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A basic understanding of thermalproperties of polymers is of fundamentalimportance for the development of advanced polymers. However, up tonow, mainly bulk properties have been investigated. To characterizelocal softening processes in polymers, a local thermal analysis (LTA)technique is applied as an add-on to a scanning probe microscope.The development of a new generation of heatable cantilever probesenables thermal analysis in the sub-μm range. This method isbased on an appropriate temperature calibration, which provides areliable correlation of the applied voltage heating the tip and theactual temperature at the tip–sample interface. As the presentedtechnique is more susceptible to environmental changes than comparablemacroscopic methods, different parameters that might influence itsperformance are evaluated like a strong dependence on sample temperature.It is shown that the measured softening temperature on a polystyrene(PS) sample decreases from 102.2 to 66.4 °C as the temperatureof the substrate is increased by 50 °C. The interaction betweenheat from the cantilever and the substrate is the reason for localsample softening, which opens new perspectives to understand the temperaturecalibration process using the melting standard method. A stepwiseguideline for a suitable temperature calibration is provided. [ABSTRACT FROM AUTHOR]

Three-dimensional polypyrrole microcapsules were prepared via chemical deposition of the polymer onto tetradecanol particles supported on solid substrates. The growing polymer deposited onto the particle surface yielded hemispherical containers that encapsulated the tetradecanol contents. Mixing the tetradecanol with other chemical species, like fluorescent dyes, allowed the entrapment of these species within the containers. It was shown that by controlling the temperature, one could reversibly melt and solidify the tetradecanol content of the capsules. The tuning of the fluorescence intensity emitted from the capsules could thus be controlled. The polypyrrole structures were characterized using several complementary experimental methods. These included microscopic (scanning electron microscopy, atomic force microscopy, and optical microscopy) and spectroscopic techniques (steady-state fluorescence, ultraviolet-visual light absorption, and infrared spectroscopy) as well as conductivity and contact angle measurements. [ABSTRACT FROM AUTHOR]

Compaction of DNA by cationic gemini surfactant hexamethylene-1,6-bis-(dodecyldimethylammoniumbromide) (C 12C 6C 12Br 2) and the subsequent decompaction of the DNA−C 12C 6C 12Br 2complexes by β-cyclodextrin (β-CD) or sodium dodecyl sulfate (SDS) have been studied by using ζ potential and particle size measurements, atomic force microscopy (AFM), isothermal titration microcalorimetry (ITC), and circular dichroism. The results show that C 12C 6C 12Br 2can induce the collapse of DNA into densely packed bead-like structures with smaller size in an all-or-none manner, accompanied by the increase of ζ potential from highly negative values to highly positive values. In the decompaction of the DNA−C 12C 6C 12Br 2complexes, β-CD and SDS exhibit different behaviors. For β-CD, the experimental results suggest that it can remove the outlayer hydrophobically bound C 12C 6C 12Br 2molecules from the DNA−C 12C 6C 12Br 2complexes by inclusion interaction, and the excess β-CD may attach on the complexes by forming inclusion complexes with the hydrocarbon chains of the electrostatically bound C 12C 6C 12Br 2that cannot be removed. The increase of steric hindrance due to the attachment of β-CD molecules results in the decompaction of the DNA condensates though the true release of DNA cannot be attained. However, for SDS, the experimental results suggest that it can realize the decompaction and release of DNA from its complexes with C 12C 6C 12Br 2due to both ion-pairing and hydrophobic interaction between SDS and C 12C 6C 12Br 2. [ABSTRACT FROM AUTHOR]

The effect of electrochemical reduction on the single-molecule conductance of fullerene C 60derivatives was studied by scanning tunneling microscopy. Three types of C 60derivatives were synthesized, a monoadduct having an amino-terminated linker and two bisadducts having two linkers at different positions (trans2 and trans3). Each C 60derivative was immobilized on a gold surface by an amino−gold linkage, confirmed by infrared reflection−absorption spectroscopy. The immobilized C 60derivatives showed reversible and multiple reduction peaks in the cyclic voltammogram in dimethylformamide (DMF) at almost the same potentials as those in solution, showing the redox properties of the molecules are intact on gold. Single-molecule conductances of the bisadducts, which can span between a scanning tunneling microscopy (STM) tip made of gold and substrate with the two linkers, were determined by the STM break-junction measurements in water and DMF. The conductances were 6.1 ± 4.5 nS in water and 4.9 ± 1.7 nS in DMF for the trans2 bisadduct and 8.4 ± 3.4 nS in water and 7.9 nS ± 2.8 in DMF for the trans3 bisadduct. By using a potential-controlled STM setup, the tunneling current through a single molecule was recorded with sweeping the potentials of the tip and substrate. The trans2 bisadduct showed significant changes in the current when the reductions of the C 60moiety occur. Some current curves showed multiple peaks, and the other curves showed stepwise increase and decrease at the C 60reduction and subsequent reoxidation. Statistical analysis afforded stepwise switching of the conductance as the average behavior and suggested that the electron tunneling through the C 60derivative is enhanced as it accepts electrons. [ABSTRACT FROM AUTHOR]

