Chinmay Khare

Influence of substrate temperature on glancing angle deposited Ag nanorods

When Ag sculptured thin films were grown with glancing angle deposition by ion beam sputtering at either room temperature or elevated substrate temperatures TS, a large morphological difference was observed. The incident particle flux reached the silicon substrate at a glancing angle β≥80° as measured to the substrate normal. A slit aperture was used in order to reduce the particle beam divergence. At room temperature, columnar structures were formed, irrespective of the presence of the slit aperture. At elevated temperatures (573 and 623 K) and collimated particle flux in the presence of the slit aperture, however, enhanced surface diffusion causes the growth of crystalline nanorod- and nanowirelike structures. In the absence of the slit aperture, the flux beam divergence is higher, resulting in island- and mountainlike crystalline structures. The density of the nanorods and nanowires was observed to be higher on the planar Si substrates in comparison to honeycomblike prepatterned substrates with differe...

Microspot sensing based on surface-enhanced fluorescence from nanosculptured thin films

Nanosculptured thin films (STF) are prepared by the oblique angle deposition technique and take different forms of nano columnar structures. Varieties of STFs were investigated to find the optimum structure for biosensing based on the surface enhanced fluorescence. A comparative study was carried out with STFs containing the nanocolumnar structures that differ in their shape, height (h), and tilt angle with respect to the surface (α), thickness (d), and arrangement. The greatest enhancement of the fluorescent signal was found for Ag-based STFs on Si(100), giving an enhancement factor of ×71, where h = 400  nm, d = 75  nm, and α = 23° relative to Ag closed film using fluorescent dye Rhodamine 123. We immobilized the fluorescent receptor to the thiol self-assembly monolayer on Ag-based STF and Ag dense film to demonstrate the applications of STFs for specific biosensing. Upon excitation of the fluorophore by an Hg light source, a CCD camera with controlled exposure time would detect the pattern of fluorescent receptor Anti-Rabbit IgG on the surfaces. A specially designed optical fiber housing attached to the microscope allowed quantitative measurement of the fluorescence spectrum on a microspot parallel to the image grab.

Optimized growth of Ge nanorod arrays on Si patterns

Self-assembly of polystyrene nanospheres and reactive ion etching have been used to seed Si substrates on which Ge nanorods could be grown by glancing angle deposition (GLAD). This method enables production of large area planar-closed-packed arrays of Ge-GLAD nanostructures on Si seed patterns. A strong column competition on a broad seed width (ws) and a narrow interseed separation distance (Rs) causes the growth of closely bunched multiple structures on the Si seeds. Nanorod growth optimization is realized through the systematic variation of Si seed widths (ws) and the interseed separation distance (Rs), which enable the growth of singular nanorods on each Si seed.

Glancing angle deposition of Ge nanorod arrays on Si patterned substrates

A periodic arrangement of Ge nanorods on a Si(111) substrate was realized by glancing angle deposition (GLAD) onto honeycomb-like arranged Au hillocks formed using a self-assembled monolayer of polystyrene nanospheres as an evaporation mask. Additionally, a honeycomb-like arrangement of Au dots was used as an etch mask in a reactive ion beam etching process for pattern transfer procedure. Resulting honeycomb patterns consisting of Si hillocks within the Si(111) substrates were utilized to deposit Ge nanorods. Effective morphological variations in shape and dimension of GLAD-grown nanorods on honeycomb-like patterned substrates with both Au dot and Si dot arrays are strongly influenced by interseed distances, seed heights, and consequently shadowing lengths. For a large pattern period, it was observed that the usual triangular shape of the nanorod changed to a hexagonal shape as an effect of additional particle flux that reached the growing nanorod from the direction of second and third-nearest neighbors d...

Metallic nanosculptured thin films for biosensing applications using surface Plasmon resonance and enhanced spectroscopies

Metallic nanosculptured thin films are made of nanorods in different shapes prepared by means of the oblique angle deposition technique. Assessment of these films for biosensing and molecular detection has been investigated by our group recently using surface Plasmon resonance (SPR), surface enhanced fluorescence (SEF), and surface enhanced Raman scattering (SERS). Using columnar thin film (CTF) as the transducer layer in SPR sensors enhances both the angular and spectral sensitivity of the sensor. Sculptured thin films (STFs) made of different materials, shapes, sizes, orientations, porosities, and deposited on different substrates were examined as SEF and SERS detection platforms. The optimal features of STFs were examined to obtain the highest enhancement of SERS and SEF. The potential of these films for biosensing and bimolecular detection was demonstrated. Stability of the films was noticed over a period of one year without significant degradation.