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International audience; Les méthodes expérimentales permettant de détecter la résonance de spin électronique de défauts ponctuels du diamant ouvrent de nouvelles perspectives pour le développement de capteurs quantiques à haute sensibilité. De tels capteurs ont notamment démontré des performances exceptionnelles pour l’imagerie magnétique aux échelles nanométriques, conduisant à une transition accélérée vers des solutions commerciales.

Graphene nanoribbons (GNRs) fabricated using electron beam lithography are investigated using tip-enhanced Raman spectroscopy (TERS) with a spatial resolution of 5 nm under ambient conditions. High-resolution TERS imaging reveals a structurally modified 5-10 nm strip of disordered graphene at the edge of the GNRs. Furthermore, hyperspectral TERS imaging discovers the presence of nanoscale organic contaminants on the GNRs. These results pave the way for nanoscale chemical and structural characterisation of graphene-based devices using TERS.

In the field of energy storage by high-rate supercapacitors, there has been an upper limit for the total interfacial capacitance of carbon-based materials. This upper limit originates from both quantum and electric double-layer capacitances. Surpassing this limit has been the focus of intense research in this field. Here, we precisely investigate the effect of chemical functional groups and physical confinement on the electrochemical performance of graphene nanoribbons. We present the results of a quasi-one-dimensional single-layer graphene nanoribbon (120 nm in width and ∼100 μm in length) microelectrode fabricated by mechanical exfoliation of graphite, followed by electron beam lithography process and oxygen plasma etching treatment. We directly measure the interfacial capacitance as a function of frequency at different potentials in an aqueous electrolyte using a three-electrode electrochemical system. Electrochemical impedance spectroscopy and cyclic voltammetry tests show an average capacitance of 75...

One common challenge highlighted in almost every review article on organic resistive memory is the lack of areal switching uniformity. This, in fact, is a puzzle because a molecular switching mechanism should ideally be isotropic and produce homogeneous current switching free from electroforming. Such a demonstration, however, remains elusive to date. The reports attempting to characterize a nanoscopic picture of switching in molecular films show random current spikes, just opposite to the expectation. Here, this longstanding conundrum is resolved by demonstrating 100% spatially homogeneous current switching (driven by molecular redox) in memristors based on Ru-complexes of azo-aromatic ligands. Through a concurrent nanoscopic spatial mapping using conductive atomic force microscopy and in operando tip-enhanced Raman spectroscopy (both with resolution

Le TERS pour tip enhanced raman scattering, est une technique de pointe (dans tous les sens du terme) basée sur l’amplification du signal Raman relative à la résonance de plasmons de surface. Cette technique non-destructive, qui ne nécessite pas de marquage particulier, permet de caractériser un échantillon à l’échelle nanométrique. Le TERS s’impose aujourd’hui pour sonder les propriétés physico-chimiques des nanomatériaux et participer ainsi au développement de nouvelles applications dans le domaine des nanotechnologies.

[object Object]Two-dimensional transition metal dichalcogenides are gaining increasing interest due to their promising optical properties. In particular, molybdenum disulfide (MoS2) which displays a band-gap change from indirect at 1.29 eV for bulk materials to direct at 1.8 eV for the material monolayer. This particular effect can lead to a strong light interaction which can pave the way for a new approach to the next generation of visible light emitting devices. In this work we show the nanoscale variation of light emission properties by tip-enhanced photoluminescence microscopy and spectroscopy in the MoS2 monolayer, grown by chemical vapour deposition. The variations of the light emission properties are due to different effects depending on the shape of the MoS2 single layer, for instance, a different concentration of point defect in an irregularly shaped flake and the presence of a nanoscale terrace in a triangular monolayer. Simultaneously, atomic force microscopy reveals indeed the presence of a nanometric terrace, composed of an additional layer of MoS2, and tip-enhanced PL intensity imaging shows a localized intensity decrease.

