Optical evidence for reactive processes when embedding Cu nanoparticles in Al(2)O(3) by pulsed laser deposition

The optical response of nanocomposite thin films formed by Cu nanoparticles (NPs) embedded in amorphous aluminium oxide (Al(2)O(3)) prepared by pulsed laser deposition (PLD) in vacuum is studied in order to investigate the possible existence of reactive processes on the Cu NPs during their covering with Al(2)O(3). The study is performed as a function of the laser fluence on the Al(2)O(3) target (0.6-4.6?J?cm(-2)), while the laser fluence for Cu ablation is kept constant (1.8?J?cm(-2)). The structural analysis of the films shows that they are formed by a high density of NPs with average dimensions in the 4.9-5.9?nm range. The optical response of the films has been followed in situ by real-time reflectivity measurements at 633?nm and after deposition by transmission measurements as a function of wavelength around the surface plasmon resonance (SPR). For low laser fluences on the Al(2)O(3) target, the absorption spectrum is dominated by a well-defined SPR absorption band at 1.9?eV. As the laser fluence is increased, the intensity of the absorption band associated with the SPR decreases and shifts to 2.1?eV. The films deposited at low fluences contain metallic Cu NPs and, as the laser fluence increases sputtering of Cu from the NPs and mixing of the species from the Al(2)O(3) deposition with the Cu from the NPs surface takes place. The latter process leads to the formation of an Al-Cu oxide cover on the Cu NPs. The present results provide evidence for mixing of species from the host and Cu at the surface of the NPs, and it is shown how the degree of mixing depends on the laser fluence used to ablate the Al(2)O(3) host target.     

On the mechanism of encapsulated particle formation during pulsed laser deposition of WSe x thin-film coatings

We have studied factors influencing the formation of particles with the structure of a spherical metal W core inside a WSe₂ shell during pulsed laser deposition (PLD) of thin films of tungsten diselenide under variable conditions (buffer gas (Ar) pressure, substrate temperature). It is established that the metal core is formed at the stage of laser ablation of a synthesized WSe₂ target, while the shell grows as a result of condensation, migration, and redistribution of atoms during deposition of a laser-initiated atomic flow on the surface of a growing film. Retardation of the atomic flow by a buffer gas at pressures within 2–10 Pa does not ensure activation of the shell condensation process on the metal core in the gas phase. Increasing the substrate temperature from room temperature up to 250°C leads to transformation of the shell structure from amorphous into laminar.     

Mobile iron nanoparticle and its role in the formation of SiO2 nanotrench via carbon nanotube-guided carbothermal reduction

The detailed role of iron nanoparticles (NPs) involved with the formation of SiO2 nanotrenches is revealed. The physical movements of iron NPs, such as levitation and adsorption, turn out to be responsible for the initiation of carbothermal reduction (C (carbon nanotube, s) + SiO2(s) <--> SiO(g) + CO(g)), which results in SiO2 nanotrenches that are fully guided by carbon nanotubes. Under the chemical vapor deposition condition with 0.1% of O2 gas, iron NPs are liberally levitated from SiO2/Si substrate then adsorbed on the sidewalls of carbon nanotubes. Depending on the numbers of iron NPs attached to carbon nanotubes, two different types of nanotrenches are determined. When multiple iron NPs are assembled on carbon nanotubes and involved in carbothermal reduction, aligned nanohole type of nanotrenches is produced (Type I). On the contrary, when single iron NPs initiate the carbothermal reduction, nanotrenches having smooth pathways and high shoulders are commonly formed (Type II).     

Effect of ZnO film deposition methods on the photovoltaic properties of ZnO–Cu2O heterojunction devices

