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487 KiB

Open AccessArticle

A Mechanochemical Approach to Porous Silicon Nanoparticles Fabrication

by Luigi Russo, Francesco Colangelo, Raffaele Cioffi, Ilaria Rea and Luca De Stefano

Materials 2011, 4(6), 1023-1033; https://doi.org/10.3390/ma4061023 - 7 Jun 2011

Cited by 75 | Viewed by 9923

Abstract

Porous silicon samples have been reduced in nanometric particles by a well known industrial mechanical process, the ball grinding in a planetary mill; the process has been extended to crystalline silicon for comparison purposes. The silicon nanoparticles have been studied by X-ray diffraction, [...] Read more.

Porous silicon samples have been reduced in nanometric particles by a well known industrial mechanical process, the ball grinding in a planetary mill; the process has been extended to crystalline silicon for comparison purposes. The silicon nanoparticles have been studied by X-ray diffraction, infrared spectroscopy, gas porosimetry and transmission electron microscopy. We have estimated crystallites size from about 50 nm for silicon to 12 nm for porous silicon. The specific surface area of the powders analyzed ranges between 100 m²/g to 29 m²/g depending on the milling time, ranging from 1 to 20 h. Electron microscopy confirms the nanometric size of the particles and reveals a porous structure in the powders obtained by porous silicon samples which has been preserved by the fabrication conditions. Chemical functionalization during the milling process by a siloxane compound has also been demonstrated. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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703 KiB

Open AccessArticle

Study of Ni Metallization in Macroporous Si Using Wet Chemistry for Radio Frequency Cross-Talk Isolation in Mixed Signal Integrated Circuits

by Xi Zhang, Chengkun Xu, Kyuchul Chong, King-Ning Tu and Ya-Hong Xie

Materials 2011, 4(6), 952-962; https://doi.org/10.3390/ma4060952 - 25 May 2011

Cited by 1 | Viewed by 6905

Abstract

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of [...] Read more.

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of selected ultra-high-aspect-ratio macroporous regions that were electrochemically etched in p⁻ Si substrates. The metallization process was conducted by means of wet chemistry in an alkaline aqueous solution containing Ni²⁺ without reducing agent. It is found that at elevated temperature during immersion, Ni²⁺ was rapidly reduced and deposited into macroporous Si and a conformal metallization of the macropore sidewalls was obtained in a way that the entire porous Si framework was converted to Ni. A conductive moat was as a result incorporated into p⁻ Si substrate. The experimentally measured reduction of crosstalk in this structure is 5~18 dB at frequencies up to 35 GHz. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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331 KiB

Open AccessArticle

Layer Transfer from Chemically Etched 150 mm Porous Si Substrates

by Barbara Terheiden, Jan Hensen, Andreas Wolf, Renate Horbelt, Heiko Plagwitz and Rolf Brendel

Materials 2011, 4(5), 941-951; https://doi.org/10.3390/ma4050941 - 23 May 2011

Cited by 10 | Viewed by 8032

Abstract

We demonstrate for the first time the successful layer transfer of an epitaxially grown monocrystalline Si film from a purely chemically etched porous Si substrate of 150 mm diameter to a glass carrier. The surface conditioning for all Si layer transfer processes based [...] Read more.

We demonstrate for the first time the successful layer transfer of an epitaxially grown monocrystalline Si film from a purely chemically etched porous Si substrate of 150 mm diameter to a glass carrier. The surface conditioning for all Si layer transfer processes based on porous Si has been, up to now without exception, carried out by electrochemical etching. In contrast, our chemical stain etching process uses an aqueous HF-rich HF/HNO₃ solution. The porosity increases with increasing doping concentration of the Si substrate wafer and with increasing porous layer thickness. In contrast to the electrochemically etched double layers, the porosity profile of the stain etched substrates is highest at the original wafer surface and lowest at the interface between the porous layer and the Si bulk. The epitaxy process is adapted to the high porosity at the surface with regard to the reorganization of the porous layer. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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1043 KiB

Open AccessArticle

Preparation, Characterization and Performance of Templated Silica Membranes in Non-Osmotic Desalination

by Bradley P. Ladewig, Ying Han Tan, Chun Xiang C. Lin, Katharina Ladewig, João C. Diniz da Costa and Simon Smart

Materials 2011, 4(5), 845-856; https://doi.org/10.3390/ma4040845 - 2 May 2011

Cited by 32 | Viewed by 8397

Abstract

In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined [...] Read more.