We studied the thermal response of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphoethanolamine (POPE) by comparing the differential scanning calorimetry (DSC) data of liposomes with atomic force microscopy (AFM) observations on supported planar bilayers. Planar bilayers were obtained by using the Langmuir−Blodgett (LB) technique: the first leaflet transferred at 30 mN m −1and the second at 25 mN m −1. The topographic evaluation of supported POPE bilayers above room temperature showed changes between 43.8 and 59.8 °C. These observations are discussed in relation to the main roughness ( R a) variations and are interpreted as the result of the lamellar liquid crystalline ( Lα) to inverted hexagonal ( HII) phase transition. High-magnification images obtained at 45 °C revealed intermediate structures in the transformation. Force spectroscopy (FS) was subsequently applied to gain further structural and nanomechanical insight into the POPE planar bilayers as a function of temperature. These measurements show that the threshold force ( Fy), which is the maximum force, that the sample can withstand before breaking, increases from 1.91 ± 0.11 nN at 21 °C up to 3.08 ± 0.17 nN at 43.8 °C. This behavior is interpreted as a consequence of the formation of intermediate structures or stalks in the transition from the Lαto HIIphase. [ABSTRACT FROM AUTHOR]

We have investigated the effect of well-defined nanoscale topography on the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicle adsorption and supported phospholipid bilayer (SPB) formation on SiO2surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Unilamellar lipid vesicles with two different sizes, 30 and 100 nm, were adsorbed on pitted surfaces with two different pit diameters, 110 and 190 nm, as produced by colloidal lithography, and the behavior was compared to results obtained on flat surfaces. In all cases, complete bilayer formation was observed after a critical coverage of adsorbed vesicles had been reached. However, the kinetics of the vesicle-to-bilayer transformation, including the critical coverage, was significantly altered by surface topography for both vesicle sizes. Surface topography hampered the overall bilayer formation kinetics for the smaller vesicles, but promoted SPB formation for the larger vesicles. Depending on vesicle size, we propose two modifications of the precursor-mediated vesicle-to-bilayer transformation mechanism used to describe supported lipid bilayer formation on the corresponding flat surface. Our results may have important implications for various lipid-membrane-based applications using rough or topographically structured surfaces. [ABSTRACT FROM AUTHOR]

The adsorption of -phage DNA onto mica was investigated with atomic force microscopy. We found that the morphologies depended on the solvent conditions in the sample preparation procedure. Flat-lying networks of hybridized single-stranded DNA were obtained if ultrapure water was used. If buffered conditions are maintained during the whole of the preparation procedure, single double-stranded DNA molecules are adsorbed. The adsorbed double-stranded DNA molecules subsequently can be condensed in situ on the surface by a brief rinse with anhydrous ethanol in the presence of divalent magnesium cations. The majority of these surface-directed and ethanol-induced condensed structures are toroids, but a small fraction of rods also has been observed. Analysis of the height and lateral dimensions shows that the toroids are single-molecular and disk-like with a height of one to two DNA diameters. The thin toroid morphology appears to be a general phenomenon of surface-directed condensation, irrespective of the nature of the condensing ligands and the specific surface interaction. [ABSTRACT FROM AUTHOR]

Alternating layers of two different organic materials, Irganox1010 and Irganox3114, have been created using vapor deposition. The layers of Irganox3114 were very thin (∼2.5 nm) in comparison to the layers of Irganox1010 (∼55 or ∼90 nm) to create an organic equivalent of the inorganic ‘delta-layers' commonly employed as reference materials in dynamic secondary ion mass spectrometry. Both materials have identical sputtering yields, and we show that organic delta layers may be used to determine some of the important metrological parameters for cluster ion beam depth profiling. We demonstrate, using a C60ion source, that the sputtering yield, S, diminishes with ion dose and that the depth resolution also degrades. By comparison with atomic force microscopy data for films of pure Irganox1010, we show that the degradation in depth resolution is caused by the development of topography. Secondary ion intensities are a well-behaved function of sputtering yield and may be employed to obtain useful analytical information. Fragments characteristic of highly damaged material have intensity proportional to S, and those fragments with minimal molecular rearrangment exhibit intensities proportional to S2. We demonstrate quantitative analysis of the amount of substance in buried layers of a few nanometer thickness with an accuracy of ∼10%. Organic delta layers are valuable reference materials for comparing the capabilities of different cluster ion sources and experimental arrangements for the depth profiling of organic materials. [ABSTRACT FROM AUTHOR]

The contribution of entropy and enthalpy to the chair−boat conformational changes (clicks) occurring during the force−extension of single molecules of an axially linked polysaccharide, dextran, was investigated. Experimental single molecule force−extension measurements were carried out by atomic force microscopy over the temperature range of 5−70 °C. This enabled the separation of the entropy and enthalpy components of the conformational change. The contribution of entropy to the Gibbs energy of the conformational transformation was found to be small (<12 J mol-1K-1), demonstrating that the click is largely (>89%) enthalpic in nature. [ABSTRACT FROM AUTHOR]

In this work, the self-assembly of the DNA base molecule adenine (A) is imaged with high-resolution scanning tunneling microscopy (STM) at the liquid (1-octanol)/solid (HOPG) interface at room temperature. Rather surprisingly, the STM results reveal, for the first time, the spontaneous formation of two coexisting distinct (homo- and heterochiral) domains of adenine, which are formed at the liquid/solid interface without changing any experimental conditions. Ab initio density functional theory (DFT) calculations support our STM findings and suggest the existence of various A networks of nearly similar stability that all are constructed from the most stable A dimer. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30−70 °C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35−40 °C indicating that sublimation is not significant below 40 °C. Above 40 °C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110−135 °C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe. [ABSTRACT FROM AUTHOR]

