Examination of nanoparticles via single large cluster impacts

This study deals with the determination of the relative abundance of the oxide layer in the near-surface volume of aluminum nanoparticles of 50-100 nm in diameter. They are bombarded with a sequence of single projectiles of Au 400(4+) accelerated to 136 keV. The ionized ejecta from each impact are recorded individually which allows identification of ions emitted from a surface volume of approximately 10 nm in diameter and 5-10 nm in depth. The mode of analyzing ejecta individually from each single cluster impact is a means to apply mass spectrometry in nanovolumes.     

多壁碳纳米管电磁参数的研究和吸波性能模拟

系统地研究了不同管径类型的多壁碳纳米管在2～18GHz的电磁参数性能,结果表明多壁碳纳米管没有磁性,而且磁损耗也很小;部分碳管的介电常数实部和虚部随管径的增大而增大,而随频率的增加而减小,20～40nm和40～60nm的CNTs在一定频段范围内介电常数的虚部大于实部,使得其损耗角正切大于1,有利于吸波性能的提高.同时对其吸波性能进行了计算机模拟和分析,结果表明,在2～18GHz范围内,当吸波层厚度设为1mm时,20～40nm的碳管复合物在10dB以上频宽可以达到7GHz,最大损耗峰出现在12.4GHz上,对应值为16.52dB,为实现吸波涂层的"宽、薄、轻"具有一定的理论指导意义.     

Magnetic Domain Studies of Cobalt Nanostructures

The pulsed laser deposition technique associated with a low energy cluster beam is used to deposit cobalt thin films with a thickness 100?C200?nm and cobalt dots of a diameter 100?C200?nm on silicon substrates. The deposited thin films of Co are composed of clusters of a?size 10?C50?nm, with very few large grains as revealed by atomic force microscopy. The observations performed by magnetic force microscopy on as-grown thin films reveal randomly distributed out-of-plane magnetic domain structures. These magnetic domains are aligned linearly by applying an external magnetic field either perpendicular or parallel to the substrate during the deposition. In addition, the effect of film thickness and roughness on multidomains is reported. The increase of roughness resulted in the decrease of magnetic domain width from 200 to 100?nm. This decrease is accompanied by the appearance of instability in the stripe domain pattern. Well separated cobalt dots of diameter in the range of 100?C200?nm are also deposited on silicon substrates, which show arc-like multidomains. The domains seem to be oriented along the long axis of the dots. The domain structure of Co nanodots is similar to that of Co thin films indicating strong magnetic coupling of clusters.     

Optical studies of electrodeposited ZnCuTe ternary nanowire arrays

The optical properties of electrodeposited zinc copper telluride (ZnCuTe) ternary nanowires on ITO substrate using polycarbonate membrane (Whatman) of diameter 200,100 and 50?nm have been studied and reported in this paper. Scanning electron microscopy confirmed the formation of the standing nanowires having uniform diameter equal to the diameter of the template used. UV–vis absorption and photoluminescence (PL) spectroscopy were used for optical studies. The optical band gaps of 200, 100 and 50?nm have been calculated as 3.19, 3.39 and 3.57?eV, respectively using UV–vis spectroscopy. The UV–visible absorption spectrometry reveals the absorption spectra of 200, 100 and 50?nm shows a blue shift. UV–visible absorption depicts that the band gap increases with decrease in the diameter size of the nanowires. Several broad emission lines have been observed over a wide wavelength range (390–690?nm) of visible light spectrum in the PL spectra of ZnCuTe nanowires of diameter 200, 100 and 50?nm. A good emission peak at around 615?nm has been observed in all nanowires.     

