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Acute and chronic pain are common among patients with active cancer and contribute significantly to the burden of illness. The constellation of these pain symptoms can often suggest specific well-characterized cancer pain syndromes which have important prognostic and therapeutic implications. These syndromes may arise from any number of underlying etiologies including direct tumor invasion / encroachment, distant metastases, as well as a consequence of current or previous treatment modalities (e.g., chemotherapy or radiation). A palliative care approach to pain should involve a methodical assessment, consideration of all potential etiologies of pain, and the formulation of a multimodal treatment plan which aligns with patient goals.

Monolayers of transition metal dichalcogenides are ideal materials to control both spin and valley degrees of freedom either electrically or optically. Nevertheless, optical excitation mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. Here we demonstrate a very efficient spin/valley optical pumping of resident electrons in n-doped WSe2 and WS2 monolayers. We observe that, using a continuous wave laser and appropriate doping and excitation densities, negative trion doublet lines exhibit circular polarization of opposite sign and the photoluminescence intensity of the triplet trion is more than four times larger with circular excitation than with linear excitation. We interpret our results as a consequence of a large dynamic polarization of resident electrons using circular light. Optical excitation of transition metal dichalcogenide monolayers mostly generates excitons species with inherently short lifetime and spin/valley relaxation time. Here, the authors demonstrate efficient spin/valley optical pumping of resident electrons in n-doped WSe2 and WS2 monolayers.

Hyperspectral imaging at cryogenic temperatures is used to investigate exciton and trion propagation in MoSe$_2$ monolayers encapsulated with hexagonal boron nitride (hBN). Under a tightly focused, continuous-wave laser excitation, the spatial distribution of neutral excitons and charged trions strongly differ at high excitation densities. Remarkably, in this regime the trion distribution develops a halo shape, similar to that previously observed in WS2 monolayers at room temperature and under pulsed excitation. In contrast, the exciton distribution only presents a moderate broadening without the appereance of a halo. Spatially and spectrally resolved luminescence spectra reveal the buildup of a significant temperature gradient at high excitation power, that is attributed to the energy relaxation of photoinduced hot carriers. We show, via a numerical resolution of the transport equations for excitons and trions, that the halo can be interpreted as thermal drift of trions due to a Seebeck term in the particle current. The model shows that the difference between trion and exciton profiles is simply understood in terms of the very different lifetimes of these two quasiparticles.

International audience; We have investigated charge and spin transport in n-type metallic GaAs nanowires (≈ 10 17 cm −3 doping level), grown by hydride vapor phase epitaxy (HVPE) on Si substrates. For this doping level, charge and spin transport might appear difficult because of the expected localization of minority holes in the valence band potential fluctuations generated by statistical fluctuations of the donor concentration. In contrast with these expectations, it is found, using spatially-and spectrally-resolved investigation of the luminescence intensity and circular polarization under laser excitation, that i) establishment of a charge thermodynamic equilibrium between the photoelectrons and the Fermi sea occurs over a distance from the excitation spot of 2 µm. At this distance, the spin polarization is still observed, implying that photoelectrons have preserved their spin orientation and that the two spin reservoirs remain distinct. ii) Charge can be transported over record distances larger than 20 µm at 6K. iii) Spatially-resolved investigations show that a photoelectron spin polarization of 20% can even be transported over a record distance of more than 20 µm. This long distance transport occurs because of the presence of large internal electric fields of ambipolar origin, further enhanced by the spatial redistribution of the Fermi sea. These findings has potential applications for long distance spin transport in n-type doped nanowires.

We have combined spatially-resolved steady-state micro-photoluminescence ($\mu$PL) with time-resolved photoluminescence (TRPL) to investigate the exciton diffusion in a WSe$_2$ monolayer encapsulated with hexagonal boron nitride (hBN). At 300 K, we extract an exciton diffusion length $L_X= 0.36\pm 0.02 \; \mu$m and an exciton diffusion coefficient of $D_X=14.5 \pm 2\;\mbox{cm}^2$/s. This represents a nearly 10-fold increase in the effective mobility of excitons with respect to several previously reported values on nonencapsulated samples. At cryogenic temperatures, the high optical quality of these samples has allowed us to discriminate the diffusion of the different exciton species : bright and dark neutral excitons, as well as charged excitons. The longer lifetime of dark neutral excitons yields a larger diffusion length of $L_{X^D}=1.5\pm 0.02 \;\mu$m.

