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

Nanoscience is the study of nanoscale materials to understand thermodynamics and chemistry of growth and correlations of material properties with size and shape, whereas nanotechnology is working towards achieving controlled growth of the nano materials for applications. 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 and various properties of 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.

Interdisciplinary Research


AIM:

1. Use optical and scanning probe microscopies together to study optical, electronic, vibrational and electrical properties of nanomaterials and nanocomposites and correlate them with their morphology (size and shape) to obtain unique information about these materials.

2. Growth of semiconductor, carbon, metal nanostructures and assembly of inorganic nanostructures, biophatoms of interest using chemical and evaporation methods.

What is the interest?

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


Nanocomposites:

Materials at nanoscale show unique properties due to their large surface-to-volume ratio and or quantum size effects. Further, nanocomposites (NCps), in which nanostructures are embedded into a processable matrix are of potential interest as the matrix provides stability and processibility to the nanostructures. This matrix can be either ceramic or polymer. With this motivation we have studied two specially chosen NCps: (i) Si-SiO2 (ceramic matrix) and ii) CdS-polyvinyl pyrrolidone (PVP: polymer matrix). In the first case, an inorganic ceramic matrix is an oxide of the same semiconductor, whereas, in the second case, organic matrix provides a completely heterogeneous NCp and thus, it is expected that the manifestation of interactions between the semiconductor nanocrystals and a matrix are quite different in these two cases.



How do we go about it?

A. Raman spectroscopy :

Our strength being Raman spectroscopy, it is our aim to use Raman spectroscopy for study of condensed matter physics. Absorption and PL spectroscopy are used to further gain information of electronic structure 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. Recently, our emphasis is using spatially resolved Raman spectroscopy/mapping in tandem with Atomic force microscopy(AFM) to obtain unique information about surface and interface of nanostructures and nanocomposites.



Schematic : Basic Raman spectroscopy set up


In nanostructures, confinement of phonons and manifestations of increased surface to volume ratio has been studied in CdS, CdSxSe1-x 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/Al0.7Ga0.3As 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.


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


Schematic representation of nanostructures/clusters studiedp


1. Size distribution from line shape of CAP Raman spectra : CdSSe nanoparticles in

Glass matrix


2. Direct evidence of clustering in soft to rigid transition in Ge-Se Glass at Ge 20%

using CAP’s in Raman spectra: Ge-Se glass provided by Dr. Awasthi (UGC- DAE

consortium, Indore)


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.

Ref:
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)


Study of stress and

accompanying disorder using


Intersubband plasmon-phonon coupling in GaAsP/AlGaAs near surface quantum well

(NSQW)


B. Scanning probe microscopy 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.

“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 and AFM mapping on the same site. We are working on substrate preparation for surface enhanced Raman scattering (SERS) using thin film coating unit, (Hind highvac, Bengluru) for generating Ag/Au films. Alternatively, we are pursuing assembly of inorganic nanoparticles (including Ag NPs for SERS) using Langmuir Blodgett (KSV-NEEMA : KN2003 with BAM attachment ) set up. This will allow us to perform Raman imaging of nanostructures more effectively along with other scanning probe microscopies.



