1,975 research outputs found
Effect of Phonon Scattering on Intrinsic Delay and Cut-Off Frequency of Carbon Nanotube FETs
The effect of phonon scattering on the intrinsic delay and cut-off frequency
of Schottky barrier carbon nanotube (CNT) FETs is examined by self-consistently
solving the Poisson equation and the Schrodinger equation using the
non-equilibrium Greens function (NEGF) formalism. Carriers are mostly scattered
by optical and zone boundary phonons beyond the beginning of the channel. We
show that the scattering has a small direct effect on the DC on-current of the
CNTFET, but it results in significant pile-up of charge and degradation of
average carrier velocity. Due to charge pile-up and random walks of carriers,
the intrinsic gate capacitance and delay significantly increase, and the
intrinsic cut-off frequency decreases. The results are important for assessing
the performance potential of CNTFETs for radio-frequency (RF) electronics and
digital electronics applications.Comment: to appear in IEEE Trans. on Electron Devic
Gate Electrostatics and Quantum Capacitance of Graphene Nanoribbons
Capacitance-voltage (C-V) characteristics are important for understanding
fundamental electronic structures and device applications of nanomaterials. The
C-V characteristics of graphene nanoribbons (GNRs) are examined using
self-consistent atomistic simulations. The results indicate strong dependence
of the GNR C-V characteristics on the edge shape. For zigzag edge GNRs, highly
non-uniform charge distribution in the transverse direction due to edge states
lowers the gate capacitance considerably, and the self-consistent electrostatic
potential significantly alters the band structure and carrier velocity. For an
armchair edge GNR, the quantum capacitance is a factor of 2 smaller than its
corresponding zigzag carbon nanotube, and a multiple gate geometry is less
beneficial for transistor applications. Magnetic field results in pronounced
oscillations on C-V characteristics.Comment: to appear in Nano Let
Enhanced Piezoelectric Performance of Printed PZT Films on Low Temperature Substrates
Since piezoelectric effect was discovered in 1880, it has been widely used in micro-actuators, sensors, and energy harvesters. Lead Zirconate Titanate (PZT) is a commonly used piezoelectric material due to the high piezoelectric response. The basic PZT film fabrication process includes deposition, sintering, and poling. However, due to the high sintering temperature (\u3e 800 °C) of PZT, only high melting point material can be served as the substrate. Otherwise, complex film transfer approach is needed to achieve flexible and foldable PZT devices. The exploration is accordingly necessary to realize direct fabrication of PZT films on low melting point substrates without affecting the piezoelectric performance. In order to lower the PZT film sintering temperature, in this work, the effect of the powder size and sintering aid on the sintering temperature was studied. A maskless, CAD driven, non-contact direct printing system, aerosol jet printer, was used to deposit PZT thick films on the substrate. This technique allows creating features without masking and etching processes that are generally required for realizing designed features via conventional deposition approaches. Broadband, sub-millisecond, high intensity flash pulses were used to sinter the PZT films. The role of all sintering parameters was investigated to regulate the sintering quality of the PZT thick films. The photonically sintered films showed much lower substrate temperature increase mainly due to the extremely short pulse duration and temperature gradient through the film thickness. The superior piezoelectric property to thermally sintered group was also obtained. This process significantly shortens the processing duration and dramatically expands the possible substrate materials. It accordingly opens the possibility of processing PZT film directly on low melting point materials. A PZT energy harvester based on this process was directly fabricated on the polyethylene terephthalate (PET) substrate to demonstrate the capability. The relation between the load and the generated power was investigated to obtain the highest output power. Up to 0.1 μW was generated from this flexible energy harvester when connected with 10 MΩ resistive load. Photonic sintering of PZT film also creates the opportunity of processing poling during sintering. Different combinations of the sintering and poling techniques were studied. It was observed that the best piezoelectric property was obtained while performing poling during photonic sintering. Consequently, a new method of printing, sintering, and poling of micro-scaled PZT films was demonstrated in this work resulting in high performance films. This process provides the capability of realizing PZT devices on low temperature substrate, facilitates the fabrication of flexible piezoelectric devices, and enhances the piezoelectric property
Switchable polarization manipulation, optical logical gates and conveyor belt based on U-shaped \ce{VO2} nanoholes
Based on U-shaped plasmonic nanoholes in an \ce{Au-VO2-Au} film, we propose
to achieve several switchable functions at the telecom wavelength by transition
from the \ce{VO2} semiconductive state to the metallic state. The first is
the polarization manipulation of four different polarization states
(-polarization, LCP, and RCP). An array of U-shaped holes constitutes of
the high efficiency SPP splitter, and thus the spin-encoded optical logical
gates can be achieved. Furthurmore, we prove that a nano-optical conveyor belt
can be build up with such U-shaped holes, making the transport of nanoparticles
over the film efficiency by transforming between two spin states periodically,
and the transport direction switchably along with the \ce{VO2} phase
High-dimensional Inference for Generalized Linear Models with Hidden Confounding
Statistical inferences for high-dimensional regression models have been
extensively studied for their wide applications ranging from genomics,
neuroscience, to economics. In practice, there are often potential unmeasured
confounders associated with both the response and covariates, leading to the
invalidity of the standard debiasing methods. This paper focuses on a
generalized linear regression framework with hidden confounding and proposes a
debiasing approach to address this high-dimensional problem by adjusting for
effects induced by the unmeasured confounders. We establish consistency and
asymptotic normality for the proposed debiased estimator. The finite sample
performance of the proposed method is demonstrated via extensive numerical
studies and an application to a genetic dataset
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