Carrier and spin recombination are investigated in p-type GaAs of acceptor concentration NA = 1.5 x 10^(17) cm^(-3) using time-resolved photoluminescence spectroscopy at 15 K. At low pho- tocarrier concentration, acceptors are mostly neutral and photoelectrons can either recombine with holes bound to acceptors (e-A0 line) or form excitons which are mostly trapped on neutral acceptors forming the (A0X) complex. It is found that the spin lifetime is shorter for electrons that recombine through the e-A0 transition due to spin relaxation generated by the exchange scattering of free electrons with either trapped or free holes, whereas spin flip processes are less likely to occur once the electron forms with a free hole an exciton bound to a neutral acceptor. An increase of exci- tation power induces a cross-over to a regime where the bimolecular band-to-band (b-b) emission becomes more favorable due to screening of the electron-hole Coulomb interaction and ionization of excitonic complexes and free excitons. Then, the formation of excitons is no longer possible, the carrier recombination lifetime increases and the spin lifetime is found to decrease dramatically with concentration due to fast spin relaxation with free photoholes. In this high density regime, both the electrons that recombine through the e-A0 transition and through the b-b transition have the same spin relaxation time., Comment: 4 pages, 5 figures

Optimization of light emitting devices when light is trapped within the dielectric structures opens the question of the management of light propagation and of control of the directionality of extracted light. These phenomena are closely connected to the so-called extraction length of light propagating within the device, a parameter that is poorly discussed when considering the design and architecture of devices. In this work, a straightforward method for the measurement of the extraction length in the case of luminescent sol–gel films patterned with a 2D photonic bandgap structure is presented. Quantitative information usually obtained by spectro-angular measurements can be retrieved from simpler standard spectrometry, allowing discussion of the influence of pattern depth, which determines the extraction by the photonic structure as compared to other uncontrolled pathways such as diffusion from defects in the film coating. These assessments provide a quick and safe method for the quantitative evaluation of light extraction strategies toward a rational design of light emitting devices with optimized properties.

Activation of myeloid cells by orthopedic particulate debris is a key event in the pathogenesis of periprosthetic osteolysis and implant loosening after total joint replacement (TJR). Several lines of evidence implicate NACHT, LRR, and PYD domains-containing protein 3 (NALP3) inflammasome-mediated production of interleukin 1 beta (IL-1β) in the pathogenesis of clinical disorders ascribable to foreign particulate materials, including asbestos, silica, and urate crystals. Recent reports indicate that orthopedic polymer products and metallic particulates and ions may activate the same pathway. Here, we investigated the contribution of the NALP3 inflammasome to the pathogenesis of peri-implant osteolysis. Pharmaceutical and genetic perturbations of caspase-1 and inflammasome components were used to assess the role of the NALP3 inflammasome in IL-1β production and osteoclast formation by human monocytes and mouse macrophages in response to polymethylmethacrylate (PMMA) particle phagocytosis. The role of caspase-1 in a mouse calvarial model of particle-mediated osteolysis was assessed using µCT. Phagocytosis of PMMA particles induces caspase-1 dependent release of IL-1β from human monocytes and mouse macrophages. Importantly, using macrophages from mice deficient in components of the NALP3 inflammasome, we show PMMA-induced IL-1β production is strictly dependent on these components. Mice lacking caspase-1, the sole effector of the NALP3 inflammasome, show reduced orthopedic wear particle-induced calvarial osteolysis compared to wild-type controls. Absence of NALP3 inflammasome components fails to alter osteoclast formation in vitro. Our findings identify the NALP3 inflammasome as a critical mediator of orthopedic wear-induced osteolysis and as a viable therapeutic target for the treatment of periprosthetic osteolysis.

We demonstrate that GaAs spin injector microcantilever probes can be produced using a novel releasable “epitaxial patch technology” assembly approach as apposed to a monolithic fabrication route i.e. surface/bulk micromachining. The GaAs microcantilevers are attached to fused silica support wafers; thus taking advantage of the optical and spin properties of GaAs and the mechanical properties of the silica. The microcantilever probes have been characterized for their spin injection properties and also used as atomic force microscopy (AFM) probes to evaluate their imagining capabilities. The assembly involved the production of released epitaxial semiconductor “patches” having a micrometer thickness. These patches are then assembled onto a pre-fabricated fused silica support wafer. AFM characterization revealed a resonant frequency and quality factor equal to commercial silicon-based AFM probes together with high quality images; the spin injection characterization demonstrated injected photocurrents of tens of nA and a spin polarization of ∼ 15 % .

Ultra-high molecular weight polyethylene is widely used as a bearing surface in prosthetic arthroplasty. Over time the generation of implant-derived wear particles can initiate an inflammatory reaction characterized by periprosthetic inflammation and ultimately bone resorption at the prosthetic bone interface. Herein we present evidence that the different sized particles as well as the different length alkane polymers generated by implant wear leads to a two component inflammatory response. Polymeric alkane structures, with side chain oxidations, directly bind and activate the TLR-1/2 signaling pathway. Whereas micron- and nanometer-sized particulate debris are extensively phagocyted and induce enlargement, fusion and disruption of endosomal compartments. The resulting lysosomal damage and subsequent enzymatic leakage induces the NALP3 inflammasome activation as determined by cathepsins S and B cytosolic release, Caspase 1 activation and processing of pro-IL-1β, and pro-IL-18. These two processes synergistically results in the initiation of a strong inflammatory response with consequent cellular necrosis and extracellular matrix degradation.