SPM integrated Raman system, WiTec, Germany


Raman mapping

of Nanostructures


Spatially resolved Raman spectra of tapered Microwirey


  • The asymmetric peak ~212–218 cm-1 occurring in InAs micro-nanowires (MNWs: diameter: 2 μm – 400 nm) is investigated using spatially resolved Raman spectroscopy of uniform, bent and long tapered MNWs grown on a Si (001) substrate.
  • It is attributed to superposition of E2h phonon (wurtzite: WZ) and TO phonon (zinc blende: ZB) of InAs. Polarized and wavelength-dependent spatially resolved Raman spectroscopy establishes the presence of WZ and ZB phases in these MNWs.
  • However, formation of WZ phase for larger diameter InAs MNWs is not commensurate with existing growth mapping studies. Further, study of these MNWs suggests that the fraction of WZ to ZB content in a MNW depends not only on the diameter but also seems to be governed by local growth seeding/conditions. This in turn leads to either tapered or uniform MNW growth under the same (external) growth conditions.
  • The variation of these wavenumbers that of bulk value is correlated to the residual stress present in ZB and WZ phases due to the presence of the other (WZ/ZB) phase. Consistently, temperature-dependent Raman data show that there is a measurable contribution of stress to dω/dT, a positive for ZB and negative for WZ phonons, due to dif erences in their thermal expansions.
  • Further, ef ective thermal expansion coef icient of WZ InAs in the presence of ZB phase is calculated to vary in the range 10-19 × 10 -6 /K from base to tip of a MNW at ~80 K, which is not possible to determine otherwise.

E2h(WZ) phonon ~ 213/4cm-1,  TO(ZB) phonon ~216/17cm-1. In x(zz)-x : Only TO phonon is allowed , whereas in x(yy)-x : Both E2h and TO phonons are allowed.

Ref :
Vandna K Gupta, Alka Ingale et al, J of Raman Spectroscopy 48, 855(2017)

Raman and AFM mapping on the same site:
Raman and AFM mapping of Si-SiO2 nanocomposites

Raman and AFM mapping of Si-SiO2 nanocomposites

The sensitivity of Raman spectroscopy to surface/interface and confinement ef ects in nanocrystals is ef ectively used to correlate Raman mapping with AFM to understand that Si NCs are clustered in i) smaller clusters (~ 100 nm) organized closely in two dimensions and ii) big (~ 2 µm) three dimensional isolated clusters.


Ref :
1. Ekta Rani, Alka A. Ingale et al, J. of Raman Spectroscopy 47(2016), 457
2. Ekta Rani, Alka A. Ingale et al , J of Alloys and Compounds 672 (2016), 403.
3. Ekta Rani, Alka A. Ingale et al; Appl. Phys. Lett. 107 (2015), 163112

1. CdS nanocrystals in PVP matrix grown using CBD :

CdS-PVP nanocomposites grown with various concentrations of Cd+/S- and PVP are studied using Raman and atomic force microscopy mapping on same selected areas.

CdS nanocrystals in PVP matrix grown using CBD

  • CdS nanocrystals are embedded in either a thin-film or spheres of PVP, formation of which depends on relative ratio of Cd+/S- concentration (density of nanocrystals) to PVP.
  • Collapse of PVP from planer matrix to the sphere morphology is correlated with the interaction between nanocrystals and polymer leading to a co-operative growth mechanism.
  • 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.


Raman image of polymer spheres


Ref :
1. Ekta Rani, Rahul Aggarwal, Alka A Ingale et al, J. of Materials Science 51 (2016), 1581.
2. Ekta Rani, Alka A Ingale and A K Sinha, Journal of Alloys and Compounds 729C (2017) 597.


2. Raman spectroscopy and atomic force microscopy study of interfacial polytypism in GaP/Ge(111) heterostructures

Impacts of lattice and polar/nonpolar mismatch for the GaP layer grown on Ge(111) substrate are investigated by spatially resolved Raman spectroscopy. The red shifted transverse optical (TO) and longitudinal optical (LO) phonons of GaP due to residual strain, along with asymmetry to TO phonon ~358 cm−1 are observed in GaP/Ge(111).

  • The peak intensity variation of mode ~358 cm−1 with respect to TO phonon across the crystallographic morphed surface of GaP micro structures is associated with the topographical variations using atomic force microscopy mapping and Raman spectroscopy performed on both in plane and cross-sectional surface.
  • Co-existence of GaP allotropes, i.e. wurtzite phase near heterojunction interface and dominant zinc-blende phase near surface is established using the spatially resolved polarized Ramanspectroscopy from the cross sectional surface of heterostructures.
  • This consistently explains ef ect of surface morphology on Raman spectroscopy from GaP(111). The study shows the way to identify crystalline phases in other advanced semiconductor heterostructures without any specific sample preparation.
  • This study provides a clear basis for future experimental investigation of interfacial polytypism in hetero-structures without requiring any sample preparation using Raman spectroscopy.

