Microscale characterization of granular deformation near a crack tip

This paper presents a study of microscale plastic deformation at the crack tip and the effect of microstructure feature on the local deformation of aluminum specimen during fracture test. Three-point bending test of aluminum specimen was conducted inside a scanning electron microscopy (SEM) imaging system. The crack tip deformation was measured in situ utilizing SEM imaging capabilities and the digital image correlation (DIC) full-field deformation measurement technique. The microstructure feature at the crack tip was examined to understand its effect on the local deformation fields. Microscale pattern that was suitable for the DIC technique was generated on the specimen surface using sputter coating through a copper mesh before the fracture test. A series of SEM images of the specimen surface were acquired using in situ backscattered electronic imaging (BEI) mode during the test. The DIC technique was then applied to these SEM images to calculate the full-field deformation around the crack tip. The grain orientation map at the same location was obtained from electron backscattered diffraction (EBSD), which was superimposed on a DIC strain map to study the relationship between the microstructure feature and the evolution of plastic deformation at the crack tip. This approach enables to track the initiation and evolution of plastic deformation in grains adjacent to the crack tip. Furthermore, bifurcation of the crack due to intragranular and intergranular crack growth was observed. There was also localization of strain along a grain boundary ahead of and parallel to the crack after the maximum load was reached, which was a characteristic of Dugdale–Barenblatt strip-yield zone. Thus, it appears that there is a mixture of effects in the fracture process zone at the crack tip where the weaker aspects of the grain boundary controls the growth of the crack and the more ductile aspects of the grains themselves dissipate the energy and the corresponding strain level available for these processes through plastic work.     

Morphology and microstructure at different scales of porous silicon prepared by a nonconventional technique

In this work we present first results concerning the detailed structure of porous silicon (PS) layers prepared by a new method using a vapour-etching (VE)-based technique. Studies of the photoluminescence properties of VE-based PS show that the visible emission occurs at high energies as compared with PS prepared by conventional techniques. To understand the VE-based PS features, we need to point out the PS microstructure throughout its general morphology. For this purpose a microscopy multiscale study was done. Scanning, conventional transmission, and high-resolution transmission electron microscopes were employed. The investigations were made on PS films prepared from moderately and heavily doped n- and p-type silicon. SEM images show that VE-based PS layers are essentially formed of clusters like interconnected structures. TEM studies show that these clusters are composed of nanocrystallites with different shapes. The effect of the doping type of the starting Si substrate on the characteristics of the PS layers was examined (thickness, porosity, behavior). Pore propagation was found to depend on doping type. The crystallinity of the PS layers was also locally studied in depth.     

Photometric stereo applied to diffuse surfaces that violate Lambert's law

This paper investigates the use of photometric stereo (PS) with reflectance functions that are diffuse but not Lambertian. We show that, for the special case where light sources are arranged at 90° intervals around the optical axis, standard PS is not limited to Lambertian surfaces, and we define criteria for its use. A series of rough test surfaces are used as models for surface microstructure-we found that the Oren Nayar (ON) reflectance model accurately predicted the surfaces' reflectance functions. The ON model does not meet our theoretical criteria for using PS, but PS performs well in simulations if the microroughness is moderate (rms slope <0.3). When PS was applied to real surfaces, the estimated and actual slopes were highly correlated, but there were significant errors in the slope estimates for the rougher samples.     

Specularity and shadow detection for the multisource photometric reconstruction of a textured surface

Textured surface analysis is essential for many applications. In this paper, we present a three-dimensional (3D) recovery approach for real textured surfaces based on photometric stereo. The aim is to be able to reconstruct the textured surfaces in 3D with a high degree of accuracy. For this, the proposed method uses a sequence of six images and a Lambertian bidirectional reflectance distribution function (BRDF) to recover the surface height map. A hierarchical selection of these images is employed to eliminate the effects of shadows and highlights for all surface facets. To evaluate the performances of our method, we compare it to other traditional photometric stereo methods on real textured surfaces using six or more images.     

Non-laser-based scanner for three-dimensional digitization of historical artifacts

A 3D scanner, based on incoherent illumination techniques, and associated data-processing algorithms are presented that can be used to scan objects at lateral resolutions ranging from 5 to 100 microm (or more) and depth resolutions of approximately 2 microm. The scanner was designed with the specific intent to scan cuneiform tablets but can be utilized for other applications. Photometric stereo techniques are used to obtain both a surface normal map and a parameterized model of the object's bidirectional reflectance distribution function. The normal map is combined with height information, gathered by structured light techniques, to form a consistent 3D surface. Data from Lambertian and specularly diffuse spherical objects are presented and used to quantify the accuracy of the techniques. Scans of a cuneiform tablet are also presented. All presented data are at a lateral resolution of 26.8 microm as this is approximately the minimum resolution deemed necessary to accurately represent cuneiform.     