Selective area growth experiments were carried out by hydride vapour phase epitaxy (HVPE) on (1 0 0) GaAs-patterned substrates for the making of GaAs tips to be used as spin injectors. The tips exhibited various morphological profiles bounded by low and high index faces. Sharp apices were formed by the intersection of four perfectly crystal-defined {1 1 0} facets. The tip height and the apex sharpness have been optimized through the control of the crystal intrinsic growth anisotropy as a function of the experimental growth parameters. A good agreement was obtained between the morphologies of the selectively grown tips and kinetic Wulff constructions based on knowledge of the growth rate anisotropy that was independently determined on low index substrates. This demonstrates that a strictly surface kinetics dependent growth regime was established. HVPE appears to be a rapid, reliable tool for the making of morphologically controlled microtips on large area wafers.

In p + GaAs thin lms, under excitation by a tightly-focussed laser, the sp atial pro le of the spin polarization ismonitored as a function of excitation power. It is found that photo electron di usion depends on spin, as a directconsequence of the Pauli principle which causes a concentration de pendence of the spin sti ness. Thermoelectriccurrents are also predicted to depend on spin under degeneracy ( spin Soret currents), but these currents play arelatively small role in this case. The spin dependence of the mobility is a lso found weak. Conversely, ambipolarcoupling with holes increases the steady-state photo-electron de nsity at the place of excitation and therefore theamplitude of the degeneracy-induced polarization decrease at the place of excitation.Keywords: Spin transport, di usion, Polarization 1. INTRODUCTION The numerous investigations of spin transport in semiconductors h ave led to the demonstration, amongothers, of various processes which can a ect this transport: i) s pin-charge couplings caused by the spin-orbitinteraction, which may be used to electrically manipulate electronic sp ins in quantum wells

In ${p}^{+}$ GaAs thin films, the effect of photoelectron degeneracy on spin transport is investigated theoretically and experimentally by imaging the spin polarization profile as a function of distance from a tightly focused light excitation spot. Under degeneracy of the electron gas (high concentration, low temperature), a dip at the center of the polarization profile appears with a polarization maximum at a distance of about $2\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ from the center. This counterintuitive result reveals that photoelectron diffusion depends on spin, as a direct consequence of the Pauli principle. This causes a concentration dependence of the spin stiffness while the spin dependence of the mobility is found to be weak in doped material. The various effects which can modify spin transport in a degenerate electron gas under local laser excitation are considered. A comparison of the data with a numerical solution of the coupled diffusion equations reveals that ambipolar coupling with holes increases the steady-state photoelectron density at the excitation spot and therefore the amplitude of the degeneracy-induced polarization dip. Thermoelectric currents are predicted to depend on spin under degeneracy (spin Soret currents), but these currents are negligible except at very high excitation power where they play a relatively small role. Coulomb spin drag and band-gap renormalization are negligible due to electrostatic screening by the hole gas.

A novel spin-spin coupling mechanism that occurs during the transport of spin-polarized minority electrons in semiconductors is described. Unlike the Coulomb spin drag, this coupling arises from the ambipolar electric field which is created by the differential movement of the photoelectrons and the photoholes. Like the Coulomb spin drag, it is a pure spin coupling that does not affect charge diffusion. Experimentally, the coupling is studied in $p^+$ GaAs using polarized microluminescence. The coupling manifests itself as an excitation power dependent reduction in the spin polarization at the excitation spot \textit{without} any change of the spatially averaged spin polarization.

Autoantibody production is a characteristic of most autoimmune diseases including rheumatoid arthritis (RA). The role of these autoantibodies in the pathogenesis of RA remains elusive, but they appear in the serum many years before the onset of clinical disease suggesting an early break in B cell tolerance. The stage of B cell development at which B cell tolerance is broken in RA remains unknown. We previously established in healthy donors that most polyreactive developing B cells are silenced in the bone marrow, and additional autoreactive B cells are removed in the periphery. B cell tolerance in untreated active RA patients was analyzed by testing the specificity of recombinant antibodies cloned from single B cells. We find that autoreactive B cells fail to be removed in all six RA patients and represent 35–52% of the mature naive B cell compartment compared with 20% in healthy donors. In some patients, RA B cells express an increased proportion of polyreactive antibodies that can recognize immunoglobulins and cyclic citrullinated peptides, suggesting early defects in central B cell tolerance. Thus, RA patients exhibit defective B cell tolerance checkpoints that may favor the development of autoimmunity.

