Vapor Deposition Of Ag Research Articles

Selective noble-metal deposition modulation on photocurable polydimethylsiloxane films for electronics device applications

Selective metal-vapor deposition on organic surfaces is an interesting phenomenon and is applicable to prepare fine metal patterns for various electronic and photonic devices based on vacuum evaporation without a shadow mask. However, selective metal-vapor deposition with photochromic diarylethenes has not been successful for noble metals such as Au, Ag and Cu, which are generally used in the electronics field. In this paper, we report deposition modulation of noble-metal vapor on a photocurable polydimethylsiloxane (PDMS) film. When Au, Ag or Cu was vacuum-deposited on the UV-curable PDMS, Au and Cu formed a film on the surface even on the uncured film. Ag, however, was desorbed from the uncured film, and a small amount of evaporated Ag atoms was absorbed into the film. This metal species dependence on metal-deposition/desorption tendency was correlated with the intrinsic vapor pressure of metal species; metals with a high vapor pressure tend to desorb. The uncured film with a small amount of Ag deposition was easily removed with a hexane rinse, leaving only Ag on the cured film. Using this principle, various Ag-film patterns were prepared by irradiating upon UV light with a photomask to form a cured pattern and using maskless Ag deposition. Furthermore, we succeeded in fabrication of fine Ag patterns with a width of several micron by UV-laser scanning and maskless Ag-vapor deposition. This method would be applied to the electrode/wiring for various electronic devices.

Solvent-free silver-nanoparticle surface-assisted laser desorption/ionization imaging mass spectrometry of the Irganox 1010 coated on polystyrene

Imaging mass spectrometry (IMS) of the antioxidant Irganox 1010 coated on a polystyrene (PS) was conducted using solvent-free silver-nanoparticle surface-assisted laser desorption/ionization (Ag-NP SALDI). The lateral resolution and probing depth of Ag-NP SALDI-IMS, which are important factors in determining the surface sensitivity, were investigated. Direct Ag vapor deposition produced a 10-nm-thick homogenous layer of Ag-NPs on the Irganox 1010/PS thin film. Ag adduct ions of Irganox 1010 and PS repeating structures, and Ag cluster ions appeared in the mass spectrum, which showed that Ag-NPs on the sample surface enhanced the ionization efficiency by functioning as cationization agents. At the lateral resolution of this method (20μm), complementary grid patterns (55 lines per inch) of Irganox 1010 on the PS were observed. The probing depth was investigated with Irganox 1010 layers of different thicknesses, the detection of silver adduct ions of PS indicated Ag-NP SALDI could ionize the PS layer beyond the Irganox 1010 layer. The probing depth was 50–100nm for 10-nm-thick Ag-NP SALDI.

Signature Vibrational Bands for Defects in CVD Single-Layer Graphene by Surface-Enhanced Raman Spectroscopy.

We report the observation of signature vibrational bands in the frequency region between 900 and 1600 cm(-1) for defects in single-layer graphene (SLG) using surface Raman spectroscopy in ultrahigh vacuum. Vapor deposition of Ag leads to the formation of surface nanoparticles that migrate to defects in the SLG, leading to surface-enhanced Raman scattering (SERS) of the graphene G and 2D bands as well as new vibrational modes ascribed to native defects. Many of the new spectral bands of these native defects are similar, although not identical, to those predicted previously for -C2 defects. These new bands are observed in addition to bands more commonly observed for defective graphene that are attributed to the D, G*, D+G, and 2D' modes. The defects observed in these SLG films are not believed to result from the Ag deposition process but are postulated to be formed during the graphene CVD growth process. These defects are then made visible by postdeposition of Ag due to SERS.

Silver Nanoparticles on Fe3O4(111): Energetics by Ag Adsorption Calorimetry and Structure by Surface Spectroscopies

The heat of adsorption of Ag atoms and the growth morphology of the resulting silver particles on the Fe3O4(111) surface at 300 K were studied by adsorption microcalorimetry, Auger electron spectroscopy (AES), and low energy ion scattering spectroscopy (LEIS). Thin films (∼6 nm thick) of Fe3O4(111) were grown on a Pt(111) single crystal. The changes in AES and LEIS signals versus Ag coverage during Ag vapor deposition onto Fe3O4(111) were indicative of Ag growing as 3D particles with a fixed density of ∼4 × 1012 particles/cm2. The heat of Ag adsorption increased with Ag coverage from ∼230 kJ/mol initially up to within a few percent of the heat of sublimation of bulk Ag (285 kJ/mol) by ∼2 ML Ag. This corresponds to an increase in Ag atom stability (decrease in chemical potential) by ∼55 kJ/mol as the Ag particle size grows from <1 to ∼4 nm effective diameter on Fe3O4(111). The Ag(solid)/Fe3O4(111) adhesion energy for the 4 nm particles was estimated from the integral heat of adsorption to be 2.5 ± 0.3 J/m2...

