Luminescence of electron-irradiated nanoporous silicate glasses

It is experimentally demonstrated that the point electron-beam irradiation of a nanoporous silicate glass leads to the appearance of or significant increase in the UV-excited luminescence from the entire sample in the spectral intervals of 500–700 and 900–950 nm. The observed effect is related to (i) partial reduction of SiO₂ and H _x SiO _y phases by electrons that spread via through pores in the glass and (ii) an increase in the number of Si-H and Si-OH bonds.     

Toughening of nanoporous glasses using porogen residuals

Nanoporous glasses are inherently brittle materials that become increasingly fragile with increasing porosity. We show that remarkable increases in fracture energy can be obtained from remnants of the porogen molecules used to create the nanoscale pores. The interfacial fracture energy of approximately 2.6 J m(-2) for dense methylsilsesquioxane glass films is shown to increase by over one order of magnitude to >30 J m(-2) for glasses containing 50 vol.% porosity. The increased fracture resistance is related to a powerful molecular-bridging mechanism that was modelled using bridging mechanics. The study demonstrates that significant increases in interfacial fracture energy may be obtained using strategies involving controlled decomposition of the porogen molecule during processing of nanoporous glasses. The implications are important for a range of emerging optical, electronic and biological technologies that use nanoporous thin films, but are limited by the degradation of mechanical properties with increasing porosity.     

Fracture toughness measurement of thin-film silicon

The fracture toughness of single‐crystal silicon thin films oriented to (100) and (110) was investigated by tensile testing under both 〈100〉 and 〈110〉 loading conditions. The specimen was fabricated from a p‐type Czochralski (CZ)‐grown wafer and passed through a thermal process during the fabrication of the test device. The measured fracture toughness is dependent on the loading direction in the tensile test and independent of the specimen surface orientation. The test results were 1.94 MPa√m in the 〈100〉 direction and 1.17 MPa√m in the 〈110〉. In these tests, no longitudinal size effect on the fracture stress or fracture toughness was observed. The SEM photographs obtained from the fracture specimens after the tensile test show that the crack initiated from the notch tip and propagated straight in the across‐the‐width direction on the (110) or (111) cleavage plane.     

All electrochemical fabrication of a platinized nanoporous Au thin-film catalyst

In an effort to decrease the high cost associated with the design, testing, and production of electrocatalysts, a completely electrochemical scheme has been developed to deposit and platinize a nanoporous Au (NPG) based catalyst for formic acid oxidation. The proposed route enables synthesis of an alternative to the most established, nanoparticles based catalysts and addresses issues of the latter associated with either contamination inherent from the synthetic route or poor adhesion to the supporting electrode. The synthetic protocol includes as a first step, electrochemical codeposition of a Au((1-x))Ag(x) alloy in a thiosulfate based electrolyte followed by selective electrochemical dissolution (dealloying) of Ag as the less noble metal, that generates an ultrathin and preferably continuous porous structure featuring thickness of less than 20 nm. NPG is then functionalized with Pt (no thicker than 1 nm) by surface limited redox replacement (SLRR) of underpotentially deposited Pb layer to form Pt-NPG. SLRR ensures complete coverage of the surface with Pt, believed to spread evenly over the NPG matrix. Testing of the catalyst at a proof-of-concept level demonstrates its high catalytic activity toward formic acid oxidation. Current densities of 40-50 mA cm(-2) and mass activities of 1-3 A.mg(-1) (of combined Pt-Au catalyst) have been observed and the Pt-NPG thin films have lasted over 2600 cycles in standard formic acid oxidation testing.     

