-
Hsieh-Cheng Han,
Cheong-Wei Chong,
Sheng-Bo Wang,
Dawei Heh,
Chi-Ang Tseng,
Yi-Fan Huang, Surojit Chattopadhyay,
Kuei-Hsien Chen,
Chi-Feng Lin,
Jiun-Haw Lee,
Li-Chyong Chen
[show abstract]
[hide abstract]
ABSTRACT: A 3D trenched-structure metal-insulator-metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ∼300 μF cm-2 is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al2O3) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (∼5 × 1010 cm-2) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal-insulator-metal or metal-insulator-semiconductor nanocapacitors using similar porosity dimensions of the support materials.
Nano Letters 02/2013; · 13.20 Impact Factor
-
Jih-Shang Hwang,
Yu-Hsiang Lin,
Jeong-Yuan Hwang,
Railing Chang, Surojit Chattopadhyay,
Chang-Jiang Chen,
Peilin Chen,
Hai-Pang Chiang,
Tsong-Ru Tsai,
Li-Chyong Chen,
Kuei-Hsien Chen
[show abstract]
[hide abstract]
ABSTRACT: Quantitative mapping of layer number and stacking order for CVD-grown graphene layers is realized by formulating Raman fingerprints obtained on two stepwise stacked graphene single-crystal domains with AB Bernal and turbostratic stacking (with ∼30°interlayer rotation), respectively. The integrated peak area ratio of the G band to the Si band, A(G)/A(Si), is proven to be a good fingerprint for layer number determination, while the area ratio of the 2D and G bands, A(2D)/A(G), is shown to differentiate effectively between the two different stacking orders. The two fingerprints are well formulated and resolve, quantitatively, the layer number and stacking type of various graphene domains that used to rely on tedious transmission electron microscopy for structural analysis. The approach is also noticeable in easy discrimination of the turbostratic graphene region (∼30° rotation), the structure of which resembles the well known high-mobility graphene R30/R2(±) fault pairs found on the vacuum-annealed C-face SiC and suggests an electron mobility reaching 14 700 cm(3) V(-1) s(-1). The methodology may shed light on monitoring and control of high-quality graphene growth, and thereby facilitate future mass production of potential high-speed graphene applications.
Nanotechnology 12/2012; 24(1):015702. · 3.98 Impact Factor
-
Jih-Shang Hwang,
Ming-Chun Kao,
Jian-Min Shiu,
Chieh-Ning Fan,
Shien-Chau Ye,
Wen-Shen Yu,
Hsiu-Mei Lin,
Tai-Yuan Lin, Surojit Chattopadhyay,
Li-Chyong Chen,
Kuei-Hsien Chen
[show abstract]
[hide abstract]
ABSTRACT: Rapid formation of radial p–n junctions on electroless-etched silicon nanowires (SiNWs) was successfully demonstrated. With a low-cost objective, a homemade nonhazardous diffusion source of high phosphor concentration annealed at a small thermal budget was used. The SiNW solar cell, with Au electrodes, has shown a power conversion efficiency of 8.41%, which is higher by 30% compared with its planar counterpart. The SiNW solar cell incorporates an inherent antireflection property, reduced diffusion length requirement, and broad-band spectral quantum efficiency. The evidence of a successful radial p–n junction formation in the NWs has been revealed through the help of a conducting atomic force microscope (AFM) scanning for the photogenerated currents on the fractured surfaces of the NWs. The demonstrated radial junction fabrication technique is believed to reduce the cost of production and promote widespread use of them.
10/2011;
-
Chi-Ta Chou,
Chien-Hung Lin,
Meng-Hsiu Wu,
Tzu-Wei Cheng,
Jiun-Haw Lee,
Chin-Hsin J Liu,
Yian Tai, Surojit Chattopadhyay,
Juen-Kai Wang,
Kuei-Hsien Chen,
Li-Chyong Chen
[show abstract]
[hide abstract]
ABSTRACT: The low molecular weight tris-(8-hydroxyquinoline) aluminum (Alq(3)) has been incorporated with magnesium (Mg) that altered the nature of its opto-electronic characteristics. The lowering of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in Mg:Alq(3), compared to pure Alq(3), creates a stronger field (exceeding the exciton binding energy) at the donor-acceptor junction to dissociate the photo-generated exciton and also provides a low barrier for electron transport across the device. In an electron-only device (described in the text), a current enhancement in excess of 10(3), with respect to pure Alq(3), could be observed at 10 V applied bias. Optimized Mg:Alq(3) layer, when introduced in the photovoltaic device, improves the power conversion efficiencies significantly to 0.15% compared to the pure Alq(3) device. The improvement in the photovoltaic performance has been attributed to the superior exciton dissociation and carrier transport.
