Laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy are complementary techniques providing respectively chemical and structural information on the sample target. These techniques are increasingly used in Earth and Planetary sciences, and often together. LIBS is locally destructive for the target, and the laser-induced effects due to LIBS laser shots on the structure and on the Raman fingerprint of a set of geological samples relevant to Mars exploration are here investigated by Raman spectroscopy and electron microscopy. Experiments show that the structure of samples with low optical absorption coefficients is preserved as well as the structural information carried by Raman spectra. By contrast, minerals with high optical absorption coefficient can be severely affected by LIBS laser shots with local amorphization, melting and/or phase transformation. Thermal modeling shows that the temperature can reach several thousands of degrees at the surface for such samples during a LIBS laser shot, but decreases rapidly with time and in space. In 2020, NASA Mars 2020 mission will send a rover equiped with a combined LIBS/Raman instrument for remote analysis (SuperCam) as well as proximity science instruments at fine scale for X-ray fluorescence called PIXL for Planetary Instrument for X-ray Lithochemistry, and deep UV Raman spectroscopy called SHERLOC for Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals. We discuss the implications of our results for the operation of these instruments and show that (i) the SuperCam analytical footprint for Raman spectroscopy is many times larger than the LIBS crater, minimizing any effects and (ii) SHERLOC and PIXL analysis may be affected if they analyze within a LIBS crater created by SuperCam LIBS.

Hollow channels in diamond are well acknowledged to be the result of dissolution processes. In this article we demonstrate that some hollow channels in natural diamonds are the consequence of intense plastic deformation by mechanical twinning. Two mixed-habit diamonds presenting numerous geometrical hollow tubes were studied. X-ray Laue analyses showed the presence of microtwins. At the intersection of microtwins, displacements and cracks are generated, creating the hollow channels observed. The presence of the cracks seems to have released the internal stress, as there was less to no signs of deformation at and around them. Further dissolutions are sometimes but not always seen within the cavities. Mechanical twinning, so far mostly identified in pink to purple diamonds, might be more widespread than originally thought in natural diamonds.

The MnAs phase transition from the hexagonal ferromagnetic alpha to the orthorhombic paramagnetic beta phase has been investigated in situ by variable-temperature scanning tunneling microscopy (STM) as a function of epilayer thickness. The alpha-beta phase coexistence leads to the formation of a self-organized stripes pattern of alternating alpha and beta regions. The morphology evolution of the alpha-beta periodic array of domains has been imaged in detail. The period and corrugation of this pattern are linear functions of the epilayer thickness with a domain periodicity nearly five times larger than film thickness. Also, STM local imaging through the phase-coexistence region (10-45 degrees C) shows unambiguously the absence of mass transport during the transition. The self-organization of alpha-beta stripes is consistent with an elastic-energy equilibrium state of the heteroepitaxial system at each temperature, as previously proposed for the origin of the modulated structure [V. M. Kaganer et al., Phys. Rev. B 66, 045305 (2002)]. Independently of self-organized alpha-beta regions, the surface displays anisotropic mounds that are elongated along MnAs a axis. This facetting process leads to a peculiar, highly anisotropic surface with oriented facets and submicron periodic modulation along the hexagonal c axis. Smoother surfaces with larger terraces are obtained following postgrowth annealing. These results suggest that a careful control of the growth temperature and annealing procedure can be used to tailor the surface morphology for specific applications requiring anisotropic templates.

End-tethered chains made of an adsorbed diblock copolymer of polystyrene (PS)-polyisoprene (PI) bearing an end-segment including a Ge atom are built by the Langmuir-Schaeffer technique. They are studied both in the dry state and in a good solvent for the PI chain using grazing incidence X-ray standing waves. The analysis of the signal provides a direct measurement of the end-segment distribution which is found to be singular and mostly localized to a plane in the dry case. In the good solvent case, end-segments are found to span the entire assembly and compare very well with results obtained by Kreer et al.

Crystal defects in Seeded Chemical Vapour Transport (SCVT) and hydrothermal ZnO substrates were characterised mainly by X-ray topography and diffraction. Zn1−xMxO (M=Co, Mn) epilayers were grown on hydrothermal ZnO(00.1¯) substrate by Pulsed Laser Deposition (PLD). It is shown that the epitaxy strains are partially relaxed through dislocations in the {10.0} glide planes. The crystal perfection of the epilayers was analysed by high-resolution X-ray diffraction. Almost intrinsic rocking curves were observed for Zn1−xCoxO epilayers and the c-axis parameter increases proportionally with the Co content. This suggests that Co atoms are well located at substitutional sites in the ZnO matrix. A larger distortion of the ZnO matrix is induced by the insertion of Mn atoms. A paramagnetic behaviour was observed in Zn1−xCoxO epilayers with a low proportion of active Co atoms. A weak ferromagnetic behaviour was observed only for Zn1−xCoxO epilayers when a few Al atoms (1.6%) were incorporated.

