Self-assembled monolayers of decanethiol on Au(111)/mica

We report here a preparation for thin gold films on mica substrates. We have investigated the influence of the substrate temperature and the evaporation rate on the morphology of the films. After careful outgasing of the substrate, 100 nm of Au is evaporated onto the mica surface maintained at high temperature. After slow cooling, ex situ characterizations are performed using AFM and STM. For our purposes, the best compromise between roughness and grain size is found to occur for an evaporation rate of 2 ?s^-1 onto a mica substrate maintained at 460 C. We have used these substrates for STM and AFM study of decanethiol self-assembled monolayers (SAMs). We present results for gold samples immersed for a few seconds in decanethiol solutions, revealing an incomplete organization of the films. The organization process is discussed through comparison between AFM and STM data recorded on the SAMs. Then we present molecular resolution STM pictures of ordered SAMs for longer immersion times. Received 25 May 1999     

On the surface temperature of substrates on a hotplate used for epitaxial growth

With the help of thin-film Au-constantan thermocouples the surface temperature of mica substrates on a hotplate was measured. The improvement of the thermal contact between the substrate and the hotplate by a thin layer of aquadag was verified and the influence of the mica thickness on its surface temperature was evaluated. The thin-film thermocouple proved useful for the investigation of the effect of radiant heat from the evaporation source on the temperature of the substrate surface.     

Epitaxial growth of al thin films on mica and investigation of film structure

The temperature dependence of the structure of the aluminium thin film was studied. Reflection and transmission electron diffraction (RED and TED, respectively) patterns show that the changes of the polar orientation (texture) and the azimuthal orientation (due to epitaxy) arise in the film as the temperature of substrate surface is increased. The simultaneous presence of spot patterns at RED and arc or ring patterns at TED in a certain temperature range is explained by the preferred orientation of the film grains in the azimuthal direction and the nearly perfect orientation in the polar direction. The particular changes of the azimuthal orientation became at the temperature of the largest desorption of water molecules from mica so that we deduce that the presence of water molecules is necessary for the particular degree of the azimuthal orientation at lower temperature. At a higher temperature (500°C) of the substrate surface the well-oriented films were prepared with the same diffraction patterns as single crystal with orientation (111)_Al// //(001)_M and (110)_Al//(010)_M (double positioning is present in the films).The author expresses his gratitude to Dr. L.Eckertová and Dr. Z.Hájek for valuable discussions and to Dr. M.Rozsíval and Dr. P.Kratochvíl for their aid at the structure analysis.     

STM study of Au(111) growth on mica

Gold films were thermally evaporated in vacuum on heated cleaved mica substrates. The substrate temperature was immediately decreased after finishing the growth. Samples prepared at various temperatures from 580 K to 890 K and evaporation rates smaller than 1 nm/s were studied by a scanning tunneling microscope (STM) under ambient conditions. Structure and defects of Au(111) surfaces were investigated and discussed with respect to growth conditions.     

X-ray pole-figure study of the epitaxial growth of C60 thin films on mica (001)

The growth of epitaxial C₆₀ thin films on mica(001) by thermal evaporation has been studied in detail by X-ray pole-figure measurements. The influence of the deposition rate, the substrate temperature and the film thickness on the in-plane epitaxial arrangements and the formation of twins has been investigated. It has been demonstrated that the C₆₀ growth is determined by two independent and equivalent C₆₀-crystal grain alignments (type-A and type-B). The nearly six-fold symmetry of the mica(001)-substrate surface offers the three-fold fcc-(111)-oriented C₆₀-crystal grains two equivalent crystal alignments. A high deposition rate of 0.5 Å/s is responsible for the formation of twins at a substrate temperature of 150°C, which diminishes by a higher substrate temperature of 200°C. By a decrease of the deposition rate down to 0.08 Å/s the twins vanish at a film thickness of 200 nm and at the substrate temperature of 150°C. Under the same sublimation conditions, in addition to the type-A and type-B crystal orientations, the growth of the thin C₆₀ films starts with a slight fibre texture which does not appear at a larger film thickness.     

