The most common fabrication technique of porous silicon (PS) is electrochemical etching of a crystalline silicon wafer in a hydrofluoric (HF) acid-based solution. The electrochemical process allows for precise control of the properties of PS such as thickness of the porous layer, porosity, and average pore diameter. The control of these properties of PS was shown to depend on the HF concentration in the used electrolyte, the applied current density, and the thickness of PS. The change in pore diameter, porosity, and specific surface area of PS was investigated by measuring nitrogen sorption isotherms.

Pushpendra Kumar

Patrick Huber

Effect of Etching Parameter on Pore Size and Porosity of Electrochemically Formed Nanoporous Silicon

A novel solution method to control the diameter of ZnO nanorods is reported. Small diameter (2-3 nm) nanorods were synthesized from trihexylamine, and large diameter (50–80 nm) nanorods were synthesized by increasing the alkyl chain length to tridodecylamine. The defect (green) emission of the photoluminescence (PL) spectra of the nanorods varies with diameter, and can thus be controlled by the diameter control. The small ZnO nanorods have strong green emission, while the large diameter nanorods exhibit a remarkably suppressed green band. We show that this observation supports surface oxygen vacancies as the defect that gives rise to the green emission.

Tamar Andelman

Yinyan Gong

Gertrude Neumark

Stephen O'Brien

Diameter Control and Photoluminescence of ZnO Nanorods from Trialkylamines

<mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>In</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> and <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>In</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>:Ag nanoparticle layers have been deposited using a two-step method consisting of chemical capping and dip coating techniques. The result of optical absorption analysis of <mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>In</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>O</mml:mtext><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>:Ag samples shows the presence of <mml:math id="E4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Ag</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mtext>O</mml:mtext></mml:mrow></mml:math> and Ag in air-annealed and vacuum-annealed samples, respectively. These results have been correlated with the gas sensing properties of these layers towards ethanol and support the proposed mechanism that increase in sensor response on Ag addition is due to the conversion of <mml:math id="E5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Ag</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mtext>O</mml:mtext></mml:mrow></mml:math> to Ag in the presence of ethanol.

Vidya Nand Singh

Bodh Raj Mehta

Rakesh Kumar Joshi

Frank Einar Kruis

Effect of Silver Addition on the Ethanol-Sensing Properties of Indium Oxide Nanoparticle Layers: Optical Absorption Study

Mixed nanoparticle films of SnO1.8: Ag prepared by the gas phase condensation method using an aerosol route have been used for the detection of CO and CH4. Particle size as estimated by transmission electron microscopy is 20 nm for both SnO1.8 and Ag nanoparticles. The gas-sensing behavior of the films for these gases has been studied in detail as a function of Ag concentration in the films. A study has been made in order to distinguish the size effect and specific surface area effect in the ethanol gas-sensing behavior of SnO1.8: Ag mixed nanoparticle films. This distinction, which has not been possible using the traditional methods of the sensor fabrication, gives evidence of the dominance of size effect of the metal dopant over the surface area effect in the gas sensing of the films. The sensors show also an increased sensor signal with increase of Ag concentration in the films for CO and CH4. It is observed from the comparative study of the sensing behavior of SnO1.8: Ag films for CO and CH4 that the sensors are more sensitive towards CO as compared to CH4. The mixed nanoparticle films were also used for the detection of CO at 100 ppm level.

Size-Selected SnO1.8: Ag Mixed Nanoparticle Films for Ethanol, CO, and CH4 Detection

