Browsing by Subject "Hall probe"

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    ItemOpen Access
    Development of nano hall sensors for high resolution scanning hall probe microscopy
    (2008-09) Dede, Münir
    Scanning Hall Probe Microscopy (SHPM) is a quantitative and non invasive method of local magnetic field measurement for magnetic and uperconducting materials with high spatial and field resolution. Since its demonstration in 1992, it is used widely among the scientific community and has already commercialized. In this thesis, fabrication, characterization and SHPM imaging of different nano-Hall sensors produced from heterostructure semiconductors and Bismuth thin films with effective physical probe sizes ranging between 50nm‐1000nm, in a wide temperature range starting from 4.2K up to 425K is presented. Quartz crystal tuning fork AFM feedback is demonstrated for the first time for SHPM over a large temperature range. Its performance has been analyzed in detail and experiments carried with 1×1μm Hall probes has been successfully shown for a hard disk sample in the temperature range of 4.2K to 425K. Other samples, NdFeB demagnetized magnet, Bi substituted iron garnet and, single crystal BSCCO(2212) High Temperature superconductor were also imaged with this method to show the applicability of the method over a wide range of specimens. By this method, complex production steps proposed in the literature to inspect the non‐conductive samples were avoided. A novel Scanning Hall probe gradiometer has also been developed and a new method to image x, y & z components of the magnetic field on the sample surface has been demonstrated for the first time with 1μm resolution. 3D field distribution of a Hard Disk sample is successfully measured at 77K using this novel approach to prove the concept.
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    ItemOpen Access
    Variable temperature-scanning Hall probe microscopy with GaN/AlGaN two-dimensional electron gas (2DEG) micro Hall sensors in 4.2-425 K range using novel quartz tuning fork AFM feedback
    (IEEE, 2008) Akram, Rizwan; Dede, Münir; Oral, Ahmet
    In this paper, we present the fabrication and variable temperature (VT) operation of Hall sensors, based on GaN/AlGaN heterostructure with a two-dimensional electron gas (2DEG) as an active layer, integrated with quartz tuning fork (QTF) in atomic force-guided (AFM) scanning Hall probe microscopy (SHPM). Physical strength and a wide bandgap of GaN/AlGaN heterostructure makes it a better choice to be used for SHPM at elevated temperatures, compared to other compound semiconductors (AlGaAs/GaAs and InSb), which are unstable due to their narrower bandgap and physical degradation at high temperatures. GaN/AlGaN micro Hall probes were produced using optical lithography and reactive ion etching. The active area, Hall coefficient, carrier concentration, and series resistance of the Hall sensors were ∼1 × 1 μm, 10 mΩ/G at 4.2 K, 6.3 × 10 12 cm -2 and 12 kΩ at room temperature and 7 mΩ/G, 8.9 × 10 12 cm -2 and 24 kΩ at 400 K, respectively. A novel method of AFM feedback using QTF has been adopted. This method provides an advantage over scanning tunneling-guided feedback, which limits the operation of SHPM the conductive samples and failure of feedback due to high leakage currents at high temperatures. Simultaneous scans of magnetic and topographic data at various pressures (from atmospheric pressure to high vacuum) from 4. to 425K will be presented for different samples to illustrate the capability of GaN/AlGaN Hall sensors in VT-SHPM.