Two-point separation in far-field super-resolution fluorescence microscopy based on two-color fluorescence dip spectroscopy, Part I: Experimental evaluation

The two-point resolution of a novel two-color far-field super-resolution fluorescence microscopy was evaluated by measuring fluorescent beads 100 nm in diameter. This microscopy is based on a combination of two-color fluorescence dip spectroscopy and a phase-modulation technique for a laser beam. By simply introducing two-color laser light, the size of the fluorescent image of a bead was shrunk down to a diameter of 250 nm from the diffraction-limited image with a diameter of 360 nm. For two closely adjacent fluorescent beads with a separation distance of 350 nm, the two-color microscope clearly gave separated fluorescence images, while the conventional one-color fluorescence microscope could not resolve them. It has been proved that our technique breaks Rayleigh's diffraction limit.     

Finite element analysis of resonant properties of silicon nanowires with consideration of surface effects

We developed a 3D finite element model taking into account the surface effects which is considered significant in nanostructures and used the model to study the resonant frequencies and Young??s modulus of silicon nanowires on both fixed/fixed and fixed/free boundary conditions with diameters between 50 and 200?nm. We found that Young??s modulus and resonant frequencies significantly decreased with decreasing diameter when the diameter was less than 100?nm for fixed/free boundary condition, while they slightly decreased for fixed/fixed boundary condition. When the diameter is larger than 200?nm, the surface stresses may be neglected.     

Carbon nanofoam formed by laser ablation

Foam-like carbon (carbon nanofoam, CNF) which belongs to the porous carbon family is formed by pulsed laser ablation of graphite in liquid nitrogen. Each bubble is about 3-10 nm in size and has a layered structure with typically one to four graphene layers. The CNF forms nanoparticles of about 100 nm in size. CNF encapsulating platinum nanoparticles (Pt@CNF) is formed when a mixture of graphite, platinum, and hexadecanoic acid is used as a target. Each bubble encapsulating a platinum nanoparticle is approximately 15 +/- 4 nm in diameter and contains typically 6 +/- 3 graphene walls. The platinum nanoparticles in the CNF are 9 +/- 4 nm in diameter. The annealing of the Pt@CNF at 300 degrees C for a week in vacuum reveals that the CNF effectively prevents the platinum nanoparticles from aggregating.     

Synthesis of nanometer-sized hematite single crystals through NAC-FAS method

Nanometer-sized spherical hematite single crystals were prepared by heating the precipitate which was synthesized from Fe(OH)(CH₃COO)₂ and NaOH in alkaline ethanol-water solutions without the deliberate addition of surfactants or adsorbing ligands. Hematite nanocrystals (5–10 nm in diameter) and ferrihydrite (<5 nm) were obtained from the mixture of H₂O/EtOH (Rs) = 100 ml/100 ml as a initial medium, whereas goethite, hematite (20–40 nm), and ferrihydrite were precipitated at Rs = 200/0. Adsorbing ligands such as acetoxy groups and ethanol on particles retarded the hematite growth and goethite formation. TEM observation of the particles prepared at Rs = 100/100 with heat treatment at 400°C for 2 hours showed them consisting of single spherical hematite crystals 22 nm in mean diameter with narrow size distribution. Various individual effects were investigated for their contributions to crystal structure and size of precipitates; they included NaOH to Fe(OH)(CH₃COO)₂ ratio, solvent, dropping rate of alkaline solution, and aging time.     

Formation of calcium phosphate nanoparticles in reverse microemulsions

Nanosized calcium phosphate powder had been synthesized via an inverse microemulsion processing route, which used cyclohexane as the oil phases, octaethylene glycol monododecyl ether (C₁₂EO₈) as surfactant phase, and an aqueous Ca(NO₃)₂ and (NH₄)₂HPO₄ solution as the water phase. A wide variety of morphologies were encountered in synthesis which produced nanosphere (25–40 nm in diameter), sheet-like (3–16 nm in width and 50–300 nm in length), rod-like (10–17 nm in diameter and 24–50 nm in length) and needle-like (4–8 nm in diameter and 80–100 nm in length). The great structural diversity was resulted from the different value of the molar ratio of water to surfactant, W₀. Particles were visualized by transmission electron microscopy (TEM) and the identities of powder confirmed by FT-IR and X-ray diffraction (XRD).     

