Immobilization of immunoglobulin G in a highly oriented manner on a protein-A terminated multilayer system

In this study, we have fabricated a multilayer system consisting of 3-glycidoxypropyldimethylmethoxysilane (GPDS), poly(dimethylsiloxane) bis 3-aminopropyl terminated (PDMS) and protein-A on a silicon wafer surface for oriented immobilization of immunoglobilin G (IgG). The multilayer system with a different component in each layer was characterized by ellipsometry, contact-angle goniometer, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) and fluorescence microscopy. The epoxy-terminated monolayer was formed by the chemisorption of GPDS molecules on the hydroxylated silicon surface. The PDMS film about 4.5 nm thick was produced on the GPDS-monolayer by the chemical reaction between the amine groups at the end of PDMS chain and the epoxy groups of GPDS molecules. By introducing the PDMS chains, the hydrophilic character of GPDS-monolayer decreased. Study of the time dependence of polymer grafting showed that the chemisorption of GPDS is fast, whereas at least 16 h is needed to generate the homogeneous PDMS layer. For immobilization of IgG molecules in a highly oriented manner, protein-A molecules were first chemically bound to an ultrathin (∼4.5 nm) PDMS reactive polymer layer and later used to capture IgG. It was shown that the existence of protein-A in the multilayer system has a strong influence on the binding properties of IgG not only in the efficiency of binding, but also in its specificity. In conclusion, the multilayer system with protein-A has the potential to be further developed into an efficient immunoassay protein chip.     

Configuration of pentacene (C22H14) films on Si(1 0 0)-2 × 1 studied by NEXAFS

Pentacene films on Si(1 0 0)-(2 × 1) surface at 300 K were investigated using near edge X-ray absorption fine structure (NEXAFS) at the carbon K-edge. NEXAFS spectra show that pentacene molecules are chemisorbed on the Si(1 0 0)-(2 × 1) surface for monolayer with flat-laying and predominantly physisorbed on the Si(1 0 0)-(2 × 1) surface for multilayer films with an upright molecular orientation. Absorption angle of pentacene molecules were measured through π^∗ transition. The angles between the double bond and the silicon surface were 35-55°, 65° and 76° at monolayer, 24 and 48 nm pentacene deposited on the Si(1 0 0) surface, respectively. We observed that the intermediate flat-laying phase is favored for monolayer coverage, while the films of molecules standing perpendicular to the Si(1 0 0) surface are favored for multilayer coverage.     

Real time investigation of the growth of silicon carbide nanocrystals on Si(1 0 0) using synchrotron X-ray diffraction

The growth of silicon carbide nanocrystals on Si(1 0 0) is studied by synchrotron surface X-ray diffraction (SXRD) during annealing at high temperature. A chemisorbed methanol monolayer is used as carbon source, allowing to have a fixed amount of carbon atoms to feed the growth. At room temperature, minor changes in the 2 × 1 reconstruction of silicon are observed due to the formation of Si-O-CH₃ and Si-H bonds from methanol molecules. When annealed at 500 °C, carbon incorporation into the silicon leads only to local modifications of the surface structure. Above 600 °C, tri-dimensional silicon carbide nanocrystals growth takes place, together with surface roughening and sharp decrease of domain sizes of the 2 × 1 reconstruction. The different processes taking place at each temperature are clearly distinguished and identified during the real time SXRD measurements.     

XPS study of annealing induced effects on surface and interface electronic properties of Si/Ge nanostructures

The present study is focused on the influence of vacuum thermal treatment on surface/interface electronic properties of Si/Ge multilayer structures (MLS) characterized using X-ray photoelectron spectroscopy (XPS) technique. Desired [Si(5 nm)/Ge(5 nm)]_×10 MLS were prepared using electron beam evaporation technique under ultra high vacuum (UHV) conditions. The core-level XPS spectra of as-deposited as well as multilayer samples annealed at different temperatures such as 100 °C, 150 °C and 200 °C for 1 h show substantial reduction in Ge 2p peak integrated intensity, whereas peak intensity of Si 2p remains almost constant. The complete interdiffusion took place after annealing the sample at 200 °C for 5 h as confirmed from depth profiling of annealed MLS. The asymmetric behaviour in intensity patterns of Si and Ge with annealing was attributed to faster interdiffusion of Si into Ge layer. However, another set of experiments on these MLS annealed at 500 °C suggests that interdiffusion can also be studied by annealing the system at higher temperature for relatively shorter time duration.     