International audience; In order to evaluate the optical efficiency of tip-based probes for future tip-enhanced optical spectroscopy applications, we developed an experimental setup based on the coupling of an achromatic inverted microscope equipped with a total internal reflection objective and an atomic force microscopy (AFM) head. This spectroscopic tool has been validated using individual nanofabricated antennas (gold nanodisks/nanocones) on a glass substrate which act as nanoresonators based on localized surface plasmons. Spectrally tunable transverse electric and magnetic plasmonic resonances are identified and are in excellent agreement with numerical calculations performed as a function of the nanoantenna geometry and size. We investigated a series of state-of-the-art gold-coated AFM probes, which are commonly used for tip-enhanced (Raman spectroscopy) optical experiments. Their scattering spectrum consists of resonances depending on the tip sharpness or granularity superimposed on a broad emission spectrum due to a semi-infinite metal layer acting as a nonresonant antenna. From the comparison between the plasmonic response of both types of optical antennas, a new generation of probes for tip-enhanced optical spectroscopy is proposed in which single plasmonic nanoantennas are engineered at the apex of a nonmetallic AFM tip. As from numerical simulation results, such tips would ensure a spectral tunability as a function of the material, size, and geometry, together with expected high enhancement factors. Such features would allow the design of spectrally tunable surface-enhanced Raman spectroscopy substrates and should be a reliable and efficient alternative to tips commonly used in tip-enhanced optical spectroscopy experiments such as tip-enhanced Raman spectroscopy.

emitter into an effi cient emitter-like III–V semiconductors. There is no need a priori to reach the direct-band gap regime to demonstrate a Ge laser source. The fi rst Ge laser demonstration was obtained with a weak tensile strain around 0.25% resulting from the difference of thermal dilation coeffi cients between Ge and the silicon substrate. [ 10,11 ] This tensile strain amplitude is not suffi cient as evidenced by the 300 kA cm −2 threshold announced for an electrically pumped laser, [ 11 ] a value too high for realistic integration purposes. Enhancing tensile strain transfer into Ge optical cavities is thus requested in order to signifi cantly decrease the lasing threshold, and different approaches have been proposed in the literature. [ 12–14 ] High level strain transfers have been evidenced using strained silicon nitride (SiNH referred to as SiN in the following) layers as stressor layers. [ 15–20 ] The use of stressor layers is widely investigated since it relies on a complementary metal oxide semiconductor (CMOS)-compatible process. There are however some trade-offs in strain engineering as evidenced by the link between strain amplitude and cavity volumes, i.e., achieving high tensile strain in large structures being challenging. In this perspective, microdisks are very interesting compact structures as one can expect to transfer high tensile strain and to obtain low lasing threshold due to whispering gallery mode confi nement. [ 21,22 ] A 1% biaxial strain transfer on the top of a Ge microdisk using strained SiN deposition has been recently demonstrated. [ 20 ] One of the drawbacks of this recent demonstration is the spatial inhomogeneity of the transferred strain. This limitation can be lifted by using an all-around stressor method in a similar way that a gate all-around design provides more fl exibility to tailor the properties of advanced CMOS transistors. [ 23 ]

We present a robust and versatile approach for the reproducible and controllable growth of single-walled carbon nanotubes (SWNTs) through a self-assembled monolayer (SAM) technique coupled with an atomic hydrogen (Hat) pretreatment to control the catalytic metallic nanoparticles size and density. The nanoparticles are obtained from a self-assembled monolayer of metal complexes or salts on a SiO2 substrate using a two-step strategy. The oxide is first functionalized by silanization with a coordinating ligand leading to the formation of an anchoring SAM on the substrate. Then, metallic complexes such as ruthenium porphyrin (RuTPP) or metallic salts (FeCl3, RuCl3) are assembled by coordination bonds on the preformed organic SAM. Pyrolysis under radical hydrogen atmosphere of the as-prepared SAM yields metallic nanoparticles whose size and density are controlled and tuned. Using the as-formed nanoparticles as catalysts, SWNTs are grown by double hot-filament-assisted chemical vapor deposition (d-HFCVD). They ...

Achieving a monolithic germanium laser source represents a major challenge for silicon photonics. Two key parameters have an impact on the laser performances including threshold, output power, reliability... The first key parameter is the germanium doping. Modeling indicates that an active electron carrier concentration of 3 - 4 x 1019 cm-3 is requested to obtain a robust gain. We will show that such doping level can be achieved for germanium grown on silicon using a co-doping method followed by thermal anneal. The thermal annealing is necessary to minimize the non-radiative recombination processes. The second key parameter is the tensile strain present in germanium. The achievement of high or even record tensile strain values in small volumes is not sufficient for lasing. The homogeneity of the strain field within the germanium volume needs to be taken into account. We will show how it is possible to maximize the tensile strain homogeneity either for straight waveguides or germanium microdisks strained by a silicon nitride stressor. The trade-off between homogeneity and maximum strain value allows one to achieve a more robust modal gain. We will finally discuss the transfer of these concepts for electrical injection.

