Showing papers by "Shuit-Tong Lee published in 2013"
TL;DR: A large-scale synthetic strategy is developed for facile one-pot aqueous synthesis of silicon nanoparticles (SiNPs) yielding SiNPs that feature strong fluorescence, favorable biocompatibility, and robust photo- and pH-stability.
Abstract: A large-scale synthetic strategy is developed for facile one-pot aqueous synthesis of silicon nanoparticles (SiNPs) yielding ∼0.1 g SiNPs of small sizes (∼2.2 nm) in 10 min. The as-prepared SiNPs feature strong fluorescence (photoluminescence quantum yield of 20–25%), favorable biocompatibility, and robust photo- and pH-stability. Moreover, the SiNPs are naturally water dispersible, requiring no additional post-treatment. Such SiNPs can serve as highly photostable bioprobes and are superbly suitable for long-term immunofluorescent cellular imaging.
359 citations
TL;DR: In this article, the authors review the recent achievements on silicon nanowires for advanced energy conversion and storage applications including photovoltaics, photocatalysis, thermoelectrics, lithium-ion batteries and supercapacitors.
259 citations
TL;DR: In this article, a green synthesis of graphitic carbon quantum dots (GCQDs) as a fluorescent sensing platform for the highly sensitive and selective detection of Fe3+ ions was reported.
Abstract: Reported here is a green synthesis of graphitic carbon quantum dots (GCQDs) as a fluorescent sensing platform for the highly sensitive and selective detection of Fe3+ ions. Through the electrochemical ablation of graphite electrodes in ultrapure water, uniform GCQDs with graphitic crystallinity and oxygen containing groups on their surfaces have been successfully prepared. The absence of acid, alkali, salt and organic compounds in the starting materials effectively avoids complex purification procedures and environmental contamination, leading to a green and sustainable synthesis of GCQDs. The oxygen functional groups (e.g., hydroxyl, carboxyl) contribute to the water solubility and strong interaction with metal ions, which enable the GCQDs to serve as a fluorescent probe for the highly sensitive and selective detection of Fe3+ ions with a detection limit as low as 2 nM. The high sensitivity of our GCQDs could be attributed to the formation of complexes between Fe3+ ions and the phenolic hydroxyls of GCQDs. The fluorescence lifetime of GCQDs in the presence and absence of Fe3+ was tested by time-correlated single-photon counting (TCSPC), which confirmed a dynamic fluorescence quenching mechanism.
245 citations
222 citations
TL;DR: Hexagonal-packed silver-coated silicon nanowire arrays as a nanogap-free SERS system with wide-range electric fields and controlled interwire separation are reported, showing that the ordered Ag/SiNW array system may serve as an excellent SERS platform for practical chemical and biological detection.
Abstract: Surface-enhanced Raman scattering (SERS) systems utilizing the interparticle nanogaps as hot spots have demonstrated ultrasensitive single-molecule detection with excellent selectivity yet the electric fields are too confined in the small nanogaps to enable reproducible biomolecule detections Here, guided by finite-difference-time-domain simulation, we report hexagonal-packed silver-coated silicon nanowire (Ag/SiNW) arrays as a nanogap-free SERS system with wide-range electric fields and controlled interwire separation Significantly, the system achieves a SERS detection of long double-strand DNA of 25–50 nm in length with a relative standard deviation (RSD) of 14% for measurements of above 4000 spots over an area of 200 × 200 μm2 The high reproducibility in the SERS detection is attributed to (1) the large interwire spacing of 150 nm that allows access and excitation of large biomolecules; and (2) 600 nm wide-range electric field generated by propagating surface plasmons along the surface of continuous
193 citations
TL;DR: In this paper, a germanium-graphene nanocomposite using a low-pressure thermal evaporation approach is reported, by which crystalline germanum particles are uniformly deposited on graphene surfaces or embedded into graphene sheets.
Abstract: The high-energy lithium ion battery is an ideal power source for electric vehicles and grid-scale energy storage applications. Germanium is a promising anode material for lithium ion batteries due to its high specific capacity, but still suffers from poor cyclability. Here, we report a facile preparation of a germanium–graphene nanocomposite using a low-pressure thermal evaporation approach, by which crystalline germanium particles are uniformly deposited on graphene surfaces or embedded into graphene sheets. The nanocomposite exhibits a high Coulombic efficiency of 80.4% in the first cycle and a capacity retention of 84.9% after 400 full cycles in a half cell, along with high utilization of germanium in the composite and high rate capability. These outstanding properties are attributed to the monodisperse distribution of high-quality germanium particles in a flexible graphene framework. This preparation approach can be extended to other active elements that can be easily evaporated (e.g., sulfur, phosphorus) for the preparation of graphene-based composites for lithium ion battery applications.
