Showing papers by "Shuit-Tong Lee published in 1999"
TL;DR: In this paper, the influence of oxidative and reductive treatments of indium-tin-oxide (ITO) on the performance of electroluminescent devices is presented.
Abstract: The influence of oxidative and reductive treatments of indium–tin–oxide (ITO) on the performance of electroluminescent devices is presented. The improvement in device performance is correlated with the surface chemical composition and work function. The work function is shown to be largely determined by the surface oxygen concentration. Oxygen-glow discharge or ultraviolet–ozone treatments increase the surface oxygen concentration and work function in a strongly correlated manner. High temperature, vacuum annealing reduces both the surface oxygen and work function. With oxidation the occupied, density of states (DOS) at the Fermi level is also greatly reduced. This process is reversible by vacuum annealing and it appears that the oxygen concentration, work function, and DOS can be cycled by repeated oxygen treatments and annealing. These observations are interpreted in terms of the well-known, bulk properties of ITO.
345 citations
TL;DR: In this paper, metal diffusion from magnesium-silver cathodes and indium-tinoxide anodes in organic light-emitting diodes has been investigated, and the presence of indium in organic films showed a correlation with performance degradation.
Abstract: Metal diffusion from magnesium–silver cathodes and indium–tin–oxide anodes in organic light-emitting diodes has been investigated. Magnesium showed no substantial diffusion under device operation and had no significant effects on luminance decay with operation time. Indium was immobile in storage at room temperature, while indium penetration into organic layers was observed after device operation. The presence of indium in organic films showed a correlation with performance degradation.
286 citations
TL;DR: In this paper, a bulk-quantity Si nanowires have been synthesized by thermal evaporation of a powder mixture of silicon and SiO2, and it was shown that at the initial nucleation stage, silicon monoxide vapor was generated from the powder mixture and condensed on the substrate.
274 citations
TL;DR: A bright-blue electroluminescent device has been fabricated by using an emissive dopant and an electron-transporting host as discussed by the authors, which shows a bright blue emission of 11000cd/m2 at a current density of 360
Abstract: A bright-blue electroluminescent device has been fabricated by using an emissive dopant and an electron-transporting host. The dopant was a highly photoluminescent silyl-substituted ter-(phenylene–vinylene) derivative [1,4-bis[4-(2-trimethylsilylvinly) styryl]-2,5-dibutoxybenzene (BTSB)]. BTSB was doped into a trimer of N-arylbenzimidazoles (TPBI) which functioned as the host and electron transporter. N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4-4′-diamine (NPB) was used as the hole transporter. The device, with a structure of indium tin oxide\NPB\TPBI:10%BTSB\TPBI\Mg:Ag, shows a bright blue emission of 11000 cd/m2 at a current density of 360 mA/cm2. The current efficiency of this device is about 3.2 cd/A at 20 mA/cm2.
270 citations
TL;DR: In this article, the energy-level alignment of a multilayer organic light-emitting diode (LED) using ultraviolet photo-emission spectroscopy was analyzed.
Abstract: Direct measurements of electronic properties have been made for the metal/organic and organic/organic interfaces in a multilayer organic light-emitting diode (LED) using ultraviolet photoemission spectroscopy. The device configuration considered is indium–tin oxide (ITO)/copper phthalocyanine (CuPc)/N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamne (NPB)/8-hydroxyquinoline aluminum (Alq)/Mg. For the material interfaces considered here, our result indicates that the traditional concept of vacuum-level alignment, though not valid for metal/organic interfaces, still holds at organic/organic interfaces. This implies that little charge transfer occurs at the interfaces due to the small interaction between organic molecules. The largest band offsets are observed between the lowest unoccupied state levels of the organic molecules. Based on the directly measured energy-level alignments, a model is proposed to explain the improved efficiency of multilayer organic LEDs, as compared to those with a single ...
214 citations
TL;DR: In this article, a silicon carbide (SiC) nanowires on a silicon substrate were prepared using hot-filament-assisted chemical-vapor deposition with a solid silicon and carbon source.
