1,720,987 research outputs found
Binding of aromatic isocyanides on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering
No full textThe adsorption structure and binding of phenyl isocyanide (PNC), 2,6-dimethyl phenyl isocyanide (DMPNC), and benzyl isocyanide (BZI) on gold nanoparticle surfaces have been studied by means of surface-enhanced Raman scattering (SERS). PNC, DMPNC, and BZI have been found to adsorb on gold assuming a standing geometry with respect to the surfaces. The presence of the v(CH) band in the SERS spectra denotes a vertical orientation of the phenyl ring of PNC, DMPNC, and BZI on An. The lack of a substantial red shift and significant band broadening of the ring breathing modes implied that a direct ring pi orbital interaction with metal substrates should be quite low. For PNC, the band ascribed to the C-NC stretching vibration was found to almost disappear after adsorption on An. On the other hand, the C-NC band remained quite strong for DMPNC after adsorption. This result suggests a rather bent angle of C-NdropC: for the nitrogen atom of the NC binding group on the surfaces, whereas a linear angle of C-NdropC: should be more favorable on gold surfaces due to an intramolecular steric hindrance of its two methyl groups. SERS of BZI on gold nano-paticles also supports a bent angle of :CdropN-CH2 for its nitrogen atom, suggesting a preference of sp(3) (or sp(2)) hybridization for the nitrogen atom
Grafting nitrilotriacetic groups onto carboxylic acid-terminated self-assembled monolayers on gold surfaces for immobilization of histidine-tagged proteins
No full textIn this paper, we report a common intermediate method to present nitrilotriacetic acid (NTA) groups on gold surfaces for immobilizing His-tagged proteins onto the surfaces, and a full characterization of self-assembled monolayers (SAMs) terminating in carboxylic acids [HS(CH2)(15)COOH (C15-COOH), HS(CH2)(11)(OCH2CH2)(3)-OCH2COOH (EG3-COOH), and HS(CH2)(11)(OCH2CH2)(5)OCH2COOH (EG5-COOH)] and coupling reactions of an NTA-containing primary amine [(1S)-N-(5-amino-l-carboxypentyl)iminodiacetic acid; NTA-NH2] with the carboxylic acid on surfaces. The lateral packing densities of the COOH-terminated SAMs were calculated to be 4.32 (for C15-COOH), 3.49 (for EG3-COOH), and 2.65 (for EG5-COOH) molecules/nm(2). The packing densities were decreased by incorporating a relatively flexible ethylene glycol (EG) group into the backbone of alkanethiols and increasing the number of the EG groups in the backbone of alkanethiols. The NTA group was then attached by coupling NTA-NH2 with the COOH group on the surfaces, followed by a Ni(II) complexation. The coupling reaction was characterized by FT-IR spectroscopy, ellipsometry, and XPS, and the coupling efficiency ("yield") was estimated by comparing the experimentally determined N 1s to S 2p (N/S) ratio of XPS data with the N/S ratio calculated for the functionalization of the SAMs presenting NTANi(II): the coupling yields were 30% (for C15-COOH) and 25% (for EG3-COOH and EG5-COOH). Preliminary experiments on the binding of His-tagged proteins onto the surfaces were also performed
Disorder-order phase change of omega-(N-pyrrolyl) alkanethiol self-assembled monolayers on gold induced by STM scans and thermal activation
Full text linkMolecular ordering of pyrrolyl-terminated alkanethiol self-assembled monolayers (PyC(n)SH SAMs) on Au(111) substrates (n = 11 or 12) was investigated by scanning tunneling microscopy (STM) and various spectroscopic methods. The SAMs, which were in a disordered state when formed at room temperature, could be ordered either globally by thermal annealing at 70 degrees C, or locally via stimulation with repetitive STM scans. The ordered phase was characterized by small domains of molecular rows formed along < 112 > directional set with an inter-row corrugation period close to 1.44 nm, in which defects were abundant. Based on the experimental results, the molecular arrangement in the ordered PyC(n)SH SAM was proposed to be a (5 x root 3)rect structure with a molecular deficiency >= 10%. While mechanical interactions between molecules and scanning probe tips had been pointed out as the major cause of scan-induced phase transformations in other SAM systems, electronic or electrostatic factors were thought to affect considerably the scan-induced ordering process in this SAM system. From comparison of surface molecular coverage between disordered and thermally ordered SAMs of PyC(12)SH, it was inferred that the disorder could be ascribed to both kinetic and thermodynamic factors. The kinetic barrier to the ordered phase was supposed to result from strong dipole-dipole interactions among the pyrrolyl endgroups