134 citations
117 citations
TL;DR: A highly specific, distinct color change in the crystals of a metal-organic framework with pendant allyl thioether units in response to Pd species was discovered, pointing to the potential use of these crystals in colorimetric detection and quantification of Pd(II) ions.
Abstract: A highly specific, distinct color change in the crystals of a metal–organic framework with pendant allyl thioether units in response to Pd species was discovered. The color change (from light yellow to orange/brick red) can be triggered by Pd species at concentrations of a few parts per million and points to the potential use of these crystals in colorimetric detection and quantification of Pd(II) ions. The swift color change is likely due to the combined effects of the multiple functions built into the porous framework: the carboxyl groups for bonding with Zn(II) ions to assemble the host network and the thioether and alkene functions for effective uptake of the Pd(II) analytes (e.g., via the alkene–Pd interaction). The resultant loading of Pd (and other noble metal) species into the porous solid also offers rich potential for catalysis applications, and the alkene side chains are amenable to wide-ranging chemical transformations (e.g., bromination and polymerization), enabling further functionalization ...
107 citations
TL;DR: Inspired by light absorption and resonance energy transfer processes of chlorophyll, a highly efficient photoelectric conversion system by introducing Carbon quantum dots (CQDs) as an electron transfer intermediary is developed.
Abstract: Compared to nature’s photoelectric conversion processes, artificial devices are still far inferior in efficiency and stability. Inspired by light absorption and resonance energy transfer processes of chlorophyll, we developed a highly efficient photoelectric conversion system by introducing Carbon quantum dots (CQDs) as an electron transfer intermediary. Compared with conventional dye-sensitized semiconductor systems, the present CQD-doped system showed significantly higher photoelectric conversion efficiency, as much as 7 times that without CQDs. The CQD-doped dye/semiconductor system may provide a powerful approach to the development of highly efficient photoelectric devices.
100 citations
TL;DR: The present synthetic route may be used to fabricate a wide range of sophisticated dual- or multicolor-emitting organic heterostructures via judicious choice of the CT complexes through a two-step seeded-growth method.
Abstract: We report a simple yet versatile solution route for constructing heterojunctions from luminescent organic charge-transfer (CT) complexes through a two-step seeded-growth method. Using this method, we achieved anisotropic and selective growth of anthracene–1,2,4,5-tetracyanobenzene (TCNB) complexes onto the tips of naphthalene–TCNB microtubes, resulting in the formation of microdumbbells. Significantly, the two-component microdumbbells appear as dual-color-emitting heterojunctions arising from integration of two distinct color-emitting materials. We further elucidated the two-step seeded-growth mechanism of the dumbbell-like organic heterostructures on the basis of structural analysis of the two crystals and surface–interface energy balance. In principle, the present synthetic route may be used to fabricate a wide range of sophisticated dual- or multicolor-emitting organic heterostructures via judicious choice of the CT complexes.
95 citations
TL;DR: In this paper, the interfacial morphologies and electronic structures between organic molecules and graphene, prepared on different substrates, are reviewed and shown to exhibit two important characteristics: (1) formation of well-ordered organic layers based on the graphene template and (2) occurrence of charge transfer between adsorbed molecules and graphite.
TL;DR: In this article, the authors demonstrate that the work function of PEDOT:PSS films plays a critical role on the electronic output characteristics of the device, and they add an aqueous solution of perfluorinated ionomer (PFI) due to its high electron affinity, which is compatible to fabricate the hybrid Si/PEDOT PSS device.
Abstract: The organic-inorganic hybrid Schottky solar cells based on solution processed poly(3,4-ethlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in combination with silicon offer the merits of simple fabrication process and potential low cost. Here, we demonstrate that the work function (WF) of PEDOT:PSS films plays a critical role on the electronic output characteristics of the device. The WF of PEDOT:PSS is tuned by adding an aqueous solution of perfluorinated ionomer (PFI) due to its high electron affinity, which is compatible to fabricate the hybrid Si/PEDOT:PSS device. With an addition of 4% (weight) PFI into PEDOT:PSS, the device achieves a fill factor (FF) as high as 0.70 without sacrifice of open-circuit voltage and short-circuit current density, which improves 20% in comparison with the pristine PEDOT:PSS (0.58). The detailed electrical output measurements reveal that the high FF is ascribed to the enhanced built-in potential as well as suppression of charge recombination at organic-inorganic interface.
TL;DR: In this paper, a chemical vapor deposition process is introduced to prepare silicon (Si)-graphene composite anode materials for lithium-ion batteries, which exhibits high utilization of Si in charge-discharge processes.