A billion-fold increase in the Raman signal over conventional tip-enhanced Raman spectroscopy/microscopy (TERS) is reported. It is achieved by introducing a stimulating beam confocal with the pump beam into a conventional TERS setup. A stimulated TERS spectrum, closely corresponding to its spontaneous TERS counterpart, is obtained by plotting the signal intensity of the strongest Raman peak of an azobenzene thiol self-assembled monolayer versus the stimulating laser frequency. The stimulated TERS image of azobenzene thiol molecules grafted onto Au ⟨111⟩ clearly shows the surface distribution of the molecules, whereas, when compared to the simultaneously recorded surface topography, it presents an image contrast of different nature. The experimentally obtained stimulated gain is estimated at 1.0 × 10(9), which is in reasonable agreement with the theoretically predicted value. In addition to the signal increase, the signal-to-noise ratio was 3 orders of magnitude higher than in conventional spontaneous TERS. The proposed stimulated TERS technique offers the possibility for a substantially faster imaging of the surface with respect to normal TERS.

For nanocrystalline silicon films deposited at high rates, the presence of a silicon–hydrogen (Si H) bond stretching mode doublet in the high wavenumber region of the Raman spectrum can be used for optimizing the stabilized efficiency of solar cells based on this material. These peaks appear often for remote-plasma high deposition rate techniques targeting intrinsic layer deposition for photovoltaics, and so their structural origin may reveal the fundamental limitations of such techniques. We present the use of Polarized Raman Spectroscopy in oblique back-scattering configuration to reveal details of the specific bonding configuration of certain silicon-hydrogen bonds in hydrogenated nanocrystalline silicon (nc-Si:H). Twinned, narrow peaks located at 2083 and 2100 cm− 1 in the infrared absorption spectroscopy and Raman scattering spectrum of nc-Si:H thin films due to Si HX stretching modes are strongly associated with films likely to oxidize and degrade rapidly, but the precise origin of these characteristic peaks is a subject of debate. Through the use of PRS, as well as numerous other complementary techniques (standard Raman scattering spectroscopy, Fourier transform infrared spectroscopy, Secondary ion mass spectrometry and X-ray diffraction), a logical conclusion can be reached, strongly suggesting that the origin of these peaks is due to the stretching modes of SiH2 bonds at {110} interfaces between crystallites, passivated by hydrogen rather than by amorphous silicon. The use of the oblique back scattering Raman configuration, combined with group symmetry considerations, allows one to compare the symmetry of the vibrational modes detected with those of possible SiHX (X = 1, 2 or 3) configurations, thus eliminating certain structures as the sources of these characteristic absorption and scattering signatures.

Room temperature optical gain and lasing have been recently demonstrated in germanium. One key ingredient to obtain positive gain is to reduce the splitting between the conduction indirect and direct valleys by introducing tensile strain. We have investigated two distinct approaches to apply a large tensile strain in germanium. The first approach relies on the growth of germanium on InGaAs buffer templates. Biaxial tensile strains up to 0.8% have been achieved by this method. The second approach relies on stress transfer through silicon nitride layers. It offers the advantage of a full compatibility with CMOS processing. We have successfully fabricated tensile-strained photonic wires which exhibit optical gain under cw optical pumping.

We report results of TERS characterization of graphene oxide and the 2D semiconductors, MoS2 and WS2. The gap mode TERS signal of these 2D materials becomes dramatically enhanced over wrinkles and creases, as well as over nanopatterns imprinted into flakes using a sharp diamond probe. The resonant Raman signal of MoS2 contains additional peaks normally forbidden by selection rules. TERS maps of few-layer-flakes of this 2D semiconductor show that the spatial distribution of Raman intensity across the flake varies for different peaks, providing interesting insights into the structure of such 2D semiconductors with 10-20 nm spatial resolution.

