Raman, photoluminescence and other scanning probe microscopies for nanoscience

We have been using Raman spectroscopy to study II-VI and III-V semiconductors (hetero and nanostructures), C 60, Carbon nanotubes  etc. for last several years. Raman spectroscopy is an excellent technique to characterise bulk, surface and interface simultaneously. It can give information regarding structure, composition, strain  and carrier concentration etc. Confinement of phonons and manifestations of increased surface to volume ratio has been studied in CdS quantum dots and porous GaP etc. using Raman scattering. Temperature dependence of photoluminescence spectroscopy of CdSe is used to understand relaxation mechanism and electron density of states in nanostructures confined to 1, 2 and 3 dimensions. In addition Raman scattering has been successfully used as local probe to investigate  clustering in  Ge doped Se glasses. Interesting observations has been made about strain relaxation in porous GaN. Effect annealing and Swift heavy ion irradiation has been extensively investigated  in CdS and C60 respectively using Raman scattering. Electronic interband related Raman scattering from quantum well directly gives the information of electronic band structure of quantum well, which is of great interest in understanding relaxation mechanisms in the semiconductor laser structures in addition to being of great fundamental interest is being studied.

Quantum confinement effects and large surface to volume ratio of nanostructures, manifests itself in distinct electronic, optical, mechanical and thermal properties, which are believed to be important to modern science and technology. To further the understanding in nanoscience, it has become essential to look for one to one correspondence between theory and experiment. Various applications in sensors and other optoelectronic devicesAcronyms have lead to the continuous quest for new techniques of characterization with nanoscale resolution along with new methods of synthesis and growth of nanostructures.

The main objective at present is to develop a facility for performing various spectroscopic studies simultaneously with topographical studies for furthering understanding of nanoscience in semiconductor nanostructures and initiate the nonclinical studies in biophysics. In addition, it is planned to use Langmuir Blodgett technique to grow appropriate samples for this purpose. At present Chemical Bath deposition (CBD) is used to grow samples of our interest along with other collaborations, wherein samples are grown by MOVPE, PLD, chemical routes etc.

Significant changes in properties of the nanostructure material compared to the bulk form can mainly be correlated to the following effects. For instance, a reduction in size results in increase in surface to volume ratio leading to increase in surface related effects such as chemical reactivity, nonradiative recombination of electron-holes etc. Size reduction also leads to confinement of electrons and confinement of phonons influencing material’s electro-optical and thermal properties, which are of great interest in device making. Further, the nanostructures in form of tubes, rods etc. shows excellent mechanical properties and useful one dimensional thermal and electrical properties. The important point is, as the size decreases, initially size and shape and later structure plays an important role in determining physical properties. Therefore, it becomes imperative to use experimental techniques to study size and shape dependence by investigating simultaneously size, shape and spectroscopy for furthering our understanding of fundamental physics in these quantum structures. Keeping this in mind we are in a process to develop a facility with “ WiTec”, Germany  Near field scanning optical microscope(NSOM), SPM integrated Raman system, which will enable us to perform Raman and  PL spectroscopy in near field geometry simultaneously with other scanning probe microscopies(SPM:AFM, EFM, MFM, PFMS etc). This system will enable us to  augment the topographic information with the structural, chemical, electrical and electronic band structure information of the material under investigation.

SELECTED RECENT PUBLICATIONS:

1. Swift heavy ion (150 MeV:Ag 13+) induced structural changes  in a-C:H films studied by Raman spectroscopy.
   Shramana Mishra, Alka Ingale, T. S. Ghosh, D. K. Avasthi
   Diamond & Related Materials 14, 1416 – 1425(2005)
   