Abstract: A chemical vapor deposition process is introduced to prepare silicon (Si)–graphene composite anode materials for lithium-ion batteries. Highly ordered crystalline Si particles are deposited onto graphene sheets by using a liquid chlorosilane as Si source. The Si–graphene composite exhibits high utilization of Si in charge–discharge processes. The capacity retention of 90 % after 500 full cycles and an average Coulombic efficiency in excess of 99.5 % are achieved in half cells. Moreover, atomic layer deposition (ALD) Al2O3 coating is directly applied on the Si-graphene electrode, which greatly suppresses the side reactions between the electrode and electrolyte, resulting in the enhancement in initial Coulombic efficiency and reversible capacity. Finally, a 3.6 V full cell device is demonstrated, which works very well by combining a Si-graphene anode with a Li-excess layer-structured composite Li1.2Ni0.2Mn0.6O2 cathode. This approach is very promising for realizing a high-energy lithium-ion battery.
TL;DR: In this article, the authors used unbalanced magnetron sputtering via adjusting the carbon target current, and their microstructure and mechanical properties were characterized using Raman spectrum, X-ray photoelectron spectroscopy and nano-indenter, respectively.
TL;DR: In this paper, a new approach was proposed to realize the light extraction enhancement in organic light-emitting diodes (OLEDs) by using platinum-cobalt (Pt3Co) alloy nanoparticles (ANPs).
Abstract: We have demonstrated a new approach to realize the light extraction enhancement in organic light-emitting diodes (OLEDs) by using platinum–cobalt (Pt3Co) alloy nanoparticles (ANPs). The current efficiencies of 19.2 cd A−1 and 29.3 cd A−1 at a current density of 20 mA cm−2 are obtained for the device with Pt3Co ANPs unannealed and annealed, respectively, which correspond to a ∼46% and ∼123% enhancement compared to the control device without Pt3Co ANPs. A systematic study on the devices with and without unannealed Pt3Co ANPs shows that the significantly enhanced efficiency is mainly due to the resonance of localized surface plasmon (LSP). The analysis of surface topography, angular-dependent EL spectra and theoretical calculations of the devices with and without annealed Pt3Co ANPs reveals that the annealing treatment of Pt3Co ANPs could result in a further enhancement in light extraction due to the increased light scattering effect, thereby achieving a double-enhancement in light extraction by simultaneously realizing the resonance of LSP and the light scattering effect.
TL;DR: The interfacial electronic structure of MoO 3− x /graphene has been investigated using photo-emission spectroscopy in this article, and the hole density of graphene was estimated to be 5.44 × 10 12 ǫ cm −2.
TL;DR: In this paper, two host materials, DBTSF2 (DBT and spirobifluorene (SF) blocks, were designed and synthesized, incorporating dibenzothiophene and SF blocks, and their thermal, electrochemical and photo-physical properties were fully characterized.
TL;DR: In this article, a nanostructured backscattering rear electrode was used to achieve an improved cell performance by maintaining simultaneously high open circuit voltage and fill factor values, while providing excellent short-circuit current enhancement through efficient backscatter-induced light trapping.
TL;DR: Amorphous carbon coatings (a-C) incorporated with various titanium and chromium content (Ti/aC and Cr/a C) were deposited on 316L substrates using unbalanced magnetron sputtering as discussed by the authors.
TL;DR: In this article, density functional theory is applied to illustrate the migration and coalescence processes of point defects in point defects and the structural rearrangement of divacancy defect and conclude the relative stability of different types of point defect.
Abstract: Graphene is a promising material due to its outstanding properties. Point defects can be created artificially and tailor/improve the relative properties of pristine graphene. Defective graphene is potential material for electronic devices and sensors. Under irradiation or heat treatment, defects may diffuse and aggregate together. Here we perform density functional theory (DFT) to illustrate the migration and coalescence processes of the point defects. We find that the presence of single-vacancy (SV) defect stimulates the migration of another SV defect to bring them together and form the adjacent single vacancy defects. The adjacent single vacancy defects can combine into a divacancy defect, and we study the path. We also study the structural rearrangement of divacancy defect and conclude the relative stability of different types of divacancy defects. In addition, we find that divacancy defect [V2 (5-8-5) defect] is ready to be healed by a neighboring adatom defect. In comparison, divacancy defect [V2 (55...
TL;DR: The better-separated single-walled TiO(2) nanotubes thus obtained show significantly improved photocatalytic efficiency compared with their non-etched counterparts.
Abstract: A facile electrochemical method to selectively remove the outer walls of anodic TiO(2) nanotubes by leaving the as-anodized nanotubes in the same electrolyte and applying an electric field parallel to the anodic film for several minutes is reported. The better-separated single-walled TiO(2) nanotubes thus obtained show significantly improved photocatalytic efficiency compared with their non-etched counterparts.
TL;DR: The results extend the functions of the SiNW sensor to SMD and provide insight into the molecule level illustration on the sensing mechanism of the nanowire sensor.
