Browsing by Author "Li, Liang-Chen"

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An Affordable Wet Chemical Route to Grow Conducting Hybrid Graphite-Diamond Nanowires: Demonstration by A Single Nanowire Device
(2017-09-11)
Shellaiah, Muthaiah
;
Chen, Tin Hao
;
Simon, Turibius
;
Li, Liang-Chen
;
Sun, Kien Wen
We report an affordable wet chemical route for the reproducible hybrid graphite-diamond nanowires (G-DNWs) growth from cysteamine functionalized diamond nanoparticles (ND-Cys) via pH induced self-assembly, which has been visualized through SEM and TEM images. Interestingly, the mechanistic aspects behind that self-assembly directed G-DNWs formation was discussed in details. Notably, above self-assembly was validated by AFM and TEM data. Further interrogations by XRD and Raman data were revealed the possible graphite sheath wrapping over DNWs. Moreover, the HR-TEM studies also verified the coexistence of less perfect sp(2) graphite layer wrapped over the sp3 diamond carbon and the impurity channels as well. Very importantly, conductivity of hybrid G-DNWs was verified via fabrication of a single G-DNW. Wherein, the better conductivity of G-DNW portion L2 was found as 2.4 +/- 1.92 x 10(-6) mS/cm and revealed its effective applicability in near future. In addition to note, temperature dependent carrier transport mechanisms and activation energy calculations were reported in details in this work. Ultimately, to demonstrate the importance of our conductivity measurements, the possible mechanism behind the electrical transport and the comparative account on electrical resistivities of carbon based materials were provided.
Anomalous optical magnetic shift of self-assembled GaSb/GaAs quantum dots
(2011-07-01)
Lin, Ta-Chun
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Li, Liang-Chen
;
Lin, Sheng-Di
;
Suen, Yuen-Wuu
;
Lee, Chien-Ping
We report the magneto-photoluminescence (PL) measurement results on type-II self-assembled GaSb/GaAs quantum dots with the magnetic field applied in Faraday and Voigt configurations. The emission of the quantum dots exhibited a typical diamagnetic blueshift when the magnetic field was applied in a Faraday configuration. However, when the magnetic field was in the Voigt configuration, an unusual redshift in the emission peak accompanied with a rapid increase of the PL intensity was observed. Guided by numerical calculations, the magnetic field applied in the Voigt configuration is found to provide an additional vertical confinement to electrons, and therefore, substantially enhance the radiative electron-hole recombination. The resulting decrease of the steady-state hole concentration gives rise to the observed anomalous magnetic redshift. (C) 2011 American Institute of Physics. [doi:10.1063/1.3607973]
Effect of Metal Ions on Hybrid Graphite-Diamond Nanowire Growth: Conductivity Measurements from a Single Nanowire Device
(2019-03-11)
Shellaiah, Muthaiah
;
Chen, Ying-Chou
;
Simon, Turibius
;
Li, Liang-Chen
;
Sun, Kien Wen
Novel Cd2+ ions mediated reproducible hybrid graphite-diamond nanowire (G-DNWs; Cd2+-NDS1 NW) growth from 4-Amino-5-phenyl-4H-1,2,4-triazole-3-thiol (S1) functionalized diamond nanoparticles (NDS1) via supramolecular assembly is reported and demonstrated through TEM and AFM images. FTIR, EDX and XPS studies reveal the supramolecular coordination between functional units of NDS1 and Cd2+ ions towards NWs growth. Investigations of XPS, XRD and Raman data show the covering of graphite sheath over DNWs. Moreover, HR-TEM studies on Cd2+-NDS1 NW confirm the coexistence of less perfect sp(2) graphite layer and sp(3) diamond carbon along with impurity channels and flatten surface morphology. Possible mechanisms behind the G-DNWs growth are proposed and clarified. Subsequently, conductivity of the as-grown G-DNWs is determined through the fabrication of a single Cd2+-NDS1 NW device, in which the G-DNW portion L2 demonstrates a better conductivity of 2.31 x 10(-4) mS/cm. In addition, we investigate the temperature-dependent carrier transport mechanisms and the corresponding activation energy in details. Finally, comparisons in electrical resistivities with other carbon-based materials are made to validate the importance of our conductivity measurements.
GaAs Polariton Interference in Magnetic Field: Oblique Incident Ellipsometry Measurement
(2014-11-15)
Su, Sheng-Kai
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Voskoboynikov, Oleksandr
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Li, Liang-Chen
;
Suen, Yuen-Wuu
;
Lee, Chien-Ping
The properties of GaAs polaritons propagating in a magnetic field have been investigated using a self-designed ellipsometry system with an oblique incident angle. Interesting fine structures, which have not been reported, have been observed and their magneto-optical behavior cannot be explained by the known properties of excitonic states. Treating the surface and the growth interface as boundaries, we attribute the fine structures to the interference among various polariton modes. A model considering the polariton spatial dispersion and exciton effective mass increase induced by its center of mass and relative motion coupling is proposed to explain the magnetic response of interference ellipsometry spectra.
