Surface modification using lasers and ion beams

Abstract

The influences of ion beam and laser treatment on the thermal oxidation and sulphidation of metallic materials and their particular features, advantages, and disadvantages are separately described and compared with conventional alloy addition. Examples of the various mechanisms involved and the associated problems are also presented. The ion beam technique considerably improves high temperature resistance, despite the shallow depths involved and ion beam deposited coatings are already in commercial production. Laser beams produce thicker coatings and have considerable industrial potential.

MST/1073     

Surface modification of polylactic acid by ion,electron beams and low-temperature plasma: a review

Journal of Materials Science - We review the work that has been done on the modification of polylactic acid by irradiation methods including low-temperature plasma treatment, electron-beam...     

Surface segregation studied by low-energy ion scattering: experiment and numerical simulation

The changes in surface composition of metallic alloys caused by segregation can be very efficiently studied by low-energy ion scattering (LEIS) due to the specific surface sensitivity of this technique. Investigations of single-crystal surfaces of ordered alloys are of particular interest because they provide the possibility to investigate the interplay between segregation effects and the order-disorder phase transition when passing through the transition temperature. Exemplifying these effects for bimetallic alloys we consider in particular the CuAu-system.For the quantitative interpretation of energy and angle resolved LEIS intensity distributions we compare experimental results with those from numerical simulations using the MARLOWE code which we extended with a detailed trajectory analysis. This allows us to apply various discrimination criteria, such as number of collisions, distance of closest approach, identification of the scattering crystal layer, total path length, etc. On this basis structural effects, ion survival probabilities and the influence of thermal vibrations can be studied.We demonstrate this potential by using CuAu(1 0 0) as a special example. The scattering potential parameters were calibrated with elemental single crystals of known structures and the anisotropic Debye temperatures taken from the literature showed good agreement, neutralization was of minor importance in this case. Our procedure could be successfully used for the quantitative analysis of the composition of the first and second layer as a function of temperature. These results are in good agreement with theoretical predictions.     

Ar+ ion beam induced silicide formation mechanism at the Pd-Si interface

Evaporated palladium films of 45 nm thickness on Si(1 1 1) were irradiated using 78 keV Ar⁺ ions with doses in the range of 1×10¹⁵ to 1.5×10¹⁶ cm^–2 for the purpose of studying silicide formation. Rutherford backscattering analysis shows that intermixing has occurred across the Pd-Si interface at room temperature. The mixing behaviour increases with increasing dose of the bombarding ions, which agrees well with a theoretical model of isotropic cascade mixing for palladium, and radiation-enhanced diffusion associated with an interstitial mechanism for silicon.     

Improved ion transmission from atmospheric pressure to high vacuum using a multicapillary inlet and electrodynamic ion funnel interface

A heated multicapillary inlet and ion funnel interface was developed to couple an electrospray ionization (ESI) source to a high-vacuum stage for obtaining improved sensitivity in mass spectrometric applications. The inlet was constructed from an array of seven thin-wall stainless steel tubes soldered into a central hole of a cylindrical heating block. An electrodynamic ion funnel was used in the interface region to more effectively capture, focus, and transmit ions from the multicapillary inlet. The interface of seven capillary inlets with the ion funnel showed more than 7 times higher transmission efficiency compared to that of a single capillary inlet with the ion funnel and a 23-fold greater transmission efficiency than could be obtained using the standard orifice-skimmer interface of a triple-quadrupole MS. The multiple-capillary inlet and ion funnel interface showed an overall 10% ion transmission efficiency and approximately 3-4% overall detection efficiency of ions from solution based (i.e., prior to electrospray). The improved performance was achieved under conditions where ESI operation is robust and results in a significant increase in dynamic range.     

Alloy formation at the tetrapod core/arm interface

The nature of the interfacial structure between the core and the arms of a tetrapod quantum dot (QD) formed during the heteroepitaxial growth of a ZnS arm onto a CdSe core is not well understood but can be analyzed through the use of high-frequency electron paramagnetic resonance (HF-EPR) spectroscopy. The spectroscopic resolution at high frequency allows the presence of unique crystal fields reflecting interfacial alloying to be analyzed by incorporating Mn(II) ions as a dopant into the QD to act as an intentional EPR active spectroscopic probe. In addition, the HF-EPR can spectroscopically observe the presence of ion vacancies that are anticipated to form at the heteroepitaxial interface to accommodate structural mismatch. The HF-EPR spectra for Mn(II) are extremely sensitive to perturbations of the microenvironment due to changes in the crystal field. The HF-EPR spectra of Mn(II) in a CdSe (core)/ZnS (arm) tetrapod exhibiting wurtzite symmetry for both core and interface of the tetrapod provide clear evidence of heteroalloying at the core-arm interface and formation of intrinsic dislocations at grain boundaries. The formation of the interfacial alloy and grain boundaries reflects short-range ion migration at the heteroepitaxial layer to reduce strain energy due to the 12% lattice mismatch between the wurtzite lattices of CdSe and ZnS.     

