You searched for +publisher:"Brown University" +contributor:("Xiao, Gang").
Showing records 1 – 3 of
3 total matches.
No search limiters apply to these results.
1.
Zou, Xiaojing.
Magnetic Domain Configurations and Huge Wall Resistivity in
Half-metallic Chromium Dioxide (CrO2) Nanostructures.
Degree: PhD, Physics, 2009, Brown University
URL: https://repository.library.brown.edu/studio/item/bdr:233/ 
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
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
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
URL: https://repository.library.brown.edu/studio/item/bdr:730643/
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
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
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
URL: https://repository.library.brown.edu/studio/item/bdr:297711/
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
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
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/
. 
Open Access Theses and Dissertations