Surface Nanomorphology Research Articles

Nanomorphology-driven two-stage hole mobility in blend films of regioregular and regiorandom polythiophenes

We report the nanomorphology-driven two-stage hole mobility in the blend films of regioregular and regiorandom poly(3-hexylthiophene) (P3HT) polymers of which regioregularity was 92.2% and 33.0%, respectively. The hole mobility of blend films was measured by employing a top-contact type organic field-effect transistor which has an aromatic polyimide gate insulating layer and silver source/drain electrodes. Results showed that the hole mobility of blend films was suddenly reduced as large as two orders of magnitude as the bulk regioregularity of blend films decreased from 89.8% to 86.3%, even though the hole mobility change was far less than one order of magnitude after and before this boundary condition. The discontinuous two-stage hole mobility trend has been attributed to the destruction of P3HT chain ordering/alignment in the blend films at the boundary blend composition, as evidenced from the huge changes in optical absorption coefficient, surface nanomorphology, and in-plane/out-of-plane nanostructures in the blend films.

Novel response function resolves by image deconvolution more details of surface nanomorphology

A novel method of image processing is presented which relies on deconvolution of data using the response function of the apparatus. It is revealed that all the surface structures observed by digital imaging are generated by a convolution of the response function of the apparatus with the surfaces’ nanomorphology, which provided images of convoluted physical structures rather than images of real physical structures. In order to restore the genuine physical information on surface structures, a deconvolution using a novel response function of the feedback circuitry is required. At the highest resolution, that is, atomic resolution, the effect of deconvolution is at its maximum, whereas images at lower resolution are sharpened by eliminating smoothing effects and shadow effects. The method is applied to measurements of imaging by in situ scanning tunnelling microscopy (in situ STM) at atomic resolution and to imaging by in situ STM of electrocrystallization of copper on gold in electrolytes containing copper sulfate and sulfuric acid. It is suggested that the observed peaks of the recorded image do not represent atoms, but the atomic structure may be recovered by image deconvolution followed by calibration of distances, correction for drift phenomena and rotation in the plane of the surface. The technology may subsequently reveal more details of molecular adsorbents. The impact of in situ STM at atomic and lower resolution on imaging is discussed in the paper.

The influence of sulfonated polyethersulfone (SPES) on surface nano-morphology and performance of polyethersulfone (PES) membrane

In this research, firstly sulfonation of polyethersulfone (PES) was carried out and then polyethersulfone (PES)/sulfonated polyethersulfone (SPES) blend membranes were prepared with phase inversion induced by immersion precipitation technique. polyvinylpyrrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. SPES was characterized by FT-IR and UV–visible spectra, ion exchange capacity and swelling ratio. The characterization of SPES polymer indicates that the sulfonic acid groups were produced on PES polymer. Also, the prepared PES/SPES blend membranes were characterized by contact angle, AFM, SEM and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicity of PES membrane is enhanced by increasing the SPES content in the casting solution. The SEM and AFM images show that the addition of SPES in the casting solution results in a membrane with larger surface pore size and higher sub-layer porosity. The mean pore size of the membrane increased from 98 nm for PES membrane to 240 and 910 nm for 50/50 and 0/100 PES/SPES blend membranes, respectively. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with SPES. Moreover, the protein rejection of PES/SPES blend membranes was lower than PES membrane.

Precursor Polymer Effect on Polyimide/Silica Hybrid Nanocomposite Films

Here we report the influence of the polyimide precursor type on the surface morphology and properties of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA PI)/silica hybrid composite films. Two types of precursor polymer were employed: poly(p-phenylene biphenyltetracarboxamic acid) (BPDA-PDA PAA) and poly(p-phenylene biphenyltetracarboxamic diethyl ester) (BPDA-PDA PES). These precursor polymers were mixed with tetraethoxysilane in the presence of HCl and H2O, which led to the precursor mixture films that contain in-situ generated silica particles via sol-gel process. Then the precursor mixture films were subject to thermal imidization to make polyimide/silica hybrid composite films. Results showed that the PAA precursor has better compatibility with silica particles, which is mainly attributed to the early making of silyl ester bonds (as evidenced by X-ray photoelectron spectroscopy) between carboxylic acid groups in the PAA and hydroxyl groups in silanol molecules. Further evidences were provided by the measurement of surface nanomorphology, crystal nanostructure, thermal/mechanical properties, and optical birefringence.

