Preparation and characterization of gold nanocrystals on NaCl(100) surfaces as labels for the dynamical x-ray tracking technique

We report on the fabrication of single crystalline gold nanocrystals of sizes between 10 nm and 25 nm. Gold was deposited under ultra high vacuum conditions on a freshly-cleaved NaCl(001) surface by means of the Molecular Beam Epitaxy technique. The preparation parameters substrate temperature and average thickness of the deposited gold were studied systematically. After the preparation, the crystals were characterized by means of different techniques, such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), X-Ray Diffractometry (XRD) and Laue Diffractometry.Measurements of the deposited cluster size, as measured by AFM, and the crystal size, as measured by XRD exhibited similar results at substrate temperatures between approx. 200 °C and 250 °C, indicating a high amount of single gold crystals. TEM images of gold crystals, made after the gold crystals had been dissolved in an aqueous 3-[(3-cholamidopropyl)dimethyl-ammonio]propane solution, support these results.Further, an effect of the substrate temperature during the deposition on the orientation of the gold crystals with respect to the NaCl(001) surface was observed. XRD measurements reveal a perpendicular texture of Au(111) parallel to NaCl(001) at approximately 310 °C. The second detected texture:Au(001)||NaCl(001) (in plane) and Au[100]||NaCl[100] (perpendicular) was observed over the complete studied temperature range (180 °C-330 °C).     

不同化学官能团对无机相碳酸钙晶体的调控

选择了具有代表性的化学官能团, 羟基(—OH)、 氨基(—NH₂)、 羧基(—COOH)和甲基(—CH₃), 通过在单晶硅片上进行接枝改性, 并在改性后的硅基底上进行碳酸钙体外矿化模拟实验, 以研究这些官能团对碳酸钙矿化的影响。利用接触角实验对接枝效果进行了分析, 结果显示接枝成功。根据拉曼光谱(Raman)确定了碳酸钙的晶型; 采用扫描电子显微镜(SEM)获得了碳酸钙的形貌、 尺寸、 数量和取向信息。结果显示羟基化硅基底上出现了方解石的聚集; 氨基化硅基底和羧基化硅基底上均出现一定量的球文石, 但形貌各异; 甲基化硅基底上晶体数目较少。通过对结果的对比分析, 认为羟基和甲基对碳酸钙的晶型选择无明显影响, 氨基和羧基能通过对碳酸根离子或钙离子的吸附而诱导球文石结晶。      

Wetting driven self-assembly as a new approach to template-guided fabrication of metal nanopatterns

Wetting driven self-assembly (WDSA) of appropriate materials in their liquid state on organic monolayer nanopatterns consisting of wettable (lyophilic) surface features surrounded by a nonwettable (lyophobic) monolayer background is shown to provide the basis of a versatile new approach to template-guided fabrication of metal nanopatterns. Monolayer nanopatterns with planned distributions of lyophilic/lyophobic surface regions are conveniently generated by constructive nanolithography upon local electrochemical oxidation of the top -CH3 groups of a highly ordered OTS (n-octadecyltrichlorosilane) monolayer self-assembled on silicon to -COOH (Adv. Mater. 2000, 12, 725-731). Retraction of such a patterned monolayer from a liquid that does not wet its nonpolar -CH3 surface (lyophobic) results in selective, site-defined immobilization of nanosized volumes of the liquid on the locally generated polar -COOH groups (lyophilic). Examples are given of WDSA of organic materials that offer further options for post-assembly chemical processing, such as nonvolatile low-melting olefins, acids, or thiols, the former being in situ reacted to generate polar functions like -COOH or -SH. Loading surface patterns created in this manner with silver or gold ions followed by further chemical processing results in elemental metal nanoparticles generated within the ion-binding organic material, which thus functions as a guiding template for planned metal deposition at predefined surface sites. WDSA is particularly versatile, as any nonvolatile material with appropriate melting temperature and surface wetting characteristics or solubility in a liquid displaying such properties may in principle be utilized to fabricate potentially useful surface nanostructures.     

