Imaging structured water and bound polysaccharide on mica surface at ambient temperature

The presence of a water layer on the surface of muscovite mica under ambient conditions is well established. The water molecules are well ordered and seem to be oriented, leading to an icelike monolayer (probably ferroelectric) in epitaxial relation with the mica surface. We have imaged and characterized the height and contact angle of ordered water layer(s) formed by wetting and de-wetting processes on mica surfaces at different states of hydration by tapping mode atomic force microscopy. Implications that the presence of such an ordered water layer may have for imaging of biological samples are also discussed, with consideration of data for the polysaccharide hyaluronan.     

Epitaxially guided assembly of collagen layers on mica surfaces

Ordered assembly of collagen molecules on flat substrates has potential for various applications and serves as a model system for studying the assembly process. While previous studies demonstrated self-assembly of collagen on muscovite mica into highly ordered layers, the mechanism by which different conditions affect the resulting morphology remains to be elucidated. Using atomic force microscopy, we follow the assembly of collagen on muscovite mica at a concentration lower than the critical fibrillogenesis concentration in bulk. Initially, individual collagen molecules adsorb to mica and subsequently nucleate into fibrils possessing the 67 nm D-periodic bands. Emergence of fibrils aligned in parallel despite large interfibril distances agrees with an alignment mechanism guided by the underlying mica. The epitaxial growth was further confirmed by the formation of novel triangular networks of collagen fibrils on phlogopite mica, whose surface lattice is known to have a hexagonal symmetry, whereas the more widely used muscovite does not. Comparing collagen assembly on the two types of mica at different potassium concentrations revealed that potassium binds to the negatively charged mica surface and neutralizes it, thereby reducing the binding affinity of collagen and enhancing surface diffusion. These results suggest that collagen assembly on mica follows the surface adsorption, diffusion, nucleation, and growth pathway, where the growth direction is determined at the nucleation step. Comparison with other molecules that assemble similarly on mica supports generality of the proposed assembly mechanism, the knowledge of which will be useful for controlling the resulting surface morphologies.     

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution. Copyright 2001 Academic Press.     

Organothiol Monolayer Formation Directly on Muscovite Mica

Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X‐ray diffraction, and vibrational sum‐frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self‐assembled into (water) stable and adaptable ultra‐flat organothiol monolayers over homogenous areas as large as 1 cm². The strength of the mica–organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth.     

X-ray diffraction study of TiO2 thin films on mica

Thin layers of polycrystalline TiO₂ were deposited on flaky muscovite and phlogopite particles. Deposition was performed in water slurry using aqueous TiCl₄ as titanium source. The effect of heat treatments on the structure of TiO₂ thin films was investigated at different layer thicknesses. On muscovite mica the films crystallized as anatase TiO₂. On phlogopite mica the increasing layer thickness favored partial rutile formation at higher calcination temperatures, although the films could not be converted to pure rutile. The preferred orientation of the TiO₂ films was evident. The most intense reflections were measured from (004) and (105) planes. The crystallite size of TiO₂ was strongly dependent on calcination temperature and TiO₂ layer thickness. It varied between 15 and 47 nm for films deposited on phlogopite, and 15 and 57 nm for films deposited on muscovite.     

Structural influence on Raman scattering of a new C60 thin film prepared by AAO template with the method of pressure difference

An anodic aluminum oxide (AAO) template is prepared by anodizing aluminum in oxalic acid solution. C60 crystals were grown, using the pressure difference method, in the pores of the template, representing a brushlike thin film layer with a honeycomb boundary structure in one side and nail arrays in the other side. Different Raman spectra of the C60 thin film from the both sides are presented, which indicate the different uniformly ordered structure character and the interface behavior of the C60 film on the surface with C60 crystals in the AAO nanopores. On the basis of energy and group theory, the strengthening of the Raman intensity and the broadening of Raman modes may imply that more transition spectral lines between vibration or rotation energy levels of C60 molecules were excited and detected.     