Discharge properties of a micro plasma cell with an MgO–NiO protecting layer

MgO thin film is widely used as a protecting layer for Alternating Current-Type Plasma Display Panels (AC-PDPs) and the study of discharge properties of micro plasma cells is the main approach on how to reduce the power consumption of AC–PDPs. In this work, MgO–NiO composite thin films were deposited by Ion Beam-Assisted Deposition (IBAD) technique. We also investigated the effects of ion irradiation on the surface nano-morphology, the crystal orientation, oxygen vacancy and breakdown voltage, which are directly related to the secondary electron emission coefficient γ of thin films. In the production of MgO thin films, it is known that the addition of small amounts of metallic element to the MgO will improve the discharge properties, even though the mechanism of emitting secondary electrons from the surface of thin films induced by low energy ions in micro plasma cells is not clarified yet. This research was focused on NiO as a minority element added to MgO due to its high solubility with MgO and its low band gap. The IBAD technique has the possibility to improve the discharge properties of micro plasma cells by increasing the density and surface morphology of the film. Therefore it is expected that by adding NiO and IBAD, the result will be a great improvement on the discharge properties of micro plasma cells. The thin film preparation was carried out by taking the ion beam energy and the NiO relative ratio as the variable. The experimental results show approximately 10% improvements in the discharge properties due to the change in the surface morphology, crystal orientations and density of the films. To find the optimum condition for making thin films, IBAD technique and MgO composite films will be a useful way to produce PDPs with low energy power consumption.

Formation and metrology of dual scale nano-morphology onSF6 plasma etched silicon surfaces

Surface roughness and nano-morphology inSF6 plasma etched silicon substrates are investigated in a helicon type plasma reactor as afunction of etching time and process parameters. The plasma etched surfaces are analyzedby atomic force microscopy. It is found that dual scale nano-roughness is formatted on thesilicon surface comprising an underlying nano-roughness and superimposed nano-mounds.Detailed metrological quantification is proposed for the characterization of dual scalesurface morphology. As etching proceeds, the mounds become higher, fewer and wider, andthe underlying nano-roughness also increases. Increase in wafer temperature leads tosmoother surfaces with lower, fewer and wider nano-mounds. A mechanism based on thedeposition of etch inhibiting particles during the etching process is proposed for theexplanation of the experimental behavior. In addition, appropriately designedexperiments are conducted, and they confirm the presence of this mechanism.

Nanoscale morphology for high hydrophobicity of a hard sol–gel thin film

It is challenging to obtain a hydrophobic smooth coating with high optical and mechanical properties at the same time because the hydrophobic additives are soft in nature resulting in reduced hardness and durability. This paper reports a durable hydrophobic transparent coating on glass fabricated by sol–gel technology and a low volume medium pressure (LVMP) spray process. The sol–gel formula consists of a pre-linked hydrophobic nano-cluster from hydroxyl-terminated polydimethylsiloxane, titanium tetraisopropoxide and a silica-based sol–gel matrix with silica hard fillers. Polydimethylsiloxane (PDMS) is uniformly distributed throughout the coating layer providing durable hydrophobic property. Mechanical properties are achieved by the hard matrix and hard fillers with the nano-structures. Due to the surface nano-morphology, a high degree of hydrophobicity was maintained with only 10 vol.% PDMS, while the hardness and abrasion resistance of the coatings were not significantly compromised. Chemical analyses by FTIR confirmed the uniform distribution of the PDMS and surface morphology analyses by atomic force microscopy (AFM) displayed the nano-surface structures that enhanced the hydrophobicity. The special surface nanostructures can be quantified using surface Kurtosis and ratio between asperity peak height to distance between peaks. The LVMP process influences the spray droplet size resulting in different surface structures.

Effect of the Surface Nanomorphology on the Growth of Al Whiskers Formed by Glancing Angle Deposition on a High Temperature Substrate

ABSTRACTWe have investigated the effect of the substrate-surface morphology on the growth of Al whiskers grown by high temperature glancing angle deposition (HT-GLAD). Before the HT-GLAD of Al at 390 °C, the morphology of the substrate was systematically modified by depositing nanocolumnar SiO2 layer of thickness between 0 and 100 nm on the flat SiO2 layer. Aluminum whiskers with the width of ≈100 nm and the length ≤ μm are found on all the samples. The number of short whiskers, which can be grown from very small nuclei, depends strongly on the thickness of the SiO2 nanocolumnar layer and shows the maximum at SiO2 thickness of 20 nm. On the other hand, the number of long whiskers, which requires extraordinary amount of Al than that deposited on the side surface of the whikers, is almost independent of SiO2 thickness. These facts suggest that the surface roughness of the substrate plays an important role in the nucleation of the whiskers and that there are some transport processes of Al, which are insensitive to the surface morphology.

