Browsing by Author "Chuu, Der-San"

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Atomistic modeling of dislocation activity in nanoindented GaAs
(2006-11-15)
Jian, Sheng-Rui
;
Fang, Te-Hua
;
Chuu, Der-San
;
Ji, Liang-Wen
;
電子物理學系
The mechanical behavior of GaAs was investigated by nanoindentation with the aid of molecular dynamics (MD) analysis based on the Tersoff potential. Particular attention was devoted to the evolution characterization of dislocation activity during deformation. The transition from elastic-to-plastic deformation behavior was clearly observed as a sudden displacement excursion occurring during the load-displacement curves of larger loads (single pop-in), faster impact velocity and higher temperature (multiple pop-ins). Even for an ultra-small penetration depth (< 3 nm), the MD simulation shows that GaAs deforms plastically and a good description is given in the results. The plastic deformation occurs due to the anticipated change in the twinning and/or dislocation motion. Dislocation nucleations occurred inside the material near the top of the surface and generated loops in the {111} slip planes. The MD analysis of the deformation behavior shows an agreement with that of previous atomic force microscopy (AFM) and transmission electron microscopy (TEM) experiments. (c) 2006 Elsevier B.V. All rights reserved.
Bias-dependent bandwidth of the conductance in the presence of electron-phonon interaction
(2010-04-01)
Tang, Ying-Tsan
;
Lin, Kao-Chin
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
We study the electronic transport in the presence of electron-phonon interaction (EPI) for a molecular electronic device. Instead of mean field approximation (MFA), the related phonon correlation function is conducted with the Langreth theorem (LT). We present formal expressions for the bandwidth of the electron's spectral function in the central region of the devices, such as quantum dot (QD), or single molecular transistor (SMT). Our results show that the out-tunneling rate depends on the energy, bias voltage and the phonon field. Besides, the predicted conductance map, behaving as a function of bias voltage and the gate voltage, gets blurred at the high bias voltage region. These EPI effects are consistent with the experimental observations in the EPI transport experiment. (C) 2010 Elsevier Ltd. All rights reserved.
Current induced entanglement of double quantum dot excitons
(2003)
Chen, Yueh-Nan
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
We propose to measure Purcell effect by observing the current through a semeiconductor quantum dot embedded inside a microcavity. The stationary current is shown to be altered if one varies the cavity length. For the double-dot system, we find that the stationary current shows oscillatory behavior as one varies the inter-dot distance. Furthermore, the current is suppressed if the dot distance is small compared to the wavelength of the emitted photon. This photon trapping phenomenon generates the entangled state and may be used to control the emission of single photons at predetermined times.
Effects of a Modulated Electric Field on the Optical Absorption Spectra in a Single-Layer Graphene
(2009-11-01)
Chiu, Yu-Huang
;
Ho, Jon-Hsu
;
Ho, Yen-Hung
;
Chuu, Der-San
;
Lin, Ming-Fa
The optical absorption spectra of a graphene monolayer in the presence of a modulated electric field are investigated by the gradient approximation with tight-binding model. Such a field could strongly affect the low-energy electronic and optical properties. The low-energy bands exhibit two kinds of band-edge states (mu and nu), which lead to many prominent asymmetric peaks in the density of states (DOS). The finite DOS at omega = 0 implies that a single layer graphene in the presence of modulated electric fields would become a semimetallic one. The low-frequency optical absorption spectra display rich peaks and they vanish at omega = 0. Such absorption peaks mainly result from the two kinds of band-edge states and could be divided into two groups. However, they could not be ascribed to an obvious selection rule. It is worth noting that the optical absorption spectra could show anisotropic features in different modulated directions. The predicted results could be verified by the experimental measurements.
Electron-photon interaction associated with uncertainty-based tunneling in a parallel double quantum dot
(2008-03-01)
Lin, Kao-Chin
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
The electron-photon interaction associated with the uncertainty based tunneling (EPAUT) in the parallel double quantum dot system is studied. In the considered system, the electron interacts with the single mode detuning quantum photon field, i.e., omega(ph)+Delta=epsilon(2)-epsilon(1), and transits between the quantum dots (QDs). The corresponding characteristic temperature is calculated and compared with the Kondo temperature to recognize the role of the related quantities. There are two energy uncertainties in the considered system. One is the energy difference between the energy of electron-photon interacting quasiparticle and the Fermi energy of the lead. The other is the detuning factor Delta. Besides, vertical bar Delta/pi vertical bar is the bandwidth of the intermediate state of EPAUT. The peak of the density of state corresponding to the EPAUT rises when the temperature is in the order of or below the characteristic temperature. The EPAUT peak can be modified via tuning the Fermi energy of the lead connected to the adjoined QD. Hence, the conductance between the connected leads is varied via tuning the Fermi energy of the lead connected to the adjoined QD.
Entanglement detection via the condition of quantum correlation
(2007-09-01)
Li, Che-Ming
;
Hsu, Li-Yi
;
Chen, Yueh-Nan
;
Chuu, Der-San
;
Brandes, Tobias
We develop a necessary condition of quantum correlation. It is utilized to construct a d-level bipartite Bell-type inequality which is strongly resistant to noise and requires only analyses of O(d) measurement outcomes compared to the previous result O(d(2)). Remarkably, a connection between the arbitrary high-dimensional bipartite Bell-type inequality and entanglement witnesses is found. Through the necessary condition of quantum correlation, we propose that the witness operators to detect truly multipartite entanglement for a generalized Greenberger-Horne-Zeilinger (GHZ) state with two local measurement settings and a four-qubit singlet state with three settings. Moreover, we also propose a robust entanglement witness to detect a four-level tripartite GHZ state with only two local measurement settings.
