Combined SPM investigation on the interfacial structure of a phthalocyanine/conjugated polymer composite film

The morphology of the composite film of organic semiconductors determines the properties and performances of devices to a large extent. In this work, we present a combined AFM and STM study on the interfacial structures of CuPcOC8 and CuPcOC8/PmPV composite films on graphite surface. For CuPcOC8 thin films, the face-on epitaxial growth of CuPcOC8 could persist within 3 to 5 monolayers and the formation of π-π stacked columns will occur with edge-on configuration when the film thickness further increases. For the CuPcOC8/PmPV composite film with 1:1 weight ratio, STM results reveal a preferential adsorption of PmPV on graphite surface, while AFM results indicate the phase segregation in the upper layer. STM also reveals in the molecular scale good compatibility of CuPcOC8 with PmPV.     

New insight into the solid electrolyte interphase with use of a focused ion beam

The formation and evolution of the solid electrolyte interphase (SEI) film on the surface of natural graphite spheres in the electrolyte of 1 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) were investigated with use of focused ion beam (FIB) technology. Secondary electron FIB images clearly show the surface and cross-section morphology of the SEI film. The composition variation along the surface and cross section of the SEI film was also explored by the elemental line scan analysis (ELSA). The initial SEI film with an apparent thickness range of approximately 450 to approximately 980 nm is rough in morphology and nonuniform in composition, and contains small splits. After certain electrochemical cycles, the thickened SEI film displays microscale holes and obvious cracks on the surface, and the content of organic compounds increases. In addition, the concept of "internal SEI film" is first proposed based on the characterization of the cross section of the natural graphite spheres with the aid of FIB. Finally, the capacity fading mechanisms of the natural graphite spheres corresponding to different electrochemical stages are discussed.     

石墨负极在Et4NBF4+LiPF6/EC+PC+DMC电解液中的电化学行为

在PC+EC+DMC复合溶剂体系中, 研究了Et4NBF4(四氟硼酸四乙基铵)与LiPF6组成的复合盐电解质对石墨负极材料界面性质的影响. 用循环伏安和恒电流充放电测试方法研究了电解液与石墨负极的相容性, 通过傅里叶变换红外光谱(FTIR)对固体电解质中间相膜(SEI)的成分变化进行了研究. 结果表明, 电解液中的Et4NBF4参与了SEI膜的形成; 当Et4NBF4浓度为0.2 和0.5 mol·L-1时, 电池首次充放电不可逆容量损失明显减少, 循环效率分别上升到76.0%和81.6%. Et4NBF4/LiPF6复合盐电解质改善了PC基电解质与石墨负极的相容性.     

Segregation and Stability in Surface Alloys: PdxRu1−x/Ru(0001) and PtxRu1−x/Ru(0001)

The stability of PdRu/Ru(0001) and PtRu/Ru(0001) surface alloys and the tendency for surface segregation of Pd and Pt subsurface guest metals in these surface alloys is studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). Atomic resolution STM imaging and AES measurements reveal that upon overgrowing the surface alloys with a 1–2 monolayer Ru film and subsequent annealing to the temperatures required for initial surface alloy formation, the Ru‐covered Pd (Pt) atoms float back to the outermost layer. The lateral distribution of these species is also essentially identical to that of the initial surface alloys, before overgrowth by Ru. In combination, this clearly demonstrates that the surface alloys represent stable surface configurations, metastable only towards entropically favored bulk dissolution, and that there is a distinct driving force for surface segregation of these species. Consequences of these data on the mechanism for surface alloy formation are discussed.     

二氟二草酸硼酸锂对LiFePO4/石墨电池高温性能的影响

研究了二氟二草酸硼酸锂(LiODFB)作为锂盐加入到碳酸丙烯酯(PC)+碳酸乙烯酯(EC)+碳酸甲乙酯(EMC)(质量比为1:1:3)混合溶剂中对LiFePO4/石墨电池高温(60 ℃)循环性能的影响. 用线性扫描伏安法(LSV)测试了电解液的电化学窗口. 通过等离子发射光谱(ICP)和能量散射光谱(EDS)对LiFePO4材料高温条件下在不同电解液中的稳定性进行了研究; 并用扫描电镜(SEM)和电化学交流阻抗谱(EIS)分析了石墨负极表面的固体电解液相界面(SEI)膜的热稳定性. 结果表明: 一方面LiODFB基电解液能抑制LiFePO4材料在高温条件下Fe(II)的溶解, 防止溶解的Fe(II)在石墨上还原, 有效地降低电池阻抗; 另一方面, 在LiODFB基电解液中形成的石墨负极表面SEI膜具有更好的热稳定性, 能显著提高LiFePO4/石墨电池的高温循环性能.     

