Thick, three-dimensional nanoporous density-graded materials formed by optical exposures of photopolymers with controlled levels of absorption

Three-dimensional (3D) intensity distributions generated by light passing through conformal phase masks can be modulated by the absorption property of photosensitive materials. The intensity distributions have extremely long depth of focus, which is proportional to the size of the phase masks, and this enables one to pattern thick (approximately 100 microm), nanoporous structures with precise control of grade density. Various density-graded 3D structures that result from computational modeling are demonstrated. Results of x-ray radiograph and the controlled absorption coefficient prove the dominant mechanism of the generated graded density is absorption of the photosensitive materials. The graded-density structures can be applied to a chemical reservoir for controlled release of chemicals and laser target reservoirs useful to shape shockless wave compression.     

Optical characterization of CdZnTe/ZnTe heterostructures modified by electron or X-ray irradiation

The effect of electron and X-ray irradiation on the optical characteristics of CdZnTe/ZnTe quantum-size structures has been investigated. A comparison between the results of both irradiations has shown an essential role of electron excitation in radiation enhancement of Cd diffusion that is one of the reasons for degradation of the II–VI-based quantum-size structures. High defect density in the barrier layer and high stress level are considered to serve as additional reasons for degradation of the CdTe-based quantum size structures under irradiation.     

Structure,optical and thermal decomposition characters of LDPE graft copolymers synthesized by gamma irradiation

Methyl methacrylate (MMA) monomer was grafted onto low density polyethylene by the direct method of radiation grafting. The effect of cohesive energy density of different organic solvents on the degree of grafting was investigated. It was found that the extent of grafting depends largely on the kind of solvent, in which the highest degree of grafting was achieved in the presence of dioxane, whereas the lowest degree of grafting occurred in the presence of methanol. This behaviour was attributed to the solubility parameters of the solvent, monomer and polymer. The change in structure of the LDPE graft copolymer films was characterized by scanning electron microscopy, X-ray diffraction, UV/vis absorption and thermogravimetric analysis. The X-ray diffraction results showed a decrease in the crystallinity of LDPE graft copolymer matrix at high degree of grafting. Studies were made on the UV-absorption edge, and indirect allowed transitions with their optical energy gaps are determined. At the same time the Urbach energy was evaluated. The activation energy of the thermal decomposition was calculated according to Horowitz and Metzger method.     

Microstructure and transport properties of porous building materials. II: Three-dimensional X-ray tomographic studies

Three-dimensional X-ray microtomography is used to obtain three-dimensional images of the microstructure of two types of brick. The images are processed to remove the noise (random and circular pattern) and then thresholded to match the porosity determined experimentally. The 3-D binary images are then analyzed to estimate their vapor diffusivity and air permeability to compare to experimental data published in part one of this report. Care must be taken in obtaining the tomographic images at a resolution that both enables isolation and quantification of the pores of interest and provides a representative elementary volume for the transport property calculations. In general, the agreement between computed and measured properties is reasonable, suggesting that X-ray microtomography can provide valuable information on the characteristics and properties of the pore networks developed in these porous building materials. A preliminary evaluation indicates that the Katz-Thompson relationship between permeability, diffusivity, and pore size is valid for these materials.

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Résumé La microtomographie à rayons X synchrotron, est utilisée pour obtenir des images tridimensionnelles de la microstructure de deux types de briques. Les images sont tout d’abord traitées pour éliminer le bruit (anneaux aléatoires_ et ensuite seuillées par ajustement avec la porosité déterminée expérimentalement. à partir des images binaires 3D, on estime numériquement la diffusivité à la vapeur et la perméabilité à l’air, les valeurs obtenues sont ensuite comparées avec les données expérimentales publiées dans la partie I de cette communication. Dans le cadre d’une telle procédure, la résolution des images doit à la fois rendre possible la discrimination et la quantification de tous les pores importants vis-à-vis du phénomène étudié et fournir un volume élémentaire représentatif pour le calcul des propriétés de transport. L’accord satisfaisant obtenu entre les valeurs calculées et mesurées montre que la microtomographie X peut fournir des informations pertinentes sur les caractéristiques et les propriétés du réseau poreux des matériaux de construction. Une évaluation préliminaire indique que la relation de Katz-Thompson entre la perméabilité, la diffusivité et la taille des pores est applicable pour ces matériaux.

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Editorial Note Mr. D. P. Bentz is a RILEm Senior, Member. He works at NIST (USA), a titular member. He is also a Member of RILEm Coordinating Committee. He was the 1998 Robert l’Hermite medallist.     