Structure and topography of molecular assemblies on solid substrates by infrared spectroscopy and scanning tunneling microscopy

Recently we have combined infrared spectroscopy and atomic resolution scanning tunneling microscopy (STM) to probe the local structure and intermolecular arrangement of molecules within thin films. IR spectroscopy provides spatially averaged information about orientation of the molecules with respect to the surface and about intermolecular arrangement within the crystallographic unit cell. STM data yields a local picture of molecular packing within the film. The requirements of an atomically flat (over distances of hundreds of angstroms) conducting substrate for the STM are fulfilled by an epitaxially grown film of gold on a cleaved mica substrate which also provides a good infrared reflective surface, enabling IR and STM measurements on identical samples. Systems investigated include Langmuir-Blodgett films of cadmium arachidate and self-assembled films of octadecyltrichlorosilane.     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

Controlled rearrangement of adsorbed undecanol films on mica surfaces induced by an atomic force microscopy tip

An undecanol film adsorbed on a mica surface was found to rearrange and spread in a position-controlled way induced by a tapping mode atomic force microscopy (AFM) probe. AFM images of varying scanning times showed that before forming an ordered monolayer the undecanol molecules were adsorbed on the mica surface in the disordered and disorganized status. With the proceeding of scanning, these undecanol molecules gradually formed an ordered and flat film. Such behavior was caused by the formation of a stable film and had never been reported for other alcohols.     

Atomic force microscopy characterization of room-temperature adlayers of small organic molecules through graphene templating

We report on the use of graphene templating to investigate the room-temperature structure and dynamics of weakly bound adlayers at the interfaces between solids and vapors of small organic molecules. Monolayer graphene sheets are employed to preserve and template molecularly thin adlayers of tetrahydrofuran (THF) and cyclohexane on atomically flat mica substrates, thus permitting a structural characterization of the adlayers under ambient conditions through atomic force microscopy. We found the first two adlayers of both molecules adsorb in a layer-by-layer fashion, and atomically flat two-dimensional islands are observed for both the first and the second adlayers. THF adlayers form initially as rounded islands but, over a period of weeks, evolve into faceted islands, suggesting that the adlayers possess both liquid and solid properties at room temperature. Cyclohexane adlayers form crystal-like faceted islands and are immobile under the graphene template. The heights of the second adlayers of THF and cyclohexane are measured to be 0.44 ± 0.02 and 0.50 ± 0.02 nm, respectively, in good agreement with the layer thicknesses in the monoclinic crystal structure of THF and the Phase I "plastic crystal" structure of cyclohexane. The first adlayers appear slightly thinner for both molecules, indicative of interactions of the molecules with the mica substrate.     

Oriented monolayers prepared from lyotropic chromonic liquid crystal

We use a layer-by layer electrostatic self-assembly technique to obtain in-plane oriented aggregates of mesogenic dye molecules cast from lyotropic chromonic liquid crystals (LCLCs) on mica substrates. The aqueous solutions of dye used for deposition are in the nematic phase. Atomic force microscopy and X-ray photoelectron spectroscopy of the dried film reveal that the LCLC molecules adsorb at the charged substrate preserving ordered aggregates of elongated shape characteristic of the nematic phase in the aqueous solution. These elongated aggregates of LCLC molecules form films with in-plane orientational order and are compositionally distinct from the substrate.     

Origins for epitaxial order of sexiphenyl crystals on muscovite(001)

The epitaxial order of sexiphenyl crystals on muscovite(001) is investigated by x‐ray diffraction, lattice misfit calculations and atomic force microscopy. Depending on the substrate temperature during the thin film growth process, different epitaxial orientations are formed. Sexiphenyl thin films prepared at 370 K preferentially form crystals with the crystallographic (11‐1) planes parallel to the substrate surface while at 434 K a strong fraction of crystals with (11‐2) orientations is grown. The epitaxial orders of sexiphenyl crystals are compared with lattice misfit calculations. The in‐plane order of the {11‐1} crystals can be explained by a point‐on‐line coincidence I, which reveals that the interface is formed by undisturbed crystal surfaces. The epitaxial order of the {11‐2} oriented crystals is characterised by the experimental observation that low indexed crystal directions in the sexiphenyl(11‐2) plane and the muscovite(001) surface coincide with each other, forming a near‐coincidence case. Corrugations of the substrate surface are responsible for this second type of epitaxial order. Characteristic features in the thin film morphology could be correlated to the two observed epitaxial orientations of the sexiphenyl crystals. Copyright © 2009 John Wiley & Sons, Ltd.     

