arXiv subjects

Harish Bhaskaran

Publications and source records attributed to Harish Bhaskaran.

27 records · Page 2Linked to original sources

arXiv2018

In-memory computing on a photonic platform

Collocated data processing and storage are the norm in biological systems. Indeed, the von Neumann computing architecture, that physically and temporally separates processing and memory, was born more of pragmatism based on available technology. As our ability to create better hardware improves, new computational paradigms are being explored. Integrated photonic circuits are regarded as an attractive solution for on-chip computing using only light, leveraging the increased speed and bandwidth potential of working in the optical domain, and importantly, removing the need for time and energy sapping electro-optical conversions. Here we show that we can combine the emerging area of integrated optics with collocated data storage and processing to enable all-photonic in-memory computations. By employing non-volatile photonic elements based on the phase-change material, Ge2Sb2Te5, we are able to achieve direct scalar multiplication on single devices. Featuring a novel single-shot Write/Erase and a drift-free process, such elements can multiply two scalar numbers by mapping their values to the energy of an input pulse and to the transmittance of the device, codified in the crystallographic state of the element. The output pulse, carrying the information of the light-matter interaction, is the result of the computation. Our all-optical approach is novel, easy to fabricate and operate, and sets the stage for development of entirely photonic computers.

cs.ET↗

arXiv2017

Hydrophobic-hydrophilic interactions drive rapid nanoparticle assembly

The unique physical and optical properties of nanoparticles make their reliable and rapid assembly an important goal for nanotechnology. To this end, many competing driving forces have been targeted to control the self-assembly, though issues with reliability and efficiency indicate that interfaces on the nanoscale are not yet fully understood. In this letter we report for the first time that the flow of water media from the interface between chemically nanopatterned hydrophobic surfaces and adjacent hydrophilic regions (a Janus interface) can effectively be employed for rapid nanoparticle assembly with single nanoparticle resolution. We find that the dewetting of water molecules from this Janus interface drives the assembly of nanoparticles from electrostatically stabilised nanoparticle colloids onto the hydrophobic areas, expedited by removing the resistance to adhesion between wetted interfaces exerted by any hydration barrier, such that nanoparticle assembly is achieved in under a minute. We call this method of controlled nanoparticle assembly Janus Interface Nanoparticle Assembly - JINA. We then demonstrate control of this mechanism through pH switching and prove its effectiveness for fabrication by rapidly creating single-nanoparticle sites and single particle wide lines whilst simultaneously densely coating macro-scale features. Not only does this assembly method have far-reaching implications in nanomanufacturing, the unanticipated nature of this mechanism also challenges many commonly held assumptions about the interfacial interactions of nanoparticle self-assembly.

cond-mat.mes-hall↗

arXiv2017

Nanomechanical resonators show higher order nonlinearity at room temperature

Most mechanical resonators are treated as simple linear oscillators. Nonlinearity in the resonance behavior of nanoelectromechanical systems (NEMS) has only lately attracted significant interest. Most recently, cubic-order nonlinearity has been used to explain anomalies in the resonance frequency behaviors in the frequency domain. Particularly, such nonlinearities were explained using cubic nonlinearity in the restoring force (Duffing nonlinearity) or damping (van der Pol nonlinearity). Understanding the limits of linear resonant behavior is particularly important in NEMS, as they are frequently studied for their potential in ultrasensitive sensing and detection, applications that most commonly assume a linear behavior to transduce motion into a detected signal. In this paper, we report that even at low excitation, cubic nonlinearity is insufficient to explain nonlinearity in graphene NEMS. Rather, we observe that higher order, in particular, the fifth order effects need to be considered even for systems at room temperature with modest quality factors. These are particularly important results that could determine the limits of linear detection in such systems and quite possibly present unconventional avenues for ultrasensitive detection paradigms using nonlinear dynamics. Such intriguing possibilities, however, hinge crucially on a superior understanding and exploitation of these inherent nonlinearities as opposed to modeling them as approximated linear or cubic systems.