PA6/磺化石墨烯功能微球的制备及性能研究

以己内酰胺(CL)、聚苯乙烯(PS)、磺化石墨烯(SG)为主要原料,通过阴离子聚合反应诱导相分离的方法,制备得到了一系列粒径可控的PA6/SG杂化微球。SG在PS的存在下,选择性分散在CL单体中,形成CL/PS/SG悬浮液;再通过CL原位阴离子聚合制备PA6/PS/SG合金,利用甲苯除去PS相后可以获得粒径分布在10~50μm的PA6/SG微球。扫描电镜及粒径测试结果表明,PS及SG含量可以影响PA6微球的形貌及尺寸。通过透射电镜可确定SG选择性分散在了PA6相中,同时SG的加入可有效地改善PA6的热稳定性、结晶性、熔融性能和烧结性能,并且适用于3D打印激光烧结领域。     

Morphological, structural and optical properties of GaN grown on porous silicon/Si(100) substrate

In the present paper, we report results of GaN layers grown at 800 °C by metal organic vapour phase epitaxy (MOVPE) on porous silicon (PS) formed on Si(100) substrates. The surface morphology and the crystallinity of the GaN films were characterized by scanning electron microscope and X-ray diffraction. It was shown that GaN grows on PS preferentially on hexagonal polycrystalline form. The SEM observation reveals roughly surface textured by disoriented GaN grains having different shapes and sizes. The surface coverage and the wetting of GaN to PS are improved when the thickness of GaN layer increases. The optical properties of GaN layers were examined by PL and CL at low and room temperatures. Besides, the near edge-band (BE) emission, shows yellow (YL) and deep localized excitons bands at approximately 2.2 and 3.3-3.36 eV respectively. The depth CL analysis shows a spatial variation of the dominating YL and BE emissions as the electron beam energy rises from 3 to 25 kV.     

Preparation polystyrene/multiwalled carbon nanotubes nanocomposites by copolymerization of styrene and styryl-functionalized multiwalled carbon nanotubes

Styryl-functionalized multiwalled carbon nanotubes (p-MWNTs) were prepared by esterification based on the carboxylate salt of carbon nanotubes and p-chloromethylstyrene in toluene. Then in situ radical copolymerization of p-MWNTs and styrene initiated by 2,2′-azobis(isobutyronitrile) (AIBN) was applied to synthesize composites of styryl-functionalized multiwalled carbon nanotubes and polystyrene (PS) (p-MWNTs/PS). Characterizations carried out by FT-IR, ¹H NMR, UV–vis show that styryl group covalently bond to the surface of MWNTs. The results of UV showed that the solutions of p-MWNTs/PS in chloroform have the hyperchromic effect. Transmission electron microscopy (TEM) images of p-MWNTs/PS composites and scanning electron microscopy (SEM) images of fracture surface of p-MWNTs/PS composites showed the functionalized nanotubes had a better dispersion than that of the unfunctionalized MWNTs in the matrix. The results of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) suggested that the thermal stability of p-MWNTs/PS composites improved in the presence of MWNTs.     

Micro-Raman spectroscopy study of colloidal crystal films of polystyrene-gold composites

Monolayers and multilayers of polystyrene (PS)-gold composite films prepared by two different deposition methods have been investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and confocal Raman microspectroscopy. The intensity of the 1001 cm(-1) ring breathing mode of PS is used to evaluate the degree of ordering of monolayers and multilayers within a colloidal crystal. The depth profiling capability of confocal Raman microscopy is used to probe the regions inside the fractures in multilayered films. The intensity profile of the 1001 cm(-1) peak revealed the presence of fractures of different shapes with some PS microspheres at the bottom of the fracture. A strong increase in the Raman intensity (by 10(3) times) has been observed when probing the regions where Au nanoparticles are concentrated in aggregates of different shapes. This enhancement is attributed to the surface plasmons generated by the periodic structure of the gold nanoparticles.     

