Hydrophilic Si Research Articles

Surface dependent thermal evolution of the nanostructures in ultra-thin copper(ii) phthalocyanine films

The thermal evolution of the nano-grain structure and surface of ultra thin copper(II) phthalocyanine (CuPc) films was investigated by real time grazing incidence small angle X-ray scattering (GI-SAXS) and X-ray reflectivity measurements. The evolution was strongly affected by the substrate surface energy. On hydrophilic Si, CuPc film consisted of disk shaped nano-grains of two different sizes. The larger grains showed lateral crystal growth and planarization by thermal annealing, while the smaller grains did not increase in size. The grains formed clusters at high temperature. On hydrophobic Si, CuPc nano-grains are more randomly distributed. The crystal size did not increase in size upon thermal annealing. Thermal annealing induced a more random distribution of nano-grains with an increase in roughness, and large islands formed by the coalescence of small grains. The different thermal evolution models of CuPc films based on GI-SAXS analysis are consistent with the different temperature behavior of the hole mobilities of organic field-effect transistor (OFET) devices fabricated on both surfaces.

Substrate and drying effect in shape and ordering of micelles inside CTAB–silica mesostructured films

Deviation from a perfect 2D-hexagonal (p6m) structure, for CTAB–silica mesostructured films prepared by adding different amounts of excess ethanol to a solution of CTAB and TEOS just before spin coating on OH- and H-terminated Si substrates, is observed from combined X-ray reflectivity and grazing incidence small angle X-ray scattering measurements. Such a deviation can be well understood in terms of the shape and ordering of the micelles, with or without the silica coating layer's contribution, inside the film. For example, cylindrical shaped micelles, which are initially circular on a hydrophilic OH-terminated Si substrate in order to form a perfect 2D-hexagonal structure, become elliptical (extended along the in-plane) on a hydrophobic H-terminated Si substrate to form a slightly compressed 2D-hexagonal structure due to a different attachment of the film to the substrate. With time, due to the drying of the silica materials and its restricted movement along the in-plane direction, the films on both the substrates are compressed along the out-of-plane direction only, to form observed centered rectangular (c2mm) structures. Also, due to the asymmetric shrinkage, stress is developed, which deteriorates the ordering in the film. The final shape of the micelles, including the silica coating layer's contribution, shows maximum and minimum deviations from the circular shape inside the thick film on a OH–Si substrate and the thin film on a H–Si substrate, respectively. The deviation in the shape of the micelles itself, which is of actual importance, seems to be maximum and minimum inside the thick film on a H–Si substrate and the thin film on a OH–Si substrate, respectively, and is essentially determined by the substrate nature and initial silica wall thickness.

Study of Hydrophilic Si Direct Bonding with Ultraviolet Ozone Activation for 3D Integration

Wafer-level hydrophilic silicon direct bonding is demonstrated using ultraviolet ozone (UVO) activation. The activation is performed at room temperature in atmospheric ambient for 3, 6, 9, and 12 min under UVO exposure, respectively. The activation process helps to form a hydrophilic surface (contact angle < 10°) for hydrophilic bonding and to improve the surface roughness to <0.25 nm possibly by removing the surface hydrocarbon contaminants. After annealing at 200°C for 3 hr, excellent bonding strength is achieved. High bonding uniformity is obtained in the bonded wafers which are activated for 3 min exposure in UVO. Helium over-pressure in a bombing chamber and helium leak rate detection by a mass spectrometer are used for hermeticity measurement of Si cavities sealed and bonded after UVO activation. The detected helium leak rate indicates that the best hermeticity can be obtained with an activation time of 3 min. The C-V curves of the metal-oxide-semiconductor (MOS) capacitors which are fabricated using UVO clean on the Si surface prove that prolonged exposure to UVO can degrade the bonding quality.

Antifogging and antireflective silica film and its application on solar modules

Superhydrophilic silica film with antifogging and antireflective properties was prepared by dip-coating the glass in SiO 2 nanoparticles sol. The transparent superhydrophilic film was composed of silica nanoparticles of about 20–30 nm in diameter. The combination of hydrophilic Si OH on the surface and nanoporous surface topography was believed to be responsible for the antifogging property. The nanopores also effectively reduced the refractive index of the film and resulted in the antireflective property. By sintering the multifunctional silica film, a pencil hardness of 2H could be obtained. Application of the functional film in full-sized photovoltaic modules (1580 × 808 × 35 mm) demonstrated an increase of the power output of about 2%, 5% and 8%, respectively, at incidence angles of 0°, 30° and 60°.