Tip enhanced Raman spectroscopy (TERS) and imaging experiments in tunnelling (gap) mode were performed on a 2 nm thick azobenzene thiol monolayer grafted on Au(111). A strong dependence on the tunnelling parameters, regulating the gold tip-gold surface gap distance,was observed for the intensity of the enhanced Raman signal. The influence of the incident light polarization is also discussed.

We present Tip Enhanced Raman Spectroscopy (TERS) results with side illumination of a scanning tunneling microscope (STM) Au tip on thin multi wall carbon nanotubes deposited on Au(1 1 1) with a ∼75 nm lateral resolution. The spectral features observed in the enhanced near-field regime are discussed considering also the presence of defects in the tube(s) structure and/or trace amounts of amorphous carbon contaminations.

Tip Enhanced Raman Scattering (TERS), a technique that provides molecular information on the nanometer scale, has been a subject of great scientific interest for 15 years. But regardless of the recent achievements and applications of TERS, ranging from material science and nanotechnology, strain measurement in semiconductors, to cell biological applications, the TERS technique has been hampered by extremely long acquisition times, measured in hours, required for collection of reasonably high pixel density TERS maps. In this talk, specifics of the TERS setup that enable fast, high pixel density nano-Raman imaging will be discussed: The innovative integration of technologies brings high-throughput optics and high-resolution scanning for high-speed imaging without interferences between the techniques. The latest developments in near-field optical probes also provide reliable solutions for academic and industrial researchers alike to easily get started with nanoscale Raman spectroscopy. Thanks to those latest instrumental developments, we will present the nanoscale imaging of chemical and physical properties of graphene, carbone nanotubes and self-assembled monolayers of organic molecules, with a spatial resolution routinely obtained in TERS maps in the 15 - 20 nm range and a best resolution achieved being of 7 nm

International audience; We report Tip Enhanced Raman Spectroscopy (TERS) mapping and Density Functional (DFT) calculations of aminothiophenol (ATP) grafted on a gold surface. The TERS mapping has demonstrated Raman modes of (ATP) and its dimerised derivative Dimercaptoazobenzene (DMAB). This feature confirms that the plasmon activated chemical reaction of ATP has occurred during TERS measurements. In some specific part of the samples some unidentified Raman modes are observed. We suggest that they could come from intermediate species formed during the conversion of ATP into DMAB. These modes are compared with calculated Raman spectra of some possible intermediate species. These results confirm the high potentiality of TERS measurements for nanochemistry.

In this chapter, we describe the determination of the stress profile in 150-nm-wide SiGe nano-stripes embedded into a Si matrix by using oblique incidence tip-enhanced Raman spectroscopy (TERS) with a spatial resolution of ~20 nm. The TERS spectra of the stripes exhibit a number of locally enhanced phonon modes that are absent when the tip is positioned out of the stripes. The hydrostatic stress component across the nano-stripe width is evaluated from the strain-induced frequency shift of the Si-Ge mode at ~380 cm -1. The stress magnitude is found to be largest in the nano-stripe center and decreases monotonously on each side down to zero at the boundaries. This behavior is quantitatively described by a classic continuous medium model. These results demonstrate the applicability of the TERS technique to stress determination in novel semiconductor structures at the nanometer scale.

The keystone to realize a monolithic integrated source on silicon with germanium is to optimize tensile strain and n-doping. In order to realize an integrated compact source, we demonstrate highly strained n-doped germanium microdisks obtained by two approaches using initially compressed silicon nitride (SiN) deposition. In the first approach, the microdisks are fabricated from relaxed Ge. In a second approach, we use tensile-strained Ge grown on a mismatched buffer layer, thus increasing the global strain in the Ge volume and lowering its gradient. A photoluminescence red-shift up to 450 nm is observed, corresponding to more than 1% biaxial strain.

Mixed thiol self-assembled monolayers (SAMs) presenting methyl and azobenzene head groups were prepared by chemical substitution from the original single-component n-decanethiol or [4-(phenylazo)phenoxy]hexane-1-thiol SAMs on polycrystalline gold substrates. Static contact-angle measurements were carried out to confirm a change in the hydrophobicity of the functionalized surfaces following the exchange reaction. The mixed SAMs presented contact-angle values between those of the more hydrophobic n-decanethiol and the more hydrophilic [4-(phenylazo)phenoxy]hexane-1-thiol single-component SAMs. By means of tip-enhanced Raman spectroscopy (TERS) mapping experiments, it was possible to highlight that molecular replacement takes place easily and first at grain boundaries: for two different mixed SAM compositions, TERS point-by-point maps with