Journal of Applied Physics 10/2011; 110(8):83104-831045. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: One-dimensional semiconductor nanomaterials form the basis for new technologies as well as driving the evolution of existing ones. Although these various technologies are in different stages of development, from nucleation to pilot production, it is difficult to ignore the tremendous potential they carry, overall, for next-generation concepts. One of the several areas that have been revolutionized by one-dimensional nanostructures, and which could not have happened at a more critical time, is energy. This review outlines the impact that one-dimensional semiconductor materials are having on energy production and conversion technologies. Instead of being extensive, we provide key developments in the areas of light-emitting diodes, solar cells, photoelectrochemistry and fuel cells.
NPG Asia Materials. 07/2011; 3(8):74-81.
-
[show abstract]
[hide abstract]
ABSTRACT: Successful deep and alignment-free patterned etching on GaN using atomic force microscope (AFM) local oxidation followed by in-situ chemical etching is demonstrated. Oxide ridges are grown on GaN on an AFM by applying positive sample bias at 80% humidity, with the oxidation reaction expedited by UV light. The oxide ridges are then etched by HCl solution, leaving troughs in the GaN surface. A dripping strategy for the in-situ chemical etching is recommended that allows deep, alignment-free multiple AFM oxidation/etching works on the GaN surface without any need of substrate removal from the AFM platform. Repeated etching followed by AFM oxidation on a spot on a GaN surface resulting in a hole as deep as 800 nm was also demonstrated. Further, a preliminary evaluation of the porosity of the AFM-grown oxide indicates that the oxide ridges grown on GaN at an AFM cantilever moving speed of 300 nm/s are porous in structure, with an estimated porosity of 86%, which porosity could be reduced if longer resident time of the AFM cantilever on the target oxidation region was used.
Journal of Nanoscience and Nanotechnology 04/2011; 11(5):3979-3984. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms.
Biosensors & bioelectronics 10/2010; 26(5):2413-8. · 5.43 Impact Factor
-
Jih-Shang Hwang,
Kuan-Yu Chen,
Shih-Jay Hong,
Shih-Wei Chen,
Wun-Shing Syu,
Chi-Wen Kuo,
Wei-Yi Syu,
Tai Yuan Lin,
Hai-Pang Chiang, Surojit Chattopadhyay,
Kuei-Hsien Chen,
Li-Chyong Chen
[show abstract]
[hide abstract]
ABSTRACT: We introduce a platform, comprised of silver nanoparticle decorated silica nanowires (SiONWs) dispersed on fused quartz substrates, for high sensitivity surface-enhanced Raman scattering (SERS) measurements using both frontal (through the analytes) and back-face (through the transparent substrate) excitation. Quasi-quantitative SERS performances on the specialized substrate, vis-à-vis a silver deposited bare fused quartz plate, showed: (i) the suitability of the Ag modified SiONW substrate for frontal as well as back-face excitation; (ii) a wider detection range with high sensitivity to Rhodamine 6G; and (iii) good underwater metal-oxide adhesion of the specialized substrates. Capable of surviving ultrasonic cleaning, the substrate introduced is one of the few reusable low-cost Ag-based nanostructured SERS substrates, requiring only a simple silver reload process (the silver mirror reaction).
Nanotechnology 01/2010; 21(2):025502. · 3.98 Impact Factor
-
Pai-Chun Wei, Surojit Chattopadhyay,
Fang-Sheng Lin,
Chih-Ming Hsu,
Shyankay Jou,
Jr-Tai Chen,
Ping-Jung Huang,
Hsu-Cheng Hsu,
Han-Chang Shih,
Kuei-Hsien Chen,
Li-Chyong Chen
[show abstract]
[hide abstract]
ABSTRACT: Photoluminescence (PL) behaviour in InN nanocolumns reveal decreasing, increasing and near invariant peak energies (E(PL)) as a function of temperature. Samples, having E(PL)~0.730 eV at 20 K, showed temperature invariance of E(PL). Samples possessing E(PL) on the lower and higher energy side of 0.730 eV demonstrate a normal redshift and anomalous blueshift, respectively, with increasing temperature. This temperature evolution can be effectively explained on the basis of a competition between a conventional red shift from lattice dilation, dominant for low carrier density sample, on one hand, and a blue shift of the electron and hole quasi Fermi-level separation, dominant for high carrier density samples, on the other.