Deciphering the Metal-C60 Interface in Optoelectronic Devices: Evidence for C60 Reduction by Vapor Deposited Al

The formation of interfacial midgap states due to the reduction of buckminsterfullerene (C60) to amorphous carbon upon subsequent vapor deposition of Al is confirmed using Raman spectroscopy and X-ray, ultraviolet, and inverse photoemission spectroscopies. We demonstrate that vapor deposition of Al results in n-type doping of C60 due to an electron transfer from Al to the LUMO of C60, resulting in the formation of midgap states near the C60 Fermi level. Raman spectroscopy in ultrahigh vacuum clearly identifies the presence of the C60 anion radical (C60(•-)) as well as amorphous carbon created by further degradation of C60(•-). In contrast, the interface formed by vapor deposition of Ag shows only a slight Ag/C60 interfacial charge displacement with no evidence for complete metal-to-C60 electron transfer to form the anion radical or its further degradation products. These results confirm previous speculations of metal-induced chemical damage of C60 films after Al deposition, which is widely suspected of decreasing charge collection efficiency in OPVs, and provide key insight into charge collection at metal/organic interfaces in such devices.

Shape Control of Ag Nanostructures for Practical SERS Substrates

Large-area, highly ordered, Ag-nanostructured arrays with various geometrical features were prepared for use as surface-enhanced Raman scattering (SERS)-active substrates by the self-assembly of inorganic particles on an SU-8 surface, followed by particle embedding and Ag vapor deposition. By adjusting the embedding time of the inorganic particles, the size of the Ag nanogap between the geometrically separated hole arrays and bowl-shaped arrays could be controlled in the range of 60 nm to 190 nm. More importantly, the SU-8 surface was covered with hexagonally ordered nanopillars, which were formed as a result of isotropic dry etching of the interstices, leading to triangular-shaped Ag plates on nanopillar arrays after Ag vapor deposition. The size and sharpness of the triangular Ag nanoplates and nanoscale roughness of the bottom surface were adjusted by controlling the etching time. The potential of the various Ag nanostructures for use as practical SERS substrates was verified by the detection of a low concentration of benzenethiol. Finite-difference time-domain (FDTD) methodology was used to demonstrate the SERS-activities of these highly controllable substrates by calculating the electric field intensity distribution on the metallic nanostructures. These substrates, with high sensitivity and simple shape-controllability, provide a practical SERS-based sensing platform.

Molecular dynamics study of interfaces in solids

The interfaces of heterostructures were studied in the framework of molecular dynamics to reveal a periodic interface stress distribution on the micro scale. The calculations were performed for copper and silver and for two different types of heterostructures: a heterostructure consisting of perfect Cu and Ag crystals and a heterostructure formed by Ag vapor deposition on a perfect Cu substrate. The calculation results allowed several conclusions about the origin of a chessboard interface structure and about certain mechanisms of its modification depending on the nanostructure size, boundary conditions, and method of heterostructure formation.

Investigation of the Interfaces of Tris-(8-hydroxyquinoline) Aluminum with Ag and Al Using Surface Raman Spectroscopy

Surface Raman spectroscopy in ultrahigh vacuum is used to interrogate interfaces formed between tris-(8-hydroxyquinoline) aluminum (Alq3) and vapor-deposited Ag and Al. Vapor deposition of Ag onto Alq3 films results in preservation of the Alq3 structure with evolution of simple surface enhancement of Alq3 spectral intensities. Changes in the relative intensities of ring breathing and ring stretching modes of Alq3 upon deposition of Ag are consistent with weak interaction of Ag with the conjugated ring of the ligand. In contrast, vapor deposition of Al onto Alq3 films results in the appearance of new vibrational modes, but only for Al coverages >10 A mass thickness, consistent with the formation of an Al−Alq3 adduct. At these coverages, slight surface enhancement of spectral intensities is also observed along with growth of several broad modes consistent with partial graphitization of the organic film.

Structure and shape transformation from multiply twinned particles to epitaxial nanocrystals: Importance of interface on the structure of Ag nanoparticles

The effect of a substrate on the structure of nanometer-sized metal particles was investigated for Ag on silicon surfaces by using high-resolution transmission electron microscope and electron diffraction. The nanometer-sized Ag particles, formed by the vapor deposition of Ag on (001) hydrogen-terminated Si (H-Si) surfaces at room temperature, adopt multiply twinned structures. Upon annealing, the multiply twinned Ag nanoparticles on H-Si (001) transform into fcc nanocrystals. The fcc Ag takes up the cube-on-cube epitaxy, with the orientation relationship of $\mathrm{Ag}(001)\text{∕∕}\mathrm{Si}(001)$ and $\mathrm{Ag}\phantom{\rule{0.3em}{0ex}}[110]\text{∕∕}\mathrm{Si}\phantom{\rule{0.3em}{0ex}}[110]$. An energetic model is developed to account for the structure and shape transition of supported multiply twinned particles to fcc epitaxial nanocrystals. Possible transition mechanisms are discussed.