2. Confined acoustic modes and spectral determination of network connectivity:
   Raman signatures of nanometric structure in g-GexSe1-x.
   D. Sharma, Alka Ingale and A. M. Awasthi
3. Solid State Communications 134, 653–658(2005).
   3.Study of Annealing-induced changes in CdS thin films using X-ray Diffraction and Raman spectroscopy
   Shramana Mishra, Alka Ingale, U. N. Roy and Ajay Gupta
   Thin solid films 516, 91(2007)
4. SEM and Raman spectroscopy studies of MWCNT grown by novel technique of ash supported catalysts.
   G.M. Bhalerao, S. Waugh, Alka Ingale, A.K. sinha, M. Babu, P. Tiwari
   and R. V. Nandedkar
   J. Nanoscience and Nanotechnology 7, 1860–1866 (2007)
5. Micro Raman and photoluminescence spectroscopy of nano-porous n and p type GaN/sapphire( 0001)
   Alka Ingale,   Suparna pal, V. K. Dixit  and  Pragya Tiwari;
   J. Nanoscience and Nanotechnology 7, 2186 (2007)
6. Lineshape analysis of ZnSe LO phonon near Eo gap excitation
   Tapas Ganguli and Alka Ingale
   Phys. Rev. B. 77, 33202 (2008)
7. Role of electron energy loss in modification of C60 thin films by swift heavy ions.
   Navdeep Bajwa, Alka Ingale, D. K. Avasthi, Ravi Kumar, A. Tripathi, Keya Dharamvir, and V. K. Jindal.
   J. Appl. Phys. 104, 54306 (2008)
8. Structural and particulate to bulk phase transformation of CdS film on annealing: A Raman spectroscopy study
   Alka A. Ingale, Shramana Mishra, U. N. Roy, Pragya Tiwari and L. M. Kukreja;
   J. Appl. Phys. 106 , 84315(2009)

CONFERENCES:

INTERNATIONAL:

1. Raman spectroscopy and structure : nano-porous GaP
   Alka Ingale, V. K. Dixit, Vijay Shukla and C. Mukherjee
   Presented at “ICORS-06”, Yokohoma, JAPAN, Aug. 2006
2. Electronic and phonon Raman scattering in ZnSe/GaAs near Eo gap
   Alka Ingale  and  Tapas Ganguli 
   Presented at “ICORS-06”, Yokohoma, JAPAN, Aug. 2006
3. Comparative studies on as-grown and nanotextured GaN:Mg epilayer
   Suparna Pal, Alka Ingale, V. K. Dixit, T. K. Sharma, S. Porwal, C. Mukherjee, and  S. M. Oak
   poster presented at IWPSD-07, Mumbai:Best poster award
4. Self assembled growth and characterization of ZnO nanostructures and CdS-ZnS nanocompsite films using chemical bath deposition.
   Alka Ingale, L. Agrawal, P. Tiwari, Tapas Ganguli, V. Shukla  and  R. Jain;
   ICONSAT 08, Feb 08, Chennai, INDIA.
5. Thin film growth of nearly monodispersive CdS nanoparticles in the PVP matrix by chemical bath deposition
    Alka A. Ingale,  Komal Bapna,  Rahul Aggarwal, pragya Tiwari  and A. K. Srivastava
   ICONSAT-2010, Feb 2010,Mumbai

NATIONAL:

1. Optical and Electrical properties of as grown and annealed oriented CdS thin films ,
   Vijay  Shukla, V. K. Dixit and  Alka  Ingale
   Proc.DAE- Solid state Physics symposium -50, 471, 2005.
2. GaAsP/AlGaAs quantum well: A Raman spectroscopy study.
   R. Aggarwal, Alka A. Ingale, Suparna Pal, T. K. Sharma, S. C. Mehnedale and S. M. Oak
   Proc. DAE Solid State Physics Symposium  54, p-763(2009)..
   

1. “Raman and PL spectroscopy of  nanostructures”
   National seminar on "Theoretical and Experimental techniques in Nanoscience & Nanotechnology", Chandigarh,  March   2007,
2. “Insight into formation of nanostructures using Raman spectroscopy”
   International conference perspectives of vibrational spectroscopy, Trivandrum, Feb 2008