Thermal stability of thiol and silane monolayers: A comparative study

The stability of self-assembled monolayers (SAMs) at elevated temperatures is of considerable technological importance. The thermal stability of 1-octadecanethiol (ODT), 16-mercaptohexadecanoic acid (MHDA) and 1H,1H,2H,2H-perfluorodecanethiol (PFDT) SAMs on gold surfaces, and of 4-aminobutyltriethoxysilane (ABTES) and 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (PFDS) assembled on hydroxylated silicon surfaces, was studied by X-ray photoelectron spectroscopy (XPS). The samples were heated in ultrahigh vacuum to temperatures in excess of that required for SAM degradation. ODT monolayers were stable to ca. 110 °C, while MHDA and PFDT SAMs were stable to ca. 145 °C. ABTES SAMs were found to be indefinitely stable to 250 °C, while PFDS SAMs were stable to 350 °C. These studies demonstrate the advantages of using silane monolayers for moderate to high temperature applications and illustrate differences that arise due to the nature of the tail group. To demonstrate the feasibility of silanes for template-directed patterning, a hydroxylated silicon oxide surface containing microcontact-printed PFDS patterns was spin-coated with a mainly hydrophilic block copolymer. Annealing the surface at 90 °C for 2 h caused the block copolymer to dewet the hydrophobic PFDS-patterned regions and adsorb exclusively on the unpatterned regions of the surface.     

Graft and characterization of 9-vinylcarbazole conjugated molecule on hydrogen-terminated silicon surface

Using wet chemical reaction between N-vinylcarbazole and hydrogen-terminated silicon surface, we present a new and simple route to directly bond π-conjugated organic molecule on silicon surface. The Si can be in the form of single crystal Si including heavily doped p-type Si, intrinsic Si, heavily doped n-type Si, on Si(1 1 1) and Si(1 0 0), and on n-type polycrystalline Si. The covalent bond between 9-vinylcarbazole and silicon surface was confirmed by reflectance FTIR, XPS and contact angle measurement, respectively. A data-encompassing explanation for the mechanism discusses the possible route of the reaction. This simple and low-costly reaction offers an attractive route to attach functional conjugated molecules onto the semiconductor surface which aims to create some unique molecular device in the future.     

Formation of relaxed SiGe on the buffer consists of modified SiGe stacked layers by Si pre-intermixing

High-quality relaxed SiGe films on Si (0 0 1) have been demonstrated with a buffer layer containing modified SiGe (m-SiGe) islands in ultra-high vacuum chemical vapor deposition (UHV/CVD) system. The m-SiGe islands are smoothened by capping an appropriate amount of Si and the subsequent annealing for 10 min. This process leads to the formation of a smooth buffer layer with non-uniform Ge content. With the m-SiGe-dot multilayer as a buffer layer, the 500-nm-thick uniform Si_0.8Ge_0.2 layers were then grown. These m-SiGe islands can serve as effective nucleation centers for misfit dislocations to relax the SiGe overlayer. Surface roughness, strain relaxation, and crystalline quality of the relaxed SiGe overlayer were found to be a function of period's number of the m-SiGe-dot multilayer. By optimizing period number in the buffer, the relaxed Si_0.8Ge_0.2 film on the 10-period m-SiGe-dot multilayer was demonstrated to have a threading dislocation density of 2.0 × 10⁵ cm⁻² and a strain relaxation of 89%.     

Nanolayered multilayer coatings of CrN/CrAlN prepared by reactive DC magnetron sputtering

Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm² at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm², respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr₂O₃ started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm² after annealing up to a temperature of 600 °C.     