We have investigated the temperature dependence of the reflectance anisotropy spectra of clean GaAs(0 0 1), with a particular emphasis on the width of the spectral features related to surface optical transitions. Fundamental differences between the characteristic lines of the Ga-rich and As-rich surfaces have been found. For the gallium-rich surface, the dependence of width of the main negative line at 2.3 eV between 90 and 700 K can be explained by the electron–phonon coupling. This width is found to be reduced by adsorption of minute amounts of cesium. For the As-rich surface, the width of the line at 3 eV weakly depends on temperature, and its value can be interpreted by dispersion in k-space.

In the present work HCl–propanol treated and vacuum annealed GaAs(1 0 0) surfaces were studied by means of soft X-ray photoemission and reflectance anisotropy spectroscopies (SXPS, RAS). On the as-treated surface, As 3d and Ga 3d core level spectra (CLs) are found to be similar to the ones observed on As-capped GaAs(1 0 0) surfaces after annealing at 350 °C, which desorbs most of the overlayer. RAS measurements of the as-treated surface and after annealing up to 350 °C show spectra similar to those detected on the as-grown surfaces with c(4×4) reconstruction. Anneals in the 380–470 °C temperature range lead to the appearance of a RAS line at 3 eV which is characteristic of As dimers. This finding coincides with the presence of a surface component in the As 3d core level spectrum with a chemical shift of −0.5 eV, which we attribute to As-dimers. Further annealing at 540 °C yields in RAS spectra an intense line at 2.2 eV due to Ga dimers, while the Ga 3d CLs do not exhibit any appreciable change.

Degeneracy of a photoelectron gas is shown to strongly affect spin polarized electron transport since the Pauli principle dictates a concentration dependence of the spin stiffness and of the mobility. This causes a spin dependence of the diffusion constant D. A spin-dependence of D as large as 50 % is measured using polarized microluminescence imaging in p + GaAs thin films, revealing a novel spin filter effect. The charge diffusion constant also depends on spin via a second order effect.

International audience; High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron mi-croscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 μm/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10 −9 m 2 /s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

Optical and electrical control of the nuclear spin system allows enhancing the sensitivity of NMR applications and spin-based information storage and processing. Dynamic nuclear polarization in semiconductors is commonly achieved in the presence of a stabilizing external magnetic field. Here we report efficient optical pumping of nuclear spins at zero magnetic field in strain-free GaAs quantum dots. The strong interaction of a single, optically injected electron spin with the nuclear spins acts as a stabilizing, effective magnetic field (Knight field) on the nuclei. We optically tune the Knight field amplitude and direction. In combination with a small transverse magnetic field, we are able to control the longitudinal and transverse components of the nuclear spin polarization in the absence of lattice strain—that is, in dots with strongly reduced static nuclear quadrupole effects, as reproduced by our model calculations., Optical control of nuclear spin polarization in semiconductor quantum dots is promising for applications in NMR imaging. Sallen et al. report efficient dynamic nuclear polarization at zero magnetic field in strain-free gallium arsenide quantum dots with Knight fields dominating the nuclear quadrupole effects.

We have monitored, using photoreflectance spectroscopy, the temperature dependence of the photovoltage induced by modulated above-bandgap light excitation of GaAs (100) before and after cesium adsorption. For the clean p-type surface in ultrahigh vacuum the modulated photovoltage decreases between 100 K and room temperature in a way similar to the photoluminescence intensity. This dependence strongly changes upon adsorption of a very small dose of cesium, whereas the model based on transport theory, which is generally used in order to analyze photoreflectance results, predicts that the modulated photovoltage should be independent of surface state concentration. This behavior is also different from that of the constant photovoltage, which shows the presence of slow surface recombination processes, so that the system cannot be considered as being at equilibrium.

We demonstrate a new approach to study semiconductor surface passivation. This approach, which we have applied to the case of GaAs(100) passivation by sodium sulfide water solutions, consists of using both reflectance anisotropy spectroscopy during passivation and ultraviolet photoemission spectroscopy after removing the sample from the solution. We find that (i) complete chemical passivation requires a treatment duration significantly longer than what was used in previous works; in our case, the oxygen contamination is strongly reduced; (ii) photochemical processes play an important role for improving the surface electronic properties. As a result, photoemission spectroscopy, which uses powerful light excitation, may strongly alter the chemical bonds. From experimental evidence and using a chemical model based on first principles estimates, we propose a detailed description both of the surface chemical reactions that occur during passivation and of the chemical bonds that are formed at the semiconductor surface and in the passivating overlayer.