Reduction of 3T3 Fibroblast Adhesion on SS316L by Methyl-Terminated SAMs

Inhibiting the non-specific adhesion of cells and proteins to biomaterials such as stents, catheters and guide wires is an important interfacial issue that needs to be addressed in order to reduce surface-related implant complications. Medical grade stainless steel 316L was used as a model system to address this issue. To alter the interfacial property of the implant, self assembled monolayers of long chain phosphonic acids with -CH(3), -COOH, -OH tail groups were formed on the native oxide surface of medical grade stainless steel 316L. The effect of varying the tail groups on 3T3 fibroblast adhesion was investigated. The methyl terminated phosphonic acid significantly prevented cell adhesion however presentation of hydrophilic tail groups at the interface did not significantly reduce cell adhesion when compared to the control stainless steel 316L.     

Comprehensive study of pulsed UV-laser modified polyamide fibers

Polyamide fibers (nylon 6) are modified by UV-radiation using a pulsed excimer laser with different treatment parameters. The treated samples are characterized by using a scanning electron microscopy (SEM), tapping mode atomic force microscopy (TM-AFM), x-ray photoelectron spectroscopy (XPS), and chemical force microscopy (CFM). Depending on the conditions during the irradiation, different surface modifications are obtained which can generally be distinguished as high-fluence (above the ablation threshold) and low-fluence (below the ablation threshold). Topographical results indicate that ripple-like structures of micrometer size are developed under high-fluence laser irradiation. On the contrary, smaller sub-micron structures are formed by low-fluence treatment. XPS results show that bond scission occurs on the polymer surface under the action of high-fluence while low-fluence modifies the sample by an oxidative process. Changes in surface chemical properties of the laser-irradiated polyamide are supported by chemical force microscopy experiments with gold-coated AFM tips modified with -COOH terminated self-assembled alkanethiol monolayers (SAMs).     

A nanometer scale surface morphology study of W thin films

Microstructure of tungsten thin films deposited by RF-sputtering is studied as a function of their thicknesses. These films have been deposited on (100) oriented single crystal Si substrate and Si substrate covered by a 100-nm-thick Ti layer. The crystalline structure is studied by X-ray Diffraction (XRD) and Grazing Incidence XRD (GIXRD). The surface and the cross-section morphology are observed by high resolution Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). XRD patterns exhibit peaks corresponding to pure W phase. GIXRD analysis shows that the more the thickness increases, the more the film is oriented along the [110] direction. AFM observations show that films exhibit a particular morphology constituted of “piles of platelets” oriented perpendicularly to the wafer surface. These “piles of platelets” are in plane randomly oriented and are sometime observed upon all the thicknesses of the layer. This particular morphology is observed whatever the substrate is, and is explained by thin layer growth theories.     

Investigation of adsorption behavior of bisphenol A on well fabricated organic surfaces using surface plasmon resonance spectroscopy

Molecular adsorption of bisphenol A (BPA) on three types of self-assembled monolayers with different functionalities, such as -CH3, -SH, and -COOH, was examined using surface plasmon resonance (SPR) spectroscopy. BPA molecules in an aqueous solution were easily adsorbed onto a hydrophobic surface compared to a hydrophilic surface. Sorption behavior of BPA into poly(2-methoxyethyl acrylate) (PMEA) layer, which is known as a biocompatible polymer, was also investigated. Sorption and desorption dynamics of BPA into PMEA were found to be very rapid and quite reversible. The swelling of PMEA by sorption of BPA results in the change in SPR angle and allows one to quantify the BPA concentration below 100 ppm. In addition, the transport mechanism of BPA within the membrane of organ can be inferred by the experimental results.     

