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Perovskite oxides are studied as electrocatalysts for oxygen evolution reactions (OER) because of their low cost, tunable structure, high stability, and good catalytic activity. However, there are two main challenges for most perovskite oxides to be efficient in OER, namely less active sites and low electrical conductivity, leading to limited catalytic performance. To overcome these intrinsic obstacles, various strategies are developed to enhance their catalytic activities in OER. In this review, the recent developments of these strategies is comprehensively summarized and systematically discussed, including composition engineering, crystal facet control, morphology modulation, defect engineering, and hybridization. Finally, perspectives on the design of perovskite oxide-based electrocatalysts for practical applications in OER are given.

Magnetic molecules on surfaces have been widely investigated to reveal delicate interfacial couplings and for potential technological applications. In these endeavors, one prevailing challenge is how to preserve or recover the molecular spins, especially on highly metallic substrates that can readily quench the magnetic moments of the admolecules. Here, we use scanning tunneling microscopy and spectroscopy to exploit the semimetallic nature of antimony and observe, surprisingly yet pleasantly, that the spin of Co-phthalocyanine is well preserved on Sb(111), as unambiguously evidenced by the emergent strong Kondo resonance across the molecule. Our first-principles calculations further confirm that the optimal density of states near the Fermi level of the semimetal is a decisive factor, weakening the overall interfacial coupling, while still ensuring sufficiently effective electron-spin scattering in the many-body system. Beyond isolated admolecules, we discover that each of the magnetic moments in a molecular dimer or a densely packed island is distinctly preserved as well, rendering such molecular magnets immense potentials for ultrahigh density memory devices.

Searching photocatalysts for efficient hydrogen production has been a challenging issue for solar-energy harvesting. Using co-catalyst is proven to be an effective approach to improve the efficienc...

The transition-metal (oxy)hydroxides have been considered as one of the promising electrocatalysts for oxygen evolution reaction (OER). Therefore, it is necessary to have in-depth study on the origin behind their favorable inherent OER activity and further improve their catalytic performance. Herein, nickel–cobalt-vanadium trimetallic (oxy)hydroxide nanosheets decorated with silver nanoparticles (Ag NPs) (Ag@NiV0.2Co0.2) are fabricated for OER by a simple spontaneous redox reaction. The Ag@NiV0.2Co0.2 can deliver an overpotential of only 255 mV at 10 mA cm−2 and a small Tafel slope of 38.3 mV dec-1 in alkaline solution. We accredit the outstanding catalytic performance to the following aspects: (1) the active (oxy)hydroxide layer on the surface of Ag@NiV0.2Co0.2 generated through the surface reconstruction, (2) the optimal local coordination induced by the interaction between Ag NPs and trimetallic system, (3) the extensively exposed active sites, and (4) the significantly improved charge-transfer ability due to the incorporation of Ag NPs. Our findings may provide deep understanding on the mechanism of OER and offers a novel strategy to design electrocatalysts with superior OER activity.

The heterostructures of the ferromagnet (Cr2Te3) and topological insulator (Bi2Te3) have been grown by molecular beam epitaxy. The topological Hall effect as evidence of the existence of magnetic skyrmions has been observed in the samples in which Cr2Te3 was grown on top of Bi2Te3. Detailed structural characterizations have unambiguously revealed the presence of intercalated Bi bilayer nanosheets right at the interface of those samples. The atomistic spin-dynamics simulations have further confirmed the existence of magnetic skyrmions in such systems. The heterostructures of ferromagnet and topological insulator that host magnetic skyrmions may provide an important building block for next generation of spintronics devices.

The instability of lead halide perovskites in various application-related conditions is a key challenge to be resolved. We investigated the formation of metal nanoparticles during transmission electron microscopy (TEM) imaging of perovskite-related metal halide compounds. The metal nanoparticle formation on these materials originates from stimulated desorption of halogen under electron beams and subsequent aggregation of metal atoms. Based on shared mechanisms, the TEM-based degradation test can help to evaluate the material stability against light irradiation.

