16 results on '"Ping Han"'
Search Results
2. Analysis of local bond-orientational order for liquid gallium at ambient pressure: Two types of cluster structures.
- Author
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Lin-Yuan Chen, Ping-Han Tang, and Ten-Ming Wu
- Subjects
- *
MICROCLUSTERS , *CHEMICAL bonds , *CRYSTAL structure , *GALLIUM , *PRESSURE , *MOLECULAR dynamics - Abstract
In terms of the local bond-orientational order (LBOO) parameters, a cluster approach to analyze local structures of simple liquids was developed. In this approach, a cluster is defined as a combination of neighboring seeds having at least nb local-orientational bonds and their nearest neighbors, and a cluster ensemble is a collection of clusters with a specified nb and number of seeds ns. This cluster analysis was applied to investigate the microscopic structures of liquid Ga at ambient pressure (AP). The liquid structures studied were generated through ab initio molecular dynamics simulations. By scrutinizing the static structure factors (SSFs) of cluster ensembles with different combinations of nb and ns, we found that liquid Ga at AP contained two types of cluster structures, one characterized by sixfold orientational symmetry and the other showing fourfold orientational symmetry. The SSFs of cluster structures with sixfold orientational symmetry were akin to the SSF of a hard-sphere fluid. On the contrary, the SSFs of cluster structures showing fourfold orientational symmetry behaved similarly as the anomalous SSF of liquid Ga at AP, which is well known for exhibiting a high-q shoulder. The local structures of a highly LBOO cluster whose SSF displayed a high-q shoulder were found to be more similar to the structure of β-Ga than those of other solid phases of Ga. More generally, the cluster structures showing fourfold orientational symmetry have an inclination to resemble more to β-Ga. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
3. Local structural effects on orientational relaxation of OH-bond in liquid water over short to intermediate timescales.
- Author
-
Lin, S. R., Ping-Han Tang, and Ten-Ming Wu
- Subjects
- *
CHEMICAL relaxation , *CHEMICAL bonds , *WATER , *CHEMICAL structure , *INTERMEDIATES (Chemistry) , *DENSITY of states , *ORIENTATION (Chemistry) - Abstract
By simulating the rigid simple point charge extended model at temperature T = 300 K, the orientational relaxation of the OH-bond in water was investigated over short to intermediate timescales, within which molecules undergo inertial rotation and libration and then enter the rotational diffusion regime. According to the second-cumulant approximation, the orientational time correlation function (TCF) of each axis that is parallel or perpendicular to an OH-bond is related to an effective rotational density of states (DOS), which is determined using the power spectra of angular velocity autocorrelation functions (AVAFs) of the other two axes. In addition, the AVAF power spectrum of an axis was approximated as the rotational stable instantaneous normal mode (INM) spectrum of the axis. As described in a previous study [S. L. Chang, T. M. Wu, and C. Y. Mou, J. Chem. Phys. 121, 3605 (2004)], simulated molecules were classified into subensembles, according to either the local structures or the H-bond configurations of the molecules. For global molecules and the classified subensembles, the simulation results for the first- and second-rank orientational TCFs were compared with the second-cumulant predictions obtained using the effective rotational DOSs and the rotational stable- INM spectra. On short timescales, the OH-bond in water behaves similar to an inertial rotor and its anisotropy is lower than that of a water molecule. For molecules with three or more H-bonds, the OH-bond orientational TCFs are characterized by a recurrence, which is an indication for libration of the OH-bond. The recurrence can generally be described by the second-cumulant prediction obtained using the rotational stable-INM spectra; however, the orientational TCFs after the recurrence switch to a behavior similar to that predicted using the AVAF power spectra. By contrast, the OH-bond orientational TCFs of molecules initially connected with one or two H-bonds decay monotonically or exhibit a weak recurrence, indicating rapid relaxation into the rotational diffusion regime after the initial Gaussian decay. In addition to accurately describing the Gaussian decay, the second-cumulant predictions formulated using the rotational stable-INM spectra and the AVAF power spectra serve as the upper and lower limits, respectively, for the OH-bond orientational TCFs of these molecules after the Gaussian decay. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
4. Instantaneous normal mode analysis for intermolecular and intramolecular vibrations of water from atomic point of view.
