Multidimensional surface patterning based on wavelength-controlled disulfide-diselenide dynamic photochemistry

Controlling surface properties in a spatiotemporal and reversible manner is highly attractive for novel functional surfaces, as it allows them to act in a much smarter way. Surface modification strategies based on photochemical metathesis reactions are seemed as promising solutions for such demands, due to their high spatiotemporal controllability and the perfect reversibility. In this paper, we demonstrate a powerful strategy to precisely manipulate the surface functions by the combination of wavelength-controlled disulfide-diselenide dynamic photochemistry and a 405 nm digital light processing (DLP) projector. We show that, by this method, the arrangement of chemical moieties on a disulfide surface can be exactly controlled, leading to complex patterned surfaces with multinary and grayscale molecular distributions. Moreover, owing to the wavelength-dependent reactivity of the -S-S- and -S-Se- groups, the surface functions can be selectively and dynamically adjusted by light with different colors (wavelength). Based on these unique features, the chemical moieties on every point of the surface can be exactly controlled and dynamically manipulated by our strategy, making the generated surfaces quite versatile and smart. We demonstrate the successful application of this method in high-level information encryption and transformation.     

Surface acoustic wave characterization of a thin, rough polymer film

Laser generated surface acoustic waves (SAW) in a heterodyne diffraction scheme is a powerful technique for elastic characterization of thin films and it is frequently used on samples of high optical quality. We show that the method can also be effectively used in difficult conditions, on rough samples. Measurements are presented on a 3 µm thick film of polymer, spin-coated on steel, and on the same sample after addition of an aluminum coating. The experimental data are interpreted using a model assuming a stack of perfect layers. The analyses show good consistency within the SAW results for both configurations, and consistency with nano-indentation results, cross-validating both approaches.     

On the Exact Solution of Boundary Value Problems with Non-separable Geometries,Like a Rough Surface

A Dirichlet problem is considered for the Helmholtz equation and for a class of geometries for which the Helmholts operator does not separate (e.g. a rough surface). It is shown that, contrary to the widely held view, it is possible to obtain the solution of this problem in a closed form which resembles closely the solutions obtained for separable geometries—expansions generated by Sturm-Liouville theory. As with separable geometries, we show in particular that the expansion coefficients can be written explicitly as integrals containing a priori known functions—that matrix inversion is not required for the determination of the expansion coefficients. The problem includes as a special case the scattering of electromagnetic waves from a rough cylindrical surface which is the boundary of a perfect conductor. The method is very general and can be used for much more complicated boundary value problems, such as scattering by dielectric interface.     

Are nanoporous materials radiation resistant?

The key to perfect radiation endurance is perfect recovery. Since surfaces are perfect sinks for defects, a porous material with a high surface to volume ratio has the potential to be extremely radiation tolerant, provided it is morphologically stable in a radiation environment. Experiments and computer simulations on nanoscale gold foams reported here show the existence of a window in the parameter space where foams are radiation tolerant. We analyze these results in terms of a model for the irradiation response that quantitatively locates such window that appears to be the consequence of the combined effect of two length scales dependent on the irradiation conditions: (i) foams with ligament diameters below a minimum value display ligament melting and breaking, together with compaction increasing with dose (this value is typically ～5 nm for primary knock on atoms (PKA) of ～15 keV in Au), while (ii) foams with ligament diameters above a maximum value show bulk behavior, that is, damage accumulation (few hundred nanometers for the PKA's energy and dose rate used in this study). In between these dimensions, (i.e., ～100 nm in Au), defect migration to the ligament surface happens faster than the time between cascades, ensuring radiation resistance for a given dose-rate. We conclude that foams can be tailored to become radiation tolerant.     