Intrinsically self-stabilized nanoparticles of a copolymer from 4-sulfonic diphenylamine (SD) and pyrrole (PY) were facilely synthesized in HCl solution at 10 °C by a chemically oxidative polymerization. The critical reaction parameters such as SD/PY ratio, polymerization time, and oxidant species were studied to significantly optimize the polymerization yield, size, conductivity, and solubility of the final copolymer particles. The molecular structure, size, size distribution, and morphology of the particles were analyzed by IR spectroscopy, laser particle-size analysis (LPA), atomic force microscopy, and transmission electron microscopy (TEM). It was found that the polymerization yield of the SD/PY (50/50) copolymers increased dramatically in the initial 2 h of polymerization and then slowly enlarged in the subsequent 22 h. However, the copolymerization yield for the polymerization time of 24 h exhibited a nonlinear dependence on the SD/PY molar ratio, i.e., a maximum at 10/90 and a minimum at 80/20. The number-average diameter, Dn, of the copolymer particles strongly depended on the SD/PY ratio, decreasing rapidly from 6402 to 291 nm as the SD/PY molar ratio changed from 30/70 to 50/50, whereas the polydispersity index, PDI Dw/Dn(where Dwis the weight-average diameter), surprisingly maintained very small values, decreasing slightly from 1.21 to 1.08. The SD/PY (80/20) copolymer particles prepared with (NH4)2S2O8as the oxidant had the smallest size of ca. 10 nm by TEM and the lowest Dw/Dnvalue of 1.03 by LPA, whereas the copolymer particles prepared with FeCl3as the oxidant exhibited the second smallest size of ca. 20 nm by TEM and the highest conductivity. The conductivity of the SD/PY (50/50) copolymers rose first and then decreased with increasing polymerization time from 10 min to 24 h, exhibiting a maximum (0.217 S/cm) at 12 h. It is of interest that the copolymer particles with SD/PY molar ratios in the range between 50/50 and 80/20 surprisingly exhibited the smallest size, the narrowest size distribution, and the highest conductivity at the same time. In particular, the copolymer nanoparticles exhibited high purity, clean surfaces, good self-stability, high conductivity, and strong chemoresistance that were very important to nanomaterial processibility and application. The obtained copolymers were partially soluble in concentrated H2SO4, demonstrating a new direction for synthesizing a soluble pyrrole copolymer. [ABSTRACT FROM AUTHOR]

Adsorption structures formed from a class of planar organic molecules on the Au(111) surface under ultrahigh vacuum conditions have been characterized using scanning tunneling microscopy (STM). The molecules have different geometries, linear, bent, or three-spoke, but all consist of a conjugated aromatic backbone formed from three or four benzene rings connected by ethynylene spokes and functionalized at all ends with an aldehyde, a hydroxyl, and a bulky tert-butyl group. Upon adsorption, the molecules adopt different surface conformations some of which are chiral. For the majority of the observed adsorption structures, chirality is expressed also in the molecular tiling pattern, and the two levels of chirality display a high degree of correlation. The formation and chiral ordering of the self-assembled structures are shown to result from dynamic interchanges between a diffusing lattice gas and the nucleated islands, as well as from a chiral switching process in which molecules alter their conformation by an intramolecular rotation around a molecular spoke, enabling them to accommodate to the tiling pattern of the surrounding molecular structures. The kinetics of the conformational switching is investigated from time-resolved, variable temperature STM, showing the process to involve an activation energy of ∼0.3 eV depending on the local molecular environment. The molecule−molecule interactions appear primarily to be of van der Waals character, despite the investigated compounds having functional moieties capable of forming intermolecular hydrogen bonds. [ABSTRACT FROM AUTHOR]

A series of studies on microgel thin films is described, wherein quartz crystal microgravimetry (QCM), surface plasmon resonance (SPR), and atomic force microscopy (AFM) have been used to probe the properties of microstructured polymer thin films as a function of film architecture and solution pH. Thin films composed of pNIPAm-co-AAc microgels were constructed by using spin-coating layer-by-layer (scLbL) assembly with poly(allylamine hydrochloride) (PAH) as a polycationic “glue”. Our findings suggest that the interaction between the negatively charged microgels and the positively charged PAH has a significant impact on the pH responsivity of the film. These effects are observable in both the optical and mechanical behaviors of the films. The most significant changes in behavior are observed when the motional resistance of a quartz oscillator is monitored via QCM experiments. Slight changes to the film architecture and alternating the pH of the environment significantly changes the QCM and SPR responses, suggesting a pH-dependent swelling that is dependent on both particle swelling and polyelectrolyte de-complexation. Together, these studies allow for a deeper understanding of the morphological changes that take place in environmentally responsive microgel-based thin films. [ABSTRACT FROM AUTHOR]

A new intermittent-contactatomic force microscopy (AFM) mode (frequency and force modulation AFM, FFM-AFM) has been recently proposed to characterize soft samples. This method uses excitation force frequency and amplitude modulation to eliminate bistability and reduce the tip−sample forces. This letter describes theoretical modeling of FFM-AFM applied to a singlebacteriorhodopsin molecule on a substrate, showing that its cross section can be measured without damage, in contrast to conventional tapping-mode AFM. Speculations are made regarding nonideal conditions and the ability of FFM-AFM to perform quantitative nanoelasticity measurements. [ABSTRACT FROM AUTHOR]

We report a scanning tunneling microscopy (STM) investigation of a dinuclear organometallic molecule, trans-Cl(dppe)2Ru(C≡C)6Ru(dppe)2Cl (Ru2), absorbed on a Au(111) surface; this molecule is a potential candidate for use in molecular quantum-dot cellular automata (QCA) devices. Isolated Ru2molecules were observed under ultra-high-vacuum conditions. Submolecular structure was clearly discernible in the STM images, with a bright feature corresponding to each of the two Ru−ligand complexes within the Ru2molecule. Rotation and translation of the Ru2molecules were observed to be induced by the STM tip under some tunneling conditions. [ABSTRACT FROM AUTHOR]

