Jeng-Tzong Sheu

Potential-controlled electrodeposition of gold dendrites in the presence of cysteine

Crystalline Au dendrites were formed by electrodeposition on a glassy carbon electrode from a solution of HAuCl(4) containing cysteine. The Au dendrites possessed a hierarchical architecture with three-fold symmetry; they comprised trunks, branches, and nanorod leaves, which all grew along the <111> direction.

Photoresponses and memory effects in organic thin film transistors incorporating poly(3-hexylthiophene)/CdSe quantum dots

This paper describes the optical responses and memory effects of poly(3-hexylthiophene) (P3HT)/CdSe quantum dot (QD) thin-film transistors (TFTs). TFTs incorporating P3HT/CdSe QD blends as the active layer exhibited higher photocurrents than did the corresponding P3HT-only devices because the heterojunction between P3HT and the CdSe QDs enhanced the separation of excitons. Moreover, the CdSe QDs served as trap centers so that the memory effect was maintained for several hours, even when the device was operated without a gating voltage. Here, we demonstrate the potential applicability of such P3HT/CdSe QD TFTs through repeated optical programming and electrical erasing.

Electric-Field Enhancement of a Gate-All-Around Nanowire Thin-Film Transistor Memory

A high-performance gate-all-around (GAA) poly-Si nanowire (NW) SONOS-type memory thin-film transistor (TFT) is presented. The presence of the corners of the GAA structure resulted in the program speed and memory window of this device being superior to those of a planar poly-Si TFT device. When erasing, planar devices exhibit a threshold-voltage shift resulting from gate injection; the GAA device was immune to this behavior. The presence of a nonuniform electric field in the channel region during programming and erasing was confirmed through simulation. The device also exhibited superior endurance and data-retention behavior.

Characteristics of Gate-All-Around Twin Poly-Si Nanowire Thin-Film Transistors

We have investigated the characteristics of gate-all-around (GAA) twin polycrystalline-silicon nanowire (NW) thin-film transistors (TFTs). The NW channel and surrounding gate imparted the GAA twin NW TFT with superior channel controllability. Moreover, the combination of the high surface-to-volume ratio of the NW and the split channel structure led to highly efficient NH3 plasma treatment, which reduced the effective grain-boundary trap-state density. The GAA twin NW TFT exhibited greatly improved electrical performance, including a lower threshold voltage, a steeper subthreshold swing (114 mV/dec), a higher on/off current ratio (> 108), and a virtual absence of drain-induced barrier lowering (13 mV/V).

Localized Joule Heating As a Mask-Free Technique for the Local Synthesis of ZnO Nanowires on Silicon Nanodevices

We report a mask-free technique for the local synthesis of ZnO nanowires (NWs) on polysilicon nanobelts and polysilicon NW devices. First, we used localized joule heating to generate a poly(methyl methacrylate) (PMMA) nanotemplate, allowing the rapid and self-aligned ablation of PMMA within a short period of time (ca. 5 μs). Next, we used ion-beam sputtering to prepare an ultrathin Au film and a ZnO seed layer; a subsequent lift-off process left the seed layers selectively within the PMMA nanotemplate. Gold nanoparticles and ZnO NWs were formed selectively in the localized joule heating region.

Growth and Field Emission of Reactive Sputtered Pd–PdO Core–Shell Nanoflakes on Platinum

Palladium oxide PdO was deposited on platinum by reactive sputter deposition, and the PdO thin film grown on the Pt substrate had a flakelike morphology. The nanosized flake had a core–shell structure with a single Pd grain encapsulated by a crystalline PdO surface layer. The formation of the PdO capped nanoflakes was ascribed to a large interfacial stress due to a lattice mismatch between PdO and Pt. Field emission characteristics of the nanoflakes were studied and a field-enhancement factor of 791 was obtained.

Electrical bistable memory device based on a poly(styrene-b-4-vinylpyridine) nanostructured diblock copolymer thin film

This paper describes the performance of a nonvolatile memory device based on a solution-processed poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer thin film. The Al/PS-b-P4VP/indium tin oxide memory device featuring metal-coordinated 30 nm P4VP cores exhibited an ON/OFF ratio of 2×105, an erase voltage of 0.75 V, a write voltage of −0.5 V, and a retention time of 104 s. The device exhibited a metallic behavior in the ON state, suggesting the formation of metallic filaments through the migration of Al atoms into the P4VP domain during writing. Such nanostructured diblock copolymer thin films open up avenues for fabricating organic memory devices using simple procedures.