Diffusion and ordering of Cs overlayers deposited at a low temperature of 90 K on GaAs(001) are observed by reflectance anisotropy (RA) spectroscopy after annealing to higher temperatures. At low coverages $(l~0.3$ monolayer), the ordering of cesium is revealed as a narrowing of the Ga-dimer line in the RA spectra, which occurs after annealing at $Tg~200$ K. A possible reason for such ordering is the diffusion of individual adatoms to preferential adsorption sites. At coverages larger than 0.5 monolayer, for which the majority of adatoms are not isolated, the diffusion-induced changes of RA spectra occur at a temperature lower than 200 K and are characterized by a broad spectrum, which suggest a change of the surface macroscopic anisotropy.

We have investigated the adsorption of cesium on GaAs(001) using synchrotron radiation excited photoemission spectroscopy and also by monitoring the optical transitions related to gallium dimers and arsenic dimers using reflectance anisotropy spectroscopy (RAS). Cesium adsorption has little effect on the Ga 3d core level shape. In sharp contrast, we observe modifications of the RA signal related to gallium dimers, induced by the modification of the electronic states involved in the corresponding surface optical transitions. The changes of the RA spectrum reveal two adsorption phases at Cs coverages above and below 0.5 monolayers. The origin for the strong sensitivity of RAS to semiconductor/alkali metal interface formation is discussed.

Spin-polarized transport of photoelectrons in bulk, $p$-type GaAs is investigated in the Pauli blockade regime. In contrast to usual spin diffusion processes in which the spin polarization decreases with distance traveled due to spin relaxation, images of the polarized photoluminescence reveal a spin-filter effect in which the spin polarization increases during transport over the first $2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ from 26% to 38%. This is shown to be a direct consequence of the Pauli principle and the associated quantum degeneracy pressure which results in a spin-dependent increase in the minority carrier diffusion constants and mobilities. The central role played by the quantum degeneracy pressure is confirmed via the observation of a spin-dependent increase in the photoelectron volume and a spin-charge coupling description of this is presented.

We have investigated the surface optical transitions on (NH4)2S‐passivated, Na2S‐passivated, and unpassivated GaAs as a function of annealing temperature. The change of the reflectance anisotropy (RA) spectrum allows us to distinguish several annealing stages, which we identify as desorption of the protective overlayer, desorption of residual impurities, and breaking of Ga–S bonds. For the case of impurity desorption, we find a very good connection between the increase of dimer concentration, as found from the RA spectrum, with the decrease of impurity concentration, as monitored by Auger spectroscopy. We find significant differences between the Na2S‐ and the (NH4)2S‐passivated surfaces. Unlike the Na2S‐passivated surface, most of the arsenic atoms situated on the (NH4)2S‐passivated surface before annealing are found to be dimerized, so that they are not involved in any chemical bonds with the overlying protective layer. Thus, in this last case, As–S bonds detected by photoemission spectroscopy are situated in the protective overlayer.

We investigate the mechanical and electrical properties of tip-less, GaAs micro-cantilevers on silica supports that are fabricated using a novel assembly approach. The resulting device is compatible with an atomic force microscope (AFM) and takes advantage of the electronic and optical properties of GaAs as well as the mechanical properties of silica. Mechanically, their resonant frequency and quality factor, as well as their AFM imaging capabilities (lateral resolution ∼10–20 nm), are comparable to commercial silicon cantilevers despite the absence of micromachined tip. In the same AFM-like configuration, they can also function as novel spin-polarized electron injectors under excitation by a circularly polarized laser from the rear. Surface nitridation of the cantilever and deposition of a hydrophobic thin polymer film on the sample surface are found to stabilize the injected photocurrent, making them potentially useful for a variety of fundamental and applied investigations in atmosphere.

Activation of myeloid cells by orthopedic particulate debris is a key event in the pathogenesis of periprosthetic osteolysis and implant loosening after total joint replacement (TJR). Several lines of evidence implicate NACHT, LRR, and PYD domains-containing protein 3 (NALP3) inflammasome-mediated production of interleukin 1 beta (IL-1β) in the pathogenesis of clinical disorders ascribable to foreign particulate materials, including asbestos, silica, and urate crystals. Recent reports indicate that orthopedic polymer products and metallic particulates and ions may activate the same pathway. Here, we investigated the contribution of the NALP3 inflammasome to the pathogenesis of peri-implant osteolysis. Pharmaceutical and genetic perturbations of caspase-1 and inflammasome components were used to assess the role of the NALP3 inflammasome in IL-1β production and osteoclast formation by human monocytes and mouse macrophages in response to polymethylmethacrylate (PMMA) particle phagocytosis. The role of caspase-1 in a mouse calvarial model of particle-mediated osteolysis was assessed using µCT. Phagocytosis of PMMA particles induces caspase-1 dependent release of IL-1β from human monocytes and mouse macrophages. Importantly, using macrophages from mice deficient in components of the NALP3 inflammasome, we show PMMA-induced IL-1β production is strictly dependent on these components. Mice lacking caspase-1, the sole effector of the NALP3 inflammasome, show reduced orthopedic wear particle-induced calvarial osteolysis compared to wild-type controls. Absence of NALP3 inflammasome components fails to alter osteoclast formation in vitro. Our findings identify the NALP3 inflammasome as a critical mediator of orthopedic wear-induced osteolysis and as a viable therapeutic target for the treatment of periprosthetic osteolysis.