Optical Image

Optical Image

Polarized Raman spectra


Ref:
1.R. Aggarwal, A A Ingale, VK Dixit,Applied Surface Science 427(B) (2018)54


Investigations on the origin of strain variation in the zinc-blende phase along the depth of GaP/Si(111) using spatially resolved polarized and wavelength dependent Raman spectroscopy

For fine tuning of properties of semiconductor nanowires, modifications of the surface and dimensions of these nanowires using laser irradiation are being suggested as one of the methods. In order to control the oxidation processes leading to surface modifications, one needs to obtain understanding of temperature rise at the surface of MNW under laser irradiation.

  • Spatially resolved & wavelength dependent Raman spectra stimulates in depth sampling of cross-sectional surface of GaP/Si(111) thick layer at a separation of ~100 nm, via spatially resolved Raman spectroscopy. The study revealed that the presence of WZ phase near interface leads to differently strained regions of ZB GaP. ZB region closer to interface is more strained due it’s proximity to WZ phase, and ZB phase near surface is less strained being away from WZ phase.

  • The experimental findings illuminate, how effectively the spatially resolved Raman spectroscopy can be employed for probing the variation of optical, structural and physical attributes (crystal structure, crystalline quality, strain, carrier concentration etc.) along the depth of hetero-structures.
The study bestows with new opportunities for engineering of the GaP/Si based crystal phase quantum structures with atomically sharp interfaces. Spatially resolved Raman spectroscopy can serve as a quick and impactful alternative to time consuming and cumbersome high-resolution transmission electron microscopy / in situ reflection anisotropy spectroscopy measurements for probing the surface and interface properties of such hetero-structures.

Ref:
R. Aggarwal, A. A. Ingale and V.K. Dixit, Appl. Surf. Sci., 2020, 514, 145933(1)-145933(6).

(a) Raman spectra (from the growth surface) arising from two types of regions of GaP/Si(111) thick layer (TL), type A) having smaller thickness of GaP and type B) having larger thickness of GaP. Inset shows the deconvolution fit, showing the doublet and singlet LO phonon features in type ‘A’ and ‘B’, respectively (b) 3-D AFM map of thick layer hetero-structure.
(a) Raman spectra (from the growth surface) arising from two types of regions of GaP/Si(111) thick layer (TL), type A) having smaller thickness of GaP and type B) having larger thickness of GaP. Inset shows the deconvolution fit, showing the doublet and singlet LO phonon features in type ‘A’ and ‘B’, respectively (b) 3-D AFM map of thick layer hetero-structure.


(a) Optical image of cross-sectional surface of GaP/Si(111) thick layer (b) Raman spectra at seven spatial positions across the cross-sectional surface marked in (a), and (c) Deconvolution of contributions to Raman spectra at positions ‘1’, ‘4’ and ‘7’ using minimum number of Lorentzian and Gaussian lineshapes. E2H (wurtzite), SO and TO/LO (zinc-blende) phonons contributions are shown in orange, magenta and blue colors, respectively. Red colour is total fit to data (+).
(a) Optical image of cross-sectional surface of GaP/Si(111) thick layer (b) Raman spectra at seven spatial positions across the cross-sectional surface marked in (a), and (c) Deconvolution of contributions to Raman spectra at positions ‘1’, ‘4’ and ‘7’ using minimum number of Lorentzian and Gaussian lineshapes. E2H (wurtzite), SO and TO/LO (zinc-blende) phonons contributions are shown in orange, magenta and blue colors, respectively. Red colour is total fit to data (+).