Solvent‐induced surface instability of thin metal films on a polymer substrate

The solvent‐provoked formation and evolution of thin film buckling‐delamination on a compliant substrate have been studied. The film surface is observed by an optical microscope showing a remarkable dynamic buckling‐delamination development and a subsequent stable branched‐straight state. It is revealed that the initiation, propagation, and the resulting patterns of film buckles are strongly dependent on the solvent type, film stress, interfacial adhesion, and film thickness. The buckling could be controlled further by a reasonable chemical solvent configuration and used to provide useful information for the pattern creation on polymer systems in diverse fields, such as micro/nanofabrication and optics.     

An approach of evaluating the effect of vinylene carbonate additive on graphite anode for lithium ion battery at elevated temperature

An approach is proposed to evaluate the VC effect in a LiFePO₄/graphite cell at 60 °C through liquid chromatography mass spectrometry (LC-MS) together with direct analysis in real time mass spectrometry (DART-MS). The LC-MS result shows that VC can effectively suppress the formation of phosphate esters as well as carbonate oligomers during the electrochemical cycling. It is also known from DART-MS analysis that VC assists the formation of thermally resistant oligomeric phosphate ester layer on the graphite surface, storing more solvent EC inside the layer. On the other hand, no compounds are observed on the LiFePO₄ cathode surface. The formation of the denser oligomeric phosphate ester layer is found to be the reason for the improved cycle stability of the cell cycled at elevated temperature.     

Manipulating double-decker molecules at the liquid-solid interface

We have used a scanning tunneling microscope (STM) to manipulate heteroleptic phthalocyaninato, naphthalocyaninato, and porphyrinato double-decker (DD) molecules at the liquid-solid interface between 1-phenyloctane solvent and graphite. We employed nanografting of phthalocyanines with eight octyl chains to place these molecules into a matrix of heteroleptic DD molecules; the overlayer structure is epitaxial on graphite. We have also used nanografting to place DD molecules in matrices of single-layer phthalocyanines with octyl chains. Rectangular scans with a STM at low bias voltage resulted in the removal of the adsorbed DD molecular layer and substituted the DD molecules with bilayer-stacked phthalocyanines from phenyloctane solution. Single heteroleptic DD molecules with lutetium sandwiched between naphthalocyanine and octaethylporphyrin were decomposed with voltage pulses from the probe tip; the top octaethylporphyrin ligand was removed, and the bottom naphthalocyanine ligand remained on the surface. A domain of decomposed molecules was formed within the DD molecular domain, and the boundary of the decomposed molecular domain self-cured to become rectangular. We demonstrated a molecular "sliding block puzzle" with cascades of DD molecules on the graphite surface.     

Deposition of densely packed gold film on an alkane derivative monolayer modified graphite surface

The growth of thin metal films is an important step in the fabrication of electronic and magnetic devices. In this work, an atomically flat graphite surface was used as a model system to understand the details of gold film growth mechanisms and kinetics. Ordered assembling monolayers of 1‐octadecanethiol and stearic acid are used to modify the surface and uniform, densely packed ultrathin gold film with the thickness less than 5 nm are formed on these monolayer‐modified graphite surfaces in a large area. The amount of gold needed to be deposited in order to form a continuous gold film is significantly reduced as compared to that needed on a bare graphite surface. Copyright © 2006 John Wiley & Sons, Ltd.     

Room‐Temperature Synthesis of Covalent Organic Frameworks with a Boronic Ester Linkage at the Liquid/Solid Interface

With various prospected applications in the field of nanoelectronics and catalysis, on‐surface synthesis of single‐layer covalent organic frameworks (surface COFs) with designable structures and properties have attracted enormous interest. Herein, we report on a scanning tunneling microscopic investigation of the surface‐confined synthesis of a covalently bonded boronic ester network directly at the octanoic acid/ highly oriented pyrolytic graphite(HOPG) interface under room temperature. The dynamic reaction process was investigated in detail. STM results indicate that the surface networks undergo structural evolution from a hybrid covalent/noncovalent multiwall porous network to single‐wall hexagonal COF with the decrease of monomer concentration. Further experimental observation disclosed that the boronic ester‐linked system is sensitive to instantaneous voltage pulses and the stimulation of the STM tip. In addition, the ¹H NMR spectra has further confirmed that the surface and octanoic acid may play important roles in promoting the reaction between 4,4′‐phenylazobenzoyl diboronic acid (ABBA) and 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) building units.     

