Water adsorption by a sensitive calibrated gold plasmonic nanosensor

International audienceWe demonstrate in this work that using nanoplasmonic sensing it is possible to follow the adsorption/desorption of water molecules on gold nanodisks nanofabricated by electron beam lithography. This quantitative method is highly sensitive allowing the detection of a few hundredths of adsorbed monolayer. Disk parameters (height, diameter, inter-disk distance) have been optimized after finite-difference time-domain (FDTD) simulations in order to obtain the best localized surface plasmon resonance (LSPR) signal-to-noise ratio. Finally, we have precisely measured the adsorption kinetics of water on gold as a function of the relative humidity of the surrounding medium

Magnetic properties of self-organized Co dimer nanolines on Si/Ag(110)

International audienceWe demonstrate the kinetically controlled growth of one-dimensional Co nanomagnets with a high lateral order on a nanopatterned Ag(110) surface. First, self-organized Si nanoribbons are formed upon submonolayer condensation of Si on the anisotropic Ag(110) surface. Depending on the growth temperature, individual or regular arrays (with a pitch of 2 nm) of Si nanoribbons can be grown. Next, the Si/Ag(110) system is used as a novel one-dimensional Si template to guide the growth of Co dimer nanolines on top of the Si nanoribbons, taking advantage of the fact that the thermally activated process of Co diffusion into the Si layer is efficiently hindered at 220 K. Magnetic characterization of the Co nanolines using X-ray magnetic circular dichroism reveals that the first atomic Co layer directly adsorbed onto the Si nanoribbons presents a weak magnetic response. However, the second Co layer exhibits an enhanced magnetization, strongly suggesting a ferromagnetic ordering with an in-plane easy axis of magnetization, which is perpendicular to the Co nanolines

Are conductance plateaus independent events in atomic point contact measurements ? A statistical approach

Room temperature conductance-elongation curves of gold atomic wires are measured using a Scanning Tunnelling Microscope Break Junction technique. Landauer's conductance plateaus are individually identified and statistically analysed. Both the probabilities to observe, and the lengths of the two last plateaus (at conductance values close to 2e2/h and 4e2/h) are studied. All results converge to show that the occurrence of these two conductance plateaus on a conductance-elongation curve are statistically independent events.Comment: 8 pages, 5 figures. Accepted for publication in Nanotechnolog

Cr doping effect on the structural, optoelectrical and photocatalytic properties of RF sputtered TiO 2 thin films from a powder target

International audienceIn this study, thin films of pure and chromium doped TiO 2 were deposited by RF magnetron sputtering technique with recourse to a low cost powder target. The dopant concentration was varied from 0 to 6 wt %. The structural, optical, electrical and photocatalytic properties of the sputtered deposited films were systematically investigated on the basis of the incorporated Cr content. XRD analysis revealed that the elaborated films are polycrystalline and have a preferential orientation along the (110) plane, characteristic of the rutile phase. The optical measurements showed a good homogeneity of the films and a high transmission that reached 85% in the visible range. The high transparency of these films allows their use as an optical window in thin film solar cells. Optical band gap decreased from 3.44 eV to 3.32 eV with the increase of the Cr content. In addition, the impedance spectroscopy analysis showed that the conductivity increases along with increasing frequency and temperature, and that the conduction mechanism follows the correlated barrier hopping model. The test of the catalytic efficiency of the chromiumdoped TiO 2 thin films at different concentrations demonstrated a degradation of the methylene blue (MB) and an improvement of the photocatalytic activity and that the 6 wt% doped thin films have the best photocatalytic activity

Step flow growth of Mn5Ge3 films on Ge(111) at room temperature

International audienceThe very first stages of the non-diffusive growth of Mn5Ge3 thin films on Ge(111) substrates are characterized by several techniques. Mn5Ge3 films are grown by molecular beam epitaxy using the co-deposition of Mn and Ge atoms at room temperature. XRD measurements demonstrate that the thin films are monocrystalline. The evolution of the RHEED intensity during the deposition and the AFM images show a step-flow growth mode. RHEED patterns, combined with TEM images, prove that the lattice mismatch of 3.7% is accommodated by the formation of an array of interfacial dislocations and by the presence of a residual strain in the thin films. These observations are supported by the numerical calculations of the critical nucleation volumes exhibiting very similar values, in the case of a pseudomorphic growth or in the case of an accommodation of the lattice mis-match by interfacial dislocations. Furthermore, the effect Ge/Mn stoichiometric and Mn-rich fluxes on the surface morphology is examined

Procédé de préparation de films minces monocristallins

The invention relates to a process for preparing single-crystal thin films of pure metals or alloys, by deposition and growth of grains on a (0001) sapphire having a miscut comprised between 0.2° and 5°, and oriented towards a specific plane. It also relates to a single-crystal thin film obtainable by such a process and uses thereof.L'invention concerne un procédé de préparation de films minces monocristallins de métaux ou d'alliages purs, par dépôt et croissance de grains sur un saphir (0001) présentant une mauvaise découpe comprise entre 0,2° et 5°, et orientés vers un plan spécifique. L'invention concerne également un film mince monocristallin pouvant être obtenu par un tel procédé et ses utilisations