International audience; We have investigated the mechanisms of photoelectron tunneling into gold from tipless, nitridized, gallium arsenide microcantilevers through thin polymers. A study of the tunnel bias, tunnel distance, and light excitation power dependence of the tunneling photo-current reveals the tunneling process to be Fowler-Nordheim like. Both the value of the dielectric constant and the sign of the tunneling photocurrent at low excitation power suggest the important role of polymer defects.

Images of the steady-state luminescence of passivated GaAs self-standing films under excitation by a tightly-focussed laser are analyzed as a function of light excitation power. While unipolar diffusion of photoelectrons is dominant at very low light excitation power, an increased power results in a decrease of the diffusion constant near the center of the image due to the onset of ambipolar diffusion. The results are in agreement with a numerical solution of the diffusion equations and with a physical analysis of the luminescence intensity at the centre of the image, which permits the determination of the ambipolar diffusion constant as a function of electron concentration., 5 figures

Experimentally and by ab initio calculations it is shown that adsorption of electropositive cesium on the As-rich surface of GaAs(001) and, in a symmetric fashion, adsorption of electronegative iodine on the Ga-rich surface, induce a decrease of the surface stability, thus facilitating surface etching. Conversely, Cs adsorption on the Ga-rich surface and I adsorption on the As-rich surface lead to an increased surface stability. Etching occurs when adsorption-induced charge transfer weakens the backbonds of the top arsenic atoms for the case of Cs on the As-rich β2(2 × 4) surface and the lateral bonds in the topmost surface layer for I on the Ga-rich ζ(4 × 2) surface. The possibilities of reversible transitions between the two reconstructed surfaces and of atomic layer etching with monolayer precision are demonstrated.

Hot-electron transport in indium phosphide is studied by means of energy-resolved field-assisted photoemission of an Ag/InP Schottky diode. The work function of the thin silver top layer is lowered by cesium and oxygen coadsorption. A quasimonoenergetic electron distribution is created close to the bottom of the conduction band in the bulk of the weakly doped p-type InP crystal by near-band-gap light excitation. The energy-distribution curves of the photoemitted electrons are measured for different values of the bias applied to the Ag/InP contact. It is demonstrated that this set of photoemission spectra constitutes a direct measurement of the evolution of the initial distribution during transport in the high electric field of the band-bending region. From this spectroscopic image of the complex multivalley transport, the relevant energy and momentum relaxation processes are clearly identified. Simple models based on the energy balance between the gain in the electric field and the losses by phonon emission account remarkably well for the experimental results. From the comparison between theory and experiment, the characteristic phonon-scattering times are deduced throughout the first conduction band.

International audience; The tunnel photocurrent between a gold surface and a free-standing semiconducting thin film excited from the rear by above bandgap light has been measured as a function of applied bias, tunnel distance and excitation light power. The results are compared with the predictions of a model which includes the bias dependence of the tunnel barrier height and the bias-induced decrease of surface recombination velocity. It is found that i) the tunnel photocurrent from the conduction band dominates that from surface states. ii) At large tunnel distance the exponential bias dependence of the current is explained by that of the tunnel barrier height, while at small distance the change of surface recombination velocity is dominant

Cesium adsorption on $(2\ifmmode\times\else\texttimes\fi{}4)$-GaAs(001) was studied by photoemission and low-energy electron diffraction. The different Cs-induced changes of $\text{As}\text{ }3d$ and $\text{Ga}\text{ }3d$ core-level spectra show that charge transfer is almost complete for Ga surface sites, but is negligible to surface As at a coverage ${\ensuremath{\Theta}}_{\text{Cs}}l0.3\text{ }\text{ML}$. The situation becomes opposite for ${\ensuremath{\Theta}}_{\text{Cs}}g0.3\text{ }\text{ML}$, at which transfer occurs to As but no longer to Ga. Charge transfer to As atoms leads to surface disordering and destabilization and induces surface conversion from As-rich to Ga-rich $(4\ifmmode\times\else\texttimes\fi{}2)$-GaAs(001) surface after annealing at a reduced temperature of $450\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$.