Elucidating the interfacial nucleation of higher-index defect facets in technologically important GaP/Si(001) by azimuthal angle-resolved polarized Raman spectroscopy

Influence of substrate crystallographic orientation and therefore the surface energy on the structural properties of grown layer is explored by investigating the epitaxy of non-polar GaP on extensively used (001) oriented Si substrate orientation i.e., closely lattice-matched GaP/Si(001) hetero-structures. Polar Raman measurements on GaP/Si(001) hetero-structures reveal that interfacial nucleation and subsequent coalescence of faceted epiltaxial micro/nano-structures give rise to higher-index defect-exposed {111} and {112} facets in the overgrowth layer.

  • The unusual observation of symmetry forbidden transverse optical (TO) phonon ~360 cm-1 having large Raman scattering cross-section is analyzed by taking into account the crystallographic disorders and topographical variations in the GaP epilayer. The polarized Raman spectroscopy study incites the azimuthal angle-dependent polarized Raman measurements for deeper understanding of higher-index defect-exposed facets near the interface.

  • The spatially resolved polar Raman dependence of TO and LO phonon spectra in parallel and perpendicular polarization configurations has deciphered scattering contributions from locally present higher-index {111} and {112} defect facets in thick epilayer, which stems from the coalescence of faceted islands formed during the initial nucleation as inferred via topographical mapping of nucleating layer.

  • The polarization dependent Raman measurements from cross-sectional surface of thick GaP layer grown on Si (001), establishes the WZ/ZB crystal phase coexistence with dominance of WZ phase near the interface. The intriguing presence of WZ phase in GaP/Si(001), is expected to be the result of manifestation of stacking faults along the sets of thermodynamically favorable intermixed high index <111> direction.

An optical (Raman) spectroscopy technique is innovatively deployed to give an expeditious and non-destructive substitute to the tedious cross-sectional high-resolution transmission electron microscopy for obtaining the immediate and appropriate growth strategy to achieve high-quality GaP/Si (001), as well as in evaluation of the grown hetero-structure for device applications.

Ref:
R. Aggarwal, A. A. Ingale and V. K. Dixit, Appl. Surf. Sci., 2021, 554, 149620(1)-149620(10)

(a) Typical schematic of Raman back-scattering configuration utilized for determining the azimuthal angle dependence of intensity of optical phonons scattered from a given crystal orientation. (ei, ki) and (es, ks) are the incident and scattered light polarization and propagation wave vectors respectively. Observed polar dependence of LO phonon of GaP/Si(001) thick layer (TL) hetero-structure in parallel (ei||es) polarization configuration arising from spatial position of (b) type ‘1′ (where peak intensity ratio R = ITO/ILO is less than unity in unpolarized spectra) and (c) type ‘2′ (where peak intensity ratio R = ITO/ILO is nearly one in unpolarized spectra). Calculated azimuthal angle dependence of LO phonon for scattering from (d) (001) and (e) (111) plane. Observed polar plots of TO phonon of thick layer hetero-structure in parallel configuration at position of (f) type ‘1′ and (g) type ‘2′ . Calculated TO phonon azimuthal dependence for scattering from (h) (111) facets and (i) combination of (001) and (111) facets.
(a) Typical schematic of Raman back-scattering configuration utilized for determining the azimuthal angle dependence of intensity of optical phonons scattered from a given crystal orientation. (ei, ki) and (es, ks) are the incident and scattered light polarization and propagation wave vectors respectively. Observed polar dependence of LO phonon of GaP/Si(001) thick layer (TL) hetero-structure in parallel (ei||es) polarization configuration arising from spatial position of (b) type ‘1′ (where peak intensity ratio R = ITO/ILO is less than unity in unpolarized spectra) and (c) type ‘2′ (where peak intensity ratio R = ITO/ILO is nearly one in unpolarized spectra). Calculated azimuthal angle dependence of LO phonon for scattering from (d) (001) and (e) (111) plane. Observed polar plots of TO phonon of thick layer hetero-structure in parallel configuration at position of (f) type ‘1′ and (g) type ‘2′ . Calculated TO phonon azimuthal dependence for scattering from (h) (111) facets and (i) combination of (001) and (111) facets.