Specular beam intensity and surface morphology of BSCO films grown by MBE

Bi-Sr-Cu-O (BSCO) thin films have been epitaxially grown on cleaned SrTiO₃ (001) substrates by a sequentially shutter-controlled molecular beam epitaxy system using an oxygen radical beam. A spot intensity of specular beam in in-situ reflection high-energy electron diffraction (RHEED) was monitored during the atomic layer epitaxy. Atomic force microscopy (AFM) images of the epitaxial thin films were observed in the atmosphere at some oscillation points of the specular beam intensities. The chemical composition ratios of the films (about 100 Å) were determined from intensities of X-ray photoemission spectroscopy. The crystallinity of the films was measured by X-ray diffraction.

The amount of metal deposition corresponding to a half cycle of the intensity oscillation of the specular spot was found to be appropriate to form the flat surface. Characteristic islands were found at the surfaces covered with excess bismuth or excess copper atoms in the AFM image. The intrinsic modulated structure of the BSCO crystal was observed at the surface after the first copper deposition on Sr/Bi/SrTiO₃ in the RHEED pattern.     

AFM Study on Interface of HTHP As-grown Diamond Single Crystal and Metallic Film

The study for the interface of as-grown diamond and metallic film surrounding diamond is an attractive way for understanding diamond growth mechanism at high temperature and high pressure (HTHP), because it is that through the interface carbon atom groups from the molten film are transported to growing diamond surface. It is of great interest to perform atomic force microscopy (AFM) experiment; which provides a unique technique different from that of normal optical and electron microscopy studies, to observe the interface morphology. In the present paper,we report first that the morphologies obtained by AFM on the film are similar to those of corresponding diamondsurface, and they are the remaining traces after the carbon groups moving from the film to growing diamond. The fine particles and a terrace structure with homogeneous average step height are respectively found on the diamond(100) and (111) surface. Diamond growth conditions show that its growth rates and the temperature gradients inthe boundary layer of the molten film at HTHP result in the differences of surface morphologies on diamond planes,being rough on (100) plane and even on the (111) plane. The diamond growth on the (100) surface at HPHT could be considered as a process of unification of these diamond fine particles or of carbon atom groups recombination on the growing diamond crystal surface. Successive growth layer steps directly suggest the layer growth mechanism of the diamond (111) plane. The sources of the layer steps might be two-dimensional nuclei and dislocations.     

Scanning hall probe microscopy (SHPM) using quartz crystal AFM feedback

Scanning Hall Probe Microscopy (SHPM) is a quantitative and non-invasive technique for imaging localized surface magnetic field fluctuations such as ferromagnetic domains with high spatial and magnetic field resolution of approximately 50 nm and 7 mG/Hz(1/2) at room temperature. In the SHPM technique, scanning tunneling microscope (STM) or atomic force microscope (AFM) feedback is used to keep the Hall sensor in close proximity of the sample surface. However, STM tracking SHPM requires conductive samples; therefore the insulating substrates have to be coated with a thin layer of gold. This constraint can be eliminated with the AFM feedback using sophisticated Hall probes that are integrated with AFM cantilevers. However it is very difficult to micro fabricate these sensors. In this work, we have eliminated the difficulty in the cantilever-Hall probe integration process, just by gluing a Hall Probe chip to a quartz crystal tuning fork force sensor. The Hall sensor chip is simply glued at the end of a 32.768 kHz or 100 kHz Quartz crystal, which is used as force sensor. An LT-SHPM system is used to scan the samples. The sensor assembly is dithered at the resonance frequency using a digital Phase Locked Loop circuit and frequency shifts are used for AFM tracking. SHPM electronics is modified to detect AFM topography and the frequency shift, along with the magnetic field image. Magnetic domains and topography of an Iron Garnet thin film crystal, NdFeB demagnetised magnet and hard disk samples are presented at room temperature. The performance is found to be comparable with the SHPM using STM feedback.     

