* Surface functionalization and Nano-bio hybrid structure:
Attempts have been made to self-assemble the nanoparticles by electrochemical based surface functionalization
procedure using DNA for reduction of size distribution and employed for technological application.
Single stranded DNA (ssDNA) tagged CdSe nanobead of 3nm size and ssDNA along with its conjugate
tagged CdSe nanowire has been synthesized using the above principle. Similarly DNA tagged HgTe nanostars
also synthesized using the same principle where the nanowire and nanostar samples were proven to be very much
useful for biomolecular recognition application. Surface functionalisation of ultra narrow monodispersed UV absorbance and
luminescence Au nanoparticles has been grown using L-Cystein and its application for glucose biosensor by means optical
spectroscopy proven to be very useful. Surface functionalization of HgTe and HgTe/CdTe core shell has also been carried
out with L-Cystein.
* Synthesis of nanostructures using chemical and electrochemical technique::
To synthesize nanoparticles/ nanorods/ nanowires, two techniques viz. Electrochemical and Chemical bath are being used. The chemical deposition technique is a simple and low cost technique and gives broad size distribution of crystallites where as the electrodeposition technique has yielded narrow size distribution and polydispersity in the crystallites. The self-assembling process have resulted single crystalline nanoparticles. Different kind of nanoparticle viz. ZnO, NiO Au, CdS, CdSe, HgS, HgTe/CdTe core shell, HgTe and posous Si etc. and nanowires viz. CdSe and HgTe have been synthesized by using these two techniques.
* Synthesis of Metallic and Metal oxide clusters using vacuum systems ::
To synthesize metallic and metal oxide nano-clusters, Low Energy Cluster Beam Deposition (LECBD) technique is being used. The electrochemical/ chemical technique involves chemistry/electrochemistry whereas LECBD technique involves vacuum cluster deposition. The metallic and metal oxide nano-clusters viz. Sb, Se, Sb2O3, and SeO2 are synthesized using LECBD technique and different properties such as structure, optical, surface and interface properties have been studied.
* Structure, Surface and Interface study of nanostructures using TEM, GXRD and AFM::
Studied the structure, surface and interface property of different nanostructures such as CdSe, CdS and HgTe, Au and HgTe/CdTe core shell using Transmisson Electron microscope (TEM), Grazing angle X-ray diffraction (GXRD) and Atomic Force Microscopy (AFM). In case of CdSe nanoparticl, the size found to be 7 nm for low current density deposited sample where as the size of the particle found to be 15 nm for higher current density sample with cubic phase. A diffusion limited aggregation (DLA) pattern fractal growth is found in case of low current density deposited sample. Similarly, a CdS and HgTe sample shows a size distribution in the nanoparticle and surface roughness increases with decreasing crystalline size.
* Optical characterization of Nanoparticles using Optical absorption, Photoluminescence, Raman scattering, and Fourier transform infrared measurements::
The optical properties of different nanostructures such as ZnO nanoros, NiO poros thin films, nanoparticles such as Au, CdSe, CdS, HgTe, HgS, HgTe/CdTe Core shell and Porous Si were studied using Photoluminescence (PL), Micro Raman and Optical absorption (UV-VIS-NIR) and Fourier Transform Infrared (FTIR) techniques. In case of CdSe nanoparticles, the PL measurement shows a unique luminescent behavior in the visible regime because of quantum confinement effect. Comparing the optical absorption and PL data, the band gap of CdSe nanoparticles is estimated as 2.22 eV. The shifting of Raman 1LO vibration mode towards higher wavenumber confirms the CdSe crystallites are small in size. Biomolecular recognition with DNA tagged CdSe NWs has been established by photoluminescence measurements. The micro Raman measurement of DNA tagged CdSe NBs and DNA tagged CdSe NWs shows a clear low-energy shift and broadening in the Raman peak due is to the phonon confinement. Similarly different optical properties of other nanostructures such as CdS, HgTe, HgS and Porous Si have been studied in detail. Similarly, UV region optical activity in HgTe NPs chemically synthesized with a organic ligand L-cysteine ethyl ester hydrochloride capping materials which produces smaller NPs with narrow size distribution. UV emitting Au NPs functionalized by L-cysteine has been prepared which can be used as one of the most efficient glucose sensor for pharmaceutical/pathological application in determining wider range glucose level in human blood.
* Fabrcation and study of Heterostructure device using nanostructure materials : :
The heterostructure devices has been fabricated using different nanostructure materials. The ITO/nano-CdSe/Au Schottky junction interface was characterized by current (I) - voltage (V) and capacitance (C) -voltage (V), as a function of frequency. The same has been compared with ITO/bulk-CdSe/Au Schottky junction interface. The rise in threshold current of the nano-CdSe/Au junction occurs at a lower voltage than that of the bulk-CdSe/Au junction which is ascribed to the presence of higher density of interface traps in the nano-CdSe/Au interface. These carriers under bias tunnel to contribute to the current flow at low voltage. Due to large surface area contact, the capacitance magnitude of nano-CdSe/Au device has been found to be much more than the bulk-CdSe device. Charge trapping and frequency dependent capacitance have been observed in nano-CdSe/Au devices. The interfacial characteristics studies of other materials like ZnO nanorods, NiO porous thin films, Au cluster, CdS, CdS-DNA, HgTe, HgTe-CdTe core shell are under progress.