cond-mat.mes-hall↗

arXiv2017

Scaling limits of graphene nanoelectrodes

Graphene is an ideal material for fabricating atomically thin nanometre spaced electrodes. Recently, carbon-based nanoelectrodes have been employed to create single-molecule transistors and phase change memory devices. In spite of the significant recent interest in their use in a range of nanoscale devices from phase change memories to molecular electronics, the operating and scaling limits of these electrodes are completely unknown. In this paper, we report on our observations of consistent voltage driven resistance switching in sub-5 nm graphene nanogaps. We find that we are able to reversibly cycle between a low and a high resistance state using feedback-controlled voltage ramps.We attribute this unexplained switching in the gap to the formation and breakdown of carbon filaments.By increasing the gap, we find that such intrinsic resistance switching of graphene nanogaps imposes a scaling limit of 10 nm (approx.) on the gap-size for devices with operating voltages of 1 to 2 volts.

cond-mat.mes-hall↗

arXiv2013

Design parameters for voltage-controllable directed assembly of single nanoparticles

Techniques to reliably pick and place single nanoparticles into functional assemblies are required to incorporate exotic nanoparticles into standard electronic circuits. In this paper we explore the use of electric fields to drive and direct the assembly process, which has the advantage of being able to control the nano-assembly process at the single nanoparticle level. To achieve this, we design an electrostatic gating system, thus enabling a voltage controllable nanoparticle picking technique. Using the nonlinear Poisson-Boltzmann equation, we can successfully characterise the parameters required for single-particle placement, the key being single particle selectivity, in effect designing a system that can achieve this controllably. We then present the optimum design parameters required for successful single nanoparticle placements at ambient temperatures, an important requirement for nanomanufacturing processes.

cond-mat.mes-hall↗

arXiv2013

Casimir probe based upon metallized high Q SiN nanomembrane resonator

We present the instrumentation and measurement scheme of a new Casimir force probe that bridges Casimir force measurements at microscale and macroscale. A metallized high Q silicon nitride nanomembrane resonator is employed as a sensitive force probe. The high tensile stress present in the nanomembrane not only enhances the quality factor but also maintains high flatness over large area serving as the bottom electrode in a sphere-plane configuration. A fiber interferometer is used to readout the oscillation of the nanomembrane and a phase-locked loop scheme is applied to track the change of the resonance frequency. Because of the high quality factor of the nanomembrane and the high stability of the setup, a frequency resolution down to $2\times10^{-9}$ and a corresponding force gradient resolution of 3 $μ$N/m is achieved. Besides sensitive measurement of Casimir force, our measurement technique simultaneously offers Kelvin probe measurement capability that allows in situ imaging of the surface potentials.

cond-mat.mes-hall↗

arXiv2012

Photonic non-volatile memories using phase change materials

We propose an all-photonic, non-volatile memory and processing element based on phase-change thin-films deposited onto nanophotonic waveguides. Using photonic microring resonators partially covered with Ge2Sb2Te5 (GST) multi-level memory operation in integrated photonic circuits can be achieved. GST provides a dramatic change in refractive index upon transition from the amorphous to crystalline state, which is exploited to reversibly control both the extinction ratio and resonance wavelength of the microcavity with an additional gating port in analogy to optical transistors. Our analysis shows excellent sensitivity to the degree of crystallization inside the GST, thus providing the basis for non-von Neuman neuromorphic computing.

physics.optics↗

arXiv2012

Casimir Force and In Situ Surface Potential Measurements on Nanomembranes

We present Casimir force measurements in a sphere-plate configuration that consists of a high quality nanomembrane resonator and a millimeter sized gold coated sphere. The nanomembrane is fabricated from stoichiometric silicon nitride metallized with gold. A Kelvin probe method is used in situ to image the surface potentials to minimize the distance-dependent residual force. Resonance-enhanced frequency-domain measurements of the nanomembrane motion allow for very high resolution measurements of the Casimir force gradient (down to a force gradient sensitivity of 3 uN/m). Using this technique, the Casimir force in the range of 100 nm to 2 um is accurately measured. Experimental data thus obtained indicate that the device system in the measured range is best described with the Drude model.

quant-ph↗

arXiv2010

Active microcantilevers based on piezoresistive ferromagnetic thin films

We report the piezoresisitivity in magnetic thin films of FeGa and their use for fabricating self transducing microcantilevers. The actuation occurs as a consequence of both the ferromagnetic and magnetostrictive property of FeGa thin films, while the deflection readout is achieved by exploiting the piezoresisitivity of these films. This self-sensing, self-actuating micromechanical system involves a very simple bilayer structure, which eliminates the need for the more complex piezoelectric stack that is commonly used in active cantilevers. Thus, it potentially opens opportunities for remotely actuated, cantilever-based sensors.

cond-mat.mes-hall↗