Crystallization of lysozyme in pores of etched heavy-ion tracks

Intensive studies of protein crystallization are provoked by the need to accumulate structural information and to open up novel potential applications in science and technology. This work focuses on the crystallization of hen egg white lysozyme (HEWL) in micrometer-size templates of etched swift-ion tracks produced in foils of polycarbonate, polyimide, and mica. HEWL deposition was accomplished by the salting with sodium chloride method at 20 and 6 °C. The crystals overgrowing the pore orifices showed no orientation when crystallized at room temperature. At 6 °C, they presented a regular habit and were uniaxially oriented on a polycarbonate substrate. Biaxial orientation was observed on polyimide membranes, and epitaxial orientation dominated on mica. However, no crystallization was observed on the mica membrane covered with a thin gold layer. The epitaxial growth of HEWL was particularly pronounced in the case of ordered substrates and low crystallization temperature, i.e. at higher supersaturation. By computer simulation it was possible to determine the surface lattice planes and thus provide the preferential crystal-growth orientation. Crystallization of lysozyme and other proteins in ion-track templates of submicrometer channels should be of high practical interest. PACS 87.14.Ee; 87.15.Nn; 81.10.Dn; 61.82.-d     

IR and SFM study of PTCDA thin films on different substrates

FT-IR spectroscopy and SFM were used to investigate the growth of thin films of the organic semiconductor 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) deposited by vacuum sublimation onto various substrates, i.e. Ag(111) layers on mica, KBr(100), mica, oxidized Si, and TiO₂ nanoparticles on Si. Layer thicknesses of PTCDA varied from 10 to 1500 nm.The anhydride vibrations of PTCDA differ for the used substrates, which can be connected to the orientation of the molecules relative to the substrate surface and the film morphology as detected in the SFM pictures.     

Effects of deposition temperature and thickness on the structural properties of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of different thicknesses were deposited onto Si(1 0 0) substrate at various substrate temperatures by thermal evaporation technique. Influences of thickness and deposition temperature on the film morphologies, microstructure, and topographies were investigated. A columnar growth of hexahedron-like grains with bimodal particle size distribution was observed at high deposition temperature. The columnar growth and the presence of large grains induce the Bi films to have large surface roughness as evidenced by atomic force microscopy (AFM). The dependence of the crystalline orientation on the substrate temperature was analyzed by X-ray diffraction (XRD), which shows that the Bi films have completely randomly oriented polycrystalline structure with a rhombohedral phase at high deposition temperature (200 °C) and were strongly textured with preferred orientation at low deposition temperatures (30 and 100 °C).     

蒸发条件对碘化铅多晶薄膜结构的影响

采用真空蒸发法在普通玻璃上制备了PbI₂多晶薄膜.研究了蒸发速率、蒸发源与衬底距离、薄膜厚度以及衬底温度等实验条件对所制备PbI₂多晶薄膜结构的影响.利用X射线衍射仪和扫描电子显微镜对样品进行了测试.结果表明，在衬底温度为室温时得到(001)择优取向的多晶PbI₂薄膜，即沿c轴垂直衬底方向取向生长的薄膜.当衬底温度升高时，薄膜的择优取向逐渐由(001)转向(003)，且晶体颗粒变大.薄膜中的内应力随衬底温度的升高而降低.     

Atomic-force microscopy of bismuth films

The surface structure of bismuth films is investigated using atomic-force microscopy. The films are prepared through vacuum thermal evaporation on mica substrates, followed by annealing. It is established that the films have a block structure with the preferred orientation of the C ₃ axis perpendicular to the substrate plane. The C ₂ axes of the neighboring blocks predominantly have mutually opposite orientations. Upon annealing, the sizes of blocks with the C ₃ axis perpendicular to the substrate plane increase at the expense of a virtually complete disappearance of blocks with random orientations of the C ₃ axis and the coalescence of blocks with the same orientation. The size and configuration of the blocks are most clearly revealed upon preliminary treatment of the films in a diluted solution of the etchant. The results obtained are of interest for the interpretation of the data on the transport phenomena occurring in bismuth films.     

