Surface Diffusion Of Ag Atoms Research Articles

Ultrathin and dense Ag nanosheets synthesis under suppressed face (111) growth and surface diffusion

Ultrathin and dense Ag nanosheets (ANS) with large electrochemically active surface area and rich edge active sites over Ag foils are synthesized via a facile electrodeposition approach in a double electrode system. By adjusting the concentration of H3BO3 and changing deposition temperature, ANS with varying thickness are fabricated. Interestingly, ANS gradually become thinner with H3BO3 concentration increasing, as BO33- ions preferentially adsorb on the Ag (111) faces, thereby inhibit the growth of Ag on the (111) faces. Furthermore, the morphologies and dimensions of ANS are also found to strongly depend on the deposition temperature. Thinner and denser ANS are more easily obtained at low deposition temperature as it can suppress the surface diffusion of Ag atoms, while when the deposition temperature is high, thinner and denser ANS can only be obtained at high H3BO3 concentration. Especially, ANS fabricated with 0.5 M H3BO3 at 0 °C (ANS-0.5M-0°C) with an ultrathin thickness of about 11 nm exhibits a remarkable CO Faradaic efficiency of 97.11% and the total current density of −11.50 mA cm−2 at −0.9 V vs. the reversible hydrogen electrode towards CO2 electroreduction.

Controlled formation of intense hot spots in Pd@Ag core-shell nanooctapods for efficient photothermal conversion

Plasmonic Ag nanostructures have been of great interest for such applications in cancer therapy and catalysis, etc. However, the relatively week Ag-Ag interaction and spontaneous atom diffusion make it very difficult to generate concaved or branched structures in Ag nanocrystals with sizes less than 100 nm, which has been considered very favorable for plasmonic effects. Herein, by employing a cubic Pd seed and a specific reducing agent to restrict the surface diffusion of Ag atoms, Pd@Ag core-shell nanooctapod structures where Ag atoms can be selectively deposited onto the corner sites of the Pd cubes were obtained. Such selective decoration enables us to precisely control the locations for the hot spot formation during light irradiation. We find that the branched nanooctapod structure shows strong absorption in the visible-light region and generates intense hot spots around the octapod arms of Ag. As such, the photothermal conversion efficiency could be significantly improved by more than 50% with a colloid solution containing only ppm-level nanooctapods compared with pure water. The reported nanostructure is expected to find extensive applications due to its controlled formation of light-induced hot spots at certain points on the crystal surface.

Optimization of Surface Layers for Suppression of Agglomeration in Ag Films

We previously reported that Al, Ti, and Nb surface layers can effectively suppress agglomeration in Ag films, which is dominated by the surface diffusion of Ag atoms. In this study, Ag films with Pd, Ni, and W surface layers were prepared by RF magnetron sputtering, and the properties of these films were compared with previous observations of the effects of Ti and Nb surface layers. The most important properties of the appropriate surface layers for the suppression of agglomeration in Ag films are a high cohesive energy or a high Gibbs free energy of formation of the oxide, and a low solid solubility in Ag.

Effect of Added Metallic Elements in Ag Alloys on the Durability against Heat and Humidity of Indium Zinc Oxide/Ag Alloy/Indium Zinc Oxide Transparent Conductive Multilayer System

We studied the effects of added metallic elements in the Ag alloy layers of the indium zinc oxide (IZO)/Ag alloy/IZO transparent conductive multilayer system on the optical and electrical properties of the multilayer. The correlation between the thickness of the Ag alloy layers and the optical and electrical properties of the multilayer was also investigated. The transmittance and sheet resistance were estimated from the optical constants and specific resistivities of Ag alloy and IZO, and then compared with the experimentally measured values. A high transmittance of 95.3% at a 550 nm wavelength and a low sheet resistance of 4.3 Ω/□ were achieved from the IZO (40 nm)/Ag (15 nm)/IZO (40 nm) multilayer. The effect of added metallic elements in the Ag alloy layers of the multilayer on the durability against heat and humidity was also investigated. The durability against heat was improved by the added metallic elements in the Ag alloy layers of the IZO/Ag/IZO multilayer system. When Ag film was heat-treated, agglomeration occurred owing to the surface diffusion of Ag atoms. The added metallic elements such as Pd, Cu, and Au increased the onset temperature and the activation energy for agglomeration. The optical and electrical properties of the IZO/Ag/IZO multilayer markedly deteriorated after the humidity test at 85 °C–85% relative humidity (RH) in air. The degradation of Ag alloy layer was due to the combined effect of heat, water vapor, and sulfur in air. However the deterioration did not occur in the IZO/Ag alloy/IZO multilayer with a AgAu layer after the humidity test. The IZO/Ag alloy/IZO multilayer with the AgAu layer containing 10 wt % Au especially exhibited superior characteristics with a high transmittance of 93.5% at a 550 nm wavelength and a low sheet resistance of 6.3 Ω/□ after the humidity test at 85 °C–85% RH in air for 720 h.