Oxidation of Ni(Pt)Si by molecular vs. atomic oxygen

X-ray photoelectron spectroscopy (XPS) has been used to characterize the oxidation of a clean Ni(Pt)Si surface under two distinct conditions: exposure to a mixed flux of atomic and molecular oxygen (O + O₂; PO+O₂ = 5 × 10⁻⁶ Torr) and pure molecular oxygen (O₂; PO₂ = 10⁻⁵ Torr) at ambient temperatures. Formation of the clean, stoichiometric (nickel monosilicide) phase under vacuum conditions results in the formation of a surface layer enriched in PtSi. Oxidation of this surface in the presence of atomic oxygen initially results in formation of a silicon oxide overlayer. At higher exposures, kinetically limited oxidation of Pt results in Pt silicate formation. No passivation of oxygen uptake of the sample is observed for total O + O₂ exposure <8 × 10⁴ L, at which point the average oxide/silicate overlayer thickness is 23 (3) Å (uncertainty in the last digit in parentheses). In contrast, exposure of the clean Ni(Pt)Si surface to molecular oxygen only (maximum exposure: 5 × 10⁵ L) results in slow growth of a silicon oxide overlayer, without silicate formation, and eventual passivation at a total average oxide thickness of 8(1) Å, compared to a oxide average thickness of 17(2) Å (no silicate formation) for the as-received sample (i.e., exposed to ambient.) The aggressive silicon oxidation by atomic oxygen, results in Ni-rich silicide formation in the substrate and the kinetically limited oxidation of the Pt.     

Photoemission electron microscopy study of anthracene growth on Si(1 1 1)

The thin film growth of anthracene films on Si(1 1 1) surfaces is studied by photoemission electron microscopy (PEEM). The thin film growth of anthracene on Si(1 1 1) is similar to the growth of pentacene on silicon. Initially a layer of flat lying molecules chemisorbs on the surface. Subsequent growth of fractal islands with standing up molecules proceeds on top of this flat layer.     

Effects of thermal treatment on the morphology of Alq3 thin layers on Si(1 1 1) substrate

Alq₃ thin layers were vapor deposited onto a single crystal of Si(1 1 1) and the morphology of the surface was investigated by the scanning tunneling microscope under ultrahigh vacuum conditions. The STM imaging showed considerable influence of the thermal processing onto the topography of the sample. Slowly raising the sample temperature to ∼160 °C caused a complete desorption of Alq₃ molecules and uncovering the clean surface of Si(1 1 1). A fast rise of the temperature (flashing) to ∼600 °C led to decomposition of the Alq₃ and resulted in remnants of a carbon-rich surface species. Then heating or flashing this surface to a temperature in excess of 1000 °C brought about the occurrence of regular shape object on the Si(1 1 1) surface.     

Effect of amorphous C films deposited by RF magnetron sputtering on smoothing K9 glass substrate

Soft X-ray multilayer reflectors must be deposited on super-smooth surface such as super-polished silicon wafers or glasses, which are complicate, time-consuming and expensive to produce. To overcome this shortage, C films deposited by RF magnetron sputtering were considered to smooth the K9 glass substrates’ surface in the present paper. The structure of C films was systematically studied by XRD and Raman spectrum. The surface morphology and rms-roughness were obtained by AFM. Then, we calculated the impact of the C layers on the reflectivity curve of Mo/Si soft X-ray multilayer reflector around 13.5 nm. The C films exhibit typical amorphous state. With the increasing of power and thickness, the content of sp3 hybrid bonding decreases while the amount or size of well-organized graphite clusters increases. The surface rms-roughness decreases from 2.4 nm to 0.62 nm after smoothed by an 80 nm thick C layer deposited in 500 W, which is the smoothest C layer surface we have obtained. The calculation results show that the theoretical normal incidence reflectivity of Mo/Si multilayer at 13.5 nm increases from 7% to 63%.     