Chemical bonds formed by hydrazine-sulfide treatment of GaAs(111) were studied by synchrotron photoemission spectroscopy. At the B surface, the top arsenic atoms are replaced by nitrogen atoms, while GaAs(111)A is covered by sulfur, also bonded to underlying gallium, despite the sulfide molar concentration being 10 3 times smaller than that of the hydrazine. This extreme dependence on surface polarity is explained by competitive adsorption processes of HS - and OH - anions and of hydrazine molecules, on Ga- adsorption

Well-ordered clean InAs(1 1 1) A and B surfaces have been prepared using HCl–isopropanol solutions and characterized using low-energy electron diffraction and photoemission spectroscopy. The as-treated surfaces are covered by a layer containing arsenic and small amounts of InClx. Annealing induces desorption of the overlayer and reveals (2 � 2) and (1 � 1) structures on the A and B surfaces, respectively. For both surfaces, the surface components of the In 4d and As 3d reveal a charge transfer from the electropositive surface indium to the electronegative surface arsenic. The major advantage of this preparation method over conventional thermal cleaning is a significant reduction in the annealing temperature (�250 C) thereby avoiding anion evaporation.

Energy analysis of the electrons photoemitted from p-type doped (100) InP crystals is performed with 20-meV resolution, at 120 K. The samples are activated to low electron affinity. Laser excitation in the photon energy range 1.96\ensuremath{\le}h\ensuremath{\nu}\ensuremath{\le}3.53 eV is used. The locations of the subsidiary minima ${\mathit{L}}_{6}$ and ${\mathit{X}}_{6}$ of the first conduction band and ${\mathit{X}}_{7\mathit{c}}$ of the second one are unambiguously measured (respectively, 0.67, 0.90, and 1.18 eV above the bottom of the conduction band). The energy dispersion of the three upper valence bands and of the first conduction band is probed over a large portion of the Brillouin zone. These experimental results are accurately described in the framework of the k\ensuremath{\cdot}p Kane model and the value of the spin-orbit-split-band mass ${\mathit{m}}_{7}$=(0.19\ifmmode\pm\else\textpm\fi{}0.01)${\mathit{m}}_{0}$ (where ${\mathit{m}}_{0}$ is the free-electron mass) is directly obtained.

Light excitation of a semiconductor, known to dynamically-polarize the nuclear spins by hyperfine contact interaction with the photoelectrons, also generates an intrinsic nuclear depolarization mechanism. This novel relaxation process arises from the modulation of the nuclear quadrupolar Hamiltonian by photoelectron trapping and recombination at nearby localized states. For nuclei near shallow donors, the usual diffusion radius is replaced by a smaller, quadrupolar, radius. If the light excitation conditions correspond to partial donor occupation by photoelectrons, the nuclear magnetization and the nuclear field can be decreased by more than one order of magnitude.

Random V(D)J gene assembly generates many autoreactive B cell receptors (BCRs). In healthy donors, most autoreactive developing B cells are removed either in the bone marrow or in the periphery, revealing two B cell tolerance checkpoints. The regulation and the mechanisms that ensure this human B cell tolerance are poorly characterized, but they require proper BCR signaling. Indeed, patients with X-linked agammaglobulinemia who carry mutations in the BTK gene, which encodes an essential BCR signaling component, fail to establish proper central B cell tolerance, as demonstrated by the release of self-reactive B cells in the periphery. In autoimmune diseases such as rheumatoid arthritis (RA), B cell tolerance is broken and autoantibodies are secreted. Our recent results show that RA patients suffer from defective central and peripheral B cell tolerance checkpoints, which may favor the development of autoimmunity. Also, about half of our RA patients display unusual immunoglobulin light chain repertoires showing impaired secondary recombination regulation, which indicates that receptor editing, one of the mechanisms that normally ensures B cell tolerance, may often be defective in RA.

The electronic properties of alkali metals (Cs and Na) deposited on the gallium-rich GaAs(0 0 1 surface), have been investigated using synchrotron-radiation photoemission spectroscopy, at liquid nitrogen temperature. From the analysis of the alkali core-level spectra and using usual criteria for metallicity (namely: appearance of the Fermi-level edge, presence of plasmon losses in core-level spectra, and disappearance of surface photovoltage) we find evidence of a surface metallic phase, both for Cs and Na. In agreement with previous determinations of the phase diagram for such system, we find that the metallic phase coexists with an insulating phase. We also observe a precursor of the surface metallic phase, for which only one of the above criteria is satisfied (plasmon losses). The formation of a Cs metallic phase leads mainly to the rising in the Cs4d core-level spectrum of a narrow component at higher binding energy. In contrast, for Na adsorption, the metallic-related component in the Na2p core-level spectrum lies at lower binding energy. These findings are discussed and tentatively explained in terms of the classical Born–Haber cycle as well as with a tight-binding description of alkali metal adsorption. The core-level photoemission results suggest a morphological model in which part of alkali atoms are bonded to the substrate (first layer; insulating phase) and part are bonded to alkali atoms (either second layer or clusters; metallic phase).

