Laser Physics Applications Section
Raman, photoluminescence and other scanning probe microscopies for nanoscience

"Science is about the humility to accept the ignorance, the sense of adventure to explore the new, the patience to suspend the conclusion till all data are in, the tenacity to explore all possible interpretations, the maturity to accept the results as they are instead of trying to fit them into the comfortable convention and the passion to enjoy every step of it."

Eunah Lee
  1. AIM
  2. WHY?
  3. HOW?
  1. Raman spectroscopy
    1. Study of size and size distribution using confined acoustic phonons
    2. Understanding of nanostructure / heterostructure using Optical phonons
  2. Scanning probe microscopies and Raman mapping
  3. Facilities
  4. Growth
  5. Selected Recent Publications
Nanoscience is the study of nanoscale materials to understand thermodynamics and chemistry of growth and correlations of material properties with structure, size and shape. Nanotechnology uses this understanding of nanostructures for working towards achieving controlled growth of the nano materials for applications. Thus to put nanotechnology in practice, one needs to use knowledge of physics, chemistry and sometimes biology (when, biological materials are involved) together for doing the required material science i.e. interdisciplinary research is the key word. Computer simulations also can be used effectively in predicting/understanding the growth as well as various properties of the nanomaterials. Until recently, nanoscience concern was mainly miniaturization. However, recently, nanoscience research have broadened the applications of nanotechnology encompassing various fields like efficient fuel, solar cells, various sensors, biotechnology etc. We work mainly in the field of semiconductor and C nanostructures.

Interdisciplinary Research

AIM:

To study semiconductor and C nanostructures, their assemblies and nanocomposites using optical and scanning probe microscopies as local probe to develope an understanding of correlation of morphology with their optical, electronic, vibrational and electrical properties. Morphology and various spectroscopies together are also used to get insight into growth mechanisms. Samples of interest are grown in house as well as are obtained through collaborations with different groups.

WHY?

Significant changes in the properties of the nanostructure material compared to the bulk form can mainly be correlated to confinement of electrons, phonons and increased surface to volume ratio. 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 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. show excellent mechanical properties and useful one dimensional thermal and electrical property. Therefore, it becomes imperative to use experimental techniques to study size and shape dependence by investigating simultaneously size, shape and spectroscopy for better understanding of properties of these quantum structures.
Schematic: Confinement
HOW?

A. Raman spectroscopy :

Our strength being Raman spectroscopy, it will be applied as main research tool supported by absorption and PL spectroscopy for investigations of nanostructures. Raman spectroscopy is an inelastic light scattering of low level excitations of the medium/material and is an excellent nondestructive technique to investigate bulk, surface and interface simultaneously. In solids, we mainly study quantized lattice vibrations (phonon) and low lying electronic excitations of the materials. Raman spectroscopy is a local probe and lattice vibrations are sensitive to composition, structure, stress, crystalline quality, local environment etc. In addition, since light interacts with lattice via electrons and hence it also gives information about electronic band structure. Low level carrier excitations can additionally predict type of carriers, carrier concentration etc. In all, Raman spectroscopy is capable of giving information about material's structural, optical and electronic properties and our results over last two decades reflects the same as summarized below.
 
Schematic : Raman spectroscopy
In nanostructures, 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 of annealing and swift heavy ion irradiation has been extensively investigated in CdS and C60 respectively using Raman scattering. From intensity dependent Raman measurements of GaAs0.86P0.14/Al 0.7Ga0.3As quantum well (QW) heterostructures with different quantum well thickness, it was concluded that modes originating from quantum well region ~284 cm-1 and ~364 cm-1 are due to photoexcited carriers (intersubband plasmon). The theory for alloyed semiconductor quantum well in presence of intersubband plasmon predicts three coupled modes and their behavior with carrier density is quite different than observed in bulk when intersubband Plasmon energy is much higher than phonon energies as observed in our case. To the best of our knowledge this is the only result, wherein both phonon like coupled modes could be observed simultaneously.

Raman spectroscopy of nanostructures/clusters:

I. Study of size and size distribution using confined acoustic phonons :

Confined acoustic phonon (CAP) frequencies are inversely proportional to size of nanocrystal and also depends on the shape of the nanostructure. Therefore determination of size and size distribution is possible using Raman spectroscopy of CAPs.