Grazing Incidence Small-Angle X-ray Scattering Analysis of Initial Growth of Planar Organic Molecules Affected by Substrate Surface Energy

Disc-type nano grains of copper(II) phthalocyanine (CuPc) were observed in an ultrathin CuPc layer (5 nm) evaporated on a hydrophilic Si surface showing the structure factor in grazing incidence small-angle X-ray scattering measurement. The disk type grains consisted of a crystalline part and a noncrystalline part. The disk type grains were smaller in the case of evaporation on an octadecyltrichlorosilane (ODTS) treated hydrophobic Si surface, which showed lower crystallinity with random distribution. Despite regularly distributed CuPc grains, the mobility was lower in a FET device fabricated on a hydrophilic surface than on an ODTS Si surface due to the lower average density of the molecules relating to porous molecular packing between nanograins on a hydrophilic surface.

Fabrication of colloidal crystals on hydrophilic/hydrophobic surface by spin-coating

Herein, we demonstrate the structure of the PS colloidal crystals which were fabricated on the hydrophilic/hydrophobic Si wafers by a spin-coating technique. Monodisperse PS colloids are spin-coated onto self-assembled monolayers of 3-(aminopropyl)triethoxysilane and propyltrimethoxysilane coated Si wafers. PS spheres organized as ordered close-packed face-centered cubic structure with (1 1 1) planes on the hydrophilic surface while they gathered without the crystal structure on the hydrophobic surface. This paper also reports a simple and rapid method to fabricate the close-packed structure of hollow TiO 2 spheres. The colloidal crystal of TiO 2 hollow spheres was prepared using the PS sphere template on the hydrophobic surface. The mechanism for the growing multilayers of self-assembled PS particles from a suspension onto a hydrophilic and hydrophobic Si wafer substrates using the spin-coating method at various rotating speeds is also discussed in this paper.

Roles of 2D Liquid in Reduction of the Glass-Transition Temperature of Thin Molecular Solid Films

To clarify the properties of a liquidlike phase formed on the surface, self-diffusion of molecules in monolayer and multilayer films has been investigated by measuring their uptake behaviors in porous Si substrates using time-of-flight secondary ion mass spectrometry and temperature programmed desorption. It is found that self-diffusion of water, ethanol, and 3-methylpentane in the first monolayer commences at temperatures of ca. 110, 85, and 50 K, respectively, which are considerably lower than the corresponding glass-transition temperatures (Tg) in the bulk. The surface mobility of water appears to be not influenced by hydrogen bonds with substrates: The molecules form droplets on the H-terminated Si substrate at 110 K, whereas they start to diffuse into pores of the OH-terminated Si substrate at the same temperature. The ethanol and 3-methylpentane molecules tend to diffuse into pores of both hydrophilic and hydrophobic Si substrates, although a small number of much slower diffusers remain on the surface. Multilayer films are also incorporated into pores at temperatures well below Tg because of sequential diffusion of the topmost-layer molecules. The origins of nanoconfinement effects on reduction of Tg are discussed based on these findings.

Surface-Induced Micelle Orientation in Nafion Films

Grazing incidence SAXS (GISAXS) was used to examine the surface structure of thin Nafion films spin-cast on hydrophobic silanized Si substrate and exposed to water and vapor. GISAXS spectra at low subcritical incidence angles, indicative of a few nanometers thick surface region, showed that in vapor Nafion micelles at the surface tend to align parallel to the surface, while under water they are preferentially oriented normal to the surface, in agreement with previously proposed structural picture and with AFM and contact angle results. However, spectra at near-critical incidence angles representing the bulk of the films indicate the micelles preferentially align normal to the surface, regardless of the external phase. This observation is in contrast with previous studies that employed hydrophilic native Si substrates, in which the observed micelle orientation was parallel to the surface. The proposed explanation assumes that lateral interactions with octadecyl tails and/or heterogeneities at the silanized...

Formation of single-domain homogeneous Au nanoparticle monolayer at the water/oil interface and its application to surface-enhanced Raman scattering

We fabricated a closely packed Au nanoparticle monolayer with millimeter dimensions on a hydrophilic Si substrate using a water/oil interface method. The surface-enhanced Raman scattering of Rhodamine 6G dye molecules adsorbed on these substrates was measured. For this structure, we simulated the electromagnetic-field enhancement when the laser light was focused on the sample, assuming the hexagonal unit cell. We suggest that the strong field enhancement arises from interstitial gaps between nanoparticles.

