ORCID Profile
0000-0002-1210-8719
Current Organisation
Institute of Materials Research and Engineering
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Publisher: American Physical Society (APS)
Date: 12-11-2020
Publisher: American Vacuum Society
Date: 15-08-2011
DOI: 10.1116/1.3622296
Abstract: Ballistic electron emission microscopy was employed in order to investigate the electronic properties of sub-nanometer high-κ dielectrics (CeO2 and La2O3). The authors found that such a thin dielectric sandwiched between Au and n-Si fails to exhibit the same electronic barrier as its bulk counterpart, but it can still significantly attenuate the ballistic electron transport. The authors attribute the observed smaller barrier height to quantum tunneling and/or induced gap states. The results suggest that such ultrathin high-κ dielectrics in a metal-dielectric-semiconductor structure do not show a fully formed electronic barrier.
Publisher: American Chemical Society (ACS)
Date: 03-11-2014
DOI: 10.1021/AM506055H
Abstract: Diffusion barriers prevent materials from intermixing (e.g., undesired doping) in electronic devices. Most diffusion barrier materials are often very specific for a certain combination of materials and/or change the energetics of the interface because they are insulating or add to the contact resistances. This paper presents graphene (Gr) as an electronically transparent, without adding significant resistance to the interface, diffusion barrier in metal/semiconductor devices, where Gr prevents Au and Cu from diffusion into the Si, and unintentionally dope the Si. We studied the electronic properties of the n-Si(111)/Gr/M Schottky barriers (with and without Gr and M=Au or Cu) by I(V) measurements and at the nanoscale by ballistic electron emission spectroscopy (BEEM). The layer of Gr does not change the Schottky barrier of these junctions. The Gr barrier was stable at 300 °C for 1 h and prevented the diffusion of Cu into n-Si(111) and the formation of Cu3Si. Thus, we conclude that the Gr is mechanically and chemically stable enough to withstand the harsh fabrication methods typically encountered in clean room processes (e.g., deposition of metals in high vacuum conditions at high temperatures), it is electronically transparent (it does not change the energetics of the Si/Au or Si/Cu Schottky barriers), and effectively prevented diffusion of the Cu or Au into the Si at elevated temperatures and vice versa.
Publisher: American Chemical Society (ACS)
Date: 15-08-2023
Publisher: Springer Science and Business Media LLC
Date: 17-09-2014
DOI: 10.1038/NCOMMS5947
Abstract: Nanoporous gold with networks of interconnected ligaments and highly porous structure holds stimulating technological implications in fuel cell catalysis. Current syntheses of nanoporous gold mainly revolve around de-alloying approaches that are generally limited by stringent and harsh multistep protocols. Here we develop a one-step solution phase synthesis of zero-dimensional hollow nanoporous gold nanoparticles with tunable particle size (150-1,000 nm) and ligament thickness (21-54 nm). With faster mass diffusivity, excellent specific electroactive surface area and large density of highly active surface sites, our zero-dimensional nanoporous gold nanoparticles exhibit ~1.4 times enhanced catalytic activity and improved tolerance towards carbonaceous species, demonstrating their superiority over conventional nanoporous gold sheets. Detailed mechanistic study also reveals the crucial heteroepitaxial growth of gold on the surface of silver chloride templates, implying that our synthetic protocol is generic and may be extended to the synthesis of other nanoporous metals via different templates.
Publisher: WORLD SCIENTIFIC
Date: 12-2010
Publisher: American Vacuum Society
Date: 07-2010
DOI: 10.1116/1.3428546
Abstract: A dual parameter representation of the barrier height and transmission extracted from ballistic electron emission spectroscopy spectra is presented and evaluated with respect to the noise present in the spectra and the conditions used for data fitting. Simulated dual parameter distributions incorporating only Gaussian (white) noise are compared to experimental dual parameter distributions for two interfaces, namely, Au/n-Si and Au entacene/n-Si. The authors find that for both measurements, noise and data fitting conditions can have significant influence on the distributions. Once these contributions are accounted for, such dual parameter representations provide statistical information related to the interfacial homogeneity of devices.
Publisher: American Vacuum Society
Date: 24-05-2012
DOI: 10.1116/1.4721640
Abstract: The effect of surface contamination on the electron tunneling in the high bias range is investigated from the perspective of ballistic electron emission microscopy (BEEM). A comparative BEEM study on the Au/SiO2/Si devices shows that there is a significant difference in the high bias range between the experiments performed with in situ and ex situ deposited Au. Detailed studies show that the difference arises from the contaminations during air exposure. These contaminations significantly accelerated the material transfer between the tip and the s le during tunneling and lead to the unreliability of BEEM studies in the high bias range on the ex situ prepared s le.
