Synthesis and characterization of mesoporous ZnS with narrow size distribution of small pores

Pure, nanocrystalline cubic ZnS forming a stable mesoporous structure was synthesized at room temperature by a non-toxic surfactant-assisted liquid–liquid reaction, in the 9.5–10.5 pH range of values. The appearance of an X-ray diffraction (XRD) peak in the region of very small angles (∼ 2°) reveals the presence of a porous material with a narrow pore size distribution, but with an irregular arrangement of the pores, a so-called worm hole or sponge-like material. The analysis of the wide angle XRD diffractograms shows the building blocks to be ZnS nanocrystals with cubic structure and average diameter of 2 nm. Transmission electron microscopy (TEM) investigations confirm the XRD results; ZnS crystallites of 2.5 nm with cubic (blende) structure are the building blocks of the pore walls with pore sizes from 1.9 to 2.5 nm, and a broader size distribution for samples with smaller pores. Textural measurements (N₂ adsorption–desorption isotherms) confirm the presence of mesoporous ZnS with a narrow range of small pore sizes. The relatively lower surface area of around 100 m²/g is attributed to some remaining organic molecules, which are filling the smallest pores. Their presence, confirmed by IR spectroscopy, seems to be responsible for the high stability of the resulting mesoporous ZnS as well. PACS  61.46.Df; 68.37.Lp; 78.67.-n; 81.05.Ea; 81.07.Bc     

Arrays of Ni nanowires in alumina membranes: magnetic properties and spatial ordering

Magnetic characteristics of arrays of Ni nanowires embedded in porous alumina are reviewed as a function of their spatial ordering. The different steps for the controlled production of highly-ordered nanowires is firstly described. Nanopores are formed into an hexagonal symmetry arrangement by self-organized process during anodization of pure Al. Parameters of the anodization allow us to control their diameter, hexagonal lattice parameter and size of crystalline domains. Subsequently, Ni nanowires are grown inside the pores by electrodeposition. Control of the pores filling and of geometrical ordering characteristics has been performed by SEM, HRSEM, RBS and AFM techniques. The magnetic characterisation of the arrays has been achieved by SQUID and VSM magnetometers, while information on the magnetic state of individual nanowires is obtained by MFM. Experimental studies are presented, particularly coercivity and remanence, for arrays with different degree of ordering (crystalline domains up to around 1 m), and for ratio diameter to lattice parameter (diameter ranging between 20 and 180 nm, and distance between 35 and 500 nm). FMR studies have allows us to obtain complementary information of the anisotropy and magnetic characteristics. A modelling of multipolar interacting nanowires is introduced to account for the influence of short and long range ordering degree of the arrays.Received: 24 November 2003, Published online: 15 June 2004PACS: 75.60.Jk Magnetization reversal mechanisms - 81.15.Pq Electrodeposition, electroplating     

Synthesis of ordered ZnO nanowire arrays from aqueous solution using AAO template

In this paper we report a simple method that enables the easy fabrication of ordered ZnO nanowire arrays using Anodic Aluminium Oxide (AAO) template. We have used a vacuum injection technique to fill solution into the pores of an AAO template. The AAO template has been fabricated by a two-step anodization process using 0.3 M oxalic acid (H₂C₂O₄) solution under a constant voltage of 40 V. The AAO template formed through this process has been detached from Al substrate via an anodic voltage pulse using perchloric acid (HClO₄) solution (70%). The nanowires of ZnO have been synthesized by injecting the saturated Zn(NO₃)₂ solution into the pores of the detached AAO template using a vacuum pump. The ZnO nanowires synthesized by this technique have been found dense & continuous with uniform diameter throughout the length of the wire. The structural characteristics of AAO template and ZnO nanowires have been studied by Field Emission Scanning Electron Microscope (FESEM), Atomic force microscope (AFM) and Transmission Electron Microscope (TEM).     

高质量规则多孔氧化铝模板的制备

在合适的条件下利用阳极氧化高纯铝片，可以获得多孔结构的氧化铝，其孔径大小和排列方式都很均匀.由于孔的深度不受限制，因此可以制备出孔深很大的多孔氧化铝.这种多孔结构可以用作制备纳米材料的模板.利用0.3mol/L的草酸溶液在40V的直流电压下，采用二步氧化法获得了高质量的氧化铝多孔模板，其典型孔径值为40—70nm，孔间距约110nm，深度可达毫米量级.分析了溶液温度对结果的影响，比较了单步法和两步法获得的样品的多孔结构，认为低温下的二步氧化法可以获得很好的多孔氧化铝模板. 关键词： 纳米材料 多孔氧化铝 二步氧化法     

Distributed feedback dye laser holographically induced in improved organic–inorganic photocurable nanocomposites

