Substrate-dependent conformational state induced by a hydrophilic group intercalated in a semi-fluorinated molecule

The structure of Langmuir monolayers and Langmuir-Blodgett (LB) films of a semi-fluorinated surfactant containing an intermediate hydrophilic group was investigated. The polar group in the middle of the molecule is shown to induce different conformational states depending on the substrate. At the air-water interface, the molecule adopts a folded shape in order to present its polar group to the water; this leads to a disordered phase. After transfer onto hydrophilic solid substrate (oxidized silicon wafers covered by a behenic acid bilayer), the molecule adopts a stretched conformation and hexagonal packing. Moreover, observed by atomic force microscopy, this LB film displays a labyrinthine morphology induced by the structure of the semi-fluorinated molecule. Finally, the influence of the conformational change of this molecule on its miscibility properties with behenic acid is studied.     

Electrodeposition of SmS optical thin films on ITO glass substrate

SmS optical thin films were deposited on the surface of ITO glass with an electrodeposition method using aqueous solution containing SmCl₃·6H₂O and Na₂S₂O₃·5H₂O. The phase composition was analyzed by X-ray diffraction (XRD) and microstructure of the film was characterized by atomic force microscope (AFM). It is showed that SmS thin film could be obtained in the solution with n(Sm)/n(S) = 1:4, pH = 4.0 and annealing in Ar atmosphere at 200 °C for 0.5 h. The as-prepared thin films on the ITO glass exhibit a dense microstructure. The band gap of the thin film has been found to be 3.6 eV.     

Ultra-thin films based on random copolymers containing perfluoropolyether side chains

Random copolymers were synthesised by copolymerizing methylmethacrylate and perfluoropolyetherurethanemethacrylate monomers, differing for the structural unit of the fluorinated chain, its end group and its molecular weight. The copolymers obtained had similar molecular weight and polydispersity, with a fluorine content between 5 and 10% wt/wt; they showed remarkable features such as biphasicity with coexistence of soft domains made of the perfluoropolyether chains and hard domains due to the methylmethacrylate backbone: the glass transition temperature T_g of the soft and hard phases was T_g1 < 90 °C and T_g2 ≅ 110 °C respectively. All the copolymers were highly hydrophobic: water contact angle was always higher than 105°. The copolymers were used for the preparation of ultra thin films by spin coatings: by atomic force microscopy and X-ray reflectivity the thickness was found in the range of 20-400 Å depending on the spinning conditions, in particular the concentration of the spun solutions. The films were also highly smooth, with a roughness lower than 5 Å.     

Low generation photochromic monodendrons on a solid surface

Zeroth through third generations of amphiphilic monodendrons containing a benzyl-15-crown-5 polar focal point, photochromic spacer, and alkyl tails as peripheral groups have been investigated for their ability to form photoresponsive surface monolayers. Thickness measurements, scanning probe microscopy, and molecular modeling were used to determine the microstructure of the monolayers. The tilted molecular packing of dendrons in the monolayers is proposed with bulky dendritic shell prohibiting dense packing of azobenzene groups and the aggregate formation. The two-stage trans–cis isomerization was observed for the photochromic monodendron layers composed of various generation dendrons. Fast changes within the first several minutes occurred in the azobenzene-containing monodendrons until the conversion of trans–cis isomerization reaches 13–33%. Then lateral steric hindrances in the monolayer decreases the transformation rate by three orders of magnitude. Diffusion limited intralayer reorganization is suggested to be a limiting factor in the rate of photoisomerization changes.     

Surface characterization of the monolayer and Langmuir–Blodgett films of tetra-tert-butyl-copper phthalocyanine

The relaxation and hysteresis phenomena of the tetra-tert-butyl-copper phthalocyanine (ttb-CuPc) monolayer were investigated. The monolayer was then transferred to a hydrophilic glass surface to prepare one monolayer of Langmuir–Blodgett (LB) films. The uniformity, stability and molecular arrangement of the LB films were studied by measurements of dynamic contact angle (DCA), and were compared with the information obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results show that the monolayer of ttb-CuPc is generally stable. The limiting area of a molecule is smaller than those reported in the literature, which is attributed to the aggregation of ttb-CuPc molecules into multilayer domains. The advancing and receding contact angles of water on these LB films are much smaller than those on a homogeneous film prepared by vacuum deposition. The wettability analysis on the LB films suggests that ttb-CuPc molecules are not arranged uniformly and continuously, and the LB film of ttb-CuPc contains a high ratio of exposed glass substrate. The surface morphology inspected by TEM and AFM shows the formation of separated domains of ttb-CuPc molecules, which is consistent with the surface condition evaluated from the surface wettability.     

Influence of deposition temperature on structure and morphology of nanostructured SnO2 films synthesized by pulsed laser deposition

Nanostructured tin oxide thin films were deposited on the Si (100) substrate using the pulsed laser deposition technique at different substrate temperatures (300, 450 and 600 °C) in an oxygen atmosphere. The structure and morphology of the as-deposited films indicate that the film crystallinity and surface topography are influenced by the deposition temperature by changing from an almost amorphous to crystalline microstructure and smoother topography at a higher substrate temperature. The photoluminescence measurement of the SnO₂ films shows three stable emission peaks centered at respective wavelengths of 591, 554 and 560 nm with increasing deposition temperature, contributed by the oxygen vacancies.     

