97444 research outputs found
Sort by
Enhanced Dynamic Annealing in Ga+ ion-implanted GaN Nanowires
No full text[[abstract]]Ga+ion implantation of chemical-vapor-deposited GaNnanowires (NWs) is studied using a 50-keV Ga+focused ion beam. The role of dynamic annealing (defect-annihilation) is discussed with an emphasis on the fluence-dependent defect structure. Unlike heavy-ion-irradiated epitaxialGaN film, large-scale amorphization is suppressed until a very high fluence of 2×1016?ions?cm?2. In contrast to extended-defects as reported for heavy-ion-irradiated epitaxialGaN film, point-defect clusters are identified as major component in irradiated NWs. Enhanced dynamic annealing induced by high diffusivity of mobile point-defects in the confined geometry of NWs is identified as the probable reason for observed differences.
Characterization of Nanodome on GaN Nanowires Formed with Ga Ion Irradiation
No full text[[abstract]]Structure of nano-domes formed by Ga+ ion irradiation with a focused ion beam (FIB) apparatus onto GaN nanowires (NWs) was examined with conventional transmission electron microscopy (CTEM), electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EF-TEM). The nano-dome consisted of metallic gallium, covered by a GaN layer, the structure of which is amorphous or liquid. It is considered that the dome structure is formed by preferential displacement of lighter element (N) and agglomeration of heavier one (Ga). 1 MeV electron irradiation onto the sample pre-irradiated by Ga+ ions at a dose below the threshold for the dome formation induced the N2 bubble formation without segregating Ga atoms, which suggests the radiation-enhanced diffusion (RED) of heavy atoms plays an important role in the nano-dome formation.
Growth, Characterization, and Functionalization of One-dimensional Nanomaterials
No full text[[abstract]]In the past year the synthesis of 1-dimensional materials of Sb/sub 2/S/sub 3/、InN、GaN、ZnO、TiO/sub 2/、Ga/sub 2/O/sub 3/ and Au has been improved significantly by C.C. Chen, L.C. Chen, J.J. Wu, and C.R.C. Wang. Besides the successful preparation nanotubes, nanowires nanorods and nanocables, special control of the growth and targeted functionality of the materials have been realized. Potential applications in sensors and biochips are also addressed. W.F. Pong utilized XANES at SRRC to study the electronic structures of our nanomaterials, while L.C. Chen applied FE-SEM equipped with EDS and cathodoluminescence (CL) to achieve nm-resolution of the morphology,composition, and optical property of the nanomaterials. Meanwhile, the UV Micro-Raman/PL system equipped with the new 325-nm laser allows effective investigation of wide bandgap materials. In functionalization and applications, C.R.C. Wang successfully applied surface plasmon resonance to the Au-nanorods for selective sensing of
biomolecules. A newly developed optothermal conversion technique has been developed. C.T. Chen has successfully applied his e-beam writer-based technique to study the transport properties of carbon
nanotubes. Clear Coulomb oscillation has been demonstrated in one of the multiwall carbon nanotubes. C.H. Lu and M.H. Chuang have make progresses in the lithium battery electrode and field emission,
respectively, utilizing the CNTs produced in this project. The charge capacitance of our samples exceed those reported in the literature.C.H. Lu also developed a nano-structured anode material for the
lithium battery, which is highly desirable for the next generation battery.
DNA-Gold Nanorod Conjugates for Remote Control of Localized Gene Expression by Near Infrared Irradiation
No full text[[abstract]]Gold nanorods were attached to the gene of enhanced green fluorescence protein (EGFP) for the remote control of gene expression in living cells. The UV?vis spectroscopy, electrophoresis, and transmission electron microscopy (TEM) were used to study the optical and structural properties of the EGFP DNA and gold nanorod (EGFP?GNR) conjugates before and after femto-second near-infrared (NIR) laser irradiation. Upon NIR irradiation, the gold nanorods of EGFP?GNR conjugates underwent shape transformation that resulted in the release of EGFP DNA. When EGFP?GNR conjugates were delivered to cultured HeLa cells, induced GFP expression was specifically observed in cells that were locally exposed to NIR irradiation. Our results demonstrate the feasibility of using gold nanorods and NIR irradiation as means of remote control of gene expression in specific cells. This approach has potential applications in biological and medical studies.
Chemical Transformation from FePt to Fe1-xPtMx (M = Ru, Ni, Sn) Nanocrystals by a Cation Redox Reaction: X-ray Absorption Spectroscopic Studies
No full text[[abstract]]New ternary metal nanocrystals of Fe1-xPtMx (M = Ru3+, Sn2+, or Ni2+) were synthesized by chemical transformation from FePt nanocrystals using a cation redox reaction in a solution. The structure and composition of resulting nanocrystals were characterized by high-resolution transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and X-ray photoemission spectroscopy (XPS). Moreover, X-ray absorption near-edge spectroscopy (XANES) was employed to confirm the chemical transformation from FePt to Fe1-xPtRux nanocrystals. The analyses of extended X-ray absorption find structure (EXAFS) revealed the detailed binding structures and coordination numbers of both FePt and Fe1-xPtRux nanocrystals. The results suggested that iron atoms of FePt lattices were oxidized to be Fe2+ and Fe3+ ions and were replaced by ruthenium atoms from the reduction of Ru3+ ions in solution to form Fe1-xPtRux lattices. Our method has opened a new route to easily and rapidly prepare a solid-solution type of ternary metal nanocrystals for catalytic applications.