The practical application of perovskite oxides as electrocatalysts for oxygen evolution reaction (OER) has been greatly hindered by their limited catalytically active sites and poor electrical conductivity. Herein, we report the use of a perovskite-oxide nanofilm as highly improved electrocatalyst for OER. A facile fabrication method, pulsed laser deposition (PLD), is employed for the first time to fabricate the SrCo0.85Fe0.1P0.05O3−δ nanofilm on nickel foam (SCFP-NF) with abundant active sites and enhanced electrical conductivity. We find that the SCFP-NF fabricated by PLD exhibits excellent OER activity and durability in alkaline solutions. Especially, the PLD method can create a large amount of oxygen vacancies on the surface of the perovskite nanofilm, leading to a high concentration of highly oxidative oxygen O22−/O−. This O22−/O− species is generally recognized to be active for OER. As a result, the SCFP-NF catalyst with low mass loading (≈30 μg cm-2) demonstrates a remarkable OER activity with a low overpotential of 290 mV and a superb stability up to 200 h at 10 mA cm−2 in alkaline media. The catalytic performance of this perovskite nanofilm is superior to most of the reported metal-oxide-based catalysts and benchmark RuO2. Our findings show that the catalytic performance of oxide-based electrocatalysts can be greatly improved by defect-engineering, and the PLD and other film fabrication methods may help us to realize practical application.

In order to investigate the genetic difference on medicinal components of Scutellaria baicalensis from different provenances on the genetic difference, the S. baicalensis provenance tests were arranged by randomized block design.Excavating the crude drugs that have been growing for three years, with the same drying process, the content of baicalin, baicalein, wogonoside, wogonin and laminarin A in S. baicalensis were detected by HPLC, and then the data were analyzed. The results indicated that the content of baicalin in different provenances of S. baicalensis was significantly different (

Topological insulators (TIs) are a new type of electronic materials in which the nontrivial insulating bulk band topology governs conducting boundary states with embedded spin-momentum locking. Such edge states are more robust in a two-dimensional (2D) TI against scattering by nonmagnetic impurities than in its three-dimensional (3D) variant, because in 2D the two helical edge states are protected from the only possible backscattering. This makes the 2D TI family a better candidate for coherent spin transport and related applications. While several 3D TIs are already synthesized experimentally, physical realization of 2D TI is so far limited to hybrid quantum wells with a tiny bandgap that does not survive temperatures above 10 K. Here, combining first-principles calculations and scanning tunneling microscopy/spectroscopy (STM/STS) experimental studies, we report nontrivial 2D TI phases in 2-monolayer (2-ML) and 4-ML Bi(110) films with large and tunable bandgaps determined by atomic buckling of Bi(110) films. The gapless edge states are experimentally detected within the insulating bulk gap at 77 K. The band topology of ultrathin Bi(110) films is sensitive to atomic buckling. Such buckling is sensitive to charge doping and could be controlled by choosing different substrates on which Bi(110) films are grown.

The atomic structures that develop as a function of coverage during deposition of Bi on Ag(111) have been studied using low-temperature scanning tunneling microscopy, low-energy electron diffraction, and ab initio calculations. The growth process involves two sequential stages. At low coverage, Bi atoms are incorporated into the topmost layer of Ag(111), resulting in the formation of an Ag${}_{2}$Bi alloy confined to the surface and ordered ($\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$)$R$30\ifmmode^\circ\else\textdegree\fi{} Ag${}_{2}$Bi islands supported on Ag(111). This mode of accommodation of Bi was found to be energetically favorable based on ab initio total-energy calculations. At coverage above a critical value of 0.55 monolayers, the Ag${}_{2}$Bi alloy phase gradually converts into an ordered Bi ($p\ifmmode\times\else\texttimes\fi{}\sqrt{3}$) overlayer structure supported on Ag(111). We postulate that the dealloying transition is likely driven by compressive strain induced by incorporation of large-size Bi atoms into Ag at a high coverage and the subsequent lack of miscibility of Ag and Bi bulk phases. After completion of the dealloying process, Bi(110) thin films can be grown epitaxially on top of Ag(111) with a chemically abrupt interface.

