Electron beam induced deposition of silicon nanostructures from a liquid phase precursor

This work demonstrates electron beam induced deposition of silicon from a SiCl(4) liquid precursor in a transmission electron microscope and a scanning electron microscope. Silicon nanodots of tunable size are reproducibly grown in controlled geometries. The volume of these features increases linearly with deposition time. The results indicate that secondary electrons generated at the substrate surface serve as the primary source of silicon reduction. However, at high current densities the influence of the primary electrons is observed to retard growth. The results demonstrate a new approach to fabricating silicon nanostructures and provide fundamental insights into the mechanism for liquid phase electron beam induced deposition.     

Self-fluorescence of chemically crosslinked MRI nanoprobes to enable multimodal imaging of therapeutic cells

Old chemistry for novel materials: Self-fluorescent high-relaxivity T(2)-weighted magnetic resonance imaging (MRI) contrast agents are produced. They are a novel type of MR/optical dual-modality in vivo imaging nanoprobe using glutaraldehyde crosslinking chemistry, and they are used to label and monitor therapeutic cells both in vitro and in vivo.     

Fabrication of nano silica dispersed permalloy composite coating

In aqueous solution, the agglomeration of silica nanopowder is a major problem which causes poor uniformity of electroplated surfaces. Silica surface is susceptible to moisture due to the hydroxyl group on its surface which causes the silica nanopowder to become agglomerated. In this study, silica nanoparticle dispersion in the electroplated layer is reported. From zeta potential analysis, silica nanopowder has a negatively charged surface in an alkaline bath. Silica nanopowder is less agglomerated in an alkaline bath than in an acidic bath due to the surface charge. Additives change the surface morphologies of the electroplated layer as well as the silica nanopowder contents. Comparing an alkaline bath and an acidic bath, the advantage of an additive to the electroplated layer is only observed in an alkaline bath. Types of sonicators and sonication periods are also surveyed for silica nanopowder dispersion. Sonication time can be reduced by a horn-type sonicator, and longer sonication time guaranteed better silica nanopowder dispersion.     

Electrochemical migration characteristics of screen-printed silver patterns on FR-4 substrate

We evaluated the electrical reliability of screen-printed silver (Ag) patterns sintered at various temperatures under variable bias voltages. Comb-type patterns were screen-printed onto a flame resistance-4 substrate using a commercial Ag nanopaste (24 nm in diameter, 73 wt% of Ag nanoparticles). The printed patterns were then sintered for 30 min in air at various temperatures ranging from 100 degrees C to 200 degrees C. The microstructures and thickness profiles of the sintered conductive patterns were identified with a field emission scanning electron microscope and a 3-D surface profiler, respectively. In this study, the phenomenon of electrochemical migration was investigated with a water drop test with deionized water. These results showed that the time required by dendrites to bridge from a cathode to an anode was affected by the sintering temperature and applied voltage; when the sintering temperature was 200 degrees C, the time to achieve a short circuit was nearly four times that of the sample sintered at 100 degrees C, and while the applied voltage increased from 3 V to 9 V, the time to reach a short circuit decreased, on average, by 11%.     

Antibacterial activity and increased freeze-drying stability of sialyllactose-reduced silver nanoparticles using sucrose and trehalose

The resistance to current antibiotics results in the emergence of health-threatening bacteria. Silver nanoparticles are known to exhibit broad-spectrum antibacterial activities without the development of resistance. Herein, we developed a green synthetic method for the preparation of silver nanoparticles with sialyllactose instead of toxic chemicals as a reducing agent, which would improve its therapeutic applicability and increase its biocompatibility. Oven incubation, autoclaving and microwave irradiation methods were applied to prepare the silver nanoparticles. High resolution-transmission electron microscopy and atomic force microscopy images revealed mostly spherical and amorphous silver nanoparticles with an average diameter of 23.64 nm. Fourier Transform-infrared spectra suggest that the N-H amide of sialyllactose might be involved in the binding of silver nanoparticles. Based on thermogravimetric analyses, 2,3-sialyllactose-reduced silver nanoparticles are composed of 54.3 wt% organic components and 45.7 wt% metallic silver. Enhanced antibacterial activities of silver nanoparticles (approximately 8-fold) were observed against Pseudomonas aeruginosa, Escherichia coli and Salmonella typhimurium (minimum inhibitory concentration 16 microg/mL). Next, we employed the use of carbohydrate stabilizers to increase the stability of silver nanoparticles during a freeze-drying process. It was found that sucrose and trehalose were the most effective stabilizers. In addition, silver nanoparticles possessed excellent salt stability as well as on-the-shelf stability in the presence of these stabilizers. Derivatives of sialic acid are known to be anti-influenza agents; therefore, the newly prepared silver nanoparticles may serve as useful antibacterial and antiviral agents to cope with both pathogenic bacteria and viruses in the near future.     