1. D. Sharma , Alka Ingale et al, SSC 134, 653-658(2005).
2. Invited talk: Alka Ingale
:"Phonons in Condensed Materials", ed.by S. P. Sanyal and R.K. Singh , Allied publishers, New Delhi, 216(2004)
3. Alka Ingale et al, Mat. Sci.& Eng. C, 23, 1115 (2003)

Schematic representation of nanostructures/clusters studied:
Schematic representation of nanostructures/clusters studied
 
II. Understanding of nanostructure / heterostructure using Optical phonons:

Raman scattering of optical phonons gives information of local environment in the material like composition, stress, carrier concentration, crystalline quality etc. This can be used to corroborate XRD, absorption spectroscopy measurements to develop understanding of the material properties.


1. R. Aggarwal, Alka Ingale et al. APL 102, 181120 (2013)
2. G.M. Bhalerao, S. Waugh, Alka Ingale, et al J NN 7, 1860–1866 (2007)
3. Alka Ingale et al JNN 7, 2186 (2007)
4. Alka Ingale et al, Proc. of “ICORS-06”, JAPAN, (2006)

1.Study of stress and accompanying disorder using Raman spectra :
 

n type GaN: etching depth

Stress calculated from microRaman spectra(GPa)

p type GaN: etching depth

Stress calculated from microRaman spectra(GPa)

DStress(GPa)   

Unetched

.457

Unetched

.246

0

0.35 µ

.274

0.05 µ

.379

+0.133

0.44 µ

.172

0.19 µ

.155

-.091

0.56 µ

.138

 

 

 

 

 

 

 

 



2.Intersubband plasmon-phonon coupling in GaAsP/AlGaAs near surface quantum well (NSQW)




B. Scanning probe microscopies and Raman mapping:

With Raman mapping and atomic force microscopy, we now aim at developing understanding of correlation of morphology with growth mechanisms and various properties of the material. The main objective of the group at present is to develop and use a facility for performing various spectroscopic studies along with topographical studies for furthering understanding of nanoscience in semiconductor and C nanostructures and their assemblies.

Recently set up “Near field scanning optical microscope (NSOM), SPM integrated Raman system of “WiTec", Germany,” has been used to perform Raman mapping and spectroscopy of semiconductor micro and nanostructures. We are working on substrate preparation for surface enhanced Raman scattering (SERS) using thin film coating unit, (Hindhighvac, Bangalore) for generating Ag/Au films. This will allow us to perform Raman imaging of nanostructures more effectively along with other scanning probe microscopies.


Near field scanning optical microscope (NSOM), SPM integrated Raman system, WiTec, Germany
Some recent results on Raman mapping:

1.InAs nano, micro rods grown using MOVPE          Samples: SCLS, RRCAT:

Raman spectroscopy/mapping gives information about structure, orientation of growth and crystalline quality of InAs as Raman selection rules depend on structure/symmetry of the material and geometry of the measurement.





2.CdS nanoparticles in PVP matrix grown using CBD:

The stoke antistoke ratio, line shape, line width of phonons observed in Raman spectra gives information of growth mechanism, crystalline quality and confirms presence of CdS in PVP balls: imaged using CdS: LO phonon peak.


CdS NPS in PVP matrix
  1. Suparna Pal, S D Singh, V K Dixit, Alka Ingale, et al ;
    Semicond. Sci. Technol. 28, 15025(2013)

  2. Ekta Rani, Alka A. Ingale and  Rahul Aggarwal;
    Presented at ICORS-2012, Bangalore, India
C. Facilities:

Present:
  1. Near field scanning optical microscope(NSOM), SPM integrated Raman system of “WiTec", Germany
  2. Raman system : RAMNOR U1000, Jobin Yvon, France,
  3. Thin film coating unit( metal coating), Hind High Vac, Banglore
  4. He closed cycle Cryostat, Laybold,Germany

Planned:
  1. Tripple stage  Raman micro/macro system with single and multichannel detection.
  2. Facilities like furnace, LB set up for growth with well equipped Chemical lab for growth of nanostructure and their assemblies.
  3. Absorption spectroscopy
  4. Microscope cryostat

