Low Energy Ion Beam Synthesis Research Articles

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.

Predictive modelling of the dielectric response of plasmonic substrates: application to the interpretation of ellipsometric spectra

A predictive modelling of plasmonic substrates appropriate to read ellipsometric spectra is presented in this work. We focus on plasmonic substrates containing a single layer of silver nanoparticles (AgNPs) embedded in silica matrices. The model uses the Abeles matrix formalism and is based on the quasistatic approximation of the classical Maxwell-Garnett mixing rule, however accounting for the electronic confinement effect through the damping parameter. It is applied on samples elaborated by: (i) RF-diode sputtering followed by Plasma Enhanced Chemical Vapor Deposition (PECVD) and (ii) Low Energy Ion Beam Synthesis (LE-IBS), and represents situations with increasing degree of complexity that can be accounted for by the model. It allows extraction of the main characteristics of the AgNPs population: average size, volume fraction and distance of the AgNPs layer from the matrix free surface. Model validation is achieved through comparison with results obtained from transmission electron microscopy approving for its applicability. The advantages and limitations of the proposed model are discussed after eccentricity-based statistical analysis along with further developments related to the quality of comparison between the model-generated spectra and the experimentally-recorded ellipsometric spectra.

Reducing adhesion energy of micro-relay electrodes by ion beam synthesized oxide nanolayers

Reduction in the adhesion energy of contacting metal electrode surfaces in nano-electro-mechanical switches is crucial for operation with low hysteresis voltage. We demonstrate that by forming thin layers of metal-oxides on metals such as Ru and W, the adhesion energy can be reduced by up to a factor of ten. We employ a low-energy ion-beam synthesis technique and subsequent thermal annealing to form very thin layers (∼2 nm) of metal-oxides (such as RuO2 and WOx) on Ru and W metal surfaces and quantify the adhesion energy using an atomic force microscope with microspherical tips.

Assessing bio-available silver released from silver nanoparticles embedded in silica layers using the green algae Chlamydomonas reinhardtii as bio-sensors

Silver nanoparticles (AgNPs) because of their strong antibacterial activity are widely used in health-care sector and industrial applications. Their huge surface-volume ratio enhances the silver release compared to the bulk material, leading to an increased toxicity for microorganisms sensitive to this element. This work presents an assessment of the toxic effect on algal photosynthesis due to small (size <20nm) AgNPs embedded in silica layers. Two physical approaches were originally used to elaborate the nanocomposite structures: (i) low energy ion beam synthesis and (ii) combined silver sputtering and plasma polymerization. These techniques allow elaboration of a single layer of AgNPs embedded in silica films at defined nanometer distances (from 0 to 7nm) beneath the free surface. The structural and optical properties of the nanostructures were studied by transmission electron microscopy and optical reflectance. The silver release from the nanostructures after 20h of immersion in buffered water was measured by inductively coupled plasma mass spectrometry and ranges between 0.02 and 0.49μM. The short-term toxicity of Ag to photosynthesis of Chlamydomonas reinhardtii was assessed by fluorometry. The obtained results show that embedding AgNPs reduces the interactions with the buffered water free media, protecting the AgNPs from fast oxidation. The release of bio-available silver (impacting on the algal photosynthesis) is controlled by the depth at which AgNPs are located for a given host matrix. This provides a procedure to tailor the toxicity of nanocomposites containing AgNPs.

Ag doped silicon nitride nanocomposites for embedded plasmonics

The localized surface plasmon-polariton resonance (LSPR) of noble metal nanoparticles (NPs) is widely exploited for enhanced optical spectroscopies of molecules, nonlinear optics, photothermal therapy, photovoltaics, or more recently in plasmoelectronics and photocatalysis. The LSPR frequency depends not only of the noble metal NP material, shape, and size but also of its environment, i.e., of the embedding matrix. In this paper, Ag-NPs have been fabricated by low energy ion beam synthesis in silicon nitride (SiNx) matrices. By coupling the high refractive index of SiNx to the relevant choice of dielectric thickness in a SiNx/Si bilayer for an optimum antireflective effect, a very sharp plasmonic optical interference is obtained in mid-range of the visible spectrum (2.6 eV). The diffusion barrier property of the host SiNx matrix allows for the introduction of a high amount of Ag and the formation of a high density of Ag-NPs that nucleate during the implantation process. Under specific implantation conditions, in-plane self-organization effects are obtained in this matrix that could be the result of a metastable coarsening regime.

Quantum dots for memory applications

In this paper, we review the fabrication and the electrical characteristics of metal–insulator–semiconductor (MIS) devices with semiconductor quantum dots (QD) embedded into the gate dielectric. Our results originate from experiments performed the last decade and cover Si QDs realized by low-energy ion-beam synthesis (IBS) as well as GaN QDs formed by molecular beam deposition (MBD). Besides the basic capacitance-to-voltage (C–V) and current-to-voltage (I–V) characterization, the memory properties of the fabricated MIS devices were investigated in terms of memory window under pulse operation and charge retention. The optimization of Si-QD memory cells is reviewed and a methodology for both the extraction of various device parameters and the identification of mechanisms governing the charge loss process are presented. GaN QDs, which exhibit negative conduction band-offset with respect to the Si conduction band, offer an interesting alternative to Si QDs as discussed herein based on our investigations of GaN-QD capacitors fabricated by a complementary-metal-oxide-semiconductor (CMOS) compatible process.