Preparation of triangular and hexagonal silver nanoplates on the surface of quartz substrate

In this paper, triangular and hexagonal silver nanoplates were prepared on the surface of quartz substrate using photoreduction of silver ions in the presence of silver seeds. The obtained silver nanoplates were characterized by atomic force microscopy and UV–vis spectroscopy. It was found that the silver seeds played an important role in the formation of triangular and hexagonal silver nanoplates. By varying the irradiation time, nanoplates with different sizes and shapes could be obtained. The growth mechanism for triangular and hexagonal nanoplates prepared on quartz substrate was discussed.     

Effect of the microwave oven on structural, morphological and electrical properties of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by a soft chemical method

Thin films of SrBi₄Ti₄O₁₅ (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P_r and a coercive field E_c values of 5.1 μC/cm² and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm² and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10¹⁰ switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.     

Conformational morphology of polyaniline grown on self-assembled monolayer modified silicon

Polyaniline (PANI) films with pyramidal shaped crystallites were prepared by self-organization on self-assembled monolayer (SAM) modified Si substrates. High-resolution atomic force microscopy (HR-AFM) shows that SAM has tridymite structural order and the PANI film has biphasic conformational morphology corresponding to face-on orientation and edge-on orientation. Order parameters obtained from power spectral density analysis of HR-AFM images of SAM and PANI films show that the pyramidal crystallites are in emeraldine salt (ES-I) form and the region between the crystallites is in emeraldine base (EB-II) form. The ordered lattice of PANI crystallites as observed by cross-sectional HR-TEM confirms its single crystalline nature as well as epitaxial growth. The heteroepitaxial growth of PANI is attributed to the structural order of interfacial SAM on Si.     

Controlled modification of octadecyltrichlorosilane self-assembled monolayer by CO2 plasma

CO₂-plasma is used to introduce functional groups on the uppermost surface of an alkoxysilane self-assembled monolayer (SAM). The structural and chemical modifications of the material surface were monitored by X-ray reflectometry, atomic force microscopy, X-ray photoelectrons spectroscopy and water contact angle measurements. Optimization of the plasma parameters is performed in order to achieve a maximum functionalization and to prevent degradation of the SAM. Finally, the ability of grafting organic compounds onto the plasma modified SAMS was demonstrated by the formation of an alkoxysilane bilayer.     

Optical properties of an octadecylphosphonic acid self-assembled monolayer on a silicon wafer

We report a study of a full-coverage octadecylphosphonic acid (OPA or ODPA) self-assembled monolayer (SAM) spin-coated on the native oxide layer (SiO₂) of a single crystalline silicon (c-Si) wafer using spectroscopic ellipsometry (SE) and reflectometry (SR). The OPA SAM showed characteristics of being a dielectric film in visible range and becoming absorbing in deep-UV range. By assuming an optical stack model of OPA/SiO₂/c-Si for the OPA monolayer system and adopting the parameterized Tauc-Lorentz dispersion model, we obtained an excellent fit of the model to the SE and SR data, from which dispersion of optical functions as well as thickness of the OPA film were deduced. The OPA film thickness measured by atomic force microscopy (AFM) on partial coverage OPA samples was used as the initial trial film thickness in the fitting processes. The deduced OPA film thickness from SE and SR data fitting was in good agreement with that obtained by AFM.     

Nanoscale mechanics of solid-supported multilayered lipid films by force measurement

Using atomic force microscopy and molecular force probe, we have studied the structure and nanomechanical response to nano-indentation of multilayered films of dioleoylphosphatidylcholine films prepared by solution spreading, spin-coating, and capillary methods. The influence of the film thickness on the apparent elastic (Young's) modulus is investigated. Young's moduli of samples prepared by the different methods were found to be similar for sufficiently thick films. An ostensible influence of substrate coupling on the apparent Young's modulus is observed for thinner lipid films. The results are discussed in comparison with previously reported estimates for supported lipid bilayers (membranes) and cells.     

Nanomechanical properties of polymer thin films measured by force-distance curves

Force-displacement curves have been acquired with a commercial atomic force microscope on thin films of poly(n-butyl methacrylate) on glass substrates. Different film thicknesses, from 10 up to 430 nm, were chosen to examine in detail the so called “mechanical double-layer” topic, i.e., the influence of the substrate on the determination of the mechanical properties of thin films. Taking advantage of the Hertz theory we calculated for all films the contact radius between tip and sample as a function of the applied load. Further Young's modulus of the samples was derived from the experimental data as a function of the applied load and, alternatively, of the deformation. The results of this analysis for 10 different film thicknesses were fitted with several half empirical equations proposed by several researchers. The focus of this work is to evaluate such existing half empirical theories for mechanical double-layers and to show the need for an alternative consistent approach.     

