Naresh Kumar

PhD candidate

Employed since: April 2015
telephone: +4489436687
G9A7, National Physical Laboratory, UK

Tip-enhanced Raman spectroscopy (TERS) is a powerful nanoanalytical technique for simultaneous chemical (molecular) and topographical mapping of a surface at the nanoscale. Since the first experimental realisation of TERS in 20001, TERS has been successfully utilised in diverse areas of scientific research such as biology, material science, polymer-blends, solar-cells, graphene and 2D materials, catalysis, single molecule imaging etc2-5. The principle of TERS involves the enhancement and confinement of electromagnetic (EM) field at the apex of a metal or metal-coated scanning probe microscopy tip, when exposed to laser excitation matching its surface plasmon resonance wavelength (λSPR). This plasmonic enhancement of the EM field leads to high chemical sensitivity and a nanoscale spatial resolution (typically < 20 nm) in TERS maps, enabling the observation of molecular phenomena far beyond the optical diffraction limit (typically 200 - 300 nm).

However, despite a significant progress in TERS instrumentation, rapid degradation of TERS probes, especially those coated with silver, is a major bottleneck to the widespread uptake of the technique and severely prohibits the success of many TERS experiments including its application in catalysis research6. Furthermore, to date nanoscale Raman imaging in a liquid environment hasn’t been achieved using TERS, which is essential for studying several industrially important heterogeneous catalysts and catalytic reactions7. Therefore, the key goals of this PhD project are as follows:

Development of TERS:

  1. To study the degradation mechanism of TERS probes, develop strategies to mitigate probe degradation and extend their plasmonic lifetime.
  2. To develop and demonstrate the capability of nanoscale Raman mapping in a liquid environment using TERS.

Application of TERS to heterogeneous catalysis research:

  1. Application of tip-enhanced Raman/photoluminescence spectroscopy to map catalytic activity in fluid catalytic cracking particles at the nanoscale.
  2. Application of tip-enhanced Raman spectroscopy to monitor catalytic hydrogenation of nitrobenzene on Pt/Pd at solid liquid interfaces.

[1] R. M. Stöckle, Y. D. Suh, V. Deckert, & R. Zenobi “Nanoscale chemical analysis by tip-enhanced Raman spectroscopy” Chem. Phys. Lett. 2000, 318(1), 131-136
[2] N Kumar, S Mignuzzi, W Su, D Roy “Tip-enhanced Raman spectroscopy: Principles and applications” EPJ Tech. Instrum. 2015, 2, 9
[3] N Kumar, B Stephanidis, R Zenobi, A J Wain, D Roy “Nanoscale mapping of catalytic activity using tip-enhanced Raman spectroscopy” Nanoscale 2015, 7, 7133–7137
[4] W Su*, N Kumar*, S Mignuzzi, J Crain, D Roy “Nanoscale Mapping of Excitonic Processes in Single layer MoS2 using Tip-enhanced Photoluminescence Microscopy” Nanoscale 2016, 8, 10564-10569 (*Equal contribution)
[5] W Su*, N Kumar*, D Roy “Nanoscale chemical mapping of intrinsic defects in graphene using tip-enhanced Raman spectroscopy” Chem. Commun. 2016, 52, 8227-8230 (*Equal contribution)
[6] N Kumar, S J Spencer, A J Wain, D Imbraguglio, A Rossi, B M Weckhuysen, D Roy “Enhancing the plasmonic lifetime of tip-enhanced Raman spectroscopy probes” Phys. Chem. Chem. Phys. 2016, 18, 13710-13716
[7] T Hartman, C S Wondergem, N Kumar, A Berg and Bert M. Weckhuysen “A Perspective on Surface- and Tip-Enhanced Raman Spectroscopy in Heterogeneous Catalysis” J. Phys. Chem. Lett. 2016, 7, 1570-1584