D.Growth:

It is planned to use Langmuir Blodgett technique to grow desired samples. At present Chemical Bath deposition (CBD) is used to grow samples of our interest along with other collaborations, wherein samples are grown by M OVPE, PLD, chemical routes etc.

i) Growth of nanostructures using chemical bath technique:
i)	Growth of nanostructures using chemical bath technique
i) Growth of CdS nanowires using template assisted electrochemical deposition technique
Growth of CdS nanowires using template assisted electrochemical deposition technique
  • SEM images by Pragya Tiwari, ISUD, RRCAT


  1. Alka Ingale, L. Agrawal et al
    ICONSAT 2008, Feb 08, Chennai, INDIA.
  2.  Alka A. Ingale,  Komal Bapna,  Rahul Aggarwal et al
    ICONSAT-2010, Feb 2010,Mumbai .

SERS substrate for  nanostructure studies

At present correlation between morphology of Ag nanostructures grown by thermal evaporation method and Raman signal enhancement is being carried out for optimization of SERS.

  • TEM image by Dr. A. K. Srivastava, ISUD, RRCAT
  • Annealing: courtesy Dr. V. K. Dixit, SCLS, RRCAT

  1. M. tech thesis of Ms. Jaya Sahu, Pt. Ravishankar Shukla University, Raipur(C.G.)


E. SELECTED RECENT PUBLICATIONS:

IN JOURNALS:

  1. Intersubband plasmon-phonon coupling in GaAsP/AlGaAs near surface quantum well
    R.  Aggarwal, Alka A. Ingale, Suparna Pal, V.K. Dixit, T. K. Sharma and S. M. Oak 
    Appl. Phys. Lett. 102, 181120 (2013)    

  2. Low- and high-density InAs nanowires on Si(0 0 1) and their Raman imaging.    
    Suparna Pal, S D Singh, V K Dixit, Alka Ingale, Pragya Tiwari, Himanshu Srivastava, Ravi Kumar, C Mukharjee, P Prakash and S M Oak ;
    Semicond. Sci. Technol. 28, 15025(2013)

  3. 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)

  4. 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)

  5. Shape analysis of ZnSe LO phonon near Eo gap excitation
    Tapas Ganguli and Alka Ingale
    Phys. Rev. B. 77, 33202 (2008)

  6. A comparative study on nanotextured high density Mg-doped and undoped GaN
    Suparna Pal, Alka Ingale, V. K. Dixit, T. K. Sharma, S. Porwal, Pragya Tiwari, and A. K. Nath
    J. Appl. Phys. 101, 044311 (2007)

  7. 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)

  8. 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)

  9. 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)

  10. 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;
    Solid State Communications 134, 653–658(2005).

  11. 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)

CONFERENCES:

INTERNATIONAL:

  1. Insight into growth of CdS - PVP nanocomposite using Raman and PL mapping.
    Ekta Rani, Alka A. Ingale and  Rahul Aggarwal;
    Presented at ICORS-2012, Banglore, India

  2. Catalyst-free Epitaxial Growth of InAs Nanowires on (001) Si.
    Suparna Pal, S. D. Singh, V. K. Dixit, Alka Ingale, Pragya Tiwari, and S. M. Oak.
    Presented at The “6th International Workshop on Nano-scale Spectroscopy and Nanotechnology”, NSS6, Japan2010.

  3. 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.

  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. 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

  6. Electronic and phonon Raman scattering in ZnSe/GaAs near Eo gap
    Alka Ingale  and  Tapas Ganguli 
    Presented at “ICORS-06”, Yokohoma, JAPAN, Aug. 2006

  7. 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

NATIONAL:

  1. Intersubband  Plasmon-phonon coupling in GaAsP/AlGaAs single quantum well : A Raman spectroscopy study.
    R. Aggarwal, Alka A. Ingale
    , Suparna Pal and S. M. Oak
    DAE Solid State Physics Symposium  2010, AIP conf. Proc.1349,1101(2011) doi: 10.1063/1.3606247

  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).

  3. 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;
    Presented at ICONSAT 08, Feb 08, Chennai, INDIA.

  4. 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.
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