We conducted a detailed experimental investigation of the Ag(977) vicinal surface, a high Miller index surface derived from the (111) surface. The sample surface was prepared using standard methodology and its quality was examined by x-ray photoelectron spectroscopy, low energy electron diffraction (LEED) and scanning tunneling microscopy. I(V)-LEED analysis was used to determine the surface structure focusing the intricate relaxation dynamics expected for this surface. Our LEED analysis revealed an inward relaxation for the step chain (SC) atoms, whereas the corner atoms (CC) relaxed outwards. To gain more information on the obtained relaxations, we also performed density functional theory (DFT) calculations for the constructed structural model. Through charge distribution analysis, we found out that the step atoms interact weakly with their adjacent counterparts, resulting in terrace atoms presenting electronic environment similar to those found on flat surfaces. Furthermore, we conducted angle-resolved photoemission spectroscopy (ARPES) measurements to map the electronic structure of the surface. The DFT calculations and ARPES results have shown that the electronic bands observed arise from the hybridization between bulk and surface electronic states.

The use of dyes as sensitizing agents to increase semiconductor activity is a strategy already adopted in the field of heterogeneous photocatalysis, but the compounds applied are noble metal-based and sometimes difficult to synthesize, which make it more expensive. In this work, it was discovered that methylene blue can perform such an effect on an iron molybdate functionalized with peroxo groups on the surface. This material, called MoOxoFe, was tested together with its analogue MoFe (produced without H2O2 in the synthesis) in the degradation of methylene blue. The rapid degradation of the dye led to the hypothesis of sensitization, which was investigated and proven by additional photocatalytic tests with sensitized material, MoOxoFe-MB, and spectroscopies, such as EPR and XPS.

Metallic nanoparticles (NPs) were decorated onto Zn-MOF-74 crystals by photoreducing different metal precursors (Pt, Au, and Ag) using ultraviolet (UV) light in an aqueous solution with different metal concentrations without using additional stabilizers. X-ray diffraction revealed the three-dimensional structural integrity and crystallinity conservation of Zn-MOF-74 crystals during the UV decoration process. Raman spectroscopy showed a minor rearrangement in the structure of the Zn-MOF-74 crystal surface after NP decoration. X-ray photoelectron spectroscopy confirmed the metal oxidation states of Zn and NPs. High-resolution transmission electron microscopy images proved the surface decoration of Zn-MOF-74 crystals with spherical metallic NPs with diameters between 2.4 and 9.8 nm.

Carbon dots (CDs) have attracted significant attention in recent years due to their interesting properties, such as photoluminescence, biocompatibility, excellent water dispersibility, as well as their potential applications in different fields. Despite these features, the complexity of their photoluminescent properties remains a subject of ongoing research and still presents unresolved questions. In this work, we investigated the preparation of various CDs from different low molecular mass starting materials containing carbon, nitrogen and/or sulfur, using hydrothermal carbonization as the preparation method. The CDs were characterized using various techniques, including TEM, FTIR, photoluminescence, UV-Vis, Raman and XPS. A detailed analysis of the initial reactions between the precursors was conducted, and our main results suggest that the optical properties of the CDs are related to fluorophores formed during the initial Michael condensation reactions between the precursors. This process produces molecular fluorescence, which plays a pivotal role in the photoluminescence properties of the nanoparticles. In addition, two of the obtained CDs were used as selective and sensitive probes for metal ions, achieving a detection limit of 0.58 mu M and 0.55 mu M. Finally, the findings described here can guide future works in fine-tuning the design of CDs with desired properties and different potential applications.

This paper reports and discusses some of our recent advances in surface science research on a silica film supported on a Ru(0001) substrate. This system is unique, as the silica is bound to the metal surface by dispersive forces only, and thus opens the possibility to study reactions in the confined space between the metal substrate and the silica film, acting as a permeable membrane. We demonstrate that this system allows for detailed insights into the complexity of reactions in confined space, including phenomena due to the response of the confined space to the presence of the reactants, and direct comparison to the situation when the same reaction occurs in open space.

Silica bilayers are stable on various metal substrates, including Ru(0001) that is used for the present study. In a systematic attempt to elucidate the detailed structure of the silica bilayer film and its registry to the metal substrate, we performed a low energy electron diffraction (I/V-LEED) study. The experimental work is accompanied by detailed calculations on the stability, orientation and dynamic properties of the bilayer at room temperature. It was determined, that the film shows a certain structural diversity within the unit cell of the metal substrate, which depends on the oxygen content at the metal-bilayer interface. In connection with the experimental I/V-LEED study, it became apparent, that a high-quality structure determination is only possible if several structural motifs are taken into account by superimposing bilayer structures with varying registry to the oxygen covered substrate. This result is conceptually in line with the recently observed statistical registry in layered 2D-compound materials.

