Pierre Louette

Single- and double- sided chemical functionalization of bilayer graphene

An experimental study on the interaction between the top and bottom layer of a chemically functionalized graphene bilayer by mild oxygen plasma is reported. Structural, chemical, and electrical properties are monitored using Raman spectroscopy, transport measurements, conductive atomic force microscopy and X-ray photoelectron spectroscopy. Single- and double-sided chemical functionalization are found to give very different results: single-sided modified bilayers show relatively high mobility (200-600 cm(2) V(-1) s(-1) at room temperature) and a stable structure with a limited amount of defects, even after long plasma treatment (>60 s). This is attributed to preferential modification and limited coverage of the top layer during plasma exposure, while the bottom layer remains almost unperturbed. This could eventually lead to decoupling between top and bottom layers. Double-sided chemical functionalization leads to a structure containing a high concentration of defects, very similar to graphene oxide. This opens the possibility to use plasma treatment not only for etching and patterning of graphene, but also to make heterostructures (through single-sided modification of bilayers) for sensors and transistors and new graphene-derivatives materials (through double-sided modification).

Synthesis and characterization of MoS2 nanosheets.

Here, we report on the synthesis of MoS2 nanosheets using a simple two-step additive-free growth technique. The as-synthesized nanosheets were characterized to determine their structure and composition, as well as their optical properties. The MoS2 nanosheets were analyzed by scanning electron microscopy, transmission electron microscopy (TEM), including high-resolution scanning TEM imaging and energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and photoluminescence (PL). The as-produced MoS2 nanosheets are vertically aligned with curved edges and are densely populated. The TEM measurements confirmed that the nanosheets have the 2H-MoS2 crystal structure in agreement with the Raman results. The XPS results revealed the presence of high purity MoS2. Moreover, a prominent PL similar to mechanically exfoliated few and mono-layer MoS2 was observed for the as-grown nanosheets. For the thin (≤50 nm) nanosheets, the PL feature was observed at the same energy as that for a direct band-gap monolayer MoS2 (1.83 eV). Thus, the as-produced high-quality, large-area, MoS2 nanosheets could be potentially useful for various optoelectronic and catalysis applications.

Poly(dimethyl siloxane) (PDMS) XPS Reference Core Level and Energy Loss Spectra

XPS measurements of poly(dimethyl siloxane) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon, oxygen, and silicon peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.

Poly(methyl methacrylate) (PMMA) XPS Reference Core Level and Energy Loss Spectra

XPS measurements of poly(methyl methacrylate) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon and oxygen peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.

Liquid-induced colour change in a beetle: the concept of a photonic cell.

The structural colour of male Hoplia coerulea beetles is notable for changing from blue to green upon contact with water. In fact, reversible changes in both colour and fluorescence are induced in this beetle by various liquids, although the mechanism has never been fully explained. Changes enacted by water are much faster than those by ethanol, in spite of ethanol’s more rapid spread across the elytral surface. Moreover, the beetle’s photonic structure is enclosed by a thin scale envelope preventing direct contact with the liquid. Here, we note the presence of sodium, potassium and calcium salts in the scale material that mediate the penetration of liquid through putative micropores. The result leads to the novel concept of a “photonic cell”: namely, a biocompatible photonic structure that is encased by a permeable envelope which mediates liquid-induced colour changes in that photonic structure. Engineered photonic cells dispersed in culture media could revolutionize the monitoring of cell-metabolism.

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.

Poly(vinyl alcohol) (PVA) XPS Reference Core Level and Energy Loss Spectra

XPS measurements of poly(vinyl alcohol) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon and oxygen peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.

Poly(ethylene terephthalate) (PET) XPS Reference Core Level and Energy Loss Spectra

XPS measurements of poly(ethylene terephthalate) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon and oxygen peaks are analyzed.

Adsorption of peroxidase on titanium surfaces: A pilot study

The present study demonstrates the in vitro and in vivo adsorption of peroxidase onto titanium surfaces. Titanium foils (mean +/- SEM: 365 +/- 2 mm(2), n = 114) were incubated during 30 min with lactoperoxidase (4 mg in 5 mL 100 mM phosphate buffer pH 7). After 15 washings by H(2)O, titanium foils were incubated with o-phenylenediamine (6 mg/mL) and H(2)O(2) (7 mM) during 30 min. The reaction was then stopped by the addition of HCI 1M and the absorbance of the liquid phase was read on a spectrophotometer at 492 nm. In vitro adsorbed lactoperoxidase onto titanium surfaces was 0.70 +/- 0.05 ng/mm(2) (mean +/- SEM, n = 30). X-ray photoelectron spectroscopy confirmed the incorporation of protein nitrogen onto titanium surfaces: the nitrogen atomic percentage increased from 0.9 +/- 0.3 to 12.7 +/- 0.2% (n = 3) and from 3.7 +/- 0.1 to 14.4 +/- 0. 4% (n = 5) when titanium foils were incubated in the lactoperoxidase solution during 30 min and 24 h respectively. In vivo, oral peroxidases adsorbed on titanium healing abutments from 0.01 to 0.58 ng/mm(2) (n = 19) after 2 weeks in the oral environment.

Poly(ethylene oxide) (PEO) XPS Reference Core Level and Energy Loss Spectra

XPS measurements of poly(ethylene oxide) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon and oxygen peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.XPS measurements of poly(ethylene oxide) recorded with a SSX-100 spectrometer in standardized experimental conditions are presented: survey scan, high resolution core level spectra as well as the energy loss regions of carbon and oxygen peaks are analyzed. This is part of a contract work aiming to record spectra in the very same conditions of some 40 different polymers.