(a) Unpolarized Raman map of GaP/Si(001) nucleating layer (NL) obtained by integrating the intensity over the spectral range 330-410 cm-1 (b) observed Raman spectra from three different spatial positions (marked in (a)) across NL (c) Polarization dependent Raman spectra from near interface region of cross-sectional surface of thick layer hetero-structure, in Y-incident and Z-incident (where ‘Z’ is along the growth direction) polarization configurations, revealing the co-dominance of wurtzite phase at GaP-Si(001) interface (d) schematic diagram illustrating the nucleation of GaP islands terminating on higher-index {111} and {112} facets.
(a) Unpolarized Raman map of GaP/Si(001) nucleating layer (NL) obtained by integrating the intensity over the spectral range 330-410 cm-1 (b) observed Raman spectra from three different spatial positions (marked in (a)) across NL (c) Polarization dependent Raman spectra from near interface region of cross-sectional surface of thick layer hetero-structure, in Y-incident and Z-incident (where ‘Z’ is along the growth direction) polarization configurations, revealing the co-dominance of wurtzite phase at GaP-Si(001) interface (d) schematic diagram illustrating the nucleation of GaP islands terminating on higher-index {111} and {112} facets.

The ongoing experimental work in Raman spectroscopy lab is focused on establishing the one-to-one correspondence between Raman spectroscopy and HRTEM. This will establish Raman spectroscopy as a standard and expeditious methodology to obtain important information on hetero-structures as well as in their evaluation for device fabrication.

Predicting surface modification of InAs nanowires on laser irradiation using transient thermal simulation and time evolution of Raman spectra:
In this work, role of temperature simulation is investigated for predicting surface modification of InAs nanowire (NW) using laser irradiation. The surface modification is monitored by Raman spectroscopy. This study provides the basis for using temperature simulation in predicting / controlling the required surface modification for other III-V NWs useful in nanotechnology.

For fine tuning of properties of semiconductor nanowires, modifications of the surface and dimensions of these nanowires using laser irradiation are being suggested as one of the methods. In order to control the oxidation processes leading to surface modifications, one needs to obtain understanding of temperature rise at the surface of MNW under laser irradiation.

In this work, we first establish correlation between simulated temperatures at the surface of a InAs nanowire (NW) with time evolution of Raman spectra, on laser irradiation. Transient thermal simulations are performed with ANSYS software using finite element method, considering 3D geometry of the irradiation setup. In the systematic study of laser irradiation (laser power densities ~ 30-636 kW/cm2) over time duration of ~ 8 minutes, the simulated temperature is found to corroborate well with the corresponding oxidation processes e.g. weak (WP), intermediate (IP) and strong (SP), occurring on the surface of InAs nanowire under various laser irradiation conditions. The predictability of the methodology was then investigated by applying it to random conditions of NW like diameter, aspect ratio and laser power density etc. for i) NWs found in the same sample and ii) InAs NWs grown elsewhere and transferred on other Si substrate. The study establishes predictability of various oxidation processes for given NW dimensions, laser power density and irradiation time, thus validating the importance of temperature simulation in predicting / controlling the required surface modification for other III-V NWs useful in nanotechnology.


Polarized Raman spectra
Ref:
Vandna K. Gupta, Alka A. Ingale, Vikas Jain, R. Aggarwal et al, Journal of Alloys and Compounds 735 (2018)1331.
1. Vandna K. Gupta, Alka A. Ingale, Arnab Bhattacharya, Mahesh Gokhale, Rahul Aggarwal et al, Nanotechnology 29(2018).

