Nicolas Reckinger

Graphene-coated holey metal films: Tunable molecular sensing by surface plasmon resonance

We report on the enhancement of surface plasmon resonances in a holey bidimensional grating of subwavelength size, drilled in a gold thin film coated by a graphene sheet. The enhancement originates from the coupling between charge carriers in graphene and gold surface plasmons. The main plasmon resonance peak is located around 1.5 μm. A lower constraint on the gold-induced doping concentration of graphene is specified and the interest of this architecture for molecular sensing is also highlighted.

Nanowire-decorated microscale metallic electrodes.

One of the challenging aspects of science and technology on a nanometer-scale is the precise three-dimensional control of nano-objects. Scanning probe microscopy manipulation, magneticor electric-field alignment and lithography-based techniques are only a few of the techniques that have been reported so far. Nevertheless, most of these techniques are still being developed and their integration for device fabrication represents a real challenge for the scientific community. Within this context, nanowires and nanotubes are of great interest because they lie between the macroscopic and atomic scales. The ability to fabricate andmanipulate such objects in a reliablemanner on a large scale will foster their use in electronic, photonic, and sensing applications. Templatebased methods have been successfully used for nanowire fabrication as they allow the realization of complex organic/ inorganic nanostructures. To date, nanoporous anodic alumina oxide (AAO) made by the electrochemical oxidation of aluminum has been extensively used because it provides a good platform for the development of various nanostructures. This interest originates from the fact that AAO membranes, having a high density of nanopores (up to 10 cm ), are easily produced over large areas with variable thicknesses. Moreover, a good chemical and mechanical stability combined with interesting electrical properties make AAO membranes good candidates for nanowire fabrication. However, the use of such nanostructures as passive or active components in emerging electronic devices requires smartly engineered arrays of nanowires with well defined position and pitch.

Self-aligned silicon-on-insulator nano flash memory device

This paper reports on the fabrication of a silicon-on-insulator nano flash memory device based on the differential oxidation rate of silicon resulting from gradients in the arsenic doping concentration. The key processes involved are the formation of the desired arsenic doping profile, electron beam lithography and wet oxidation. The resulting device is a triangular-channel MOSFET with a nanocrystal floating gate embedded in the gate oxide. The length, width and height of the nanocrystal are 10, 10 and 20 nm, respectively. As long as the control gate voltage does not exceed +/-2V, the device behaves like a thin and narrow P-channel MOSFET. When a voltage of -5 or +5 V is applied to the control gate at room temperature, holes are injected into the floating gate or removed from it, respectively. This effect induces a persistent shift of the threshold voltage of the device, which acts as a miniature EEPROM

Energy-Band Engineering for Improved Charge Retention in Fully Self-Aligned Double Floating-Gate Single-Electron Memories

We present a new fully self-aligned single-electron memory with a single pair of nano floating gates, made of different materials (Si and Ge). The energy barrier that prevents stored charge leakage is induced not only by quantum effects but also by the conduction-band offset that arises between Ge and Si. The dimensions and position of each floating gate are well-defined and controlled. The devices exhibit a long retention time and single-electron injection at room temperature.

Low Schottky barrier height for ErSi2−x/n-Si contacts formed with a Ti cap

In this paper, the formation of Er disilicide (ErSi2−x) with a Ti cap on low doping n-type Si(100) is investigated. After deposition in ultrahigh vacuum, the solid-state reaction between Er and Si is performed ex situ by rapid thermal annealing between 450 and 600 °C in a forming gas ambience with a 10 nm thick Ti capping layer to protect Er from oxidation. X-ray diffraction analyses have confirmed the formation of ErSi2−x for all annealing temperatures. The formed films are found to be free of pinholes or pits and present a sharp and smooth interface with the Si bulk substrate. The extracted Schottky barrier height (SBH) corresponds to the state-of-the-art value of 0.28 eV if the annealing temperature is lower than or equal to 500 °C. This result demonstrates the possibility to form low SBH ErSi2−x/n-Si contacts with a protective Ti cap. However, when the annealing temperature is set to a higher value, the SBH concomitantly rises. Based on our experiments, this SBH increase can be mainly related to an enhanced diffusion of oxygen through the stack during the annealing, which degrades the quality of the ErSi2−x film.