Tunneling between a photo-excited p-type silicon tip and a gold surface is studied as a function of tip bias, tip/sample distance and light intensity. In order to extend the range of application of future spin injection experiments, the measurements are carried out under nitrogen gas at room temperature. It is found that while tunneling of valence band electrons is described by a standard process between the semiconductor valence band and the metal, the tunneling of photoelectrons obeys a Fowler-Nordheim-like process directly from the conduction band. In the latter case, the bias dependence of the photocurrent as a function of distance is in agreement with theoretical predictions which include image charge effects. Quantitative analysis of the bias dependence of the dark and photocurrent spectra gives reasonable values for the distance, and for the tip and metal work functions. For small distances image charge effects induce a vanishing of the barrier and the bias dependence of the photocurrent is exponential. In common with many works on field emission, fluctuations in the tunneling currents are observed. These are mainly attributed to changes in the prefactor for the tunneling photocurrent, which we suggest is caused by an electric-field-induced modification of the thickness of the natural oxide layer covering the tip apex., Comment: 12 pages, 11 figures. Submitted to Phys. Rev. B

In the present work HCl-isopropanol treated and vacuum annealed InP(0 0 1) surfaces were studied by means of low-energy electron diffraction (LEED), soft X-ray photoemission (SXPS), and reflectance anisotropy (RAS) spectroscopies. The treatment removes the natural oxide and leaves on the surface a physisorbed overlayer containing InClx and phosphorus. Annealing at 230 � C induces desorption of InClx overlayer and reveals a P-rich (2 · 1) surface. Subsequent annealing at higher temperature induces In-rich (2 · 4) surface. The structural properties of chemically prepared InP(0 0 1) surfaces were found to be similar to those obtained by decapping of As/P-capped epitaxial layers. � 2006 Elsevier B.V. All rights reserved.

We proved experimentally that Cs adsorption on the clean arsenic-rich GaAss001d-s234d /cs238d surface followed by annealing at 450 °C–470 °C, induced conversion to the s432d /cs832d gallium-rich reconstruction. Thus, the conversion temperature is lower by ,100 °C than that required to produce the Ga-rich surface by a conventional ultrahigh vacuum annealing without preliminary Cs adsorption. This effect is monitored using low-energy electron diffraction, reflectance anisotropy spectroscopy, and photoreflectance spectroscopy. We propose that the conversion is due to Cs-induced weakening of arsenic bonds on the surface, which, in its turn, is supposedly caused by electron charge redistribution between Cs adatoms and GaAs surface atoms. Along with the transformation of surface stoichiometry and structure, Cs passivates intrinsic electronic surface states and thus leads to unpinned behavior of the Fermi level at the surface. In combination with the iodineinduced conversion from the Ga-rich to As-rich reconstruction, which was observed earlier, the reverse sAsrich to Ga-richd low-temperature Cs-induced conversion presented here is promising for the development of atomic-layer etching of GaAss001d.

Upon adsorption of Cs, the As-rich $c(2\ifmmode\times\else\texttimes\fi{}8)/(2\ifmmode\times\else\texttimes\fi{}4)$ reconstruction of GaAs(001) is found to exhibit an intense negative signal between 3 eV and 5 eV in the reflectance anisotropy spectrum. This signal has a universal character in that similar features also appear on the Ga-rich surface. The mechanism of this signal is interpreted using ab initio calculations of Cs adsorption at As and Ga sites of the As-rich surface. The calculations succeed in explaining the universality of the signal. In the vicinity of the ${E}_{0}^{\ensuremath{'}}$ bulk critical point at 4.5 eV, the signal arises from perturbation of bulk states terminating at the surface. At lower energies, the signal arises from the creation of new surface resonances induced by the Cs adatom.

Atomic ordering of HCl-isopropanol (HCl-iPA) treated and vacuum annealed (100) InAs surfaces was studied by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and reflectance anisotropy spectroscopy (RAS). On the as-treated surface, a diffused (1 x 1) pattern is observed, which successively evolves to the beta(2)(2 x 4)/c(2 x 8) and (4 x 2)/c(8 x 2) ones after annealing to 330degreesC and 410degreesC respectively. At the intermediate temperature of 370degreesC, an alpha(2)(2 x 4)/(4 x 2) mixed reconstruction is observed. Reflectance anisotropy spectra are compared with those of the corresponding reconstructions observed after As-decapping and found to be quite similar. Therefore we conclude that high-quality (100) InAs surfaces can be obtained by wet chemical treatment in an easy, inexpensive and practical way. (C) 2004 Elsevier B.V. All rights reserved.