Publications by authors named "Kunal Lulla"

3 Publications

  • Page 1 of 1

Mapping nanoscale dynamic properties of suspended and supported multi-layer graphene membranes via contact resonance and ultrasonic scanning probe microscopies.

Nanotechnology 2020 Oct 18;31(41):415702. Epub 2020 Jun 18.

Physics Department, Lancaster University, Lancaster LA1 4YB, United Kingdom.

Graphene's (GR) remarkable mechanical and electrical properties-such as its Young's modulus, low mass per unit area, natural atomic flatness and electrical conductance-would make it an ideal material for micro and nanoelectromechanical systems (MEMS and NEMS). However, the difficulty of attaching GR to supports, coupled with naturally occurring internal defects in a few layer GR can significantly adversely affect the performance of such devices. Here, we have used a combined contact resonance atomic force microscopy (CR-AFM) and ultrasonic force microscopy (UFM) approach to characterise and map with nanoscale spatial resolution GR membrane properties inaccessible to most conventional scanning probe characterisation techniques. Using a multi-layer GR plate (membrane) suspended over a round hole, we show that this combined approach allows access to the mechanical properties, internal structure and attachment geometry of the membrane providing information about both the supported and suspended regions of the system. We show that UFM allows the precise geometrical position of the supported membrane-substrate contact to be located and provides an indication of the local variation of its quality in the contact areas. At the same time, we show that by mapping the position sensitive frequency and phase response of CR-AFM response, one can reliably quantify the membrane stiffness, and image the defects in the suspended area of the membrane. The phase and amplitude of experimental CR-AFM measurements show excellent agreement with an analytical model accounting for the resonance of the combined CR-AFM probe-membrane system. The combination of UFM and CR-AFM provide a beneficial combination for the investigation of few-layer NEMS systems based on two dimensional materials.
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http://dx.doi.org/10.1088/1361-6528/ab9e27DOI Listing
October 2020

Heat conduction measurements in ballistic 1D phonon waveguides indicate breakdown of the thermal conductance quantization.

Nat Commun 2018 10 16;9(1):4287. Epub 2018 Oct 16.

Institut NÉEL, CNRS, 25 avenue des Martyrs, 38042, Grenoble, France.

Emerging quantum technologies require mastering thermal management, especially at the nanoscale. It is now accepted that thermal metamaterial-based phonon manipulation is possible, especially at sub-kelvin temperatures. In these extreme limits of low temperatures and dimensions, heat conduction enters a quantum regime where phonon exchange obeys the Landauer formalism. Phonon transport is then governed by the transmission coefficients between the ballistic conductor and the thermal reservoirs. Here we report on ultra-sensitive thermal experiments made on ballistic 1D phonon conductors using a micro-platform suspended sensor. Our thermal conductance measurements attain a power sensitivity of 15 attoWatts [Formula: see text] around 100 mK. Ballistic thermal transport is dominated by non-ideal transmission coefficients and not by the quantized thermal conductance of the nanowire itself. This limitation of heat transport in the quantum regime may have a significant impact on modern thermal management and thermal circuit design.
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http://dx.doi.org/10.1038/s41467-018-06791-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6191430PMC
October 2018

Specific heat measurement of thin suspended SiN membrane from 8 K to 300 K using the 3ω-Völklein method.

Rev Sci Instrum 2013 Sep;84(9):094902

Institut NÉEL, CNRS-UJF, 25 avenue des Martyrs, 38042 Grenoble Cedex 9, France.

We present a specific heat measurement technique adapted to thin or very thin suspended membranes from low temperature (8 K) to 300 K. The presented device allows the measurement of the heat capacity of a 70 ng silicon nitride membrane (50 or 100 nm thick), corresponding to a heat capacity of 1.4 × 10(-10) J/K at 8 K and 5.1 × 10(-8) J/K at 300 K. Measurements are performed using the 3ω method coupled to the Völklein geometry. This configuration allows the measurement of both specific heat and thermal conductivity within the same experiment. A transducer (heater/thermometer) is used to create an oscillation of the heat flux on the membrane; the voltage oscillation appearing at the third harmonic which contains the thermal information is measured using a Wheatstone bridge set-up. The heat capacity measurement is performed by measuring the variation of the 3ω voltage over a wide frequency range and by fitting the experimental data using a thermal model adapted to the heat transfer across the membrane. The experimental data are compared to a regular Debye model; the specific heat exhibits features commonly seen for glasses at low temperature.
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http://dx.doi.org/10.1063/1.4821501DOI Listing
September 2013
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