Single-walled carbon nanotubes (SWCNTs) were prepared by a modified arc discharging furnace using Fe-Ni-Mg powders as catalyst at <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mrow><mml:mn>600</mml:mn></mml:mrow><mml:mo>∘</mml:mo></mml:msup><mml:mtext>C</mml:mtext></mml:mrow></mml:math>. The effects of catalyst composition and content on the production rate and purity of SWCNTs are investigated in this paper. When the Fe-Ni-Mg catalyst composition is 2: 1: 2 <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>wt</mml:mtext><mml:mi>%</mml:mi></mml:mrow></mml:math> and the catalyst content is 5 <mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mtext>wt</mml:mtext><mml:mi>%</mml:mi></mml:mrow></mml:math>, the experimental results indicate that the production of SWCNTs is 12 grams per hour, and the purity and diameter of SWCNTs are <mml:math id="E4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>70</mml:mn><mml:mi>%</mml:mi></mml:mrow></mml:math> and 1.22 <mml:math id="E5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>∼</mml:mo></mml:math>1.38 nm, respectively. The results indicate that the cooperative function of catalyst composition and content plays an important role in the production of SWCNTs. The aim of this work is to control the production process of SWCNTs efficiently.

Tingkai Zhao

Qinghu Tang

Yongning Liu

Changchun Zhu

Xiang Zhao

Catalyst Composition and Content Effects on the Synthesis of Single-Walled Carbon Nanotubes by Arc Discharge

We demonstrated a new technique to sort nanoparticles based on their dimensions. Due to the interactions between charged droplets and a nonlinear electrostatic field, nanoparticles with different dimensions were deposited at different spatial locations on a given target substrate. By using this principle, we have been able to sort nanocups into three groups with mean diameters of 0.31 <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>m, 0.7 <mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>m, and 1.1 <mml:math id="E3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>μ</mml:mi></mml:math>m and a standard deviation of 20<mml:math id="E4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>%</mml:mi></mml:math>. This technique improves the nanoparticle fabrication process not only by decreasing the standard deviation of its dimensions but also by increasing its yield since nanoparticles with different mean diameters can be generated at the same time.

Parag Deotare

Jun Kameoka

Sorting of Silica Nanocups by Diameter during Fabrication Process

A 55 nm samarium film capped with a 10 nm palladium overlayer switched from a metallic reflecting to a semiconducting, transparent in visible state during ex-situ hydrogen loading via electrochemical means in 1 M KOH electrolytic aqueous solution at room temperature. The switching between metal to semiconductor was accompanied by measurement of transmittance during hydrogen loading/unloading. The effect of current density on switching and thermodynamic properties was studied between dihydride state (FCC phase) and trihydride state (hexagonal phase). From the plateau of partial pressure of hydrogen at <mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>x</mml:mi><mml:mo>=</mml:mo><mml:mn>2.6</mml:mn></mml:mrow></mml:math>, enthalpy of formation was calculated at different current densities. The diffusion coefficients 
 and switching kinetics are shown to depend on applied current density.

L. K. Malhotra

Effect of Current Density on Thermodynamic Properties of Nanocrystalline Palladium Capped Samarium Hydride Thin Film Switchable Mirrors

Creation of controlled and reproducible nanostructures on material surfaces using scanning tunneling microscope is a novel technique, which can be used for a variety of applications. We have examined the shape of the nanostructures so formed on the gold film using tungsten tip and examined the formation parameters, which govern their shape and size. During our investigations it is found that the reproducibility of mound formation can reach up to 90<mml:math id="E1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>%</mml:mi></mml:math> under optimum operating conditions, whereas the pit formation can be made with almost 100<mml:math id="E2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>%</mml:mi></mml:math> reproducibility. Formation mechanism of such nanostructures is also discussed.

Subhashis Gangopadhyay

Asit Kumar Kar

Balbir Kumar Mathur

Shape of Field-Induced Nanostructures Formed by STM

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Journal of Nanomaterials publishes research on nanoscale and nanostructured materials with an emphasis on synthesis, processing, characterization, and the applications of nanomaterials.

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Chief Editor Stefano Bellucci is Professor of Theoretical Physics at the National Institute for Nuclear Physics in Frascati, Italy. His research interests include&nbsp;nanoscience and nanotechnology, nanocarbon-based composites, and the biomedical applications of nanomaterials.

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Journal of Nanomaterials - Table of contents 2007

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Journal of Nanomaterials publishes research on nanoscale and nanostructured materials with an emphasis on synthesis, processing, characterization, and the applications of nanomaterials.

Journal of Nanomaterials