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics as that of the usual XSW on a bulk crystal surface. Thus, XSW provide a direct method to probe the atom position in a thin film. The method was applied to an epilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order to determine the Co-atom position. The XSW established that Co atoms occupy the substitutional Zn site in the ZnO matrix, although their coherent fraction, which measures the degree of order, is rather low. Moreover, the measurement of the Zn fluorescence in the film gives approximately the same value for the coherent fraction of the Zn atoms. Besides, by using the substrate rocking curve, it is shown that the XSW signal of the Zn atoms in the substrate can be detected through the film. This interesting approach allows the coherent fraction of an element of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk. These results should relate to strains and defects on both sides of the interface.

X-ray standing waves (XSW) in a thin epitaxic film are treated in the framework of the dynamical theory. It is demonstrated that the fluorescence yield around the main peak of the rocking curve has essentially the same characteristics as that of the usual XSW on a bulk crystal surface. Thus, XSW provide a direct method to probe the atom position in a thin film. The method was applied to an epilayer of the diluted magnetic semiconductor Zn0.94Co0.06O, in order to determine the Co-atom position. The XSW established that Co atoms occupy the substitutional Zn site in the ZnO matrix, although their coherent fraction, which measures the degree of order, is rather low. Moreover, the measurement of the Zn fluorescence in the film gives approximately the same value for the coherent fraction of the Zn atoms. Besides, by using the substrate rocking curve, it is shown that the XSW signal of the Zn atoms in the substrate can be detected through the film. This interesting approach allows the coherent fraction of an element of a substrate below an interface to be probed in situ. For the Zn fluorescence, the coherent fraction is lower near the interface than in the bulk. These results should relate to strains and defects on both sides of the interface.

The x-ray standing wave method is used in correlation with reflection high-energy electron diffraction and scanning tunneling microscopy to investigate the crystallographic features of MnTe monolayers inserted in CdTe (001). Either conventional molecular beam epitaxy or atomic layer epitaxy were employed for the formation of the CdTe starting surface, the deposition of the MnTe fractional monolayer, and its encapsulation by CdTe. Significant differences concerning the ratio of Mn atoms involved in MnTe clusters to those incorporated as part of a CdMnTe alloy are observed between the samples. Those differences are due to differing CdTe starting surface roughness.

The case of a crystal containing a thin buried layer is analysed within the dynamical theory of X-ray diffraction. In this case, the upper thin part of the crystal, above the buried layer, is only shifted with respect to the lower bulk part. The main feature is the phase shift phi for the structure factors between the upper thin part and the lower bulk part. Owing to this phase shift, the backward wavefield, the wavefield with the energy flux directed out of the crystal, is excited in the thin part of the crystal. It is found that only the backward wavefield may be excited within the Bragg total reflection. This gives rise to anomalous transmission of the X-rays in the crystal. When the crystal is tilted across the Bragg angle, the variation of the intensity of X-rays in the buried layer due to the transmission term may be stronger than the one due to the anomalous absorption. Thus, this phenomenon should be taken into account in X-ray standing-wave (XSW) analysis. The excitation of the backward wavefield is also responsible for the appearance of oscillations in the reflectivity profile. The oscillation period is determined by the thickness of the upper thin part. The position and the amplitude of the oscillation directly provide the value of the phase phi. It is thus interesting to simultaneously record the X-ray reflectivity and the XSW measurements when studying the buried layer.

The epitaxy-induced tetragonal strain in one monolayer of InAs buried in a GaAs(100) crystal is determined by measuring weak oscillations in X-ray reflectivity profiles. It is shown that the reflectivity of such heterostructure consists of a sinusoidal modulation of the usual rocking curve of a thick crystal. The oscillation period provides the distance of the buried layer from the crystal surface and the maximum positions in oscillations give the displacement induced by the buried layer. The vertical spacing between the In and As atom planes is found to be 1.64 +/- 0.02 Angstrom, which is consistent with an elastic behaviour.