Abstract: Silicon carbide (SiC) nanowires on a silicon substrate were prepared using hot-filament-assisted chemical-vapor deposition with a solid silicon and carbon source. The SiC nanowires show good field-emitting properties as revealed by the current–voltage characteristics. Together with its ease of preparation, these SiC nanowires are shown to have great potential in the area of electron field-emitting devices.
207 citations
TL;DR: In this article, a continuous SiNW film was prepared by grinding the pieces of sponge-like SiNWs to powder, then dispersing and sticking the powder onto a Si wafer.
Abstract: Silicon nanowires (SiNWs) were synthesized using laser ablation. A continuous SiNW film was prepared by grinding the pieces of sponge-like SiNWs to powder, then dispersing and sticking the powder onto a Si wafer. The field emission characteristics of the SiNW film were studied based on current–voltage measurements and the Fowler–Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. A hydrogen plasma treatment of the SiNW film aimed at reducing the oxide overlayer improved the emission uniformity of the film.
190 citations
TL;DR: In this article, the oxide-assisted nanowire growth has been studied and shown that oxides play a dominant role in the nucleation and growth of high-quality semiconductor nanowires.
Abstract: Semiconductor wires with nanometer widths have attracted much attention in recent years for their potential applications in mesoscopic research and nanodevices. Since the 1960s, Si whiskers grown from the vapor-liquid-solid (VLS) reaction have been extensively studied. In the VLS reaction, Au particles are generally used as the mediating solvent on a Si substrate since Au and Si form a molten alloy at a relatively low temperature. Si in the vapor phase diffuses into the liquid-alloy droplet and bonds to the solid Si at the liquid-solid interface, which results in the growth of Si whiskers. The diameter of the whisker is determined by the diameter of the liquid-alloy droplet at its tip. Si whiskers generally grow along ⟨111⟩ directions epitaxially on Si(111) substrates in the form of single crystals by the VLS reaction.In different materials systems, however, a variety of whisker forms can be obtained. For example, GaP whiskers display rotational twins around their ⟨111⟩ growth axes, while GaAs whiskers grow in the form of the wurtzite structure.Thus far, the synthesis of one-dimensional nanostructured materials on a large scale remains a challenge. In recent years, many efforts have been made to synthesize Si nanowires by employing different methods such as photolithography and etching techniques and scanning tunneling microscopy. One method of particular interest is a recently developed laser ablation of metal-containing semiconductor targets, by which bulk quantities of semiconductor nanowires can be readily obtained. Our recent studies show that oxides play a dominant role in the nucleation and growth of high-quality semiconductor nanowires in bulk quantities by laser ablation, thermal evaporation, or chemical vapor deposition. A new growth mechanism called oxide-assisted nanowire growth has therefore been established. The ability to synthesize large quantities of high-purity (no contamination), ultra-long (in millimeters), and uniform-sized semiconductor nanowires (a few nanometers to tens of nanometers in diameter) from this new technique offers exciting possibilities in fundamental and applied research.
179 citations
TL;DR: In this paper, a new growth mechanism was proposed on the basis of microstructure and different morphologies of the nanowires observed, which is based on the decomposition of semiconductor suboxides and defect structures.
Abstract: Highly pure, ultralong, and uniform-sized semiconductor nanowires in bulk quantity were synthesized by thermal evaporation or laser ablation of semiconductor powders mixed with oxides. Transmission electron microscopy study shows that decomposition of semiconductor suboxides and defect structures play important roles in enhancing the formation and growth of high-quality nanowires. A new growth mechanism is proposed on the basis of microstructure and different morphologies of the nanowires observed.
128 citations
TL;DR: In this article, a thin film of copper phthalocyanine (CuPc) was employed for cathode preparation in organic light emitting diodes (OLEDs), which was found to be an effective buffer layer in preventing sputter damage to the OLED layer structure.
Abstract: Sputter deposition was employed for cathode preparation in organic light emitting diodes (OLEDs). A thin film of copper phthalocyanine (CuPc) was found to be an effective buffer layer in preventing sputter damage to the OLED layer structure. However, the CuPc layer forms an electron-injection barrier with the underlying Alq layer, resulting in increased electron-hole recombination in the nonemissive CuPc layer, and thus a substantial reduction in electroluminescence efficiency. Incorporation of Li at the CuPc/Alq interface from a sputter-deposited Al (Li) cathode was found to reduce the injection barrier at the interface and make the overall device efficiency comparable to a device having an evaporated MgAg cathode. The devices exhibited good operational stability with a half lifetime greater than 3800 h at 20 mA/cm2.
