Hoël Guerin

Coulomb blockade phenomenon in ultra-thin gold nanowires

Ultra-thin gold nanowires with uniform diameters of 2 nm and lengths of over 100 μm are synthesized via the reduction of gold(III) chloride in an oleylamine matrix. The gold nanowires, dispersed on an oxidized substrate, are top-contacted with metallic electrodes to manufacture back gated transistors. We investigate the transport properties in the fabricated devices as a function of the gate voltage, the bias voltage, and the temperature. The nonlinear current-bias voltage characteristics from 7 K up to 300 K are well described by the Coulomb blockade model in a nearly one-dimensional quantum dot array (which results from the gold nanowires’ thermal fragmentation into a granular material). Our results support a picture in which the electronic transport is governed by sequential tunneling at an applied bias above the global Coulomb blockade threshold, whereas in the Coulomb blockade regime, inelastic cotunneling is dominant up to 70 K, at which point it crosses over to activated behavior. The current depen...

Single electron transistors with ultra-thin Au nanowires as a single Coulomb island

Single electron transistors exhibiting transport properties based on a single Coulomb island have been fabricated using ultra-thin gold nanowires (AuNWs), which are synthesized via a chemical reduction process. The AuNWs are bottom-contacted with source and drain electrodes to avoid damaging the AuNWs under fabrication processes. We investigate the transport properties in the fabricated devices as a function of the bias and gate voltages at room and low temperatures. At 0.23 K, the periodical Coulomb oscillations and diamonds are clearly observed indicating that an individual AuNW acts as a single Coulomb island. These transport properties can be explained by the orthodox Coulomb blockade theory.

Heterogeneous integration of low power pH FinFET sensors with passive capillary microfluidics and miniaturized Ag/AgCl quasi-Reference Electrode

This work presents one of the first low power pH sensing microfluidic chip based on the heterogeneous integration of: (i) high-k FinFET sensors with liquid gate, (ii) miniaturized Ag/AgCl quasi-Reference Electrode and (iii) passive microfluidic. The integration of these three components provides a fully integrated and compact platform that could be exploited for ionic monitoring in biofluids for healthcare applications. We describe the full fabrication process for the microfluidic system with the embedded reference electrode. The electrical characterization of heterogeneously integrated pH FinFET sensor with the integrated reference electrode shows Id-Vg characteristics with subthreshold swing SS~141mV/dec, low Ioff current and ION/IOFF > 105. When applying a constant current operation scheme, a sensitivity of 8mV/pH of the output drain voltage is reported. Due to the biocompatibility of the selected materials and small size, the resulting microsystem-on-chip could be used as a noninvasive wearable sensor for continuous monitoring of pH in sweat.

Carbon nanotube resistors as gas sensors: Towards selective analyte detection with various metal-nanotubeinterfaces

This paper reports the fabrication of conductance-based gas sensors based on horizontal, dense carbon nanotube (CNT) arrays directly integrated between metal electrodes via a selective and directional catalytic growth process performed in-situ and at the wafer-scale. We originally propose to use a functionalization strategy focusing on the key role of the electrode-CNT junction, for increased selectivity. Devices based on CNT arrays have been fabricated using various designs and different metals: Pt, Pd and Au, to top-contact the CNT arrays so as to provide several types of metal-CNT junctions. The sensors have been exposed to low concentrations of H2 as well as NH3, toluene, ethanol and relative humidity. We demonstrate that the CNT resistors responses to gases are hardly dependent on the design, the CNT surface developed between the electrodes, but very specific to the metal-CNT interface. Therefore, we postulate that gases interact in a metal-specific way and modify the metal-CNT contact resistance of the resistors but the device sensitivity cannot simply be ascribed to the modulation of Schottky barriers as reported in literature. Since the main issue with CNT sensors is their lack of selectivity, we believe that this method provides an easy to implement strategy and shows potential for room temperature discriminative gas detection.

3D Heterogeneous Integration for Nanosensor Systems – the EU-Project e-BRAINS

A few examples of innovative nanosensors for gas detection and biofludic applications have been successfully implemented and heterogeneous integrated within the European e-BRAINS project showing efficient miniaturization and extremely low detection

Coulomb blockade in a granular material made of gold nanowires

Uniform, 2 nm diameter gold nanowires were synthesized through the reduction of gold(III) chloride in an oleylamine matrix. They were top-contacted on a Si/SiO2 substrate with metallic electrodes to manufacture back-gated transistors. Due to thermal breakage, the gold nanowires were fragmented into a granular material and the non-linear current-bias voltage characteristics measured on the devices from 7 K up to 300 K were described by the Coulomb blockade theory in a nearly one-dimensional quantum dot array. The electronic transport was governed by sequential tunneling at an applied bias above the global Coulomb blockade threshold, whereas in the Coulomb blockade regime, inelastic cotunneling was dominant up to 70 K, at which point it crossed over to activated behavior. The current dependence on the gate voltage that showed irregular oscillations was explained by the superimposition of Coulomb oscillation patterns generated by each different dot in the one-dimensional array. The competitive effects of excitation energy and stochastic Coulomb blockade balanced the number of current peaks observed.