Arvind Narayanaswamy | Columbia University (original) (raw)

Papers by Arvind Narayanaswamy

ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 2012

ABSTRACT

Arxiv preprint arXiv: …, 2010

Karthik Sasihithlu and Arvind Narayanaswamy∗ Department of Mechanical Engineering, Columbia Unive... more Karthik Sasihithlu and Arvind Narayanaswamy∗ Department of Mechanical Engineering, Columbia University New York, NY 10027 (Dated: October 6, 2010) Though the dependence of near–field radiative transfer on the gap between two planar objects is well understood, that between ...

Nano letters, 2009

Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar ... more Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such surface waves can lead to breakdown of the Planck's blackbody radiation law in the near field. Here, we experimentally demonstrate that surface phonon polaritons dramatically enhance energy transfer between two surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies.

Optics express, Jan 4, 2011

Near-field radiative transfer between two objects can be computed using Rytov's theory of flu... more Near-field radiative transfer between two objects can be computed using Rytov's theory of fluctuational electrodynamics in which the strength of electromagnetic sources is related to temperature through the fluctuation-dissipation theorem, and the resultant energy transfer is described using the dyadic Green's function of the vector Helmholtz equation. When the two objects are spheres, the dyadic Green's function can be expanded in a series of vector spherical waves. Based on comparison with the convergence criterion for the case of radiative transfer between two parallel surfaces, we derive a relation for the number of vector spherical waves required for convergence in the case of radiative transfer between two spheres. We show that when electromagnetic surface waves are active at a frequency the number of vector spherical waves required for convergence is proportional to Rmax/d when d/Rmax → 0, where Rmax is the radius of the larger sphere, and d is the smallest gap be...

Optics express, Jan 16, 2014

We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that... more We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that R2 ≲ 40R1. For R2 = 40R1, the smallest gap to which we have been able to compute radiative transfer is d = 0.016R1. To accomplish these computations, we have had to modify existing methods for computing near-field radiative transfer between two spheres in the following ways: (1) exact calculations of coefficients of vector translation theorem are replaced by approximations valid for the limit d ≪ R1, and (2) recursion relations for a normalized form of translation coefficients are derived which enable us to replace computations of spherical Bessel and Hankel functions by computations of ratios of spherical Bessel or spherical Hankel functions. The results are then compared with the predictions of the modified proximity approximation.

Review of Scientific Instruments, 2014

Thermal conductance measurements are performed on individual polystyrene nanowires using a novel ... more Thermal conductance measurements are performed on individual polystyrene nanowires using a novel measurement technique in which the wires are suspended between two bi-material microcantilever sensors. The nanowires are fabricated via electrospinning process. Thermal conductivity of the nanowire samples is found to be between 6.6 and 14.4 W m(-1) K(-1) depending on sample, a significant increase above typical bulk conductivity values for polystyrene. The high strain rates characteristic of electrospinning are believed to lead to alignment of molecular polymer chains, and hence the increase in thermal conductivity, along the axis of the nanowire.

We have designed and fabricated bi-material microcantilevers with low conductance by minimizing t... more We have designed and fabricated bi-material microcantilevers with low conductance by minimizing the width and thickness of the cantilevers while keeping them suitable for detection with an optical deflection technique. The conductance of a cantilever is determined experimentally to be 330 6 20 nWK À1 . Using this cantilever, we have measured less than 1 pW of heat flow through the cantilever. The thermal noise-limited resolution of the cantilever is expected to be %50 fW. Such cantilevers give us additional tools to probe thermal transport through nanostructures, especially through single molecules where picowatt-level sensitivity is necessary. V C 2013 American Institute of Physics. [http://dx.

In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we ... more In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we demonstrate that the effective thermal conductance of the cantilever and the temperature at the tip of the cantilever can be determined by measuring the bending of the cantilever in response to two different thermal inputs: power absorbed at the tip and ambient temperature.

Proceeding of the 4th International Symposium on Radiative Transfer, 2004

... δ, phase shift angle (0 to 2π). *, complex conjugate. ... The method used to determine the GF... more ... δ, phase shift angle (0 to 2π). *, complex conjugate. ... The method used to determine the GF for1D periodic media is described briefly below. Normally, for periodic media, Bloch's theorem is used to determine the band structure, transmissivity, reflectivity, and other such properties. ...