98 citations
TL;DR: Based on experimental observations of silicon nanowire growth, a new mechanism has been proposed for one-dimensional growth of crystalline nanowires from the vapor phase as discussed by the authors, where an amorphous matrix is deposited from a vapor phase of unsaturated oxide nanoclusters, and subsequent phase separation in the matrix leads to the formation of a single crystalline core and an oxide sheath.
TL;DR: In this article, the carrier mobilities of organic electroluminescent materials, N, N ′-bis-(1-naphhyl)- N, N ²-diphenyl-1,1′-biphenylon-4,4′-diamine (NPB), tris(8-hydroxyquinoline) aluminum (Alq), and Tb(AcA) 3 phen (AcA: acetylacetone, phen: phenanthroline) (Tb-complex), were measured.
TL;DR: In this paper, the formation of nanowires into different shapes was explained by the two-step growth model based on the vapor-liquid-solid mechanism, which showed that the most abundant smooth-surface nanowsires were spring-shaped, fishbone-shaped and frog-egg-shaped.
Abstract: Silicon nanowires have been synthesized by laser ablation of Si powder targets at 1200 °C. Transmission electron microscopy study showed that most Si nanowires had smooth surfaces and nearly the same diameter of about 16 nm. Beside the most abundant smooth-surface nanowires, four other forms of nanowires, named spring-shaped, fishbone-shaped, frog-egg-shaped, and necklace-shaped nanowires, were observed. The formation of nanowires into different shapes was explained by the two-step growth model based on the vapor–liquid–solid mechanism.
Patent•
08 Jun 1999TL;DR: In this article, a method to produce large amounts of silicon nanowires without requiring the use of any catalysts that may cause contamination is described. But it is not suitable for use in the field of medical applications.
Abstract: Silicon nanowires and silicon nanoparticle chains are formed by the activation of silicon monoxide in the vapor phase. The silicon monoxide source may be solid or gaseous, and the activation may be by thermal excitation, laser ablation, plasma or magnetron sputtering. The present invention produces large amounts of silicon nanowires without requiring the use of any catalysts that may cause contamination.
TL;DR: Si nanowires with different diameters have been synthesized by laser ablation in different ambient gases as mentioned in this paper, and they exhibited photoluminescence and spectral blue-shift with diameter reduction.
Abstract: Si nanowires (SINWs) with different diameters have been synthesized by laser ablation in different ambient gases. SINWs with the diameter distribution peaks at ∼13.2 and ∼9.5 nm have been obtained respectively in He and Ar (5% H2). SINWs produced in N2 had the smallest peak diameter at 6 nm, and are mixed in with some spherical particles with diameters ranging from ∼9 nm to several hundreds nm. Elements from the ambient gas were not detected in the SINWs. SINWs produced in Ar(5% H2) and N2 atmospheres exhibited photoluminescence and spectral blue-shift with diameter reduction, which are attributable to two-dimensional quantum confinement effects in crystalline nanowires.
TL;DR: In this article, a vacuum-deposited light-emitting device which emits light from its top surface through an Al cathode using p-type doped silicon as the anode material is described.
Abstract: We report the fabrication of a vacuum-deposited light-emitting device which emits light from its top surface through an Al cathode using p-type doped silicon as the anode material. Enhanced hole injection is clearly demonstrated from the p-Si anode as compared to the indium–tin–oxide (ITO) anode. The mechanisms of hole injection from both the p-Si and ITO anodes into the organic layer are investigated and a possible model based on anode surface band bending is proposed. During the operation of the organic light-emitting device, the surface band bending of the anode plays a very important role in modifying the interfacial barrier height between the anode and the organic layer.
Patent•
18 Feb 1999TL;DR: In this paper, a method and an apparatus have been developed to grow beta-silicon carbide nanorods, and prepare patterned field-emitters using different kinds of chemical vapor deposition methods.
