THE PREPARATION OF TITANIUM OXIDE OVERLAYER ON Fe(110) FOR SURFACE SCIENCE STUDIES

The preparation, characterization and properties of titania overlayer on Fe(110) substrate is hereby reported. The TiO_X overlayer was found to form in a layer-by-layer mode with a suboxide of titanium in the form of TiO migrating into the Fe substrate and Fe migrating into the deposited layer of TiO_X simultaneously during the deposition.

Surface science approach to the heterogeneous cycloaddition of CO_(2) to epoxides catalyzed by site-isolated metal complexes and single atoms: a review

The cycloaddition of CO_(2) to epoxides to afford cyclic organic carbonates is an increasingly relevant non-reductive strategy to convert CO_(2) to useful products able to serve as high-boiling solvents,chemical intermediates,and monomers for the preparation of more sustainable polymers.The development of efficient and robust hetero-geneous catalysts for such transformation is,therefore,crucial and can be carried out by several strategies that often require the preparation of sophisticated and/or expensive organic networks,linkers,or compounds.A different approach to the preparation of heterogeneous catalysts for CO_(2)-epoxide coupling is by applying surface science methodologies to graft molecular fragments or single atoms on various supports leading to well-defined active sites.In this context,surface organometallic chemistry(SOMC),along with comparable methodologies,is a valuable approach for the preparation of efficient,single-site Lewis acids and catalysts for the target cycloaddition reaction on metal oxides,whereas,other grafting methodologies,can be applied to prepare analogous catalysts on different kinds of surfaces.Finally,we discuss very recent advances in the application of surface methodologies for the preparation of single atom catalysts as an increasingly relevant approach towards highly active Lewis acids for the cycloaddition of CO_(2) to epoxides.Overall,we show that Lewis acids and catalysts prepared by facile surface methodologies hold significant potential for future application is the synthesis of cyclic carbonates from CO_(2).

Combination of a reaction cell and an ultra-high vacuum system for the in situ preparation and characterization of a model catalyst

An in-depth understanding of the structure-activity relationship between the surface structure,chemical composition,adsorption and desorption of molecules,and their reaction activity and selectivity is necessary for the rational design of high-performance catalysts.Herein,we present a method for studying catalytic mechanisms using a combination of in situ reaction cells and surface science techniques.The proposed system consists of four parts:preparation chamber,temperatureprogrammed desorption(TPD)chamber,quick load-lock chamber,and in situ reaction cell.The preparation chamber was equipped with setups based on the surface science techniques used for standard sample preparation and characterization,including an Ar+sputter gun,Auger electron spectrometer,and a low-energy electron diffractometer.After a well-defined model catalyst was prepared,the sample was transferred to a TPD chamber to investigate the adsorption and desorption of the probe molecule,or to the reaction cell,to measure the catalytic activity.A thermal desorption experiment for methanol on a clean Cu(111)surface was conducted to demonstrate the functionality of the preparation and TPD chambers.Moreover,the repeatability of the in situ reaction cell experiment was verified by CO_(2) hydrogenation on the Ni(110)surface.At a reaction pressure of 800 Torr at 673 K,turnover frequencies for the methanation reaction and reverse water-gas shift reaction were 0.15 and 7.55 Ni atom^(-1) s^(-1),respectively.

Selectivity control in alkyne semihydrogenation:Recent experimental and theoretical progress

Researchers have been attempting to characterize heterogeneous catalysts in situ in addition to correlating their structures with their activity and selectivity in spite of many challenges.Here,we review recent experimental and theoretical advances regarding alkyne selective hydrogenation by Pd‐based catalysts,which are an important petrochemical reaction.The catalytic selectivity for the reaction of alkynes to alkenes is influenced by the composition and structure of the catalysts.Recent progress achieved through experimental studies and atomic simulations has provided useful insights into the origins of the selectivity.The important role of the subsurface species(H and C)was revealed by monitoring the catalyst surface and the related catalytic performance.The atomic structures of the Pd catalytic centers and their relationship with selectivity were established through atomic simulations.The combined knowledge gained from experimental and theoretical studies provides a fundamental understanding of catalytic mechanisms and reveals a path toward improved catalyst design.

Microstructure and sliding wear behavior of pseudo-alloy PS45/CuAl8 composite coating sprayed by HVAA technique

A pseudo-alloy PS45/CuAl8 composite coating was sprayed on steel substrate by high-velocity activated arc spraying (HVAA) process. Its sliding wear behavior at room temperature was evaluated by M-2000 wear tester. For comparison, a single CuAl8 coating was also prepared and tested under the same conditions. It is found that the pseudo-alloy composite coating consists of α-Cu and γ-Ni metallic matrix phases together with homogenously distributed minor Al 2 O 3 , Cr 2 O 3 oxide phases. Moreover, pseudo-alloy coating possesses much better sliding wear resistance than CuAl8 coating due to the enhanced hardness and microstructural homogenization. Fatigue wear and abrasive wear are responsible for the wear-down mechanism of the pseudo-alloy coating.