The introduction of atoms of different chemical species between epitaxial graphene and the SiC substrate by means of an intercalation process has been a reliable route to modify the interaction of this 2D material and its underlying substrate. Distinct atomic species have been intercalated so far and studies focusing on bond states of the electronically active layers were successful, retrieving the local chemical environment. However, the structure of interfacial layers is strongly affected whenever a more reactive atom is used in the intercalation process. In this work, we present experimental evidence based on X-ray crystal truncation rod scattering and photoelectron diffraction showing the coexistence of crystalline and amorphous regions in the oxidized interface. This interface between a bilayer graphene and the SiC substrate is generated by O-intercalation. Such fluctuations of the local structure are crucial to understand the abundant existence of silicon oxycarbides structures (SiOXCY) within the interfacial layer, which has been associated with the limited electronic properties of O-intercalated graphene bilayers. Consequently, this may be considered as a deterministic factor that affects device potentialities in these systems.

Whereas observed and explored for over 40 years, there are still open questions regarding the nature of the Strong Metal-Support Interaction (SMSI) effect. The lack of a precise determination of the atomic mechanisms of electronic and geometrical factors of the SMSI effect hinders the application of metal-support systems towards several catalytic reactions. The present study sheds light on the electronic factor of the SMSI effect in Pd/TiO2 nanoparticles by using Near Ambient Pressure Photoelectron Spectroscopy (NAP-XPS), Ultraviolet Photoelectron Spectroscopy (UPS), and Density Functional Theory (DFT) calculations. The electronic and geometrical factor of the SMSI effect were observed during reduction treatment at 300 degrees C and 500 degrees C, respectively. The results enable mapping the electronic factor during reduction treatment at 300 degrees C, where a charge transfer from Pd nanoparticles to TiO2 support through Pd-O-Ti entities existing at the Pd-TiO2 interface is observed. Furthermore, the charge transfer is mediated by O p states present at the Pd-TiO2 interface.

The Ce 3d XPS data were analyzed with different sets of constraints and no significant change was observed both in the trend and in the absolute values of the Ce( iii ) fraction reported.

Low-dimensionality materials are highly susceptible to interfaces. Indeed, intercalation of different chemical species in between epitaxial graphene and silicon carbide (SiC), for instance, may decouple the graphene with respect to the substrate due to the conversion of the buffer layer into a graphene layer. O-intercalation is known to release the strain of such 2D material and to lead to the formation of high structural quality AB-stacked bilayer graphene. Nonetheless, this interface transformation concomitantly degrades graphene electronic transport properties. In this work we employed different techniques in order to better understand the structure of the graphene/SiC interface generated by O-intercalation and to elucidate the origin of the poor electronic properties of graphene. Experimental results revealed the formation of a SiO2 rich layer with a defective transition layer in between it and the SiC, which is characterized by the existence of silicon oxycarbide structures. Scanning tunneling spectroscopy measurements revealed an extensive presence of electronic states just around the Fermi level all over the sample surface, which may suppress the charge carriers mobility around this region. According to theoretical calculations, such states are mainly due to the formation of silicon oxicarbides within the interfacial layer.

The presence of mesopores matters when choosing the optimal surface oxygen vacancy population for improved photocatalysis of cerium oxide nanoparticles.

High surface area cerium oxide (CeO2-x) nanoparticles (S = 170 m(2)/g) were synthesized by the precipitation method with a narrow band gap (2.73 +/- 0.03 eV). In comparison to typical band gap values for cerium oxide, it presents a red shift in the light absorption spectrum from UV to visible region. X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS) measurements were conducted aiming to elucidate this promising property for photocatalytic applications of the nanoparticles synthesized. It was obtained that the high structural disorder and O vacancy population of the nanoparticles synthesized are responsible for the narrow band gap found. Furthermore, the CeO2-x nanoparticles were applied to the photocatalytic H(2)( )production reaction and presented activity 10 times higher than the commercial CeO2-x standard, besides a much better performance than typical results found for CeO2-x in the literature.