While pore formation has been suggested as an important step in the membrane disruption process induced by antimicrobial peptides, membrane pore formation has never been directly visualized. We report on the dynamics of membrane disruption by antimicrobial peptide protegrin-1 (PG-1) on dimyristoyl-sn-glycero-phosphocholine-supported bilayer patches obtained via atomic force microscopy. The action of PG-1 is found to be concentration-dependent. At low PG-1 concentrations (1 < PG-1 < 4 g/mL), the peptide destabilizes the edge of the membrane to form fingerlike structures. At higher concentrations, PG-1 induces the formation of a sievelike nanoporous structure in the membrane. The highest degree of disruption is attained at concentrations ≥20 g/mL, at which PG-1 disrupts the entire membrane, transforming it into stripelike structures with a well-defined and uniform stripe width. This first direct visualization of these membrane structural transformations helps elucidate the PG-1-induced membrane disruption mechanism. [ABSTRACT FROM AUTHOR]

The growth and annealing behavior of ultrathin Au films on Pd111 were monitored with scanning tunneling microscopy (STM) and medium energy ion scattering (MEIS). The adsorption of acetic acid on both clean and deliberately carbon-contaminated bimetallic surfaces was investigated with reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD). We report that the surface chemistry of acetic acid is strongly modified by the presence of Au in the bimetallic surface which acts both to stabilize adsorbed acetate and to decrease the tendency of acetic acid to decompose on adsorption to produce adsorbed carbon. The adsorption of acetic acid at 300 K is found to cause measurable segregation of Pd to the surface for all surface compositions tested. [ABSTRACT FROM AUTHOR]

The chemisorptive bonding of methanethiolate (CH3S) on the Au(111) surface has been investigated at a single-molecule level using low-temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT). The CH3S species were produced by STM-tip-induced dissociation of methanethiol (CH3SH) or dimethyl disulfide (CH3SSCH3) at 5 K. The adsorption site of an isolated CH3S species was assigned by comparing the experimental and calculated STM images. We conclude that the S-headgroup of chemisorbed CH3S adsorbs on the 2-fold coordinated bridge site between two Au atoms, consistent with theoretical predictions for CH3S on the nondefective Au(111) surface. Our assignment is also supported by the freezing of the tip-induced rotational dynamics of a single CH3SH molecule upon conversion to CH3S via deprotonation. [ABSTRACT FROM AUTHOR]

In this study, we examined the influence of illumination and the presence of poly(ethylene oxide) (PEO) as an additive for the copper electrodeposition process onto n-Si(100). The study was carried out by means of cyclic voltammetry (CV) and the potential steps method, from which the corresponding nucleation and growth mechanism (NGM) were determined. Likewise, a morphologic analysis of the deposits obtained at different potential values by means of atomic force microscopy (AFM) was carried out. In a first stage, Mott−Schottky measurements so as to characterize the energetics of the semiconductor/electrolyte interface were made. Also, parallel capacity measurements were carried out in order to determine the surface state density of the substrate. It was found that when PEO concentration is increased, the number of these surface states decreases. The CV results indicated that the presence of PEO inhibits the photoelectrochemical reaction of oxide formation on the surface of the semiconductor. This allows a decrease in the overpotential associated with the electrodeposition process. The analysis of the j/ttransients shows that the NGM corresponds to progressive three-dimensional (3D) diffusional controlled (PN3DDiff), which was confirmed by the AFM technique. Neither illumination nor the presence of PEO changes the mechanisms. Their influence is in that they diminish the size of the nuclei and the speed with which these are formed, which produces a more homogeneous electrodeposit. [ABSTRACT FROM AUTHOR]

Using first-principles density-functional calculations, we investigated two competing pathways for the dissociation of water and ammonia on a Si(001) surface. For both systems, we found that, in addition to the conventionally accepted intradimer transfer of the H atom, the interdimer transfer of the H atom can be equally probable with the same reaction mechanism. Our analysis shows that the two dissociation pathways occur through the Lewis acid−base reaction between the partially positive H ion and the electron-abundant up atom of the buckled Si dimer. The result of the interdimer H transfer not only supports a recently proposed model for C-defect on Si(001) but also corresponds to the recent scanning tunneling microscopy data of ammonia dissociation on Si(001). [ABSTRACT FROM AUTHOR]

A direct conformational analysis using scanning tunneling microscopy (STM) has been performed for individual adsorbed -octithiophene molecules on Cu(100). s-cis and s-trans conformational isomers are induced by the rotational flexibility of individual thiophene rings. By adding bulky N-silyl substituents to octithiophene, we successfully identify the s-cis and s-trans conformational isomers using STM. The obtained relative abundances of the s-cis and s-trans conformations are analyzed using ab initiomolecular orbital calculations. [ABSTRACT FROM AUTHOR]

We study how a local air plasma treatment affects the mechanical properties of polystyrene by performing indentation measurements on the polymer in the elastic and plastic regime. The local exposure to plasma was obtained by placing a shadow-mask with quadratic holes of 45 × 45 m2on top of the polymer substrate, providing uncovered (exposed to the plasma) and covered (protected from the plasma) areas. We have analyzed quantitatively the topography and the elastic-plastic properties of such a sample with atomic force microscopy (AFM) measurements, both before and after plasma treatment. To enhance the differences between covered and uncovered areas, the sample has been exposed to solvent vapor. This generates regions which are differently swollen. The quantitative investigation of the mechanical properties of the swollen sample for different solvent exposure times gives further insight into the changes of polystyrene mechanical properties caused by the plasma. [ABSTRACT FROM AUTHOR]