B. Growth:
Growth of semiconductor, metal nanostructures and biophantoms are proposed to be grown using different chemical ( CBD and LB ) and evaporation ( vacuum furnace) techniques. i) Growth of nanostructures using chemical bath Deposition:


Growth of nanostructures
Ref:
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 .

ii) Growth of CdS nanowires using template assisted electrochemical deposition technique and vacuum furnace


Growth of CdS nanowires
Collaboration : P. Ram sankar, CTF
SEM images by SUS & LFMD, RRCAT

Ref:
1. Rahul Aggarwal, P. Ram Sankar, Akanksha Sahu, Alka A. Ingale et al. Journal of Materials Science: Materials in Electronics 29 (2017), 427
2. M.Tech thesis ( 2015), Ms. Akansha Sahu, , Pt. Ravishankar Shukla University, Raipur(C.G.)

iii) Assembly of nanostructures using Langmuir set up : 

High dielectric constant and excellent photo catalytic activity in thin films of TiO2 anoparticles find potential uses in sensors, memory applications, coatings (anti-reflection, superhydrophobic/philic etc.) etc. Nanoparticle assembly is a nascent field and a step forward in realizing use of nanoparticles for device fabrication/s. Langmuir Blodgett deposition method for nanoparticles is being employed for generating ordered film of TiO2 nanoparticles.


Conventionally, Langmuir films are made of amhiphilic molecules, which allow formation of a layer of these organic molecules on air-water interface using Langmuir technique. However, for inorganic molecules/particles, they tend to go into the water subphase, unless functionalized by organic amhiphilic molecules. This is not a desirable way of achieving floating of these particles on water subphase, as amhiphilic molecules needs to be separated or may have effect on the functional properties of Langmuir films of these inorganic materials. Thus, the critical part of the work is to form Langmuir layer of TiO2 nanoparticles on a air water interface without functionalizing it with amhiphilic molecules. We have employed methodology of two dimensional aggregation of the particles to make them floating at air-water interface. Brewster angle microscope (BAM) images in process of TiO2 film formation on air water interface are shown below.



Growth of CdS nanowires

Ref:
M.Tech thesis (2016) of Geethy Purushothaman, International School of Photonics Cochin University of Science and Technology, India

iv)Growth of biophantoms useful for energy storage applications using LB set up :

Solid biopolymer electrolytes (SBPE) are being intensively studied for their possible application as electrolytes in solid state electrochemical devices such as fuel cells, batteries, super capacitors, sensors, etc. The advantages of SBPEs over conventional liquid electrolytes are high energy density, leak proof, high ionic conductivity, wide electrochemical stability windows, light weight, solvent free condition and easy to design to any shape etc. Recently, chitosan has been extensively studied because of its biodegradable, biocompatible, and non-toxic behaviour. Langmuir Bldogett technique is used to deposit chitosan based film on microslides.


Among various technologies, The Langmuir-Blodgett (LB) provides methods of preparing organized molecular assemblies (monolayer/multilayer). LB technology offers the possibility to prepare biomimic layers. Chitosan is a polycationic polymer due to the existence of one amino group and two hydroxyl groups in its repeating units. It is a non amphiphillic bioelectrolyte, however taking support of amphiphillic molecules such as lipids it may form films. We are pursuing studies to develop LB films of chitosan, taking support of stearic acid as the supportive amphiphillic molecule. A representative pressure–area curve of one of the studies is shown in the following figure. It shows shift in monolayer formation area with increase in chitosan concentration indicating inclusion of chitosan in the film. The BAM images of Langmuir layer at various stages of formation from gaseous to liquid condensed to monolayer are also shown in the following.



Growth of CdS biophantoms

Ref:
M.Sc. thesis of Ms. Artha S., Department of Physics, Central University of Karnataka, Gulbarga, 2019

v) Preaparathion of SERS substates using different growth techniques:

     a) Chemical route : Ag nanoprisms
     b)Vacuum deposition of Ag/Au nanoparticles films
     c)LB film preparation of Ag nanospeheres.



Preaparathion of SERS substates

Jaya’s data for SERS, Bansley’s SERS
Ref:
M. tech thesis (2010) of Ms. Jaya Sahu, Pt. Ravishankar Shukla University, Raipur (C.G.)