Fabrication and photovoltaic properties of heterostructured TiO2 nanowires

One-dimensional heterostructured TiO2 nanowires were successfully fabricated by an electrospinning technique and modified by hydrolysis. We investigated their structure, morphology, chemical composition, and optical properties by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy. In the case of the photovoltaic performance, the short-circuit current density and cell efficiency of the DSSCs employing single TiO2 nanowires and heterostructured TiO2 nanowires improve from 6.90 to 11.38 mA/cm2 and from 2.56 to 4.29%, respectively. The results show that the photoconversion efficiency of the heterostructured TiO2 nanowires could be improved by more than approximately 67% compared to that of the single TiO2 nanowires because of the enhanced specific surface area that facilitates dye adsorption.     

Control of magnetic domains in Co/Pd multilayered nanowires with perpendicular magnetic anisotropy

Magnetic domain wall (DW) motion induced by spin transfer torque in magnetic nanowires is of emerging technological interest for its possible applications in spintronic memory or logic devices. Co/Pd multilayered magnetic nanowires with perpendicular magnetic anisotropy were fabricated on the surfaces of Si wafers by ion-beam sputtering. The nanowires had different sized widths and pinning sites formed by an anodic oxidation method via scanning probe microscopy (SPM) with an MFM tip. The magnetic domain structure was changed by an anodic oxidation method. To discover the current-induced DW motion in the Co/Pd nanowires, we employed micromagnetic modeling based on the Landau-Lifschitz-Gilbert (LLG) equation. The split DW motions and configurations due to the edge effects of pinning site and nanowire appeared.     

Effect of curing temperature on nano-silver paste ink for organic thin-film transistors

Silver (Ag) metal electrode having 20 microm channel length was printed by reverse offset printing (ROP) using nano-silver paste ink for the source/drain of organic thin-film transistors (OTFT). Specific resistance and surface roughness of printed Ag electrodes with increasing curing temperature were investigated, and surface morphology and grain growth mechanism were systematically verified using a scanning electron microscope (SEM) and atomic force microscope (AFM) in order to obtain an optimized ROP Ag electrode. The Ag electrode was applied to fabricate top-gate/bottom-contact poly(3-hexylthiophene) OTFT devices, which showed reproducible OTFT characteristics such as the field-effect mobility, threshold voltage, and an on/off-current ratio of -10(-3) cm2/Vs, 0.36 V, and -10(2), respectively.     

Unique ordered domains of biphenylthiol self-assembled monolayers on Au(111)

The surface structure and adsorption conditions of biphenylthiol (BPT) self-assembled monolayers (SAMs) on Au(111) were examined using scanning tunneling microscopy (STM) and X-ray photoelectron microscopy (XPS). STM imaging revealed that the structural order of BPT SAMs formed in a 0.01 mM ethanol solution at 60 degrees C decreases with increasing immersion time. Interestingly, BPT SAMs formed after 30 min have unique ordered domains containing well-ordered (square root of 3 x square root of 3)R30 degrees structures and bright rows that are connected by small aggregated domains with a periodicity of approximately 10 angstroms, results that have never been observed for other thiol SAM systems. Distances between the bright rows were 20-35 angstroms. The bright small domains contained five or six BPT molecules each, which may have originated from differences in the adsorption orientations of biphenyl groups that were induced by localized interactions between them. XPS measurements for BPT SAMs on Au(111) showed the two sulfur peaks at 161.2 and 162.2 eV, implying the formation of chemisorbed monolayers. Our results are anticipated to be useful for understanding the formation and structure of BPT SAMs on gold surfaces.