High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayers

High temperature annealing effect on structural and magnetic properties of Ti/Ni multilayer (ML) up to 600 °C have been studied and reported in this paper. Ti/Ni multilayer samples having constant layer thicknesses of 50 Å each are deposited on float glass and Si(1 1 1) substrates using electron-beam evaporation technique under ultra-high vacuum (UHV) conditions at room temperatures. The micro-structural parameters and their evolution with temperature for as-deposited as well as annealed multilayer samples up to 600 °C in a step of 100 °C for 1 h are determined by using X-ray diffraction (XRD) and grazing incidence X-ray reflectivity techniques. The X-ray diffraction pattern recorded at 300 °C annealed multilayer sample shows interesting structural transformation (from crystalline to amorphous) because of the solid-state reaction (SSR) and subsequent re-crystallization at higher temperatures of annealing, particularly at ≥400 °C due to the formation of TiNi₃ and Ti₂Ni alloy phases. Sample quality and surface morphology are examined by using atomic force microscopy (AFM) technique for both as-deposited as well as annealed multilayer samples. In addition to this, a temperature dependent dc resistivity measurement is also used to study the structural transformation and subsequent alloy phase formation due to annealing treatment. The corresponding magnetization behavior of multilayer samples after each stage of annealing has been investigated by using Magneto-Optical Kerr Effect (MOKE) technique and results are interpreted in terms of observed micro-structural changes.     

A scanning tunneling microscopy study on the effect of post-deposition annealing of copper phthalocyanine thin films

Using scanning tunneling microscopy, overlayer lattice structures and thin film morphology of copper phthalocyanine (CuPc) have been investigated while varying posterior, annealing temperatures. The room temperature deposition of CuPc on Ag(1 1 1) resulted in ordered domains, which were three molecular layers high and separated with disordered regions. The ordered surface also exhibited an oblique lattice with the lattice constants of 13.3 Å and 16.4 Å and the angle of 74° between the two. By annealing the thin films systematically to 580 K, the symmetry of overlayer lattice increased from the oblique to the square lattice, commonly observed on various substrates. Further annealing to 780 K desorbed much of the CuPc molecules. However, the remaining molecules reacted and formed dendrite-like chains, in which each CuPc molecule was linked through its isoindole rings. A possible model for the formation of dendritic chains through polymerization is discussed.     

STM study of acetylene reaction with Si(1 1 1): observation of a carbon-induced Si(1 1 1)√3×√3R30° reconstruction

The first stages of acetylene reaction with the Si(1 1 1)7 × 7 reconstructed surface kept at 600 °C are studied by recording scanning tunneling microscopy (STM) images during substrate exposure at a C₂H₂ pressure of 2 × 10⁻⁴ Pa (2 × 10⁻² mbar). We observed the progressive substitution of the 7 × 7 reconstruction with a carbon induced Si(1 1 1)√3×√3R30° reconstruction characterized by an atomic distance of 0.75 ± 0.02 nm, very close to that of the silicon 7 × 7 adatoms. This means that a carbon enrichment of the silicon outermost layers occurs giving rise to the formation of a Si-C phase different from the √3×√3R30° reconstruction typical of Si terminated hexagonal SiC(0 0 0 1) surface with an atomic distance of 0.53 nm. To explain STM images, we propose a reconstruction model which involves carbon atoms in T₄ and/or S₅ sites, as occurring for B doped Si(1 1 1) surface. Step edges and areas around the silicon surface defects are the first regions involved in the reaction process, which spreads from the upper part of the step edges throughout the terraces. Step edges therefore, progressively flakes and this mechanism leads, for the highest exposures, to the formation of large inlets which makes completely irregular the straight edge typical of the Si(1 1 1)7 × 7 terraces. These observations indicate that there occurs an atomic diffusion like that driving the meandering effect. Finally, the formation of a few crystallites is shown also at the lowest acetylene exposures. This is the first STM experiment showing the possibility to have carbon incorporation in a Si(1 1 1) matrix for higher amounts than expected, at least up to 1/6 of silicon atomic layer.     

Angle-resolved study of hydrogen abstraction on Si(1 0 0) and Si(1 1 1): Evidence for non-activated pathways

The abstraction of chemisorbed hydrogen on Si(1 0 0) and Si(1 1 1) induced by atomic hydrogen has been investigated by studying with a rotatable mass spectrometer the angle-resolved molecular hydrogen desorption from a Si surface exposed to a chopped beam of atomic hydrogen. The angular distributions of desorbing molecules can be fitted independent of the surface temperature and the surface reconstruction by a cosⁿθ function with n < 1 for Si(1 0 0) and Si(1 1 1). These results are interpreted by non-activated pathways involving site-specific hot-atom abstraction on two adjacent silicon atoms with one having a dangling bond. Possible mechanisms according to the surface reconstructions are discussed.     