Phantom nanoparticles as probes of biomolecular interactions

A new light-scattering-based method to detect molecular interactions at the surface of low-refractive-index nanoparticles was recently proposed. Water-dispersed nanoparticles functionalized with receptors typical of immature bacteria cell walls were used to study the activity of the antibiotic vancomycin. This method subtly depends on the specific properties of the nanoparticles. Here we discuss, by comparative experiments and through theoretical evaluation, the effects of size, refractive index, electric charge, and dilution on the reliability and accuracy of the method. Quite surprisingly, perfect index matching and minimal size (i.e., maximum surface), which is almost attained in one of the colloids here employed, do not represent the ideal conditions. Rather, we show that a nanoparticle radius of 100 nm and a refractive index slightly below that of water yields the best signal/background amplitude. We also show that repulsive interactions can lead to artifacts in the adsorption isotherm, thus indicating that electrostatic stabilization should be kept at a minimum. The close agreement between the interaction strengths, as measured with two different nanoparticle systems, testifies to the reliability of the method.     

Color constancy from blackbody illumination

We present a theoretical analysis of what we believe to be a new color constancy method that inputs two chromaticities of an identical surface taken under two blackbody illuminations. By using the Planck formula for modeling spectra of outdoor illumination and by assuming that a narrowband camera sensitivity function is sufficiently narrow, surface colors can be estimated mathematically. Experiments with simulation and real data have been conducted to evaluate the effectiveness of the method. The results showed that although this method is a perfect vehicle for simulation data, it produces significant errors with real data. A thorough investigation of the cause of errors indicates how important the assumptions on both blackbody illuminations and narrowband camera sensitivities are to the method. Finally, we discuss the robustness of our method and the limitation of solving color constancy using the illumination constraint.     

Testing fast aspheric concave surfaces with a cylindrical null screen

A noncontact test procedure to obtain the shape of fast concave surfaces is described. A cylindrical null screen with a curved grid drawn on it in such a way that its image, which is formed by reflection on a perfect concave surface, yields a perfect square grid is proposed. The cylindrical null screen design and the surface evaluation algorithm are presented. Experimental results for the testing of an elliptical mirror of 164 mm in diameter (f/0.232) are shown.     

Boundary Element Calculation of Eddy Currents in Cylindrical Structures Containing Cracks

Electromagnetic fields due to excitation coils in boreholes containing cracks have been calculated using a boundary element method formulated in terms of a scalar decomposition of the field. By using a Green's kernel that ensures continuity of the tangential electric and magnetic field at the cylindrical surface, it is only necessary to render the flaw region in a discrete form. The effect of an ideal crack, one with zero opening but acting as a perfect barrier to eddy currents, is here represented by a current dipole layer orientated normal to the crack surface. An integral equation determines the source density on the crack and a numerical solution is found using boundary elements. The coil impedance change due to the crack is then computed using an expression based on a reciprocity principle.      

Tunable dual-band nearly perfect absorption based on a compound metallic grating

Traditional metallic gratings and novel metamaterials are two basic kinds of candidates for perfect absorption. Comparatively speaking, metallic grating is the preferred choice for the same absorption effect because it is structurally simpler and more convenient to fabricate. However, to date, most of the perfect absorption effects achieved based on metamaterials are also available using an metallic grating except the tunable dual(multi)-band perfect absorption. To fill this gap, in this paper, by adding subgrooves on the rear surface as well as inside the grating slits to a free-standing metallic grating, tunable dual-band perfect absorption is also obtained for the first time. The grooves inside the slits is to tune the frequency of the Cavity Mode(CM) resonance which enhances the transmission and suppresses the reflectance simultaneously. The grooves on the rear surface give rise to the phase resonance which not only suppresses the transmission but also reinforces the reflectance depression effect. Thus, when the phase resonance and the frequency tunable CM resonance occur together, transmission and reflection can be suppressed simultaneously, dual-band nearly perfect absorption with tunable frequencies is obtained. To our knowledge, this perfect absorption phenomenon is achieved for the first time in a designed metallic grating structure.     