Ge nanocrystals in HfO2/SiN dielectric stacks by low energy ion beam synthesis

Germanium nanocrystals (Ge-NCs) have been obtained by low energy ion beam synthesis in a SiNx/HfO2 stack layer. The effect of the Ge implanted dose variations on structural characteristics (size, position, chemical bonding) of Ge-NCs have been investigated by Transmission Electron Microscopy and Raman spectroscopy. Our results show that several processes (damage, diffusion, oxidation …) that depend on the Ge implanted dose, take place during the synthesis and complicate the expected behavior of the ion beam synthesized system. However, significant memory windows with good retention properties have been observed in these stack structures, indicating their feasibility for low operating voltage, non-volatile memory devices.

(Invited) Ultra Low Energy Ion Beam Synthesis as a New Route toward Nanocrystal Memories

not Available.

Low-Energy Ion Beam Synthesis as a New Route toward Plasmonic Nanostructures

AbstractSingle δ-layers of dispersed silver (Ag) nanoparticles are obtained by low-energy ion beam implantation in a silica thin film. TEM microscopy reveals that the obtained Ag particles are spherical, crystalline, and the particles layer is located at only few nanometers below the free silica surface. We use reflectivity measurements to probe the optical/plasmonic response of the fabricated structures and exploit plasmon resonance and optical interference effects in the silica film to record the Raman scattering by quadrupolar vibrations of the spherical particles.

Oxide–nitride–oxide dielectric stacks with Si nanoparticles obtained by low-energy ionbeam synthesis

Formation of a thin band of silicon nanoparticles within silicon nitride films by low-energy(1 keV) silicon ion implantation and subsequent thermal annealing is demonstrated.Electrical characterization of metal–insulator–semiconductor capacitors reveals thatoxide/Si-nanoparticles-nitride/oxide dielectric stacks exhibit enhanced charge transfercharacteristics between the substrate and the silicon nitride layer compared to dielectricstacks using unimplanted silicon nitride. Attractive results are obtained in terms ofwrite/erase memory characteristics and data retention, indicating the large potentialof the low-energy ion-beam-synthesis technique in SONOS memory technology.

Oxide-nitride-oxide Dielectric Stacks with Embedded Si-nanoparticles Fabricated by Low-energy Ion-beam-synthesis

AbstractThis work reports on the formation of Si-nanocrystals within silicon nitride layers by low-energy Si ion implantation. Electrical characterization of oxide/Si-nanocrystal-nitride/oxide dielectric stacks demonstrates regions of negative differential resistance at low-fields. In addition, the memory characteristics in terms of charge trapping, write/erase response and retention properties of the dielectric stacks were recorded. The results indicate the large potential of the low-energy ion beam synthesis method in nitride memory technology.

Effect of annealing environment on the memory properties of thin oxides with embedded Si nanocrystals obtained by low-energy ion-beam synthesis

The effect of annealing in diluted oxygen versus inert environment on the structural and electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals fabricated by very low-energy silicon implantation (1 keV) is reported. Annealing in diluted oxygen increases the thickness of the control oxide, improves the integrity of the oxide and narrows the size distribution of the nanocrystals without affecting significantly their mean size (∼2 nm). Strong charge storage effects at low gate voltages and enhanced charge retention times are observed through electrical measurements of metal-oxide-semiconductor capacitors. These results indicate that a combination of low-energy silicon implants and annealing in diluted oxygen allows for the fabrication of improved low-voltage nonvolatile memory devices.

Effects of annealing conditions on charge storage of Si nanocrystal memory devices obtained by low-energy ion beam synthesis

The structural and electrical characteristics of thin silicon dioxide layers with embedded Si nanocrystals are reported fabricated by low-energy silicon implantation and with subsequent annealing in inert and diluted oxygen. Thermal treatment in diluted oxygen increases the thickness of the control oxide, does not affect significantly the size of the nanocrystals, and improves the integrity of the oxide. As a result, strong charge storage effects at low gate voltages and enhanced charge retention times are observed through electrical measurements of MOS capacitors. These results indicate that a combination of low-energy silicon implants and annealing in diluted oxygen permits the fabrication of low-voltage nonvolatile memory devices.

Room-temperature single-electron charging phenomena in large-area nanocrystal memory obtained by low-energy ion beam synthesis

We investigated the dependence of implantation dose on the charge storage characteristics of large-area n-channel metal–oxide–semiconductor field-effect transistors with 1-keV Si+-implanted gate oxides. Gate bias and time-dependent source–drain current measurements are reported. Devices implanted with 1×1016 cm−2 Si dose exhibit a continuous (trap-like) charge storage process under both static and dynamic conditions. In contrast, for 2×1016 cm−2 implanted devices, electrons are stored in Si nanocrystals in discrete units at low gate voltages, as revealed by a periodic staircase plateau of the source–drain current with a low gate voltage sweep rate, and the step-like decrease of the time-dependent monitoring of the channel current. These observations of room-temperature single-electron storage effects support the pursuit of large-area devices operating on the basis of Coulomb blockade phenomena.