Formation of Extended Covalently Bonded Ni Porphyrin Networks on the Au（lll） Surface

The growth and ordering of {5,10,15,20-tetrakis(4-bromophenyl)porphyrinato}nickel(II) (NiTBrPP) molecules on the Au(111) surface have been investigated using scanning tunnelling microscopy, X-ray absorption, core-level photoemission, and microbeam low-energy electron diffraction. When deposited onto the substrate at room temperature, the NiTBrPP forms a well-ordered close-packed molecular layer in which the molecules have a flat orientation with the porphyrin macrocycle plane lying parallel to the substrate. Annealing of the NiTBrPP layer on the Au(111) surface at 525 K leads to dissociation of bromine from the porphyrin followed by the formation of covalent bonds between the phenyl substituents of the porphyrin. This results in the formation of continuous covalently bonded porphyrin networks, which are stable up to 800 K and can be recovered after exposure to ambient conditions. By controlling the experimental conditions, a robust, extended porphyrin network can be prepared on the Au(111) surface that has many potential applications such as protective coatings, in sensing or as a host structure for molecules and clusters.     

Fe Nanoclusters on the Ge（001） Surface Studied by Scanning Tunneling Microscopy,Density Functional Theory Calculations and X-Ray Magnetic Circular Dichroism

The growth of Fe nanoclusters on the Ge(001) surface has been studied using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM results indicate that Fe nucleates on the Ge(001) surface, forming well-ordered nanoclusters of uniform size. Depending on the preparation conditions, two types of nanoclusters were observed having either four or sixteen Fe atoms within a nanocluster. The results were confirmed by DFT calculations. Annealing the nanoclusters at 420 K leads to the formation of nanorow structures, due to cluster mobility at such temperature. The Fe nanoclusters and nanorow structures formed on the Ge(001) surface show a superparamagnetic behaviour as measured by X-ray magnetic circular dichroism.      

Anomalous moire pattern of graphene investigated by scanning tunneling microscopy： Evidence of graphene growth on oxidized Cu（111）

The growth of graphene on oriented （111） copper films has been achieved by atmospheric pressure chemical vapor deposition. The structural properties of as-produced graphene have been investigated by scanning tunneling microscopy. Anomalous moir6 superstructures composed of well-defined linear periodic modulations have been observed. We report here on comprehensive and detailed studies of these particular moir6 patterns present in the graphene topography revealing that, in certain conditions, the growth can occur on the oxygen-induced reconstructed copper surface and not directly on the oriented （111） copper film as expected.     

Self-Assembly and Ordering of C60 on the WO2/W（110） Surface

The growth and ordering of C₆₀ molecules on the WO₂/W(110) surface have been studied by low-temperature scanning tunnelling microscopy and spectroscopy (STM and STS), low-energy electron diffraction (LEED), and density functional theory (DFT) calculations. The results indicate the growth of a well-ordered C₆₀ layer on the WO₂/W(110) surface in which the molecules form a close-packed hexagonal structure with a unit cell parameter equal to 0.95 nm. The nucleation of the C₆₀ layer starts at the substrate’s inner step edges. Low-temperature STM of C₆₀ molecules performed at 78 K demonstrates well-resolved molecular orbitals within individual molecules. In the C₆₀ monolayer on the WO₂/W(110) surface, the molecules are aligned in one direction due to intermolecular interaction, as shown by the ordered molecular orbitals of individual C₆₀. STS data obtained from the C₆₀ monolayer on the WO₂/W(110) surface are in good agreement with DFT calculations.     

Steric and electronic selectivity in the synthesis of Fe- 1,2,4,5-tetracyanobenzene （TCNB） complexes on Au（111）： From topological confinement to bond formation

A study of the surface assisted self-assembly of 1,2,4,5-tetracyanobenzene （TCNB） acceptor molecules and Fe atoms on an Au（111） surface is presented. While conditions to get the two-dimensional arrays of stable Fe（TCNB）4 complexes are clearly identified, ultrahigh vacuum scanning tunneling microscopy and spectroscopy （STM/STS） coupled with first-principles calculations reveals that situations may occur where Fe and TCNB survive on the surface （as Fe-4TCNB entities） at a higher density than the original molecular monolayer without forming coordination bonds with each other. It is found that the square planar coordination of the Fe（TCNB）4 monomer complexes cannot fully develop in the presence of lateral strain due to growth-induced confinement. A phenomenon similar to steric hindrance involving a strongly modified chirality with a Fe-N-C bond angle of 120° compared to the 180° for the stable complex may then explain why the Fe atom keeps its metallic bond with the surface. The competition between steric and electronic effects, not reported before, may arise elsewhere in surface chemistry involved in the synthesis of new and potentially useful organic nanomaterials.     

