Browsing by Author "Chen, LC"

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Color-tunable multilayer light-emitting diodes based on conjugated polymers
(2004-02-16)
Huang, CC
;
Meng, HF
;
Ho, GK
;
Chen, CH
;
Hsu, CS
Wide-range low-voltage continuous color tuning is achieved in multilayer light-emitting diodes based exclusively on the commonly used high-efficiency electroluminescent conjugated polymers. There are three layers for red, green, and blue emission, and one extra layer for electron blocking. The color of the emitted photon depends on the position of the electron-hole recombination. Due to the stronger field dependence of the electron mobility relative to the hole mobility, the recombination zone is pushed away from the cathode and concentrated in different emissive layers as the voltage increases. (C) 2004 American Institute of Physics.
Comparative studies on field emission properties of carbon-based materials
(2000-04-01)
Chen, KH
;
Wu, JJ
;
Chen, LC
;
Wen, CY
;
Kichambare, PD
Comparative studies on field emission properties of various carbon-related materials including diamond, amorphous carbon, SiCN films, SiCN nanorods, and carbon nanotubes are presented. While diamond is well known for its potential use in cold cathodes, the emission current of a hydrogen-treated diamond film is relatively small compared to that of amorphous carbon or diamond-like-carbon film. Meanwhile, carbon nanotubes have demonstrated large emission currents at much lower threshold voltages, showing their potential for applications. However, the emission from carbon nanotubes is subjected to significant decay under long-term operation. The emission current and long-term stability can be improved using a new SiCN compound with nanorod morphology. The effective barrier height and the held enhancement factor derived from the Fowler-Nordheim equation are discussed in this paper. (C) 2000 Elsevier Science S.A. All rights reserved.
Comparison of the electronic structures of AIN nanotips grown on p- and n-type Si substrates
(2005-12-07)
Chiou, JW
;
Tsai, HM
;
Pao, CW
;
Dong, CL
;
Chang, CL
At and N K-edge x-ray absorption near-edge structure (XANES), scanning photoelectron microscopy (SPEM) and x-ray emission measurements were performed on AIN nanotips grown on p- and n-type Si substrates (p-AIN and n-AIN). Features and intensities in the Al and N K-edge XANES spectra of these AIN nanotips overall are similar. In contrast, the intensities of the valence-band SPEM spectra of p-AIN are apparently larger than those of n-AIN, which indicates that the valence-band density of states of p-AIN exceeds that of n-AIN. This result may be related to the observed enhancement of field-emission intensity of AIN nanotips grown on the p-type Si substrate.
Controlling steps during early stages of the aligned growth of carbon nanotubes using microwave plasma enhanced chemical vapor deposition
(2002-10-01)
Chen, LC
;
Wen, CY
;
Liang, CH
;
Hong, WK
;
Chen, KJ
Vertically aligned carbon nanotubes (CNTs) with controllable length and diameter fabricated by microwave plasma enhanced chemical vapor deposition (MPECVD) are of continuing interest for various applications. This paper describes the role of process gas composition as well as the pre-coating catalytic layer characteristics. It is observed that nucleation of CNTs was significantly enhanced by adding nitrogen in the MPECVD process, which also promoted formation of bamboo-like structures. The very first key step toward growth of aligned CNTs was the formation of high-density fine carbon onion encapsulated metal (COEM) particles under a hydrogen plasma. Direct microscopic investigation of their structural evolution during the very early stages revealed that elongation, necking, and splitting of the COEM particles occurred accompanying the growth of CNTs, such that one of the split portions rode on the top of the growing tube while the remaining one resided on the root. Our results suggest that CNTs grow via the "tip-growth" as well as "root-growth" mechanisms.