Publisher: IOP Publishing
Date: 14-01-2016
Publisher: AIP Publishing
Date: 03-09-2007
DOI: 10.1063/1.2780084
Abstract: An advanced bilayer gate dielectric stack consisting of Sc2O3∕La2O3∕SiOx annealed in nitrogen at 300°C was studied by scanning tunneling microscopy using bias dependent imaging. By changing the s le bias, electrical properties of different layers of the dielectric stack can be studied. At a s le bias of +3.5V, the conduction band of the La2O3 layer is probed revealing a polycrystalline film with an average grain size of about 27nm, in good agreement with that determined from planar transmission electron microscopy. High conductivity at grain boundaries, due possibly to dangling bonds, can be observed in this layer, as also observed in grain boundary assisted current conduction in metal-oxide-silicon structures. Imaging at a s le bias of −4V probes the interfacial SiOx layer and an amorphouslike image of the interfacial layer is obtained.
Publisher: AIP Publishing
Date: 19-08-2013
DOI: 10.1063/1.4818998
Abstract: Two-probe electronic transport measurements on a Molybdenum Disulphide (MoS2) surface were performed at low temperature (30 K) under ultra-high vacuum conditions. Two scanning tunneling microscope tips were precisely positioned in tunneling contact to measure the surface current-voltage characteristics. The separation between the tips is controllably varied and measured using a high resolution scanning electron microscope. The MoS2 surface shows a surface electronic gap (ES) of 1.4 eV measured at a probe separation of 50 nm. Furthermore, the two- probe resistance measured outside the electronic gap shows 2D-like behavior with the two-probe separation.
Publisher: AIP Publishing
Date: 2012
DOI: 10.1063/1.3672698
Abstract: We report upon a comprehensive investigation of the subthreshold characteristics of the ballistic electron emission microscopy (BEEM) current in ballistic electron emission spectroscopy. Starting from the Bell-Kaiser model, we derive an analytical equation to describe the subthreshold behavior of the BEEM current. It is found that the BEEM current in this region should exhibit a subthreshold swing of ∼60 mV/decade at room temperature, which we experimentally verified. This finding provides a rule of thumb for the detectability of the subthreshold behavior in a spectrum. For spectra where the subthreshold behavior is discernible above the signal noise, it is demonstrated that significant deviations in the near-threshold region can occur when fitting with a simple quadratic model that ignores the subthreshold behavior. To take the subthreshold behavior into account, a simple analytical model is proposed. This model not only fits significantly better in the near threshold region than the square model, but also gives a barrier height closer to the one extracted from the Bell-Kaiser model. More significantly, this model provides a quick method to estimate the subthreshold BEEM current litude based on the BEEM current above the barrier height.
Publisher: American Chemical Society (ACS)
Date: 03-03-2015
DOI: 10.1021/PH5004303
Publisher: American Physical Society (APS)
Date: 17-04-2009
Publisher: AIP Publishing
Date: 03-2012
DOI: 10.1063/1.3693556
Abstract: A systematic study on silicon native oxides grown in ambient air at room temperature is carried out using ballistic electron emission microscopy. The electronic barrier height of Au/native oxide was directly measured for native oxides at different oxidation stages. While the ballistic electron transmission decreases with increasing oxidation time, the electronic barrier height remains the same, even after oxidation for 1 week. After oxidation for 26 months, the oxide layer showed the bulk-like SiO2 barrier however, some local areas still show the same barrier height as that of an Au/n-Si device. This demonstrates the non-uniformity of native oxide growth.
Publisher: American Chemical Society (ACS)
Date: 30-06-2007
DOI: 10.1021/LA063165F
Abstract: Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74+/-5 degrees and 46+/-5 degrees molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46 degrees for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase".
Publisher: IOP Publishing
Date: 02-10-2008
DOI: 10.1088/0957-4484/19/44/445718
Abstract: The well-known Au/n-Si(111) Schottky interface is modified by a discontinuous pentacene film (∼1.5 nm thick) and studied using spatially resolved ballistic electron emission spectroscopy (BEES). The pentacene film introduced subtle changes to the interface which cannot be definitively detected by current-voltage measurements or a standard BEES analysis of the barrier height. In contrast, analyzing the BEES results in a dual-parameter (transmission attenuation and barrier height) space allows the effect of the pentacene film on the Au/n-Si(111) interface to be clearly demonstrated. We found that the pentacene film behaves like a tunneling barrier and increases the distribution of local barrier heights with a tendency toward lower values. Our results highlight the potential of the dual-parameter BEES analysis for understanding local interface modification by molecules.
Publisher: American Vacuum Society
Date: 2012
DOI: 10.1116/1.3675606
Abstract: Ballistic electron emission spectroscopy (BEES) was used to determine the electron barrier height at the interface of Au and an oxidized GaAs film. Two thresholds were observed in the spectra. In a two-step procedure, we identified the first threshold at ∼1.4 eV, which we show arose from electron-hole pairs excited by photons emitted during scanning tunneling microscopy (STM), and the second threshold at ∼3.55 eV, which is attributed to the Au/oxidized-GaAs barrier. Our results demonstrate that the two-threshold behavior observed in BEES studies on metal/oxide s les is amenable to a physical model comprising of STM photocurrent and a metal/oxide interface barrier.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Cedric Troadec.