Studies on visual sensor from self-assembled polypeptides

A silane terminated poly (ε-benzyloxycarbonyl-l-lysine) was synthesized and deposited as a self-assembled monolayer on the pre-colored silica substrate which was fabricated by Langmuir–Blodgett (LB) method. The monolayer was covalently attached to silica surface through terminal silane groups. The secondary structure of polymer, α-helix, was confirmed by circular dichroism spectroscopy. Furthermore, the conversion of the monolayer surface from non-ionic to cationic was accomplished by removal of ε-benzyloxycarbonyl group (Z group). The uniform monolayer on silica substrate and the changes occurring in the tethered monolayer were analyzed by atomic force microscopy (AFM). RNA aptamer with 72 sequences of nucleotides could be immobilized on the poly (l-lysine) cationic surface through electrostatic interaction. The superior recognition capability of RNA aptamer with specific microorganism is becoming a promising candidate in detection of bacteria. In this study, the binding of target bacteria, Sphingobium yanoikuyae, to the resulting RNA probe leads to a color change at the surface which is visually observed by real-time and confirmed through UV-reflective spectrophotometer. The RNA probes can be used as a high efficiency and versatile tool to visually sense the bacterial contamination in the food products.     

High-yield self-assembly of flower-like ZnO nanostructures

High-yield three-dimensional (3D) flower-like nanostructures self-assembled from 1 D ZnO nanorods and nanotubes are experimentally demonstrated. The Zn and O terminated crystal planes of ZnO nanorods results in positively and negatively charged top (001) and bottom (00-1) surfaces, respectively. The nanorods self-assembled into 3D nanostructures via the electrostatic interaction between the crystal planes with opposite charges. Moreover, on the basis of the different stability of polar and nonpolar planes in wurtzite-type ZnO, the nanorods based 3D nanostructures transformed into nanotubes based ones spontaneously. This provides a new approach to prepare multi-dimensional materials without the necessity to employ any external intervention.     

Arsenic ion implantation induced structural effects in C60 films

C₆₀ films grown on Si (001) by vacuum evaporation were implanted with 100 keV positive arsenic ions to various doses in the range 1 × 10¹³ to 1 × 10¹⁵ ions/cm². The structural properties of the implanted films were studied using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS results indicate the formation of arsenic buried layer within C₆₀ film leading to the anisotropy stress in the film. XRD results reveal the preferential orientation of the film along the (531) plane on implantation and it can be due to the re-alignment of the grains as evidenced by our AFM measurement. AFM measurements also reveal the reduction in the grain size and the surface roughness on implantation.     

Growth and relaxation processes in Ge nanocrystals on free-standing Si(001) nanopillars

We study the growth and relaxation processes of Ge crystals selectively grown by chemical vapour deposition on free-standing 90 nm wide Si(001) nanopillars. Epi-Ge with thickness ranging from 4 to 80 nm was characterized by synchrotron based x-ray diffraction and transmission electron microscopy. We found that the strain in Ge nanostructures is plastically released by nucleation of misfit dislocations, leading to degrees of relaxation ranging from 50 to 100%. The growth of Ge nanocrystals follows the equilibrium crystal shape terminated by low surface energy (001) and {113} facets. Although the volumes of Ge nanocrystals are homogeneous, their shape is not uniform and the crystal quality is limited by volume defects on {111} planes. This is not the case for the Ge/Si nanostructures subjected to thermal treatment. Here, improved structure quality together with high levels of uniformity of the size and shape is observed.     

ADP晶体的生长丘、台阶微观形貌及台阶棱边能

ADP晶体{100}面族生长的实时与非实时AFM(atomic force microscopy,AFM)研究表明,过饱和度σ处于0.005～0.04,生长温度介于293～313K之间时,晶面上观察到位错生长丘和其它晶体缺陷所形成的生长丘,晶面主要为台阶推进方式生长;位错生长丘上空洞的出现与位错弹性理论相符;随过饱和度σ降低,台阶形貌会发生相应变化;生长温度为298K时,台阶棱边能不小于6.2×10-7J/cm2.     