Low energy ion induced secondary electron emission coefficient of magnesium oxide films

Magnesium oxide (MgO) film is widely employed as a protective layer for plasma display panels (PDPs). The aim of this paper was to investigate the relationship between secondary electron emission coefficient (γ) of the MgO films and conditions of ion beam assisted deposition (IBAD). Elemental ratio, density, crystal orientation and surface nano-morphology of the films were also analyzed. The authors developed a low energy ion beam source and applied it to measurement of the γ. The experimental results suggest that the γ decreased drastically as the ion beam energy increased more than or equal to 1000eV. This is attributed to (200)-oriented film with low γ that was grown preferentially as the beam energy increased. On the other hand, dense and smooth films with high sputtering resistance could be obtained by IBAD. This leads to the long lifetime of the PDPs.

Epoxy‐Carbazole Polymeric Network Nanolayers for Organic Light‐Emitting Devices

We report the study of epoxy‐carbazole polymeric network (ECzPN) nanolayers as a hole injection/transport layer in organic light‐emitting devices. The ECzPN nanolayers were prepared by the thermal curing reaction of epoxidized cresol novolak and 3,6‐ diaminocarbazole in the presence of catalytic amount of triphenyl phosphine. The curing reaction was examined with Fourier transformed infrared spectroscopy, whilst the thermal stability was studied with thermogravimetric analysis. Optical absorption and emission spectroscopy were employed to investigate the optical properties of ECzPN nanolayers, whilst atomic force microscopy was used to examine the surface nanomorphology of ECzPN nanolayers. The result showed that the device performance was greatly influenced by the weight ratio of monomers, because the highest occupied molecular orbital level of ECzPN was significantly changed with the ratio. This is attributed to the ground‐state complexes induced by the specific interaction (hydrogen bonding) between the lone pair electrons in amines of carbazole moieties and the hydroxyl group of ring‐opened epoxide moieties.

Ion beam modification of polyimides with linear ion source

AbstractPolyimide films are widely used in various industrial fields. Some typical products are flexible printed circuits (FPCs), flexible displays, and electronic papers. Good adhesion between metal thin films and polyimide films is required for their long lifetime. Ion beam irradiation to the polyimide films modifies the chemical compositions, the chemical states, and the surface nanomorphology. These modifications are potential techniques to improve the adhesion. In this study, the authors employed a linear ion source, which is able to irradiate ion beam on large surfaces homogeneously. The linear ion source is desirable for industrial usage because of its high productivity. The aim of this work was to investigate the effect of modification using the linear ion source. The chemical states of the interface were characterized using x-ray photoelectron spectroscopy (XPS). The surface nanomorphology was investigated by atomic force microscopy (AFM). The performance of the modification system will be discussed, and the characteristics of the modified polyimide will be investigated in detail.

Ion beam processing of magnesium oxide thin films for PDP application

In plasma display panels (PDPs), MgO (magnesium oxide) thin film is used as a protective layer that is placed between the electrodes on the front glass panel on one side of the discharge cells. The aim of this study is to improve the secondary electron emission coefficient of the protective layer. This improvement leads to reduction in consumption of energy. In this study, MgO thin films were prepared using electron beam evaporation method. The ion beam-assisted deposition (IBAD) technique is used to control the crystal orientation, surface nano-morphology, density, and composition. Oxygen ion beam was utilized to irradiate the growing films. In order to control the film properties, the acceleration energy and current density of ion beam and the deposition rate were taken as the variables. The crystallinity, density, composition of the films were analyzed by X-ray diffraction (XRD) and Rutherford backscattering spectroscopy (RBS). The secondary electron emission coefficients were measured by an apparatus developed in this study. The experimental results show that the irradiation of ion beam during deposition changes the crystal structure of the films and it influences their secondary electron emission coefficient.

Characteristics of ion beam modified magnesium oxide films

In this investigation, a novel technique was applied to MgO films for the purpose of improving the secondary electron emission coefficient. It is believed that a high secondary electron emission coefficient of an MgO protective layer could lead to a high performance of a plasma display panel. An oxygen ion beam irradiation was employed at varying modification time. Characterization of the modified MgO surface was performed using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The secondary electron emission coefficient of MgO films was measured using a newly developed apparatus. It was observed that the oxygen ion irradiation increased the secondary electron emission coefficient of MgO films. A significant increase was observed for the MgO films with low ion irradiation time. Results obtained from XPS and AFM suggested that the secondary electron emission coefficient of MgO films was considerably dependent on the surface nano-morphology. High secondary electron emission coefficient was observed for MgO films with a smooth surface.

Protein adsorption and fibroblast adhesion on irradiated polysiloxane surfaces.