Fluoride and tellurite glasses for thin-film IR viewers

We have studied optical characteristics of Er³⁺-, Ho³⁺-, and Yb³⁺-doped ZBLAN and TWL glasses. Their luminescence was excited at wavelengths of 975, 378, and 449 nm. The 975-nm radiation excited the Yb³⁺ (² F _7/2 → ² F _5/2), and the excitation energy was then transferred to the Er³⁺ and Ho³⁺. The short-wavelength excitation led to cross-relaxation processes: (⁴ F _7/2, ² F _7/2) → (⁴ I _11/2, ² F _5/2) for the Er³⁺-Yb³⁺ pair (378 nm) and (⁵ F ₃, ² F _7/2) → (⁵ I ₅, ² F _5/2) for the Ho³⁺-Yb³⁺ (449 nm). At the three excitation wavelengths, we observed green luminescence in the range 525–550 nm. Using the glasses studied here, we prepared thin colorless lacquer films potentially attractive for hidden information recording and hidden labeling of various objects and materials.     

Fracture propagation in organic glasses

A quantitative assessment of the density of hyperbolic markings in the fracture surfaces of polymethyl methacrylate has been made showing that the density is proportional to the fracture toughness. In general the fracture toughness at any instance is a random function, but there is a definite tendency for it to increase with velocity of fracture propagation.It is suggested that the craze material ahead of the true crack tip may be assumed to have constant strength and Dugdale's model for elasto—plastic materials applied to organic glasses as well.

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Zusammenfassung Es wurde eine quantitative Einschätzung der Festigkeit von Hyperbelmarkierungen in den Bruchoberflachen von Polymethyl-Methacrylaten vorgenommen welche zeigte, dass die Festigkeit proportional zur Bruchfestigkeit ist. Die Bruchfestigkeit ist gewöhnlich eine Zufallsfunktion, aber sie hat definitive Tendenz sich mit der Bruchverbreltungsgeschwindigkeit zu vergrössern.Es wurdeangenommen, dass das Rissmaterial vor der wahren Rissspitze konstante Kraft hat and dasDugdale's Modell für elastisch—plastisches Material auch für organisches Glass angewandt werden kann.

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Résumé Une mesure quantitative de la densité de stries hyperboliques sur les surfaces de rupture de methacrylate de polymethyle a permis de démontrer que la densite des stries est proportionnelle a la ténacité à la rupture du materiau. En règle générale, la ténacité est à tout moment une fonction statistique; il semble toutefois qu'elle tende a s'accroître avec la vitesse de propagation de fissure.On suggère que la zone de matière qui se trouve en avant de 1'extrémité de la fissure réelle puisse être considérée comme ayant une résistance constante, et que le modèle de Dugdale pour l'ètude des matériaux élasto-plastiques est applicable a l'étude des verres organiques.

     

Fracture toughness of some metallic glasses

The critical stress intensity factor of Fe₄₀Ni₄₀B₂₀, Fe₃₀Cr₁₀Ni₄₀B₂₀, Ni₈₀Si₁₀B₁₀ and Ni₈₀Si₅B₁₅ metallic glass ribbons was measured. Stressing by ultrasound, a new method for preparation a sharp crack in a metallic glass, was used. Only shear rupture failures was investigated for all alloys.     

Fracture of Ni-Fe base metallic glasses

The fracture toughnesses of specimens of three transition metal base metallic glasses, Ni₄₈Fe₂₉P₁₄B₆Al₃, Ni₃₉Fe₃₈P₁₄B₆Al₃ and Ni₄₉Fe₂₉P₁₄B₆Si₂ are reported. Each alloy was tested in a characteristic thickness, i.e., 25m (Ni₄₈), 43m (Ni₃₉) and 72 m (Ni₄₉) andK _C values of 120, 62 and 30 kg mm^–3/2, respectively, were observed. It is suggested that this variation is associated primarily with a transition from plane strain (K _IC 30 kg mm^–3/2) toward plane stress conditions as sample thickness is decreased. The fatigue crack propagation rate in the Ni₃₉ alloy is also reported;da/dn (mm/cycle) 2×10^–8 K ^2.25, whereK has units of kg mm^–3/2. When the respective data are plotted in terms of (K/E), whereE is Young's modulus, the crack growth behaviour for the Ni-Fe glasses approximates that for crystalline ferrous alloys. A classical chevron pattern, macroscopically at 90° to the tensile axis, is observed when amorphous metallic alloy strips fracture under plane strain conditions. On a finer scale, the chevrons exhibit a sawtooth structure, and the sawtooth surfaces show a fine scale, equi-axed vein pattern. This indicates that local failure occurs by shear rupture.     