Influence of phonon-associated tunneling rate on transport through a single-molecule transistor
(2011-01-01)
Tang, Ying-Tsan
;
Chuu, Der-San
;
Lin, Kao-Chin
;
電子物理學系
;
Department of Electrophysics
We study the electronic transport through a single-molecule transistor (SMT) by considering the phonon-associated tunneling rate We find that the electron-phonon interaction (EPI) changes the constant conductivities of the leads into a multi-channel structure of single vibration frequency This interference of the multi-channel tunneling process results in a bias-dependent tunneling rate and obscures the conductance peaks at large bias voltage The bias-dependent tunneling rate further causes a remarkable conductivity gap between the chemical potential of the leads (n = 0) and the first phonon sideband (n = 1) These anomalies are consistent with the experimental observations in transport experiments (C) 2010 Elsevier Ltd All rights reserved
Localized electrochemical oxidation of p-GaAs(100) using atomic force microscopy with a carbon nanotube probe
(2006-08-14)
Huang, Wu-Ping
;
Cheng, Hung-Hsiang
;
Jian, Sheng-Rui
;
Chuu, Der-San
;
Hsieh, Jin-Yuan
The nanometre-scale oxidation characteristics of a p-GaAs(100) surface are investigated by atomic force microscope (AFM) electrochemical nanolithography with a multiwalled carbon nanotube (MWCNT) probe. The electrochemical parameters, such as anodizing voltages, scanning rate and modulated voltages, and how they affect the creation and growth of the oxide nanostructures are explored. The present results reveal that the initial growth rate (similar to 600 nm s(-1) for 10 V) decreases rapidly as the electric field strength is decreased. The oxide practically ceases to grow as the electric field is reduced to the order of similar to 1.2 x 10(7) V cm(-1). Also, the oxide growth rate depends not only on the electric field strength but also on the applied anodizing voltage. The present results show that the height of the oxide structures can be significantly improved at an applied anodizing voltage of 10 V by using a CNT probe. In addition, Auger electron spectroscopy (AES) measurements performed in the present work confirm that modified structures replace the form of anodizing p-GaAs(100).
Observation of localized surface plasmons in spatially controlled array structures
(2009-07-29)
Chou, J. W.
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Lin, Kao-Chin
;
Lee, Yao-Jen
;
Yuan, Chi-Tsu
;
Hsueh, Fu-Kuo
We observed the reflectance spectra of three different nano-scale array structures of Au-coated silicon nanorods. The trends of the reflectance spectra indicate that the localized surface plasmon modes can be spatially controlled by manipulating geometric parameters, namely the lattice constants of the array. In addition, the experimental results were compared with 2D numerical simulations based on the finite element method. Satisfactory agreement between the experimental observations and numerical results was obtained.
On a family of quantum search algorithms robust against phase imperfections
(2007-12-01)
Li, Che-Ming
;
Hsieh, Jin-Yuan
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
A family of algorithms has been recently considered for sure-success quantum search problems. When the phase inversion operations of these algorithms are identical to those of the standard Grover algorithm, it is found that this family of algorithms is robust against the inevitable phase imperfections.
QUANTUM SECRET ENCRYPTION AND DECRYPTION IN CAVITY QED
(2009-04-01)
Li, Che-Ming
;
Hsu, Li-Yi
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
We present a proposal of the quantum secret encryption, transmission, and decryption implementation for quantum secret-sharing protocol using cavity QED. In the proposed scheme, the information is stored in two identical two-level atoms, and the two-qubit logic transformation is realized through the interaction between atoms and a nonresonant cavity mode. The proposed scheme requires no ancilla states to assist the intermediate atomic transitions and conditional quantum dynamics for quantum phase flip and quantum state diffusion. The encryption and decryption of quantum states are mostly governed by the Hamiltonian of an atom-cavity system. Moreover, secret transmission using quasi-swap gates for entanglement swapping has also been presented. With fewer supplements of external fields, a speed quantum protocol can be realized without universal gates.
Raman spectroscopy study of Zn1-xMnxSe thin films under high-pressure
(2007-05-15)
Lin, Chih-Ming
;
Chuu, Der-San
;
電子物理學系
;
Department of Electrophysics
Raman spectroscopy was used to study phase transitions of substrate-free Zn1-xMnxSe thin films, x=0.07, 0.17, and 0.29, under high pressure up around 20.0 GPa at ambient temperature. One Raman mode, transverse optical split mode, was observed before metallization at 2.9 +/- 1.0, 2.4 +/- 0.8, and 2.1 +/- 0.6 GPa for Zn0.71Mn0.29Se, Zn0.83Mn0.17Se, and Zn0.93Mn0.07Se thin films, respectively. The semiconductor-metallic transition pressure for Zn0.71Mn0.29Se, Zn0.83Mn0.17Se, and Zn0.93Mn0.07Se thin films was observed at 9.4 +/- 0.4, 10.9 +/- 0.6, and 11.7 +/- 0.2 GPa, respectively. It was found that the relation of the ionicity and the reduction of the pressure in transition from semiconductor to metal phase for Zn1-xMnxSe thin films was not the same as that of bulk crystals. The percentage of the increasing of the Gruneison parameter of longitudinal optical mode for semiconductor to metal phase transition might be the important factor inherently related to the reduction of phase transition pressure for substrate-free Zn1-xMnxSe thin film systems. (c) 2007 American Institute of Physics.