Influence of surface temperature and surface modifications on the initial layer growth of para-hexaphenyl on mica (0 0 1)

Ultra-thin films of para-hexaphenyl (6P) were prepared on muscovite mica (0 0 1) utilizing organic molecular beam deposition (OMBD) under well defined ultra high vacuum (UHV) conditions. The 6P growth characteristics were studied as a function of substrate temperature and substrate surface conditions. For the initial state of layer growth, thermal desorption spectroscopy (TDS) was used to verify the existence of a wetting layer. In this monomolecular continuous wetting layer, the molecules lie flat on the surface and are rather strongly bonded. For thicker films, in-situ X-ray photoelectron spectroscopy (XPS) in combination with (TDS) was applied to reveal the kinetics of the layer growth. Ex-situ atomic-force microscopy (AFM) was used to determine the film morphology. In particular, the influence of surface modifications (carbon contamination, sputtering) on 6P layer growth was investigated. XPS and low energy electron diffraction (LEED) were used to characterize the mica surface before the film deposition. TDS and AFM revealed a considerable change in film growth, from a needle-like island growth of flat laying molecules on top of the wetting layer (for the air cleaved mica) to terrace-like film growth of standing molecules, without a wetting layer (after surface modifications).     

Low-Dimensional Forest-Like and Desert-Like Fractal Patterns Formed in a DDAN Molecular System

Two kinds of forest-like and desert-like patterns are formed by thermal evaporation of 4-dicyanovinyl-N, Ndimethylamino-1-naphthalene （DDAN） onto SiO2 substrates. Based on thermal kinetics of the molecules on the substrate the transformation between the forest and desert patterns is due to two factors. The first one is the diffusion length, which is related to the deposition rate, the diffusion potential energy barrier and the substrate temperature. The second one is the strong interaction between the two polarity chemical groups of the molecules, which is beneficial to the formation of branches. Totally different patterns are also found on mica substrates, and are attributed to the anisotropic diffusion and the stronger interaction between DDAN molecules and the mica surface.     

Visualization and Characterization of Discontinuous Particle Films of Polystyrene by Atomic Force Microscopy

Discontinuous particle films of polystyrene (PS) with different molecular weights were prepared by the methods of spin coating (SPC) and droplet evaporation (DE) at room temperature on mica substrates. Visualization and characterization of these samples were performed by atomic force microscopy (AFM). The results showed that the dimensions of the particles in the films increased with molecular weight. The dimensions of the particles in the films derived from SPC exhibited better uniformity than those from DE. During the steps of particle film formation by SPC, the PS molecules gathered in large clusters at the early stage, then the polymer aggregates were separated or spun off, and more and more particles emerged, finally the clusters vanished and the particle film formed. The particles of the spin-coated film dewetted after annealing and numerous individual polymer chains appeared newly on the mica substrate.     

Attachment limited versus diffusion limited nucleation of organic molecules: Hexaphenyl on sputter-modified mica

The nucleation and growth of organic molecules is usually discussed in the framework of diffusion limited aggregation (DLA). In this letter we demonstrate for the rod-like organic molecules hexaphenyl (6P) on sputter-modified mica, that under specific experimental conditions the nucleation has to be described by attachment limited aggregation (ALA). The crucial parameter for the growth mode is the roughness of the substrate surface, as induced by ion sputtering. With decreasing surface roughness the diffusion probability of the molecules increases and the growth mode changes from DLA to ALA. This was derived from the deposition rate dependence of the island density. A critical size of i = 7 molecules was determined for the nucleation of 6P on a moderately sputtered mica surface.     

The electrical properties of evaporated films of cadmium sulphide

The electrical properties of vacuum evaporated layers of CdS on amorphous substrates have been investigated as a function of the various preparative parameters, i.e. evaporation rate, substrate temperature, thickness of the layers and purity of the source. The degree of preferential orientation of the crystallites which comprise the film has also been examined. It is shown that the resistivity of the films decreases with increasing thickness. This effect is associated with a corresponding increase in the density of free electrons, which it is suggested is associated with an increasing deviation from stoichiometry of the source as the evaporation proceeds. The variation of the Hall mobility with thickness can be explained in terms of surface scattering. A tentative model of the evaporation process is proposed which gives some insight into many of the experimental observations.     