Self‐Assembled Monolayers of Alkoxy‐Substituted Octadehydrodibenzo[12]annulenes on a Graphite Surface: Attempts at peri‐Benzopolyacene Formation by On‐Surface Polymerization

Self‐assembled monolayers of a series of tetraalkoxy‐substituted octadehydrodibenzo[12]annulene (DBA) derivatives 1 c – g possessing butadiyne linkages were studied at the 1,2,4‐trichlorobenzene (TCB) or 1‐phenyloctane/graphite interface by scanning tunneling microscopy (STM). The purpose of this research is not only to investigate the structural variation of two‐dimensional (2D) monolayers, but also to assess a possibility for peri‐benzopolyacene formation by two‐dimensionally controlled polymerization on a surface. As a result, the formation of three structures, porous, linear, and lamella structures, were observed by changing the alkyl chain length and the solute concentration. The formation of multilayers of the lamella structure was often observed for all compounds. The selection of molecular networks is basically ascribed to intermolecular and molecule–substrate interactions per unit area and network density. The selective appearance of the linear structure of 1 d is attributed to favorable epitaxial registry matching between the substrate lattice and the overlayer lattice. Even though the closest interatomic distance between the diacetylenic units of the DBAs in the lamella structure (≈0.6 nm) is slightly larger compared to the typical distances necessary for topochemical polymerization, the reactivity toward external stimuli (electronic‐pulse irradiation from an STM tip and UV irradiation) was investigated. Unfortunately, no evidence for polymerization of the DBAs on the surface was observed. The present results indicate the necessity for further designing a suitable system for the on‐surface construction of structurally novel conjugated polymers, which are otherwise difficult to prepare.     

二氟草酸硼酸钠作为电解液添加剂对石墨负极性能的影响

锂离子电池日益广泛的应用对其性能提出越来越高的要求,而在电解液中加入适当的添加剂能够显著提升电极材料的电化学性能. 本文首次在1 mol·L^-1 LiPF₆/EC + DMC + EMC（体积比1:1:1）的电解液中添加一定量的二氟草酸硼酸钠(NaDFOB),并通过循环伏安（CV）、电化学阻抗图谱（EIS）和扫描电子显微镜（SEM）等分析考察了其对石墨负极材料性能的具体影响. 结果显示,添加NaDFOB的电解液显著提高了石墨材料在常温下的可逆充放电容量和循环性能,同时明显改善了石墨材料的高温循环性能. 其机理在于NaDFOB的阴阳离子同时参与了石墨表面固体电解质界面膜（SEI）的形成,形成高稳定性的电解液/电极界面.     

Photochemical Reactions in Self‐Assembled Organic Monolayers Characterized by using Scanning Tunneling Microscopy

Research on the supramolecular self‐assembly behavior at interfaces is of great importance to improving the performance of nanodevices that are based on optical functional materials. In this Minireview, several photoinduced isomerization and polymerization reactions in self‐assembled organic monolayers on surfaces are discussed. Typical organic molecules contain azobenzene, alkynyl, or olefins groups. The feature surface base is a highly oriented pyrolytic graphite (HOPG) surface or a gold surface. Scanning tunneling microscopy (STM) is used as a strong tool to characterize new species’ structures before and after illumination.     

Role of solution structure in the electrochemical intercalation of Ca2+ into graphite layers

In this study, we investigated the electrochemical intercalation of Ca²⁺ into graphite as an anode material for calcium-ion batteries (CIBs). The electrochemical intercalation of Ca²⁺ into a graphite electrode is possible when γ-butyrolactone (GBL) is utilized as a solvent, resulting in a reversible charge/discharge capacity. The GBL-based electrolyte allows a reversible redox reaction, thereby resulting in the intercalation and deintercalation of Ca²⁺ within the graphite electrode. Conversely, Ca²⁺ cannot be intercalated between the graphite layers in the ethylene carbonate–diethyl carbonate (EC–DEC)–based electrolyte. Analyses of the solution structures of both cases indicated that the interaction between the GBL solvent and Ca²⁺ was weak whereas that between the EC–DEC solvent and Ca²⁺ was strong. As a result of analyzing the surface of the negative electrode after charging and discharging from XPS, it was confirmed that a component that seems to be a solid electrolyte interphase (SEI) was confirmed in the graphite electrode using the GBL-based electrolyte.

     

Bilayer Molecular Assembly at a Solid/Liquid Interface as Triggered by a Mild Electric Field

The construction of a spatially defined assembly of molecular building blocks, especially in the vertical direction, presents a great challenge for surface molecular engineering. Herein, we demonstrate that an electric field applied between an STM tip and a substrate triggered the formation of a bilayer structure at the solid–liquid interface. In contrast to the typical high electric‐field strength (10⁹ V m^?1) used to induce structural transitions in supramolecular assemblies, a mild electric field (10⁵ V m^?1) triggered the formation of a bilayer structure of a polar molecule on top of a nanoporous network of trimesic acid on graphite. The bilayer structure was transformed into a monolayer kagome structure by changing the polarity of the electric field. This tailored formation and large‐scale phase transformation of a molecular assembly in the perpendicular dimension by a mild electric field opens perspectives for the manipulation of surface molecular nanoarchitectures.     

