Vertical array of Si (100) nanowires (NWs) were fabricated by one step electroless metal-assisted chemical etching (MacEtch) of p-type Si (100) wafer in an aqueous solution comprising of AgNO₃ and HF at 60 °C for different time durations ranging from 15 to 120 min. The as-etched Si wafer surface was covered with vertically aligned NW arrays along with dense dendritic Ag structures. After dissolving the Ag dendrites using HNO₃ solution, vertical array of Si NWs became clearly visible. Straight Si NW bundles were uniformly distributed across the wafer surface, with NW diameters ranging from 100 to 150 nm. The NW sidewalls exhibited significant roughness due to the formation of Si nanocrystals (NCs), with mean diameter of 6 nm, on the nanowire surfaces. The lengths of the NWs were measured to be 3.8, 6.2, 18, and 24.5 μm for the etching durations of 15, 30, 60 min, and 120 min, respectively, indicating a nearly linear growth rate with the etching time duration. The NWs retained the crystalline orientation of the Si (100) wafer, confirming that they are single-crystalline with the Si (100) planes aligned perpendicular to the nanowire axis. The Si NWs exhibited strong visible photoluminescence, originating primarily from the embedded Si NCs as a result of quantum confinement effect. The Si NWs exhibited enhanced Raman scattering, primarily attributed to the partial localization of the excitation light resulting from multiple elastic scattering within the NW array. Additionally, plasmon-assisted Raman enhancement from the Ag dendrites further contributed to the overall signal amplification.

This chapter aims to describe multifarious schemes of detecting biomolecules by using surface enhanced Raman spectroscopy (SERS)-substrates. At first, current state of knowledge concerning the mechanism of SERS, SERS-active materials and various parameters that influence SERS have been discussed. Classification of SERS substrates, depending on their physical structures, has been reported in the following section. Finally, fabrication methods and recent applications of SERS including sensing, single molecule SERS, and real-world applications for bio-molecular probing have been highlighted.

Reddish-yellow color colloid consisting of silver nanoparticles (Ag NPs) has been synthesized by reducing aqueous AgNO3 solution by photo-induced citrate reduction technique under UV light. As prepared colloid exhibits single and intense plasmonic absorption peak in the violet region of the visible spectra with the peak centered at similar to 405 nm. The NPs are fine and spherical with diameter ranging from 5 to 10 nm. These colloidal NPs have been used for the quantitative detection of uric acid by UV-VIS spectroscopy. A linear red shifting of the characteristics Plasmonic absorption peak of Ag NPs is observed with uric acid concentration. Uric acid can be detected by UV-VIS spectroscopy down to 5 nM limit using the prepared colloid.

Vertically aligned single crystalline Si nanowire (NW) array has been fabricated on Si substrate by electroless metal assisted chemical etching (MacEtch) of heavily doped Si (100) wafer in aqueous AgNO3 and HF solution. Vertically aligned NW-arrays, covered with dense dendritic structure of Ag, are found all over the surface. Vertical array of Si NWs are clearly found after dissolving the Ag dendrites in HNO3. NWs have diameters ranging from similar to 100 to 150 nm and have rough side walls. The NWs maintain the same crystalline orientation of the Si wafer used. Vertically aligned Si NW arrays fabricated by MacEtch technique have been used as anode material for rechargeable Li-ion battery to take the advantage of the very large capacity of Si, large rough surface area of the NWs. Si NW-array based anode shows significantly large areal capacity at C/10 current rate. The cell collapses after four discharging/charging cycles due to abnormal volume expansion of the NWs due to Li intake in Si matrix.

