Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Adsorption properties of BSA and DsRed proteins deposited on thin SiO2 layers: optically non-absorbing versus absorbing proteins

Protein adsorption on solid surfaces is of interest for many industrial and biomedical applications, where it represents the conditioning step for micro-organism adhesion and biofilm formation. To understand the driving forces of such an interaction we focus in this paper on the investigation of the adsorption of bovine serum albumin (BSA) (optically non-absorbing, model protein) and DsRed (optically absorbing, naturally fluorescent protein) on silica surfaces. Specifically, we propose synthesis of thin protein layers by means of dip coating of the dielectric surface in protein solutions with different concentrations (0.01-5.0 g l^-1). We employed spectroscopic ellipsometry as the most suitable and non-destructive technique for evaluation of the protein layers' thickness and optical properties (refractive index and extinction coefficient) after dehydration, using two different optical models, Cauchy for BSA and Lorentz for DsRed. We demonstrate that the thickness, the optical properties and the wettability of the thin protein layers can be finely controlled by proper tuning of the protein concentration in the solution. These results are correlated with the thin layer morphology, investigated by AFM, FTIR and PL analyses. It is shown that the proteins do not undergo denaturation after dehydration on the silica surface. The proteins arrange themselves in a lace-like network for BSA and in a rod-like structure for DsRed to form mono- and multi-layers, due to different mechanisms driving the organization stage.

Vibrational density of states and thermodynamics at the nanoscale: the 3D-2D transition in gold nanostructures

Surface enhanced Raman scattering (SERS) is generally and widely used to enhance the vibrational fingerprint of molecules located at the vicinity of noble metal nanoparticles. In this work, SERS is originally used to enhance the own vibrational density of states (VDOS) of nude and isolated gold nanoparticles. This offers the opportunity of analyzing finite size effects on the lattice dynamics which remains unattainable with conventional techniques based on neutron or x-ray inelastic scattering. By reducing the size down to few nanometers, the role of surface atoms versus volume atoms become dominant, and the “text-book” 3D-2D transition on the dynamical behavior is experimentally emphasized. “Anomalies” that have been predicted by a large panel of simulations at the atomic scale, are really observed, like the enhancement of the VDOS at low frequencies or the occurrence of localized modes at frequencies beyond the cut-off in bulk. Consequences on the thermodynamic properties at the nanoscale, like the reduction of the Debye temperature or the excess of the specific heat, have been evaluated. Finally the high sensitivity of reminiscent bulk-like phonons on the arrangements at the atomic scale is used to access the morphology and internal disorder of the nanoparticles.

Transient Enhanced Diffusion of Dopants in Preamorphised Si Layers

Transient Enhanced Diffusion (TED) of dopants in Si is the consequence of the evolution, upon annealing, of a large supersaturation of Si self-interstitial atoms left after ion bombardment. In the case of amorphizing implants, this supersaturation is located just beneath the c/a interface and evolves through the nucleation and growth of End-Of-Range (EOR) defects.

For this reason, we discuss here the relation between TED and EOR defects. Modelling of the behavior of these defects upon annealing allows one to understand why and how they affect dopant diffusion. This is possible through the development of the Ostwald ripening theory applied to extrinsic dislocation loops. This theory is shown to be readily able to quantitatively describe the evolution of the defect population (density, size) upon annealing and gives access to the variations of the mean supersaturation of Si self-interstitial atoms between the loops and responsible for TED. This initial supersaturation is, before annealing, at least 5 decades larger than the equilibrium value and exponentially decays with time upon annealing with activation energies that are the same than the ones observed for TED. It is shown that this time decay is precisely at the origin of the transient enhancement of boron diffusivity through the interstitial component of boron diffusion. Side experiments shed light on the effect of the proximity of a free surface on the thermal behavior of EOR defects and allow us to quantitatively describe the space and time evolutions of boron diffusivity upon annealing of preamorphised Si layers.

Controlled fabrication of Si nanocrystals embedded in thin SiON layers by PPECVD followed by oxidizing annealing

The controlled fabrication of Si nanocrystals embedded in thin silicon oxynitride films (<15 nm) on top of a silicon substrate has been realized by PPECVD with N(2)O-SiH(4) precursors. The effect of inert and oxidizing annealing processes on the Si nanocrystal spatial and size distributions is studied by coupling ellipsometry measurements and cross-sectional transmission electron microscopy observations. This study gives an interesting insight into the physics underlying the Si nanocrystal nucleation, growth and oxidation mechanisms. In particular, it evidences the presence in the as-deposited films of a high density of small amorphous Si particles that crystallize after high temperature thermal annealing. Annealing under oxidizing conditions is shown to be a powerful way to create tunnel oxides of good quality and controlled thickness needed to design future memory devices.

High-k Hf-based layers grown by RF magnetron sputtering

Structural and chemical properties of Hf-based layers fabricated by RF magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy and attenuated total reflection infrared spectroscopy versus the deposition parameters and annealing treatment. The deposition and post-deposition conditions allow us to control the temperature of the amorphous-crystalline phase transition of HfO(2)-based layers. It was found that silicon incorporation in an HfO(2) matrix plays the main role in the structural stability of the layers. It allows us not only to decrease the thickness of the film/substrate interfacial layer to 1 nm, but also to conserve the amorphous structure of the layers after an annealing treatment up to 900-1000 degrees C.