A new source of X-ray line broadening: inhomogeneous strains induced by uniform homogeneous temperature conditions in polyphase or non-cubic materials

Thermal strains may contribute to X-ray diffraction line broadening in both single-phase non-cubic and in polyphase cubic polycrystalline materials even under uniform temperature conditions. A method is developed for calculating the magnitude of these thermally induced strains directly from the measured diffraction peak profiles. Corrections for particle-size effects can be made readily if particle-size broadening is significant, and the thermal diffuse scattering (TDS) contribution to the diffracted intensity can be taken into account experimentally. By this method, the strains in a Mg-5 wt% Si alloy were found to be increased by as much as 35% by a 190° C temperature change. Even in the case of this relatively low melting point alloy, the TDS effect causes only a maximum of 15% error in these measured strain effects. The interpretation of these isothermally induced strains in terms of crystal anisotropy, grain morphology and orientation and the relative sizes of phases and grains is discussed.     

Hollow-walled lattice materials by additive manufacturing: Design,manufacture, properties,applications and challenges

The rapid growth of additive manufacturing (AM) technologies has enabled the emergence of geometrically sophisticated materials or structures with tailored and/or enhanced mechanical responses. In addition to dense-walled lattice structures, innovation within the past decade has identified that hollow-walled lattice topologies exhibit the multifaceted potential of competitive strength and rigidity, whilst displaying unique deformation behaviours, indicating that they may be an important subsequent step in lattice evolution. Hollow-walled sections facilitate density and geometrical parameters well below what is achievable by dense-walled sections, providing additional hierarchies of architecture at micrometre to even nanoscale proportion. Their wall thickness can range from 20 nm to 800 µm while the relative density can span three orders of magnitude between 0.01% and 30%. Despite nearly a decade of research into hollow-walled lattice topologies, no meta-analysis exists to provide an informative overview of these structures. This research addresses this deficiency and provides a data-driven review of hollow-walled lattice materials. It elucidates how these hollow-walled lattices deviate from the current limitations of dense-walled lattices and the underlying mechanisms that dictate their performance, with data accumulated from an exhaustive collection of literature sources. A range of new insights into their design and manufacture is discussed for their future research and applications in different engineering fields.     

Optical excitation of LiF:Mg,Ti following alpha and beta irradiation

It is demonstrated experimentally that optical excitation of irradiated LiF:Mg,Ti (TLD-100) by 4 eV photons has the same effect for both alpha particle (high-ionisation density) irradiation and photon/electron irradiation. In both cases, peak 5a converts to peak 4 causing peak 4 to increase following the bleach. Such an observation is consistent with the major premise of track structure theory that radiation effects following heavy changed particle (HCP)/neutron irradiation are due exclusively to the interaction of the secondary electrons created by the HCP slowing down.     

Extension of optical properties of ZnO/SiO2 materials induced by incorporation of Au or NiO nanoparticles

Incorporating noble metal nanoparticles (NPs) and oxides has been proved to be an effective method to tune the optical properties of silica based materials. In this paper the optical and photocatalytic properties have been studied for ZnO/SiO₂ modified with Au or NiO nanoparticles. Changes in the optical properties of semiconductor ZnO particles have been observed due to the deposition of coloured Au and NiO nanoparticles by reducing the band gap energy and thus extending light absorption to visible domain. The excellent surface characteristics of NiO/ZnO/SiO₂ and Au/ZnO/SiO₂ favour the adsorption behaviour of these materials and limit the recombination of electron–holes pairs. Crystal Violet degradation under VIS light proved to have higher efficiency in the presence of Au/ZnO/SiO₂ (97%) than for NiO/ZnO/SiO₂ (60%).     

Synthesis of ZnOAl2O3 core-shell nanocomposite materials by fast and facile microwave irradiation method and investigation of their optical properties

Alumina (Al₂O₃) coated ZnO core-shell structures were synthesized by a novel, fast, and facile route utilizing microwave (MW) irradiation to control photocatalytic property of ZnO. The phase analysis and the core–shell structure development were corroborated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The XPS results affirmed that elements on the coated surface were Al and O. Zeta potential analysis predicted the presence of Al₂O₃ layer on ZnO due to almost similar zeta potential curve for pure Al₂O₃ and Al₂O₃ coated ZnO nanoparticles. There was no significant change in band gap energy of ZnO after amorphous Al₂O₃ coating as obtained from derived data of the reflectance spectra but gradual decreasing of reflectance in the visible range, measured by UV–vis spectroscopy, of the prepared core-shell nanoparticle may be due to the coating of amorphous Al₂O₃ on ZnO. The photocatalytic efficiency of ZnO was reduced after amorphous Al₂O₃ layer as confirmed by the photodegradation of methylene blue under UV irradiation.     