Template-directed self-assembly of a designed amphiphilic hexapeptide on mica surface

Self-assembly of small molecules into highly ordered nanostructures offers many important potential applications in science research and industry. Precise self-assembling with the assistance of inorganic substrate is considered as an ideal strategy. In this experiment, the highly ordered mica surface was used to template the assembling of a novel designed amphiphilic hexapeptide to form orderly parallel fibers. The nanostructure and the self-assembly mechanism were investigated by atomic force microscopy (AFM), transmission electron microscopy, Fourier transform infrared spectroscopy, and circular dichroism techniques. By the experimental results, a dramatic conformation transition from random coil and/or α-helix into β-sheet was found after the peptide assembled on the mica surface under certain conditions, which was considered as a key factor for the ordered nanostructure. Finally, according to the AFM images and the simulated length of peptide molecules, a trilaminar β-sheet structure model was proposed to explain the hierarchical self-assembly mechanism.     

Fulvic acid sorption on muscovite mica as a function of pH and time using in situ X-ray reflectivity

Interfacial structures of the basal surface of muscovite mica in 100 mg kg (-1) Elliott Soil Fulvic Acid II solutions were investigated using in situ X-ray reflectivity. Molecular-scale variations in the thickness and internal structure of the fulvic acid (FA) film were observed and quantified as a function of pH (2-12) and reaction time (3-500 h at pH 3.7). At pH < or =6, the electron-density profile of the FA layer sorbed on the muscovite surface was composed of one near-surface peak followed by a broad peak that diminished in electron density with distance from the surface. The presence of the near-surface peak is attributed to condensation of FA molecules during sorption. The apparent thickness of the FA layer decreased from 12.3 to 7.2 to 6.4 A as pH increased from 2 to 3.7 to 6, respectively. At pH > or =8.5, a distinct interfacial structure was observed, consisting of sharper peaks similar to those previously observed for muscovite in the absence of FA. These peaks are most likely composed of smaller aqueous species, such as H 2O molecules, metal ion impurities from FA, and Na (+) from NaOH. The FA sorbed on the muscovite surface at pH 3.7 maintained a relatively constant thickness after 3 hours. However, the electron density of the near-surface FA peak increased by about 24% from 3 to 12 hours, and remained relatively constant from 12 to 500 hours. The electron density of the more distant part of the sorbed FA layer increased slightly after 12-50 hours of reaction but then decreased, and the broad peak flattened by 500 hours. Internal structural changes are possibly due to the slow sorption rate of FA molecules, or a fractionation effect, i.e., continuous subsitution of smaller FA molecules by larger FA molecules.     

Investigation of mechanical properties of insulin crystals by atomic force microscopy

