Encapsulation of fresh silicon nanocrystals in carbon nanotube cavity

An approach for filling the carbon nanotubes (CNTs) with silicon nanocrystals (Si-ncs) during the fragmentation process of silicon micrograins in de-ionized water is presented. An efficient fragmentation of homogenously aqueous dispersed micrograins and filling of the CNTs cavity with Si-ncs is demonstrated by nanosecond pulsed-laser irradiation. Direct laser ablation has a unique surface Si-ncs chemistry in water and following aqueous in-situ CNT cavity stabilization prevents pollution, agglomeration of Si-ncs and can lead to 1D nano-composite material.     

High-quality liquid phase-pulsed laser ablation graphene synthesis by flexible graphite exfoliation

This work reports a one-pot procedure of laser ablation on a graphite target in a liquid medium, based on the variation of different parameters such as target type, laser wavelength, and ablation medium,to obtain high-quality graphene nanosheets. The morphology of derived products was characterized by the field emission scanning electron microscopy(FE-SEM). Then, the morphology and structure of the optimized sample were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD), ultraviolet-visible-near infrared(UV–vis-NIR) spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy(XPS). By controlling the laser ablation parameters, we were able to prepare micrometer-sized few-layer graphene nanosheets with mainly less than ten layers. Such synthesized graphene nanosheets were grown at the surface of a flexible graphite target, indicating many potential applications in fundamental research, electrochemical and as hydrophobic surfaces.     

GaAs/AIGaAs laser arrays with and without proton isolation

Abstract

Two types of GaAs/AIGaAs laser arrays, each consisting of five emitters and suitable for high power operations, have been fabricated and tested. They are easily fabricated, have high yield and deliver high power. The first array structure was fabricated using proton implantation to define the active lasing channels. Damage introduced by proton bombardment provides both electrical and optical confinement for the lasing channels. We have investigated the effect of heat treatment on the performance of these lasers and have found that the heat treated samples had a lower threshold current and higher quantum efficiency. For 400 μm long devices, with uncoated facets, we have measured a threshold current of 200 mA and a peak power of 231 mW/facet. The highest external quantum efficiency is 60%. We have also fabricated laser arrays with a simple, self‐aligned, index guided ridge waveguide structures. We have obtain a pulsed output power of up to 551 mW/facet with a quantum efficiency of 37.4%. The typical threshold current is 370 mA.     

Surface ablation of RbTiOPO4 by femtosecond laser

We report here the results obtained in surface ablation of RbTiOPO₄ single crystals by femtosecond laser. We fabricated and characterized one-dimensional (1D) diffraction gratings with different lattice spacings of 15 and 20 μm, and with a sub-modulation of the period introduced in the later. The optical and electronic microscopy characterization and filling factor analysis of these diffraction gratings are reported. We also show that the roughness generated on the grooves by the ablation process can be improved by chemical etching.     

Optimisation of the epi-ready semi-insulating GaAs wafer preparation procedure

The surface quality is crucial for growth of epitaxial layers on III-V semiconductor substrates. In this work the procedures of epi-ready semi-insulating (SI) GaAs wafer preparation were developed. The atomic force microscopy (AFM), triple crystal X-ray diffraction (TCD) and X-ray photoelectron spectroscopy (XPS) were used to monitor morphology and composition of substrates with different chemical treatment history. We propose an optimised epi-ready SI GaAs wafer preparation procedure involving NH₄OH:H₂O₂:H₂O/NaOCl:H₂O₂:H₂O etching/polishing.     

飞秒激光烧蚀制备纳米结构IT0薄膜

利用飞秒激光烧蚀ITO与ZnO双层薄膜的方法,制备具有大面积表面纳米结构的ITO薄膜.在激光频率lkHz、脉冲宽度130fs、波长775nm、能量20μJ时,在ITO薄膜表面,获得了大面积的周期为176nm左右的周期性平行条纹结构.通过改变激光能量,研究了大面积纳米结构与激光能量之间的关系,发现这种大面积纳米结构是在激...     