Modification of silicon waveguide structures using ion implantation induced defects

The structure of re-crystallized silicon films is investigated using transmission electron microscopy, spectroscopic ellipsometry and positron annihilation spectroscopy. Samples were prepared via amorphization of the silicon overlayer of silicon-on-insulator substrates, and subsequent thermal annealing. For an annealing temperature of 650 °C we show that the silicon film has a poly-crystalline structure. Its refractive index measured at 1550 nm is comparable to that of crystalline silicon following re-crystallization at 750 °C. Positron measurements indicate a high concentration of open-volume point defects in the re-crystallized films. We discuss the potential importance of these structures with regard to defect engineering for silicon photonic devices.     

Thermal evolution of surface blistering and exfoliation due to ion-implanted hydrogen monomers into Si〈1 1 1〉

This study investigated the dependence of surface blistering and exfoliation phenomena on post-annealing time in H⁺-implanted Si〈1 1 1〉. Czochralski-grown n-type Si〈1 1 1〉 wafers were room-temperature ion-implanted with 40 keV hydrogen monomers to a fluence of 5×10¹⁶ cm⁻², and followed by furnace annealing treatments at 400 and 500 °C for various durations ranging from 0.25 to 3 h. The corresponding analysis results for Si〈1 0 0〉 [1] (Liang et al., 2008); [2] (Bai, 2007) were adopted in order to make comparisons. The evolution of blister formation and growth for Si〈1 1 1〉 at 400 °C has a shorter characteristic time compared to Si〈1 0 0〉. However, there is a longer characteristic time when annealing takes place at 500 °C. In addition, no craters were observed for Si〈1 1 1〉 annealed at 400 °C while the opposite is true for Si〈1 0 0〉. The evolution of crater development for Si〈1 1 1〉 annealed at 500 °C has a longer characteristic time compared to Si〈1 0 0〉. These results are attributed to the fact that compared to Si〈1 0 0〉, Si〈1 1 1〉 has a smaller surface binding energy of silicon atoms and a larger areal number density of silicon atoms on the plane perpendicular to the incident-ion axis. Furthermore, Si〈1 1 1〉 has a greater areal number density, smaller diameter, and a similar covered-area fraction of optically-detectable blisters compared to Si〈1 0 0〉. However, Si〈1 1 1〉 has a lower areal number density and a smaller covered-area fraction of craters than does Si〈1 0 0〉. Increasing post-annealing temperature from low (e.g. 400 °C) to high (e.g. 500 °C) revealed that Si〈1 1 1〉 tends to create more blisters while Si〈1 0 0〉 tends to develop larger blisters as well as create more craters.     

SR-PES and STM observation of metastable chemisorption state of oxygen on Si(1 1 0)-16 × 2 surface

Initial adsorption of oxygen molecules on the Si(1 1 0)-16 × 2 surface and subsequent modification of the bonding states induced by mild (300 °C) annealing have been studied by synchrotron-radiation photoemission spectroscopy and scanning-tunneling microscopy. It has been shown that upon annealing, the intensity and the energy positions of the Si 2p suboxide components shift towards the values characteristic for the thermal oxide. This indicates the presence of a metastable chemisorption state of oxygen on the Si(1 1 0)-16 × 2 surface.     

Structure and composition of chemically prepared and vacuum annealed InSb(0 0 1) surfaces

The InSb(0 0 1) surfaces chemically treated in HCl-isopropanol solution and annealed in vacuum were studied by means of X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and electron energy-loss spectroscopy (EELS). The HCl-isopropanol treatment removes indium and antimony oxides and leaves on the surface about 3 ML of physisorbed overlayer, containing indium chlorides and small amounts of antimony, which can be thermally desorbed at 230 °C. The residual carbon contaminations were around 0.2-0.4 ML and consisted of the hydrocarbon molecules. These hydrocarbon contaminations were removed from the surface together with the indium chlorides and antimony overlayer. With increased annealing temperature, a sequence of reconstructions were identified by LEED: (1 × 1), (1 × 3), (4 × 3), and (4 × 1)/c(8 × 2), in the order of decreasing Sb/In ratio. The structural properties of chemically prepared InSb(0 0 1) surface were found to be similar to those obtained by decapping of Sb-capped epitaxial layers.