Mechanical properties of protein crystals and aggregates depend on the conformational and structural properties of individual protein molecules as well as on the packing density and structure within solid materials. An atomic force microscopy (AFM)-based approach is developed to measure the elastic modulus of small protein crystals by nanoindentation and is applied to measure the elasticity of insulin crystals. The top face of the crystals deposited on mica substrates is identified as the (001) face. Insulin crystals exhibit a nearly elastic response during the compression cycle. The elastic modulus measured on the top face has asymmetric distribution with a significant width. This width is related to the uncertainty in the deflection sensitivity. A model that takes into account the distribution of the sensitivity values is used to correct the elastic modulus. Measurements performed in aqueous buffer on several crystals at different locations with three different AFM probes give a mean elastic modulus of 164 +/- 10 MPa. This value is close to the static elastic moduli of other protein crystals measured by different techniques that are usually measured in the range from 100 MPa to 1 GPa. The measured modulus of insulin crystals falls between the elastic modulus values of insulin amyloid fibrils measured previously at two orthogonal directions (a modulus of 14 MPa was measured by compressing the fibril in the direction perpendicular to the fibril axis, and a modulus of 3.3 GPa was measured in the direction along the fibril axis). This comparison indicates the heterogeneous structure of fibrils in the direction perpendicular to the fibril axis, with a packing density of the amyloid fibril core that is higher than the average packing density in insulin crystals. The mechanical wear of insulin crystals is detected during AFM measurements. In nanoindentation experiments on insulin crystal, the compressive load by the AFM tip ( approximately 1 nN, corresponding to a pressure of around 5 MPa) occasionally removes protein molecules from the top or the second top layer of insulin crystal in a sequential manner. The molecular model of this surface damage is proposed. In addition, the removal of the multiple layers of molecules is observed during the AC-mode imaging in aqueous buffer. The number of removed layers depends on the scan size.     

Densely packed overlayer of iron phthalocyanine molecules grown on single-layer graphene

The FePc molecules form a series of order superstructures on single-layer graphene grown on Ru(0001) with increasing molecular coverage.     

Oxygen on Fe(100) and Fe(110)

Investigations of the electronic and magnetic properties of oxygen adsorbed on magnetized iron films have been carried out by means of angle and spin resolving photoelectron spectroscopy. Iron, epitaxially grown on W(100) and W(110) crystals, served as the ferromagnetic substrate. Exchange splittings of the O 2p_x derived level have been detected, demonstrating a magnetic coupling between the chemisorbate and the iron layer. Variations of the exchange splitting have occurred as a function of the oxygen coverage, photon energy, and emission angle. High oxygen exposures have lead to a FeO overlayer at the surface.     

Oxygen on Fe(100) and Fe(110)

Investigations of the electronic and magnetic properties of oxygen adsorbed on magnetized iron films have been carried out by means of angle and spin resolving photoelectron spectroscopy. Iron, epitaxially grown on W(100) and W(110) crystals, served as the ferromagnetic substrate. Exchange splittings of the O 2p_x derived level have been detected, demonstrating a magnetic coupling between the chemisorbate and the iron layer. Variations of the exchange splitting have occurred as a function of the oxygen coverage, photon energy, and emission angle. High oxygen exposures have lead to a FeO overlayer at the surface.     

钇掺杂有序大孔TiO_2微球的制备与光催化性能研究

采用溶胶-凝胶法、胶体晶体模板法制备了钇掺杂有序多孔TiO2微球,利用FTIR,SEM,XRD,XPS,UV-V is分析对其进行表征,并研究钇掺杂前后材料的光催化性能。结果表明:钇掺杂有序多孔TiO2微球规整致密,但局部有孔洞的塌陷。钇掺杂前后有序多孔TiO2微球的晶型没有改变,仍为锐钛矿型。XPS分析发现钇掺杂有序多孔TiO2微球是可行的,材料中含有钇元素含量约为1.0%。UV-V is分析表明钇掺杂使得TiO2吸收光红移至可见光区,甲基橙降解实验显示掺钇有序多孔TiO2微球的光催化性能好于未掺钇TiO2的光催化性能。     

Nano‐ice on Boron Nitride Nanomesh: Accessing Proton Disorder

Water was investigated on a h‐BN/Rh(111) nanomesh template using variable temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. Below 52 K, two distinct phases self‐assemble within the 3.2 nm unit cell of the nanomesh that consists of “holes” and “wires”. In the 2 nm holes, an ordered phase of nano‐ice crystals with about 40 molecules is found. The ice crystals arrange in a bilayer honeycomb lattice, where hydrogen atoms of the lower layer point to the substrate. The phase on the 1 nm wires is a low density gas phase. Tunneling barrier height dI/dz spectroscopy measurements reveal the dipoles of individual molecules in the nano‐ice clusters and access proton disorder.