The electronic structure of ultrathin ZnO (000 (1) over bar) films grown on Au (111) was investigated by scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and X-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Our results show evidence of O-terminated films and formation of bulk-like ZnO (2 x 2) surface reconstruction for films with > 4 monolayers. The measurements indicate that the metal substrate plays a decisive role in the electronic structure of films since p-type doping is obtained as observed from the valence band energy shifts. Moreover, finite-size effects appear to significantly modify the Zn and O core-level energy positions. These electronic effects may account for the role of ZnO catalytic performance in ZnO/metal systems, as well as for their nanostructure optoelectronic properties.

It is known that Sb2Se3 does not exhibit topological insulator behavior due to its orthorhombic structure. The introduction of a small amount of bismuth and tellurium may change its structure to hexagonal, leading to a stable topological insulator compound. We report here the synthesis and the structural, chemical, and electronic properties of the topological insulator BiSbSe2.5Te0.5. Combining X-ray and electron diffraction measurements, we demonstrate the formation of this stable quaternary hexagonal single crystal. We used X-ray photoelectron spectroscopy to determine quantitatively the exact chemical composition of the sample. The topological insulating behavior is similar to that of other bismuth chalcogenides, as probed by angle-resolved photoemission spectroscopy. A p-type doping, leading to a 0.15 eV shift of the Fermi level was found. This value compensates the intrinsically n-type doping produced by selenium vacancies. We also found a smaller effective mass and a higher electron group velocity for the electrons in the topological states compared with Bi2Se3.

We report on an experimental investigation of serpentine, an abundant phyllosilicate, as an alternative source of two-dimensional (2D) nanomaterials. We show, through scanning probe microscopy (SPM) measurements, that natural serpentine mineral can be mechanically exfoliated down to few-layer flakes, where monolayers can be easily resolved. The parent serpentine bulk material was initially characterized via conventional techniques like XRD, XPS, FTIR and Raman spectroscopies and the results show that it is predominantly constituted by the antigorite mineral. From ab initio calculations using density functional theory, we also determine the geometry and electronic structure of antigorite, the observed structural form of serpentine. Additionally, we further characterized electrical and mechanical properties of the obtained 2D material flakes using SPM and broadband synchrotron infrared nanospectroscopy. Wavelength tuning of the serpentine vibrational resonances, assigned to in-and out-of-plane molecular vibrations, are observed and compared with the FTIR characterization of the parent bulk material. They show that there is no degradation of serpentine's structural properties during its mechanical exfoliation down to nanometer-thin sheets. Therefore, our results introduce the serpentine mineral as an attractive low-cost candidate in 2D materials applications.

In this work, we present an investigation regarding how and why molecular hydrogen (H-2) changes the electronic properties of graphene field effect transistors (GFETs). We demonstrate that interaction with H-2 leads to local doping of graphene near of the graphene-contact heterojunction. We also show that such interaction is strongly dependent on the characteristics of the metal-graphene interface. By changing the type of metal in the contact, we observe that Ohmic contacts can be strongly or weakly electrostatically coupled with graphene. For strongly coupled contacts, the signature of the charge transfer effect promoted by the contacts results on asymmetric ambipolar conduction, and such asymmetry can be tunable under interaction with H-2. On the other hand, for contacts weakly coupled with graphene, the hydrogen interaction has a more profound effect. In such a situation, the devices show a second charge neutrality point (CNP) in graphene transistor transfer curves (a double-peak response) upon H-2 exposure. We propose that this double-peak phenomenon arises from the decoupling of the work function of graphene and that of the metallic electrodes induced by the H-2 molecules. We also show that the gas-induced modifications at the metal-graphene interface can be exploited to create a controlled graphene p-n junction, with considerable electron transfer to graphene layer and significant variation in the graphene resistance. These effects can pave the way for a suitable metallic contact engineering providing great potential for the application of such devices as gas sensors.

The possibility of utilizing the rich spin-dependent properties of graphene has attracted much attention in the pursuit of spintronics advances. The promise of high-speed and low-energy-consumption devices motivates the search for layered structures that stabilize chiral spin textures such as topologically protected skyrmions. Here we demonstrate that chiral spin textures are induced at graphene/ferromagnetic metal interfaces. Graphene is a weak spin-orbit coupling material and is generally not expected to induce a sufficient Dzyaloshinskii-Moriya interaction to affect magnetic chirality. We demonstrate that indeed graphene does induce a type of Dzyaloshinskii-Moriya interaction due to the Rashba effect. First-principles calculations and experiments using spin-polarized electron microscopy show that this graphene-induced Dzyaloshinskii-Moriya interaction can have a similar magnitude to that at interfaces with heavy metals. This work paves a path towards two-dimensional-material-based spin-orbitronics.