Self-assembled structures of alkoxylated benzoccinnoline derivatives prepared on highly oriented pyrolytic graphite at room temperature from their solutions in solvents such as 1-phenyloctane, toluene, and 1-octanol were studied by scanning tunneling microscopy. The alkoxy chain length markedly affected the molecular conformations in 2-dimensional assemblies of these derivatives. Long-chain derivatives adopted the trans conformations more often than cis, whereas short-chain derivatives took exclusively the cis conformations in the self-assembled monolayers (SAMs). For the derivatives of intermediate chain lengths, polymorphism existed, with four molecular conformations identified experimentally. Experimental evidence substantiated the formation of chiral SAM structures at the surface, which can be explained by the conformations of the molecules. The chirality was also affected by the chain length of the molecules. A simple method analyzing the angles between different domains in the SAMs was used to identify the molecular conformations and to predict their relative structures. [ABSTRACT FROM AUTHOR]

Ultrathin ordered titanium oxide films on a Pt(111) surface have been prepared by reactive deposition and characterized by low-energy electron diffraction and scanning tunneling microscopy (STM). According to the postdeposition annealing condition, three different phases have been prepared which show a wagon-wheel-like (hereafter ww) morphological pattern. Two of them can be prepared as single phases (w-and w‘-TiOx) and one (wint-TiOx) as a mixed phase which always coexists with at least one of the other two phases. All of them are formed by a Ti−O bilayer, where the Ti atoms are located at the interface with the substrate, but they show a rather distinct STM wwpattern. The experimental STM contrast has been discussed on the basis of a Moiré-like model, i.e., as deriving from a modulation of the Ti occupancy of the different substrate sites (i.e., hollow, bridge and on-top sites). The major part of the STM data can be easily interpreted on the basis of this simplified model. [ABSTRACT FROM AUTHOR]

Uniform sized PMMA-beads were deposited as a monolayer on silicon substrates using dip-coating techniques. High-resolution grazing incidence X-ray small angle scattering experiments were performed using a micrometer sized beam (-GISAXS) to determine the structure of a highly ordered monolayer with two-dimensional hexagonal arrays. A clear and strong interference pattern coming from the reflection and refraction effects of particles on flat surfaces with small uncorrelated roughnesses is shown. The quantitative analysis and simulations of the X-ray scattering pattern have been performed, and a detailed explanation of the analysis is reported. The results were directly compared and verified with atomic force microscopy (AFM) measurements and their resulting FFT spectra. [ABSTRACT FROM AUTHOR]

We present an analytical model that explains how, in humid environments, the electric field near a sharp tip enhances the formation of water menisci and bridges between the tip and a sample. The predictions of the model are compared with experimental measurements of the critical distance where the field strength causes bridge formation. [ABSTRACT FROM AUTHOR]

Separated domains of 1-dodecanethiolate were fabricated via solution displacement of preformed 1-adamantanethiolate self-assembled monolayers on Au111. Subsequently, the 1-adamantanethiolate domains were desorbed selectively, and the substrate was exposed to a 1-octanethiol solution, creating artificially separated self-assembled monolayers of 1-dodecanethiolate and 1-octanethiolate. The molecular order of each lattice type and the apparent height differences imaged with scanning tunneling microscopy and the two distinct cathodic peaks observed with cyclic voltammetry indicated distinct separated domains of each lattice type in the separated self-assembled monolayers. By manipulating the intermolecular interaction strengths of the patterned molecules, we are able to control the structure and properties of the separated self-assembled monolayers via the exploitation of competitive adsorption and the utilization of electrochemical processing, which can be extended to other self-assembly patterning techniques such as microdisplacement printing. [ABSTRACT FROM AUTHOR]

The reduction mechanism of the RuO2(110) surface by molecular hydrogen exposure is unraveled to an unprecedented level by a combination of temperature programmed reaction, scanning tunneling microscopy, high-resolution core level shift spectroscopy, and density functional theory calculations. We demonstrate that even at room temperature hydrogen exposure to the RuO2(110) surface leads to the formation of water. In a two-step process, hydrogen saturates first the bridging oxygen atoms to form (Obr−H) species and subsequently part of these Obr−H groups move to the undercoordinated Ru atoms where they form adsorbed water. This latter process is driven by thermodynamics leaving vacancies in the bridging O rows. [ABSTRACT FROM AUTHOR]

The atomic arrangements inside Ru and Os nanoislands spontaneously deposited on Pt(111) electrode surface were observed with electrochemical scanning tunneling microscopy. The surperlattice of the pristine Ru nanodeposits is (√3×√3)R30°-RuO. Upon reduction, the Ru nanodeposits are compressed to a uniaxially incommensurate (√3×√2)R30°-Ru structure, which does not change during the following reoxidation. The atomic arrangement inside the pristine Os nanodeposits is an incommensurate (√2×√2)-OsOstructure, which does not transform during the subsequent reduction−oxidation cycles. The structures of the Ru and Os nanodeposits are discussed in terms of removal and insertion of oxygen ions depending on electrode potential. [ABSTRACT FROM AUTHOR]

From the interplay of scanning tunneling microscopy and theoretical calculations, we study the chiral self-assembly of achiral HtB−HBC molecules upon adsorption on the Cu(110) surface. We find that chirality is expressed at two different levels:  a ±5° rotation of the molecular axis with respect to the close-packed direction of the Cu(110) substrate and a chiral close-packed arrangement expected for star-shaped molecules in 2D. Out of the four possible chiral expressions, only two are found to exist due the effect of van der Waals (vdW) interactions forcing the molecules to simultaneously adjust to the atomic template of the substrate geometry and self-assemble in a close-packed geometry. [ABSTRACT FROM AUTHOR]

