Mayukh Banik | University of California, Irvine (original) (raw)

Papers by Mayukh Banik

Journal of Physical Chemistry Letters

We present a theoretical analysis of Raman intensities for a molecule that bridges a current carr... more We present a theoretical analysis of Raman intensities for a molecule that bridges a current carrying junction. Experimental data is used to estimate parameters for the theoretical model. The recently reported staircase of Raman intensities observed during the fusion of nanodumbbell is reproduced.

Nature Photonics, 2014

The motion of chemical bonds within molecules can be observed in real time in the form of vibrati... more The motion of chemical bonds within molecules can be observed in real time in the form of vibrational wave packets prepared and interrogated through ultrafast nonlinear spectroscopy. Such nonlinear optical measurements are commonly performed on large ensembles of molecules and, as such, are limited to the extent that ensemble coherence can be maintained. Here, we describe vibrational wave packet motion on single molecules, recorded through time-resolved, surfaceenhanced, coherent anti-Stokes Raman scattering. The sensitivity required to detect the motion of a single molecule under ambient conditions is achieved by equipping the molecule with a dipolar nano-antenna (a gold dumbbell). In contrast with measurements in ensembles, the vibrational coherence on a single molecule does not undergo pure dephasing. It develops phase fluctuations with characteristic statistics. We present the time evolution of discretely sampled statistical states, and highlight the unique information content in the characteristic, early-time probability distribution function of the signal.

By taking advantage of the tensor nature of surfaceenhanced Raman scattering (SERS), we track tra... more By taking advantage of the tensor nature of surfaceenhanced Raman scattering (SERS), we track trajectories of the linker molecule and a CO molecule chemisorbed at the hot spot of a nano-dumbbell consisting of dibenzyldithio-linked silver nanospheres. The linear Stark shift of CO serves as an absolute gauge

ABSTRACT The motion of chemical bonds within molecules can be observed in real time, in the form ... more ABSTRACT The motion of chemical bonds within molecules can be observed in real time, in the form of vibrational wavepackets prepared and interrogated through ultrafast nonlinear spectroscopy. Such nonlinear optical measurements are commonly performed on large ensembles of molecules, and as such, are limited to the extent that ensemble coherence can be maintained. Here, we describe vibrational wavepacket motion on single molecules, recorded through time-resolved, surface-enhanced, coherent anti-Stokes Raman scattering. The required sensitivity to detect the motion of a single molecule, under ambient conditions, is achieved by equipping the molecule with a dipolar nano-antenna (a gold dumbbell). In contrast with measurements in ensembles, the vibrational coherence on a single molecule does not dephase. It develops phase fluctuations with characteristic statistics. We present the time evolution of discretely sampled statistical states, and highlight the unique information content in the characteristic, early-time probability distribution function of the signal.

The Journal of Physical Chemistry C, 2012

We describe combined AFM/Raman measurements on single nanodumbbells, consisting of silver nanosph... more We describe combined AFM/Raman measurements on single nanodumbbells, consisting of silver nanospheres linked with dibenzyl-4,4′dithiol (DBDT). The measured surface-enhanced Raman scattering (SERS) enhancement factor, EF exp = 3 × 10 7 at 532 nm, corresponds to the observed signal strength of a single DBDT molecule, the Raman cross section of which was determined to be dσ/dΩ = 6 × 10 −28 cm 2 /sr. We show that the product of the local field enhancement, EF P = (E i /E 0 ) 2 (E s /E 0 ) 2 = 3 × 10 6 , and the chemical contribution due to reduced detuning, EF C = (Δ 0 /Δ) 2 = 12, account for the observed effect. The chemical contribution is assessed by exploring model structures Ag n −S−DB−S−Ag m (n, m = 0, 3, 7, 20). The π−π* transition at 287 nm, which determines the polarizability of the bare molecule, acquires a DBDT-to-silver charge-transfer character upon binding to silver. The CT transition near 400 nm reduces the detuning but remains nonresonant at 532 nm. We observe a soft polarization dependence, which suggests optical activity, which in part is ascribed to coupling between plasmons and conjugated electrons of DBDT. Modest enhancement factors are sufficient to detect single molecules through nonresonant SERS.

The Journal of Physical Chemistry Letters, 2013

ABSTRACT We present a theoretical analysis of Raman intensities for a molecule that bridges a cur... more ABSTRACT We present a theoretical analysis of Raman intensities for a molecule that bridges a current carrying junction. Experimental data is used to estimate parameters for the theoretical model. The recently reported staircase of Raman intensities observed during the fusion of nanodumbbell is reproduced.

Infrared Physics & Technology, 2007

Efficiency as high as 26% is obtained for generation of mid-infrared radiation at 6.04 lm by freq... more Efficiency as high as 26% is obtained for generation of mid-infrared radiation at 6.04 lm by frequency doubling of ammonia laser emission at 12.08 lm in a 15 mm long type-I cut AgGaSe 2 crystal. The NH 3 laser used for this work is optically pumped by a commercial TEA CO 2 laser operating on 9.22 lm and produces pulsed output of 210mJwithadurationof210 mJ with a duration of 210mJwithadurationof200 ns at 12.08 lm. The generated radiation at 6.04 lm is separated out from the residual radiation at 12.08 lm by exploiting the principle of polarization dependent diffraction of reflection grating.

ACS Nano, 2012