The effect of ZnO film depositions using various film deposition methods such as magnetron sputtering (MSP), pulsed laser deposition (PLD) and vacuum arc plasma evaporation (VAPE) on the photovoltaic properties of ZnO–Cu₂O heterojunction solar cells is described in this report. In addition, the relationship between the resulting photovoltaic properties and the film deposition conditions such as supply power and substrate arrangement was investigated in Al-doped ZnO (AZO)–Cu₂O heterojunction devices fabricated using AZO thin films prepared by d.c. magnetron sputtering (d.c.MSP) or r.f. magnetron sputtering (r.f.MSP). The results showed that the measured photovoltaic properties of devices fabricated with films deposited on substrates oriented perpendicular to the target were better than those of devices fabricated with films deposited on substrates oriented parallel to the target. It was also found that ZnO film depositions under conditions where a relatively weaker oxidizing atmosphere was used yield better properties than films derived from MSP, which utilizes a high-density and high-energy plasma. Using VAPE and PLD, for example, high efficiencies of 1.52 and 1.42%, respectively, were obtained under AM2 solar illumination in devices fabricated at a substrate temperature around 200 °C.     

以Al2O3为过渡层脉冲激光法制备PZT铁电薄膜

为实现PZT铁电薄膜与半导体衬底的直接集成引入Al2O3为过渡层，首先用真空电子束蒸发法在Si(100)，多昌金刚石（111）衬底上生长约20nm厚的Al2O3过渡层，接着在上述衬底上采用脉冲激光淀积（PLD）法淀积PZT薄膜，衬底温度为350-550℃。X光电子能谱（XPS）测试表明，在高真空下，电子束蒸发Al2O3固态源能获得化学配比接近蒸发源的Al2O3薄膜。X射线衍射（XRD）测试说明，不论衬底是硅还是多晶金刚石，当衬底温度为550℃时，PZT在Al2O3过渡层上呈现（222）取向的焦绿石相结构，当衬底是金刚石时，通过如下工艺：（1）较低温度（350℃）淀积；（2）空气氛围650℃快速退火5min，可以在Al2O3过渡层上获得高度（101）取向的钙钛矿结构的铁电相PZT薄膜，最后AFM测试显示，在硅衬底上，PZT薄膜的表面均方根粗糙度为9.78nm；而在多晶金刚石衬底上，PZT薄膜的表面均方根粗糙度为17.2nm。     

Non-chemical approach toward 2D self-assemblies of Ag nanoparticles via cold plasma treatment of substrates

The nano-modification of selected substrates by means of atmospheric cold plasma treatment was exploited for the two-dimensional (2D) self-assembling of silver nanoparticles (Ag NPs). Such a useful combination of the cold plasma treatment of substrate surface and an immediate easy deposition of Ag NPs creating the 2D self-assemblies on the substrates is published for the first time, to the best of our knowledge. Except for the cold plasma treatment, mainly the following parameters influenced the resulting NP assemblies: the choice of solvent mixture, concentration of Ag NP dispersions, and the deposition technique. The 2D self-assemblies of Ag NPs, providing the same work function as a Ag electrode, were formed on the cold plasma-treated substrates when a drop-casting technique was employed. The possibility of an easy preparation of the Ag NP 2D self-assemblies on substrates without using any chemical agents and/or evaporating chamber could be exploited, e.g.?in photovoltaic and light-emitting diode devices.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

Study of electrical and micro-structural properties of high-κ gate dielectric stacks deposited using pulse laser deposition for MOS capacitor applications

The electrical properties of hafnium oxide (HfO₂) gate dielectric as a metal–oxide–semiconductor (MOS) capacitor structure deposited using pulse laser deposition (PLD) technique at optimum substrate temperatures in an oxygen ambient gas are investigated. The film thickness and microstructure are examined using ellipsometer and atomic force microscope (AFM), respectively to see the effect of substrate temperatures on the device properties. The electrical J–V, C–V characteristics of the dielectric films are investigated employing Al–HfO₂–Si MOS capacitor structure. The important parameters like leakage current density, flat-band voltage (V_fb) and oxide-charge density (Q_ox) for MOS capacitors are extracted and investigated for optimum substrate temperature. Further, electrical studies of these MOS capacitors have been carried out by incorporating La₂O₃ into HfO₂ to fabricate HfO₂/La₂O₃ dielectric stacks at an optimized substrate temperature of 800 °C using a PLD deposition technique under oxygen ambient. These Al–HfO₂–La₂O₃–Si dielectric stacks MOS capacitor structure are found to possess better electrical properties than that of HfO₂ based MOS capacitors using the PLD deposition technique.     