This work presents an electrochemical scanning tunneling microscopy study of Sb irreversibly adsorbed on Pt(111) at various potentials. At an open circuit potential (0.46 V vs a Ag/AgCl electrode), well-ordered structures of SbOwere found:  four (4 × 3)-3SbOstructures and one (2√3 × 2√3)R30°-3SbOstructure. In addition, several unidentifiable transient structures of SbOwere observed, and their relations to the well-ordered structures of (4 × 3) and (2√3 × 2√3)R30°, regarding structural evolution, were proposed. At a reducing potential (0 V), the Pt(111) surface was covered with irreversibly adsorbed Sb which consisted of three different domains:  protruded domain, domain of uniaxially incommensurate (√3 × √2)-Sb, and domain of bare (1 × 1) Pt(111). During oxidation of elemental Sb at 0.30 V, the Sb domains of the (√3 × √2) structure were oxidized, while the protruded domains were not oxidized. After underpotential deposition of additional Sb onto the Pt(111) covered with irreversibly adsorbed Sb, the whole surface was filled with the Sb domains where each Sb atoms were separated by the √2adistance (a one Pt−Pt distance, 0.277 nm). The observed electrochemical inactivity below 0.3 V was discussed in terms of the protruded domain of a presumable incommensurate (√2 × √2) structure. [ABSTRACT FROM AUTHOR]

We report the direct measurement of photoinduced surface potential differences of wild-type (WT) and mutant D96N bacteriorhodopsin (BR) membranes at pH 7 and 10.5. Atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM) were used to measure the BR membrane with the extracellular side facing up. We present AFM and SSPM images of WT and mutant D96N in which the light-dark transition occurred in the mid-scan of a single BR membrane. Photosteady-state populations of the M state were generated to facilitate measurement in each sample. The photoinduced surface potential of D96N is 63 mV (peak to valley) at pH 10.5 and is 48 mV at pH 7. The photoinduced surface potential of WT is 37 mV at pH 10.5 and ∼0 at pH 7. Signal magnitudes are proportional to the amount of M produced at each pH. The results indicated that the surface potentials were generated by photoformation of surface charges on the extracellular side of the membrane. Higher surface potential correlated with a longer lifetime of the charges. A mechanistic basis for these signals is proposed, and it is concluded that they represent a steady-state measurement of the B2 photovoltage. [ABSTRACT FROM AUTHOR]

Electrochemical techniques, coupled with in situ scanning tunneling microscopy, have been used to examine the mechanism of CO oxidation and the role of surface structure in promoting CO oxidation on well-ordered and disordered Pt(111) in aqueous NaOH solutions. Oxidation of CO occurs in two distinct potential regions:  the prepeak (0.25−0.70 V) and the main peak (0.70 V and higher). The mechanism of reaction is Langmuir−Hinshelwood in both regions, but the OH adsorption site is different. In the prepeak, CO oxidation occurs through reaction with OH that is strongly adsorbed at defect sites. Adsorption of OH on defects at low potentials has been verified using charge displacement measurements. Not all CO can be oxidized in the prepeak, since the Pt−CO bond strength increases as the CO coverage decreases. Below CO 0.2 monolayer, CO is too strongly bound to react with defect-bound OH. Oxidation of CO at low coverage occurs in the main peak through reaction with OH adsorbed on (111) terraces, where the Pt−OH bond is weaker than on defects. The enhanced oxidation of CO in alkaline media is attributed to the higher affinity of the Pt(111) surface for adsorption of OH at low potentials in alkaline media as compared with acidic media. [ABSTRACT FROM AUTHOR]

Finite element electromagnetic simulations of scanning probe microscopy tips and substrates are presented. The enhancement of the scattered light intensity is found to be as high as 1012 for a 20 nm radius gold tip, and tip−substrate separation of 1 nm. Molecular resolution imaging (<1 nm) is achievable, even with a relatively large radius tip (20 nm). We also make predictions for imaging in aqueous environments, noting a sizable red shift of the spectral peaks. Finally, we discuss signal levels, and predict that high-speed Raman mapping should be possible with gold substrates and a small tip−substrate separation (<4 nm). [ABSTRACT FROM AUTHOR]

A combination of high-resolution electrical and electrochemical imaging techniques, in conjunction with cathodoluminescence (CL), is used to investigate the electrochemical behavior of oxygen-terminated highly doped polycrystalline boron doped diamond (BDD). The BDD has a dopant density ∼7b× 1020 atoms cm-3, grain size ca. 5−40 μm, and thickness 500 μm. CL imaging demonstrates that boron uptake is nonuniform across the surface of BDD, and conducting atomic force microscopy (C-AFM) highlights how this impacts on the local conductivity. While C-AFM shows no evidence for enhanced grain boundary conductivity, two characteristic conductivity domains are found with resistances of ca. 100 kΩ and ca. 50 MΩ. With the use of scanning electrochemical microscopy (SECM), local heterogeneities are also observed in the electroactivity of the BDD surface, consistent with the two different types of conducting regions. Local currents of the magnitude expected for metal-like behavior are observed in some regions, suggesting degenerative doping of the grains (supported by CL studies). In other regions, slower electron transfer is apparent. However, even for the reduction of Ru(NH3)63+, which occurs at potentials far negative of the flat-band potential for oxygen-terminated BDD, all areas of the surface show some electroactivity. This study highlights that the spatially heterogeneous conductivity and corresponding electroactivity of BDD are readily resolved using a combination of C-AFM, SECM, and CL. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) assembling behaviors of the endohedral metallofullerene Y@C82 on bare, C60-modified, and iodine-modified Au(111) surfaces have been investigated in 0.1 M HClO4 solution employing electrochemical scanning tunneling microscopy (ECSTM). The results show that Y@C82 molecules are mobile and aggregate to the terrace edges on bare and C60-modified Au(111) surfaces, but monodispersion of the Y@C82 molecules is achieved on the iodine-modified Au(111) surface. The improvement of Y@C82 dispersion on an iodine-modified gold surface is due to the strong Y@C82−substrate interactions. The modified-substrate method provides an effective strategy to disperse endohedral metallofullerenes. [ABSTRACT FROM AUTHOR]