MOSSBAUER STUDY ON REDUCIBILITY OF SUPPORTED Eu_2O_3

The reduction process of Eu2O3 on TiO2 and other supports is investigated in detail by Mossbauer spectroscopy. The reducibility of Eu2O3 is greatly enhanced when it is supported on a surface of support. This is due to the solid-solid interaction between the oxide and the support.

Experimental evidence of surface copper boride

To validate the crystal structure and elucidate the formation mechanism of the unexpected surface copper boride,a systematic scanning tunneling microscope,X-ray photoelectron spectroscopy,angle-resolved photoemission spectroscopy,and aberrationcorrected scanning transmission electron microscopy investigations were conducted to confirm the structure of copper-rich boride Cu_(8)B_(14)after depositing boron on single-crystal Cu(111)surface under ultrahigh vacuum.First-principles calculations with defective surface models further indicate that boron atoms tend to react with Cu atoms near terrace edges or defects,which in turn shapes the intermediate structures of copper boride and leads to the formation of stable Cu-B monolayer via large-scale surface reconstruction eventually.

Review of ice-pavement adhesion study and development of hydrophobic surface in pavement deicing

Ice adhesion to materials is a significant concern in many fields. Hydrophobic surface has been used for anti-icing in fields of aircraft or transmission line, which prove to be efficacious and economical. However, such technique is seldom employed for road deicing, because of the texture and service environment of pavement. Instead, deicers such as rock salt are frequently used, which leads to serious corrosion problem of roads and bridges. In this paper, a number of studies that characterize mechanism of ice adhesion to common substrates, specifically to pavement, are reviewed. The most important researches undertaken on ice adhesion strength affecting factors are presented. An overview of studies carried out to find hydrophobie surface for asphalt and cement concrete pavement antiicing are presented. It was verified that the hydrophobicity had high correlation with icephobicity, and nano-engineered asphalt and cement concrete pavement surface exhibited favorable hydrophobicity, and also had good performance on weakening pavement-ice bonding. However, most ice-repelling pavements obtain hydrophobic surface via low surface energy coating, which could not exist on pavement for a long time under wheel abrasion. And the nano/micro structures on hydrophobic surfaces are also vulnerable and consumable. Thus, the long-term effect of hydrophobic surface still need to be improved, and durability of the hydrophobic surface should be the research and development priorities of ice-repelling pavement.

Retrospect and prospect of Geographical Sciences in China： A comparison with the Strategic Directions for Geography in the USA

Understanding the Changing Planet： Strategic Directions for the Geographical Sciences （UCP）, published by the National Research Council （USA）, and its comments in The Professional Geographer propose that uppercase and plural ＂Geographical Sciences＂ （GS） is the strategic direction for geography in the next decade for better understanding of our rapidly changing planet. According to these comments, UCP valued technologies and tools exces- sively （＂task＂）, and did not pay much attention to methodology （＂discipline＂）. Actually, both ＂task＂ and ＂discipline＂ are geographical wings, especially in the time of ＂big science＂. Enlightenment from UCP and its comments is the strategic direction that should be balanced between ＂task＂ and ＂discipline＂, GS should be a three-dimensional construct of a disciplinary system, methodology, and technologies and tools, and this system should be scientific hu- manism based on scientific spirit and directed by humanism. During the last 60 years, Chi- nese geographers devoted themselves to GS, including practice and theory. Obviously pro- gress and outlook are proposed as interdisciplinary GS, Earth Surface Sciences （ESS） and Geographical Construction （GC）. The disciplinary system of GS is very complex, and is composed of such human knowledge domains as sciences, technologies, engineering, and philosophy. The main mission is to research the open, complex, and macro earth system （not only scientifically, but also humanistically）, and one significant methodology is ＂comprehen- sive integration of qualitative and quantitative means＂ （CIQQM）. At the same time, another changing direction in Chinese geography is Human-Economic Geography （HEG）.

Self-Organized Growth of Complex Nanotube Patterns on Crystal Surfaces

The organization of carbon nanotubes into well-dened straight or curved geometries and arrays on surfaces is a critical prerequisite for their integration into nanocircuits and a variety of functional nanosystems.We review the recent development of a new approach to carbon nanotube organization based on self-organized growth directed by well-defined crystal surfaces,or“nanotube epitaxy”.We identify three different modes of surface-directed growth,namely by atomic rows,atomic steps,and nanofacets.Particular emphasis is given here to the combinations of such surface-directed growth with external forces-like those exerted by an electriceld or gas o-wfor the creation of well-de-ned complex geometries,including crossbar architectures,serpentines,and coils.