High-quality planar light emitting diode formed by induced two-dimensional electron and hole gases
(2014-02-24)
Van-Truong Dai
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Lin, Sheng-Di
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Lin, Shih-Wei
;
Lee, Yi-Shan
;
Zhang, Yin-Jie
A high-quality planar two-dimensional p-i-n light emitting diode in an entirely undoped GaAs/AlGaAs quantum well has been fabricated by using conventional lithography process. With twin gate design, two-dimensional electron and hold gases can be placed closely on demand. The electroluminescence of the device exhibit high stability and clear transition peaks so it is promising for applications on electrically-driven single photon sources. (C) 2014 Optical Society of America
Improved morphological characteristics and electronic properties of MAPbI(3) thin film with multiple methylamine spray treatments
(2020-03-01)
Chiao, Guan-Haw
;
Li, Liang-Chen
;
Shellaiah, Muthaiah
;
Sun, Kien Wen
;
應用化學系
We demonstrated that the quality of the film can be significantly improved by using multiple treatments with methylamine (CH3NH2, MA) spray to the spin-coated perovskite thin films on poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/ITO glass substrates, leading to more efficient and reproducible photovoltaic and optoelectronic devices. Our X-ray diffraction and scanning electron microscopy measurements indicated an increase in the homogeneity, grain size, and crystallinity of the spin-coated MAPbI(3) thin film after multiple MA vapor treatments. The influence of MA vapor treatments on emission, absorption, energy gap, and carrier lifetime were investigated through the absorption, steady-state, and time-resolved photoluminescence (PL) spectroscopy. The peak position and full width at half maximum of the MA spray-treated film PL were slightly blue shifted and narrowed, respectively, because of the reduced defect states in the band tail and gain boundary. However, the PL intensity of the treated film was lower than that of the untreated one due to the increased carrier diffusivity in larger grains. The carrier type, concentration, mobility, electrical resistivity, and photoconductivity of the MA spray-treated MAPbI(3) thin film was also investigated using the Hall and current-voltage measurements. The improvements in the morphological characteristics and crystallinity of the treated perovskite thin film were reflected in the enhanced carrier mobility, electrical conductivity, photo response, and suppressed carrier recombination.
Lateral Two-Dimensional p-i-n Diode in a Completely Undoped GaAs/AlGaAs Quantum Well
(2013-01-01)
Van-Truong Dai
;
Lin, Sheng-Di
;
Lin, Shih-Wei
;
Wu, Jau-Yang
;
Li, Liang-Chen
A lateral two-dimensional p-i-n junction in an entirely undoped GaAs/AlGaAs quantum well has been fabricated. The optical and electrical characteristics of the junction are reported. The threshold voltage of the junction and the electroluminescence spectrum of the quantum well confirm the formation of the lateral two-dimensional junction. (C) 2013 The Japan Society of Applied Physics
Low temperature and high magnetic field spectroscopic ellipsometry system
(2014-05-01)
Su, Sheng-Kai
;
Li, Liang-Chen
;
Suen, Yuen-Wuu
;
Wu, Jau-Yang
;
Kuo, Hong-Rong
We report on the design and implementation of a spectral ellipsometer at near-infrared wavelength (700-1000 nm) for samples placed in high magnetic fields (up to 14 T) at low temperatures (similar to 4.2 K). The main optical components are integrated in a probe, which can be inserted into a conventional long-neck He dewar and has a very long free-space optical path (similar to 1.8 mx2). A polarizer-sample-(quarter-wave plate)-rotating analyzer configuration was employed. Two dielectric mirrors, one before and one after the sample in the optical path, helped to reflect the light back to the analyzer and a two-axis piezo-driven goniometer under the sample holder was used to control the direction of the reflected light. Functional test results performed on an intrinsic GaAs wafer and analysis on the random error of the system are shown. We obtained both amplitude and phase ellipsometric spectra simultaneously and observed helicity transformation at energies near the GaAs exciton transitions in the phase spectra. Significant shifts of them induced by magnetic fields were observed and fitted with a simple model. This system will allow us to study the collective magneto-optical response of materials and spatial dispersive exciton-polariton related problems in high external magnetic fields at low temperatures. (C) 2014 AIP Publishing LLC.