In this work we investigate the potential of a polyethylene glycol-polypropylene glycol-polyethylene glycol, tri-block copolymer as a template for a hybrid carbon/silica membrane for use in the non-osmotic desalination of seawater. Silica samples were loaded with varying amounts of tri-block copolymer and calcined in a vacuum to carbonize the template and trap it within the silica matrix. The resultant xerogels were analyzed with FTIR, Thermogravimetric analysis (TGA) and N₂ sorption techniques, wherein it was determined that template loadings of 10 and 20% produced silica networks with enhanced pore volumes and appropriately sized pores for desalination. Membranes were created via two different routes and tested with feed concentrations of 3, 10 and 35 ppk of NaCl at room temperature employing a transmembrane pressure drop of 85% (in most cases >95%) and fluxes higher than 1.6 kg m⁻² h⁻¹. Furthermore, the carbonized templated membranes displayed equal or improved performance compared to similarly prepared non-templated silica membranes, with the best results of a flux of 3.7 kg m⁻² h⁻¹ with 98.5% salt rejection capacity, exceeding previous literature reports. In addition, the templated silica membranes exhibited superior hydrostability demonstrating their potential for long-term operation. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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414 KiB

Open AccessArticle

Gold Nanostructures for Surface-Enhanced Raman Spectroscopy, Prepared by Electrodeposition in Porous Silicon

by Kazuhiro Fukami, Mohamed L. Chourou, Ryohei Miyagawa, Álvaro Muñoz Noval, Tetsuo Sakka, Miguel Manso-Silván, Raúl J. Martín-Palma and Yukio H. Ogata

Materials 2011, 4(4), 791-800; https://doi.org/10.3390/ma4040791 - 14 Apr 2011

Cited by 35 | Viewed by 10731

Abstract

Electrodeposition of gold into porous silicon was investigated. In the present study, porous silicon with ~100 nm in pore diameter, so-called medium-sized pores, was used as template electrode for gold electrodeposition. The growth behavior of gold deposits was studied by scanning electron microscope [...] Read more.

Electrodeposition of gold into porous silicon was investigated. In the present study, porous silicon with ~100 nm in pore diameter, so-called medium-sized pores, was used as template electrode for gold electrodeposition. The growth behavior of gold deposits was studied by scanning electron microscope observation of the gold deposited porous silicon. Gold nanorod arrays with different rod lengths were prepared, and their surface-enhanced Raman scattering properties were investigated. We found that the absorption peak due to the surface plasmon resonance can be tuned by changing the length of the nanorods. The optimum length of the gold nanorods was ~600 nm for surface-enhanced Raman spectroscopy using a He-Ne laser. The reason why the optimum length of the gold nanorods was 600 nm was discussed by considering the relationship between the absorption peak of surface plasmon resonance and the wavelength of the incident laser for Raman scattering. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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727 KiB

Open AccessArticle

A Preliminary Study on the Effect of Macro Cavities Formation on Properties of Carbon Nanotube Bucky-Paper Composites

by Ludovic Dumée, Kallista Sears, Jürg Schütz, Niall Finn, Mikel Duke and Stephen Gray

Materials 2011, 4(3), 553-561; https://doi.org/10.3390/ma4030553 - 10 Mar 2011

Cited by 15 | Viewed by 8416

Abstract

In this study, we focus on processing and characterizing composite material structures made of carbon nanotubes (CNTs) and reproducibly engineering macro-pores inside their structure. Highly porous bucky-papers were fabricated from pure carbon nanotubes by dispersing and stabilizing large 1 μm polystyrene beads within [...] Read more.