Abstract: A method and an apparatus have been developed to grow beta-silicon carbide nanorods, and prepare patterned field-emitters using different kinds of chemical vapor deposition methods. The apparatus includes graphite powder as the carbon source, and silicon powder as silicon sources. Metal powders (Fe, Cr and/or Ni) are used as catalyst. Hydrogen was the only feeding gas to the system.
TL;DR: A nonplanar derivative of perylene, 2,5,8,11-tetra-tertbutylperylene (TBPe), was synthesized via the Friedel-Crafts alkylation reaction as discussed by the authors.
Abstract: A nonplanar derivative of perylene, 2,5,8,11-tetra-tertbutylperylene (TBPe), was synthesized via the Friedel–Crafts alkylation reaction. Electroluminescent (EL) devices were made using TBPe or perylene as a dopant in bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III) and their EL performance was compared. Similar to the device doped with the parent perylene molecule, the device doped with TBPe also emitted strongly in the blue. As the concentration of TBPe increased from 1% to 5%, the color coordinates in CIE 1931 chromaticity of the TBPe-doped device changed only slightly from (0.168,0.273) to (0.175,0.273), whereas the perylene-doped device exhibited a much larger shift from (0.165,0.196) to (0.178,0.252). The constancy of EL color and efficiency with respect to TBPe dopant concentration is attributable to diminishing molecular aggregation in the nonplanar perylene derivative, TBPe, due to the steric hindrance of the tert-butyl groups.
TL;DR: In this article, the authors obtained germanium dioxide (GeO2) whiskers in bulk quantity by ablating a target at 820°C with a pulsed KrF excimer laser in an argon atmosphere.
Abstract: We obtained germanium dioxide (GeO2) whiskers in bulk quantity by ablating a germanium target at 820 °C with a pulsed KrF excimer laser in an argon atmosphere. Most of the GeO2 whiskers were smooth and straight with hexagonal or triangular, or quadrilateral cross sections while some of them had a bamboo-shoot-shaped form. Results of scanning electron microscopy, transmission electron microscopy, and x-ray diffraction showed that the whiskers are hexagonal crystalline GeO2.
TL;DR: By heating a pressed tablet of graphite powder mixed with nickel in a quartz tube mounted inside a high-temperature tube furnace at 1200°C, amorphous carbon nanowires were formed on the inner wall of the quartz tube near a copper cooling finger.
Abstract: By heating a pressed tablet of graphite powder mixed with nickel in a quartz tube mounted inside a high-temperature tube furnace at 1200 °C, amorphous carbon nanowires were formed on the inner wall of the quartz tube near a copper cooling finger. Bright-field images of transmission electron microscopy show that the diameters of the nanowires are around 40 nm. Selected-area electron diffraction and Raman study reveal that the nanowires have an amorphous structure.
TL;DR: In this paper, the authors have fabricated organic electroluminescent devices with crystalline organic layers and showed that substantial increases in luminescent efficiency and brightness have been observed in the device thus fabricated.
Abstract: Crystallization and interdiffusion of organic layers have been widely considered to be important causes for performance degradation of organic electroluminescent devices. By using high substrate temperature during vapor deposition, we have fabricated organic electroluminescent devices with crystalline organic layers. Contrary to the common belief, substantial increases in luminescent efficiency and brightness have been observed in the device thus fabricated. Such devices also showed much improved storage stability against high humidity compared to the conventional ones with amorphous organic layers.
TL;DR: By using a KrF excimer laser to ablate a target of SiC powder mixed with 10 wt.% SiO 2 powder at 1400°C, Si nanowires were deposited on the inner wall of a ceramic tube as discussed by the authors.
TL;DR: In this article, a triaryl pyrazoline derivative was synthesized and used as a dopant in blue organic electroluminescent devices, which achieved a blue emission peaking around 470 nm and a luminance of 5500 cd/m2 at a current density of about 300 mA/cm2.
TL;DR: In this article, the hardness and optical bandgap of the resulting diamond-like carbon (DLC) and nitrogenated DLC (a-C:N) films were investigated and correlated to the elemental and phase composition.