C) Growth of Ag nanostructures and their assembly employing Langmuir Blodgett technique for SERS applications :

Assembly of functional nanomaterials is one of the most important process in development of nanotechnology. Understanding fundamental physics of these assemblies is essential in order to use them in various applications and devices. For this purpose, to increase Raman spectroscopy signal in nanomaterials (very small volume), surface enhanced Raman scattering (SERS) is employed using rough/nanostructure metal surfaces.

To obtain uniformity and larger signal to noise ratio, SERS substrate of Ag nanostructures (Ag NS ~ 200 nm) was prepared using Langmuir Blodgett (LB) technique. The material to be studied i.e. TiO2 nanoparticulate (~20nm) film, was deposited on this substrate also using LB technique. We find that this methodology gives uniform SERS with enhancement factor ~ 10-15, whereas, it is ~2-3 for SERS substrate grown using other techniques like drop method, spin coating etc. This study shows that SERS using LB technique is very useful to investigate nanostrucrtures in the case of non resonant Raman spectroscopy.



Growth of Ag nanostructures and their assembly

Optical Image of TiO2 nanoparticulate Monolayer a) Deposited on Glass and b) Deposited over Ag NS monolayer substrate and c) Raman spectra on marked points on the optical images shows SERS for TiO2 NCs.
Ref:
M. tech thesis(2017) of Ms. Ankita Tiwari, Pt. Ravishankar Shukla University, Raipur(C.G.)


D. Facilities:
Present:

  1. Triple stage Raman system, S & I, Instruments, Germany.
  2. SPM integrated Raman system of “WiTec", Germany
  3. Raman system : RAMNOR U1000, Jobin Yvon, France,
  4. He closed cycle Macro Cryostat, Laybold, Germany
  5. Thin film coating unit (metal coating), Hind High Vac, Bengluru
  6. Langmuir Blodgett (LB) set up with BAM, Biolin scientific, Sweden
  7. Chemical lab
  8. Single zone vacuum furnace

Planned :
  1. Absorption microscopy set up
  2. Microscopy cryostat
  3. Spectrophotometer
  4. Multizone vacuum furnace

E. SELECTED PUBLICATIONS :
IN JOURNALS :
  1. Elucidating the interfacial nucleation of higher-index defect facets in technologically important GaP/Si(001) by azimuthal angle-resolved polarized Raman spectroscopy
    R. Aggarwal, A. A. Ingale and V. K. Dixit, Appl. Surf. Sci., 2021, 554, 149620(1)-149620(10)

  2. Investigations on the origin of strain variation in the zinc-blende phase along the depth of GaP/Si(111) using spatially resolved polarized and wavelength dependent Raman spectroscopy
    R. Aggarwal, A. A. Ingale and V.K. Dixit, Appl. Surf. Sci., 2020, 514, 145933(1)-145933(6).

  3. Raman spectroscopy investigation of inter-diffusion in GaP/Ge(111) heterostructures
    R. Aggarwal, Alka A. Ingale, V. K. Dixit and V. Sathe Superlattices and microstructures125, 190 (2019)

  4. Understanding effect of nanowire orientation on time evolution of Raman spectra from laser irradiated InAs nanowire surface
    Vandna K Gupta, Alka A Ingale, Arnab Bhattacharya, Mahesh Gokhale, R. Aggarwal and Suparna Pal; Nanotechnology 29, 425709 (2018)

  5. Predicting surface modification of InAs nanowires on laser irradiation using transient thermal simulation and time evolution of Raman spectra.
    Vandna K. Gupta, Alka A. Ingale, Vikas Jain, R. Aggarwal, S. Pal; Journal of Alloys and Compounds735,1331 (2018)

  6. Band gap tuning in Si-SiO2 nanocomposite: Interplay of confinement effect and surface/ interface bonding.
    Ekta Rani, Alka Ingale, D. M. Phase, A. Chaturvedi, C. Mukherjee, M. P. Joshi and L. M. Kukreja Applied Surface Science 425C, 1089 (2017).