等离子喷涂碳化硼/钼涂层氚的滞留性能研究

为了保证核能源的使用安全, 对氚在第一壁材料表面的滞留数量以及深度进行定量表征非常重要。在本研究中, 制备了一系列潜在的第一壁材料B₄C/Mo 涂层, 并采用成像板(IP)和β射线激发X射线(BIXS)法对其表面的氚滞留情况进行了测定。IP 图像表明, 涂层表面吸附的氚含量遵循以下顺序: B₄C>BM15>BM5>Mo。而BIXS结果进一步表明, 对于B₄C涂层, 大部分氚扩散到了涂层内部; 而对于其他三种涂层, 氚仅在其表面发生吸附。扫描电镜(SEM)结果显示, B₄C涂层气孔率最高, 而其他三种涂层尽管气孔率较低, 但其截面仍能观察到大量气孔和微裂纹的存在。涂层中的这些缺陷为氚的吸收和扩散提供了通道, 而气孔与微裂纹的尺寸最终决定了氚在涂层表面的吸附数量。实验结果还表明, 涂层杂质成分Ti的存在也对氚的滞留产生了一定影响。     

Fabrication of multi-walled carbon nanotube reinforced polyelectrolyte hollow nanofibers by electrospinning

Hybrid hollow multi-walled carbon nanotubes (MWCNTs)/polyelectrolytes (PE) nanofibers were prepared by a combination of the electrospinning method and layer-by-layer (LbL) technique. The mixed polystyrene (PS)/MWCNTs nanofibers were obtained by electrospinning method, which were employed as templates to self-assembly multilayered polyelectrolytes by LbL technique. Hollow MWCNTs/PE nanofibers were obtained by selectively removed part of the template: PS, which is confirmed by Raman spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM).     

Three-dimensional reconstruction of fracture surfaces

An original method is presented to improve fracture surface characterization through an accurate three-dimensional (3-D) reconstruction. The method, based on digital image-processing techniques, was developed under the Khoros system. The reconstruction technique is based upon the stereoscopic principle to extract the surface local elevations from the stereo-pair images. The fractographs that compose the stereo pair are obtained by scanning electron microscopy from two points of view by tilting the object at two observation angles. The first step of image processing is the alignment of the two images. Next, an iterative processing based on the cross-correlation operation builds a very dependable high resolution elevation map of the fracture surface. Finally, the elevation map can be used to provide a 3-D perspective view of the surface by using various visualization tools. Also, profiles and horizontal sections are generated by sectioning the 3-D reconstructed surface.     

Tailoring the morphology of raspberry-like carbon black/polystyrene composite microspheres for fabricating superhydrophobic surface

In our previous report, raspberry-like carbon black/polystyrene (CB/PS) composite microsphere was prepared through heterocoagulation process. Based on the previous study, in the present work, the morphology of raspberry-like CB/PS particle is tailored through adjusting the polarity and the concentration ratio of CB/PS colloidal suspension with the purpose to prepare particulate film for the fabrication of superhydrophobic surface. Scanning electron microscope (SEM) confirms the morphology of raspberry-like particle and the coverage of CB. Rough surfaces fabricated by raspberry-like particles with proper morphology are observed by SEM and clear evidence of superhydrophobic surface is shown. The structure of raspberry-like particle is analyzed by atom force microscope. The proposed relationship between the hydrophobicity and the structure of CB aggregates on the surface of PS microsphere is discussed in details.     

Porous silicon nanowires fabricated by electrochemical and laser-induced etching

Electrochemical and laser-induced etching processes were simultaneously used to synthesize the nanowires structure of porous silicon (PS). Surface morphology and structural properties of nanostructured silicon were characterized by using scanning electron microscopy (SEM) and atomic forces microscopy (AFM) images. Nanowires with dimensions of few nanometers were formed on the whole etched surface. The optical properties of silicon nanostructures were studied. Raman spectra were shifted and broadened relatively to 519.9 cm⁻¹ of PS prepared by electrochemical etching, and shifted to 517.2 cm⁻¹ for laser-induced etching process and to 508.9 cm⁻¹ for electrochemical and laser etching simultaneously. Blue shift luminescence was observed at 649.6 nm for PS produced by electrochemical etching, and at 629.5 nm for laser-induced etching. PS produced a blue shift at 626.5 nm using both etching procedures simultaneously. X-Ray diffraction (XRD) was used to investigate the crystallites size of the PS as well as to provide an estimate of the degree of crystallinty of the etched sample.     