Minimizing the exposure of airborne pathogens by upper-room ultraviolet germicidal irradiation: an experimental and numerical study

There has been increasing interest in the use of upper-room ultraviolet germicidal irradiation (UVGI) because of its proven effectiveness in disinfecting airborne pathogens. An improved drift flux mathematical model is developed for optimizing the design of indoor upper-room UVGI systems by predicting the distribution and inactivation of bioaerosols in a ventilation room equipped with a UVGI system. The model takes into account several bacteria removal mechanisms such as convection, turbulent diffusion, deposition and UV inactivation. Before applying the model, the natural die-off rate and susceptibility constants of bioaerosols were measured experimentally. Two bacteria aerosols, Escherichia coli and Serratia marcescens, were tested for this purpose. It was found out that the general decay trend of the bioaerosol concentration predicted by the numerical model agrees well with the experimental measurements. The modelling results agree better with experimental observations for the case when the UVGI inactivation mechanism dominates at the upper-room region than for the case without UVGI. The numerical results also illustrate that the spatial distribution of airborne bacteria was influenced by both air-flow pattern and irradiance distribution. In addition to predicting the local variation of concentration, the model assesses the overall performance of an upper-room UVGI system. This model has great potential for optimizing the design of indoor an upper-room UVGI systems.     

Surface structural changes,surface energy and antiwear properties of polytetrafluoroethylene induced by proton irradiation

In this work, the polytetrafluoroethylene (PTFE) surface was modified with 25 keV proton beam irradiation in vacuum condition. Multiple characterization techniques including X-ray photoelectron spectroscopy, Raman spectroscopy and infrared spectroscopy were employed for research on microstructure changes in the PTFE surface. The changes in the surface energy and antiwear properties of PTFE were evaluated using contact angle analysis and a ball-on-disk tribometer, respectively. Experimental results showed that the surface energy of PTFE obviously increased from 13.17 mJ/m² to 33.73 mJ/m² and the wear rate decreased from 8.9 × 10^− 3 mm³/Nm to 5.8 × 10^− 4 mm³/Nm after proton irradiation for 15 min. Moreover, TRIM simulation indicated that the H⁺ ions cannot penetrate through the PTFE block and only stop at a depth of about 730 nm from the material surface. Proton irradiation has been proved to be a simple, rapid and effective measure for the surface modification of PTFE with distinctly improved surface energy and antiwear properties, and the possible reaction mechanism taking place in PTFE was also discussed in this paper.     

Origins of peaks of graphitic and pyrrolic nitrogen in N1s X-ray photoelectron spectra of carbon materials: quaternary nitrogen,tertiary amine,or secondary amine?

X-ray photoelectron spectroscopy (XPS) is among the most powerful techniques to analyse structures of nitrogen-doped carbon materials. However, reported assignments of (1) graphitic nitrogen (N)/substitutional N, quaternary N (Q–N), or tertiary amine (T–N) and (2) pyrrolic N/secondary amine or T–N are questionable. Most reports assign peaks at ca. 401 eV as Q–N or graphitic N, whereas raw materials in most of those works contain neither counter anion nor halogen. Besides, the peak at ca. 400 eV has been assigned as pyrrolic N, but the presence of N–H is generally not confirmed. In this work, it was clarified that one of the reasons for the prevailing ambiguous assignments is the presence of N in heptagonal and pentagonal rings. The peaks at 400.1–401.2 eV were determined to be T–N, but not Q–N by analyzing graphitized polyimide (with the oxygen content of 0.01 at% or lower and the hydrogen content of 0 at%) using Raman spectroscopy, XPS, X-ray diffraction, total neutron scattering, elemental analysis, and molecular dynamics simulation. Besides, it was revealed that the peak at 400.1 eV originated from T–N on 5-membered rings or 7- and 5-membered rings, but not pyrrolic N because graphite including no hydrogen was used for analysis.

Graphical abstract

     

Thermal stability of embedded metal nanoparticles elongated by swift heavy ion irradiation: Zn nanoparticles in a molten state but preserving elongated shapes

Solid Zn and V nanoparticles (NPs) embedded in silica were elongated by swift heavy ion (SHI) irradiation with 200 MeV Xe(14+) ions to a fluence of 5.0 × 10(13) ions cm(-2). Isochronal annealing was carried out in a vacuum from 200 to 1000 °C in steps of 100 °C for 10 min each. The degree of shape elongation was evaluated at room temperature (RT) by two different optical methods: linear dichroism spectroscopy and birefringence spectroscopy. In the as-irradiated state, the samples showed an absorption band at 5 eV due to radiation-induced defects in the silica in addition to the anisotropic absorption due to the elongated metal NPs. After annealing at 400 °C the defect band had completely disappeared, while the degree of shape elongation was almost unchanged or rather slightly increased in both the Zn and V NPs. The elongation of the Zn NPs slightly decreased but maintained a certain value after annealing at 500 °C, which is much higher than the melting point (MP) of Zn NPs (~420 °C). This observation indicates that shape elongation is mostly maintained even if the Zn NPs are in the molten state to some extent during annealing. The elongation of the Zn NPs was almost eliminated after annealing at 600 °C. In the case of the V NPs, elongation was maintained up to 800 °C but mostly eliminated at 900 °C. Since the recovery temperature of 900 °C from the elongated to the spherical shape is much lower than the MP of bulk V (1890 °C), we consider that the elongation is eliminated without melting of V NPs, i.e. via solid state mass transportation. The melting of NPs is not the key factor for the recovery to the spherical shape.     