A very peculiar case of differential cell response towards polysiloxane surfaces of very similar composition is investigated. Poly(hydroxymethylsiloxane) (PHMS) surfaces treated either by O(2)-plasma or 6 keV Ar(+)-beams have been used to test the adhesion, proliferation and spreading of human fibroblasts. The surface chemical structure and nanomorphology were investigated by means of X-ray photoelectron spectroscopy (XPS), surface free energy measurements and atomic force microscopy (AFM). In spite of the close compositional and morphological similarity of the modified surfaces, the viability of the adhered cells, evaluated by means of optical microscopy and epifluorescence microscopy, was found to be very different in the two cases. The study of the features of the adsorbed protein adlayer on the two types of surfaces was performed by XPS and AFM and indicated that the overall cell behavior is connected to a quite different protein aggregation process, occurring respectively on the plasma- and Ar(+)-modified polysiloxane surfaces. It is suggested that the specific biological response of the modified surfaces is determined by the chemical structure at the nanometric level.

The boiling crisis phenomenon: Part I: nucleation and nucleate boiling heat transfer

This paper (Part I) and the companion paper (Part II, Exp. Therm. Fluid. Sci. 26 (6–7) (2002) 793–810) present results of an experimental study on nucleate pool boiling. The experiments were conducted under highly-controlled conditions, using electrically heated, vapor-deposited sub-micron metallic films. A high-speed, high-resolution infrared camera was used to visualize dynamic thermal patterns on the heater's surface over a broad range of heat fluxes, starting from the onset of nucleation and up to boiling crisis. Both fresh heaters and aged heaters were experimented with. The heaters' surface nanomorphology and chemistry were characterized with atomic force microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. First-of-a-kind experimental data on nucleation and boiling heat transfer at high heat fluxes are presented, and a stark difference between fresh and aged heaters is revealed. Remarkable are the origin, evolution and dynamics of the heater dryout process (leading to burnout), identified quantitatively and captured in action for the first time.

Changes in chemical states of PET films due to low and high energy oxygen ion beam

The effects of low (1.0, 3.0 keV) and high (1.0 MeV) energy reactive oxygen ion beam irradiation on surface nano-morphology and chemical state of the constituent elements in the surface layer of a polyethylene terephthalate thin film (thickness 25 μm) are studied in this paper. PET thin film, which has a high potential as a material for biomedical and electrical industries, was irradiated by oxygen ions of variable doses. The treated films were investigated by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). AFM observation revealed that an increase in dose increased the surface roughness. The significant changes in the chemical composition of the surface layer were confirmed by XPS quantitatively. The scission of the chains in the surface layer of PET film was induced by oxygen ion beam irradiation, and the atomic ratio (O1s/C1s) was decreased. The selective sputtering of oxygen atoms in PET film was occurred. This phenomenon is responsible for the creation of carbon-rich surface layer.

Variation of the surface properties of nickel oxide upon heat treatment evidenced by temperature programmed desorption and inverse gas chromatography studies

The surface properties (dispersive component γSdof surface energy and surface nanomorphology) of nickel oxide samplessubmitted to heat treatments up to 550°C were examined bytemperature programmed desorption (TPD) and inverse gaschromatography (IGC) methods. It is shown that the variation ofγSd is complex, first increasing as thetemperature reaches about 300°C, then decreasing and goingagain through a maximum, of lower amplitude, for a treatmenttemperature of about 600°C. These variations follow closelythe TPD curves that related the rate of H2O and, in a much lesserextend of CO2 releases as the heat treatment temperature augments.The surface nanomorphology changes also during this treatment. TheNiO surface becomes very interactive when treated around 250°C. The determination of the adsorption energy distributioncurves (energetic heterogeneity) clearly demonstrates the change insurface properties and development of the population of highadsorption energy sites. Rehydration of the sample treated at 300°C was not possible under our experimental conditions.

Tapping Mode AFM Studies of Nano-Phases on Fluorine-Containing Polyester Coatings and Octadecyltrichlorosilane Monolayers

Lightly cross-linked films were made by solvent casting hydrocarbon polyester solutions containing trace fluorocarbon in the bulk and then curing or cross-linking the film to anchor the fluorine groups. The surface nano-morphology was studied by AFM techniques based on tapping mode AFM which allows very low contact forces and gives indirect surface chemical mapping of different domain morphologies with high lateral resolution. The contrast is usually from different local stiffness variations of domains at or near the surface. More conventional friction force microscopy techniques were also applied to verify the results. The percent coverage of fluorine-rich domains was quantitatively related to that determined from hexadecane contact angles. A low-coverage self-assembled octadecyltrichlorosilane (OTS) monolayer system, exhibiting nano-patches on Si substrate, was used as a control for a newly applied ultra-light-tapping technique which derives its chemical resolution from hydrophilicity differences of the...