Emergent Dirac fermion states underlie many intriguing properties of graphene, and the search for them constitute one strong motivation to explore two-dimensional (2D) allotropes of other elements. Phosphorene, the ultrathin layers of black phosphorous, has been a subject of intense investigations recently, and it was found that other group-Va elements could also form 2D layers with similar puckered lattice structure. Here, by a close examination of their electronic band structure evolution, we discover two types of Dirac fermion states emerging in the low-energy spectrum. One pair of (type-I) Dirac points is sitting on high-symmetry lines, while two pairs of (type-II) Dirac points are located at generic $k$-points, with different anisotropic dispersions determined by the reduced symmetries at their locations. Such fully-unpinned (type-II) 2D Dirac points are discovered for the first time. In the absence of spin-orbit coupling, we find that each Dirac node is protected by the sublattice symmetry from gap opening, which is in turn ensured by any one of three point group symmetries. The spin-orbit coupling generally gaps the Dirac nodes, and for the type-I case, this drives the system into a quantum spin Hall insulator phase. We suggest possible ways to realize the unpinned Dirac points in strained phosphorene., 30 pages, 6 figures

By measuring the growth data of Scutellaria baicalensis in different cutting-seedling and determined active ingredient contents by HPLC and ultraviolet spectrophotometric determination. such as flavonoids. baicalin. wogonoside. baicalein. wogonin. oroxylin A. scutellarin. luteolin. and apigenin in the whole plant. Under circumstances of guaranteeing the quality and yield of medicinal materials. the yield of medicinal materials. and stems and leaves reached 193.60,63.21 kg/mu after twice cutting seedling. Not only yield but also active ingredient contents have been improved to some extent. the contents of flavonoids. baicalin. wogonoside. baicalein. wogonin. oroxylin A reached 18.52%. 15.13%. 4.03%. 1.04%. 1.04%. 0.12%. respectively in roots. Luteolin was not detected in young stems and leaves of S. baicalensis,the contents of other active ingredients such as scutellarin. luteolin and apigenin reached 7.00%. 0.96%. 0.04% respectively under twice cutting seedling. Therefore. regular cutting seedling could be regard as a new cultivation technique for wider range of promotion. And gaining high quality and yield of medicinal materials and tea with the purpose of rational utilization of natural resources and promoting the development of integration of herbal combination.

The surface morphology of Mn, Sb and MnSb nanostructures grown on highly-oriented pyrolytic graphite (HOPG) has been studied in detail with scanning tunneling microscopy in ultrahigh vacuum. At the initial stage of growth, three dimensional (3D) clusters and islands of Mn, Sb and MnSb are formed at step edges and other defect sites. In middle stage, crystalline 2D islands and 1D nanorods of Sb can be observed together with crystalline 3D islands, whereas single- and double-layer cluster chains of Mn are obtained at room temperature (RT). MnSb crystallites form after deposition of both Mn and Sb on HOPG surface and annealing at T ~ 375 K. The ex-situ X-ray photoemission spectroscopy measurement revealed the formation of MnSb compound on graphite. Ferromagnetism was observed at RT for the 50-nm MnSb thin film using vibrating sample magnetometer.

The adsorption of S2 on the Si(1 1 1)-(7 × 7) surface and the interaction of copper and sulfur on this sulfur-terminated Si(1 1 1) surface have been studied using synchrotron irradiation photoemission spectroscopy and scanning tunneling microscopy. The adsorption of S2 at room temperature results in the passivation of silicon dangling bonds of Si(1 1 1)-(7 × 7) surface. Excessive sulfur forms Sn species on the surface. Copper atoms deposited at room temperature directly interact with S-adatoms through the formations of Cu–S bonds. Upon annealing the sample at 300 °C, CuSx nanocrystals were produced on the sulfur-terminated Si(1 1 1) surface.

