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The ternary system Cu–Sn–S was re-investigated and the phase diagram Cu2S–SnS2 studied in detail by differential thermal analysis and X-ray diffractometry. Three phases of composition Cu4SnS4, Cu2SnS3 and Cu2Sn3+xS7+2x(0≤×≤1) were found exhibiting melting points at 833, 856 and 803 °C, respectively. Ellipsometric and diffuse reflectance measurements revealed that the latter two sulfides possess a fundamental band gap of 0.93 eV followed by a higher transitions. For the first time it could be demonstrated that Cu2Sn3S7 has semiconducting properties and an absorption coefficients of the order 105 cm−1.

Cs was adsorbed at room temperature onto the (0001) cleavage planes of 1T–TaSe2. The deposited Cs forms no metallic overlayer, but intercalates after an initial adsorption stage into the van der Waals gap of the layered crystal. A limit of the relative concentration ratio cCs/cTa of ca. 60% is observed. Due to the electron transfer associated with the intercalation the charge density wave induced p( 13 × 13 )R13.89° superstructure exhibits a phase transition to a c( 2 3 ×4 )rect. structure. As a further consequence of the intercalation a metal to semiconductor transition occurs. The change in the electronic structure could not be interpreted within the rigid band model, but is tentatively explained by an localization effect, caused by the charge density wave phase transition.

The electronic structure of heterojunctions between II-VI semiconductors (CdS, CdTe) and layered transition metal dichalcogenide semiconductors (MoTe2, WSe2) were investigated by soft x-ray photoelectron spectroscopy. The interfaces were formed sequentially by molecular beam epitaxy (MBE) of the II-VI semiconductors on van der Waals (0001)-surfaces of layered compound single crystals. The II-VI semiconductors grow with their polar hexagonal axis ([111] for CdTe, [0001] for CdS) parallel to the non-polar substrate [0001]-axis, without evidence for lattice distortions as prooved by TEM and LEED. Band offsets were determined from soft x-ray photoelectron spectra. Large substrate independent interface dipoles of 1.2 eV for CdS and 0.8 eV for CdTe were determined. The deviation of experimental band offsets from the electron affinity rule prediction is described by a simple model which takes the polarity of the grown interfaces into account.

Cu was locally deintercalated from intercalated 1T TaSe2 and 1T TiSe2 single crystals by applying a voltage pulse between the sample surface and an atomic force microscope (AFM) tip under ambient conditions. Using this method, clusters with diameters of approximately 60 nm were grown. This would allow the use of intercalated transition metal dichalcogenides as mass-storage devices. The intercalated samples were prepared in ultrahigh vacuum (UHV) and characterised by X-ray as well as ultraviolet photoelectron spectroscopy (XPS, UPS). It is shown that the preparation of metal-free surfaces requires prolonged heating steps.

Using EPR we have investigated bulk single crystals of \ensuremath{\mathrm{B}}-${\mathrm{FeSi}}_{2}$ grown by chemical vapor transport. By an interpretation of the hyperfine structure combined with intentional doping during crystal growth, we prove that most of the paramagnetic centers observed arise from isolated iron group impurities. The 3d transition metals Cr, Mn, and Co, and with less certainty Ni and Cu, have been identified. The angular variations of the corresponding spectra show orthorhombic symmetry and can be explained with an electronic spin S=. The substructure of the EPR lines due to the ligand hyperfine interaction indicates an eightfold Si coordination. The simple center model of an impurity atom substituting for iron is consistent with the observed spin, symmetry, and coordination. Whereas Cr and Mn can occupy either of both crystallographically inequivalent Fe sites Co, Ni, and Cu prefer one site. For Cu, however, an interstitial incorporation also seems possible.

The II–VI semiconductor CdTe was sequentially deposited onto the (0001) van der Waals surfaces of the layered compound semiconductors MoTe₂ and WSe₂ by molecular beam epitaxy. Growth could only be achieved after deposition of a nucleation layer of CdTe at room temperature. After nucleation subsequent deposition steps followed at increased substrate temperatures (T=170–370 °C) in order to increase the crystalline quality of the films. The deposited films were investigated after each growth step by low energy electron diffraction and photoelectron spectroscopy. The diffraction pattern indicates a facetting of the (111) oriented film surfaces. From photoemission data we exclude interface reactions between substrate and film material. Transmission electron microscopy was used to examine the film morphology after the UHV experiments. The mean diameter of the film crystallites is 200–400 A.

