Backscattered electrons from gold surface films deposited on silicon substrates: a joint experimental and computational investigation to add new potentiality to electron microscopy

This paper addresses the problem of the thickness determination of thin gold overlayers deposited on silicon bulk substrates by looking at the electron backscattering coefficient involved in scanning electron microscopy (SEM). A Monte Carlo code, used to calculate the backscattering coefficient, together with a simple experimental setup, which uses a conventional SEM, allow to determine thin film thickness (in the range 25–200 nm) with an estimated accuracy of 20%. This adds obviously new potentiality to SEM. Copyright © 2012 John Wiley & Sons, Ltd

Increasing Efficiency in Single-Walled Carbon Nanotube/n-Si Photodetectors by Voltage Doping

Single walled carbon nanotube (SWCNT) ultrathin films were deposited on n doped Si substrates provided with three electrodes for photoconductive measurements. Without illumination the devices show good rectifier properties and holes mobility in the range 105 cm/V.s which makes very promising for fast switching applications. Measuring the current voltage characteristics of the SWCNT film under illumination, an increase in the device performance is observed when a voltage VG is applied to the third electrode. In particular, increasing VG towards the breakdown region, an increase of more than 10 times is recorded in the photocurrent and in the external quantum efficiency with respect to the values measured at VG=0. The experimental data are interpreted considering a hole doping of the SWCNT film by the action of the third electrode voltage VG

On the Optimization of a MEMS Device for Chemoresistive Gas Sensors

In recent years, research in the gas sensor field has experienced a significant boost [1]. Gas sensors represent crucial elements in gas monitoring systems and olfactory systems for several applications: environmental monitoring, safety and security, quality control of food production, medical diagnosis and so on [2]. From the point of view of the gas sensing design, the substrate plays a fundamental role, because it acts as a heater, mechanical support and transducer of the sensor response. The application of MEMS technology for the fabrication of a silicon device with very low power consumption has offered new opportunities for innovative gas sensor design. In this work, we studied different approaches in order to realize an adapt silicon microheaters for chemiresistive gas sensors, available for high operating temperatures (650°C) through MEMS technology. In order to assess a reliable microdevice for this application field, in this work, we studied the different processing steps required to obtain a silicon microheater: layout of the device, types of metals used as a heater and interdigitated contacts, type of insulator and heat treatment to be adopted during the microfabrication. Finally, we propose the processing that provided the best results

Single walled carbon nanotube/Si heterojunctions for high responsivity photodetectors

Single Walled Carbon Nanotube/n-Si (SWCNT/n-Si) hetero-junctions have been obtained by depositing SWCNT ultra-thin films on the surface of an n-Si substrate by dry transfer method. The as obtained junctions are photo sensitive in the measured wavelength range (300 nm-1000 nm) and show zero bias responsivity and detectivity values of the order of 1 A/W and 1014 Jones respectively, which are higher than those previously observed in carbon based devices. Moreover, under on-off light excitation, the junctions show response speed as fast as 1 μs or better and noise equivalent powers comparable to commercial Si photomultipliers. Current-voltage measurements in dark and under illumination suggest that the devices consist of Schottky and semiconductor/semiconductor junctions both contributing to the fast and high responses observed

100% internal quantum efficiency in polychiral single-walled carbon nanotube bulk heterojunction/silicon solar cells

Bulk heterojunction films made of polychiral single-walled carbon nanotubes (SWCNTs) form efficient heterojunction solar cells with n-type crystalline silicon (n-Si), due to their superior electronic, optical, and electrical properties. The films are multi-functional, since their hierarchical surface morphology provides a biomimetical anti-reflective, air-stable, and hydrophobic encapsulation for Si. Also, the films have a large effective area conferring them high optical absorption, which actively contribute to the solar energy harvesting together with Si. Here, we report photovoltaic devices with photoconversion efficiency up to 12% and a record 100% internal quantum efficiency (IQE). Such unprecedented IQE value is truly remarkable and indicates that every absorbed photon from the device, at some wavelengths, generates a pair of separated charge carriers, which are collected at the electrodes. The SWCNT/Si devices favor high and broadband carrier photogeneration; charge dissociation of ultra-fast hot excitons; transport of electrons through n-Si and high-mobility holes through the SWCNT percolative network. Moreover, by varying the film thickness, it is possible to tailor the physical properties of such a two-dimensional interacting system, therefore the overall device features. These results not only pave the way for low-cost, high-efficient, and broadband photovoltaics, but also are promising for the development of generic SWCNT-based optoelectronic applications

Fabrication and Optical Characterization of 2-dimensional Si3N4 waveguides

We present the fabrication and optical characterization of stoichiometric Silicon Nitride waveguides of different structures on silicon. Stoichiometric silicon nitride is of special interest for planar waveguides in the visible range of light due to the low absorption losses. We investigated the optical properties as a function of wave-guide geometry and fabrication technolog in order to optimize the waveguide performance. In view of the integration of the waveguides within a silicon chip for optical bus applications, we have produced the waveguides within a CMOS fabrication pilot-lin