We report the fabrication of one-dimensional (1D) Bi nanowires grown on Ag(1 1 1) with average lateral width from 9 to 20 nm by physical vapor deposition in ultra high vacuum conditions. In situ low-temperature scanning tunneling microscopy analyses reveal that the preferred growth of 1D Bi nanostructures is driven by the highly anisotropic bonding in the crystallographic structure of the Bi(1 1 0) plane. The Bi nanowires grow along Bi [ 1 1 ¯ 0 ] direction and align with the [ 1 1 ¯ 0 ] directions on Ag(1 1 1). The growth of the Bi nanowires proceeds in a bilayer growth mode resulting from the layer pairing in Bi(1 1 0) which saturates the dangling bonds and lowers the total energy.

The growth and surface morphology of indium and aluminum nanostructures on highly oriented pyrolytic graphite (HOPG) and molybdenum disulphide (MoS 2 ) surfaces were investigated using scanning tunneling microscopy in ultra-high vacuum. Mostly triangular and hexagonal In islands with (111) orientation were obtained along the steps of HOPG at room temperature (RT). Triangular, round-shape and large irregular In islands were found on MoS 2 surfaces at different growth conditions. Al island chains as well as isolated triangular islands were found on HOPG whereas nanoparticles and ramified Al islands were obtained on MoS 2 at RT. The shapes of these self-assembled metal nanostructures were controlled by varying growth conditions. The different shapes of nanostructures on these inert substrates can be explained in terms of differences in energetic and kinetic properties of atoms and clusters of each elements as well as the nature of substrates.

We demonstrate the growth of Fe-induced magic clusters on Si(1 1 1)-(7 × 7) template by in situ scanning tunneling microscopy (STM). These clusters form near a dimer row at one side of the half-unit cell (HUC); and with three different equivalent orientations. A cluster model comprising three top layer Si atoms bonded to six Fe atoms at the next layer in the 7 × 7 faulted-half template is proposed. The optimized cluster structure determined by first-principles total-energy calculation shows an inward-shifting of the three center Fe atoms. The clusters and the nearby center-adatoms of the next HUCs appear with a significantly reduced height below bias voltages 0.4 V in high resolution empty-state STM images, suggesting an energy gap opening near the Fermi level at these localized cluster and adatom sites. We explain the stabilization of the clusters on the 7 × 7 template using the gain in electronic energy as the driving force for cluster formation.

We present a study on the adsorption and thermal decomposition of C 60 on Co covered Si(111)-7 × 7 using scanning tunneling microscopy and X-ray photoelectron spectroscopy. Co-induced magic clusters grown on Si(111)-7 × 7 are identified as a possible adsorption site where 51 ± 3% of C 60 molecules adsorb at room temperature. On Co/Si(111)-7 × 7, C 60 molecules start to decompose at 450 °C, and are completely dissociated to form SiC by 720 °C. This temperature is significantly lower than 910 °C at which C 60 completely dissociates on clean Si(111)-7 × 7. This is a possible low temperature method for growing crystalline SiC films using C 60 as a precursor molecule.

We present a scanning tunnelling microscopy (STM) investigation of Co silicide cluster and island formation on Si(111)-(7 × 7). We identify sub-nanometre clusters, which we propose to be the precursors to Co silicide nucleation and growth. The observation of metastable phases and various domains on the surface suggest significant Si rearrangement during silicide formation. Surface diffusion of both Si and type-1 clusters plays a vital role in the nucleation of Co silicide islands. With the help of density functional theory calculations, we propose a model for the surface structure of atomically flat CoSi2(111)-(2 × 2) islands.

Germanium was deposited onto highly oriented pyrolytic graphite (HOPG) with and without antimony in ultra-high vacuum. The surface morphology was analyzed using in situ scanning tunneling microscopy (STM) at room temperature (RT). The film grows exclusively in 3D island mode and was affected significantly by substrate defects. At initial stage, nucleation of cluster occurred at step edges and defect sites. Later, we found various types of Ge nanostructures on HOPG in different deposition conditions and stages, including cluster chains, cluster islands, nanowires, and double layer ramified islands at RT. Compact Ge islands were observed when depositing at a substrate temperature of 450 K or after an annealing at 600 K following RT deposition. In addition, the pre-deposited Sb on graphite enhances the sticking probability and suppresses the surface diffusion of Ge atoms, resulting in a significant increase in Ge cluster island density on HOPG terraces.