A combined ultrahigh vacuum scanning tunneling microscopy (STM-UHV) and energy dispersive X-ray diffractometry/reflectometry (EDXD/EDXR) study of the evolution of face-centered cubic (fcc) Pt layer growth on MgO(100) by pulsed laser deposition as a function of the process parameters such as deposition temperature and deposition duration has been carried out. The aim of this study is to define the best experimental conditions to obtain a controlled film deposition selective on the Pt growth direction (either [111] or [002]). The evolution of the Pt surface morphology as a function of the deposition temperature (Tdep) from 300 to 700 °C has been studied with STM and ED techniques. Results show that the Pt surface, characterized at Tdep = 300 °C by a 3D island morphology, evolves at higher temperatures to a morphology in which the original islands coexist with a distribution of orthogonal 2D stripes. The two features can be associated with the [111] and [002] Pt growth directions of the fcc phase, respectively. For Tdep = 700 °C, the island morphology of the (111) face completely disappears, while the merging process of the (002) stripes reaches completion. The evolution of the morphology at Tdep = 600 °C as a function of the deposition time and thickness has then been studied with STM-UHV, revealing an initial growth of mosaic-like 3D islands. These independent islands, already interconnected, expand along two orthogonal directions and, for longer deposition times, lead to the texture of orthogonal stripes. The EDXR characterization providing the morphological parameters of the films, i.e., thickness and roughness, confirms the above observation and quantifies the effect of such morphological changes on the surface roughness of the Pt film, an important parameter for applications of Pt films as underlayer in magnetic recording media. [ABSTRACT FROM AUTHOR]

We have deposited Au atoms on the surface of titania without sintering or surface damage. Mass-selected Au+ atoms were deposited from the gas phase at room temperature with kinetic energies from <3 to 190 ± 3.5 eV. Scanning tunneling microscopy reveals island formation following deposition at <3 eV, while mainly atomic features are observed for energies between ∼35 and ∼190 eV. A mixture of islands and atomic features is observed at a landing energy of 20 ± 3.5 eV, suggesting a critical energy above which pinning occurs. Cluster size is also probed as a function of coverage in the deposition of Au+ with 100 eV of energy, revealing that sintering begins at a coverage of only 0.06 ML. These observations suggest a mechanism in which high-energy collision leads to the annealing of any impact-created surface damage and the pinning of Au atoms to the surface. We provide a new method of preparing isolated Au atoms on an oxide surface, which can serve as a platform for catalytic studies. [ABSTRACT FROM AUTHOR]

The conductive properties of vertically aligned germanium nanowires, with mean diameters of 50 and 100 nm, within anodized aluminum oxide (AAO) templates have been characterized by conductive atomic force microscopy (C-AFM) and macrocontact measurements. C-AFM was used to determine the electrical transport properties of individual nanowires within the arrays, while macrocontacts were used to measure the mean current−voltage characteristics of groups of nanowires. Contact resistance between the nanowires and metal macrocontacts was minimized by polishing and gradual etching of the AAO surface, to expose the nanowires, prior to deposition of the contacts. Impedance measurements were used to analyze the importance of defects on the charge transport properties of the germanium nanowire arrays. Conductivity data from C-AFM and macrocontact measurements were found to be comparable suggesting that both methods are inherently suitable for evaluating the electrical transport properties of encapsulated nanowires within a matrix. These results are significant as the ability to make good ohmic contacts to nanowires, within well-defined arrays, is key for the future “bottom-up” fabrication of multilayered device architectures for future electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

We study the capillary force in atomic force microscopy by using Monte Carlo simulations. Adopting a lattice gas model for water, we simulated water menisci that form between a rough silicon-nitride tip and a mica surface. Unlike its macroscopic counterpart, the water meniscus at the nanoscale gives rise to a capillary force that responds sensitively to the tip roughness. With only a slight change in tip shape, the pull-off force significantly changes its qualitative variation with humidity. [ABSTRACT FROM AUTHOR]

An approach is demonstrated for growing aligned ZnO nanowire/nanorod arrays following a predesigned pattern and feature with controlled site, shape, distribution, and orientation. The technique relies on an integration of atomic force microscopy (AFM) nanomachining with catalytically activated vapor−liquid−solid (VLS) growth. The pattern and growth locations are defined by the catalyst distribution created by AFM, and the orientation is determined by the epitaxial growth on a single-crystal substrate. The technique opens a variety of possibilities of using nanowire arrays as sensor arrays, piezoelectric antenna arrays, nanolasers, photonic band gap crystal, biosensors, and field emitters with controlled density, location, shape, and distribution according to a designed pattern and feature. [ABSTRACT FROM AUTHOR]

Nanometer-scale patterning and charging in layer-by-layer (LbL) ultrathin films of quinquethiophene (5TN)/phthalocyanine (CuPS) provides a novel write−read device using a standard current-sensing atomic force microscopy (CS-AFM). The AFM height images showed dented or raised morphological features that could be selectively manipulated by changing the direction of the bias voltages. The conductivity was repeatedly changed between a conductive and insulating state, originating from an electrochemical charging−discharging effect. This was attributed to electrochemical ion transport and the residual mobile ions present in LbL films. Finally, the nanocharge pattern was written by CS-AFM and read out in a conductivity map image. [ABSTRACT FROM AUTHOR]