Low temperature and high magnetic field spectroscopic ellipsometry system
(2014-05-01)
Su, Sheng-Kai
;
Li, Liang-Chen
;
Suen, Yuen-Wuu
;
Wu, Jau-Yang
;
Kuo, Hong-Rong
We report on the design and implementation of a spectral ellipsometer at near-infrared wavelength (700-1000 nm) for samples placed in high magnetic fields (up to 14 T) at low temperatures (similar to 4.2 K). The main optical components are integrated in a probe, which can be inserted into a conventional long-neck He dewar and has a very long free-space optical path (similar to 1.8 mx2). A polarizer-sample-(quarter-wave plate)-rotating analyzer configuration was employed. Two dielectric mirrors, one before and one after the sample in the optical path, helped to reflect the light back to the analyzer and a two-axis piezo-driven goniometer under the sample holder was used to control the direction of the reflected light. Functional test results performed on an intrinsic GaAs wafer and analysis on the random error of the system are shown. We obtained both amplitude and phase ellipsometric spectra simultaneously and observed helicity transformation at energies near the GaAs exciton transitions in the phase spectra. Significant shifts of them induced by magnetic fields were observed and fitted with a simple model. This system will allow us to study the collective magneto-optical response of materials and spatial dispersive exciton-polariton related problems in high external magnetic fields at low temperatures. (C) 2014 AIP Publishing LLC.
Low-Frequency Contact Noise of GaN Nanowire Device Detected by Cross-Spectrum Technique
(2011-06-01)
Li, Liang-Chen
;
Huang, Kuo-Hsun
;
Wei, Jia-An
;
Suen, Yuen-Wuu
;
Liu, Ting-Wei
We report the properties of low-frequency contact noise of multielectrode GaN nanowire (NW) devices. A two-port cross-spectrum technique is used to discriminate the noise of the ohmic contact from that of the NW section. The diameter of the GaN NW is around 100 nm. The Ti/Al electrodes of the NWs are defined by e-beam lithography. The typical resistance of a NW section with a length of 800nm is about 5.5 k Omega and the two-wire resistance is below 100 k Omega. The results show that the low-frequency excess noise of the GaN NW is much smaller than that of the current-flowing contact, indicating that the contact noise dominates the noise behavior in our GaN NW devices. A careful study of the noise amplitude (A) of the 1/f noise of different types of NW and carbon nanotube devices, both in our work and in the literature, yields an empirical formula for estimating A from the two-wire resistance of the device. (C) 2011 The Japan Society of Applied Physics
Structural and Photophysical Properties of Methylammonium Lead Tribromide (MAPbBr(3)) Single Crystals
(2017-10-20)
Wang, Kai-Hung
;
Li, Liang-Chen
;
Shellaiah, Muthaiah
;
Sun, Kien Wen
;
應用化學系
The structural and photophysical characteristics of MAPbBr(3) single crystals prepared using the inverse temperature crystallization method are evaluated using temperature-dependent X-ray diffraction (XRD) and optical spectroscopy. Contrary to previous research reports on perovskite materials, we study phase transitions in crystal lattice structures accompanied with changes in optical properties expand throughout a wide temperature range of 300-1.5 K. The XRD studies reveal several phase transitions occurred at similar to 210 K, similar to 145 K, and similar to 80 K, respectively. The coexistence of two different crystallographic phases was observed at a temperature below 145 K. The emission peaks in the PL spectra are all asymmetric in line shape with weak and broad shoulders near the absorption edges, which are attributed to the Br atom vacancy on the surface of the crystals. The time-resolved PL measurements reveal the effect of the desorption/adsorption of gas molecules on the crystal surface on the PL lifetimes. Raman spectroscopy results indicate the strong interplays between cations and different halide atoms. Lastly, no diamagnetic shift or split in emission peaks can be observed in the magneto-PL spectra even at an applied magnetic field up to 5 T and at a temperature as low as 1.5 K.
Structural, Photophysical, and Electronic Properties of CH3NH3PbCl3 Single Crystals
(2019-09-16)
Hsu, Hao-Ping
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Li, Liang-Chen
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Shellaiah, Muthaiah
;
Sun, Kien Wen
;
應用化學系
Methylammonium lead chloride (CH3NH3PbCl3 or MAPbCl(3)) single crystals were fabricated using the inverse temperature crystallization method, and their structural, photophysical, and electronic characteristics were studied using temperature dependent optical spectroscopy, X-ray diffraction (XRD), current-voltage, and Hall measurements. The changes in absorption and photoluminescence properties accompanied with structural changes in crystal lattice were studied within a broad temperature range of 300-20 K. XRD investigations reveal that phase changes took placed around 180 K and 175 K. At a temperature below 170 K, two different crystallographic phases were found to co-exist in the photoluminescence spectra. An asymmetric line shape with broad and weak shoulders near the absorption edges was observed in all of the major PL peaks. The weak shoulders are attributed to the missing chloride atoms on the crystal surface. The photoluminescence intensity of the crystals was strongly influenced by the environment, thereby indicating that the carrier recombination is affected by the physical desorption/absorption of gas molecules at the crystal surface. Moreover, vibronic replicas in the photoluminescence spectra at low temperature were observed for the first time. The origins of these replicas are attributed to the coupling between the vibrational/librational motions of the organic cations and the photoexcited electrons. Finally, the Hall and current-voltage measurements confirm that the crystal is an n-type semiconductor with a carrier concentration of similar to 2.63 x 10(11) cm(-3), a mobility of 4.14 cm(2)/V.s, and a conductivity of 1.8 x 10(-8) Omega(-1 )cm(-1) under dark and room temperature conditions.