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You searched for +publisher:"Brown University" +contributor:("Xiao, Gang"). Showing records 1 – 3 of 3 total matches.

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1. Zou, Xiaojing. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.

Degree: PhD, Physics, 2009, Brown University

We have fabricated and investigated the electrical and magnetic behavior of polycrystalline and epitaxial CrO2 nanostructures, grown using selective-area growth technique. Magnetic domain structures were studied by magnetic force microscopy, and in-plane, lamellar domain structure with fragmented walls aligned along the magnetic easy axis direction have been observed, indicating a large magnetocrystalline anisotropy in epitaxial CrO2 nanostructures. Low-temperature transport measurements on nanowires have shown that the dc resistivity of polycrystalline CrO2 wires is strongly dependent on the linewidth. Below a critical temperature, a transition from a positive to a negative temperature coefficient of resistivity have been observed, which we attribute to a competition between the scattering of the conduction electrons inside the grains and scattering across the grain boundaries. Using a model based on grain boundary scattering, we estimate a mean transmission probability through the grain boundaries to be on the order of 10?1. Furthermore, magnetoresistance (MR) measurement indicates that the MR behavior of polycrystalline wires is dominated by the shape anisotropy; however, for epitaxial wires, both the shape and magnetocrystalline anisotropy play important roles, and the resulting MR properties are found to be closely related to the orientation of the wire axis. By studying the MR curves, we inferred the internal domain structures in various single crystal CrO2 wires and found that the spin-dependent transport is much stronger across a grain boundary than a domain wall. We have also studied the magnetotransport properties of CrO2 nanocontacts. Manipulating the domain walls using a large dc current in the contact area yields a magnetoresistance of up to 25%, which is the largest ever seen in a single ferromagnetic film. The single domain-wall-resistance is determined to be three orders of magnitude larger than that of conventional 3d ferromagnets, as a result of the material's half-metallicity. We have measured DWR and the spin-torque effect along different crystallographic axes and at varying temperatures. Finally, we present the results of a theoretical analysis of this system, based on its half-metallic character and on the intrinsic magnetic behavior of CrO2. Advisors/Committee Members: Xiao, Gang (director), Sun, Shouheng (reader), Mitrovic, Vesna (reader).

Subjects/Keywords: Chromium Dioxide

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APA (6th Edition):

Zou, X. (2009). Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:233/

Chicago Manual of Style (16th Edition):

Zou, Xiaojing. “Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.” 2009. Doctoral Dissertation, Brown University. Accessed January 20, 2021. https://repository.library.brown.edu/studio/item/bdr:233/.

MLA Handbook (7th Edition):

Zou, Xiaojing. “Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures.” 2009. Web. 20 Jan 2021.

Vancouver:

Zou X. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. [Internet] [Doctoral dissertation]. Brown University; 2009. [cited 2021 Jan 20]. Available from: https://repository.library.brown.edu/studio/item/bdr:233/.

Council of Science Editors:

Zou X. Magnetic Domain Configurations and Huge Wall Resistivity in Half-metallic Chromium Dioxide (CrO2) Nanostructures. [Doctoral Dissertation]. Brown University; 2009. Available from: https://repository.library.brown.edu/studio/item/bdr:233/

2. Zhang, Peng. Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive.

Degree: Physics, 2017, Brown University

Nanowire (NW) research has emerged as a quickly growing field, mainly due to its unique electronic and optical properties. This thesis focused on utilizing Si NW arrays for solar cells and SiGe hetero-NWs for tunneling field-effect transistors (TFETs) and negative transconductance (NTC) devices. A SiGe CMOS-compatible bipolar-enhanced TFET (BET-FET) device aiming to improve the TFETs ON current was also studied. We characterized the performance of solar cells made from axial p-i- n Si NW arrays with diameter < 200 nm that were grown by vapor-liquid- solid method. Both sparse arrays and dense arrays by nanoimprint lithography were studied. The improved light absorption in NW array solar cells was verified by reflectance measurements. The improvements on photovoltaic performance for passivated samples were explained by reduced surface recombination. Higher EQE and IQE in the visible spectral range were obtained for samples with higher NW density of different NW lengths, due to improved absorption. Axial p-Ge/i- Si/n-Si hetero-NW TFETs were also fabricated and characterized. The hetero-NWs were realized using VLS method with better abruptness of axial modulation of doping and composition. The tri-gated devices showed good performance with ON current of up to 2 μA/μm and best sub threshold swing (SS) of 55 mV/decade over 3 orders of drain current. NTC behavior with highest current peak-to-valley ratio of 47.9 at reverse bias voltage of -0.2 V was observed for the same device. We explain it by the gate-induced depletion in the p-Ge section that eventually reduces the maximum electric field, which was confirmed by a 3D Sentaurus TCAD simulation. Finally, stemming from improvement of ON current in the Si/Ge hetero-NW platform, we proposed and simulated a BET-FET device with a lateral layout that is fully FDSOI compatible. The simulated device combined the sharp-switching character of the TFET and high current gain of the heterojunction bipolar transistor, and enjoyed a high ON current of 260 μA/μm and a SS well below 60 mV/decade over seven decades. Advisors/Committee Members: Zaslavsky, Alexander (Director), Marston, John (Reader), Xiao, Gang (Reader).