Synthesis and optical properties of vanadium dioxide nanoparticles in nanoporous glasses

A method for the synthesis of vanadium dioxide (VO₂) nanoparticles in nanoporous silicate glass matrices with a pore size of 17 and 7 nm has been developed. According to this, vanadium pentoxide (V₂O₅) nanoparticles are initially grown in the pores, and then V₂O₅ is reduced to VO₂ in hydrogen. The optical transmission spectra of 1-mm-thick VO₂-modified glass samples have been measured. The temperature dependence of the transmission coefficient has been studied in the course of the semiconductor-metal phase transition in VO₂ nanoparticles.     

Fracture resistance of technical and optical glasses: edge flaking of specimens

We present the results of fracture resistance tests for technical and optical glasses performed by indentation flaking of the rectangular specimen edge. The features of crack propagation in these glasses are analyzed during chipping fracture caused by indentation with blunt and sharp diamond indenters. By comparative analysis of the values for resistance to edge flaking and those for fracture resistance, new data on the mechanical behavior of the above glasses in fracture are obtained. In particular, it is shown that these glasses, along with ceramic materials used to produce armor, have an enhanced resistance to the onset of fracture.     

All-nanoparticle thin-film coatings

All-nanoparticle thin-film coatings that exhibit antireflection, antifogging (superhydrophilicity), and self-cleaning properties have been prepared via layer-by-layer deposition of TiO(2) and SiO(2) nanoparticles. The porosity and chemical composition of the coatings were determined using a simple method that is based on ellipsometry and does not require any assumptions about the refractive indices of the constituent nanoparticles. The presence of nanopores in the TiO(2)/SiO(2) nanoparticle coatings results in superhydrophilicity as well as antireflection properties. The superhydrophilicity of contaminated coatings could also be readily recovered and retained after ultraviolet irradiation.     

纳米孔"炭"和纳米孔"碳"——对碳质多孔材料的几点思考

对碳质纳米孔隙材料提出一种新的分类方法——基于孔壁结构分类。根据这种方法，碳质多孔材料分为：纳米孔“碳”（石墨烯纳米孔材料）和纳米孔“炭”（类石墨微晶纳米孔材料）。具有相近比表面积的两种碳质材料由于具有不同的孔壁结构而可能具有完全不同的物理化学性质（比如：电化学性质）。文中简要介绍了两种新型的纳米孔“碳”——单壁微孔“碳”和碳纳米管-DNA杂化物以及区分纳米孔“碳”和纳米孔“炭”的重要判据：拉曼光谱。     

Fracture toughness of CaO-P2O5-B2O3 glasses and glass-ceramics determined by indentation

The fracture toughness, (K _IC) of CaO-P₂O₅-B₂O₃ glasses and glass-ceramics was investigated using both Vickers indentation and the notched beam technique (NBT). Five representative equations were applied and it was found that for the variation of K _IC with B₂O₃ content, the Lawn and Fuller equation showed the best correspondence with the NBT. The values of fracture toughness obtained from the Lawn and Fuller equation showed the same trend with B₂O₃ content as that determined by NBT, although the values from indentation were on average 33% lower. The determination of absolute fracture toughness by indentation requires a correction factor which can be obtained by calibration using NBT. A significant increase in K _IC occurred after a 37CaO-37P₂O₅-20B₂O₃-6Al₂O₃ (mol%) glass was converted to a glass-ceramic. The much higher K _IC for the glass-ceramic measured by NBT (1.32 MN m^–3/2) compared with that from indentation (0.89 MN m^–3/2) is attributed to internal stresses due to thermal expansion differences between the crystalline and residual glass phases leading to additional microcrack toughening.     