Review of Scientific Instruments, 2013

Low thermal conductance bi-material microcantilevers are fabricated with a pad area near the free... more Low thermal conductance bi-material microcantilevers are fabricated with a pad area near the free end to accommodate a focused laser spot. A pair of such cantilevers are proposed as a configuration for measuring thermal conductance of a nanostructure suspended between the two. We determine the resolution of such a device by measuring the stray conductance it would detect in the absence of any nanostructure. Stray conductance, primarily due to optical coupling, is measured for cantilevers with varying pad size and found to be as low as 0.05 nW K(-1), with cantilevers with larger pad size yielding the smallest stray conductance.

Physical Review Letters, 2004

A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals... more A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals is presented. Normal emission results consistent with those assuming Kirchoff's law are obtained; i.e., a photonic crystal does not emit more than what a blackbody does. Significant enhancement, however, can be achieved over the radiation intensity from a uniform slab, indicating the potential usefulness of photonic crystals in incandescent lighting and thermal photovoltaic applications.

Physical Review B, 2008

Radiative energy transfer between closely spaced bodies is known to be significantly larger than ... more Radiative energy transfer between closely spaced bodies is known to be significantly larger than that predicted by classical radiative transfer because of tunneling due to evanescent waves. Theoretical analysis of near-field radiative transfer is mainly restricted to radiative transfer between two half-spaces or spheres treated in the dipole approximation (very small sphere) or proximity force approximation (radius of sphere much greater than the gap). Sphere-sphere or sphere-plane configurations beyond the dipole approximation or proximity force approximation have not been attempted. In this work, the radiative energy transfer between two adjacent non-overlapping spheres of arbitrary diameters and gaps is analyzed numerically. For spheres of small diameter (compared to the wavelength), the results coincide with the dipole approximation. We see that the proximity force approximation is not valid for spheres with diameters much larger than the gap, even though this approximation is well established for calculating forces. From the numerical results, a regime map is constructed based on two non-dimensional length scales for the validity of different approximations. * Electronic address: arvindn@alum.mit.edu † Electronic address: gchen2@mit.edu

Physical Review B, 2011

Though the dependence of near-field radiative transfer on the gap between two planar objects is w... more Though the dependence of near-field radiative transfer on the gap between two planar objects is well understood, that between curved objects is still unclear. We show, based on the analysis of the surface polariton mediated radiative transfer between two spheres of equal radii R and minimum gap d, that the near-field radiative transfer scales as R/d as d/R → 0 and as ln (R/d) for larger values of d/R up to the far-field limit. We propose a modified form of the proximity approximation to predict near-field radiative transfer between curved objects from simulations of radiative transfer between planar surfaces. PACS numbers: 44.40.+a,41.20.Jb,42.50.Lc,73.20.Mf For more than a century, Planck's theory of blackbody radiation and the radiative transfer theory (RTT) have been successful at predicting radiative heat transfer between objects when all length scales involved are much larger than the characteristic thermal wavelength λ T given by Wien's displacement law (λ T ≈ 1.27 c/k B T , where 2π is the Planck's constant, c is the speed of light in vacuum, k B is the Boltzmann constant and T is the absolute temperature). However, at shorter length scales, radiative transfer between two objects can exceed the predictions of Planck's theory due to electromagnetic near-field effects. Recent precision experiments 1-3 for measuring radiative heat transfer between a silica microsphere and a planar silica substrate have begun to shed new light on the enhancement of radiative transfer at nanoscale gaps due to surface phonon-polaritons. While near-field enhancement between parallel surfaces is well understood theoretically, 4-7 that between curved surfaces is still unclear. Though near-field radiative exchange between a nanosphere and a plane has been calculated under different approximations, 8,9 rigorous numerical computation of near-field radiative transfer between a sphere of arbitrary diameter and a planar surface has not yet been possible due to computational difficulties. In order to understand the effect of curvature on enhancement of radiative transfer at nanoscale gaps, we investigate the near-field radiative transfer between two spheres of equal radii by rigorous simulations based on the dyadic Green's function technique 10 and fluctuationdissipation theorem. 11

Physical Review B, 2004

ABSTRACT

Physical Review B, 2005

Calculations of the dispersion relation and of the propagation length of surface phonon-polariton... more Calculations of the dispersion relation and of the propagation length of surface phonon-polariton modes in a micrometric glass waveguide have been performed. The dispersion relation was solved in two ranges of frequency where SPP appear in glass. We succeeded in showing a maximal propagation length of 35 µm in a 10 µm radius waveguide with a 1 µm thick wall.

ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 2012

ABSTRACT

Arxiv preprint arXiv: …, 2010

Karthik Sasihithlu and Arvind Narayanaswamy∗ Department of Mechanical Engineering, Columbia Unive... more Karthik Sasihithlu and Arvind Narayanaswamy∗ Department of Mechanical Engineering, Columbia University New York, NY 10027 (Dated: October 6, 2010) Though the dependence of near–field radiative transfer on the gap between two planar objects is well understood, that between ...