Third-harmonic generation from single gold nanoparticles

We report the first observation of third-harmonic signals from individual gold colloids down to 40 nm diameter. Excited with 1-ps pulses at 1500 nm, the colloids generate 500-nm light, close to the plasmon resonance. The third-harmonic intensity varies as the square of the colloid surface area. Although weak, the third-harmonic signals of gold labels as small as 15 nm in diameter are expected to be accessible with 100-fs pulses. They could be used in microscopy for single-biomolecule tracking.     

超声波作用下对位芳纶纤维的超微结构

用X射线衍射和扫描电子显微镜（SEM）对超声波处理的对位芳纶纤维的结晶结构和形态结构进行研究,以揭示对位芳纶纤维的超微结构特点。研究表明,对位芳纶纤维具有皮芯层结构和多重原纤结构特征,纤维表层大量原纤沿纤维轴向高度取向,直径约600 nm;纤维内部圆柱状的微原纤平行于纤维轴,直径为30 nm,且微原纤间存在缝隙和孔洞;...     

结合溶胶-凝胶和微波法制备二氧化钛纳米管

以溶胶-凝胶法制备得到的TiO_2纳米粉体为原料,采用微波法制备TiO_2纳米管,用透射电子显微镜和扫描电子显微镜对纳米管和纳米粉体进行表征,结果表明,制得的TiO_2纳米管形貌比较完整,其外径为8-15nm、内径为5-10nm、长50-100nm,同时发现,未经HCl酸洗的TiO_2纳米管在电镜下非常完整,而经过HCl酸洗的TiO_2纳米管则局部遭到破坏。     

Catalytic characteristics of MnO2 nanostructures for the O2 reduction process

Nanorods with an α type MnO(2) structure and a diameter ranging from 25 to 40 nm, along with tipped needles with a β MnO(2) structure and a diameter of 100 nm were obtained. The 25 nm diameter α MnO(2) nanorods showed the best catalytic activity for dissociation of HO(2)(-) formed during oxygen reduction in a KOH solution. The MnO(2) nanostructures preferably followed a two-electron oxygen reduction mechanism in a LiOH solution. The size of the catalyst also affected the specific capacities of the non-aqueous Li/O(2) batteries fabricated using the MnO(2) based air electrode. The highest specific capacity of 1917 mA h g(-1) was obtained for an α MnO(2) nanorod catalyst having a diameter of 25 nm. The cation present in the MnO(2) nanostructures appears to determine the catalytic activity of MnO(2).     

高Co-Ni超高强度钢强化析出相的微观分析

使用透射电子显微镜(TEM)观察了高Co-Ni超高强度钢AetMet100在510℃,5h回火后的强化析出相,并利用选区电子衍射方法(SAD)确定了强化相.结果表明,AetMet100钢在超细板条马氏体基体上同时存在两种不同形态的细小强化析出相且尺寸相当:一种是已为很多试验研究所报道过的棒状M2C碳化物,长轴沿基体〈001〉M三个方向互相垂直分布,长度约17.5nm,直径约6nm,与基体的取向关系为(011)M//(001)M2C,[100]M//[100]M2C;另一种是椭球状Fe2Mo金属间化合物(Laves相),直径约11.5nm,与基体的取向关系为(1-12-)M//(001)L,[11-1-]M//[100]L.     