Supercritical angle Raman microscopy: a surfacesensitive nanoscale technique without field enhancement

Raman scattering microscopy is a versatile tool for label-free imaging and molecular fingerprint analysis.Here,we provide the first demonstration that the selective collection of scattered signals exceeding the critical angle for total internal reflection enables surface-confined spontaneous Raman investigations at nanometre resolution.This high-axial selectivity leads to improved signal-to-background ratios,thus making this technique an excellent probe for surface-related molecular specimens.The richness of the spectroscopic information obtained through the supercritical angle Raman(SAR)collection path was proven by comparing its output with that of a parallel far-field collection path.Furthermore,we demonstrated that the proposed SAR technique is a versatile microscopy approach that can be used alone or in combination with amplified Raman modalities such as surfaceenhanced resonance Raman scattering.

Liquid-phase epitaxy of metal organic framework thin films

Metal-organic framework(MOF) thin films are multilayer materials ranging from nanometers to micrometers in thickness,physically or chemically adhesive to a(functionalized) substrate and,in an ideal case,exhibiting low roughness and high homogeneity.Various innovative approaches have been developed for MOF thin film fabrication.Among these advanced materials,surface-attached metal-organic frameworks(SURMOFs) are an important class of MOF films.SURMOFs,fabricated in a step-by-step liquid phase epitaxial(LPE) fashion by alternating deposition of metal and organic linker precursors on a functionalized substrate,for example,thiolate-based self-assembled monolayers(SAMs),have already exhibited their utility in both research and potential applications.SURMOFs combine surface science and the chemistry of MOFs,possessing the following unique advantages that cannot be accessed through other methods:(i) precisely controlling thickness,roughness and homogeneity as well as growth orientation,(ii) studying of MOF growth mechanism,(iii) modifying/tailoring MOFs' structures during the SURMOF growth and thus creating customizable properties,and(iv) existing in the form of thin film/membrane for direct applications,for example,as sensors.This review discusses the oriented and crystalline SURMOFs fabricated by LPE approach,covering their preparation,growth mechanism,and characterization methodology as well as applications based upon the most newly updated knowledge.

Building 2D quasicrystals from 5-fold symmetric corannulene molecules

The formation of long-range ordered aperiodic molecular films on quasicrystalline substrates is a new challenge that provides an opportunity for further surface functionalization. This aim can be realized through the smart selection of molecular building blocks, based on symmetry-matching between the underlying quasicrystal and individual molecules. It was previously found that the geometric registry between the C60 molecules and the 5- and 10-fold surfaces was key to the growth of quasiperiodic organic layers. However, an attempt to form a quasiperiodic C60 network on i-Ag-In-Yb substrates was unsuccessful, resulting in disordered molecular films. Here we report the growth of 5-fold symmetric corannulene C20H10 molecules on the 5-fold surfaces of i-Ag-In-Yb quasicrystals. Low-energy electron diffraction （LEED） and scanning tunneling microscopy （STM） revealed long-range quasiperiodic order and 5-fold rotational symmetry in self-assembled corannulene films. Recurrent decagonal molecular rings were seen, resulting from the decoration of specific adsorption sites with local pentagonal symmetry by corannulenes, adsorbed with their bowl-openings pointing away from the surface. They were identified as （Ag, In）-containing rhombic triacontahedral （RTH） duster centers and pentagonal Yb motifs, which cannot be occupied simultaneously due to steric hindrance. It is proposed that symmetry-matching between the molecule and specific substrate sites drives this organization. Alteration of the molecular rim by the introduction of CH substituents appeared to increase molecule mobility on the potential energy surface and facilitate trapping at these specific sites. This finding suggests that rational selection of molecular moiety enables the templated self-assembly of molecules leading to an ordered aperiodic corannulene layer.

Self-assembly of L-tryptophan on Cu(111) studied by low-temperature scanning tunneling microscopy

The self-assembly of L-tryptophan on Cu(111) is investigated by an ultrahigh vacuum scanning tunneling microscope(STM) at 4.4 K.When deposited onto the substrate at around 120 K with a coverage of 0.1 monolayer,molecular trimers,tetramers,hexamers,and chains coexist on Cu(111).Then almost all molecules self-assemble into chiral hexamers after being annealed at room temperature.When increasing molecular coverage to the full layer,a new type of chain is observed on the surface.Based on the high-resolution STM images at sub-molecular level,we suggest that the L-tryptophan molecules are present in neutral,zwitterionic or anionic states in these structures.