G. Viera

Bio: G. Viera is an academic researcher from University of Barcelona. The author has contributed to research in topics: Plasma-enhanced chemical vapor deposition & Silicon. The author has an hindex of 11, co-authored 29 publications receiving 398 citations.

Nanoparticle formation in low-pressure silane plasmas: bridging the gap between a-Si:H and μc-Si films

Abstract: Detailed analysis of the structure of silicon films prepared under particular rf glow discharge conditions conclusively show that nanometer-size (∼2 nm) ordered regions can be present in the matrix of this disordered semiconductor. The obtaining of such a type of `nanostructured' silicon films, referred to as polymorphous silicon in the following, under a wide range of plasma conditions, is attributed to the contribution of silicon `nanoparticles' to the growth of the films.

Atomic structure of the nanocrystalline Si particles appearing in nanostructured Si thin films produced in low-temperature radiofrequency plasmas

Abstract: Nanostructured Si thin films, also referred as polymorphous, were grown by plasma-enhanced chemical vapor deposition. The term “polymorphous” is used to define silicon material that consists of a two-phase mixture of amorphous and ordered Si. The plasma conditions were set to obtain Si thin films from the simultaneous deposition of radical and ordered nanoparticles. Here, a careful analysis by electron transmission microscopy and electron diffraction is reported with the aim to clarify the specific atomic structure of the nanocrystalline particles embedded in the films. Whatever the plasma conditions, the electron diffraction images always revealed the existence of a well-defined crystalline structure different from the diamondlike structure of Si. The formation of nanocrystallinelike films at low temperature is discussed. A Si face-cubic-centered structure is demonstrated here in nanocrystalline particles produced in low-pressure silane plasma at room temperature.

Effect of the nanoparticles on the structure and crystallization of amorphous silicon thin films produced by rf glow discharge

Abstract: Thin films of nanostructured silicon (ns-Si:H) were deposited by plasma-enhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 °C substrate temperature using a silane and hydrogen gas mixture under continuous wave (cw) plasma conditions. The nanostructure of the films has been demonstrated by diverse ways: transmission electron microscopy, Raman spectroscopy, and x-ray diffraction, which have shown the presence of ordered silicon clusters (1–2 nm) embedded in an amorphous silicon matrix. Because of the presence of these ordered domains, the films crystallize faster than standard hydrogenated amorphous silicon samples, as evidenced by electrical measurements during the thermal annealing.

Enhancement of oxidation rate of a-Si nanoparticles during dehydrogenation

Abstract: Oxidation of amorphous silicon (a-Si) nanoparticles grown by plasma-enhanced chemical vapor deposition were investigated. Their hydrogen content has a great influence on the oxidation rate at low temperature. When the mass gain is recorded during a heating ramp in dry air, an oxidation process at low temperature is identified with an onset around 250 °C. This temperature onset is similar to that of hydrogen desorption. It is shown that the oxygen uptake during this process almost equals the number of hydrogen atoms present in the nanoparticles. To explain this correlation, we propose that oxidation at low temperature is triggered by the process of hydrogen desorption.

Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane

Abstract: The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma‐enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (<1 Torr) and low frequency square‐wave modulated rf power (13.56 MHz). The a‐Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4])...

Colloquium: Reactive plasmas as a versatile nanofabrication tool

Abstract: The underlying physics of the application of low-temperature, low-pressure reactive plasmas in various nanoassembly processes is described. From the viewpoint of the ``cause and effect'' approach, this Colloquium focuses on the benefits and challenges of using plasma-based systems in nanofabrication of nanostructured silicon films, low-dimensional semiconducting quantum structures, ordered carbon nanotip arrays, highly crystalline ${\mathrm{TiO}}_{2}$ coatings, and nanostructured hydroxyapatite bioceramics. Other examples and future prospects of plasma-aided nanofabrication are also discussed.

Plasma nanoscience: from nano-solids in plasmas to nano-plasmas in solids

Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale soild-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter to nano-plasma effects and nano-plasmas of different states of matter.

Preparation of titania nanotubes and their environmental applications as electrode.

Abstract: Titanium oxide nanotubes were successfully grown from a titanium plate by direct anodic oxidation with 0.2 wt % hydrofluoric acid being the supporting electrolyte. These nanotubes are of uniform size and are well-aligned into high-density arrays. They look like honeywell with the structure similar to that of porous alumina obtained by the same technique. TiO2 anatase phase was identified by X-ray diffraction. Significant blue-shift in the spectrum of UV−vis absorption was observed. The mechanism of the novel, simple, and direct growth of the nanotubes was postulated. To investigate their potentials in environmental applications, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photoelectrocatalytic (PEC) processes, comparing with electrochemical process (EP) and photocatalytic (PC). A significant photoelectrochemical synergetic effect was observed. The kinetic constant of PEC degradation of PCP using TiO2 nanotubes electrode was 86.5% higher than that using TiO2 film electr...

Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids

Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale solid-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter, to nano-plasma effects and nano-plasmas of different states of matter.

Colloidal silicon quantum dots: from preparation to the modification of self-assembled monolayers (SAMs) for bio-applications

Abstract: Concerns over possible toxicities of conventional metal-containing quantum dots have inspired growing research interests in colloidal silicon nanocrystals (SiNCs), or silicon quantum dots (SiQDs). This is related to their potential applications in a number of fields such as solar cells, optoelectronic devices and fluorescent bio-labelling agents. The past decade has seen significant progress in the understanding of fundamental physics and surface properties of silicon nanocrystals. Such understanding is based on the advances in the preparation and characterization of surface passivated colloidal silicon nanocrystals. In this critical review, we summarize recent advances in the methods of preparing high quality silicon nanocrystals and strategies for forming self-assembled monolayers (SAMs), with a focus on their bio-applications. We highlight some of the major challenges that remain, as well as lessons learnt when working with silicon nanocrystals (239 references).