Subramanian Krishnan

Pd Nanoparticles and Thin Films for Room Temperature Hydrogen Sensor

We report the application of palladium nanoparticles and thin films for hydrogen sensor. Electrochemically grown palladium particles with spherical shapes deposited on Si substrate and sputter deposited Pd thin films were used to detect hydrogen at room temperature. Grain size dependence of H2sensing behavior has been discussed for both types of Pd films. The electrochemically grown Pd nanoparticles were observed to show better hydrogen sensing response than the sputtered palladium thin films. The demonstration of size dependent room temperature H2sensing paves the ways to fabricate the room temperature metallic and metal–metal oxide semiconductor sensor by tuning the size of metal catalyst in mixed systems. H2sensing by the Pd nanostructures is attributed to the chemical and electronic sensitization mechanisms.

Rectenna developments for solar energy collection

The rectenna concept for solar energy collection rests on the dual wave/photon nature of light. The recent developments in nanotechnology and manufacturing led to the re-examination of the rectenna concept for solar energy collection. Two fundamental physical limitations, skin effect resistance and very low voltage per antenna element, were identified for the rectenna system. This paper reports on research efforts to identify the problems through experimentation at lower frequencies and simulation at the light frequencies and has identified possible design solutions to some of the problems.

A review of self-assembled monolayers as potential terahertz frequency tunnel diodes

AbstractIn this review, we describe the principles of the tunnel junction, self-assembled monolayer (SAM) application techniques, experimental testbed fabrication, and characterization of the films and devices. In addition, techniques for directed application, removal, and functionalization of the monolayers are discussed. Bottom-up fabrication techniques have seen increased attention because of their versatility and ease of use. These films see mechanical uses as surface modifiers and micro-scale lubricants. Advances in nanowatt electronics and ultra-low power sensors have opened up an energy harvesting niche for solutions which would have proven ineffective just some years ago. The focus of this study is the two-terminal junction which has potential applications in THz rectification for energy harvesting, medical imaging, and defense sensing. The quantum theory of operation behind these devices is touched on briefly—describing tunneling through the organic monolayers. Commentary on trends in research and potential future work are presented as well.

Tunnel Junction based Rectenna - A Key to Ultrahigh Efficiency Solar/Thermal Energy Conversion

This paper presents a quantum approachto increasing the efficiency of solar/thermal energyconversionby converting waste heat to electrical energy using rectenna. The approach of using a rectenna (a combination of high frequency antennae and tunnel diodes) would improve efficiency of all systems. This paper presents the current state of the art in the field of rectenna based conversion with a focus on its critical component‐a nanoscale MIM diode.

One pot, single step, room temperature dielectrophoretic deposition of gold nanoparticles clusters on polyethylene terephthalate substrate.

The major challenge of plastic electronics is the deposition of gold nanoparticles (AuNPs) on flexible substrates at room temperature. Here, we show fast, single step, room temperature deposition of AuNPs on polyethylene terephthalate (PET) and biaxially oriented PET (BoPET) substrate by employing dielectrophoresis. The deposition has been carried out using two‐electrode system, with BoPET (or PET) and metallic (Pt or stain steel) mesh, under an AC signal of 20 kHz and 20 V peak‐to‐peak (Vpp) (signal for PET is 6 Vpp and 6 kHz). In this method, we show how to deposit AuNPs on PET‐like insulator by exploiting its polarization capability under an AC signal. The polarization of PET has been confirmed by change in the Raman spectra of the PET film under in situ AC signals. Furthermore, we show that using this dielectrophoretic deposition method, the PET films can be patterned by AuNPs at room temperature without any pre‐ and posttreatment.

Nanomanufacturability Of Thin Film MIM Diodes

Ni/NiO/Cr MIM diodes with various structures namely, stacked, stepped self aligned, stepped manual aligned and stepped spacer, were fabricated. Their dc electrical responses were analyzed to identify the effects of diode design on asymmetry and emission current. It was found that the stepped structure with an oxide spacer prevented shorting at the step thus circumventing premature breakdown as exhibited by the other structures. These structures demonstrated better asymmetry and a high enough emission current alleviating the issues caused by the other structures. It was also observed that the current density of the self aligned stepped structure showed less variance across devices than the stepped spacer structure. On the other hand, the resistance of the same structure showed to be more ohmic in nature when compared to the stepped structure with spacer.

Fabrication and Characterization of Thin-Film Metal-Insulator-Metal Diode for use in Rectenna as Infrared Detector

Uncooled Infrared detectors with high sensitivity and shorter response times are preferred as through the wall detection device. An alternate approach for making these sensors, being pursued by us is to use the concept of rectenna with tunnel diodes. Successful fabrication of such high frequency switching diodes with antenna as detectors, offer a much faster response time than existing bolometer. This paper presents the fabrication and characterization of thin-film MIM diode for use in rectenna as an Infrared detector. MIM diodes operate on the basis of quantum mechanical phenomenon, i.e., when a sufficiently thin barrier ( 2 contact areas with cut-off frequency ∼0.1THz. The electrodes of the Ni-NiO-Cr MIM diodes have been fabricated through Photolithography, e-beam lithography, followed by conventional lift-off process. The dielectric layer (NiO) was deposited through plasma oxidation to obtain 2nm thin films. The composition and the thickness of the insulator layer are characterized by metrological tools like SEM and Spectroscopic Ellipsometer. The diode characteristics presented in this paper have been found to be stable and reproducible with the established fabrication conditions. Electrical behaviour (I-V) of the MIM junctions were investigated and compared with the theoretical tunnelling characteristics of the Ni-NiO-Cr MIM diodes. For devices with such non-linear electrodes, excellent agreement is obtained between the measured and the calculated result with the forward bias current as 0.8mA at 0.2V and the reverse bias current as −0.2mA at −0.2V.

Development of a through wafer 3D vertical micro-coaxial probe

A through wafer 3D vertical micro-coaxial probe flushed in a silicon substrate has been designed and fabricated. As a result of using silicon as a dielectric, the probes compatibility with commercial applications has significantly increased. The probe has been designed using radio frequency (RF) calculations and consists of 100 µm inner diameter and 300 µm outer diameter vias, which corresponds to a 1:3 inner/outer conductor ratio. Fabrication results indicate that the probe through holes can be formed using standard photolithography techniques and Boschs process for deep reactive ion etching. The probe vias were successfully metalized with a diluted silver paste using a novel filling method. Measured results demonstrate that the probe has good signal transmission with a reflection coefficient less than −10 dB from 15 to 57 GHz. By developing an RF based three-dimensional micro-coaxial probe, its use as vertical interconnects in high frequency system-in-package technologies have considerably improved.

Status of the linac booster for NSC pelletron

This paper reviews the progress made in the development of the linac booster for Nuclear Science Centre (NSC). The prototype resonator for the booster has surpassed design accelerating field. A cryostat has been fabricated to house this prototype for in beam tests. The cryogenic system has been installed and several rf modules have been constructed.

Ferroeletric like characteristics in redox active polymer of 5,10,15,20 tetra(4-hydroxyphenyl)-porphyrin at room temperature

We report ferroelectric behaviors in electrochemically polymerized 5,10,15,20 tetra(4-hydroxyphenyl)-porphyrin. The ferroelectric behaviors are due to conformational changes that occur during the reduction and oxidation of the polymer under electric field. The conformational changes were studied by in situ Raman spectroscopy and frequency response analysis. The present findings will open up an alternative route for organic ferroelectrics which is presently in urgent need of approaches and materials.