Growth of Ge , Al and Sb on highly oriented pyrolytic graphite (HOPG) was systematically investigated using in situ scanning tunneling microscopy (STM). At room temperature (RT), three dimensional (3D) clusters of all three elements nucleate and grow at the step edges and defect sites of HOPG. The clusters of Al and Ge form chains, while Sb islands are mostly isolated. With further deposition at RT, Al clusters grow and coarsen into faceted islands with craters on the top (111) facets, whereas ramified single- and double-layer cluster islands are observed for Ge . When deposited or annealed at T ≥ 175° C , Ge forms crystallites but with randomly oriented facets. As spherical Sb islands grow beyond certain size, (111) facets appear on the top. Additionally, crystalline 2D films and 1D nanorods are observed for Sb deposited at RT. At T ≈ 100° C and higher flux, only the 2D and 1D Sb islands are formed. These different growth behaviors reflect the unique nature in which the atoms (molecules), clusters and crystallites of each element interact with HOPG surface and with each other.

Antimony islands of different shapes and dimensions were grown on highly oriented pyrolytic graphite (HOPG) at room temperature in ultrahigh vacuum. Three-dimensional (3D) spherical, 2D thin films and 1D nanorods of Sb on graphite were studied using in situ scanning tunnelling microscopy. Sb was evaporated in the form of Sb4, which interacts with HOPG weakly and exhibits a high surface mobility, resulting in preferential nucleation of 3D spherical islands at defect sites. Surface diffusion and aggregation lead to the formation of nanoparticles with various shapes and sizes. The shape and size of islands depend on growth parameters, i.e. flux and deposition time. The 3D and 2D structures of Sb on graphite have the same bulk crystalline rhombohedral (α-Sb) structure, but the 1D nanorods show a highly compressed structure different from the α-Sb lattice.

Germanium was deposited onto highly oriented pyrolytic graphite (HOPG) with and without antimony in ultra-high vacuum. The surface morphology was analyzed using in situ scanning tunneling microscopy (STM) at room temperature (RT). The film grows exclusively in 3D island mode and was affected significantly by substrate defects. At initial stage, nucleation of cluster occurred at step edges and defect sites. Later, we found various types of Ge nanostructures on HOPG in different deposition conditions and stages, including cluster chains, cluster islands, nanowires, and double layer ramified islands at RT. Compact Ge islands were observed when depositing at a substrate temperature of 450 K or after an annealing at 600 K following RT deposition. In addition, the pre-deposited Sb on graphite enhances the sticking probability and suppresses the surface diffusion of Ge atoms, resulting in a significant increase in Ge cluster island density on HOPG terraces.

Growth of Ge, Al and Sb on highly oriented pyrolytic graphite (HOPG) was systematically investigated using in situ scanning tunneling microscopy (STM). At room temperature (RT), three dimensional (3D) clusters of all three elements nucleate and grow at the step edges and defect sites of HOPG. The clusters of Al and Ge form chains, while Sb islands are mostly isolated. With further deposition at RT, Al clusters grow and coarsen into faceted islands with craters on the top (111) facets, whereas ramified single- and double-layer cluster islands are observed for Ge. When deposited or annealed at T ≥ 175°C, Ge forms crystallites but with randomly oriented facets. As spherical Sb islands grow beyond certain size, (111) facets appear on the top. Additionally, crystalline 2D films and 1D nanorods are observed for Sb deposited at RT. At T ≈ 100°C and higher flux, only the 2D and 1D Sb islands are formed. These different growth behaviors reflect the unique nature in which the atoms (molecules), clusters and crystallites of each element interact with HOPG surface and with each other.