Nano-cube MgO formed on silicon substrate using pulsed laser deposition

Nano-cube MgO particles were formed on Si substrates by deposition of an MgO target using pulsed laser deposition method. An epitaxial film grows on Si(001) substrate with its contraction of lattice constants. In this study, expecting high quality MgO film, the MgO film prepared in the oxygen pressure ranging from 75-400 mTorr at the high temperature of -750 degrees C. The deposited MgO showed the growth of (001) preferred orientation on the Si(001) substrate. However, X-ray Photoelectron Spectroscopy (XPS) indicated the MgO film did not form a continuous film on the Si surface. Interestingly, the surface morphology observed by an Atomic Force Microscopy (AFM) showed nano-cube MgO particles scattered on the smooth surface of Si substrate. After annealing the nano-cube MgO, the shape of MgO particles were changed from nano-cube to round shaped particles. The AFM image of the surface showed round shaped MgO nanoparticles scattered on rough surface. X-ray Diffraction (XRD) revealed the epitaxial growth of MgO(001) with cubic on cubic arrangement on the Si(001) substrate (MgO[100] parallel to Si[100]).     

Atomic force microscopy study of the surface morphology of a TlGaSe<Subscript>2</Subscript> crystal

The surface morphology of a TlGaSe₂ single crystal has been studied by atomic force microscopy (AFM). Using an appropriate imaging mode, we obtained three-dimensional AFM images of the crystal surface, its Fourier spectrum, and height distribution. The crystal is shown to be rather uniform in surface profile, with a local surface height within 25 nm in a 5 × 5 μm area.     

退火温度对NiZn铁氧体薄膜性能的影响

采用射频磁控溅射法在Si(100)基片上制备了NiZn铁氧体薄膜,研究了退火温度对薄膜性能的影响.采用XRD分析仪分析了薄膜的相结构,原子力显微镜分析了薄膜的表面形貌,振动样品磁强计测量了薄膜的磁性能,结果表明,随着退火温度的升高,薄膜的结晶状态越好,晶粒尺寸越大,饱和磁感应强度越高,面内矫顽力越小.     

Exposing {001} Crystal Plane on Hexagonal Ni‐MOF with Surface‐Grown Cross‐Linked Mesh‐Structures for Electrochemical Energy Storage

Hexagonal nickel‐organic framework (Ni‐MOF) [Ni(NO₃)₂·6H₂O, 1,3,5‐benzenetricarboxylic acid, 4‐4′‐bipyridine] is fabricated through a one‐step solvothermal method. The {001} crystal plane is exposed to the largest hexagonal surface, which is an ideal structure for electron transport and ion diffusion. Compared with the surrounding rectangular crystal surface, the ion diffusion length through the {001} crystal plane is the shortest. In addition, the cross‐linked porous mesh structures growing on the {001} crystal plane strengthen the mixing with conductive carbon, inducing preferable conductivity, as well as increasing the area of ion contact and the number of active sites. These advantages enable the hexagonal Ni‐MOF to exhibit excellent electrochemical performance as supercapacitor electrode materials. In a three‐electrode cell, specific capacitance of hexagonal Ni‐MOF in the 3.0 m KOH electrolyte is 977.04 F g^?1 and remains at the initial value of 92.34% after 5,000 cycles. When the hexagonal Ni‐MOF and activated carbon are assembled into aqueous devices, the electrochemical performance remains effective.     

KDP晶体单点金刚石切削脆塑转变机理的研究

加工超光滑表面的KDP晶体是现代超精密加工技术领域的重点研究课题。实验采用维氏压痕法研究KDP晶体脆性材料(001)面不同晶向的硬度、断裂韧性的变化规律。通过建立KDP晶体脆塑转变临界切削厚度模型,研究了KDP晶体金刚石切削脆塑转变机理。结果表明,脆塑转变临界最小切削厚度出现在断裂韧性最小而硬度最大的[110]方向;脆塑转变临界切削最大厚度出现在断裂韧性最大而硬度最小的[001]方向。并利用超精密机床加工了KDP晶体,加工结果与理论推导结论相符合,在[001]方向加工出表面粗糙度为7.5nm(RMS)的超光滑表面。