锰硅化物在Si(111)-7×7表面的制备及其STM研究

利用超高真空扫描隧道显微镜研究了室温至610℃的条件下锰在Si(111)-7×7表面的反应生长情况,制备出了锰纳米团簇和几种锰硅化物。实验结果表明:温度低于260℃时,生成了占据在衬底7×7结构亚单胞上大小统一的锰纳米团簇;温度高于500℃时,生成的锰硅化物可分为三类:纳米线、平板状的岛和三维不规则的岛。除此以外,390℃至610℃锰硅化物岛的成核密度符合传统成核理论。     

锰硅化物在Si(111)-7×7表面的制备及其STM研究

利用超高真空扫描隧道显微镜研究了室温至610℃的条件下锰在Si(111)-7×7表面的反应生长情况,制备出了锰纳米团簇和几种锰硅化物.实验结果表明温度低于260℃时,生成了占据在衬底7×7结构亚单胞上大小统一的锰纳米团簇;温度高于500℃时,生成的锰硅化物可分为三类纳米线、平板状的岛和三维不规则的岛.除此以外,390℃至610℃锰硅化物岛的成核密度符合传统成核理论.     

An in situ STM study of cobalt electrodeposition on Au(111) in BMIBF4 ionic liquid

The initial stage of Co electrodeposition on Au(111) from CoCl₂ and Co(BF₄)₂ in a room-temperature ionic liquid of BMIBF₄ is investigated by in situ STM. Preferential nucleation of Co at structure imperfections of the reconstructed Au(111) surface is observed for deposition from CoCl₂ at a surprisingly negative potential (?2.05?V vs. Pt wire). Monoatomic-height Co clusters of 2–3?nm in diameter are formed, which develop into Co islands with size confinement of 3–4?nm after prolonged deposition. The large driving force required for Co deposition from CoCl₂ is attributed to the molecular type of the salt in the ionic liquid together with the tip shielding effect. This is proved by the pronounced difference of Co deposition from Co(BF₄)₂, which takes place at a much less negative potential and proceeds in a 3D progressive nucleation and growth mode without preference in nucleation sites. Surface alloying accompanies the island formation, which is confirmed by pit generation upon stripping of the Co islands. The results are discussed in comparison with features of Co deposition in UHV and in aqueous solutions.     

Assembling of redox proteins on Au(111) surfaces: A scanning probe microscopy investigation for application in bio-nanodevices

The morphology and conductive properties of azurin molecules, chemically attached to sulfhydryl terminated alkanethiol monolayer assembled on Au(111) surface, are mapped at single molecule level and compared with those observed for the same molecule immobilised on bare Au(111). High-resolution Tapping Mode Atomic Force Microscopy shows that the protein molecules immobilised on modified gold, better reproduces the crystallographic height of the protein, than that immobilised on bare gold. Such a height recovering is also found in the Scanning Tunnelling Microscopy images. Consistently, a good tunnelling conduction of azurins on the modified gold electrode is demonstrated by Tunnelling Spectroscopy. Cyclic voltammetry measurements show, in addition, that the redox activity of azurin molecules covalently immobilised on sulfhydryl functionalised Au(111) surface is retained. These results are discussed in connection with possible use of this linker in the assembling of nano-hybrid systems.     

Tuning the structures of two-dimensional cuprous oxide confined on Au(111)

Two-dimensional (2D) cuprous oxide (Cu₂O) nanostructures (NSs) of monolayer thickness were synthesized on Au(111) and characterized using atomic-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. The surface and edge structures of 2D Cu₂O were resolved at the atomic level and found to exhibit a graphene-like lattice structure. Cu₂O NSs grew preferentially at the face centered cubic (fcc) domains of Au(111). Depending on the annealing temperature, the shapes and structures of Cu₂O NSs were found to vary from elongated islands with a defective hexagonal lattice (mostly topological 5–7 defects) to triangular NSs with an almost-perfect hexagonal lattice. The edge structures of Cu₂O NSs also varied with the annealing temperature, from predominantly the arm-chair 56 structure at 400 K to almost exclusively the zig-zag structure at 600 K. DFT calculations suggested that the herringbone ridges of Au(111) confined the growth and structure of Cu₂O NSs on Au(111). As such, the arm-chair edges of Cu₂O NSs, which are less stable than the zig-zag edges, could be exposed preferentially at 400 K. Cu₂O NSs developed into the thermodynamically-favored triangular form and exposed zig-zag edges at 600 K, when the Au(111) substrate became mobile. The confined growth of 2D cuprous oxide on Au(111) demonstrated the importance of metal-oxide interactions in tuning the structures of supported 2D oxide NSs.

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Quasi-freestanding,striped WS2 monolayer with an invariable band gap on Au(001)

Revealing the structural/electronic features and interfacial interactions of monolayer MoS2 and WS2 on metals is essential to evaluating the performance of related devices.In this study,we focused on the atomic-scale features of monolayer WS2 on Au(001) synthesized via chemical vapor deposition.Scanning tunneling microscopy and spectroscopy reveal that the WS2/Au(001) system exhibits a striped superstructure similar to that of MoS2/Au(001) but weaker interfacial interactions,as evidenced by experimental and theoretical investigations.Specifically,the WS2/Au(001) band gap exhibits a relatively intrinsic value of ～ 2.0 eV.However,the band gap can gradually decrease to ～ 1.5 eV when the sample annealing temperature increases from ～370 to 720 ℃.In addition,the doping level (or Fermi energy) of monolayer WS2/Au(001) varies little over the valley and ridge regions of the striped patterns because of the homogenous distributions of point defects introduced by annealing.Briefly,this work provides an in-depth investigation into the interfacial interactions and electronic properties of monolayer MX2 on metal substrates.     