Magnetic amphiphilic composites based on carbon nanotubes and nanofibers grown on an inorganic matrix: effect on water-oil interfaces

New magnetic amphiphilic composites were prepared by the catalytic carbon vapor deposition (CVD) growth of carbon nanotubes and nanofibers using ethanol as carbon source and red mud waste (RM, a by-product of the Bayer process of alumina production) as catalyst and support. Temperature-programmed CVD (TPCVD), analyses by X-ray diffractometry (XRD), Mössbauer spectroscopy, energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, thermogravimetry (TG/DTA), elemental analysis (CHN), superficial area determination (BET), scanning (SEM) and transmission (TEM) electron microscopies and magnetic measurements showed that ethanol reduces the iron ions in the red mud to form magnetic phases, e.g., Fe3O4 and Fe0, and carbon deposits (5-42 wt.%), particularly nanotubes and nanofibers. The combination of the hydrophobic carbon nanostructures with the hydrophilic Al, Si and Ti oxides present in the RM produced amphiphilic materials with excellent interaction with the water-oil interface. Soybean oil or decalin mixtures with water (completely immiscible) were easily emulsified in the presence of the amphiphilic composites. When the composites were added to stable biodiesel-water emulsions, the amphiphilic particles diffused to the interface oil-water. These composite particles were attracted by a magnet, carrying the oil droplets with them and leading to the complete demulsification and separation of the biodiesel from the water.

Effect of water and air–water interface on the structural modification of Ni-arachidate Langmuir–Blodgett films

Nickel arachidate (NiA) Langmuir-Blodgett (LB) films have been deposited on hydrophilic Si(0 0 1) substrates by three (up-down-up) and five (up-down-up-down-up) strokes. During deposition, substrates were kept inside the water subphase for different times after each down stroke. Structural information of all the LB films have been obtained from X-ray reflectivity (XRR) studies. One and two symmetric monolayer (SML) was deposited on top of the asymmetric monolayer (AML) in three and five stokes respectively. All the preformed LB films were then used to go through the air-water interface with the same speed that was used at the time of film deposition. Structural information obtained from the XRR studies show that mainly the top layer density decreases after passing through the air-water interface but the layered structure remains the same. Information obtained from both the XRR and atomic force microscopy (AFM) studies suggest that molecules peeled from the top SML layer do not reincorporate with the LB film through tail-tail hydrophobic interaction. Our study shows that NiA LB film has better stability compared with cadmium arachidate LB film inside the water subphase without forming any out-of-plane molecular reorganization.

Effect of surface hydrophilicity on the nanofretting behavior of Si(100) in atmosphere and vacuum

With an atomic force microscopy, the effect of surface hydrophilicity on the nanofretting behavior of Si(100) against SiO2 microsphere was investigated under vacuum and atmosphere conditions, respectively. The surface hydrophilicity revealed a strong effect on the motion behavior, adhesion force, friction force, and nanofretting damage of Si(100)/SiO2 pairs. The increase in the hydrophilicity of Si(100) surface could expand the stick regime of Si(100)/SiO2 pairs into a higher value of displacement amplitude. While the nanofretting ran in atmosphere, both adhesion and friction forces in the initial cycle would be larger when the Si(100) surface was more hydrophilic. However, because of the in situ chemical modification of SiO2 tip in nanofretting, they might reveal a decrease with increasing nanofretting cycles. Either in vacuum or in atmosphere, the nanofretting damage was weaker when the Si(100) surface was more hydrophobic. Because of the lack of oxygen and vapor in vacuum, the nanofretting damage on the Si(100) surface was dominated by mechanical interaction. The damage was characterized as the depression of 0.1–0.2 nm in depth on hydrophilic Si and the hillocks of 0.8–0.9 nm in height on hydrophobic Si and original Si. However, the nanofretting damage in atmosphere was much more serious, which was identified as the grooves of 8–11 nm in depth on Si(100) surfaces. Analysis indicated that even if the nanofretting damage in atmosphere was the coupled results of mechanical interaction and tribochemical reaction, the tribochemical reaction played a dominated role. These results will help us to understand the effect of surface properties on nanofretting of silicon and optimize the surface treatment technology to minimize the potential nanofretting failure of microdevices in microelectromechanical system (MEMS).

Photoetching of Silicon by N-Fluoropyridinium Salt

A photoetching method with -fluoropyridinium salts is proposed in this study. Si is etched by applying -fluoropyridinium salts to its surface and exposing the surface to light. The etched surface that uses liquid -fluoropyridinium salts is smoother than when solid -fluoropyridinium salts are used. The etching depth increases with exposure time. H-terminated hydrophobic Si is easier to etch than OH-terminated hydrophilic Si. is produced by photoetching. This suggests that -fluoropiridinium salts receive excited electrons from Si and supply Si with active F species.

Effect of Free Radical Activation for Low Temperature Si to Si Wafer Bonding

In this study, a comparison of different surface treatments for direct Si to Si wafer bonding is reported. Hydrophilic and hydrophobic Si wafers have been exposed to a range of pretreatments, involving oxygen and nitrogen radical activation before in situ wafer bonding in vacuum. After low temperature annealing at 200 and , the formation of voids has been observed by using scanning acoustic microscope inspection. A comparison of the bonding energy has been conducted and analyzed as a function of the surface treatments. Our experiments demonstrate that the remote plasma pretreatment is a very suitable process for surface modification of hydrophilic and hydrophobic Si to Si direct wafer bonding.