Single Electron Charging Effect at Ag Droplets Grown on Sb-terminated Silicon Surface at Room Temperature
No full textLocal inhomogeneity in gate hysteresis of carbon nanotube field-effect transistors investigated by scanning gate microscopy
No full textLocal nature of gate hysteresis in a carbon nanotube field-effect transistor (CNFET) was Studied using scanning gate microscopy (SGM). A sequential set of SGM images of the CNFET fabricated on a SiO2/Si Substrate was obtained at a low temperature under all Ultra-high vacuum. Comparisons of the SGM images obtained at decreasing and increasing gate voltage steps revealed that the order of appearance of SGM defects could not be accounted for by a Uniform distribution of hysteretic gate screening along the carbon nanotube (CNT) channel. It was concluded that the gate hysteresis in the CNFET had Substantial local variations along the CNT. The local inhomogeneity in gate hysteresis was attributed to inhomogeneous distribution of screening charge traps or sources on the SiO2 surface. (C) 2008 Elsevier B.V. All rights reserved
Surface-initiated, enzymatic polymerization of biodegradable polyesters
No full textEnzyme-catalyzed, ring-opening polymerization of biodegradable aliphatic polyesters has successfully been applied to surface-initiated polymerization (see Figure). Using lipase B as a catalyst, a thin film of poly (epsilon-caprolactone) (PCL) and poly(p-dioxanone) (PPDX) on a gold substrate (after a formation of self-assembled monolayers terminating in hydroxyl groups) is formed
Temperature-induced control of aspect ratio of gold nanorods
No full textAspect ratio of gold nanorods can be controlled by simply adjusting the reaction temperature in the seed-mediated synthesis of the nanorods. The gold nanorods were synthesized by the injection of gold nanoparticle seeds of around 4 nm in diameter into a reaction mixture containing hydrogen tetrachloroaurate, hexadecyltrimethylammonium bromide, and ascorbic acid. Average aspect ratio of the resulting nanorod increases from 1 to about 40 with decreasing the reaction temperature from 315 to 276 K, which can be attributed to the temperature-induced change in the shape of the micellar templates. For further understanding of the growth mechanism, silver nanoparticles were also used as seeds in the preparation of the gold nanorod. (c) 2006 American Vacuum Society
Origin of gate hysteresis in carbon nanotube field-effect transistors
No full textWe have studied gate hysteresis of carbon nanotube field-effect transistors (CNFETs) on silicon oxide substrates in an ultrahigh vacuum (UHV) at low temperatures. It is found that the hysteresis is neither reduced by thermal annealing at temperatures over 300 C under UHV nor significantly affected by independent adsorption of ammonia or water at T = 56 K. However, the hysteresis decreases greatly upon coadsorption of water and ammonia below condensation temperatures and restores completely with desorption of the adsorbed water layer. On the basis of these results, it is concluded that the main cause of gate hysteresis in CNFETs on silicon oxide substrate is charge transfer between the carbon nanotube and charge traps at the silicon oxide/ambient interface. We propose a mechanism for gate hysteresis that involves surface silanol groups as the major sources of screening charges. This surface silanol model is supported by results from scanning surface potential microscopy (SSPM)
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