Fabrication of Ta nanoparticles induced by nanosecond laser ablation in ethanol: the study of laser fluence effects

Tantalum nanoparticles (Ta NPs) were synthesized in ethanol solution by ablation with a 1064 nm Nd:YAG laser. Prepared NPs were investigated by UV-visible absorption spectroscopy, Transmission electron microscopy, X-ray diffraction and Photoluminescence measurement. The average sizes of NPs were calculated to be in the range of 12–18 nm. From the UV-visible studies, the plasmon peak position of Ta NPs was observed in the spectral range of 206–208 nm. The XRD spectra clearly showed the crystalline structure of NPs and various peaks of Ta and Ta₂O₅. Moreover, the UV region in the PL spectrum included the free exciton and the bound exciton emission correlated with the defect concentration. In fact, the laser ablation in the organic and inorganic solvents is a strong technique to obtain some NPs with particular structures, which are impossible to produce by conventional methods.     

Porous nanostructured ZnO films deposited by picosecond laser ablation

Porous nanostructured polycrystalline ZnO films, free of large particulates, were deposited by picosecond laser ablation. Using a Zn target, zinc oxide films were deposited on indium tin oxide (ITO) substrates using a picosecond Nd:YVO₄ laser (8 ps, 50 kHz, 532 nm, 0.17 J/cm²) in an oxygen atmosphere at room temperature (RT). The morpho-structural characteristics of ZnO films deposited at different oxygen pressures (150–900 mTorr) and gas flow rates (0.25 and 10 sccm) were studied. The post-deposition influence of annealing (250–550 °C) in oxygen on the film characteristics was also investigated. At RT, a mixture of Zn and ZnO formed. At substrate temperatures above 350 °C, the films were completely oxidized, containing a ZnO wurtzite phase with crystallite sizes of 12.2–40.1 nm. At pressures of up to 450 mTorr, the porous films consisted of well-distinguished primary nanoparticles with average sizes of 45–58 nm, while at higher pressures, larger clusters (3.1–14.7 μm) were dominant, leading to thicker films; higher flow rates favored clustering.     

Luminescence hydrogenated nanoamorphous Si films fabricated by reactive pulsed laser ablation

Hydrogenated nanoamorphous Si (na-Si:H) films have been fabricated by reactive pulsed laser ablation technique with hydrogen as reactive gas. It is found that the hydrogen pressure has a great effect on both the structure and photoluminescence (PL) properties of the films. Increasing the hydrogen pressure leads to a structural transition of the films from amphorous Si to na-Si:H, and the PL center wavelength of the na-Si:H films is varied with the hydrogen pressure. The PL decay times of the na-Si:H films are in the nanosecond scale and are shorter on the high energy side of their PL spectrum. The results demonstrate that the na-Si:H films are promising candidates for visible, tunable and high-performance light-emitting devices.     

飞秒激光烧蚀Ag膜的研究

研究飞秒激光烧蚀Ag膜表面,采用扫描电镜(SEM)观测其表面烧蚀形貌,发现烧蚀点大致分为3个区域,烧蚀面积随着脉冲能量的增大而增大,脉冲数的增加而增大,但当脉冲数达到一定值后烧蚀面积变化不大.改变脉冲数在烧蚀点得到了周期为650和150nm的长短周期条纹结构.根据烧蚀区域面积与脉冲能量的关系算出单脉冲与多脉冲的烧蚀阈值...     