Abstract: One-dimensional nanowire (NW) optical sensors have attracted great attention as promising nanoscale tools for applications such as probing inside living cells. However, achieving single molecule detection on NW sensors remains an interesting and unsolved problem. In the present paper, we investigate single-molecule detection (SMD) on a single SiNW based surface-enhanced Raman scattering (SERS) sensor, fabricated by controllably depositing silver nanoparticles on a SiNW (AgNP–SiNW). Both Raman spectral blinking and bi-analyte approaches are performed in aqueous solution to investigate SMD on individual SiNW SERS sensors. The results extend the functions of the SiNW sensor to SMD and provide insight into the molecule level illustration on the sensing mechanism of the nanowire sensor.
TL;DR: In this article, the hole electrical transporting properties effect on the organic-Si hybrid Schottky solar cells was investigated, and it was shown that the increased conductivity reduced the series resistance (RS) within the cell, and the higher WP generated the larger built-in potential (Vbi) which resulted in the improvement of the open-circuit voltage.
Abstract: In this work we investigated the hole electrical transporting properties effect on the organic-Si hybrid Schottky solar cells. By changing the post-annealing atmosphere of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) film, the power conversion efficiencies of the Schottky Si/PEDOT:PSS cell boosted from 6.40% in air to 9.33% in nitrogen. Current-voltage, capacitance-voltage, external quantum efficiency, and transient photovoltage measurements illustrated that the enhanced power conversion efficiency of the cell was ascribed to the increase in both conductivity and work function (WP) of PEDOT:PSS film. The increased conductivity reduced the series resistance (RS) within the cell, and the higher WP generated the larger built-in potential (Vbi) which resulted in the improvement of the open-circuit voltage. In addition, the decreased RS and enlarged Vbi were beneficial for the efficient charge transport/collection, contributing to the enhancement of the fill factor. Our results indicated that the conductivity as well as the WP of the hole transporting layer played an important role in the organic-Si Schottky solar cell.
TL;DR: In this paper, the authors used a hydrothermal method to construct a light emitting diodes (LEDs) based on arrays of n-type ZnO Nanorods.
TL;DR: A bias-mediated electron/energy transfer process at the CQDs-TiO(2) interface for the dynamic modulation of opto-electronic properties is shown.
Abstract: Here we show a bias-mediated electron/energy transfer process at the CQDs–TiO2 interface for the dynamic modulation of opto-electronic properties. Different energy and electron transfer states have been observed in the CQDs–TNTs system due to the up-conversion photoluminescence and the electron donation/acceptance properties of the CQDs decorated on TNTs.
TL;DR: In this article, the fabrication of an ultrathin silver oxide shell covered silver nanoparticles embedded in silicon nanowire film (Ag@AgxO-SiNW) by a facile method was reported.
Abstract: This paper reported the fabrication of an ultrathin silver oxide shell covered silver nanoparticles embedded in silicon nanowire film (Ag@AgxO-SiNW) by a facile method. The amorphous ultrathin silver oxide layers, which can keep Ag nanoparticles from agglomerating, were confirmed by HRTEM and STEM mapping. The Ag@AgxO-SiNW was employed as a surface-enhanced Raman scattering substrate and exhibited excellent enhancement for the concentration detection (1 × 10−7 M) of rhodamine 6 G and crystal violet with the relative standard deviation of the main Raman vibration modes less than 20%. This core@shell structure may be explained by the surface doping of silicon nanowires.
TL;DR: These nanowires were employed as starting materials to fabricate piezoelectric nanogenerators, which could convert kinetic energy into electrical one, exhibiting an output voltage of 36.5 V and a response current of 1.4 μA under a free-falling object of 300 g at a height of 30 cm.
Abstract: Silicon nanowires are important semiconductor with core/shell structure. In this work, the piezoelectric material alpha-quartz was grown in the interface of silicon nanowires by thermal treatment at 600 °C for 0.5 h. These nanowires were employed as starting materials to fabricate piezoelectric nanogenerators, which could convert kinetic energy into electrical one, exhibiting an output voltage of 36.5 V and a response current of 1.4 μA under a free-falling object of 300 g at a height of 30 cm.
TL;DR: The results revealed that the chromium carbide nano-clusters were formed when the Cr content exceeded 4.9at. as discussed by the authors The critical load increased while the hardness decreased after the Cr element incorporation.
TL;DR: In this article, the role of hydrogenation on titanium dioxide (TiO2) by using DFT+U calculations was investigated and it was shown that hydrogenation is more favorable on oxygen than on titanium.
Abstract: We investigate the role of hydrogenation on titanium dioxide (TiO2) by using DFT + U calculations. We find that hydrogenation on oxygen is more favorable than on titanium, which reduces Ti4+ into Ti3+ on the surface and introduces mid-gap state into TiO2 for enhanced optical absorption.