Distributed feedback (DFB) lasing in permanent volume transmission gratings formed in a laser dye-doped organic–inorganic nanocomposite has been investigated. DFB laser cavities were fabricated using one-step two-beam holographic exposure of Pyrromethene 567 (PM567) doped photopolymerizable acrylate monomers containing inorganic (LaPO₄) nanoparticles. Compared to the formulation previously utilized, the material composition presented provides longer lifetime of the laser. Spectral and polarization properties, input–output and stability characteristics of the laser output have been investigated by varying the material composition and the patterning parameters. DFB lasing emission of the second and the third diffraction orders has been demonstrated. The spectral linewidth of ∼0.08 nm has been observed at a pump energy threshold of about 0.2 μJ/pulse for the second-order DFB lasing when pumped with 532 nm 500 ps laser pulses. Spectral tuning of the lasing output over ∼56 and ∼7 nm was obtained by varying the grating period and the content of inorganic nanoparticles in the polymer matrix, respectively.     

New route to form micro-pores on 316L stainless steel surface

In order to seek an effective way for preventing restenosis after coronary stent implantation, a proposal of increasing the amount of loaded drug without changing the size of struts was given. Thereafter, a process of fabricating in-situ formed sub-micro-pores on 316L stainless steel (316L SS) was demonstrated. An aluminum thin film was deposited by magnetron sputtering on a 316L substrate. The aluminum film was then anodized in different acids (0.3 M oxalic and 10 vol.% sulfuric) by regulating direct current power supply. Through an appropriate chemical dissolution, the anodic alumina film was removed and the underlying porous 316L was obtained. The morphology of the porous 316L surface was examined by scanning electron microscope and the composition of the pores was investigated by energy dispersive X-ray analysis. The corrosion behavior of the porous 316L was evaluated by the polarization measurement. The results indicate that the shape and size of pores could be affected evidently by the acids used in anodization. The pores density is found to change with variation of the applied voltage in anodization. The corrosion current of the anodized specimens decrease and the corrosion voltage increase, compared with the untreated specimens.     

Controllable fabrication of highly ordered thin AAO template on Si substrate for electrodeposition of nanostructures

In this work, simple fabrication of hexagonally highly ordered porous anodic aluminum oxide (AAO) of Al thin film (1 μm) on Si substrate is described using two-step anodization method for electrochemical synthesis of nanostructures. In this method, the templates were prepared under the controllable conditions of the parameters, which give rise to the possibility of highly ordered nanopore arrays with a well aspect ratio. Pore widening was then fulfilled in 5 wt% phosphoric acid solution at 25 °C. The pore diameter and spacing are proportional to the applied voltage, which is due to the mechanical stress associated with the volume expansion of the aluminum during the anodization according to the mechanical stress model. Pore-widening solution adjusted the pore diameter and thinned the AAO barrier layer at room temperature under the control of etching time. As an application, Cu nanorods arrays embedded in anodic alumina (AAO) template were fabricated by dc electrodeposition. The characterization of the AAO templates and the Cu nanorods produced was made by X-ray diffraction, field emission scanning microscope, energy dispersive X-ray spectroscopy and atomic force microscope (AFM). The images of AFM show that porous AAO template under constant voltage is 40 V which presents the optimum ordering.     

Anodization of aluminium thin films on pSi and annihilation of strong luminescence from Al2O3

Photoluminescence (PL) of Al₂O₃ films obtained by anodization of thermally evaporated and annealed thin Al films on p⁺⁺Si in 0.3 M oxalic acid has been investigated. Thermal annealing at 200–950 °C under the dry nitrogen atmosphere was used for deactivation of luminescence centres. Luminescence from as grown films was broad and located at 425 nm. This luminescence reached to highest level after annealing at 600 °C. Maximum 10 min was required for full optical activation and prolonged annealing up to 4 h did not change the luminescence intensity. Because of deep levels, absorption band edge of as grown films was shifted to the lower energy which is 3.25 eV. Annealing above 800 °C reduced the PL intensity and this observation was correlated with the blue shift of band edge as the defects annealed out. Disappearing PL intensity and blue shift of band edge absorption after annealing at 950 °C was mainly attributed to the oxygen-related defects and partly to impurities that may be originated from oxalic acid. AFM results did not show any hexagonally ordered holes but uniformly distributed nanosized Al₂O₃ clusters that were clearly seen. XRD measurements on as grown Al₂O₃ showed only [1 1 0] direction of α phase. Debye–Scherer calculation for this line indicates that cluster size is 35.7 nm. XRD and AFM pictures suggest that nanocrystalline Al₂O₃ are embedded in amorphous Al₂O₃.     