In this study, we focus on processing and characterizing composite material structures made of carbon nanotubes (CNTs) and reproducibly engineering macro-pores inside their structure. Highly porous bucky-papers were fabricated from pure carbon nanotubes by dispersing and stabilizing large 1 μm polystyrene beads within a carbon nanotube suspension. The polystyrene beads, homogeneously dispersed across the thickness of the bucky-papers, were then either dissolved or carbonized to generate macro cavities of different shape and properties. The impact of adding these macro cavities on the porosity, specific surface area and Young’s modulus was investigated and some benefits of the macro cavities will be demonstrated. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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Review

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1113 KiB

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Magnetic Nanoparticles Embedded in a Silicon Matrix

by Petra Granitzer and Klemens Rumpf

Materials 2011, 4(5), 908-928; https://doi.org/10.3390/ma4050908 - 17 May 2011

Cited by 32 | Viewed by 8193

Abstract

This paper represents a short overview of nanocomposites consisting of magnetic nanoparticles incorporated into the pores of a porous silicon matrix by two different methods. On the one hand, nickel is electrochemically deposited whereas the nanoparticles are precipitated on the pore walls. The [...] Read more.

This paper represents a short overview of nanocomposites consisting of magnetic nanoparticles incorporated into the pores of a porous silicon matrix by two different methods. On the one hand, nickel is electrochemically deposited whereas the nanoparticles are precipitated on the pore walls. The size of these particles is between 2 and 6 nm. These particles cover the pore walls and form a tube-like arrangement. On the other hand, rather well monodispersed iron oxide nanoparticles, of 5 and 8 nm respectively, are infiltrated into the pores. From their size the particles would be superparamagnetic if isolated but due to magnetic interactions between them, ordering of magnetic moments occurs below a blocking temperature and thus the composite system displays a ferromagnetic behavior. This transition temperature of the nanocomposite can be varied by changing the filling factor of the particles within the pores. Thus samples with magnetic properties which are variable in a broad range can be achieved, which renders this composite system interesting not only for basic research but also for applications, especially because of the silicon base material which makes it possible for today’s process technology. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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1209 KiB

Open AccessReview

Electrochemically Formed Porous Silica

by Jean-Noël Chazalviel and François Ozanam

Materials 2011, 4(5), 825-844; https://doi.org/10.3390/ma4050825 - 26 Apr 2011

Cited by 10 | Viewed by 7761

Abstract

Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be [...] Read more.

Controlled electrochemical formation of porous silica can be realized in dilute aqueous, neutral-pH, fluoride medium. Formation of a porous film is initiated by sweeping the potential applied to silicon to values higher than 20 V. Film formation, reaching a steady state, may be pursued in a wide range of potentials, including lower potentials. The origin of a threshold potential for porous film initiation has been explained quantitatively. All of the films appear mesoporous. Films grown at high potentials exhibit a variety of macrostructures superimposed on the mesoporosity. These macrostructures result from selective dissolution of silica induced by local pH lowering due to oxygen evolution. Films grown at potentials lower than 15 V appear uniform on the micrometer scale. However, all of the films also exhibit a stratified structure on the scale of a few tens of nanometres. This periodic structure can be traced back to the oscillatory behavior observed during the electrochemical dissolution of silicon in fluoride medium. It suggests that periodic breaking of the growing film may be responsible for this morphology. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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351 KiB

Open AccessReview

Progress of Application Researches of Porous Fiber Metals

by Zhengping Xi, Jilei Zhu, Huiping Tang, Qingbo Ao, Hao Zhi, Jianyong Wang and Cheng Li

Materials 2011, 4(4), 816-824; https://doi.org/10.3390/ma4040816 - 19 Apr 2011

Cited by 66 | Viewed by 10334

Abstract

Metal fiber porous materials with intrinsic properties of metal and functional properties of porous materials have received a great deal of attention in the fundamental research and industry applications. With developments of the preparation technologies and industrial requirements, porous fiber metals with excellent [...] Read more.

Metal fiber porous materials with intrinsic properties of metal and functional properties of porous materials have received a great deal of attention in the fundamental research and industry applications. With developments of the preparation technologies and industrial requirements, porous fiber metals with excellent properties are developed and applied in many industry areas, e.g., sound absorption, heat transfer, energy absorption and lightweight structures. The applied research progress of the metal fiber porous materials in such application areas based on the recent work in our group was reviewed in this paper. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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