- Author
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Chen, Yu-Chun, Tang, Ping-Han, and Wu, Ten-Ming
- Subjects
- *
MOLECULAR structure of water , *MECHANICAL vibration research , *INTERMOLECULAR forces , *INTRAMOLECULAR forces , *ATOMIC theory , *CHEMICAL bonds - Abstract
By exploiting the instantaneous normal mode (INM) analysis for models of flexible molecules, we investigate intermolecular and intramolecular vibrations of water from the atomic point of view. With two flexible SPC/E models, our investigations include three aspects about their INM spectra, which are separated into the unstable, intermolecular, bending, and stretching bands. First, the O- and H-atom contributions in the four INM bands are calculated and their stable INM spectra are compared with the power spectra of the atomic velocity autocorrelation functions. The unstable and intermolecular bands of the flexible models are also compared with those of the SPC/E model of rigid molecules. Second, we formulate the inverse participation ratio (IPR) of the INMs, respectively, for the O- and H-atom and molecule. With the IPRs, the numbers of the three species participated in the INMs are estimated so that the localization characters of the INMs in each band are studied. Further, by the ratio of the IPR of the H atom to that of the O atom, we explore the number of involved OH bond per molecule participated in the INMs. Third, by classifying simulated molecules into subensembles according to the geometry of their local environments or their H-bond configurations, we examine the local-structure effects on the bending and stretching INM bands. All of our results are verified to be insensible to the definition of H-bond. Our conclusions about the intermolecular and intramolecular vibrations in water are given. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
5. Melting behavior of Ag14 cluster: An order parameter by instantaneous normal modes.
- Author
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Tang, Ping-Han, Wu, Ten-Ming, Hsu, P. J., and Lai, S. K.
- Subjects
- *
SILVER clusters , *MOLECULAR dynamics , *FUSION (Phase transformation) , *TEMPERATURE effect , *EIGENVECTORS , *ROTATIONAL motion - Abstract
This paper studies the melting behavior of Ag14 cluster employing the instantaneous normal mode (INM) analysis that was previously developed for bimetallic cluster Ag17Cu2. The isothermal Brownian-type molecular dynamics simulation is used to generate atom configurations of Ag14 at different temperatures up to 1500 K. At each temperature, these atomic configurations are then analyzed by the INM technique. To delve into the melting behavior of Ag14 cluster which differs from Ag17Cu2 by the occurrence of an anomalous prepeak in the specific heat curve in addition to the typical principal peak, we appeal to examining the order parameter τ(T) defined in the context of the INM method. Two general approaches are proposed to calculate τ(T). In one, τ(T) is defined in terms of the INM vibrational density of states; in another, τ(T) is defined considering the cluster as a rigid body with its rotational motions described by three orthogonal eigenvectors. Our results for Ag14 by these two methods indicate the mutual agreement of τ(T) calculated and also the consistent interpretation of the melting behavior with the specific heat data. The order parameter τ(T) provides in addition an insightful interpretation between the melting of clusters and the concept of broken symmetry which has been found successful in studies of the melting transition of bulk systems. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
6. Comparative study of cluster Ag17Cu2 by instantaneous normal mode analysis and by isothermal Brownian-type molecular dynamics simulation.
- Author
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Tang, Ping-Han, Wu, Ten-Ming, Yen, Tsung-Wen, Lai, S. K., and Hsu, P. J.