Photo-etching of Silicon by N-Fluoropyridinium Salt

Silicon is etched by applying N-fluoropyridinium salts to its surface and exposing the surface to light. Etching depth increases with exposure time. The H-terminated hydrophobic Si is easier to be etched than the OH-terminated hydrophilic Si. SiF4 is produced by the photo-etching.

Heat shock structure of luciferase on wet-treated Si surface

Heat shock structure of luciferase on a wet-treated Si surface was estimated by molecular dynamics simulations. The structural changes in the active site of luciferase were smaller on the hydrophobic Si surface than on the hydrophilic Si surface at high temperature, although the structural changes in the active site of luciferase were smaller on the hydrophilic Si surface than on the hydrophobic Si surface at room temperature. The fine wet-treatment could improve the heat shock resistance of luciferase on the Si surface.

Mechanical Properties and Chemical Reactions at the Directly Bonded Si–Si Interface

Directly bonded interfaces of hydrophilic and hydrophobic Si(100) wafers were studied from the viewpoint of bonding energy and chemical products as a function of the annealing temperature. The experimental results indicated that for both hydrophilic and hydrophobic Si/Si bonded wafer pairs, the behavior of the bubbles at the bonding interface and the bonding energy were closely related to the behavior of the hydrogen and oxygen atoms at the bonding interface. The bonding mechanisms for both cases have been discussed on the basis of the chemical reactions induced by the annealing temperature.

Non-fluorinated superamphiphobic surfaces through sol–gel processing of methyltriethoxysilane and tetraethoxysilane

In this study, a simple approach was developed to fabricate an extremely superamphiphobic coating material by the tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) sol–gel derived materials. TEOS and MTES derived moieties were designed for a physical roughness and hydrophobic surface characteristic, respectively. The 29Si solid-state NMR and ESCA analysis showed the coated silica composition was similar to the feeding ratios of TEOS/MTES. The surface structure characterized from SEM and TEM suggested the nanoparticle-based silica surface was observed at a high TEOS/MTES content but changed to a relatively smooth surface at a low TEOS content. The contact angles of water and CH 2I 2 on the pure TEOS derived coated surface were both 0° due to the hydrophilic Si–OH group. As the MTES composition increased to 25 mol% (T5M3), the coated surface had the contact angles of 149.8° and 133.1° for water and CH 2I 2, respectively. It revealed that the T5M3-coated surface exhibited both super-hydrophobicity and super-oleophobicity, i.e., superamphiphobicity. Also, it had a relatively low-surface energy (1.38 mJ m −2) considerably lower than that of the F-silane-coated surface with 39.3 mJ m −2. As the MTES composition increased further, both contact angles of water and CH 2I 2 decreased. Especially, they decreased dramatically at the MTES feeding composition higher than 75 mol%, due to the much less rough surface at a higher MTES composition. The present study suggests that superamphiphobic surface could be achieved by non-fluorinated sol–gel derived silica materials.

Characteristics of silicon oxide thin films prepared by sol electrophoretic deposition method using tetraethylorthosilicate as the precursor

Silicon dioxide films were prepared on p-type Si (1 0 0) substrates by sol electrophoretic deposition (EPD) using tetraethylorthosilicate (TEOS) at low temperature. According to the variation of sol dipping conditions, we estimated the characteristics of SiO 2 films, such as composition, surface morphology, wet etch rate, breakdown voltage, etc. The growth rate of the film increased linearly with increasing TEOS quantity in solution. It increased exponentially with the increase in deposition time, and the film thickness was saturated at approximately 200 nm on hydrophilic Si surface after more than 6 days. The growth rate of the EPD SiO 2 films on the hydrophobic Si surface was much lower than that of the film on the hydrophilic Si surface.

Thermal Behavior of Luciferase on Nanofabricated Hydrophilic Si Surface

The thermal behavior of luciferase on nanofabricated hydrophilic Si surface was investigated using molecular dynamics simulations. At high temperature, LUC_CHANGES (structural changes in the active site of luciferase) were smaller on the nanofabricated hydrophilic Si surface than on a non-nanofabricated hydrophilic Si surface, although LUC_CHANGES were slightly larger on the nanofabricated hydrophilic Si surface than on a non-nanofabricated hydrophobic Si surface. At room temperature, LUC_CHANGES were smaller on the nanofabricated hydrophilic Si surface than on a non-nanofabricated and wet-treated Si surface. Thus, nanofabricated hydrophilic Si surface would be preferable for practical applications.