  7. Raman spectroscopy and atomic force microscopy study of interfacial polytypism in GaP/Ge (111) heterostructures.
    R Aggarwal, A A Ingale, VK Dixit Applied Surface Science 427(B), 54 (2018) [doi.org/10.1016/j.apsusc.2017.09.006]

  8. Interaction between CdS nanocrystals and PVP leading to co-operative growth of CdS PVP nanocomposites: A Raman and AFM mapping study.
    Ekta Rani, Alka A Ingale and A K Sinha Journal of Alloys and Compounds 729C, 597 (2017)

  9. Template based room temperature growth of high density CdS nanowires from aqueous electrolyte using high frequency alternating current.
    Rahul Aggarwal, P. Ram Sankar, Akanksha Sahu, Alka A. Ingale, Anil K Sinha, Chandrachur Mukherjee, Journal of Materials Science: Materials in Electronics 29, 427 (2017)

  10. Spatially resolved Raman spectroscopy study of uniform and tapered InAs micro-nano wires: Correlation of strain and polytypism.
    Vandna K. Gupta, Alka A. Ingale, Suparna Pal, R. Aggarwal and V. Sathe J. Raman spectroscopy 48, 855 (2017).

  11. Corroboration of Raman and AFM mapping to study Si nanocrystals embedded in SiO2;
    Ekta Rani, Alka A. Ingale, A. Chaturvedi, M. P. Joshi and L. M. Kukreja. J of Alloys and Compounds 672, 403 (2016).

  12. Insight into one-step growth of nearly monodispersive CdS nanocrystals embedded in polyvinyl pyrrolidone spheres;
    Ekta Rani, Rahul  Aggarwal, Alka A Ingale, K. Bapna, C. Mukherjee, M. K. Singh, P. Tiwari  and A. K. Srivastava, J. of Materials Science 51, 1581 (2016).

  13. Resonance Raman mapping as a tool to monitor and manipulate Si nanocrystals in Si-SiO2 nanocomposite;
    Ekta Rani, Alka A. Ingale, A. Chaturvedi, M. P. Joshi and L. M. Kukreja. Appl. Phys. Lett. 107, 163112 (2015).

  14. Correlation of size and oxygen bonding at the interface of Si nanocrystal in Si-SiO2 nanocomposite: A Raman mapping study.
    Ekta Rani, Alka A. Ingale, A. Chaturvedi, C. Kamal, D. M. Phase, M. P. Joshi, A. Chakrabarti, A. Banerjee and L. M. Kukreja, J. of Raman Spectroscopy 47, 457 (2016)

  15. Time evolution studies of laser induced chemical changes in InAs nanowire using Raman spectroscopy.
    Suparna Pal, R. Aggarwal, Vandna Kumari Gupta and Alka Ingale Appl. Phys. Lett. 105, 012110 (2014).

  16. 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)

  17. 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)

  18. 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)

  19. 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)

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

  21. 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)

  22. 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)

  23. 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)

  24. 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)

  25. 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).

  26. 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)

  27. Photoluminescence in Fullerene doped porous glass
    Joshi M.K., Ingale Alka Applied Physics B 72, 941(2001).

  28. Effect of heavy ion irradiation on C60
    S.Lotha, Ingale A.A., D.K.Awasthi, V.K.Mittal, S.Mishra, Rustagi K.C. Solid State Communications 111, 55 (1999).

  29. Growth and Characterization of oriented Cadmium Sulphide nanocrystals under Langmuir-Blodgett Monolayer of Arachidic acid
    Roy U. N., Ingale A.A., Kukreja L.M., Mishra S., Ganesan V., Rustagi K.C. Applied Physics A 69, 385 (1999).

  30. Raman and photoluminescence investigations of disorder in ZnSe films deposited on n-GaAs.
    Ganguli T., Ingale A. A. Physical Review B 60, 11618 (1999).

  31. Raman spectra of CdSxSe1-x nanoparticles: disordered activated phonons
    Ingale A. Alka, Rustagi K.C. Physical Review B 58, 7197 (1999).

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