Optics Express 08/2009; 17(14):11690-7. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a rationale for using GaN nanowires (GaNNWs) in label-free DNA-sensing using dual routes of electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) measurements, employing a popular target DNA with anthrax lethal factor (LF) sequence. The in situ EIS reveals that both high surface area and surface band-bending in the nanowires, providing more binding sites and surface-enhanced charge transfer, respectively, are responsible for the enhanced sensitivity to surface-immobilized DNA molecules. The net electron-transfer resistance can be readily deconvoluted into two components because of the coexistence of two interfaces, GaN/DNA and DNA/electrolyte interfaces, in series. Interestingly, the former, decreasing with LF concentration (C(LF)), serves as a signature for the extent of hybridization, while the latter as a fingerprint for DNA modification. For PL-sensing, the band-edge emission of GaNNWs serves as a parameter for DNA modification, which quenches exponentially with C(LF) as the incident light is increasingly blocked from reaching the core nanowire by rapidly developing a UV-absorbing DNA sheath at high C(LF). Furthermore, successful application for detection of "hotspot" mutations, related to the human p53 tumor-suppressor gene, revealed excellent selectivity and specificity, down to picomolar concentration, even in the current unoptimized sensor design/condition, and in the presence of mutations and noncomplementary strands, suggesting the potential pragmatic application in complex clinical samples.
Analytical Chemistry 01/2009; 81(1):36-42. · 5.86 Impact Factor
-
Chien-Hung Lin, Surojit Chattopadhyay,
Chia-Wen Hsu,
Meng-Hsiu Wu,
Wei-Chao Chen,
Chien-Ting Wu,
Shao-Chin Tseng,
Jih-Shang Hwang,
Jiun-Haw Lee,
Chun-Wei Chen,
Cheng-Hsuan Chen,
Li-Chyong Chen,
Kuei-Hsien Chen
Advanced Materials 12/2008; 21(7):759 - 763. · 13.88 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: High-quality crystalline (c) InN thin films have been obtained via gas-source molecular beam epitaxy, using hydrazoic acid ( HN <sub>3</sub>) precursor, on indium tin oxide/glass, c -sapphire, and c -GaN substrates at growth temperatures between 623 and 823 K. A systematic study of thermal diffusivity has been performed using the traveling-wave method. We report a high thermal diffusivity value of 0.55 cm <sup>2</sup>/ s for a combined 1.7 μ m thick InN film grown on GaN substrates not observed before. X-ray diffraction data of InN grown on GaN substrates indicated lattice shrinkage with increasing thickness of the film that supports efficient phonon propagation and resulting higher thermal diffusivity. The lattice vibrational modes expressed in the Raman spectroscopic data corroborate the diffraction results. The thickness dependence of the thermal diffusivity has been modeled to estimate a bulk value of the essential thermal property.
Journal of Applied Physics 10/2008; · 2.17 Impact Factor
-
Yi-Fan Huang, Surojit Chattopadhyay,
Yi-Jun Jen,
Cheng-Yu Peng,
Tze-An Liu,
Yu-Kuei Hsu,
Ci-Ling Pan,
Hung-Chun Lo,
Chih-Hsun Hsu,
Yuan-Huei Chang,
Chih-Shan Lee,
Kuei-Hsien Chen,
Li-Chyong Chen
[show abstract]
[hide abstract]
ABSTRACT: Nature routinely produces nanostructured surfaces with useful properties1, 2, 3, 4, such as the self-cleaning lotus leaf5, the colour of the butterfly wing6, the photoreceptor in brittlestar7 and the anti-reflection observed in the moth eye8. Scientists and engineers have been able to mimic some of these natural structures in the laboratory and in real-world applications9, 10, 11, 12. Here, we report a simple aperiodic array of silicon nanotips on a 6-inch wafer with a sub-wavelength structure that can suppress the reflection of light at a range of wavelengths from the ultraviolet, through the visible part of the spectrum, to the terahertz region. Reflection is suppressed for a wide range of angles of incidence and for both s- and p-polarized light. The antireflection properties of the silicon result from changes in the refractive index caused by variations in the height of the silicon nanotips, and can be simulated with models that have been used to explain the low reflection from moth eyes8, 13, 14. The improved anti-reflection properties of the surfaces could have applications in renewable energy and electro-optical devices for the military.