Chemical Enhancer Induced Changes in the Mechanisms of Transdermal Delivery of Zinc Oxide Nanoparticles
No full text[[abstract]]The overlapping wavelength of photoluminescence (PL) of zinc oxide nanoparticles (ZnO NPs) and autofluorescence (AF) from the stratum corneum (SC) has for a long time held back researchers from investigating the chemically enhanced penetration pathways of ZnO NPs into the SC lipids. However, the non-linear polarization effect of second harmonic generation (SHG) may be used for ZnO NPs to be distinguished from the AF of the SC. This study combined the SHG of ZnO NPs and the AF of the SC to image the transdermal delivery of ZnO NPs under the chemical enhancer conditions of oleic acid (OA), ethanol (EtOH) and oleic acid-ethanol (OA-EtOH). In addition to qualitative imaging, the microtransport properties of ZnO NPs were quantified to give the enhancements of the vehicle-to-skin partition coefficient (K), the SHG intensity gradient (G) and the effective diffusion path length (L). The results showed that OA, EtOH and OA-EtOH were all capable of enhancing the transdermal delivery of ZnO NPs by increasing the intercellular lipid fluidity or extracting lipids from the SC.
Direct evidence of type II band alignment in nanoscale P3HT/CdSe heterostructures
No full text[[abstract]]Due to inherent advantages of both constituent materials, organic/inorganic hybrid composites have attracted increasing attention. One of the fundamental issues needed to be resolved is their band alignment, which governs most of the electrical and optical properties. Here, we report the investigation of optical transition in poly(3-hexylthiophene) (P3HT)/CdSe nano-composites (NCs). It is found that the relaxation dynamics of photo-carriers in NCs is dominated by charge separation effects. Based on the band bending effect and the quantum confinement energy of electrons in the conduction band of CdSe quantum dots, we provide direct evidence of type II band alignment in P3HT/CdSe NCs. The establishment of a type II transition in NCs is very useful for the future design of efficient optoelectronic devices based on conjugated polymer/semiconductor hybrid systems.
Low operation voltage macromolecular composite memory assisted by graphene nanoflakes
No full text[[abstract]]The trend towards simple and low-cost processing is one of the most important for macromolecular memory development. Here, bistable memory devices using a solution-processable active material, a mixture of graphene nanoflakes (GNFs) and insulating poly(vinyl alcohol) (PVA), are investigated, which serve as the first example for the direct integration of as-prepared nanoscale graphene into macromolecular memory devices through a one-step low-temperature processing method. Bistable electrical switching behavior and nonvolatile rewritable memory effects are realized by using an indium–tin-oxide/GNF–PVA/silver (ITO/GNF–PVA/Ag) sandwich structure. The resulting device exhibits low operation voltages of +1.4 V (turn-on) and ?1.3 V (turn-off), which is promising for memory cells with low power consumptions. The programmable ON- and OFF-states possess a retention time of over 104 s and endure up to 107 read pulses. The carrier transport in the OFF- and ON-states follows the typical trap-limited space charge limited current and Ohmic laws, respectively. The asymmetric electrical switch behavior is therefore attributed to conducting filaments formed in the PVA layer assisted by the charged GNFs that induce the transition of the conductivity. Our study provides a potential approach for integrating as-prepared graphene into macromolecular memory devices with excellent performances through a simple solution-process.
Exploring visuospatial thinking in chemistry learning
No full text[[abstract]]In this article, we examine the role of visuospatial cognition in chemistry learning. We review three related kinds of literature: correlational studies of spatial abilities and chemistry learning, students' conceptual errors and difficulties understanding visual representations, and visualization tools that have been designed to help overcome these limitations. On the basis of our review, we conclude that visuospatial abilities and more general reasoning skills are relevant to chemistry learning, some of students' conceptual errors in chemistry are due to difficulties in operating on the internal and external visuospatial representations, and some visualization tools have been effective in helping students overcome the kinds of conceptual errors that may arise through difficulties in using visuospatial representations. To help students understand chemistry concepts and develop representational skills through supporting their visuospatial thinking, we suggest five principles for designing chemistry visualization tools: (1) providing multiple representations and descriptions, (2) making linked referential connections visible, (3) presenting the dynamic and interactive nature of chemistry, (4) promoting the transformation between 2D and 3D, and (5) reducing cognitive load by making information explicit and integrating information for students.