Plasma-Enhanced Atomic Layer Deposition of Nanostructured Gold Near Room Temperature

ALD and CVD deposition of pure thin gold films from a stable dimethylgold(III) precursor

The synthesis and thermal properties of a volatile dimethylgold(III) complex Me2AuSSP(OiPr)2 are reported. Unlike most other volatile Au(I) and Au(III) compounds, the complex is stable upon storage, does not require any special handling conditions, and exhibits both good volatility and thermal stability. The compound was tested as a CVD and ALD precursor, yielding good quality films in both processes. The influence of hydrogen and vacuum ultraviolet on the morphology and composition of the gold films in CVD processes was investigated. The growth rate in ALD experiments was from 0.47 to 1.13 Å per cycle at deposition temperatures of 130-170 °C. Both CVD and ALD grown films exhibited a polycrystalline structure, a high conductivity (3.1-55.7 μΩ cm) and a low amount of impurities (<6 at%).

State of the art of ultra-thin gold layers: formation fundamentals and applications

Fabrication of ultra-thin gold (Au) layers (UTGLs) has been regarded as the key technique to achieve applications with tunable optical response, flexible sensors and electronic devices. Various strategies have been developed to optimize the wetting process of Au, resulting in the formation of UTGLs at a minimum thickness. The related studies on UTGLs attracted huge attention in recent years. On the one hand, the growth processes of UTGLs on different substrates were in-depth probed by advanced in situ characterization techniques and the effects of optimization strategies on the growth of UTGLs were also revealed. On the other hand, based on the understanding of the growth behavior and the assistance of optimization strategies, various applications of UTGLs were realized based on optical/plasmon responses, surface-enhanced Raman scattering and as electrodes for various sensors and electronic devices, as well as being seed layers for thin film growth. In this focused review, both the fundamental and practical studies on UTGLs in the most recent years are elaborated in detail. The growth processes of UTGLs revealed by in situ characterization techniques, such as grazing-incidence small-angle X-ray scattering (GISAXS), as well as the state of the art of UTGL-based applications, are reviewed.

Critical Aspects of Various Techniques for Synthesizing Metal Oxides and Fabricating Their Composite-Based Supercapacitor Electrodes: A Review

Supercapacitors (SCs) have attracted attention as an important energy source for various applications owing to their high power outputs and outstanding energy densities. The electrochemical performance of an SC device is predominantly determined by electrode materials, and thus, the selection and synthesis of the materials are crucial. Metal oxides (MOs) and their composites are the most widely used pseudocapacitive SC electrode materials. The basic requirements for fabricating high-performance SC electrodes include synthesizing and/or chemically modifying unique conducting nanostructures, optimizing a heterostructure morphology, and generating large-surface-area electroactive sites, all of which predominantly rely on various techniques used for synthesizing MO materials and fabricating MO- and MO-composite-based SC electrodes. Therefore, an SC’s background and critical aspects, the challenges associated with the predominant synthesis techniques (including hydrothermal and microwave-assisted syntheses and chemical-bath and atomic-layer depositions), and resulting electrode electrochemical performances should be summarized in a convenient, accessible report to accelerate the development of materials for industrial SC applications. Therefore, we reviewed the most pertinent studies on these synthesis techniques to provide insight into the most recent advances in synthesizing MOs and fabricating their composite-based SC electrodes as well as to propose research directions for developing MO-based electrodes for applications to next-generation SCs.

Gold-induced photothermal background in on-chip surface enhanced stimulated Raman spectroscopy

Surface enhanced Raman spectroscopy (SERS) and stimulated Raman spectroscopy (SRS) are well established techniques capable of boosting the strength of Raman scattering. The combination of both techniques (surface enhanced stimulated Raman spectroscopy, or SE-SRS) has been reported using plasmonic nanoparticles. In parallel, waveguide enhanced Raman spectroscopy has been developed using nanophotonic and nanoplasmonic waveguides. Here, we explore SE-SRS in nanoplasmonic waveguides. We demonstrate that a combined photothermal and thermo-optic effect in the gold material induces a strong background signal that limits the detection limit for the analyte. The experimental results are in line with theoretical estimates. We propose several methods to reduce or counteract this background.

