GaN will further increase. To meet this high demand, higher throughput and more economical manufacturing technologies must be advanced. In this work, GaN thin films are deposited by reactive sputter deposition from a liquid gallium target at a substrate temperature of 900 °C. The layers are grown epitaxially on c-plane oriented sapphire in an industrial-scale sputter tool from Evatec AG. Due to the growth rate of >1 nm/s and the fast substrate heat-up time, the throughput in a production setup can be increased compared to other GaN growth techniques. The resistivity of the intrinsic insulating GaN can be lowered by intentional Si doping during the sputter deposition process by three orders of magnitude. Thereby, conductive n-type GaN can be grown with different dopant amounts. The carrier mobility of the sputter deposited film is 45 cm2 V−1 s−1 at a carrier concentration of 1.1 × 1020 cm−3 based on room temperature Hall measurements using a van der Pauw geometry. The lowest resistivity reaches 1300 μΩ cm, which is confirmed by sheet resistance measurements. Undoped films exhibit an x-ray diffraction rocking curve full width at half maximum of 0.2°, which increases up to 0.5° for highly Si-doped layers. The presented results show that GaN prepared by reactive sputter deposition from a liquid gallium source is a viable alternative to conventional deposition techniques for GaN.

Diffusion of Phosphorus and Gallium from a Deposited Layer of Gallium Phosphide into Silicon

Abstract: Diffusion from a layer of gallium phosphide GaP deposited onto a silicon surface was studied. After diffusion, the silicon samples were examined by the Van der Pauw method, and a scanning electron microscope was used to determine the concentration distribution of phosphorus and gallium atoms impurity. Keywords: diffusion, gallium phosphide, silicon, solubility, concentration, binary complexes.

Dopant Activation Depth Profiling for Highly Doped Si:P By Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM)

Abstract: Heavily n-doped epitaxially grown Si layers are of great importance for source/drain (S/D) application in advanced node nMOS devices. For contact resistivity reduction, the dopant activation level is very important. Various techniques are being used to evaluate dopant activation in Si:P layers. Among these two methods are Scanning Spreading Resistance Microscopy (SSRM) and Differential Hall Effect Metrology (DHEM). SSRM uses an atomic force microscope equipped with a hard conductive probe that is scanned in contact mode on the cross-sectioned sample’s surface and measures spreading resistance. Measured resistance values as a function of depth are converted into resistivity and carrier concentration depth profiles using calibration measurements and conversion relationships. DHEM provides depth profiles of mobility, resistivity and carrier concentration through a semiconductor layer by making successive sheet resistance (R s ) and Hall voltage measurements using Hall effect/Van der Pauw techniques, as the electrically active thickness of the layer is reduced through successive oxidation steps. Controlled oxidation is achieved by electrochemical anodization. Data collected can then be processed to yield the depth profiles. In this contribution we have carried out SSRM and DHEM measurements on Si:P epi layers subjected to different processing conditions including annealing and ohmic contact fabrication. Secondary Ion Mass Spectrometry (SIMS) was used to measure the total (active + inactive) dopant profiles through the films. Effects of these processes on dopant diffusion and activation were studied and the results from DHEM and SSRM were compared. In-situ phosphorus (P) doped Si epi-layers were grown over 300mm diameter boron doped monitor wafers. While one set was kept as the reference, a second set was treated by a spike-annealing process at 1000 °C. In a third set a Ti/TiN contact fabrication process was carried out and the contact was removed before analysis. In the fourth set contact process was applied to the spike annealed wafer before removal of the Ti/TiN layers. Bulk sheet resistance measurements were made using 4-point probe (4PP) for all the samples. SSRM measurements were carried out at IMEC. Cross-shaped Van der Pauw test-patterns were formed on 8mmx8mm areas on the samples and DHEM measurements were performed at ALP. Figure below shows the dopant depth profiles obtained by SIMS and the carrier concentration profiles from DHEM and SSRM techniques for samples D02 (as deposited Si:P) and D03 (spike annealed). One can make some general observations from the data in this figure. The total dopant concentration as measured by SIMS is ~ 1.4E21/cm 3 . There is only a small difference in the total dopant distribution profiles (SIMS) between the as deposited sample and the spike annealed sample. However, the spike annealed sample shows much higher dopant activation as measured by DHEM. Carrier concentration is ~2.5x higher in sample D03 (~5E20/cm 3 ) compared to sample D02 (~2E20/cm 3 ). Activation levels measured by SSRM, however, are lower for both samples, and the peak carrier concentration value increases only slightly upon spike annealing, going from ~2E20/cm 3 in sample D02 to ~2.2E20/cm 3 in sample D03. DHEM clearly indicates the sharp interface between the p-type substrate and the n-type epi-layer and its depth calibration agrees well with the expected thicknesses of the epi layers. The tail of the SSRM data is much more graded. Data from other samples will be presented and discussed in the final manuscript. Figure 1

Optimization of the Van Der Pauw Method for Measuring the Electrical Properties Spectrum of Biological Solutions

Abstract: Measuring the electrical properties of biological solutions is of great importance in biological studies and reveals many facts about the function of microscopic organisms. Four-electrode methods are commonly used to measure the electrical conductivity spectrum. In this study, an optimized bioimpedance sensor based on the Van Der Pauw’s (VDP) theory was proposed to measure the electrical conductivity of biological solutions at the frequency band of 50 kHz–2 MHz. For this purpose, by simulating the bioimpedance sensor in COMSOL software, the effect of various factors on measuring the electrical conductivity was investigated. Using the Nyquist curve, it was found that when the chamber diameter of the bioimpedance sensor is approximately selected three times the electrode diameter, the measurement error calculated by normalized root mean squared error (NRMSE) criterion would be less than 1%. Then, for the practical evaluation, the bioimpedance sensor with five different chamber diameters was constructed. The electrical conductivity spectrum of the saline solution with three different concentrations was measured using the bioimpedance sensors. The NRMSE criterion practically showed that if the electrode diameter be about one third of the chamber diameter, the measurement error would be less than 2%.

Too Late for the Prayers: Music by Justinian Tamusuza & Michael Blake - Too Late for the Prayers: Music by Justinian Tamusuza & Michael Blake. Pauw, Duo Infinite. AOI Edition, AOI CD02.

Abstract: Too Late for the Prayers: Music by Justinian Tamusuza & Michael Blake - Too Late for the Prayers: Music by Justinian Tamusuza & Michael Blake. Pauw, Duo Infinite. AOI Edition, AOI CD02. - Volume 76 Issue 301

Investigation of transition metal-doped zinc oxide for spintronics

Abstract: Transition metal-doped zinc oxide (ZnTMO) grown using metal-organic chemical vapor deposition exhibited spinrelated properties at room temperature that are driven by secondary phases, defects, transition metal clusters, and extrinsic carrier scattering. ZnTMO has been an interesting material for spintronics and has shown ferromagnetism at room temperature in the literature. However, the mechanism for spin-characteristics is not clear. In this work, Anomalous Hall Effect measurements were performed to investigate these mechanisms. A non-linear trend of transverse Hall resistvity with externally applied field indicated spin polarization in the material. However, variations in transverse resistivity with applied magnetic field follow same trend as four-point Van der Pauw resistivity. Hence, the Anomalous Hall Effect is likely not due to intrinsic free carriers. Spin-related properties of ZnTMO are dominantly influenced by secondary phases, native defects, and other extrinsic carrier-scattering centers such as transition metal clusters. This work contributes towards the understanding of ZnTMO for spintronic applications and provides better clarity regarding the underlying phenomena for its spin-related properties.