- Subjects
- *
MOLECULAR dynamics , *SILVER compounds , *CLUSTER analysis (Statistics) , *WIENER processes , *TEMPERATURE effect , *SPECIFIC heat , *SIMULATION methods & models , *OPERATOR theory - Abstract
We perform isothermal Brownian-type molecular dynamics simulations to obtain the velocity autocorrelation function and its time Fourier-transformed power spectral density for the metallic cluster Ag17Cu2. The temperature dependences of these dynamical quantities from T = 0 to 1500 K were examined and across this temperature range the cluster melting temperature Tm, which we define to be the principal maximum position of the specific heat is determined. The instantaneous normal mode analysis is then used to dissect the cluster dynamics by calculating the vibrational instantaneous normal mode density of states and hence its frequency integrated value Ij which is an ensemble average of all vibrational projection operators for the jth atom in the cluster. In addition to comparing the results with simulation data, we look more closely at the entities Ij of all atoms using the point group symmetry and diagnose their temperature variations. We find that Ij exhibit features that may be used to deduce Tm, which turns out to agree very well with those inferred from the power spectral density and specific heat. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
7. Mechanical Problem in 3D Printed Ankle-Foot Orthoses with Function of Energy Storage.
- Author
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Chien-Hsien Yeh, Yi-Chun Tsai, Fong-Chin Su, Li-Chieh Kuo, Kai Chang, and Ping-Han Chuang
- Subjects
STROKE patients ,ENERGY storage ,ORTHOPEDIC apparatus ,NYLON ,DORSIFLEXION - Abstract
Ankle-foot orthoses (AFO) were well-used for stroke patients. Our study developed a new 3D printed AFO with the function of Energy Storage. It would be expected to improve the gait of the stroke patients. This study made a 3D printed joint part fixed between the foot plate and shank structure of AFO. The joint part was made of Nylon and inserted a steel plate to increase the strength against the inversion motion of foot. The potential energy from the dorsiflexion of ankle could be saved in the joint part and released in the pre-swing phase of the gait cycle to help walking. Due to the local health insurance policy patients can replace a new AFO every three months. The life of 3D printed AFO which was used in the condition of 2000 steps one day should last at least 3 months. Therefore this study tested the life of 3D printed AFO using the material test machine. The reciprocating motion of 3D printed AFO was limited in the range of 3 degree of plantarflexion and 10 degree of dorsiflexion. The results showed the shank structure broke in the clamping site of the jig after 144000 times of bending. The broken part showed the separating direction was not in the depositing direction of 3D printing path. It means the printing pattern of every layer is also a key issue for the strength of 3D printed object. In the future, this study will check the strength of 3D printed samples with different printing patterns and redesign the shank structure for the better life. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
8. Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of γ-LiAlO2.
- Author
-
Jun Zou, Shengming Zhou, Jun Xu, Lianhan Zhang, Zili Xie, Ping Han, and Rong Zhang
- Subjects
CRYSTAL growth ,CRYSTALLIZATION ,SEPARATION (Technology) ,CRYSTALS ,RAMAN effect ,LIGHT scattering - Abstract
γ-LiAlO
2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 °C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190–1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398×10-6 /°C to 16.5240×10-6 /°C, and that for c axis drops from 10.7664×10-6 /°C to 10.0786×10-6 /°C. [ABSTRACT FROM AUTHOR]- Published
- 2005
- Full Text
- View/download PDF
9. Optical Properties of Jet-Vapor-Deposited TiAlO and HfAlO Determined by Vacuum Utraviolet Spectroscopic Ellipsometry.
- Author
-
Nguyen, N.V., Jin-Ping Han, Jin Yong Kim, N.V., Wilcox, Eva, Yong Jai Cho, Eva, Wenjuan Zhu, Zhijiong Luo, and Ma, T.P.