Mitigation of photon background in nanoplasmonic all-on-chip Raman sensors

In the quest for a more compact and cheaper Raman sensor, photonic integration and plasmonic enhancement are central. Nanoplasmonic slot waveguides exhibit the benefits of SERS substrates while being compatible with photonic integration and mass-scale (CMOS) fabrication. A difficulty in pursuing further integration of the Raman sensor with lasers, spectral filters, spectrometers and interconnecting waveguides lies in the presence of a photon background generated by the excitation laser field in any dielectric waveguide constituting those elements. Here, we show this problem can be mitigated by using a multi-mode interferometer and a nanoplasmonic slot waveguide operated in back-reflection to greatly suppress the excitation field behind the sensor while inducing very little photon background.

Behavior of Muscle-Derived Stem Cells on Silica Nanostructured Substrates

The aim of the present work was to evaluate the responses of rat muscle-derived stem cells (rMDSCs) to growth on silica nanostructured substrates (SN) with nanoscale topographic surfaces. SN of different sizes (SN-60, SN-150, SN-300, SN-500, and SN-700) were prepared using silica nanoparticles with sizes of 60-700 nm. The prepared SN showed roughness at the nanoscale level. The total number of adherent cells on SN increased with increasing nanoscale level and incubation time. The rMDSCs attached to SN-500 and SN-700 were extensively flattened, whereas those grown on SN-60, SN-150, and SN-300 were more rounded. The rank order of the cell length and height of attached rMDSCs at 5 d on different surfaces was SN-60 ≈ SN-150 >> SN-300 > SN-500 > SN-700 > glass. Compared with rMDSCs grown on SN-60, SN-150, or SN-300, those attached to SN-500 and SN-700 exhibited a distinct morphology with filopodial extensions and stronger expression of focal adhesion, integrin, and actin. An evaluation of the gene expression of adhered rMDSCs showed that rMDSCs grown on SN-300 exhibited a higher environmental stress response than those grown on glass or SN-700. Collectively, our data provide fundamental insight into the cellular response and gene expression of rMDSCs grown on nanostructured substrates.

Reaction mechanism of the Me3AuPMe3-H2 plasma-enhanced ALD process

The reaction mechanism of the recently reported Me₃AuPMe₃-H₂ plasma gold ALD process was investigated using in situ characterization techniques in a pump-type ALD system. In situ RAIRS and in vacuo XPS measurements confirm that the CH₃ and PMe₃ ligands remain on the gold surface after chemisorption of the precursor, causing self-limiting adsorption. Remaining surface groups are removed by the H₂ plasma in the form of CH₄ and likely as PH_xMe_y groups, allowing chemisorption of new precursor molecules during the next exposure. The decomposition behaviour of the Me₃AuPMe₃ precursor on a Au surface is also presented and linked to the stability of the precursor ligands that govern the self-limiting growth during ALD. Desorption of the CH₃ ligands occurs at all substrate temperatures during evacuation to high vacuum, occurring faster at higher temperatures. The PMe₃ ligand is found to be less stable on a gold surface at higher substrate temperatures and is accompanied by an increase in precusor decomposition on a gold surface, indicating that the temperature dependent stability of the precursor ligands is an important factor to ensure self-limiting precursor adsorption during ALD. Remarkably, precursor decomposition does not occur on a SiO₂ surface, in situ transmission absorption infrared experiments indicate that nucleation on a SiO₂ surface occurs on Si-OH groups. Finally, we comment on the use of different co-reactants during PE-ALD of Au and we report on different PE-ALD growth with the reported O₂ plasma and H₂O process in pump-type versus flow-type ALD systems.