STM study of di-indenoperylene molecules on Cu(1 0 0) surfaces: Mobility, stability and epitaxy

We report a detailed study of the self-assembly process of di-indenoperylene (DIP) on Cu(1 0 0) surfaces, investigated by variable temperature scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions. During the initial growth stages a preferred nucleation at the step edges is revealed. Subsequently, large ordered 2D islands grow from the step edges, while smaller 2D islands form on the terrace sites. The equilibrium fluctuation of these 2D clusters has been monitored in real-time, thereby obtaining a direct insight into the temperature dependence of the molecular surface diffusion. The substrate–adsorbate interactions determine the azimuthal molecular orientation, finally lead to the formation of highly ordered chiral domains which are commensurate with the substrate.     

Experimental investigation of liquid drop evaporation on a heated solid surface

Evaporation of a water drop was studied experimentally at a temperature difference between the solid surface and surrounding atmosphere from 30 to 60 °C. The studies were performed on the substrates with micro- and nanocoatings with different wettability. The features of evaporation were studied for the pinned, partially pinned, and depinned three-phase contact line (solid-liquid?gas interface). It is shown that with a decrease in the water drop volume, the specific evaporation rate (mass flow per unit of surface area) increases, particularly at the last stage of evaporation.     

An improved reflectometric method to measure the azimuthal anchoring energy of nematic liquid crystals

Some years ago we developed an automatized reflectometric method to measure the surface azimuthal anchoring energy of nematic liquid crystals on an optically isotropic substrate. This method provides a high accuracy and sensitivity but requires the use of wedge glass plates and a sufficiently high anisotropy of the intensity reflectivity coefficients. This latter condition restricts greatly the number of possible substrates that can be investigated with this technique. Here we develop a new reflectometric method which offers comparable or better accuracy and sensitivity but does not require wedge plates and high anisotropy of the reflectivity coefficients. The method is fully automated and provides a direct measurement of the azimuthal director angle. The experimental procedure exploits the dependence of the reflectivity tensor on the surface director orientation. The measurement of the azimuthal angle does not require any knowledge of the optical parameters of the nematic material and of the optically isotropic substrate, and provides an absolute accuracy better than 0.2^° in the whole range 0-360^° and a sensitivity better than 0.1^°. This reflectometric method can be also used with weakly anisotropic substrates as well as thin rubbed polymeric layers. In this latter case, the effective uncertainty in the measurement of the director azimuthal angle depends on the substrate anisotropy. A simple and direct experimental procedure to estimate this uncertainty is proposed. Received 8 January 2002 and Received in final form 27 February 2003 / Published online: 15 April 2003 RID="a" ID="a"e-mail: faetti@df.unipi.it     

Atomic-force microscopy of bismuth film defects decorated by oxidation

A method has been developed for revealing intercrystalline boundaries and mutual orientation of crystallites in bismuth films with the use of natural oxidation in combination with atomic-force microscopy. For bismuth films prepared through vacuum thermal evaporation on mica substrates, the block boundaries have been revealed, the sizes of blocks have been determined, and their mutual crystallographic orientation has been established. The results obtained have been used to determine thermal evaporation conditions that ensure a higher perfection of the film structure.     

低温CVD法在玻璃衬底上制备ZnO纳米线阵列

采用化学气相沉积(CVD)法在镀Cr(20nm)的玻璃衬底上,低温制备了ZnO纳米线阵列。利用扫描电子显微镜(SEM)和X射线衍射(XRD)对样品的表面形貌和微结构进行了分析表征。结果表明:源分解温度1350℃,衬底温度450～500℃,氩气流量为35sccm时,ZnO纳米线在玻璃衬底上呈现有序生长;XRD谱图中只观测到ZnO(002)衍射峰。表明制备的纳米线阵列具有高度c轴择优取向生长特性和较高的结晶质量。