Ozone-enhanced molecular beam deposition of nickel oxide (NiO) for sensor applications

For the deposition of nickel oxide (NiO) a molecular beam deposition process in an ozone atmosphere was developed. Pure gaseous ozone is received from a cooling system, which stores only O₃ at −78°C from a O₂/O₃ gas mixture stream, created with an ozone generator. The ozone is released by heating up the system to room temperature. For the deposition process nickel is evaporated while a constant ozone partial pressure is adjusted in the growth chamber. The reactive species of ozone reacts on the substrate surface with the impinging metal atoms to form the compound. This process was carried out in an ultra high vacuum (UHV) chamber to create pure nickel oxide films at room temperature and to study the fundamental layer properties for sensor applications. These films were characterized with respect to their stoichiometric and optical properties by Auger Electron spectroscopy and ellipsometry. The gas sensitivity of the films (as deposited and annealed) on various gases (H₂, NH₃, NO₂, SO₂, CO) was investigated by work function measurements.     

Synthesis of large area, homogeneous, single layer graphene films by annealing amorphous carbon on Co and Ni

The synthesis of large area, homogenous, single layer graphene on cobalt (Co) and nickel (Ni) is reported. The process involves vacuum annealing of sputtered amorphous carbon (a-C) deposited on Co/sapphire or Ni/sapphire substrates. The improved crystallinity of the metal film, assisted by the sapphire substrate, proves to be the key to the quality of as-grown graphene film. The crystallinity of the Co and Ni metal films was improved by sputtering the metal at elevated temperature as was verified by X-ray diffraction (XRD). After sputtering of a-C and annealing, large area, single layer graphene that occupies almost the entire area of the substrate was produced. With this method, 100 mm²-area single layer graphene can be synthesized and is limited only by the substrate and vacuum chamber size. The homogeneity of the graphene film is not dependent on the cooling rate, in contrast to syntheses using polycrystalline metal films and conventional chemical vapor deposition (CVD) growth. Our facile method of producing single layer graphene on Co and Ni metal films should lead to large scale graphene-based applications.     

Direct fabrication of metavanadate phosphor films on organic substrates for white-light-emitting devices

White-light-emitting materials have attracted considerable attention because of their applications, such as large-surface emitting devices. Inorganic phosphor films are expected to be applied to these devices because of good chemical stability; however, a substantial reduction of fabrication temperature is required for future industrial uses such as lighting materials fabricated onto flexible organic substrates. Here we show the optical properties of white-light-emitting metavanadate phosphors, AVO3 (A: K, Rb and Cs), and we report a new direct fabrication process for RbVO3 films onto flexible polyethylene terephthalate (PET) substrates by means of a vacuum ultraviolet irradiation using an excimer lamp. In addition, the (Ca,Sr,Pr)TiO3/a-Al2O3/RbVO3/PET heterostructure prepared by an excimer-laser-assisted metal-organic deposition process has demonstrated the possibility of colour modification for RbVO3 films on PET. Our findings suggest new possibilities for further development of large-surface emitting lighting devices.     

Combined vacuum plasma surface treatment for increase of durability of face milling cutters from high‐speed steel

The article deals with the influence of the vacuum plasma surface treatment on the life of the face milling cutter of high‐speed steel R6M5 (analog M2 (USA, AISI/ASTM)). Such processing combines ion nitriding in gas plasma and the deposition of the wear‐resistant TiAlN layer in the metal gas plasma of the vacuum‐arc discharge. Research verifies that the use of vacuum plasma treatment combining the formation of the transition nitrided layer in the gas plasma and the subsequent deposition of TiAlN coating in metal gas plasma created by a vacuum‐arc discharge is an effective way to improve the tool life of high‐speed steel face milling cutters.     

Fabrication of ZnO nanorods using metal nanoparticles as growth nuclei

ZnO nanorods were produced by pulsed laser deposition (PLD). Drops of nanoparticle colloid (gold or silver) were placed on silica substrates to form growth nuclei. All nanoparticles were monocrystalline, with well-defined crystal surfaces and a negative electrical charge. The ZnO nanorods were produced in an off-axis PLD configuration at oxygen pressure of 5 Pa. The growth of the nanorods started from the nanoparticles in different directions, as one nanoparticle could become a nucleus for more than one nanorod. The low substrate temperature used indicates the absence of a catalyst during the growth of the nanorods. The diameters of the fabricated 1-D ZnO nanostructures were in the range of 50-120 nm and their length was determined by the deposition time.     