Structures of surface hydroxyl groups arranged on a reduced TiO2(110) surface that had line oxygen vacancies were studied using noncontact atomic force microscopy (NC-AFM). NC-AFM results revealed that by increasing the density of oxygen vacancies on the TiO2(110) surface, line oxygen vacancies were formed by removal of oxygen atoms in a bridge oxygen row on the TiO2(110) surface. After the TiO2(110) surface with the line oxygen vacancies was exposed to water, the surface showed hydroxyl chain structures that were composed of hydroxyl groups linearly arranged in a form of two rows on the line oxygen vacancies and on a neighboring bridge oxygen row. In-situ NC-AFM measurements of these surfaces exposed to water at room temperature revealed that hydroxyl chain structures were formed at the line oxygen vacancy. Annealing above 500 K was sufficient to remove the hydroxyl chain structures on the TiO2(110) surface and allowed line oxygen vacancies to reappear on the surface. The line oxygen vacancies are active sites for water dissociation. In conclusion, the formation of the hydroxyl chain structure suggests that the surface hydroxyl groups on a TiO2(110) surface can be controlled by preparing oxygen vacancy structures on the surface. [ABSTRACT FROM AUTHOR]

Electroactive tetrathiafulvalene thiol islands embedded in an n-alkanethiol SAM matrix were studied under potential control using in situ scanning tunneling microscopy. Unlike previously studied stochastic switching, the apparent height of the island could be intentionally controlled in the present system by choosing the appropriate potential and the island size. The dependence of the height change on the potential and the size is explained as structural change of the island induced by the charging effect of the electroactive moiety. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of arrays of Au nanoparticles assembled on Au electrodes modified by 11-mercaptoundecanoic acid (MUA) and poly-l-lysine (PLYS) was investigated as a function of the particle number density. The self-assembled MUA and PLYS layers formed compact ultrathin films with a low density of defects as examined by scanning tunneling microscopy. The electrostatic adsorption of Au particles of 19 ± 3 nm on the PLYS layer resulted in randomly distributed arrays in which the particle number density is controlled by the adsorption time. In the absence of the nanoparticles, the dynamics of electron transfer involving the hexacynoferrate redox couple is strongly hindered by the self-assembled film. This effect is primarily associated with a decrease in the electron tunneling probability as the redox couple cannot permeate through the MUA monolayer at the electrode surface. Adsorption of the Au nanoparticles dramatically affects the electron-transfer dynamics even at low particle number density. Cyclic voltammetry and impedance spectroscopy were interpreted in terms of classical models developed for partially blocked surfaces. The analysis shows that the electron transfer across a single particle exhibits the same phenomenological rate constant of electron transfer as for a clean Au surface. The apparent unhindered electron exchange between the nanoparticles and the electrode surface is discussed in terms of established models for electron tunneling across metal−insulator−metal junctions. [ABSTRACT FROM AUTHOR]

Through the use of monodisperse core/shell quantum dots (QDs) as photosensitizers for the first time, a novel strategy for the fabrication of QD-photosensitized nano-TiO2 films was demonstrated. Core/shell QDs were self-assembled on nano-TiO2 films through carboxyls as anchoring groups to metal oxides. Atomic force microscopy and some other experiments showed the fabrication strategy is successful. Reactive oxygen species detection experiments indicated that such films have photosensitization ability. The results of bactericidal and DNA damage experiments demonstrate that such films have excellent photoactivity. [ABSTRACT FROM AUTHOR]

We demonstrate here the thermochemical hole burning (THB) effect on a series of N-substituted morpholinium 7,7,8,8-tetracyanoquinodimethane charge-transfer (C-T) complexes for ultra-high-density data storage. A correlation between the decomposition temperature of the charge-transfer complex and the threshold voltage of hole burning was observed:  the higher the decomposition temperature, the larger the writing threshold value, suggesting the possibility of molecular design for optimizing the hole burning performance. The macroscopic decomposition properties of these charge-transfer complexes were studied by thermal gravimetry combined with mass spectrometry. Theoretical estimation of the temperature rise induced by scanning tunneling microscopy current heating was also conducted, which indicated that the maximum temperature certainly exceeds the decomposition temperatures of these C-T complexes. These observations are consistent with the thermochemical hole burning mechanism. [ABSTRACT FROM AUTHOR]

The chemisorption of the undissociated CH3SH molecule on the Au(111) surface has been studied at 5 K using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The molecule was found to adsorb on atop Au sites on the defect-free surface. CH3SH undergoes hindered rotation about the Au−S bond on the defect-free surface which is seen in STM as a time-averaged 6-fold pattern. The pattern suggests that the potential minima directions occur for the rotating molecule at the six hollow sites surrounding the atop adsorption site. The barrier for rotation, obtained by DFT calculations, is ~0.1 kcal·mol-1. At low coverages, preferential adsorption occurs at defect sites in the surface, namely, the herringbone “elbows” and random atomic step sites. Molecules adsorbed on these sites do not exhibit rotational freedom. [ABSTRACT FROM AUTHOR]

A host supramolecular structure consisting of bis-(2,2‘:6‘,2‘ ‘-terpyridine)-4‘-oxyhexadecane (BT−O−C16) is shown to respond to guest molecules in dramatic ways, as observed by using scanning tunneling microscopy (STM) on a highly oriented pyrolytic graphite surface under ambient conditions. It is observed that small linear molecules can be encapsulated within the host supramolecular lattice. The characteristics of the host structure were nearly unaffected by the encapsulated guest molecules of terphthalic acid (TPA) dimers, whereas appreciable changes in cavity dimension can be observed with azobenzene-4,4‘-dicarboxylic acid. The STM study and density functional theory (DFT) analysis reveal that intermolecular hydrogen bonding interaction plays an essential role in forming the assembling structures. The difference in guest molecule length is considered the important cause for the different guest−host complexes. [ABSTRACT FROM AUTHOR]