Study of the structure of carbon matrices for radionuclide encapsulation by small-angle neutron scattering

The structure of carbon matrices prepared from diphtalocyanines using pyrolysis to encapsulate metal atoms (Y, Sm, U) inside small pores is studied by small-angle neutron scattering. It is shown that the structure of the porous matrix at a scale of 10⁰–10² nm is characterized by two levels — small pores with the characteristic radii of 3–7 nm aggregated into entities with sizes of 40–100 nm and higher. The scattering data fit the values of the sample density and the total volume of pores in the matrices.     

IR spectroscopy of the acetonitrile molecules in porous glasses

The results of investigation of the IR spectra of optical density under the condition of attenuated total internal reflection of acetonitrile in porous glasses with the pores of different radii are presented. It is established that interaction between the acetonitrile molecules and the porous glass matrix with the pores of small dimensions (1.3–4 nm) significantly effects the spectral characteristics of these molecules.     

Fabrication and characterization of porous silicon layers for applications in optoelectronics

In the present paper, several samples of porous silicon monolayers and multilayers were prepared at different anodization conditions with fixed HF concentration. The room temperature photoluminescence wavelength observed to be increased with increased etching time and current density respectively. By Raman measurement it has been observed that as the size of silicon crystallites decreased with increased etching time, the silicon optical phonon line shifted somewhat to lower frequency from 520.5 cm⁻¹ and became broader asymmetrically. The surface roughness and pyramid like hillocks surface was confirmed by AFM measurement. In SEM images, the porous silicon layers were clearly observed by white and black strips. It was also observed that the reflectivity increased as the number of porous silicon layers was increased.     

Optical description of HfO2/Al/HfO2 multilayer thin film devices

A three-layer system of dielectric/metal/dielectric (D/M/D) has been prepared on Marienfeld commercial glass substrates with Metal = Al, and Dielectric = HfO₂ for energy efficient windows applications. Subsequently, HfO₂/Al/HfO₂ multilayers have been deposited with 10 nm each HfO₂ layer and 5 nm thick Al layer using electron beam evaporation. The microstructural characteristics of D/M/D thin films have been investigated using X-ray diffraction (XRD) and atomic force microscopy (AFM). Present results indicate the formation of HfO₂ weak polycrystals embedded in the disordered lattice. AFM data reveals quite a smooth surface involving a structure of slightly elongated grains with almost Gaussian size distribution with mean grain size in the range from 7 to 23 nm. Regarding optical properties, maximum transmittance of the D/M/D structure is noticed to occur in the UV-region, whereas reflectance rises to ∼60% in the visible to near infrared (NIR)-regions. To optimize the performance of these D/M/D devices, computer calculations have been performed by varying either the thickness of both HfO₂ layers and/or thickness of metallic Al layer. A satisfactory agreement between theoretical and experimental spectra is noticed. Such D/M/D structures can be useful in heat mirror applications involving energy efficient windows etc.     

Luminescence in the 1.54 µm region for erbium in two-dimensional and three-dimensional mesoscopic structures

We have studied the luminescence and luminescence excitation spectra of erbium in the 1.54 μm region in titanium oxide and silicon oxide xerogels, formed in the mesoscopic pores of three-dimensional synthetic opals and two-dimensional porous aluminum oxide structures. For erbium-doped titanium oxide films formed in opal, in contrast to analogous films on porous aluminum oxide, in the luminescence excitation spectra we observe an intense broad band with a maximum in the ∼360 nm region. We discuss the possible nature of this band. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 5, pp. 622–626, September–October, 2007.     

Hydrophobic polymers modification of mesoporous silica with large pore size for drug release

Mesostructure cellular foam (MCF) materials were modified with hydrophobic polyisoprene (PI) through free radical polymerization in the pores network, and the resulting materials (MCF-PI) were investigated as matrices for drug storage. The successful synthesis of PI inside MCF was characterized by Fourier transform infrared (FT-IR), hydrogen nuclear magnetic resonance (¹H NMR), X-ray diffraction patterns (XRD) and nitrogen adsorption/desorption measurements. It was interesting to find the resultant system held a relatively large pore size (19.5 nm) and pore volume (1.02 cm³ g⁻¹), which would benefit for drug storage. Ibuprofen (IBU) and vancomycin were selected as model drugs and loaded onto unmodified MCF and modified MCF (MCF-PI). The adsorption capacities of these model drugs on MCF-PI were observed increase as compared to that of on pure MCF, due to the trap effects induced by polyisoprene chains inside the pores. The delivery system of MCF-PI was found to be more favorable for the adsorption of IBU (31 wt%, IBU/silica), possibly attributing to the hydrophobic interaction between IBU and PI formed on the internal surface of MCF matrix. The release of drug through the porous network was investigated by measuring uptake and release of IBU.     