- Subjects
- *
OXIDES , *TITANIUM compounds , *HAFNIUM compounds , *ELLIPSOMETRY , *ULTRAVIOLET spectroscopy - Abstract
In this report we use vacuum ultraviolet spectroscopic ellipsometry (VUV-SE) to determine the optical as well as structural properties of high-k metal oxides, in particular, of hafnium aluminates and titanium aluminates grown by jet-vapor deposition. In our opinion, the adapted approach employed in this study can be applied in most other high-k dielectric thin films which are of great interest in developing a new material replacement for the SiO2 gate dielectric in CMOS and other IC devices. Specifically, VUV spectroscopic ellipsometry measurements were performed on a commercial ellipsometer with spectral range from 1.0 eV (1240 nm) to 8.7 eV (143 nm). The Generalized Tauc-Lorentz (GTL) dispersion was used to determine the dielectric functions of these films. An ellipsometric model consisting of two layers of different film densities was found to be in excellent agreement with the experimental data. For the TiAlO films, only one film was needed in the model to fit the data. The optical bandgaps are seen to increase, while the relative film densities decrease, with increasing Al in the films. In addition, the optical dielectric functions shift to higher energy and decrease in magnitude as the films become more insulating. As a result, the Al appears to be mixed at the atomic level instead of forming a phase separation between HfO2 and Al2O3. For TiAlO, we observed similar results except that the fundamental optical bandgap was not strongly affected by the amount of Al incorporated in the films. In our opinion, the adapted approach employed in this study can be applied in most other high-k dielectric thin films which are of great interest in developing a new material replacement for SiO2 in CMOS and other IC devices. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
10. 2.6 μm MBE grown InGaAs detectors with dark current of SRH and TAT.
- Author
-
Xiaoli Ji, Baiqing Liu, Hengjing Tang, Xuelin Yang, Xue Li, HaiMei Gong, Bo Shen, Ping Han, and Feng Yan
- Subjects
PHOTODETECTORS ,MOLECULAR beam epitaxy ,DARK currents (Electric) ,SPECTRUM analysis ,PHOTOELECTRIC devices ,QUANTUM tunneling - Abstract
We fabricate 2.6 μm InGaAs photodetectors by MBE technology and study its dark current mechanisms. Deep-level transient spectroscopy (DLTS) demonstrates a deep-level trap located at E
c - 0.25 eV in the absorption layer. Using the trap parameters, a dark current model is constructed and the device simulation generates the dark current characteristic which agrees well with the experimental data. The model suggests that the dark current at low reverse voltage is dominated by the Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT). Furthermore, it predicts some basic rules for suppressing the dark current in 2.6 μm InGaAs detectors. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
11. Ge-dot/Si multilayered structures through Ni-induced lateral crystallization.
- Author
-
Bo Yan, Yi Shi, Lin Pu, Jianmin Zhu, Kuangji Zhang, Guobin Ma, Ping Han, Rong Zhang, and Youdou Zheng
- Subjects
NICKEL films ,MULTILAYERED thin films ,CRYSTALLIZATION ,GERMANIUM ,INTERFACES (Physical sciences) ,RAMAN spectroscopy - Abstract
We demonstrate a method for fabricating high-quality Ge-dot/Si multilayered structures. High-density self-assembled Ge dots are grown on amorphous Si layer periodically by low-pressure chemical vapor deposition, and then the amorphous Si are crystallized through Ni-based metal-induced lateral crystallization. Optical microscopy, micro-Raman spectroscopy, and electron microscopy observations reveal that the crystallized Si film has large leaflike grains elongated along the lateral crystallization direction, which shows (110) preference. Furthermore, this preference is found to deliver to different Si layers. The strain shift of Ge dots deduced from Raman spectroscopy reveals a formation of a high-quality interface between the crystallized Si and Ge dot. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
12. Influence of buffer layer thickness on memory effects of SrBi2Ta2O9/SiN/Si structures.
- Author
-
Jin-Ping Han, Sang-Mo Koo, Richter, Curt A., and Vogel, Eric M.
- Subjects
- *
THIN films , *SOLID state electronics , *SILICON nitride , *NITRIDES , *SEMICONDUCTORS , *POLARIZATION (Electricity) - Abstract
We deposited SrBi2Ta2O9 (SBT) thin films on silicon–nitride (SiN) buffered Si(100) substrates to form metal–ferroelectric–insulator–semiconductor structures and observed a significant influence of the buffer layer thickness on the magnitude and direction of the capacitance–voltage (C–V) memory window. As the SiN buffer layer thickness was decreased from 6 nm to 2 nm, the C–V memory hysteresis direction changed from memory direction dominated by ferroelectric polarization (i.e., counterclockwise for n-Si) to a trapping-related hysteresis direction (i.e., clockwise for n-Si). The memory windows for both cases exhibited a similar temperature dependence. The memory window approached zero at temperatures from 340 °C to 380 °C, which corresponds to the Curie temperature (TC) of the ferroelectric SBT films. When the temperature was returned to room temperature, the hysteresis windows were recovered. A detailed study has led us to believe that the switching of polarization of the ferroelectric SBT plays a key role in the observed temperature dependence, for both the ferroelectric polarization-dominated and the trapping-dominated memory window. [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
