Van der Pauw method

About: Van der Pauw method is a research topic. Over the lifetime, 1682 publications have been published within this topic receiving 25364 citations.

Terahertz wafer-scale mobility mapping of graphene on insulating substrates without a gate

Abstract: We demonstrate wafer-scale, non-contact mapping of essential carrier transport parameters, carrier mobility (µdrift), carrier density (Ns), DC sheet conductance (σdc), and carrier scattering time (τsc) in CVD graphene, using spatially resolved terahertz time-domain conductance spectroscopy. σdc and τsc are directly extracted from Drude model fits to terahertz conductance spectra obtained in each pixel of 10 × 10 cm2 maps with a 400 µm step size. σdc- and τsc-maps are translated into µdrift and Ns maps through Boltzmann transport theory for graphene charge carriers and these parameters are directly compared to van der Pauw device measurements on the same wafer. The technique is compatible with all substrate materials that exhibit a reasonably low absorption coefficient for terahertz radiation. This includes many materials used for transferring CVD graphene in production facilities as well as in envisioned products, such as polymer films, glass substrates, cloth, or paper substrates.

Fabrication and Thermal Properties of Carbon Nanotube/Nickel Composite by Spark Plasma Sintering Method

Abstract: Multiwall carbon nanotube (MWNT) materials are attractive because they possess excellent thermal conductivity and mechanical properties. However, few reports exist that focus on improving the thermal conductivity of MWNT by combining it with a metal matrix. Thus to improve the thermal conductivity, a nickel-matrix composite with MWNT was prepared by slurry mixing process using ethanol as a solvent. Using spark plasma sintering (SPS), MWNT/Nickel nanocomposites were fabricated and the fabrication conditions were investigated. The sintered relative densities of the composites containing up to 5 vol% of MWNT were above 99%. The thermal and electrical behaviors of the MWNT/Nickel composites were determined using the laser flash and van der Pauw methods, respectively, and were found to be anisotropic. The thermal conductivity was found to increase by 10% for the composition with 3 vol% MWNT.

Electrical characteristics of thin Ni2Si, NiSi, and NiSi2 layers grown on silicon

Abstract: We have determined the resistivity, carrier concentration, and Hall mobility as a function of thickness (700–3000 A) of Ni2Si, NiSi, and NiSi2 layers formed by vacuum annealing at 270÷v300°C, ≈ 400°C, and ≈ 800°C, respectively, of nickel films vacuum-deposited on a silicon substrate (111 n-type and 100 p-type Si ρ ≈ 1KΩ). The layer thicknesses were measured by 2 MeV4He+ backscattering spectrometry. The silicide phase was confirmed by x-ray measurements. The electrical measurements were carried out using van der Pauw configuration. We found the electrical transport parameters to be independent of the film thickness within the experimental uncertainty. The Hall factors were assumed to be unity. The majority carriers are electrons in NiSi and holes in Ni2Si and NiSi2. The resistivity values are 24±2, 14±1, and 34±2 μΩcm, the electron concentrations are 9±3, 10 and 7±1, and ≈ 2 × 1022 cm−3, and the Hall mobilities are 3±1, ≈ 4.5 and 6, and ≈ 9 cm2/Vs for Ni2Si, NiSi (〈100〉 and 〈111〉), and NiSi2, respectively. The systematic error in the measured values caused by currents in the high resistivity substrate is estimated to be less than 6% for the Hall coefficient. The results show that Ni2Si, NiSi, and NiSi2 layers formed by a thin film reaction are electrically metallic conductors, a result which concurs with those reported previously (1) for refractory metal silicides. The Hall mobility increases with the Si content in the silicide. The electron concentration is lowest for NiSi2 leading to the highest resistivity for the epitaxial phase of NiSi2.

Graphene Magnetoresistance Device in van der Pauw Geometry

Abstract: We have fabricated extraordinary magnetoresistance (EMR) device, comprising a monolayer graphene with an embedded metallic disk, that exhibits large room temperature magnetoresistance (MR) enhancement of up to 55 000% at 9 T. Finite element simulations yield predictions in excellent agreement with the experiment and show possibility for even better performance. Simplicity, ease of implementation and high sensitivity of this device imply great potential for practical applications.