Subjects/Keywords: Nanowire; Solar cell; Tunneling; Negative Transconductance

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APA (6th Edition):

Zhang, P. (2017). Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive. (Thesis). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:730643/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Zhang, Peng. “Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive.” 2017. Thesis, Brown University. Accessed January 20, 2021. https://repository.library.brown.edu/studio/item/bdr:730643/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Zhang, Peng. “Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive.” 2017. Web. 20 Jan 2021.

Vancouver:

Zhang P. Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive. [Internet] [Thesis]. Brown University; 2017. [cited 2021 Jan 20]. Available from: https://repository.library.brown.edu/studio/item/bdr:730643/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Zhang P. Nanowire array solar cells and tunneling transistors with negative transconductance and high current drive. [Thesis]. Brown University; 2017. Available from: https://repository.library.brown.edu/studio/item/bdr:730643/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

3. Zhang, Wenzhe. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.

Degree: PhD, Physics, 2012, Brown University

We systematically studied the spin-dependent transport and electrical noise characteristics of MgO-based magnetic tunnel junctions (MTJs). Utilizing the coherent tunneling effect in the MgO tunnel barrier, we have successfully fabricated MTJ devices with large tunneling magnetoresistance (TMR) ratios. To explore the magnetization properties of these devices at a fundamental level, we first investigated the magnetization dynamics of sputtered CoFeB thin films used as the free layers in MgO-based MTJ stacks by a broad-band FMR spectrometer. Then we presented a new method for estimating the magnetic anisotropy dispersion in MTJ arrays in serial configurations, using the simulated field sensitivity maps. Based on a revised Stoner-Wohlfarth model, we were able to assign dispersion parameters to an actual MTJ array with arbitrary magnetic attributes such as TMR ratio, coercivity and hysteresis loops. As a result of our work, the field sensitivity of an MTJ array was found to be inversely correlated to its anisotropy dispersion and magnetic coercivity. In the second part, we focused on the noise properties of MTJ systems. At low frequencies, the flicker noise was measured in two distinct MTJ arrays: MTJ Wheatstone bridges and MTJ discrete resistors, each in their own serial arrays. For MTJ bridges, the statistical dispersion in device resistance and normalized voltage noise were attributed to the greater-than-expected magnetization noise, whereas magnetic coupling among tightly-packed MTJ elements was found to amplify the magnetic fluctuations in the MTJ discrete resistors. Finally, high frequency shot noise measurements were carried out to study the spin-dependent charge transport in MTJ systems. The normalized shot noise, or Fano factor, exhibited a sinusoidal-like variation with a continuous change in the relative orientation between the magnetization vectors of MTJ free and reference layers. We explained the noise behavior with a model of sequential tunneling in the spin-blockade regime, in which the faster transport of majority spin electrons in tunnel barriers is modulated by the slower tunneling of minority spin electrons. Advisors/Committee Members: Xiao, Gang (Director), Mitrovic, Vesna (Reader), Dell'Antonio, Ian (Reader).

Subjects/Keywords: magnetic tunnel junctions

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Zhang, W. (2012). Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. (Doctoral Dissertation). Brown University. Retrieved from https://repository.library.brown.edu/studio/item/bdr:297711/

Chicago Manual of Style (16th Edition):

Zhang, Wenzhe. “Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.” 2012. Doctoral Dissertation, Brown University. Accessed January 20, 2021. https://repository.library.brown.edu/studio/item/bdr:297711/.

MLA Handbook (7th Edition):

Zhang, Wenzhe. “Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions.” 2012. Web. 20 Jan 2021.

Vancouver:

Zhang W. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. [Internet] [Doctoral dissertation]. Brown University; 2012. [cited 2021 Jan 20]. Available from: https://repository.library.brown.edu/studio/item/bdr:297711/.

Council of Science Editors:

Zhang W. Noise and Spin-dependent Transport in MgO-based Magnetic Tunnel Junctions. [Doctoral Dissertation]. Brown University; 2012. Available from: https://repository.library.brown.edu/studio/item/bdr:297711/

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