Co-P-B catalyst thin films prepared by electroless and pulsed laser deposition for hydrogen generation by hydrolysis of alkaline sodium borohydride: A comparison

Co-P-B catalyst thin films have been synthesized on Ni-foam and glass substrate by using electroless deposition (ED) and pulsed laser deposition (PLD) respectively. The efficiency of these catalyst films was tested by catalytic hydrolysis of NaBH₄ for H₂ generation. While the chemically produced Co-P-B film on Ni-foam shows similar activity as that of their corresponding powder, the Co-P-B film deposited by PLD exhibits much superior H₂ generation rate as compared to Co-P-B powder. We attribute this increased efficiency to the special features of the Co-P-B films which are in the form of nanoparticle-assembled films, a peculiar characteristic of PLD films for appropriate choice of the pulse laser parameters. The surface nanoparticle-configuration increases the active surface area and also favors electronic exchange mechanisms to promote hydrolysis process for H₂ gas generation. The films deposited by using laser energy density of 3 J/cm² show the highest activity in connection to the best configuration of the ablated nanoparticles. Different numbers of Co-P-B layers were deposited on Ni-foam by ED and it was found that at least four layers are required for complete coverage of the foam to have the best activity.     

Nanostructured Ag(4)O(4) films with enhanced antibacterial activity

Ag(4)O(4) (i.e.?silver(I)-silver(III) oxide) thin films with tailored structure and morphology at the nanoscale have been grown by reactive pulsed laser deposition (PLD) in an oxygen-containing atmosphere and they are shown to exhibit a very strong antibacterial activity towards Gram-negative bacteria (E. coli) and to completely inhibit the growth of Gram-positive bacteria (S. aureus). The formation of this particular high-valence silver oxide is explained in terms of the reactions occurring during the expansion of the ablated species in the reactive atmosphere, leading to the formation of low-stability Ag-O dimers and atomic oxygen, providing reactive species at the substrate where the film grows. PLD is shown to allow control of the structure (i.e.?crystallinity and grain size) and of the morphology of the films, from compact and columnar to foam-like, thus allowing the deposition of nanocrystalline films with increased porosity and surface area. The antibacterial action towards E. coli is demonstrated and is shown to be superior to that of nanostructured Ag-based medical products. This can be related to the release of Ag ions with high oxidation number, which are known to be very reactive towards bacteria, and to the peculiar morphology at the nanoscale resulting in a large effective surface area.     

氧离子束辅助激光淀积生长ZnO/Si的XPS探究

为了探究ZnO/Si内部化学成分及有关信息,用氧离子束辅助(O+-assisted)脉冲激光淀积(PLD)法在不同实验条件下生长成ZnO/Si(111)样品.利用X射线光电子能谱(XPS)对长成的ZnO/Si异质结构进行了异位测试.通过对O1s峰及其肩状结构进行拟合、分析,得到了原子数密度比n(O)∶n(Zn),进而探究了原子数密度比与生长质量的关系.结果表明,用氧离子束辅助PLD法,可在较低的衬底温度190℃和适当O+束流条件下,生长出正化学比接近于1,且c轴单一取向最佳的ZnO/Si薄膜.用氧离子束辅助PLD淀积法生长ZnO薄膜,可以改善缺氧状况,能提供一个富氧环境.     