Facile fabrication of ultrathin freestanding nanoporous Cu and Cu-Ag films with high SERS sensitivity by dealloying Mg-Cu(Ag)-Gd metallic glasses

Nanoporous metals prepared by dealloying have attracted increasing attention due to their interesting size-dependent physical,chemical,and biological properties.However,facile fabrication of metallic ultra-thin freestanding nanoporous films(UF-NPFs)by dealloying is still challenging.Herein,we report a novel strategy of facile preparation of flexible Cu,Cu3Ag,and CuAg UF-NPFs by dealloying thick Mg-Cu(Ag)-Gd metallic glass ribbons.During dealloying,the local reaction latent heat-induced glass transition of the precursor ribbons leads to the formation of a solid/liquid interface between the initially dealloyed nanoporous layer and the underlying supercooled liquid layer.Due to the bulging effect of in situ gen-erated H2 on the solid/liquid interface,Cu,Cu3Ag,and CuAg UF-NPFs with thicknesses of～200 nm can self-peel off from the outer surface of the dealloying ribbons.Moreover,it was found that the surface-enhanced Raman scattering(SERS)detection limit of Rhodamine 6G(R6G)on the Cu and CuAg UF-NPF substrates are 10-6 M and 10-11 M,respectively,which are lower than most of the Cu and Cu-Ag sub-strates prepared by other methods.This work presents a reliable simple strategy to synthesize a variety of cost effective and flexible metallic UF-NPFs for functional applications.     

Ordered nanoporous polymer-carbon composites

Nanostructured organic materials, particularly those constructed with uniform nanopores, have been sought for a long time in materials science. There have been many successful reports on the synthesis of nanostructured organic materials using the so-called, 'supramolecular liquid crystal templating' route. Ordered nanoporous polymeric materials can also be synthesized through a polymerization route using colloidal or mesoporous silica templates. The organic pore structures constructed by these approaches, however, are lower in mechanical strength and resistance to chemical treatments than nanoporous inorganic, silica and carbon materials. Moreover, the synthesis of the organic materials is yet of limited success in the variation of pore sizes and structures, whereas a rich variety of hexagonal and cubic structures is available with tunable pore diameters in the case of the inorganic materials. Here we describe a synthesis strategy towards ordered nanoporous organic polymers, using mesoporous carbon as the retaining framework. The polymer-carbon composite nanoporous materials exhibit the same chemical properties of the organic polymers, whereas the stability of the pores against mechanical compression, thermal and chemical treatments is greatly enhanced. The synthesis strategy can be extended to various compositions of hydrophilic and hydrophobic organic polymers, with various pore diameters, connectivity and shapes. The resultant materials exhibiting surface properties of the polymers, as well as the electric conductivity of the carbon framework, could provide new possibilities for advanced applications. Furthermore, the synthesis strategy can be extended to other inorganic supports such as mesoporous silicas.     

Au-Ag alloy nanoporous nanotubes

Metallic nanostructures with hollow interiors or tailored porosity represent a special class of attractive materials with intriguing chemicophysical properties. This paper presents the fabrication of a new type of metallic nanoporous nanotube structure based on a facile and effective combination of nanocrystal growth and surface modification. By controlling the individual steps involved in this process, such as nanowire growth, surface modification, thermal diffusion, and dealloying, one-dimensional (1-D) metallic nanostructures can be prepared with tailored structural features and pre-designed functionalities. These tubular and porous nanostructures show distinct optical properties, such as tunable absorption in the near-infrared region, and enhanced capability for electrochemiluminescence signal amplification, which make them particularly desirable as novel 1-D nanocarriers for biomedical, drug delivery and sensing applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.