Selective deposition of gold nanoparticles on SiO2/Si nanowires for molecule detection

The selective deposition of gold nanoparticles on the surface of N-(2-Aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS)-pretreated silicon nanowire (SiNW)s for molecule detection was demonstrated. The SiNWs were fabricated by scanning probe lithography (SPL) and tetramethyl ammonium hydroxide (TMAH) wet etching. The width and height of the SiNWs were 60 nm and 10 nm, respectively. The gold nanoparticles were synthesized by the chemical reduction method. The electronic properties of the SiNWs in response to the binding of different molecules on the surface of the SiNWs subsequently were discussed. A dynamic observation of the change in conductance was conducted to monitor the reaction between gold nanoparticles and the AEAPTMS-pretreated surface of the SiNWs. The reaction of gold nanoparticles on the surface of the SiNWs took about 750 s before conductance saturation. Finally, an engineered enzyme, KSI-126C, with a thiol terminal was designed to bind with the gold nanoparticles on the surface of the SiNWs. Shifts in turn-on voltage in I–Vds characteristics have clearly been observed after the binding of molecules and gold nanoparticles.

A possibility of detection of the non-charge based analytes using ultra-thin body field-effect transistors.

Ultra-thin body of p-type field-effect transistors were developed as transducer for biosensors. Changes of conductance resulted from the changes of the surface potentials of ultra-thin body field-effect transistors (UTB-FETs) due to surface chemical modifications were demonstrated. The channel surface of UTB-FETs were modified with N-[3-(trimethoxysilyl)propyl]ethylenediamine (AEAPTMS) and then gold nanoparticles (AuNPs) to immobilize the bio-component, the genetically engineered Delta(5)-3-ketosteroid isomerase (Art_KSI) or the Art_KSI conjugated with charged reporter (Art_KSI_mA51). The binding of charge-based molecules or nanoparticles has been demonstrated to strongly affect the conductivity of UTB-FETs; the increase or decrease of the conductance depends on the polarity of the immobilized molecules or nanoparticles. A new protocol involving the detection of a non-charged analyte relied on the competitive binding of analyte (19-norandrostendione) and a charged reporter (mA51) with KSI. When exposed to a 19-norandrostendione solution (10 microM), the conductance of Art_KSI_mA51-modified UTB-FET increased by 265 nS ( approximately 12%). On the other hand, conductance of Art_KSI-modified UTB-FET showed no distinct change under the same detection conditions.

Fluorescence enhancement and multiple protein detection in ZnO nanostructure microfluidic devices

In this study, different morphological ZnO nanostructures, those of sharp nanowires (NWs), rod NWs, and hexahedral-puncheon nanostructures, were grown in microfluidic channels on the same glass substrate. Characterizations of correspondent biomolecule binding properties were simulated and demonstrated. The surface was modified using 3-ammineopropyl-triethoxysilane (3-APTES) and biotin-N-hydroxysuccinimide ester (NHS-biotin). Different concentrations (4.17pM to 41.7nM) of dye-conjugated streptavidin were simultaneously infused through the second microfluidic channels, which lie 90° from the first microfluidic channels. The florescent intensity at the crossover areas showed good agreement with simulations, with sharp ZnO NWs exhibiting the largest dynamic range and the highest fluorescent intensity. We further characterize correspondent protein detection using sharp ZnO NWs. The surfaces of these ZnO NWs were modified with mouse immunoglobulin G (IgG), infused through the second microfluidic channels with dye-conjugated (Alexa 546) anti-mouse IgG in different concentrations. Concentrations ranging from 417fM to 41.7nM can be resolved using sharp ZnO NWs. Finally, multiple protein detection was demonstrated using a five-by-eight microfluidic channel array. Fluorescence images present clear multiple detections at the crossover areas when using the sharp ZnO NWs for simultaneous dye-conjugated anti-mouse IgG and dye-conjugated anti-rabbit IgG (Alexa 647) detection.