13. Room-temperature blue luminescence of thermally oxidized Si[sub 1-x-y]Ge[sub x]C[sub y] thin...
- Author
-
Xuemel Cheng, Youdou Zheng, Xiabing Liu, Lan Zang, Zhiyun Lo, Shunming Zhu, Ping Han, and Ruolian Jiang
- Subjects
THIN films ,SILICON ,PHOTOLUMINESCENCE - Abstract
Measures at room temperature the photoluminescence spectra of the thermally oxidized Si[sub 1-x-y]Ge[sub x]C[sub y] thin films grown on silicon substrates by plasma-enhanced chemical vapor deposition. Wet oxidization of the thin films; Observation of the photoluminescence band.
- Published
- 1999
- Full Text
- View/download PDF
14. Electrode dependence of hydrogen-induced degradation in ferroelectric Pb(Zr,Ti)O[sub 3] and....
- Author
-
Jin-Ping Han and Ma, T.P.
- Subjects
- *
ELECTRODES , *THIN films , *ANNEALING of crystals - Abstract
Examines the electrode dependence of hydrogen-induced degradation in Pb(Zr,Ti)O[sub 3] and SrBi[sub 2]Ta[sub 2]O[sub 9] thin films. Basis of the model on the catalytic activities of the top electrode; Explanation of the recovery phenomenon resulting from oxygen annealing; Fabrication of samples on Pt/SiO[sub 2]/Si bottom electrodes.
- Published
- 1997
- Full Text
- View/download PDF
15. Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of γ-LiAlO2.
- Author
-
Jun Zou, Shengming Zhou, Jun Xu, Lianhan Zhang, Zili Xie, Ping Han, and Rong Zhang
- Subjects
- *
CRYSTAL growth , *CRYSTALLIZATION , *SEPARATION (Technology) , *CRYSTALS , *RAMAN effect , *LIGHT scattering - Abstract
γ-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 °C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190–1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398×10-6/°C to 16.5240×10-6/°C, and that for c axis drops from 10.7664×10-6/°C to 10.0786×10-6/°C. [ABSTRACT FROM AUTHOR]
- Published
- 2005
- Full Text
- View/download PDF
16. Analysis of local bond-orientational order for liquid gallium at ambient pressure: Two types of cluster structures.
- Author
-
Chen LY, Tang PH, and Wu TM
- Abstract
In terms of the local bond-orientational order (LBOO) parameters, a cluster approach to analyze local structures of simple liquids was developed. In this approach, a cluster is defined as a combination of neighboring seeds having at least nb local-orientational bonds and their nearest neighbors, and a cluster ensemble is a collection of clusters with a specified nb and number of seeds ns. This cluster analysis was applied to investigate the microscopic structures of liquid Ga at ambient pressure (AP). The liquid structures studied were generated through ab initio molecular dynamics simulations. By scrutinizing the static structure factors (SSFs) of cluster ensembles with different combinations of nb and ns, we found that liquid Ga at AP contained two types of cluster structures, one characterized by sixfold orientational symmetry and the other showing fourfold orientational symmetry. The SSFs of cluster structures with sixfold orientational symmetry were akin to the SSF of a hard-sphere fluid. On the contrary, the SSFs of cluster structures showing fourfold orientational symmetry behaved similarly as the anomalous SSF of liquid Ga at AP, which is well known for exhibiting a high-q shoulder. The local structures of a highly LBOO cluster whose SSF displayed a high-q shoulder were found to be more similar to the structure of β-Ga than those of other solid phases of Ga. More generally, the cluster structures showing fourfold orientational symmetry have an inclination to resemble more to β-Ga.
- Published
- 2016
- Full Text
- View/download PDF
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