Effects of Ni cladding layers on suppression of Ag agglomeration in Ag-based Ohmic contacts on p-GaN

We investigate effects of Ni cladding layers on suppression of Ag agglomeration in Ag contacts on p-GaN using high-resolution x-ray diffraction. In the annealed Ag contact, Ag (100) grains disappear and agglomerate to form a selectively epitaxial growth of Ag (111). An ultrathin Ni contact layer (10 Å) below Ag film plays a role to epitaxially grow (111) Ag films on GaN, leading to the suppression of Ag agglomeration. A 20-Å-thick Ni overlayer effectively acts as a passivation layer to prevent the surface diffusion of Ag atoms during annealing, leading to high light reflectance and low contact resistivity.

Self-encapsulation effects on the electromigration resistance of silver lines

Silver, the most conductive room-temperature material, has drawn attention as a potential interconnect replacement material. In this study, Ag lines were self-encapsulated by annealing a Ag/Ti/SiO 2/Si structure in a flowing NH 3 ambient. The microstructure of this structure after the anneal was studied by the use of cross-section transmission electron microscopy (XTEM). Upon the anneal, the Ag surface was encapsulated by a TiN(O) layer, and a bilayer formed at the initial Ti/SiO 2 interface. Electromigration testing shows that the self-encapsulation process improved the electromigration resistance of the Ag lines substantially by inhibition of the surface diffusion of Ag atoms.

Enhancement of Ag electromigration resistance by a novel encapsulation process

The Ag lines on Ti/SiO 2/Si stack structures were fabricated by using conventional photolithography and a reactive ion etch (RIE) in an O 2 plasma, and subsequently encapsulated by annealing in a flowing NH 3 ambient. A thin TiN(O) layer formed at the Ag surface and a Ti(O)/Ti 5Si 3 bilayer formed at the initial Ti/SiO 2 interface. Electromigration testing was performed on both bare and encapsulated Ag lines. A partial depletion region in the near-cathode segment and its drift towards the anode were observed at the early stage for the bare Ag test lines. Afterwards, the side-by-side distribution of clusters of voids and hillocks was also noted in other segments. After the encapsulation process, the electromigration resistance of the Ag lines was significantly improved due to the inhibition of the surface diffusion of Ag atoms by the encapsulation layer. This encapsulation process was also expected to address some other issues associated with the applications of the Ag metallization in advanced integrated circuits.

Initial stage of Ag epitaxial growth on Sb-terminated Si(111) surface

In the initial stage of Ag film growth on the Sb-terminated Si(111) surface, we have found that the surface diffusion of Ag atoms was greatly suppressed, thereby producing atomically uniform epitaxial Ag films. It was also found that the crystallographic direction of the grown Ag islands matched well with that of the substrate. The aspect ratios (height-to-diameter) of the Ag islands did not increase noticeably even after thermal annealing, which is quite different to the case of Ag growth on clean Si(111). The effects of the thermally stable Sb-terminated Si(111) surface and Sb segregation on Ag islands on the formation of atomically uniform Ag films are also discussed.

Uniform Ag Thin Film Growth on an Sb-terminated Si(111) Surface

We report on the room-temperature-growth of highly uniform and ultrathin Ag films on Sb-terminated Si(111) surfaces, as evidenced from a scanning tunneling microscopy (STM) study in an UHV system. With predeposition of one monolayer (ML) of Sb, uniform growth of Ag islands was observed at room temperature. The Sb layer suppresses the surface diffusion of Ag atoms on Si surface and increases the Ag island density, and then the increased island density is believed to cause coalescence of Ag islands before the beginning of multilayer growth in higher coverages, resulting in the growth of atomically flat and uniform islands on the Sb surfactant layer.

Structural transformation of hydrogen-adsorbed Si(111)-√3×√3-Ag surfaces induced by electron-stimulated desorption

Atomic hydrogen irradiated Si(111)-√3×√3-Ag surfaces, which involve nanometer size Ag clusters and hydrogen terminated regions, are studied by combined surface analysis with ultrahigh-vacuum scanning electron microscopy (UHV-SEM), scanning reflection electron microscopy (SREM), microprobe reflection high-energy electron diffration (μ-RHEED) and Auger electron spectroscopy (AES). Electron beam irradiation onto this surface results in disappearance of the Ag clusters, and subsequent low-temperature annealing at 275°C transforms the surface to the original √3×√3-Ag structure. Hydrogen removal from the Si surface induced by electron-stimulated desorption (ESD) and surface diffusion of Ag atoms on the bare regions by low-temperature annealing explain this structural transformation.

Ag growth on Si(111) with an Sb surfactant investigated by scanning tunneling microscopy

We have investigated a room-temperature growth mode of ultrathin Ag films on a Si(111) surface with an Sb surfactant using STM in a UHV system. On the Sb-passivated Si surface, small sized islands were formed up to 1.1 ML. Flat Ag islands were dominant at 2.1 ML, coalescing into larger islands at 3.2 ML. Although the initial growth mode of Ag films on the Sb-terminated Si(111) surface was Volmer-Weber (island growth), the films were much more uniform than Ag growth on clean (Si(111) at the higher coverages. From the analysis of STM images of Ag films grown with and without an Sb surfactant, the uniform growth of Ag films using an Sb surfactant appears to be caused by the kinetic effects of Ag on the preadsorbed Sb layer. Our STM results indicated that Sb suppresses the surface diffusion of Ag atoms and increases the Ag-island density. The increased island density is believed to cause coalescence of Ag islands at higher coverages of Ag, resulting in the growth of atomically flat and uniform Ag islands on the Sb surfactant layer.