Structural evolution of PZTN thin films produced by pulsed laser ablation deposition

The study of highly oriented Nb-doped PZT thin films deposited by laser ablation on n-type (111) Si substrates is reported. Sintered ceramics based on the nominal composition Pb_0.995(Zr_0.65Ti_0.35)_0.99Nb_0.01O₃ (PZTN) with an excess of PbO were used as targets. The films were deposited using the 3rd harmonic (355 nm) of a pulsed Nd:YAG laser (7 ns pulse duration) with 7 J/cm² fluence, at different oxygen pressures (from 10⁻¹ to 10⁻⁴ mbar) and at a vacuum of 10⁻⁶ mbar. The substrate temperature was varied in the range of 500-600 °C. In optimized conditions, the as-deposited PZT-based films show perovskite structure oriented along the (110) direction with minor impurities (PbO), as revealed from X-ray diffraction spectra. Further, microstructural analysis of the as-grown including chemical composition is also presented. The relationship between composition of the target, deposition conditions and film properties are then discussed.     

Room-temperature deposition of carbon nanomaterials by excimer laser ablation

Numerous investigators have reported on pulsed laser deposition of carbon nanotubes, mostly using the Nd:YAG laser for ablation. In all cases the depositions have been conducted at high-temperatures and high pressures. Here we report on the deposition of carbon nanostructures at room temperature using a 248 nm excimer laser nm to ablate mixed graphite-nickel/cobalt targets. We find that the formation of the carbon nanomaterials is dependent on the particular ambient gas employed. In O₂ gas, carbon nanotubes and nano-onions are produced. The nanotubes have notably large channel diameters of 100-200 nm and the nano-onion structures are 100-200 nm in diameter, also much larger than previously observed. High-resolution, in-situ, time-resolved emission spectroscopy has been used to follow the production of molecular carbon species such as C₂ and C₃, as well as metals such as Ni or Co in the different ambients employed. Spectral modeling reveals significant differences in the vibrational-rotational temperatures of C₂ spectra in O₂ versus Ar. Mechanistic details of the formation of carbon nanotubes and nano-onions, and in-situ optical emission spectroscopy are described.     

ZnO(101) films by pulsed reactive crossed-beam laser ablation

We have employed pulsed reactive crossed-beam laser ablation (PRCLA) to deposit a (101) oriented ZnO film. In this method, a supersonic jet of oxygen pulse is made to cross the laser plume from a zinc metal target while being carried to the Si(111) substrate. The obtained deposit was nanocrystalline ZnO as confirmed by a host of characterization techniques. When the substrate was held at varying temperatures, from room temperature to 900°C, the crystallinity of the obtained films increased as expected, but importantly, the crystallographic orientation of the films was varied. High substrate temperatures produced the usual (001) oriented films, while lower substrate temperatures gave rise to increasingly (101) oriented films. The substrate held at room temperature contained only the (101) orientation. The film morphology also varied with the substrate temperature, from being nanoparticulate to rod-like deposits for higher deposition temperatures. Surprisingly, the (101) orientation showed reactivity with acetone forming carbonaceous nanostructures on the surface.     

Microstructure and optical characterization of nanometric silicon films prepared by pulsed laser ablation

The effect of laser energy density, during pulsed laser ablation, on the microstructure and optical properties of silicon films has been investigated using techniques such as atomic force microscopy, scanning electron microscopy, X-ray diffraction, and UV–visible absorption/transmission spectroscopy. The thickness of prepared films increases with increase in laser energy density. The crystallite size and hence the crystallinity of prepared films have been estimated by X-ray diffraction and found to be dependent on laser energy density. The transmittance of films changes with laser energy density. The absorption coefficient of films has been found to be?>10⁴?cm^?1 in wavelength region 450–1100?nm. The band gap of silicon films has been determined as 2.27, 2.11, and 1.90?eV corresponding to laser energy density of 1.5, 2.5, and 3.5?J?cm^?2, respectively.     

Laser power effect on morphology and photoluminescence of ZnO nanostructures by laser ablation in water

The morphology and photoluminescence of ZnO nanostructures formed by laser ablation in water were found to be susceptible to the applied laser power. The products varied from nanoflakes to nanoparticles, then to short nanorods with the increase of laser power. Correspondingly, the relative intensity of violet emission decreased and that of green emission increased. The morphology formation mechanism and defect relaxation were analyzed from a view of laser power effect on the induced plasma states, which includes plasma intensity, lifetime, distribution, and thus on defect type. These results would be of great importance for understanding the growth dynamics of nanomaterials under extreme conditions.     