The role of a Si spacer layer in improving the uniformity of multilayer coherent Ge quantum dots on Si(001) is investigated using scanning tunneling microscopy. Deposition of the Si spacer layer at room temperature and subsequent annealing lead to the formation of (001)-oriented Si mesas on top of Ge islands (pyramids and huts). One mesa forms when the island beneath is pyramid-like, whereas a few mesas form when the island beneath is an elongated hut. The mesas are found to be preferential nucleation sites for the Ge islands in consecutive stacked layers. The vertical-pyramid-replicating and hut-breaking processes play key roles in the improvement of island size, shape and spacing uniformity.

Evolution and ordering of multilayer Ge islands (up to 14 layers) on Si (001), prepared by physical vapor deposition at about 550°C; were studied using Scanning Tunneling Microscope (STM). In the growth process, it was observed that long huts split during the deposition of Si buffer layer. It can be explained as a consequence of strain due to lattice mismatch and intermixing of Si and Ge to form solid solution. Such a mechanism of splitting could lead the dots to order and uniformity in the subsequent layers. Apart from splitting of huts, the surface corrugation of Si spacer layer influences the nucleation of Ge islands in the next layer.

The binding and interaction of Cu on Si(1 1 1)-(7 × 7) at room temperature have been studied using scanning tunneling microscopy. Self-organized growth of ordered Cu nanostructures was observed. At low coverage, the two-dimensional Cu nanostructures are predominantly assembled at the faulted halves of the (7 × 7) unit cells. High coverage leads to Cu-binding on the unfauled halves. Our results also show that the two-dimensional nanostructure consists of six Cu-atoms with three on the center adatoms and the others on the rest atoms within one half of a unit cell. The Cu nanostructure formed may have potential applications in the fabrication of nanoscale devices and chemical modification of semiconductor surfaces.

Calculated band structure of a few bilayer (BL) Sb films with and without SOC. (a) 1 BL, (c) 2 BL, (e) 4 BL, (g) 5 BL, and (i) 10 BL with SOC; (b) 1 BL, (d) 2 BL, (f) 4 BL, (h) 5 BL, and (j) 10 BL without SOC. Figure S2. Calculated band structures of H-covered a few bilayers (BL) Sb films with SOC: (a) 1 BL, (b) 2 BL, (c) 4 BL, (d) 5 BL, (e) 6 BL, and (f) 10 BL. Figure S3. Calculated band structures of Ag-covered a few bilayers (BL) Sb films with SOC: (a) 1 BL, (b) 2 BL, (c) 4 BL, (d) 5 BL, (e) 6 BL, and (f) 10 BL. Figure S4. Calculated band structures of a few BL Sb films with two surface covered by O atoms by considering SOC: (a) 4 BL and (b) 5 BL. Figure S5. Calculated band structures of 3-BL Sb films with two surface covered by Au atoms by considering SOC. (DOC 131 kb)

Perfectly ordered arrays of identical Al and Ga clusters of nanometre size and spacing were spontaneously obtained using a novel technique, in which surface-mediated magic clustering is used to achieve the identical cluster size while the Si(111)-7 × 7 surface is used as a template for positioning the clusters in order. The atomic structures, formation mechanism and stability of the nanoclusters were studied with in situ scanning tunnelling microscopy combined with first-principles total energy calculations. The very high stability of these nanocluster arrays provides unprecedented opportunities for exploring new physical phenomena and great potential in technological applications.

The nucleation and growth of Si and Ge clusters/crystallites on SiNx films, which act as relative inert substrates, proceed in a quite complicated manner compared with conventional epitaxial processes. We examine the size dependence of the shape, surface structures and orientation of nano-scale clusters/crystallites. Facets are not observed until the crystallite diameter reaches ~40 nm. Due to the isotropic surface energy and a weak interaction with the substrate, the orientation of the clusters/crystallites is random initially. A preferred orientation, however, emerges on crystalline SiNx films as the crystallite size increases. The growth nature of nano-particles, their interactions with the substrates and among themselves determine the overlayer texture as the amount of material deposition increases.

The growth modes of Ge islands on SiNx-covered Si with and without a surfactant Sb layer are studied by scanning tunnelling microscopy. It is observed that on SiNx/Si(111), Sb cannot enhance the coverage of (111) facets of Ge islands, which are the dominant features in the late stage of Ge overlayer growth when Sb is not used. However, on SiNx/Si(001), Sb favours the growth of Ge(001) facets, which will shrink during the islanding growth if Sb is not used. The different behaviours with the (111) and (001) substrates suggest that the surfactant effect of Sb on the islanding growth of Ge on SiNx/Si is strongly orientation dependent.