Crystalline SiCN: a hard material rivals to cubic BN
(1999-11-01)
Chen, LC
;
Chen, KH
;
Wei, SL
;
Kichambare, PD
;
Wu, JJ
Growth and mechanical properties of SiCN materials prepared by microwave plasma enhanced chemical vapor deposition (CVD) as well as electron cyclotron resonance plasma CVD are reported. Large (several tens of microns), well-faceted ternary SiCN crystals were grown by microwave plasma-enhanced chemical vapor deposition. whereas amorphous SiCN films were deposited by ECR-CVD. The ternary crystalline compound (C; Si)(x)N-y exhibits a hexagonal structure and consists of a network wherein the Si and C are substitutional elements. While the N content of the crystalline compound is about 50 at.%, the extent of Si substitution varies and can be as low as 10 at.%. The amorphous SIGN films contain only about 30 at.% N. Nano-indentation studies were employed to investigate the mechanical properties of the SiCN materials. From the load versus displacement curves. we estimated the hardness and the effective modulus of the SIGN crystals to be around 30 and 321.7 GPa, respectively. The corresponding values for the amorphous SiCN were around 22 and 164.4 GPa, respectively. These values are well above most reported values for CN films. (C) 1999 Elsevier Science S.A. All rights reserved.
Deposition of silicon carbon nitride films by ion beam sputtering
(1999-11-01)
Wu, JJ
;
Wu, CT
;
Liao, YC
;
Lu, TR
;
Chen, LC
Silicon carbon nitride films have been successfully synthesized at a temperature below 100 degrees C from an adenine(C5N5H5)-silicon-mixed target sputtered by Ar ion beam. The effects of Ar ion sputtering voltage, area ratio of Si to adenine in the mixed target and nitrogen atom addition during deposition on the film growth are investigated. XPS, XRD, and ellipsometry were employed to characterize the composition, chemical bonding, structure, and optical property of the films. The growth characteristic and film properties of the silicon carbon nitride films are also compared with those of the carbon nitride films deposited from an adenine target to elucidate the effect of silicon incorporation. The silicon content of the resultant films increased significantly as the area ratio of Si to adenine increased, whereas a higher Ar ion voltage led to a lower level of silicon incorporation, presumably due to differential sputtering yield of Si and adenine. XPS chemical stare analysis revealed multiple bonding structures for every element in the SiCN films, of which possible implications are given. XRD studies showed that only amorphous films for Si-rich SiCN were obtained, while the films with low Si incorporation and deposited at high Ar ion beam voltage contained nanocrystallites. Furthermore, the: refractive index of the SiCN films increased with increasing silicon content. The appearance of the nanocrystalline structure in the films led to a reduction in the refractive index. (C) 1999 Elsevier Science S.A. All rights reserved.
Effect of target materials on crystalline carbon nitride film preparation by ion beam sputtering
(1999-08-01)
Kuo, CT
;
Chen, LC
;
Chen, KH
;
Chen, TM
;
Lu, TR
In order to provide abundant chemical information, two novel bio-molecular target materials, instead of the conventional graphite target, were successfully developed to determine the possible formation mechanisms of carbon nitride during ion beam deposition. The azaadenine and adenine targets consist of carbonitro bonding, high N/C ratio as well as a six-fold carbonitro ring structure similar to that in hypothetical C3N4. Mass spectroscopy was used to determine the possible mechanisms of these two target materials. A lower electron beam energy at 75 eV was adopted to generate as abundant fragmental ions during the decomposition of these targets. Mass spectroscopy study on these two different targets indicates that the adenine target exhibits a more complex decomposition mechanism than the azaadenine target. However, the seven common hydrogenated carbonitro-species may suggest the same predominant mechanism during the decomposition of these two targets under the present deposition condition. The good correlation is one reason why two different targets can make almost the same quality crystalline carbon nitride films, including bonding, composition and structure. (C) 1999 Elsevier Science S.A. All rights reserved.
Effects of high-density oxygen plasma posttreatment on field emission properties of carbon nanotube field-emission displays
(2005-11-01)
Juan, CP
;
Tsai, CC
;
Chen, KH
;
Chen, LC
;
Cheng, HGC
The effects of oxygen plasma posttreatment (PPT) on the morphology and field emission properties of carbon nanotube (CNT) arrays grown on silicon substrates are proposed and experimental results are reported. Oxygen PPT led to an enhancement in the emission properties of CNTs, which showed an increase in total emission current density and a decrease in turn-on field after plasma treatment. Scanning electron microscopy (SEM) images showed reduced densities of the CNTs, which resulted in a decrease of the screening effect in the electric field. Raman spectra showed an increase in the number of defects which served as field-emission sites when the plasma power or treatment time with the plasma increased. Transmission electron microscopy (TEM) images were used to identify the quality of the nanotubes, so that we could clearly find evidences of improvement in the field emission properties after plasma treatment. The measurement of electrical characteristics revealed improved field emission properties under proper plasma conditions. The turn-on field decreased from 4.8 to 2.5 V/mu m, and the emission current density increased from 78.7 mu A/cm(2) to 18 mA/cm(2) at an applied field of 5.5 V/mu m.