Nature Nanotechnology 12/2007; 2(12):770-774. · 27.27 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A “step-edge” model has been proposed to explain the growth of solid nanotips of aluminum nitride (AlN) and indium nitride (InN) grown by thermal and metal organic chemical vapor depositions, respectively. The model predicts a set of apex angles that solid AlN and InN nanotips can have. A statistical distribution of the apex angle in InN nanotips indicates the discrete set of apex angles and its probability of nucleation.
Applied Physics Letters 11/2006; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The optical properties of aluminum nitride nanotips (AlNNTs) synthesized via vapor transport and condensation process have been studied by cathodoluminescence, photoluminescence (PL), thermoluminescence (TL), and UV absorption measurements. Two defect related transitions around 2.1 and 3.4 eV and an excitonic feature at 6.2 eV were identified. Compared to the AlN macropowders, the AlNNTs showed a blueshift (+0.2 eV ) of the ∼3.2 eV peak. Analysis of both PL and TL excitation measurements indicated the existence of subband gap multiple energy levels in AlNNTs. A significant TL intensity even at 145 ° C suggests possible ultraviolet detector and dosimetric applications of these AlNNTs.
Applied Physics Letters 11/2006; · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The wetting properties of silicon nanotips (SiNTs) are discussed. SiNTs were prepared by single step dry etching of silicon wafers in an electron cyclotron resonance plasma of silane, methane, argon and hydrogen and water contact angles were measured as a function of their aspect ratio (α) and the inter-tip distance. The hydrophilic nature of the SiNTs is tunable with α and the inter-tip distance. Super-hydrophilicity with water contact angles close to 2° was observed with α>12 (length ~1500 nm). Upon coating a 1500 nm long SiNT with TiO2, the water contact angle jumped from 2° to ~140°, demonstrating a switchover from super-hydrophilic to hydrophobic surface properties.
Nanotechnology 04/2006; 17(10):2542. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report metalorganic chemical vapor deposition of indium nitride (InN) nanotips with apex angles of 10° and length and base diameter of around 1 μm and 200 nm, respectively. The structure of the hexagonal InN nanotips growing along [002] was studied by electron microscopy and x-ray diffraction, and the optical properties were studied using temperature-dependent photoluminescence (PL) measurements. A narrow emission peak with a 18 meV full width at half maximum positioned at 0.77 eV was obtained with no visible emission. A PL quenching of only 14% was observed with a temperature scan of 15–320 K.
Applied Physics Letters 11/2005; 87(20):203103-203103-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the field emission properties of the quasi-aligned aluminum nitride (AlN) nanotips grown on differently doped (p+, p, n+, and n type) silicon (Si) substrates by thermal chemical vapor deposition. The AlN nanotips were 10 nm at the apex, 100 nm at the bottom, and 1200 nm in length. The AlN nanotips grown on p+-Si substrate showed the lowest turn-on field of 6 V/μm (highest current density of 0.22 A/cm2 at a field of 10 V/μm), whereas no significant emission could be obtained using n+- and n-Si substrates. Band diagrams of the Si–AlN heterojunction have been used to explain the phenomenon. A 5% variation of the applied field was observed while drawing a current density of 100 μA/cm2 from the nanotips grown on p+-Si substrates.
Applied Physics Letters 08/2005; 87(7):073109-073109-3. · 3.84 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A fully plasma-based technique of generating ultrafine (sub-10-nm) nanocrystalline silver particulates on wide band gap and chemically inert hexagonal aluminum nitride nanorod templates has been demonstrated. These specially prepared substrates are ready to use for molecular sensing by room-temperature surface-enhanced Raman scattering. An enhancement factor of 2 x 106 was observed for micromolar solutions of Rhodamine 6G.
Journal of the American Chemical Society 04/2005; 127(9):2820-1. · 9.91 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new substrate for surface-enhanced Raman spectroscopy has been developed in the form of silicon nanotips, by electron cyclotron resonance plasma chemical vapor deposition, with apex diameters of 2 nm, lengths of 1000 nm, and densities of 1011/cm2. The surface areas of the nanotips are 150 m2cm-3, comparable with the best-quality porous silicon. Ion-beam-sputtered silver self-assembles on these substrates as nanoparticles of 4−10 nm diameter and these metallic nanoparticles act as surface enhancement centers for Raman spectroscopy. Standard molecules such as Rhodamine 6G and trans-1,2-bis(4-pyridyl)ethylene (BPE) of concentrations in the range of 10-6 to 10-10 M have been studied on these substrates and enhancements in the range of 106 to 108 were observed. These dry etched substrates, unlike those conventionally prepared by wet chemistry, are compatible with silicon device technology and are remarkably stable and reproducible.
01/2005;