The growth of epitaxial CdS (wurtzite-type) films on the Van der Waals (0001) surface of the layered compound semiconductors WSe2 and MoTe2 is presented. The film and the heterointerfaces are investigated by electron diffraction, photoelectron spectroscopy, and transmission electron microscopy (TEM). At room temperature and above, the CdS sticking coefficient on Van der Waals surfaces is very low. Film growth could only be achieved by decreasing the substrate temperatures to 170 K for the initial deposition steps. On WSe2, textured films of CdS are grown with the c-axis parallel to the substrate c-axis. The crystallites of mean diameter 200 A have random azimuthal orientation. On MoTe2 the CdS films are aligned with their c- and a-axis parallel to the respective axes of the substrate.

Epitaxial GaSe films have been prepared on WSe2 (0001) substrates with 14% lattice mismatch and characterized by photoelectron spectroscopy, electron diffraction, and ex situ by tunneling microscopy. The films grow in the Frank–van der Merve growth mode. The best films with perfect azimuthal orientation are formed after an annealing step at 720 K. The basic mechanisms of this van der Waals epitaxy are qualitatively discussed in terms of thermodynamic and kinetic parameters.

Joint use of XPS and STS methods for MoSx van der Waals face cleaned by removal of a few layers in air have allowed to determine the connection between change of electronic properties and variation in Mo content for MoSx surface layers. STS results (I–V curves with electron transport across MoSx layers) show the p-type conductivity for MoS2; p- and n- regions for MoS1.6. The surface state density is higher for p- MoS1.6 than for p-MoS2. From I–V curve with electron transport along layers for MoS1.6 surface the bandgap above 1.1 eV and |Ef - Ec|≌ 0.4 eV are determined. For results explanation we assume that: surface states creation occurs due to top layer defects formation under top layer breaks ; n- type regions creation is caused by growth of concentration of donor centers associated with excess Mo atoms.

Epitaxial films of Wurtzite CdS in (0001) orientation have been grown on MoTe2 (0001) substrates in spite of a lattice mismatch of 15%. The film growth was in situ monitored by soft x‐ray photoelectron spectroscopy and low energy electron diffraction. The interface is found to be nonreactive and atomically abrupt. The CdS overlayer tends to grow in three‐dimensional clusters (Volmer–Weber growth mode).

The intercalation of Cu adsorbed onto IT TaSe(2) and TiSe(2) (0001) van der Waals planes as well its deintercalation by adsorbed Br(2) is studied by synchrotron induced photoelectron spectroscopy and low energy electron diffraction. Cu intercalation into 1T TaSe(2) leads to a change in lattice distortion (charge density waves) as is evident from a transition of a commensurate root 13x root 13 to a 3x3 superstructure and changes in Ta 4f core line and valence band spectra. For 1T TiSe(2) intercalation follows closely the rigid band model. After adsorption of Br(2) at 100 K and annealing to room temperature a CuBr overlayer is detected on both samples. The substrate spectra indicate the deintercalation of near surface Cu. The experimental results suggest that the diffusion of Cu proceeds normal to the van der Waals plane. Ionics

Single crystalline and polycrystalline CuInS2 samples prepared by different methods are characterized by Raman spectroscopy. The measured spectra are fitted according to the phonon confinement model. Correlation lengths were obtained, which correspond to the size of domains of perfect crystallinity. These correlation lengths are in good agreement with distances between twin defects observed by transmission electron microscopy in polycrystalline CuInS2. Additionally, the strain present in the samples was determined from the Raman spectra. A tensile strain was obtained for the polycrystalline CuInS2 thin films, which agrees well with published values for the same material.

{100} surfaces, produced from sublimation grown PbS single crystals by cutting, mechanical and chemical polishing, were characterized with regard to topography, structure and chemical composition. For this purpose, some methods independent from another were used, for instance profile measuring, dislocation etching, X-ray rocking-curves, RHEED, Rutherford backscattering (RBS), and AES. The results allow to describe the change of structural perfection with the depth (damage depth), the concentration profile of the main components (half-quantitatively), and the significant decreasing of contamination. Following from this study, the model of the damage layer near the surface discussed earlier for PbTe is modified slightly.

The II-VI semiconductor CdS was grown by molecular beam epitaxy on the van der Waals faces of the layered semiconductor InSe. Chemical, electronic and morphological properties of the deposited films were investigated by means of low energy electron diffraction (LEED), soft x-ray photoelectron spectroscopy (SXPS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). In contrast to observations made on other layered crystals, nucleation of CdS on InSe is possible also at elevated temperatures which is attributed to the small lattice mismatch. The growth front of CdS corresponds to the sulfur terminated polar (111)-B surface which has a strong tendency to form facets.