The growth of Si and Ge on silicon nitride surfaces has been investigated using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and Auger electron spectrometer (AES). In the early stages, Si or Ge nanoclusters appeared irrespective of the different substrates. When annealed, the Si clusters were more stable against coalescence than those of Ge. As these clusters continued to grow, crystalline facets started to form. Both Si and Ge islands grew predominantly with (111)-oriented top facets on the crystalline Si 3 N 4 (0001)/Si(111). By contrast, they both grew in random orientation on the amorphous Si 3 N 4 surface. Low-index facets such as (111) and (001) coexisted with high-index facets such as (113).

The surface of Si(1 1 1) exposed to NH3 or NO is analyzed with scanning tunneling microscopy, low-energy electron diffraction (LEED), Auger electron spectroscopy, and transmission electron microscopy. Crystalline silicon nitride thin films are formed on Si(1 1 1) after nitridation at T>1075 K. Corresponding to the 8×8 LEED pattern, a 30.7-A periodic superstructure is observed. The film thickness is saturated at 20 A. Among all known Si3N4 phases, the nitride film on Si(1 1 1) probably is β-Si3N4, then the 30.7-A superstructure is the 4×4 reconstruction on Si3N4(0 0 0 1). The possibility that the film is a new silicon nitride phase also exists. An 8/3×8/3 quasi-periodic structure is formed at T⩽1075 K or when the gas purity is degraded. The “quadruplet” LEED spots are related to carbon contamination. Etching happens during nitridation, which limits the nitride film thickness. Impurities in the nitridant enhance etching. The effectiveness of different nitridants is discussed.

Endohedral metallofullerene Tb@C82 molecules adsorbed on the C60 film and Si(100) 2 × 1 have been investigated by scanning tunneling microscopy (STM). The C60 film was obtained by depositing 2−3 monolayers (ML) of C60 molecules on a highly oriented pyrolytic graphite (HOPG) surface. Tb@C82 molecules have great mobility and aggregate along the edges of terraces on the C60 film, and form a close-packing monolayer with increasing coverage. Very few trimers or dimers were imaged on the surface of C60 film. In contrast, the Tb@C82 molecules were randomly distributed on the surface of Si(100). These nucleation behaviors of Tb@C82 molecules can be explained by the interaction of Tb@C82−Si and Tb@C82−Tb@C82 that were brought on by the permanent dipole moment of Tb@C82 molecules.

Silicon carbide(SiC) nano-crystallites are formed by the thermal reaction of C60 molecules with silicon atoms on Si(0 0 1) and Si(1 1 1) surfaces at 900–11508C. The surface morphologies and structures of the cubic b-SiC islands on Si(0 0 1) and Si(1 1 1) are investigated in situ using scanning tunneling microscopy. Comparing to bulk SiC crystals, distinctive atomic structures are formed on the surfaces of the SiC crystallites: a (2 � 3) on SiC(0 0 1) and a ð2 ffiffiffi 3 p �

The surface structures of 3C–SiC(1 1 1) crystallized islands formed by thermal chemical reaction between silicon substrate and adsorbed C 60 molecules at high temperatures are studied using ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The STM images show a strong bias voltage dependence, transforming between (2×2), (2 3 ×2 3 ) - R 30° and Y-type patterns under different bias voltages. A surface atomic structural model containing quarter coverage of vacancies and three different sites of surface silicon atoms is proposed to interpret the experimental observations. The dangling bond electronic states contributed by these different site Si atoms on the outermost surface layer and by the carbon atoms surrounding the vacancies are suggested to be responsible for the different tunneling conditions under different bias voltages in STM images.