Nano letters, 2009

Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar ... more Surface phonon polaritons are electromagnetic waves that propagate along the interfaces of polar dielectrics and exhibit a large local-field enhancement near the interfaces at infrared frequencies. Theoretical calculations show that such surface waves can lead to breakdown of the Planck's blackbody radiation law in the near field. Here, we experimentally demonstrate that surface phonon polaritons dramatically enhance energy transfer between two surfaces at small gaps by measuring radiation heat transfer between a microsphere and a flat surface down to 30 nm separation. The corresponding heat transfer coefficients at nanoscale gaps are 3 orders of magnitude larger than that of the blackbody radiation limit. The high energy flux can be exploited to develop new radiative cooling and thermophotovoltaic technologies.

Optics express, Jan 4, 2011

Near-field radiative transfer between two objects can be computed using Rytov's theory of flu... more Near-field radiative transfer between two objects can be computed using Rytov's theory of fluctuational electrodynamics in which the strength of electromagnetic sources is related to temperature through the fluctuation-dissipation theorem, and the resultant energy transfer is described using the dyadic Green's function of the vector Helmholtz equation. When the two objects are spheres, the dyadic Green's function can be expanded in a series of vector spherical waves. Based on comparison with the convergence criterion for the case of radiative transfer between two parallel surfaces, we derive a relation for the number of vector spherical waves required for convergence in the case of radiative transfer between two spheres. We show that when electromagnetic surface waves are active at a frequency the number of vector spherical waves required for convergence is proportional to Rmax/d when d/Rmax → 0, where Rmax is the radius of the larger sphere, and d is the smallest gap be...

Optics express, Jan 16, 2014

We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that... more We compute near-field radiative transfer between two spheres of unequal radii R1 and R2 such that R2 ≲ 40R1. For R2 = 40R1, the smallest gap to which we have been able to compute radiative transfer is d = 0.016R1. To accomplish these computations, we have had to modify existing methods for computing near-field radiative transfer between two spheres in the following ways: (1) exact calculations of coefficients of vector translation theorem are replaced by approximations valid for the limit d ≪ R1, and (2) recursion relations for a normalized form of translation coefficients are derived which enable us to replace computations of spherical Bessel and Hankel functions by computations of ratios of spherical Bessel or spherical Hankel functions. The results are then compared with the predictions of the modified proximity approximation.

Review of Scientific Instruments, 2014

Thermal conductance measurements are performed on individual polystyrene nanowires using a novel ... more Thermal conductance measurements are performed on individual polystyrene nanowires using a novel measurement technique in which the wires are suspended between two bi-material microcantilever sensors. The nanowires are fabricated via electrospinning process. Thermal conductivity of the nanowire samples is found to be between 6.6 and 14.4 W m(-1) K(-1) depending on sample, a significant increase above typical bulk conductivity values for polystyrene. The high strain rates characteristic of electrospinning are believed to lead to alignment of molecular polymer chains, and hence the increase in thermal conductivity, along the axis of the nanowire.

We have designed and fabricated bi-material microcantilevers with low conductance by minimizing t... more We have designed and fabricated bi-material microcantilevers with low conductance by minimizing the width and thickness of the cantilevers while keeping them suitable for detection with an optical deflection technique. The conductance of a cantilever is determined experimentally to be 330 6 20 nWK À1 . Using this cantilever, we have measured less than 1 pW of heat flow through the cantilever. The thermal noise-limited resolution of the cantilever is expected to be %50 fW. Such cantilevers give us additional tools to probe thermal transport through nanostructures, especially through single molecules where picowatt-level sensitivity is necessary. V C 2013 American Institute of Physics. [http://dx.

In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we ... more In this letter, based on the beam theory and the thermal analysis of a bimaterial cantilever, we demonstrate that the effective thermal conductance of the cantilever and the temperature at the tip of the cantilever can be determined by measuring the bending of the cantilever in response to two different thermal inputs: power absorbed at the tip and ambient temperature.

Proceeding of the 4th International Symposium on Radiative Transfer, 2004

... δ, phase shift angle (0 to 2π). *, complex conjugate. ... The method used to determine the GF... more ... δ, phase shift angle (0 to 2π). *, complex conjugate. ... The method used to determine the GF for1D periodic media is described briefly below. Normally, for periodic media, Bloch's theorem is used to determine the band structure, transmissivity, reflectivity, and other such properties. ...