Schottky barrier lowering with the formation of crystalline Er silicide on n-Si upon thermal annealing

The evolution of the Schottky barrier height (SBH) of Er silicide contacts to n-Si is investigated as a function of the annealing temperature. The SBH is found to drop substantially from 0.43 eV for the as-deposited sample to reach 0.28 eV, its lowest value, at 450 degrees C. By x-ray diffraction, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy, the decrease in the SBH is shown to be associated with the progressive formation of crystalline ErSi2-x.

Gas sensing with gold-decorated vertically aligned carbon nanotubes.

Summary Vertically aligned carbon nanotubes of different lengths (150, 300, 500 µm) synthesized by thermal chemical vapor deposition and decorated with gold nanoparticles were investigated as gas sensitive materials for detecting nitrogen dioxide (NO2) at room temperature. Gold nanoparticles of about 6 nm in diameter were sputtered on the top surface of the carbon nanotube forests to enhance the sensitivity to the pollutant gas. We showed that the sensing response to nitrogen dioxide depends on the nanotube length. The optimum was found to be 300 µm for getting the higher response. When the background humidity level was changed from dry to 50% relative humidity, an increase in the response to NO2 was observed for all the sensors, regardless of the nanotube length.

Anomalous moiré pattern of graphene investigated by scanning tunneling microscopy: Evidence of graphene growth on oxidized Cu(111)

The growth of graphene on oriented (111) copper films has been achieved by atmospheric pressure chemical vapor deposition. The structural properties of as-produced graphene have been investigated by scanning tunneling microscopy. Anomalous moiré superstructures composed of well-defined linear periodic modulations have been observed. We report here on comprehensive and detailed studies of these particular moiré patterns present in the graphene topography revealing that, in certain conditions, the growth can occur on the oxygen-induced reconstructed copper surface and not directly on the oriented (111) copper film as expected.

A Simple Method for Measuring Si-Fin Sidewall Roughness by AFM

The gate oxide reliability and the electrical behavior of FinFETs are directly related to the surface characteristics of the fin vertical sidewalls. The surface roughness of the fin sidewalls is one of the most important structural parameters to be monitored in order to optimize the fin patterning and postetch treatments. Because of the nanometer-scale dimensions of the fins and the vertical orientation of the sidewall surface, their roughness measurement is a serious challenge. In this paper, we describe a simple and effective method for measuring the sidewall morphology of silicon fins by conventional atomic force microscopy. The present methodology has been employed to analyze fins as etched by reactive ion etching and fins repaired by sacrificial oxidation. The results show that sacrificial oxidation not only reduces the roughness of the sidewalls, but also rounds the top corners of silicon fins. The present method can also be applied to characterize sidewall roughness of other nanostructures and materials such as the polysilicon gate of transistors or nanoelectromechanical beams.

Damage evaluation in graphene underlying atomic layer deposition dielectrics

Based on micro-Raman spectroscopy (μRS) and X-ray photoelectron spectroscopy (XPS), we study the structural damage incurred in monolayer (1L) and few-layer (FL) graphene subjected to atomic-layer deposition of HfO2 and Al2O3 upon different oxygen plasma power levels. We evaluate the damage level and the influence of the HfO2 thickness on graphene. The results indicate that in the case of Al2O3/graphene, whether 1L or FL graphene is strongly damaged under our process conditions. For the case of HfO2/graphene, μRS analysis clearly shows that FL graphene is less disordered than 1L graphene. In addition, the damage levels in FL graphene decrease with the number of layers. Moreover, the FL graphene damage is inversely proportional to the thickness of HfO2 film. Particularly, the bottom layer of twisted bilayer (t-2L) has the salient features of 1L graphene. Therefore, FL graphene allows for controlling/limiting the degree of defect during the PE-ALD HfO2 of dielectrics and could be a good starting material for building field effect transistors, sensors, touch screens and solar cells. Besides, the formation of Hf-C bonds may favor growing high-quality and uniform-coverage dielectric. HfO2 could be a suitable high-K gate dielectric with a scaling capability down to sub-5-nm for graphene-based transistors.