After exposing Si(111) to NH 3 at about 1075 K, a 10.2-A surface periodic structure (the ‘8/3×8/3’ reconstruction) is observed in scanning tunneling microscopy images. When the nitridation temperature is above 1125 K, a silicon nitride film with a surface superstructure with a period of 30.7 A and a minimum step height of 2.9 A is obtained. Our systematic analyses suggest that the 30.7-A superstructure is the 4×4 reconstruction on the Si 3 N 4 (0001) surface of the crystalline silicon nitride ( β -Si 3 N 4 ) thin film formed on Si(111), while the 10.2-A periodic structure is an incomplete nitridation phase on Si(111) surface. The surface structure has been found to be sensitive to the impurities in NH 3 .

Atomic force microscope lithography has been used to create a variety of Si structures on Si(001). Oxide mask thicknesses of 1–3 nm are needed to produce structures of 300–400 nm in height during KOH etching. Processes for cleaning the structures following transfer into ultrahigh vacuum (UHV) were investigated, and only chemical pre-cleaning followed by flashing to 1200°C in UHV was found to result in clean surfaces without carbide pinning centers. This procedure results in unavoidable smoothing of the initially prepared structures. A structure of 275 nm initial height and nominal initial side-wall angle of 54.7° decays to a height of 80 nm and an angle of approximately 5° during the cleaning process. The decay of initially square ‘doughnut’ structures following sequential anneals in UHV was measured as a function of cumulative annealing time. The inside of the square rounds quickly, but the outside maintains an appreciable square asymmetry even after a decay to half of its post-clean height. The inner region of the square shows an initial decrease in height, and then fills in as the walls broaden in the late stages of decay. The rounding observed in the interior region of the structure is consistent with the behavior recently reported for the decay of biperiodic structures on Si(001).

We have studied changes in surface morphology of vicinal Si(111) surfaces with a miscut of 1.3° in the [ 2 11] direction after Al deposition at elevated temperatures. The clean surface phase separates into a (111)-oriented phase and a stepped phase. Submonolayer Al deposition at 650°C, the normal preparation temperature of the Al/Si(111)- ( 3 × 3 ) R30° structure, only induces minor changes in the surface morphology. However, after Al deposition at temperatures above the order–disorder phase transition temperature, the step bunches break apart into a uniform array of single height steps with an average step–step separation determined by the macroscopic miscut. From a quantitative analysis of the amount of meandering of steps and the terrace width distribution, we determined the diffusivity of steps and the strength of the repulsive step–step interaction. The repulsive interaction between steps is enhanced by the Al adsorption compared to both the high-temperature (1×1) and (7×7) phases of the clean surface.

To investigate the effects of chemisorption on step energetics, Si surfaces miscut by 1.2° to 12° from the (111), as well as Si(335) and Si(112), have been exposed to bromine, and studied using scanning tunneling microscopy. As the atomic structure on (111) terraces changes from the (7 × 7) or (5 × 5) reconstruction to a (1 × 1) after Br exposure and annealing at 800-900 K, the density of triple-layer steps on samples miscut towards [211] decreases dramatically. The structures of the steps themselves have been measured with high resolution. The edges of a triple step on the Br-covered surfaces resembles a (112) facet, while it is (113)-like on a clean surface. Br-chemisorption extends the miscut angle range over which the sample can be described as a vicinal Si(111) surface from ≤14° for clean Si to ∼19°. Analysis of kink densities shows that step diffusivity on Br-covered surfaces is governed by the intrinsic step misorientation as on the clean surfaces, however the kink size is registered to the 1 × 1 lattice on the Br-covered surface. The measured terrace width distributions are the same on the clean and Br-covered surfaces, indicating the same ratio of step diffusivity to direct step-interaction energy. The coexistence of single and triple steps on both the clean and Br-chemisorbed surfaces can be described semi-quantitatively with a model based on elasticity theory. The analysis shows that the reduced triple-step density is due to both the seven-fold decrease in step-step repulsion energy and the seven-fold increase in triple-step formation energy after Br-chemisorption. On the equilibrium step-bunched structures that form on surfaces miscut towards [211], removal of the 7 × 7 reconstruction during halogen exposure and annealing below 900 K does not break the step-bunching.