Damage mode tensile testing of thin gold films on polyimide substrates by X-ray diffraction and atomic force microscopy

In situ tensile testing has been performed on thin gold film, 320 nm thick, deposited on polyimide substrates. During the tensile testing, strain/stress measurements have been carried out by X-ray diffraction using the d-sin²ψ method. The X-ray stress analysis suggests crack formation in the films for stresses greater than 670 MPa. The surface of the deformed specimen observed by atomic force microscopy (AFM) exhibits both cracks and two types of straight-sided buckling patterns lying perpendicular to the tensile axis. These buckling patterns can have a symmetrical or asymmetrical shape. The evolution of these two kinds of buckling structures under tensile stress has been observed in situ by AFM and compared to X-ray stress data. The results indicate that symmetrical straight-sided buckling patterns are induced by the compressive stress during unloading, whereas the asymmetrical result from the delamination of the film during the tensile deformation.     

Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method

ZnO:SiO₂ films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO₂ films are of great interest as catalyst and gas-sensing materials. The sol-gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO₂ films obtained by the sol-gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO₂ films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO₂ nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol-gel method.     

Focused ion beam milled pattern structures induced by laser pulse on AgInSbTe phase change films

Uniform and regular pattern structure array were fabricated on carbon (20 nm) /AgInSbTe (200 nm) / glass film by laser direct-writing technology with green and blue laser, respectively. The focused ion beam was used to mill the patterned structures to obtain the morphology inside the structures. The microscopy results indicate that the interior of the structure is hollow and the material is resolidified. Many shrinkage cavities and pores, the main characteristics of rapid solidification, were found inside the structures. The strong convection flow from the center of the molten pool to its periphery was the main cause of microbump formation. Material volume expansion from solid to liquid, and even to gas, also contributed to bump formation.     

The influence of the additives composition and concentration on the properties of SnOx thin films used in photocatalysis

The aim of this study is to investigate the influence of different organic additives on the surface properties of SnO_x thin films used for photocatalytic degradation of methylene blue. The films were obtained by anodic oxidation of tin substrate in electrolyte solutions containing green additives based on hydrophobic and hydrophilic maleic anhydride copolymers. The hydrophobic copolymer leads to the formation of thin films with increased specific area which generates a larger interfacial area between the layers and the dye solution. The consequence is an improvement in the photocatalytic efficiency: up to 16% compared to less than 5% for samples electrodeposited without polymer. The hydrophilic copolymer presence in the electrolyte solution leads to higher grain size and lower surface energy which significantly reduce the photocatalytic properties of the layers. The use of copolymers can be a tool for enhancing the surface roughness and film's wettability and thus the photodegradation efficiency.     

Dynamic behaviour of a nanoscale-patterned phospholipid thin film on mica and silicon studied by atomic force microscopy

The temporal evolution of the morphology of nanoscale-patterned phospholipid thin films on mica and silicon surfaces has been investigated with an atomic force microscope (AFM). The AFM images reveal that nanoscale scratch lines on thin films prepared on mica contract with time and eventually form roundish holes. An elevated sample temperature accelerates this morphological evolution. We model such an evolution based on the interplay of the thin-film surface line tension and the friction between the thin film and the substrate. The results show that the temperature-dependent contraction is governed by the ratio of the friction coefficient and the surface line tension. The friction at the lipid/mica interface decreases to a seventh as the sample temperature rises from 18 to 60 °C. This model is supported by experiments on silicon surfaces, on which contraction of the scratch patterns is limited because of an expected greater interfacial friction.     

A study of size dependent structure, morphology and luminescence behavior of CdS films on Si substrate

Size tunable cadmium sulfide (CdS) films deposited by a dip coating technique on silicon (100) and indium tin oxide/glass substrates have been characterized using X-ray diffraction, X-ray reflectivity, transmission electron microscopy, atomic force microscopy and photoluminescence spectroscopy. The structural characterization indicated growth of an oriented phase of cadmium sulfide. Transmission electron microscopy used to calculate the particle size indicated narrow size dispersion. The tendency of nanocrystalline CdS films to form ordered clusters of CdS quantum dots on silicon (100) substrate has been revealed by morphological studies using atomic force microscopy. The photoluminescence emission spectroscopy of the cadmium sulfide films has also been investigated. It is shown that the nanocrystalline CdS exhibit intense photoluminescence as compared to the large grained polycrystalline CdS films. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the observed photoluminescence behavior of CdS is substantially enhanced when the nanocrystallites are assembled on silicon (100) substrate.     

Study on chemical vapor deposited copper films on cyano and carboxylic self-assembled monolayer diffusion barriers

Thin copper films were produced by chemical vapor deposition using the precursor Cu^IIbis-hexafluoroacetylacetonate on the SiO₂/Si substrate modified with cyano and carboxylic self-assembled monolayers (SAMs) as diffusion barriers. The characterizations of the deposited copper films were measured by various thin film analysis techniques, i.e., scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. The comparison between copper deposited on SiO₂ and on the SAM-modified SiO₂ substrates indicates that the copper films tend to be deposited onto the SAM-modified substrate, which is further proved by the calculation results of the interaction energies of copper and the SAMs with density functional theory method.