Growth Of Dihydrotetraazapentacene Layers On Cu(110)

The adsorption of 5,14-dihydro-5,7,12,14-tetraazapentacene (DHTAP) on Cu(110) has been investigated at different temperatures and coverages by means of scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Our results show that the interaction of DHTAP with the Cu(110) surface differs considerably from that of pentacene on the same surface. The DHTAP molecules are chemisorbed on the surface via strong Cu-N bonds with an adsorption energy of roughly 3 eV/molecule, twice as high as the value for pentacene. We could identify three different ordered superstructures, which are commensurate with the substrate and characterized by the matrices (6 -1 | 1 2), (7 0 | 1 2), and (6 0 | 1 2), respectively

CO and O2 Adsorption and CO Oxidation on Pt Nanoparticles by Indirect Nanoplasmonic Sensing

International audienceWe used indirect nanoplasmonic sensing (INPS) coupled with mass spectrometry to study CO and oxygen adsorption as well as CO oxidation, on Pt nanoparticles, in the Torr pressure range. Due to an optimization of the physical parameters of our plasmonic sample, we obtain a highly sensitive probe that can detect gas adsorption of a few hundredths of a monolayer, even with a very low number density of Pt particles. Moreover and for the first time, a similarity is observed between the sign and the evolution of the localized surface plasmon resonance (LSPR) peak shift and the work function measurements for CO and oxygen chemisorption. Controlling the size, shape, and surface density of Pt particles, the turnover frequency (TOF) has also been accurately determined. For similar experimental conditions, the TOF is close to those measured on Pt/oxide powder catalysts and Pt(100) single crystals

Indirect nanoplasmonic sensing: a very sensitive and promising probe

International audienceWe study gas adsorption and interaction on nanoparticles (NPs) deposited on Au nanodisks acting individually as plasmonic detectors. For this purpose, it is necessary to deposit a thin layer of insulator on the Au nanostructures to make them more stable at high temperatures and to eliminate any (electronic) interactions between the reactive NPs and Au disks. NPs can react with gas molecules that modify the dielectric properties on the surface of the NP and cause a localized surface plasmon resonance (LSPR) shift of the underlying Au detector (Fig. 1). This is called indirect nanoplasmonic sensing (INPS), making it possible to follow, at any pressure, the reactivity with the surrounding gas of small NPs, which by nature do not give measurable LSPR signals. We used INPS to follow, with high sensitivity, the interaction of water vapor on soot particles [1] that are a major contributor to global warming. CO and oxygen adsorption as well as CO oxidation, on Pt NPs, have also been studied by INPS [2]. Due to an optimization of the physical parameters of our plasmonic detector, and coupling with mass spectrometry, we obtain a quantitative and a very sensitive probe that can detect gas adsorption of a few hundredths of a monolayer, even with a very low density of NPs.References: [1] B. Demirdjian, F. Bedu, A. Ranguis, I. Ozerov, A. Karapetyan, and C. R. Henry, Indirect Nanoplasmonic Sensing to Probe with a High Sensitivity the Interaction of Water Vapor with Soot Aerosols, The Journal of Physical Chemistry Letters, 6, 4148-4152 (2015)[2] B. Demirdjian, I. Ozerov, F.Bedu, A. Ranguis and C. R. Henry, CO, and O2 adsorption, CO oxidation on Pt nanoparticles by indirect nanoplasmonic sensing, ACS Omega, 6, 13398-13405 (2021

Nanoplasmonics for efficient gas sensing and detection

International audienceUnderstanding how gas molecules such as water, oxygen, or carbon monoxide interact with nanoparticles NPs remains an important challenge in the studies of atmospheric chemistry and catalysis reactions.When gas molecules are directly adsorbed onto Au nanodisks (direct nanoplasmonic sensing DNPS) or when they interact with NPs supported on Au nanodisks (indirect nanoplasmonic sensing INPS), they modify the local dielectric properties of the surrounding media. Such a modification induces a wavelength shift of the localized surface plasmon resonance (LSPR) of Au nanodisks which can be easily detected by UV-Vis spectroscopy.We measured water adsorption isotherms by DNPS following the Au LSPR shift when water molecules adsorb/desorb on Au nanodisks [1]. With high sensitivity, we used INPS to follow also the interaction of water molecules on soot NPs that are a significant contributor to global warming in the atmosphere.Then, CO and oxygen adsorption as well as CO oxidation, on Pt NPs, have also been followed by INPS coupled with mass spectrometry [2]. We obtained a quantitative and very sensitive probe even for a very low Pt NPs density. For both DNPS and INPS, we could detect small molecule quantities such as a few hundredths of an adsorbed monolayer. Moreover, we can use nanoplasmonic sensing in a large range of pressure and temperature.FDTD calculations are performed to interpret LSPR spectra and to optimize the physical parameters of our plasmonic nanosensors