TL;DR: In this article, the PM3 method of the molecular orbital theory has been used to study the interaction between the magnesium (Mg) atom and the Alq3 molecule in organic light emitting devices.
Abstract: The interaction between the magnesium (Mg) atom and Alq3 molecule in organic light emitting devices has been theoretically studied using the PM3 method of the molecular orbital theory. It has been shown that various interactions can happen when the Mg atom approaches the Alq3 molecule, leading to significant changes in the molecular geometry and electronic structure of Alq3. The resulting configurations with insertion of Mg into the central part of the Alq3 molecule are found to be energetically more favorable than those with Mg forming bond(s) with a benzene ring of Alq3. In agreement with recent experiments, this result shows that the interaction between Mg and the Alq3 molecule depends on the order of deposition. Interestingly, the density of states calculated for these systems reveals that the creation of the new electronic gap states observed in the experiments is mainly relating to the aluminum atomic orbital due to interaction, instead of a direct contribution of Mg.
Patent•
21 Jan 1999TL;DR: In this article, an organic electroluminescent device with improved luminescent efficiency has been fabricated upon inclusion of an inorganic buffer layer in the hole injecting or electron injecting regions.
Abstract: An organic electroluminescent device (OELD) with improved luminescent efficiency has been fabricated upon inclusion of an inorganic buffer layer in the hole injecting or electron injecting regions. The structure of the device can be as follows (from bottom to top): ITO\buffer layer\NPB\Alq\Mg:Ag. In comparison with devices without the buffer layer, the present OELD may be more efficient in a proper bias condition.
TL;DR: In this paper, the hardness of the C 0.5(BN)0.5 plate was found to be twice that of graphite and three times that of nanocrystalline BN.
TL;DR: The structure of the hydrogen terminated, $(2mmode\times\else\texttimes\fi{}1)$ reconstructed diamond (100) surface has been investigated by low-energy electron-diffraction (LEED) intensity versus energy $[I(E)]$ measurements in combination with tensor LEED calculations.
Abstract: The structure of the hydrogen terminated, $(2\ifmmode\times\else\texttimes\fi{}1)$ reconstructed diamond (100) surface has been investigated by low-energy electron-diffraction (LEED) intensity versus energy $[I(E)]$ measurements in combination with tensor LEED calculations. It has been found that the surface corresponds to the formation of symmetric dimers on the top C layer, with a dimer length of 1.60 \AA{}. The top layer shows slight inward relaxation; the interlayer spacing between the first and second C layers reduces to 0.81 \AA{}, which corresponds to an \ensuremath{\sim}7% contraction compared to the bulk value. The structural details of the first four carbon layers have been determined and are compared to those given by theoretical calculations.
TL;DR: Hard diamond-like carbon (DLC) films have been prepared on PMMA (Polymethyl methacrylate), glass, and Si(100) substrates using C{sub 2}H{ sub 2}-Ar plasma immersion ion processing (PIIP) as mentioned in this paper.
TL;DR: The morphology and microstructure of BaTiO3/SrTiOO3 (BTO/STO) superlattices grown epitaxially on STO (001) substrates by a computer-controlled laser molecular-beam epitaxy deposition system have been characterized by means of atomic force microscopy and high-resolution transmission electron microscopy (HRTEM) as mentioned in this paper.
Abstract: The morphology and microstructure of BaTiO3/SrTiO3 (BTO/STO) superlattices grown epitaxially on STO (001) substrates by a computer-controlled laser molecular-beam epitaxy deposition system have been characterized by means of atomic force microscopy and high-resolution transmission electron microscopy (HRTEM). It is found that the HRTEM images taken along the [120] direction of BTO and STO show the maximal contrast difference. It is, therefore, observed that the superlattices consist of a highly oriented and single-crystalline multilayered structure. As identified by HRTEM, the number of unit cells in each BTO or STO layer matches very well with that obtained from reflection high-energy electron diffraction oscillations. The surfaces and interfaces of the superlattices are atomically smooth. In the superlattices, the ratio between the c axis of BTO and STO is about 4% larger than that measured from BTO or STO bulk crystals.