Efficient white light emission in conjugated polymer homojunctions
(2004-11-15)
Ho, GK
;
Meng, HF
;
Lin, SC
;
Horng, SF
;
Hsu, CS
We study polymer light-emitting diodes with a homojunction, i.e., junction between two layers with the same host material. One layer is poly (9,9-dioctylfluorene-2,7-diyl) (PFO) host blended with a small amount of poly (2-methoxy-5 (2'-ethyl-hexyloxy)-1,4-phenylene vinylene), another layer is either pure PFO or PFO host blended with green-emitting polyfluorene copolymers. Such homojunction devices are solution processed and show efficient white light emission. The peak luminance 3000 cd/m(2) is reached at 10 V with Internationale de L'Eclairage (CIE) coordinate (0.34, 0.34). (C) 2004 American Institute of Physics.
Enhancement in field emission of silicon microtips by bias-assisted carburization
(2000-11-01)
Kichambare, PD
;
Tarntair, FG
;
Chen, LC
;
Chen, KH
;
Cheng, HC
Ultrathin carbon layers with thicknesses below 50 Angstrom have been deposited on silicon microtip arrays by bias-assisted carburization (BAC) using microwave plasma chemical vapor deposition. The tip radius of these silicon tips is reduced below 55 nm under low deposition temperature. The field emission characterization has been performed in a high-vacuum environment. An enhancement in the field emission is observed of about 3 orders of magnitude in BAC silicon microtips over untreated silicon microtips. With an applied voltage of 1100 V, emission currents of 80 and 120 muA have been achieved for the films grown (at de bias of -200 V for 40 min) with 15% and 25% CH4/H-2 gas ratio, respectively. An emission current of 40 muA has been achieved for the film grown (at de bias of -300 V for 30 min) with 3.5% CH4/H-2 ratio. The BAC silicon emitter has good emission stability at a constant voltage of 1100 V. These investigations indicate that further improvement of this technology will lead to simple and inexpensive field emission display devices. (C) 2000 American Vacuum Society. [S0734-211X(00)10706-1].
Exploring behavior of E-journal users in science and technology: Transaction log analysis of Elsevier's ScienceDirect OnSite in Taiwan
(2002)
Ke, HR
;
Kwakkelaar, R
;
Tai, YM
;
Chen, LC
;
資訊工程學系
In the era of digital libraries, Web-based electronic databases have become important resources for education and research, providing functionality and ease of use superior to print products. Analysis of usage of such online systems can provide valuable information on user behavior, and on usage of electronic information in general. Furthermore, the findings can be used to improve effectiveness of these electronic systems and identify areas for improvement, ranging from user interface and functionality to documentation and product training. This article analyzes usage of the Taiwan-based ScienceDirect OnSite E-journal system, one of the largest and most heavily used full-text Science, Technology, and Medicine (STM) databases worldwide. (C) 2002 Elsevier Science Inc. All rights reserved.
Fabrication and characterization of carbon nanotube triodes
(2001-05-01)
Hong, WK
;
Chen, KH
;
Chen, LC
;
Tarntair, FG
;
Chen, KJ
To achieve high emission current density, carbon nanotube triodes have been proposed using recessed oxide as the insulator between the gate and the carbon nanotubes to replace the conventional spacer. An anode current of 10 muA was achieved with a gate voltage of 98 V for a nanotube sample prepared with a growth time of 12 min. Carbon nanotubes synthesized with various growth times were analyzed using a scanning electron microscope and Raman spectroscopy. By increasing the growth time, longer carbon nanotubes were obtained. Effects of the length of the carbon nanotubes on the field emission of the triodes are discussed, Enhanced luminance was obtained as the anode voltage increased from 600V to 1000V. Such carbon nanotube triodes are promising for utilization in future field-emission displays.