Review of Scientific Instruments, 2013

Low thermal conductance bi-material microcantilevers are fabricated with a pad area near the free... more Low thermal conductance bi-material microcantilevers are fabricated with a pad area near the free end to accommodate a focused laser spot. A pair of such cantilevers are proposed as a configuration for measuring thermal conductance of a nanostructure suspended between the two. We determine the resolution of such a device by measuring the stray conductance it would detect in the absence of any nanostructure. Stray conductance, primarily due to optical coupling, is measured for cantilevers with varying pad size and found to be as low as 0.05 nW K(-1), with cantilevers with larger pad size yielding the smallest stray conductance.

Physical Review Letters, 2004

A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals... more A classical simulation of equilibrium thermal emissivity from dispersive, lossy photonic crystals is presented. Normal emission results consistent with those assuming Kirchoff's law are obtained; i.e., a photonic crystal does not emit more than what a blackbody does. Significant enhancement, however, can be achieved over the radiation intensity from a uniform slab, indicating the potential usefulness of photonic crystals in incandescent lighting and thermal photovoltaic applications.

Physical Review B, 2008

Radiative energy transfer between closely spaced bodies is known to be significantly larger than ... more Radiative energy transfer between closely spaced bodies is known to be significantly larger than that predicted by classical radiative transfer because of tunneling due to evanescent waves. Theoretical analysis of near-field radiative transfer is mainly restricted to radiative transfer between two half-spaces or spheres treated in the dipole approximation (very small sphere) or proximity force approximation (radius of sphere much greater than the gap). Sphere-sphere or sphere-plane configurations beyond the dipole approximation or proximity force approximation have not been attempted. In this work, the radiative energy transfer between two adjacent non-overlapping spheres of arbitrary diameters and gaps is analyzed numerically. For spheres of small diameter (compared to the wavelength), the results coincide with the dipole approximation. We see that the proximity force approximation is not valid for spheres with diameters much larger than the gap, even though this approximation is well established for calculating forces. From the numerical results, a regime map is constructed based on two non-dimensional length scales for the validity of different approximations. * Electronic address: arvindn@alum.mit.edu † Electronic address: gchen2@mit.edu

Physical Review B, 2011

Though the dependence of near-field radiative transfer on the gap between two planar objects is w... more Though the dependence of near-field radiative transfer on the gap between two planar objects is well understood, that between curved objects is still unclear. We show, based on the analysis of the surface polariton mediated radiative transfer between two spheres of equal radii R and minimum gap d, that the near-field radiative transfer scales as R/d as d/R → 0 and as ln (R/d) for larger values of d/R up to the far-field limit. We propose a modified form of the proximity approximation to predict near-field radiative transfer between curved objects from simulations of radiative transfer between planar surfaces. PACS numbers: 44.40.+a,41.20.Jb,42.50.Lc,73.20.Mf For more than a century, Planck's theory of blackbody radiation and the radiative transfer theory (RTT) have been successful at predicting radiative heat transfer between objects when all length scales involved are much larger than the characteristic thermal wavelength λ T given by Wien's displacement law (λ T ≈ 1.27 c/k B T , where 2π is the Planck's constant, c is the speed of light in vacuum, k B is the Boltzmann constant and T is the absolute temperature). However, at shorter length scales, radiative transfer between two objects can exceed the predictions of Planck's theory due to electromagnetic near-field effects. Recent precision experiments 1-3 for measuring radiative heat transfer between a silica microsphere and a planar silica substrate have begun to shed new light on the enhancement of radiative transfer at nanoscale gaps due to surface phonon-polaritons. While near-field enhancement between parallel surfaces is well understood theoretically, 4-7 that between curved surfaces is still unclear. Though near-field radiative exchange between a nanosphere and a plane has been calculated under different approximations, 8,9 rigorous numerical computation of near-field radiative transfer between a sphere of arbitrary diameter and a planar surface has not yet been possible due to computational difficulties. In order to understand the effect of curvature on enhancement of radiative transfer at nanoscale gaps, we investigate the near-field radiative transfer between two spheres of equal radii by rigorous simulations based on the dyadic Green's function technique 10 and fluctuationdissipation theorem. 11

Physical Review B, 2004

ABSTRACT

Physical Review B, 2005

Calculations of the dispersion relation and of the propagation length of surface phonon-polariton... more Calculations of the dispersion relation and of the propagation length of surface phonon-polariton modes in a micrometric glass waveguide have been performed. The dispersion relation was solved in two ranges of frequency where SPP appear in glass. We succeeded in showing a maximal propagation length of 35 µm in a 10 µm radius waveguide with a 1 µm thick wall.