Si nanocrystal synthesis in HfO2/SiO/HfO2 multilayer structures

The synthesis of two-dimensional arrays of Si nanocrystals in an HfO2 matrix has been achieved by deposition of HfO2/SiO/HfO2 multilayer structures followed by high temperature (1100 degrees C) thermal treatment in nitrogen atmosphere. Silicon out-diffusion from the SiO layer through the HfO2 films has been shown to be the limiting factor in the formation of the Si nanocrystals. Suitable strategies have been identified in order to overcome this limitation. Si nanocrystal formation has been achieved by properly adjusting the thickness of the SiO layer.

The synthesis of single layers of Ag nanocrystals by ultra-low-energy ion implantation for large-scale plasmonic structures

Single layers of silver (Ag) nanoparticles embedded in silica (SiO2) have been fabricated by ultra-low-energy ion implantation. The distance between the Ag particles and the free SiO2 surface is controlled with nanometer precision. Raman scattering and reflectivity measurements strongly correlate to transmission electron microscopy analyses, allowing the use of these non-invasive techniques to monitor structural and dynamical properties. These results open up new opportunities to manipulate electromagnetic near-field interactions on wafer-scale plasmonic devices.

Temperature-dependent low electric field charging of Si nanocrystals embedded within oxide-nitride-oxide dielectric stacks

In this work we examine the current peaks and the negative differential resistance that appear in the low electric field regime of oxide-nitride-oxide structures with a two-dimensional band of silicon nanocrystals embedded in a nitride layer. The silicon nanocrystals were synthesized by low energy ion implantation (1 keV, 1.5 x 10(16) Si(+) cm(-2)) and subsequent thermal annealing (950 degrees C, 30 min). Electrical examination was performed at temperatures from 20 to 100 degrees C using constant voltage ramp-rate current measurements. This approach enables us to determine the origin of the observed current peaks as well as to extract the trapping location of the injected carriers within the dielectric stack. The results confirm that the carriers are trapped within the Si nanocrystal band, verifying that this region corresponds to energy minima of the dielectric stack.

Auger quenching-based modulation of electroluminescence from ion-implanted silicon nanocrystals

We describe high-speed control of light from silicon nanocrystals under electrical excitation. The nanocrystals are fabricated by the ion implantation of Si(+) in the 15 nm thick gate oxide of a field effect transistor at 6.5 keV. A characteristic read-peaked electroluminescence is obtained either by DC or AC gate excitation. However, AC gate excitation is found to have a frequency response that is limited by the radiative lifetimes of silicon nanocrystals, which makes impossible the direct modulation of light beyond 100 kb s(-1) rates. As a solution, we demonstrate that combined DC gate excitation along with an AC channel hot electron injection of electrons into the nanocrystals may be used to obtain a 100% deep modulation at rates of 200 Mb s(-1) and low modulating voltages. This approach may find applications in biological sensing integrated into CMOS, single-photon emitters or direct encoding of information into light from Si-nc doped with erbium systems, which exhibit net optical gain. In this respect, the main advantage compared to conventional electro-optical modulators based on plasma dispersion effects is the low power consumption (10(4) times smaller) and thus the inherent large scale of integration. A detailed electrical characterization is also given. An Si/SiO(2) barrier change from Φ(b) = 3.2 to 4.2 eV is found while the injection mechanism is changed from Fowler-Nordheim to channel hot electron, which is a clear signature of nanocrystal charging and subsequent electroluminescence quenching.

Imaging Si nanoparticles embedded in SiO(2) layers by (S)TEM-EELS

Fabrication of systems in which Si nanoparticles are embedded in a thin silica layer is today mature for non-volatile memory and opto-electronics applications. The control of the different parameters (position, size and density) of the nanoparticles population is a key point to optimize the properties of such systems. A review of dedicated transmission electron microscopy (TEM) methods, which can be used to measure these parameters, is presented with an emphasis on those relying on electron energy-loss spectroscopy (EELS). Defocused bright-field imaging can be used in order to determine topographic information of a whole assembly of nanoparticles, but it is not efficient for looking at individual nanoparticles. High-resolution electron imaging or dark-field imaging can be of help in the case of crystalline particles but they always provide underestimated values of the nanocrystals population. EELS imaging in the low-energy-loss domain around the Si plasmon peak, which gives rise to strong signals, is the only way to visualize all Si nanoparticles within a silica film and to perform reliable size and density measurements. Two complementary types of experiments are investigated and discussed more extensively: direct imaging with a transmission electron microscope equipped with an imaging filter (EFTEM) and indirect imaging from spectrum-imaging data acquired with a scanning transmission electron microscope equipped with a spectrometer (STEM-PEELS). The direct image (EFTEM) and indirect set of spectra (STEM-PEELS) are processed in order to deliver images where the contribution of the silica matrix is minimized. The contrast of the resulting images can be enhanced with adapted numerical filters for further morphometric analysis. The two methods give equivalent results, with an easier access for EFTEM and the possibility of a more detailed study of the EELS signatures in the case of STEM-PEELS. Irradiation damage in such systems is also discussed.