Nanoporous alumina membrane prepared by nanoindentation and anodic oxidation

The fabrication of nanopatterned surfaces at large scale attracts the interest of research groups from a wide range of areas as biotechnology, nanoelectronics and nanomagnetism. An extended method to pattern the surface in the nanoscale is the fabrication of ordered arrays of nanoelements based on porous templates as Nanoporous Anodic Aluminium Oxide (NAAO). One of the challenges of the NAAO fabrication, based on self-organized methods, is the control of the symmetry and lattice parameter of the ordered nanoporous films. In this work, we present a combined method based on Atomic Force Microscopy (AFM) nanoimprint and anodic oxidation of Al surface. AFM nanoindentations substitute the first anodization process and even more important, allow us to control the symmetry and the lattice parameter of the ordered arrays. In addition, by using AFM nanoimprint method it is possible to select the region were the ordered alumina grows. We demonstrate that square nanoporous arrays of alumina with lattice parameter of 105 nm can be obtained by this method.     

Detection of mercury in water by laser-induced breakdown spectroscopy with sample pre-concentration

A method based on pre-concentration, using electrolysis, has been proposed and used for the improvement of detection sensitivity of mercury ions at ultra-trace level of concentration in an aqueous matrix by laser-induced breakdown spectroscopy (LIBS). The experimental evaluation of this method was carried out on mercury chloride (HgCl₂) in triple-distilled water for a concentration range of the element of 0.01–10 mg l⁻¹. A pre-concentration factor of ∼180 was obtained for LIBS detection of mercury emission line at 253.65 nm. The limit of detection (LoD) of ∼0.011 mg l⁻¹ (or ∼11 ppb) for mercury in the water sample was achieved.     

Self-assembled mesoporous silicon in the crossover between irregular and regular arrangement applicable for Ni filling

Porous silicon (PS) channels fabricated during an electrochemical anodization process in hydrofluoric acid solution, without pre-structuring, normally arrange in an irregular morphology. In this work self-organized quasi-2D regular pore arrangements have been fabricated by accurate mutual control of various process parameters. Self-organized pore formation can be tailored and periodic pore arrangements are possible. A particular parameter to vary the inter-pore spacing is mainly the HF concentration, whereas the pore diameter primarily depends on the current density. The well-separated pores are highly oriented perpendicular to the surface and the pattern of self-organized pores is quadratic like due to the (1 0 0)-crystal orientation of the wafer. The isolated pores show little dendritic growth and their diameter can be tuned between 10 and 100 nm, thus belonging to the meso-porous up to the macro-porous regime. The pore growth occurs in an anisotropic manner which means that the channels grow significantly faster in (1 0 0) direction than in (1 1 1) direction. Into this self-assembled PS template metallic Ni is deposited using an electrochemical deposition step which results in a PS/Ni-nanocomposite with potential for applications as magnetic and magneto-optical devices. The filling process is performed under cathodic conditions and could be refined by pulsed current charging.     

Magnetic behaviour of a magnetite/silicon nanocomposite

Mesoporous silicon is utilized to infiltrate quite monodisperse iron oxide nanoparticles into the pores. This semiconducting matrix exhibits oriented pores, clearly separated from each other, with an average pore diameter of 55 nm. Iron oxide nanoparticles of 8 nm and 5 nm in size which are coated with a surfactant are prepared by high temperature decomposition in the presence of an organic precursor. The achieved nanocomposite consists of dispersed Fe₃O₄-nanoparticles within the pores and offers magnetic properties which are determined by the morphology of the silicon matrix as well as by the distribution of the particles within the individual pores. Thus, the change of regime between a superparamagnetic and a blocked state of the system can be tuned. Furthermore, magnetic anisotropy between the two magnetization directions, normal and parallel to the sample surface, is observed due to the oriented and separated pores of the template which are quasi-regular arranged. This porous silicon/magnetite composite with its adjustable magnetic properties is also of interest for possible applications in biomedicine due to the low toxicity of both materials.     

Photoluminescence properties of the composite of porous alumina and poly (2,5-dibutoxy-1,4 phenylenevinylene)

The spin coating method was used to assemble polymer (Poly (2,5-dibutoxy-1,4-phenylenevinylene)) (DBO-PPV) into the pores of porous alumina which was prepared by anodization. Four peaks in the photoluminescence (PL) spectra of the composite, with contributions from the DBO-PPV and porous alumina, were found. It was also found that the light emitting from the porous alumina could excite the photoluminescence of DBO-PPV. The nanometer effect of the porous alumina can lead to a blue shift of 90 nm of the PL peaks of DBO-PPV.     

Uniform self-organized grating fabricated by single femtosecond laser on dense flint (ZF6) glass

Uniform self-organized grating is fabricated by scanning of a single femtosecond laser on ZF6 glass. The scanning electron microscope and atom force microscope results show that the period and tooth length of the uniform coarse grating are ∼750 nm and ∼20 μm, respectively. The period of the grating is independent of pulse number, neighboring dots intervals, and laser powers, whereas the uniformity of the grating is largely determined by the above three factors.