催化剂对螺旋形碳晶须生长的影响

以Ni粉为催化剂,用化学气相沉积(CVD)法,在高温下催化热解乙炔(C2H2),制备出了螺旋形碳晶须材料。实验结果表明,Ni粉的颗粒尺寸及表面形貌对螺旋形碳晶须的形貌、直径、螺距有较大的影响。用直径为几十微米,表面为熔融状的小颗粒Ni粉作催化剂,制备的碳晶须呈绞绳状的较多,螺旋直径为130-180nm,螺距为100-350nm;用直径为几百纳米、表面为毛刺状的Ni粉作催化剂,则制备的碳晶须呈管状的较多,其螺旋直径为280-310nm,螺距为150-180nm。     

Growth characteristics of GaAs nanowires obtained by selective area metal-organic vapour-phase epitaxy

GaAs nanowires were selectively grown by metal-organic vapour-phase epitaxy within a SiO(2) mask window pattern fabricated on a GaAs(111)B substrate surface. The nanowires were 100-3000?nm in height and 50-300?nm in diameter. The height decreased as the mask window diameter was increased or the growth temperature was increased from 700 to 800?°C. The dependence of the nanowire height on the mask window diameter was compared with a calculation, which indicated that the height was inversely proportional to the mask window diameter. This suggests that the migration of growth species on the nanowire side surface plays a major role. Tetrahedral GaAs grew at an early stage of nanowire growth but became hexagonal as the growth process continued. The calculated change in Gibbs free energy for nucleation growth of the crystals indicated that tetrahedra were energetically more favourable than hexagons. Transmission and scanning electron microscopy analyses of a GaAs nanowire showed that many twins developed along the [Formula: see text] B direction, suggesting that twins had something to do with the evolution of the nanowire shape from tetrahedron to hexagon.     

Optical properties of zigzag twinned geometry of Zn2SnO4 nanowires

High-density single-crystalline Zn2SnO4 nanowires have been successfully synthesized by using a simple thermal evaporation method by heating a mixture of ZnO and SnO2 nano powders. The products in general contain various geometries of wires, with an average diameter of 80-100 nm. These nanowires are ultra-long, up to 100 microns. The transmission electron microscopy study showed that these nanowires exhibited zigzag twinned geometry, and grow along the (111) direction. Low-temperature photoluminescence properties of the nanowires were measured, showing a strong green emission band at about 515 nm and a weak peak corresponding to UV emission at about 378 nm, which have not been reported before.     

The sub-micron hole array in sapphire produced by inductively-coupled plasma reactive ion etching

The sub-micron hole array in a sapphire substrate was fabricated by using nanosphere lithography (NSL) combined with inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. Polystyrene nanospheres of about 600 nm diameter were self-assembled on c-plane sapphire substrates by the spin-coating method. The diameter of polystyrene nanosphere was modified by using oxygen plasma in ICP-RIE system. The size of nanosphere modified by oxygen plasma was varied from 550 to 450 nm with different etching times from 15 to 35 s. The chromium thin film of 100 nm thick was then deposited on the shrunk nanospheres on the substrate by electron-beam evaporation system. The honeycomb type chromium mask can be obtained on the sapphire substrate after the polystyrene nanospheres were removed. The substrate was further etched in two sets of chlorine/Argon and boron trichloride/Argon mixture gases at constant pressure of 50 mTorr in ICP-RIE processes. The 400 nm hole array in diameter can be successfully produced under suitable boron trichloride/Argon gas flow ratio.     

Bidirectional optical sorting of gold nanoparticles

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle's geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.     

超声波辅助扩孔对氧化铝模板结构的影响

在0.3mol/dm3的草酸溶液中,采用二次阳极氧化法制备多孔氧化铝模板,研究了阳极氧化后的扩孔处理对多孔膜形貌和结构的影响.SEM和FE-SEM结果表明,经20min超声波扩孔处理后,多孔氧化铝模板纳米孔的结构更加趋于规则,表观孔径从30nm增大到70nm,其扩孔效果较常规扩孔方法更为明显.超声波扩孔时间增加到40min后,多孔膜孔径扩大至100nm,但某些区域的纳米孔壁已被部分溶解.在一定的电压范围内,随着电压增加,经超声波扩孔后的多孔氧化铝膜孔径增大,有序度有较大提高.