Industrially-styled room-temperature pulsed laser deposition of titanium-based coatings

Titanium-based compounds are widely used as coating materials for mechanical, tribological, electrical, optical, catalytic, sensoric, micro-electronical applications due to their exceptionally physical and chemical properties. Recently, the trend of using temperature-sensitive materials like polymers and tool steels with the highest hardness demands new low-temperature coating techniques for protective surface finishing as well as for surface functionalization, but up to now there is lack of industrially scaled vacuum coating techniques at temperatures below 50 °C. An alternative for overcoming this problem is the pulsed laser deposition (PLD) technique, which was up-scaled for industrial demands at Laser Center Leoben of JOANNEUM RESEARCH Forschungsgesellschaft mbH.The current paper summarizes the application of the industrially-scaled PLD technique on the deposition of the presently most important Ti-based coatings: metallic titanium, titanium nitride (TiN), titanium oxide (TiO₂) and titanium carbonitride (TiCN). PLD coating allows, even at room temperature, the formation of film structures of Zone-T type of Thornton's structure zone model, both on substrates aligned normal and parallel to the incident vapor flux. The high-energetic deposition conditions are revealed by the occurrence of (2 2 0) textures for the fcc TiN-based films. The dense grown structure affects advantageously the tribological behavior—generally, low wear rates and (for TiCN) very low friction coefficients were found. For TiO₂ coatings, growing as a mixture of β-TiO₂ and amorphous phases, the easily reproducible change of deposition parameters in the room-temperature PLD allows large differences in the optical transmission and electrical resistance.     

Co-Cr perpendicular magnetic recording tape by vacuum deposition

The relation between the incident angle and the crystallographic orientation of a vacuum deposited Co-Cr film is discussed. Also presented are the magnetic properties and the orientation of both a Ni-Fe underlayer and the Co-Cr film for the double layer medium, and the experimental results about the composition distribution in the co-cr film. The films were deposited on a transporting polymer substrate by continuous vacuum deposition. It is found that the orientation of the Co-Cr film is determined only by the incident angle at the initial point of the film formation, and that deposition efficiency more than 50% can be achieved easily. A double layer medium with Ti film under the Ni-Fe film (Co-Cr/Ni-Fe/Ti medium), which is suitable for perpendicular magnetic recording, is produced by vacuum deposition. Auger depth profile in radial direction of the column of the Co-Cr film shows directly that there is Cr segregation near the columnar grain boundaries.     

Study of adhesion of carbon nitride thin films on medical alloy substrates

The adhesion improvement of biocompatible thin films on medical metal alloy substrates commonly used for joint replacement implants is studied. Diamond-like carbon (DLC) and carbon nitride (CN) thin films are, because of their unique properties such as high hardness, wear resistance and low friction coefficient, candidates for coating of medical implants. However, poor adhesion on substrates with high thermal expansion coefficient limits their application. We deposited CN films by pulsed DC discharge vacuum sputtering of graphite target on CoCrMo and Ti6Al4V substrates. Surface nitridation of the substrate, changing the deposition parameters and use of interlayer led to improved adhesion properties of the films. Argon and nitrogen gas flow, thickness of the film and frequency of the deposition pulses had significant influence on the adhesion to the substrate. Properties of deposited films were analyzed using Scanning Electron Microscopy, Raman spectroscopy and tribology tests.     

Atomic layer deposition of Al(2)O(3) and ZnO at atmospheric pressure in a flow tube reactor

Improving nanoscale thin film deposition techniques such as atomic layer deposition (ALD) to permit operation at ambient pressure is important for high-throughput roll-to-roll processing of emerging flexible substrates, including polymer sheets and textiles. We present and investigate a novel reactor design for inorganic materials growth by ALD at atmospheric pressure. The reactor uses a custom "pressure boost" approach for delivery of low vapor pressure ALD precursors that controls precursor dose independent of reactor pressure. Analysis of continuum gas flow in the reactor shows key relations among reactor pressure, inert gas flow rate, and species diffusion that define conditions needed to efficiently remove product and adsorbed reactive species from the substrate surface during the inert gas purge cycle. Experimental results, including in situ quartz crystal microbalance (QCM) characterization and film thickness measurements for deposition of ZnO and Al(2)O(3) are presented and analyzed as a function of pressure and gas flow rates at 100 °C. At atmospheric pressure and high gas flow, ZnO deposition can proceed at the same mass uptake and growth rate as observed during more typical low pressure ALD. However, under the same high pressure and flow conditions the mass uptake and growth rate for Al(2)O(3) is a factor of ～1.5-2 larger than at low pressure. Under these conditions, Al(2)O(3) growth at atmospheric pressure in a "flow-through" geometry on complex high surface area textile materials is sufficiently uniform to yield functional uniform coatings.