International audience; Four novel phenyl-end-capped π-conjugated polymers comprising alkyl chains of different lengths were synthesized: the poly(9,9-dihexyl-2,7-fluorene-alt-9,9-dioctylfluorene) (P0), the alternating fluorene-carbazole copolymers P1 and P2 comprising 20% and 50% of carbazole, respectively, and the homopolymer poly(9-hexyl-9H-carbazole) (P3). The non-end-capped alternating fluorene-carbazole copolymer P4 comprising 20% of carbazole was also synthesized for the sake of comparison with P1. P0-P2 and P4 were synthesized by a Pd-catalyzed Suzuki-Miyaura coupling in good yields (80-89%), while P3 was obtained by a Ni-catalyzed Yamamoto coupling reaction from the 3,6-dibromocarbazole monomer in a moderate yield (52%). P0-P4 polymers were characterized by NMR, elemental analysis, and GPC. The molecular weights are 40.30, 23.42, 14.33, 3.92, and 37.49 kDa, with polydispersity indices of 2.5, 1.7, 1.8, 1.3, and 2.6, for P0, P1, P2, P3, and P4, respectively. These polymers were found to show a high thermal stability, with decomposition temperatures in the range of 395-420 °C, and the glass transition temperature was found to regularly increase with the amount of carbazole inserted in the conjugated backbone. AFM images obtained on thin films (thickness of about 90 nm) of P0-P2 revealed films with surfaces of good quality, being homogeneous with low roughness (0.2 nm for the smaller ones). These polymers were found to be blue-emitting both in diluted dichloromethane and chlorobenzene solutions as well as in thin films and exhibit relatively high values of the absolute quantum yields in the range of 100-5.5% in dichloromethane and 51.4-7.7% in thin films. Blue-emitting electroluminescent devices were obtained with P0 and P1 as emitting layers, respectively. The device built with P1 showed improved performances (EQE of 1.32%) with respect to the one built with the parent polyfluorene material (EQE of 0.75%).

The Polarized Instrument for Long wavelength Observation of the Tenuous interstellar medium (PILOT) is a balloon borne experiment designed to measure the polarized emission from dust grains in the galaxy in the submillimeter range. The payload is composed of a telescope at the optical focus of which is placed a camera using 2048 bolometers cooled to 300 mK. The camera performs polarized optical measurements in two spectral bands (240 μm and 550 μm). The polarization measurement is based on a cryogenic rotating half-wave plate and a fixed mesh grid polarizer placed at 45o separating the beam into two orthogonal polarized components each detected by a detector array. The Institut d’Astrophysique Spatiale (Orsay, France) is responsible for the design, integration, tests and spectral calibration of the camera. Two optical benches have been designed for its imaging and polarization characterization and spectral calibration. Theses setups allow to validate the alignment of the camera cryogenic optics, to check the optical quality of the images, to characterize the time and intensity response of the detectors, and to measure the overall spectral response. A numerical photometric model of the instrument was developed for the optical configuration during calibration tests (spectral), functional tests (imager) on the ground, and flight configuration at the telescope focus, giving an estimate of the optical power received by the detectors for each configuration.

International audience; We show, through several selected case studies, the potential benefits that can be obtained by controlling the polarization states of the exciting and scattered radiations in a Raman scattering experiment. When coupled with polarization control, Raman spectroscopy is thus capable of providing extra information on the structural properties of the materials under investigation. The experimental examples presented in this work are taken from the area of both conventional, i.e., far-field, as well as from near-field Raman spectroscopy. They cover topics such as the stress tensor measurement in strained semiconductor structures, the vibration mode assignment in pentacene thin films and the Raman scattering tensor determination from near-field measurements on azobenzene monolayers. The basic theory necessary for modelling the far- and near-field polarized Raman responses is also given and the model efficiency is illustrated on the experimental data.