Fabrication and characterization of lateral field emission device based on carbon nanotubes
(2003)
Tsai, CC
;
Juan, CP
;
Chen, KJ
;
Chen, KH
;
Chen, LC
Fabrication and characterization of lateral field emission device based on carbon nanotubes
(2005-04-01)
Juan, CP
;
Tsai, CC
;
Chen, KH
;
Chen, LC
;
Cheng, HC
We have proposed and fabricated a vertical lateral field emission device (LFED) based on carbon nanotubes (CNTs). It combines high-performance nanomaterials with mature solid-state fabrication technology to produce miniaturized vacuum devices with superior field emission characteristics. The techniques employed are very simple and allow for good reproducibility in controlling the short distance from the polysilicon anode to the CNTs cathode inter-electrode distance. The inter-electrode gap can be easily fabricated to be less than 1 mu m by a wet etching process without using fine lithography. The CNTs were selectively grown using a microwave-plasma enhanced chemical vapor deposition system (MPCVD). The anode-to-emitter gap distance and the length of carbon nanotubes are well controlled to enable investigation of their effect on the field emission properties. The turn-on voltage of the fabricated device with an inter-electrode gap of 0.53 mu m is as low as 0.2V, and the emission current is as high as 9.72mA at 10V. The emission current fluctuation is approximately +/- 3.5% for 1500s.
Fabrication and characterization of low turn-on voltage carbon nanotube field emission triodes
(2001-08-01)
Cheng, HC
;
Chen, KJ
;
Hong, WK
;
Tantair, FG
;
Lin, CP
Based on selective growth, carbon nanotubes (CNTs) for low turn-on voltage field emission triodes have been grown via microwave plasma-enhanced chemical vapor deposition. The triode devices fabricated with standard integrated circuit process contain 4 x 4 emitting cells with extraction gates and each individual cell is 4 mum in diameter. With the phosphor-coated indium tin oxide glass as the anode away from the CNTs triodes with similar to1 mm above, the triode devices achieved low turn-on gate voltage of 30 V and high emission current density of 0.7 A/cm(2) at 50 V. The results exhibit CNTs for potential application in field emission display. (C) 2001 The Electrochemical Society.
Field electron emission from C-based emitters and devices
(2001)
Chen, LC
;
Hong, WK
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Tarntair, FG
;
Chen, KJ
;
Lin, JB
We present the fabrication, characterization and field emission properties of various C-based emitters and devices, which include (1) the diode-type emitters consisting of arrays of carbon-coated Si microtips and carbon nanotubes (CNTs), (2) CNT triodes. and (3) thin-film-transistor (TFT)-controlled CNT field emission devices (FEDs). All the CNTs were deposited by microwave plasma-enhanced chemical vapor deposition. For the first type, each array contains 50 x 50 emitting cells and each individual cell is 3 microns square. Compared to the Si microtips with bias-assisted carburization or diamond cladding, enhancement in field emission by several orders of magnitude of the CNTs arrays was observed. While the diode-type CNT emitters easily achieve the goal of drawing high electron emission current at low macroscopic field, their long-term stability is not satisfactory for practical applications. For the triode-type CNT-FEDs, vertically aligned CNTs with controlled length were directly grown on the Fe-coated Si substrate pre-patterned by photolithography and etching using oxide as the gate insulator, and the emission current from the CNTs was controlled via the gate voltage. For the TFT-controlled CNT-FEDs, CNTs were selectively grown on the drain region of the TFT and the emission current from the CNTs was controlled via the TFT drain current. It should be mentioned that the fabrication procedures are straightforward and can be integrated with current technologies in the well-established semiconductor industry. Both the triode-type CNTs as well as the TFT-controlled CNT-FEDs have demonstrated improved controllability and stability while maintaining high emission current density.
Field emission from quasi-aligned SiCN nanorods
(2000-05-01)
Tarntair, FG
;
Wen, CY
;
Chen, LC
;
Wu, JJ
;
Chen, KH
We report on the preparation and field emission properties of quasi-aligned silicon carbon nitride (SiCN) nanorods. The SiCN nanorods are formed by using a two-stage growth method wherein the first stage involves formation of a buffer layer containing high density of nanocrystals by electron cyclotron resonance plasma enhanced chemical vapor deposition and the second stage involves using microwave plasma enhanced chemical vapor deposition for high growth rate along a preferred orientation. It should be noted that growth of the SiCN nanorods is self-mediated without the addition of any metal catalyst. Scanning electron microscopy shows that the SiCN nanorods are six-side-rod-shaped single crystals of about 1-1.5 mu m in length and about 20-50 nm in diameter. Energy dispersive x-ray spectrometry shows that the nanorod contains about 26 at. % of Si, 50 at. % of C, and 24 at. % of N. Characteristic current-voltage measurements indicate a low turn-on field of 10 V/mu m. Field emission current density in excess of 4.5 mA/cm(2) has been observed at 36.7 V/mu m. Moreover, SiCN nanorods exhibited rather stable emission current under constant applied voltage. (C) 2000 American Institute of Physics. [S0003-6951(00)01117-7].