Dynamical behaviour of nanocrystals in transmission electron microscopy: size,temperature or irradiation effects

High-resolution transmission electron microscopy shows that metal nanoparticles sinter within a fraction of a second under an electron beam at 'room temperature' as long as classical models of thermal equilibrium apply. Images exhibit crystal planes that change in orientation with time as if the particle was undergoing melting and resolidification processes. We explore whether these dynamical effects are the result of heating or transformation effects in the electron microscope or quantum fluctuations in small systems.     

Surface properties of electrodeposited a-Si:C:H:F thin films by X-ray photoelectron spectroscopy

Surface properties of amorphous silicon thin films containing hydrogen, flourine and carbon obtained from hydrofluosilicic acid and ethylene glycol using the electrodeposition method are reported as a function of current density and deposition time. The Si2p core level X-ray photoelectron spectra exhibited binding-energy shifts corresponding to SiFx (x=1–4), SiC, Si-H and Si-O2 type bond formations. The shifts in 1s spectra of fluorine, carbon and oxygen confirmed the presence of fluorine, carbon and oxygen in bonded form. Theoretical binding-energy shifts calculated from Pauling's electronegativity values were in close agreement with the measured values. The relative concentration values of C/Si estimated in these films were found to be larger than those of F/Si and O/Si. The results were corroborated with infrared spectroscopy and scanning electron microscopy data. This revised version was published online in November 2006 with corrections to the Cover Date.     

Characterization of multilayered materials for optoelectronic components by high-resolution X-ray diffractometry and reflectometry: contribution of numerical treatments

Both X-ray reflectometry and X-ray diffractometry techniques are used for the assessment of individual layer thicknesses inside complicated semi-conductor heterostructures, in particular for opto-electronic applications. The use of Fast Fourier transform-based numerical treatments applied to the reflectivity curve allows a fast determination of the individual layer thicknesses. We demonstrate the capability of this method by reporting X-ray reflectometry study on superlattices, multiple quantum wells, and other complicated structures. Typical layer thicknesses from 0.5 nm to 500 nm were successfully investigated. Fast Fourier transform-based procedure has also been employed successfully on high resolution X-ray diffraction spectra. We finally show the complementary of both techniques.     

溶胶-凝胶法纳米WO3材料的合成、表征及气敏性能

采用溶胶-凝胶法制备了一系列掺杂有SiO2的WO3纳米粉体,通过TEM、XRD等分析手段对产物粉体的粒度、晶相结构进行了表征,测试了材料的气敏性能,探讨了煅烧温度、掺杂量、工作温度对材料气敏性能的影响。结果表明：适量SiO2的掺杂有利于提高WO3对NO2气体的灵敏度,其中掺杂量为3％（质量分数）的气敏元件在较低的工作温度下气敏性能突出。     

Comparative studies of optoelectrical properties of prominent PV materials: Halide perovskite,CdTe, and GaAs

We compare three representative high performance PV materials: halide perovskite MAPbI₃, CdTe, and GaAs, in terms of photoluminescence (PL) efficiency, PL lineshape, carrier diffusion, and surface recombination and passivation, over multiple orders of photo-excitation density or carrier density appropriate for different applications. An analytic model is used to describe the excitation density dependence of PL intensity and extract the internal PL efficiency and multiple pertinent recombination parameters. A PL imaging technique is used to obtain carrier diffusion length without using a PL quencher, thus, free of unintended influence beyond pure diffusion. Our results show that perovskite samples tend to exhibit lower Shockley–Read–Hall (SRH) recombination rate in both bulk and surface, thus higher PL efficiency than the inorganic counterparts, particularly under low excitation density, even with no or preliminary surface passivation. PL lineshape and diffusion analysis indicate that there is considerable structural disordering in the perovskite materials, and thus photo-generated carriers are not in global thermal equilibrium, which in turn suppresses the nonradiative recombination. This study suggests that relatively low point-defect density, less detrimental surface recombination, and moderate structural disordering contribute to the high PV efficiency in the perovskite. This comparative photovoltaics study provides more insights into the fundamental material science and the search for optimal device designs by learning from different technologies.