International audience; Nanodiamond particles with typical diameters of 20 and 6 nm produced by high pressure high temperature or detonation processes have been studied by micro-Raman spectroscopy. We show that the frequency downshift and broadening of the first-order diamond phonon band is not uniquely related to phonon confinement, as commonly assumed. Local heating caused by the focused laser light must be also taken in account, since it may affect the Raman spectrum in a similar fashion, even at relatively low laser power levels. A combined theoretical model considering both effects (quantum confinement and local heating) on the excited phonon modes is presented and adopted for the simulation of the experimental data. We observe different heating behaviours upon laser illumination depending on the particles origin, thus underscoring the importance to compensate for this effect before retrieving structural parameters.

We report on the influence of the laser heating effect, potentially present in a Raman scattering experiment, on the behaviour of carbon phonon lines in the spectra of nanodiamond particles. Aside from the laser power used in the experiment, the extent of the thermal effect in question depends also on the nanodiamonds origin (obtained through detonation and high pressure high temperature techniques) as well as on the nanoparticles size. Laser heating should be properly taken into account when discussing Raman spectra of carbonaceous species, in particular, prior to addressing peak assignment and possible quantum confinement effects.

International audience; The present study focuses on the interaction of hydrogen microwave CVD plasma with nanodiamonds (NDs). Hydrogen treated NDs (H-NDs) were characterized using electron spectroscopies (XPS, AES) without air exposure. A surface temperature higher than 700 °C is needed to remove the oxygen present on raw NDs. The kinetics of oxygen removal were investigated. Moreover, UHV annealings of H-NDs after ageing in ambient air clearly underline that 75% of the oxygen is related to physisorbed species. Finally, H-NDs were efficiently grafted using photochemical reaction with alkenes and a spontaneous coupling of aryldiazonium salts. These results confirm similar electronic surface properties between bulk and nano diamond materials.

Graphene has been given great attention to overcome current physical limits in electronic devices and its synthesis routes are developing rapidly. However, graphene film manufacturing is still hindered by either low throughput or low material quality. Here, we present a low temperature PE-CVD assisted graphene growth process on nickel thin films deposited on silicon oxide. Furthermore, our process leads to the formation of two separated graphene films, one at the nickel surface and the other at the Ni/SiO2 interface. A mixture of methane and hydrogen was employed as carbon precursor and activated by DC plasma. We found that the number of graphene layers on top of nickel can be controlled by carbon exposure time, from 1 to around 10 layers. Further annealing process of samples allowed us to achieve improved graphene films by the dissolution and segregation-crystallization process.

We present a study of the charge state conversion of single nitrogen-vacancy (NV) defects hosted in nanodiamonds (NDs). We first show that the proportion of negatively-charged NV$^{-}$ defects, with respect to its neutral counterpart NV$^{0}$, decreases with the size of the ND. We then propose a simple model based on a layer of electron traps located at the ND surface which is in good agreement with the recorded statistics. By using thermal oxidation to remove the shell of amorphous carbon around the NDs, we demonstrate a significant increase of the proportion of NV$^{-}$ defects in 10-nm NDs. These results are invaluable for further understanding, control and use of the unique properties of negatively-charged NV defects in diamond, 6 pages, 4 figures

International audience; Nanodiamond (ND) seeding is a well-established route toward the CVD (chemical vapor deposition) synthesis of diamond ultrathin films. This method is based on the deposition onto a substrate of diamond nanoparticles which act as pre-existing sp$^3$ seeds. Here, we report on a straightforward method to disperse diamond nanoparticles on a substrate by taking advantage of the electrostatic interactions between the nanodiamonds and the substrate surface coated with a cationic polymer. This layer-by-layer deposition technique leads to reproducible and homogeneous large-scale nanoparticle deposits independent of the substrate’s nature and shape. No specific functionalization of the nanoparticles is required, and low concentrated solutions can be used. The density of ND on the substrate can be controlled, as shown by in situ ATR-FTIR (attenuated total reflection Fourier transform infrared) analysis and QCM (quartz crystal microbalance) measurements. Highly dense and compact ND deposits can be obtained, allowing CVD growth of nanocrystalline diamond ultrathin films (70 nm) on various substrates. The synthesis of 3D structured and patterned diamond thin films has also been demonstrated with this method.