Concise route to styryl-modified multi-walled carbon nanotubes for polystyrene matrix and enhanced mechanical properties and thermal stability of composite

Effective functionalization of multi-walled carbon nanotubes (MWCNTs) with styryl group was carried out via the esterification reaction of the carboxylate salt of carbon nanotubes and 4-vinylbenzyl chlorides in toluene. The functionalized MWCNTs were characterized through FTIR and Raman spectra to confirm the styryl groups covalently connected to the surface of MWCNTs. The weight loss of functionalized moieties determined by thermogravimetry-differential scanning calorimertry analysis is around 36%. Nanotube-reinforced polystyrene were fabricated by mixing functionalized MWCNTs and polystyrene. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the functionalized nanotubes had a better dispersion than the unfunctionalized MWCNTs in the matrix. Moreover, styryl-modified MWCNTs/PS nanocompsite presented obvious improvements in mechanical properties and thermal stability.     

A study of the chemical and morphological alterations of PS and PC surfaces induced by excimer laser treatments

The effect of laser irradiation on polystyrene (PS) and bisphenol-A polycarbonate (PC) has been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), optical microscopy and surface profilometry. The dependence of the surface chemical and morphological properties on wavelength and fluence has been investigated.On both materials no apparent chemical modification was induced by irradiation at 350 nm, there is no evidence of non-linear effects. Morphological alterations were induced in the PS subsurface, due to thermal shock effects. The irradiation of both polymers at 248 and 193 nm did not result in photoassisted oxidation. In the case of PS, etching is evident at 193 nm. Irradiation of PC at 248 nm induces oxygen depletion and photo-Fries rearrangements, whereas at 193 nm oxygen depletion and etching are predominant. In both polymers etching yields peculiar surface morphologies, namely the formation of debris and cone-like structures.     

Spectrum analysis of the reduction degree of two-step reduced graphene oxide (GO) and the polymer/r-GO composites

In this paper, the reduction degree of graphene oxide (GO) reduced using chemical reduction and thermal reduction methods was characterized by spectrum analysis. The optimized conditions of reducing GO were determined that the hydrazine hydrate is the best reducing agent and the appropriate thermal reduction temperature is at 240 °C. The obtained GO solution was mixed with polystyrene (PS) solution to prepare PS/r-GO composites by using two-step reduction technique under the optimized conditions. The structure and micro-morphology of GO, r-GO and PS/r-GO composites were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) respectively. It is also observed that the two-step reduction pathway is more effective than one-step reduction for improving the reduction degree of GO. Accordingly, the electric conductivity of PS/r-GO composites prepared by two-step reduction technique is as high as 21.45 S m⁻¹, which is much higher than that of composites fabricated by one-step reduction method. The spectrum techniques will highlight new opportunities for investigating the reduction degree of GO in polymer composites.     

Novel Nanostructured MnO_2 Prepared by Pulse Electrodeposition:Characterization and Electrokinetics

Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcMD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFM）. SEM image revealed that pulse current could improve the current distribution. This was confirmed by AFM images showing a decrease in surface roughness of pcMDs in comparison to amorphous samples, which were deposited by direct current （dcMD）. Higher distortion of MnO6 octahedral environment of dcMD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcMD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcMD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcMD grains.     

Design of molecular devices based on metalloproteins: a new approach

In this study, cytochrome c and azurin proteins were immobilized onto a porous silicon (PS) surface using the self-assembly technique. The heterostructures were maintained at ambient conditions for several days. Experimental results showed long term stability of proteins in solid state working as electron-transfer devices. Atomic force microscopy showed similar roughness of the surface for both protein heterostructures (14.5 and 11.3 nm, respectively) and globular morphology. Analysis of samples, using scanning electron microscopy, revealed a porous surface of 20–24 nm, whereas cross-section indicated a thickness between 3.6 and 3.8 μm. The fluorescence peak at room temperature, corresponding to blue emission, was observed at 362–550 nm. This is due to the quantum confinement effect through the silicon. Raman measurement showed one Raman’s peak, confirming that the prepared sample retained the crystallinity of bulk silicon; immobilization of proteins produced loss of crystallinity. Reflection spectra revealed the PS, changes in the refractive index profile at the interface of the PS, and the modified surface.     

One experimental proof of the evolution of electrodeposited microcrystals via a high-temperature state

The surface of voids formed during the electrolytic growth of silver microcrystals has been studied by scanning electron microscopy (SEM). SEM images reveal the dendrite morphology of the surface of voids. This is additional evidence for the validity of a model proposed previously, according to which an island growing during electrocrystallization passes via a high-temperature state.