Cathodoluminescence property of ZnO nano-phosphors fabricated by pulsed Nd:YAG laser ablation in plasma circumstance

Cathodoluminescence (CL) with energy-controlled electron beams was used to study the inner structure of ZnO nano-phosphors fabricated by YAG laser ablation under oxygen gas and oxygen plasma circumstances. Varying accelerating voltages of electron beams from 1.0 to 3.0 kV, it was clearly seen that the CL spectrum in the case of ZnO nano-phosphors fabricated under the oxygen gas background changed from a broad one centered at approximately 500 nm to a narrow one peaked at 380∼400 nm. This result indicates that there is an oxygen vacancy-rich shell in the surface area and a fine crystalline ZnO structure in the inner core region. Under the oxygen plasma circumstance at 500 Pa, however, we found that there is a crystalline structure in the surface layer of ZnO nano-phosphors due to the sufficient supply of oxygen ions and atoms and suppression of the formation of oxygen vacancy.     

Optical measurement in carbon nanotubes formation by pulsed laser ablation

Carbon nanotubes (CNTs) were produced by laser ablation of a graphite composite target in argon and nitrogen ambient gas. To investigate the effect of nitrogen gas on CNTs formation, the plasma plume was examined using optical emission spectroscopy. The vibrational temperature of C₂ molecules was estimated by fitting of a Swan band spectrum. The temperature in N₂ ambient gas is lower than that in Ar ambient gas. In a nitrogen atmosphere, the spectrum intensity of C₂ Swan band was enhanced and CN violet system was also observed. Soot collected in the reaction tube was observed using FE-SEM and TEM. The soot deposited in the nitrogen gas contained more bundled CNTs than those in Ar ambience.     

CO sensing devices based on indium oxide nanoparticles prepared by laser ablation in water

A simple and effective solution route for synthesizing colloidal indium oxide (In₂O₃) nanocrystallites, i.e. laser ablation in liquid (LAL), is reported. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). The results showed the formation of In₂O₃ nanoparticles with a bimodal distribution, consisting mainly of particles of small diameters (2-5 nm). Sensor devices prepared by spraying directly the LAL colloidal solutions on interdigitated alumina substrates exhibited good sensing properties for the detection of CO at very low concentrations.     

Random lasing in a dye-doped polymer thin film waveguide deposited on a Si surface microstructured by femtosecond laser ablation

Random laser action with ~8 nm of bandwidth from a special waveguide structure is reported. The waveguide structure is composed of a layer of rhodamine 6G-doped PMMA film and a silicon substrate with a microstructured surface induced by a femtosecond laser. The silicon substrate featured two-dimensional island-like microstructures with average sizes ranging from 0.8 μm to 3 μm and average heights at about 0.7 μm. A red-shift of laser peak positions and decrease of threshold were observed with decreasing size of silicon surface microstructures. The spectra at different probe directions were also measured, and the results reveal that the waveguide laser action is strongly confined within ±10° from the direction of the edge. The lasing modes emitted from the edge of the waveguide are found to be mainly transverse electric-polarized. Our experiments demonstrate a promising method to achieve waveguide random lasers.     

A finite element model to predict the ablation depth in pulsed laser ablation

This work presents development of a two-dimensional finite element model to predict temperature distribution and ablation depth in a laser ablation process. The model considers a number of aspects of the process, which hitherto have been considered independently in the literature. The aspects considered include: temperature dependent material properties of the target material, effect of plasma shielding on the incident laser flux, and temperature dependent absorptivity and absorption coefficient of the target. It was evident that these considerations have resulted in a significant improvement in the ability of the model to predict the ablation depth. Finally, the predicted ablation depth was found to match extremely well with experimental results at lower laser fluences, though at higher fluences there is a marginal overestimation.