Within this article, the stability of high index faces (or facets) linked to the reconstruction upon dense faces will be evaluated on the basis of crystallographic arguments. First of all, several concepts are specified or introduced. Secondly, based on experimental results, we will provide several rules which explain or predict the stability of high index faces in connection with the structure of the dense faces.

The structural evolution of all the (hk0) faces between Ni(100) and Ni(210) under activated nitrogen adsorption has been investigated by low energy electron diffraction and Auger electron spectroscopy. The structural behaviour of these faces gives a prototypical example of the influence of the steps in a dense face structure with adsorbate-induced surface reconstruction (here p4g(2 × 2)). Firstly, the quasi-centre of symmetry of the p4g(2 × 2) structure is revealed. Secondly, strong changes in the step characteristics and faceting are observed.

The epitaxial growth of very thin GaSe films on H-Si(111), 7 x 7-Si(111), and root 3 x root 3 Ga-Si(111) has been investigated using the x-ray standing-wave technique. The interface structure was found to be identical whatever the Si(111) surface preparation used and consists of a GaSe half-layer. Ga atoms are covalently bonded with Si top atoms and are located in T sites. Beyond the interface, the growth proceeds layer by layer and not atomic plane by atomic plane. Moreover, the first complete layer above the interface is almost completely relaxed with respect to the Si substrate.

The x-ray standing wave method is used to investigate some crystallographic features of the first stages of growth of ultrathin pseudomorphic MnTe(001) strained layers buried in CdTe on CdTe(001) substrates. Experiments with 004 and 113 reflecting planes show evidence of the presence of both MnTe clusters and diluted CdMnTe alloy.

The epitaxial growth of the layered compound GaSe on three-dimensional materials (GaAs and Si) has already been achieved by several research groups and is often referred to as “Van der Waals epitaxy”. To check this assumption very thin films (approximately half a layer) of GaSe were grown, by molecular beam epitaxy, on HSi(111) substrates. The X-ray standing waves technique was used to determine the structure of the interface. The Ga atoms are located in T sites, straight above top Si atoms, with a SiGa bond length of 2.37 Å. The position of Se atoms was found to be in agreement with the one calculated from GaSe bulk structure. Therefore, and at least for HSi(111) substrates, the GaSeSi(111) heteroepitaxy is in fact a “classical” pseudomorphic epitaxy. Half a GaSe layer is firstly bonded to Si by covalent bonds and Van der Waals growth of GaSe layers occurs in a second stage.

The resistance of the As-terminated Si(001) surface to oxidation in O2 is the subject of this study. Photoemission spectra of As3d and Si2p core levels excited with synchrotron radiation reveals that spectral changes are evident, simultaneously for As and Si, only from ∼1012 L (Langmuir) on, in stark contrast with a previous report indicating a saturation coverage in the 400–2000 L range. Oxidation proceeds slowly, as dimerized As remain intact (∼24%) up to exposures of ∼1013 L. In the oxidized areas, the four Si oxidation states (indicative of subsurface oxidation) and three As oxidation states plus metallic arsenic show up. This suggests a reduction of the arsenic oxide by silicon. Arsenic losses are also observed, probably via sublimation of As4O6 molecules.

The strong resistance of the As-terminated Si(001) surface to oxidation in molecular oxygen at room temperature is the subject of this study. As3d and Si2p photoemission spectra, as well as valence band spectra, excited with synchrotron radiation (135 eV less than or equal to hv less than or equal to 165 eV), have been recorded as a function of increasing O-2 exposures, over the range 2400-1.4 X 10(13) L (langmuir). Spectral changes, simultaneously observed in the As3d and Si2p core-levels near similar to 10(12) L are indicative of the onset of oxidation. However a modification of the valence band, due to the contribution of O 2p states, is clearly evident from similar to 10(11) L, pointing to the presence of weakly bound oxygen species at that exposure. These results are confronted with a previous Auger study reporting an oxygen saturation coverage (0.5 monolayer) already in the 400-2000 L range, interpreted as the insertion of an oxygen atom between two dimerized arsenic atoms.On the contrary our data show that surface oxidation is a slow process, spatially inhomogeneous, as some dimerized As remain intact (similar to 24%) up to exposures as large as similar to 10(13) L. Oxidation is not limited to the outermost layer, as three arsenic oxidation states and the four silicon oxidation states (indicative of subsurface oxidation) are detected simultaneously. Moreover metallic arsenic shows up: this suggests a reduction of the arsenic oxide by silicon. Arsenic losses are also observed, probably via sublimation of As4O6 molecules.