In this article, microstructural changes in anatase titania (TiO2) nanotubes (NTs) upon electrochemical lithium (Li)-insertion/de-insertion using ex situ transmission electron microscopy (TEM) have been reported. TiO2 NT-arrays have been fabricated by coating the wall of the pores of the nanoporous anodic aluminum oxide (AAO) templates using atomic layer deposition (ALD). Anatase TiO2 NT-array based anode with the wall thickness of similar to 14 nm shows a reversible discharge capacity of similar to 175 mAh g(-1) (i.e., Liconcentration (x) of similar to 0.53) in the second discharge cycle. The NTs are structurally intact and maintain their high crystalline quality after many repetitions of charging and discharging. Reversible phase transformations from tetragonal (anatase) to orthorhombic (Li-titanate) polymorphs and back to tetragonal (anatase) in complete discharging/charging cycled TiO2 NTs are observed ex situ. Electrical conductivity of the NTs decreases a bit due to lithiation. Arrays of the anatase TiO2 NTs as anode in Li-ion secondary batteries show satisfactory cycle response and structural stability even after 50 cycles of charging/discharging. (C) 2013 Elsevier B.V. All rights reserved.

We report the synthesis of titania (TiO2) nanotubes (NTs) with precisely controlled wall thickness by atomic layer deposition (ALD) using alumina membranes as template and their application as anode material for lithium (Li) ion storage in secondary battery. As-grown nanotubes are amorphous in nature and transform into anatase phase by subsequent thermal annealing. The charge/discharge capacities and rate performance are found to be dependent on the wall thickness, which is highly uniform, of the NTs. Maximum reversible capacity for Li-insertion in anatase TiO2∼330mAhg−1 has been achieved by reducing the tube wall thickness to 5nm. NTs with the wall thickness of 40nm show reversible capacity of ∼170mAhg−1 which is similar to the maximum theoretical capacity of the bulk anatase as reported. With decrease in the wall thickness, rate performance of the NTs is significantly improved. NTs with 5nm in the wall thickness render excellent rate capability and cycle response.

Step-shaped bismuth (Bi) nanowires were fabricated by direct current electrochemical deposition technique using diameter-modulated anodic aluminum oxide membranes (AAO) as templates. The nanowires have core-sheath structure with a crystalline rhombohedral Bi core surrounded by a mixed oxide (amorphous and monoclinic Bi2O3) layer. We observed transition of nanowire property from semimetal to semiconductor at wire diameter below 50 nm. Based on the semimetal to semiconductor transition property with just changing the wire diameter, the step-shaped Bi nanowires could be predicted to form a semimetal-semiconductor self-homojunction. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3569112] All rights reserved.

This chapter contains sections titled: Introduction Growth Techniques Step Coverage Models in ALD Experimental Verifications of Step Coverage Models Summary References

The effect of Fe and Ni catalysts on the synthesis of carbon nanotubes (CNTs) using atmospheric pressure chemical vapor deposition (APCVD) was investigated. Distribution of the catalyst particles over the Si substrate was analyzed by atomic force microscopy (AFM). Characterization by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopic measurements over the grown species is reported. The study clearly shows that the catalyst strongly influences morphology and microstructure of the grown CNTs.

β-SiC nanowires have been synthesized on etch-patterned wafers in a chemical vapor deposition (CVD) system without using any metal catalyst. The nanowires were grown selectively inside the ‘V-groove’ of etch-patterned silicon (110) substrate which was used as a template for nanostructure growth. Nanowire growth was hardly found on the sample which was not previously etched. The nanowires have a core-sheath structure with the SiC core surrounded by an amorphous SiO2 sheath layer. The etching of the patterned Si (110) wafers was carried out by a 50 % aqueous KOH solution. The SiC growth was performed in a resistively heated atmospheric pressure chemical vapor deposition (APCVD) system by using hexamethyldisilane (HMDS) as the single source for Si and C at 1150oC. The as-grown samples and the patterned wafers were characterized by field emission electron microscopy, energy dispersive x-ray spectroscopy, X-ray diffraction, micro-Raman spectroscopy and Fourier transform infrared spectroscopy. Etching is one of the key factors for nanostructure growth and the patterning in the wafer provides selectivity. The growth process was governed by vapor-solid (VS) mechanism.