Synthesis, aggregation, and adsorption phenomena of shape-persistent macrocycles with extraannular polyalkyl substituents

The synthesis of shape-persistent macrocycles based on the phenyl-ethynyl backbone containing various extraannular alkyl side chains is described. Although compound solubility increases with increasing size of the side groups, decreasing the solvent polarity induces aggregation of the rings by nonspecific interactions. This was investigated by proton NMR spectroscopy. The magnitude of aggregation can be varied by using solvent mixtures of different hexane content, supporting the model of a solvophobic effect. From 1,2,4-trichlorobenzene solution the macrocycle 1c adsorbs at the surface of highly oriented pyrolitic graphite (HOPG). The two-dimensional order of the structure was investigated by scanning tunneling microscopy (STM) revealing the formation of a two-dimensional lattice of p1(2)mm symmetry with lattice parameters A = 3.6 nm, B = 5.7 nm, and Gamma = 74 degrees.     

Self‐Assembly of a Mononuclear [FeIII(L)(EtOH)2] Complex Bearing an n‐Dodecyl Chain on Solid Highly Oriented Pyrolytic Graphite Surfaces

The synthesis and structures of the N‐[(2‐hydroxy‐3‐methyl‐5‐dodecylphenyl)methyl]‐N‐(carboxymethyl)glycine disodium salt (H L ) ligand and its neutral mononuclear complex [Fe^III( L )(EtOH)₂] ( 1 ) are reported. Structural and electronic properties of 1 were investigated by using scanning tunneling microscopy (STM) and current imaging tunneling spectroscopy (CITS) techniques. These studies reveal that molecules of 1 form well‐ordered self‐assemblies when deposited on a highly oriented pyrolytic graphite (HOPG) surface. At low concentrations, single or double chains (i.e., nanowires) of the complex were observed, whereas at high concentration the complex forms crystals and densely packed one‐dimensional structures. In STM topographies, the dimensions of assemblies of 1 found on the surface are consistent with dimensions obtained from X‐ray crystallography, which indicates the strong similarities between the crystal form and surface assembled states. Double chains are attributed to hydrogen‐bonding interactions and the molecules align preferentially along graphite defects. In the CITS image of complex 1 a strong tunneling current contrast at the positions of the metal ions was observed. These data were interpreted and reveal that the bonds coordinating the metal ions are weaker than those of the surrounding ligands; therefore the energy levels next to the Fermi energy of the molecule should be dominated by metal‐ion orbitals.     

Nanometer-scale ordering in cast films of columnar metallomesogen as revealed by STM observations

STM observations were performed on a cast film of a columnar metallomesogen ([Cr(5C8)3]; 5C8 = 1-(3,4,5-trioctyloxyphenyl)-3-(3,4-dioctyloxyphenyl)propane-1,3-dionate anion) on a graphite surface, revealing the nanometer-scale surface ordering into an oblique lattice (a = 10.5 nm, b = 11.5 nm, alpha = 55 degrees) possibly due to the DeltaLambda-chiral interactions.     

Template-assisted assembly: scanning tunneling microscopy study of solvent-dependent adlattices of alkyl-derivatized tetrathiafulvalene

The self-assembly of an adsorbate as a function of the strength of solvent-substrate adsorption is an important yet relatively unexplored subject. In this study, how the strength of solvent-substrate adsorption and solvent-solvent attraction affects the assembly of tetrakis(octadecylthio)tetrathiafulvalene (1) is scrutinized by scanning tunneling microscopy (STM). For solvents with strong intermolecular interactions and adsorption onto graphite, such as long n-alkanes (C(n)H(2n+2), n ≥ 13), STM reveals that the solvent molecules form lamellae which become a template to direct the assembly of 1 into one-dimensional arrays. The lengths of one of the unit cell vectors for the assemblies are increased and well correlated with the solvent sizes. In situ STM monitoring of 1 introduced onto graphite with preadsorbed n-tetradecane adlattices shows that the developed assemblies of 1 have striped features aligned parallel to the underlying template. In contrast, for solvents with weak adsorption, such as short n-alkanes (C(n)H(2n+2), n ≤ 12), toluene, and 1,2,4-trichlorobenzene, the adlattice structures of 1 are solvent-independent.