Gas-source molecular beam epitaxy of Si(111) on Si(110) substrates by insertion of 3C-SiC(111) interlayer for hybrid orientation technology

A method to realize a novel hybrid orientations of Si surfaces, Si(111) on Si(110), has been developed by use of a Si(111)/3C-SiC(111)/Si(110) trilayer structure. This technology allows us to use the Si(111) portion for the n-type and the Si(110) portion for the p-type channels, providing a solution to the current drive imbalance between the two channels confronted in Si(100)-based complementary metal oxide semiconductor (CMOS) technology. The central idea is to use a rotated heteroepitaxy of 3C-SiC(111) on Si(110) substrate, which occurs when a 3C-SiC film is grown under certain growth conditions. Monomethylsilane (SiH₃-CH₃) gas-source molecular beam epitaxy (GSMBE) is used for this 3C-SiC interlayer formation while disilane (Si₂H₆) is used for the top Si(111) layer formation. Though the film quality of the Si epilayer leaves a lot of room for betterment, the present results may suffice to prove its potential as a new technology to be used in the next generation CMOS devices.     

The mechanical properties and resistivity of Au/NiCr/Ta multi-layered films on Si-(111) substrate

Au/NiCr/Ta multi-layered metallic films were deposited on Si substrate by magnetron sputtering at different substrate temperatures. The residual stress, hardness and resistivity were investigated as a function of substrate temperature by laser polarization phase shift technique, nanoindentation technique and four point probe method, respectively. The residual stress in as-deposited films at different substrate temperatures was tension with 385 MPa-606 MPa. Nanoindentation tests at shallow indentation depths (h ≤ t/4) where the hardness is reliable for metal films on hard substrate. Au film at deposition temperature 200 °C has the highest hardness 4.2 GPa. The resistivity in the deposited films reached the lowest value 3.1 μΩ.cm at substrate temperature 200 °C. The most interesting facts are that the hardness decreases with increasing residual stress and resistivity increases with increasing residual stress. The relationship of residual stress and resistivity may hint that there is a definite correlation between the mechanical properties and electrical properties in the metallic films.     

Comparative study of surface morphology of copper phthalocyanine ultra thin films deposited on Si (111) native and RCA-cleaned substrates

Comparative study of substrate doping influence on surface morphology of 16-nm CuPc ultra-thin layers deposited on RCA-cleaned Si (111)/SiO₂ substrates was carried out. The structure and the morphology of thin films were investigated by X-ray photoelectron spectroscopy and atomic force microscopy. The investigations were aimed to provide information whether substrate doping type can be used as one of the parameters for engineering of the sensing layers structure. Atomic force microscopy images and results of photoemission experiments did not reveal any significant differences in morphology and surface chemistry between used substrates. Observed differences in surface morphology of organic overlayer could be caused by different substrate doping. The CuPc film grown on p-type RCA-Si (111) shows a compact network of densely packed crystallites, while the CuPc film deposited on n-type RCA-Si (111) reveals a slightly more open network of larger crystallites. These observations are confirmed by values of roughness, which is 0.97 nm and 1.47 nm for CuPc film on RCA-cleaned p- and n-type substrates, respectively. Results were compared with data obtained for similar 16-nm-thick CuPc layers deposited on n- and p-type Si (111) covered with native oxide. Good agreement between results of both studies was found out.     

Growth of columnar aluminum nitride layers on Si(111) by molecular beam epitaxy

Single crystalline aluminum nitride (AlN) thin films are deposited by molecular beam epitaxy (MBE) using thermally evaporated aluminum and RF-plasma excited nitrogen gas. In this paper we report on films grown on Si(111) at substrate temperatures of 800° with growth rates between 65 and 350 nm h⁻¹. All layers consist of hexagonal and exactly c-axis oriented AlN crystals with column-like structure. For the smoothest layers surface roughness (rms) around 1 nm is obtained. In the XRD-spectra (ω-scan) we have achieved a minimum FWHM of 0.4° (=25′) for the AlN(00.2) reflex. At maximum growth rates (350 nm h⁻¹) for AlN a transition zone of about 200 nm is formed with high defect density compared to the subsequent growth. For lower growth rates (65 nm h⁻¹) no transition zone exists. Application of a substrate nitridation leads to a partial loss of epitaxial relation between AlN layer and Si(111)-substrate.     

Si(111)表面亚稳态重构的STM研究

利用扫描隧道显微镜 (STM) ,研究了Si(111)表面的 2× 2、c2× 4、9× 9和 11× 11等各种亚稳态结构。与已经发表的研究结果相比 :2× 2和c2× 4重构区域规则且面积更大 ,原子分辨的图像清晰稳定 ;在不同亚稳态之间的畴界处 ,发现存在2种不同的环形结构。从原子密度和能量两方面 ,对各种亚稳态重构的形成机制进行了讨论