Numerical exploration of plastic deformation mechanisms of copper nanowires with surface defects

Based on the molecular dynamics simulation, plastic deformation mechanisms associated with the zigzag stress curves in perfect and surface defected copper nanowires under uniaxial tension are studied. In our previous study, it has found that the surface defect exerts larger influence than the centro-plane defect, and the 45° surface defect appears as the most influential surface defect. Hence, in this paper, the nanowire with a 45° surface defect is chosen to investigate the defect’s effect to the plastic deformation mechanism of nanowires. We find that during the plastic deformation of both perfect and defected nanowires, decrease regions of the stress curve are accompanied with stacking faults generation and migration activities, but during stress increase, the structure of the nanowire appears almost unchanged. We also observe that surface defects have obvious influence on the nanowire’s plastic deformation mechanisms. In particular, only two sets of slip planes are found to be active and twins are also observed in the defected nanowire.     

表面粗糙度对喷丸残余应力场的影响

为定性研究表面粗糙度对喷丸残余应力场的影响,采用余弦曲线模拟靶材粗糙表面,建立喷丸二维有限元模型,采用ABAQUS/EXPLICIT求解器对喷丸过程进行数值模拟,研究了表面粗糙度喷丸残余应力场的影响规律,分析了同一粗糙度下弹丸尺寸和喷射速度对喷丸残余应力场的影响规律,并与表面理想光滑时的情况进行了对比.结果表明,表面粗糙度的增加使残余压应力区变浅变薄,甚至使靶材表面产生残余拉应力,不利于喷丸强化件抗疲劳性能的提高,喷丸件表面应尽可能光滑以改善喷丸效果.     

A one-step method to fabricate lotus leaves-like ZnO film

Superhydrophobic surface is commonly fabricated by a combination of micro- and nano-scale structure and low surface energy materials. In this paper we fabricated a lotus leaves-like ZnO nano-forest surface by alkaline hydrothermal method, and the formation of micro- and nano-scale structured surface is controlled by the growth of the ZnO nanoseed layer. The growing ZnO nano-forest exhibits a perfect superhydrophilicity with a low water droplet CA about 1°. After modification with Teflon AF, the surface exhibits a superhydrophobicity with a water CA above 170°. The method is simply controllable, cost-effective, and has a wide range of potential applications such as self-cleaning superhydrophobic coating on large areas of different substrates.     

真空浸渍树脂法制备烧结金属材料金相样品

详细介绍了真空浸渍树脂法制备金相样品的制备过程.实践表明,采用真空浸渍树脂法能够填充材料表面的连通孔隙,保护原有孔隙的形貌、数量和分布,并能够较好地保护涂层、精细和易碎材料免受机械损伤;且能够防止在研磨和侵蚀的过程中研磨剂和腐蚀剂对样品的污染.     

Development-process-of-nonlinearity-based reliability evaluation of structures

A reliability evaluation approach based on the development process of the structural nonlinearity is presented. The traditional structural system reliability theory for structural safety regarding combination of failure modes is first revisited. It is seen that it stemmed from, and was heavily affected by, the assumption of perfect elasto-plasticity of materials. This will make the number of the failure modes increase in a non-polynomial form against the number of the potential plastic hinges. Moreover, the above methodology does not work appropriately in the case of nonlinearity in general form other than perfect elasto-plasticity, as commonly encountered in engineering practice. Discussions show that total information of the structure is involved in the development process of its nonlinearity, be it a deterministic case or stochastic counterpart. The information needed for reliability evaluation of structures could be extracted, for example, by capturing the probabilistic information of the extreme value of the corresponding response, which could be obtained by using the probability density evolution method. Therefore, the reliability evaluation for structural safety could then be directly evaluated without searching the failure modes. Taking a 10-bar truss as an example, the proposed method is theoretically elaborated and numerically exemplified.     

