Pabitra Das

Local electron beam excitation and substrate effect on the plasmonic response of single gold nanostars

We performed cathodoluminescence (CL) spectroscopy and imaging in a high-resolution scanning electron microscope to locally and selectively excite and investigate the plasmonic properties of a multi-branched gold nanostar on a silicon substrate. This method allows us to map the local density of optical states from the nanostar with a spatial resolution down to a few nanometers. We resolve, both in the spatial and spectral domain, different plasmon modes associated with the nanostar. Finite-difference time-domain (FDTD) numerical simulations are performed to support the experimental observations. We investigate the effect of the substrate on the plasmonic properties of these complex-shaped nanostars. The powerful CL-FDTD combination helps us to understand the effect of the substrate on the plasmonic response of branched nanoparticles.

Probing Ar ion induced nanocavities/bubbles in silicon by small-angle x-ray scattering

Small-angle x-ray scattering (SAXS) measurements have been performed to investigate the nanocavities/bubbles and the amorphous silicon surrounding the cavities/bubbles generated after high fluence medium-energy (60 keV) Ar ion implantation in single crystalline Si as a function of incidence angle (with respect to the surface normal of the sample). The measurements were carried out using a high flux/high transmission laboratory scale SAXS set up with Mo-Kα radiation in transmission geometry. The scattering data have been used to calculate the average size (Dave), number density (dN), and volume fraction (Vf) of cavities/bubbles in ion induced amorphous layer of the crystalline Si substrate. The novelty of the SAXS technique applied in the present case lies on its ability to detect ultrafine defect features of size even less than 1 nm, which is otherwise impossible from the transmission electron microscopy measurements usually employed for inert gas ion induced cavities/bubbles in amorphous silicon.

Evolution Of Surface Topography On GaAs(100) And GaAs(111) At Normal And Oblique Incidence Of Ar+‐Ions

Nanoscale surface structures emerging from medium energy (50–60 keV) Ar+‐ion sputtering of p‐type GaAs(100) and semi‐insulating GaAs(111) substrates have been investigated. For normally incident 50 keV Ar+‐ions of fluence 1×1017 ions/cm2 on GaAs(100) and GaAs(111) features in the form of nanoscale pits/holes without short range ordering are observed with densities 5.2×109 /cm2 and 5.9×109 /cm2, respectively along with irregularly shaped patches of islands. For GaAs(111) on increasing the influence to 5×1017 /cm2 the pit density increases marginally to 6.2×109 /cm2. For 60° off‐normal incidence of 60 keV Ar.+‐ions of fluence 2×1017 ions/cm2 on GaAs(100) microscale wavelike surface topography is observed. In all cases well‐defined nanodots are absent on the surface.

Tomography and optical properties of silver nano-inukshuk

Following a simple dip-and-rinse galvanic displacement reaction silver nano-inukshuks were prepared directly on germanium surfaces. Morphology, 3-dimensional (3D) structure, chemical composition and optical properties of the silver nanostructurs were investigated using scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and cathodoluminescence (CL) spectroscopy. Exact 3D morphology was reconstructed in the by tomography mode of TEM.

Probing the plasmonic response of an isolated Au nanorod using cathodoluminescence

The spatial and spectral characteristics due to localized surface plasmon resonance of individual gold nanorod (NR) have been studied using cathodoluminescence (CL) in a high resolution scanning electron microscope (SEM). Simultaneous determination of morphology and luminescence with spatial resolution down to a few nanometers, from the same area of interest enables us to map different plasmonic modes supported by Au NR.

Ion erosion induced nanostructured semiconductor surfaces

We consider nanostructures formed on semiconductor surfaces of Si(100), InP(100) and GaAs using medium energy (50–100 keV) Ar+–ion beam sputtering. The issues of dependence of nanostructure formation on these semiconductor substrates on ion–energy, –fluence, –flux, angle of incidence, and crystallographic orientation are addressed. The threshold fluence for formation of nano–islands on Si(100) implanted with normally incident 50 keV Ar+–ions was found to be 2 × 1017 ions/cm². For InP(100) implanted with 100 keV Ar+–ions an increase in angle of incidence results in decrease of surface roughness. Surfaces of GaAs(100) and GaAs(111) implanted with normally incident 50 keV Ar+–ions show nanopits of density 3–4 × 109/cm². The existing theories are applied to explain the formation of observed surface nanostructures.