Field emission properties of two-layer structured SiCN films
(2001-03-15)
Tarntair, FG
;
Wu, JJ
;
Chen, KH
;
Wen, CY
;
Chen, LC
The electron emission characteristics of two-layer structured silicon carbon nitride (SiCN) films, which were composed of amorphous and nanocrystalline phases, were studied. Rutherford backscattering spectroscopy (RBS) was used to determine the composition of the SiCN film. The ratio (Si;C)/N of the SiCN film was kept at approximately 0.75, which is identical to that of Si3N4 him. High resolution X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to investigate the bonding structures of the SiCN films. In comparison with silicon nitride films, the turn-on Voltage (for an emission current of 0.01 mA/cm(2)) of the SiCN films was rower and the emission current densities of the SiCN significantly enhanced. The promising emission properties of the SiCN film could be due to the unique two-layer structure wherein nanocrystalline SiCN was grown on top of the amorphous interlayer with sp(2) CN bond in the SiCN film. (C) 2001 Elsevier Science B.V. All rights reserved.
Four-dimensional dielectric property image obtained from electron spectroscopic imaging series
(2001)
Lo, SC
;
Kai, JJ
;
Chen, FR
;
Chang, L
;
Chen, LC
We have demonstrated a new quantitative method to characterize two- dimensional distributions of energy-dependent dielectric function of materials from low loss electron spectroscopic image (ESI) series. Two problems associated with extracted image-spectrum from the low-loss image series, under-sampling and loss of energy resolution, were overcome by using fast Fourier transformation (FFT) interpolation and maximum entropy deconvolution method. in this study, Black Diamond(TM)/Si3N4/SiO2/Si-substrate dielectric layer designed for copper metallization was used as the sample. We show that the reconstructed (FFT interpolated and maximum entropy deconvoluted) image-spectrum obtained from ESI series images can be quantified with the same accuracy as conventional electron energy-loss spectroscopy spectra. Since the analysis of the dielectric function is sensitive to the local thickness of the specimen using Kramers-Kronig analysis, we also developed a new method to quantitatively determine the dielectric constant for low-k materials. We have determined the thickness of the Black Diamond using the extrapolated thickness method from the materials of known dielectric constants. Using Kramers-Kronig formula, the dielectric function map can be deduced front two-dimensional reconstructed single scattering spectra with providing the information of thickness. We proposed a four-dimensional data presentation for revealing the uniformity of the energy dependent property. The accuracy of our methods depends on the thickness determination and on the quality of the reconstructed spectra from the image series.
GaN-based light-emitting diodes with Ni/AuBe transparent conductive layer
(2003-10-01)
Chen, LC
;
Hsu, CY
;
Lan, WH
;
Teng, SY
;
材料科學與工程學系
Ni/AuBe as p-type ohmic contact to p-GaN in the heat treatment process are reported. By selection of an optimum condition, the best construction of Ni/AuBe bi-layers is 5 nm/5 nm thick. The light-transmission is about 75% for 470 nm blue light and the lowest specific contact resistance obtained is 2 x 10(-3) Omega cm(2) examined by transmission line model after heat treatment process at 500 degreesC alloying temperature during 10 min in nitrogen ambient. The Be atom may plays an important role in the formation of good ohmic contacts. On the other hand, Ni/AuBe bi-layers are also applied to GaN-based light-emitting diodes (LEDs) as p-type ohmic contact electrode. The typical I-V characteristics of the GaN-based LEDs with 5 nm/5 nm-thick Ni/AuBe TCL exhibit a forward-bias voltage of 3.41 V at injection Current of 20 mA. (C) 2003 Elsevier Ltd. All rights reserved.