Material sensitive scanning probe microscopy of subsurface semiconductor nanostructures via beam exit Ar ion polishing

Whereas scanning probe microscopy (SPM) is highly appreciated for its nanometre scale resolution and sensitivity to surface properties, it generally cannot image solid state nanostructures under the immediate sample surface. Existing methods of cross-sectioning (focused ion beam milling and mechanical and Ar ion polishing) are either prohibitively slow or cannot provide a required surface quality. In this paper we present a novel method of Ar ion beam cross-section polishing via a beam exiting the sample. In this approach, a sample is tilted at a small angle with respect to the polishing beam that enters from underneath the surface of interest and exits at a glancing angle. This creates an almost perfect nanometre scale flat cross-section with close to open angle prismatic shape of the polished and pristine sample surfaces ideal for SPM imaging. Using the new method and material sensitive ultrasonic force microscopy we mapped the internal structure of an InSb/InAs quantum dot superlattice of 18 nm layer periodicity with the depth resolution of the order of 5 nm. We also report using this method to reveal details of interfaces in VLSI (very large scale of integration) low k dielectric interconnects, as well as discussing the performance of the new approach for SPM as well as for scanning electron microscopy studies of nanostructured materials and devices.     

Effect of different structures on the gas sensing property of ZnO

We have successfully reported a new diamond-like morphology of zinc oxide (ZnO) structures via a simple hydrothermal method and discussed its probable growth mechanism. Compared with other morphologies of ZnO structures (microrods and nanosheets), nanodiamonds have excellent gas-sensing property owning to its large specific surface area, holding the perfect promise for ZnO powders as underlying gas-sensing materials. Furthermore, the as-prepared nanosheets assisted with the sodium citrate as an additive were found to show better gas-sensing property due to the smaller size than microrods. We found the positive role of the sodium citrate and reaction time in the growth of nanosheets and nanodiamonds respectively and the corresponding influences on growth mechanism were discussed.     

Effect of grooves on adsorption of RGD tripeptide onto rutile TiO2 (110) surface

Molecular dynamics (MD) simulations have been performed to investigate the adsorption mechanism of Arg-Gly-Asp (RGD) tripeptide onto perfect and grooved rutile TiO₂ (110) surfaces, respectively. The simulation results suggest that RGD tripeptide can strongly adsorb onto TiO₂ surface through specified Ti coordination sites. Analysis of adsorption energy, mean-squared displacements and radial distribution functions indicates that the adsorption of RGD onto grooved surface is more stable and rapid than that onto the perfect surface, with the adsorption energy around −331.59 kcal/mol. And among the chosen groove surfaces, adsorption energies, adsorption speeds and adsorption depths of RGD onto the surfaces increase evidently with the extension of groove dimensions. For both perfect and grooved surfaces, once bonded to the surfaces by interactions of carboxyl groups or carbonyl groups with nearby surface Ti atoms, RGD tripeptides show a reasonable propensity to remain there and undergo relatively limited hinge-bending motions.     

制备条件对NZP族磷酸盐粉体材料物性的影响

用化学共沉淀法配合高温煅烧合成了几种不同化学组成的NZP族磷酸盐粉体材料,从实验结果和对共沉淀反应过程的理论分析两方面入手,着重研究了反应体系的pH值与形成单相NZP族晶体化合物的关系,以及煅烧温度对NZP族粉体比表面积的影响规律.结果表明:控制液相反应过程的pH值=8.5有利于形成单相的NZP族晶体化合物,结晶形态完整的NZP族化合物的比表面积＜30m2/g,在低于晶化温度下煅烧则可以制备大比表面积的NZP族粉体.此外,本研究所合成的NZP族化合物在pH=3～9的水溶液体系中表面带负电荷.     

The asymmetric lossy near-perfect lens

We extend the ideas of the perfect lens recently proposed [J.B. Pendry, Phys. Rev. Lett. 85, 3966 (2000)] to an alternative structure. We show that a slab of a medium with negative refractive index bounded by media of different positive refractive index also amplifies evanescent waves and can act as a near-perfect lens. We examine the role of the surface states in the amplification of the evanescent waves. The image resolution obtained by this asymmetric lens is more robust against the effects of absorption in the lens. In particular, we study the case of a slab of silver, which has a negative dielectric constant, with air on one side and other media such as glass or GaAs on the other side as an ‘asymmetric’ lossy near-perfect lens for p-polarized waves. It is found that retardation has an adverse effect on the imaging due to the positive magnetic permeability of silver, but we conclude that subwavelength image resolution is possible in spite of it.