The formation of hydrogen overlayers on the Zn-terminated ZnO(0001) surface has been reexamined by angle-resolved photoemission spectroscopy (ARPES). While low-energy electron diffraction patterns display the same (1 x 1) symmetry for different surface preparations, the electronic structure feature close to the Fermi level shows the formation of electron pockets, compatible with hydrogen-induced metallic states. Using ARPES and density functional theory (DFT) calculations, we show that hydrogen adspecies can also lead to metallization of this zinc-oxide surface in a similar manner as observed previously on ZnO(10 (1) over bar0) and O-terminated ZnO(000 (1) over bar). Importantly, our DFT calculations indicate that these electron pockets are formed by sp hybridized states and therefore the angular distribution of the emitted photoelectron is significantly suppressed at the normal emission.

High Resolution Transmission Electron Microscopy allows the determination of the crystalline structure of materials through various methods of electron diffraction or direct imaging. However, the interpretation and quantification of the high‐resolution images are complex, because of the strong interaction between the electron beam and the material [1]. Besides, the material's exit wave function is modified by the components of the microscope [2]. As the high‐resolution microscopy images are a convolution between the exit wave function of the sample and the function of the microscope, the interference fringes can be modified changing the condition of defocus [3]. The aim of the research is to understand the focal series reconstruction routines and use them in the study of bismuth telluride and its alloys, in order to identify their crystalline structure. Through focal series reconstruction is a technique consisting in obtaining high‐resolution image series with different values of defocus, generating different conditions of constructive and destructive interference fringes. At the same time, high‐resolution images are simulated from a theoretical model of the crystal convoluted with the transfer function of the microscope, considering several types of aberration of the microscope, where the spherical aberration of the objective lens and the chromatic aberration are dominant. The simulated images are compared with the experimental images and through the correlation between them the theoretical model is optimized. There are several software packages which can be used to simulate the structure and/or generate a focal series: JEMS, True Image, FTSR, IWFR and REW. The present work shows the first results on focal series reconstruction routine using REW [4]. Bismuth telluride, Bi 2 Te 3 , is a thermoelectric material with high coefficients at room temperature [5] and has recently been identified as a topological insulator [6], with rhombohedral crystal structure and space group R(‐3)m with five atoms per unit cell. When aligned in the [2,‐1,‐1,0] direction is possible to visualize the quintuple layer structure of Te‐Bi‐Te‐Bi‐Te. Studies related to the doping of Bi 2 Te 3 , in which some elements are intercalated among their quintuple layers [7], have been conducted in order to determine the variations of their basic properties. The focal series reconstruction will be used to verify the quality of the intercalation experiment. A through focal series of 20 high resolution images was taken of a Bi 2 Te 3 sample prepared via ultramicrotomy, approximately 20‐30 nm thick, using a Tecnai G‐20 LaB6 S‐Twin (Cs = 1.2 mm) at 200 keV. A magnification of 490kx was used over a range of focus of ‐180.09 nm to 9.09 nm, with a focus variation of approximately of 10 nm. The HRTEM image at the Scherzer focus is shown in Figure 1, and the image of amplitude and phase resulting from the exit wave reconstruction of the sample using the software REW are shown in Figure 2 and Figure 3. It is possible to identify the atomic position of bismuth and tellurium in the quintuple layers of the phase image obtained from the focal series reconstruction, as shown in Figure 4, using a conventional transmission electron microscope.

The structural properties of graphene/Ni(111) are investigated by a combination of low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), angle-scanned photoelectron diffraction (PED), and first-principles calculations. XPS data indicate that graphene interacts strongly with the topmost Ni layer. Diffraction data show that graphene is deposited commensurably with the underlying Ni surface atoms. Twelve different graphene preparations were analyzed by LEED and one by PED. Considering the relative position between the carbon and Ni atoms, five experimental sets indicate a top-fcc structure, three show a bridge-top structure, and four have a mixed structure. The analysis of the PED experiment suggests the top-fcc termination. Our first-principles calculations show that the total energies of the top-fcc and bridge-top structures are nearly degenerate, which corroborates the observed bistability of those phases. Moreover, by comparing the structural parameters obtained by the three methods (LEED, PED, and ab initio calculations), excellent agreement is achieved.