International audience; This article reports a new approach for probe manufacturing, which is the key component in scanning near-field optical microscope (SNOM). The wet-etching process, to create the tip at the apex of a tapered fiber, has been optimized. Typical tip features are short tapers, large cone angles (30°), and very small diameters (

We have investigated the optical properties of tensile-strained germanium grown on InGaAs buffer layers as a function of film thickness and buffer layer composition. We study the dependence of the photoluminescence as a function of the strain amplitude and degree of relaxation which are also monitored by X-ray diffraction and Raman spectroscopy. We show that 0.75% biaxially strained germanium can be obtained up to a thickness of 150 nm, a value sufficiently high to allow confinement of the spontaneous emission in a guiding structure. For large thicknesses (>200 nm) and large indium content in the buffer layer, a partial relaxation of the film is observed characterized by a large in-plane anisotropy of the germanium lattice. In this case, a difference of strain magnitude deduced either by microphotoluminescence spectra or by X-ray or Raman measurements is reported. We explain this difference by the sensitivity of microphotoluminescence to the local properties of the material. This study provides guidelines...

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Germanium ridge waveguides can be tensilely strained using silicon nitride thin films as stressors. We show that the strain transfer in germanium depends on the width of the waveguides. Carrier population in the zone center Γ valley can also be significantly increased when the ridges are oriented along the 〈100〉 direction. We demonstrate an uniaxial strain transfer up to 1% observed on the room temperature direct band gap photoluminescence of germanium. The results are supported by 30 band k·p modeling of the electronic structure and the finite element modeling of the strain field.

We show that high quality tensile-strained n-doped germanium films can be obtained on InGaAs buffer layers using metal-organic chemical vapor deposition with isobutyl germane as germanium precursor. A tensile strain up to 0.5% is achieved, simultaneously measured by x-ray diffraction and Raman spectroscopy. The effect of tensile strain on band gap energy is directly observed by room temperature direct band gap photoluminescence.

ZnO:Al thin films were prepared on glass substrates by radio frequency RF magnetron sputtering from a ceramic ZnO target mixed with Al2 O3 (1 wt%) in pure argon atmosphere with a power of 250 W. Two series of samples were deposited, the first one as a function of the substrate temperature (between 20 and 325 °C) at 0.12 Pa, the second one as a function of the working pressure (between 0.01 and 2.2 Pa) at room temperature. The influence of these deposition parameters was studied by a detailed microstructural analysis using X-Ray diffraction and Raman spectroscopy. Their electrical properties were characterized by Hall effect measurements. As the substrate temperature is increased, crystallite size increases while the strain and the electrical resistivity decrease. An improvement of the crystallinity is deduced from Raman spectra and X-Ray diffraction patterns. From the pressure series, an electrical optimum is observed at 0.12 Pa. Above 0.12 Pa, there is a degradation of the crystallinity, attributed to the low mobility of the adatoms and below 0.12 Pa, high-energy sputtered particles damage the growing films. The trends given by Thornton structure zone model are also consistent with X-Ray diffraction results.

A simple and reproducible method for nanoaperture opening of metal film covered tapered optical fibers is reported as the last step of the manufacturing process for near-field scanning optical microscopy (NSOM) probes. It uses a microspark between the biased tip and another plane electrode working as a coronalike discharge in point-to-plane configuration. The resultant high electric field is enhanced at the extremity of the metallized tip self-focusing the discharge ions. The opening process is performed in situ in a specially designed plasma reactor which also allows, for the optical fiber tips, their surface cleaning and silver coating. Nanoaperture diameter can be controlled between 30 and 100nm. These probes are able to generate subwavelength resolved images and are appropriate for high resolution NSOM.

International audience; Post-growth transfer and high growth temperature are two major hurdles that research has to overcome to get graphene out of research laboratories. Here, using a plasma-enhanced chemical vapour deposition process, we demonstrate the large-area formation of continuous transparent graphene layers at temperatures as low as 450 °C. Our few-layer graphene grows at the interface between a pre-deposited 200 nm Ni catalytic film and an insulating glass substrate. After nickel etching, we are able to measure the optical transmittance of the layers without any transfer. We also measure their sheet resistance directly and after inkjet printing of electrical contacts: sheet resistance is locally as low as 500 Ω sq-1. Finally the samples equipped with printed contacts appear to be efficient humidity sensors.

This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, as well as hosting the potential of a rich return in further science. SO/PHI measures the Zeeman effect and the Doppler shift in the FeI 617.3nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO_3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders (LCVRs). The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2kx2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope (FDT), covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope (HRT), can resolve structures as small as 200km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line., Comment: 36 pages, 41 figures