XPS investigations on the interactions of 1,6-hexanedithiol/Au(1 1 1) layers with metallic and ionic silver species

Abstract Surfaces of densely packed aliphatic (di)thiol/gold self-assembled monolayers (SAMs) with one thiolate–gold bond per molecule are prepared and used as models for functionalized polymer/metal interfaces. In detail, the penetration of metallic or ionic silver species through 1-hexanethiol/Au(1 1 1) and 1,6-hexanedithiol/Au(1 1 1) layers is investigated with X-ray photoelectron spectroscopy (XPS). These organic films are readily penetrated by silver species as well during Ag vapor deposition as during immersion in silver sulfate solution. As a driving force for the layer penetration strong Ag–thiolate interactions are discussed. Experimental proof for such bonding is provided by several findings. Ag–thiolate bond fission is observed to occur at higher temperatures than Au–thiolate decomposition. Furthermore, the deposition of metallic silver via UHV evaporation reveals the formation of Ag–thiolates at the SAM surface in the case of 1,6-hexanedithiol/Au(1 1 1) SAMs. Finally, the characterization of the dithiol/gold system indicates the chemisorption of hydrated Ag+ ions at the interface between the SAM and a silver sulfate electrolyte.

Sers-Active Ag Films from Photoreduction of Ag+ on TiO2

Because of the tremendous information content, single-molecule detection with a vibrational spectroscopic technique is a goal well worth pursuing. The vibrational technique most suitable for single-molecule detection is surface-enhanced Raman spectroscopy (SERS). For example, Kneipp et al. recently demonstrated detection of 100 molecules of rhodamine 6G using surface-enhanced resonance Raman. Van Duyne and co-workers have recently detected just 10 molecules of pyridine using SERS and Raman microscopy. The key to sensitive detection using SERS lies in optimization of the enhancing surface. For excitation with easily accessible wavelengths, as well as ease of preparation and nearly ideal surface characteristics, Ag is often the metal of choice. SERS-active Ag has been prepared in a variety of ways, such as Ag colloids, vapor-deposited thin films, electrochemically roughened electrodes, nitric-acid-etched foils, thin films from the Tollens reaction, lithographically produced islands on Si posts, and, recently, vapor-deposition of Ag over a monolayer (or double layer) of nanospheres, followed by removal of the nanospheres. Each of the methods mentioned for the generation of SERS-active surfaces has advantages and limitations; i.e., there is still room for improvement and optimization of SERS-active surfaces.

Processing dependence of the interfacial microstructure of Ag contacts to YBa2Cu3O7−δ thin films

The interfacial microstructure of three differently prepared silver contacts on c-axis oriented YBa2Cu3O7−δ (YBCO) thin films was examined using high-resolution transmission electron microscopy (HRTEM). For contacts prepared in situ by Ag sputter deposition on films maintained at elevated temperature and ex situ by Ag vapor deposition on films annealed in ultrahigh vacuum prior to metallization, regions of atomically sharp YBCO(001)/Ag interfaces were observed. In contrast, the cross-section HRTEM images of contacts prepared by in situ Ag deposition at room temperature reveal an amorphous interfacial zone, typically 20 Å thick. Scattered Y2O3 precipitates are found at the YBCO surface of all three contacts. The data suggest that intrinsic reactions between Ag and YBCO(001) are negligible, and that the amorphous interface layer for in situ contacts to cold films must be ascribed to reactions with gaseous impurities in the sputter chamber ambient. In conclusion, we strongly emphasize the importance of using ultrahigh purity process gases in order to avoid formation of a resistive interfacial barrier.

Surface-enhanced raman scattering on silver-coated teflon sphere substrates

A simple experimental method for detecting organic species adsorbed on surfaces by surface-enhanced Raman scattering (SERS) is described. The rough silver surfaces were obtained by vapor deposition of Ag on teflon spheres of uniform size and shape on glass substrates. The spectra obtained from adsorbed phthalic acid, benzoic acid, and nitrobenzoic acid excited by the 514.5 nm substrates. The spectra obtained from adsorbed phthalic acid, benzoic acid, and nitrobenzoic acid these bands were not present and characteristic line spectra were obtained. The reproducibility of the method due to the well-defined roughness of the substrate constitutes a good tool by which theory can be tested.