Evaluation of bond quality at the interface between steel bar and concrete using the small-dimension break-off test

This paper investigates the feasibility of using the small-dimension break-off test for evaluation of the bond quality at the interface between steel bar and concrete. Experimental studies were performed on bar-type concrete specimens and reinforced concrete beams. Twelve bar-type concrete specimens containing plain and deformed steel bars with different diameters were used to develop the relationship between the break-off moment and the adhesive strength at the steel bar/concrete interface. Subsequently, three reinforced concrete beams containing normal reinforcing bars, epoxy-coated reinforcing bars, and bars smeared with oil to simulate various adhesive conditions at the bar/concrete interface were used to study how the break-off moment and the bond strength were affected by the different adhesive conditions. In addition, two beam specimens containing normal reinforcing bars were vibrated severely on a self-made shaking table shortly after initial setting of concrete to simulate the bond damage in fresh reinforced concrete beams due to unexpected vibration or impact. Experimental results show that the effective break-off moment has a good correlation with the adhesive strength at the interface between steel bar and concrete. The break-off moment increases with an increase in bond strength. It is demonstrated that the small-dimension break-off test is capable of evaluating damage at the steel bar/concrete interface.     

Hydrodynamic study of ion transfer at the liquid/liquid interface: the channel flow cell

A hydrodynamic system based on the channel flow cell for voltammetric detection of ions at the liquid/liquid interface is reported. The current response for tetraethylammonium ion transfer across a membrane-supported liquid/liquid interface is shown to be consistent with existing theory for both the flow rate and voltage scan rate dependence of such processes, with no calibration factors or other adjustable parameters required. The analytical utility of such a device is discussed with specific regard to in situ measurements in flow systems.     

Rubrene/TPD表面及其界面的AFM和XPS研究

在indium-tin-oxide(ITO)玻璃上采用多源蒸发的方法制备了红荧烯(Rubrene)/TPD样品。由原子力显微镜(AFM)得到的表面形貌图显示Rubrene膜具有良好的均匀性。利用X射线光电子能谱仪(XPS)研究了两种材料表面和界面的电子态。由Rubrene/TPD的表面分析可知,C1s精细谱中有3个峰最强的峰是由氧化造成的,而不是对应于芳香碳(284.55eV)。空气中的O2和H2O扩散到样品里形成O1s峰。用氩离子束溅射剥蚀表面,随着时间的增长,芳香碳对应的峰越来越强,282.45和289.62eV处的峰则迅速消失,当溅射时间超过4920s时,在2847eV处引入了一个新的峰,对应于C—N键。O1s峰迅速减弱是因为氧沾污的去除。N1s谱中的N—C键缓慢增强,到达界面附近时峰的强度变得稳定。C1sN1s和O1s谱中都有峰发生化学位移。     

Titanium deposition onto ion-bombarded and plasma-treated polydimethylsiloxane: Surface modification,interface and adhesion

Titanium films were deposited by electron beam evaporation onto polydimethylsiloxane (PDMS) substrates. Ar⁺ bombardment as well as O₂ plasma pretreatments were found to enhance the adhesion of the titanium films markedly. X-ray photoelectron spectroscopy and scanning electron microscopy were used to study the influence of the pretreatments on the PDMS surface morphology. Both pretreatments resulted in cross-linking and thereby an increased strength of the substrate surface. X-ray photoelectron spectroscopy was also used, together with in situ electron beam evaporation, to study the initial titanium film growth on as-prepared and Ar⁺-bombarded samples. The C 1s and O 1s peak shifts showed an enhanced film-substrate interaction attributed to formation of Ti-C and Ti-O bonds respectively. The film-substrate interaction was also observed as a change in the titanium film growth mode. If the samples were ion bombarded prior to deposition the film growth changed from a pronounced three-dimensional growth towards a more two-dimensional growth mode.     

Femtosecond microscopy of surface plasmon polariton wave packet evolution at the silver/vacuum interface

A movie of the dispersive and dissipative propagation of surface plasmon polariton (SPP) wave packets at a silver/vacuum interface is recorded by the interferometric time-resolved photoemission electron microscopy with 60 nm spatial resolution and 330 as frame interval. The evolution of SPP wave packets is imaged through a two-path interference created by a pair of 10 fs phase correlated pump-probe light pulses at 400 nm. The wave packet evolution is simulated using the complex dielectric function of silver.     

Microstructure and phase constitution near the interface of Cu/Al vacuum brazing using Al-Si filler metal

Brazing of Cu to Al using Al-Si filler metal has been carried out by vacuum brazing technology. The microstructure and the phase constitution in Cu/Al joint were studied by means of metallography, electron probe microanalyser (EPMA) and X-ray diffraction (XRD). Experimental results obtained showed that two kinds of intermetallic compounds (IMCs) are formed near the interface of copper and brazing seam region and those are Cu₃Al₂ and CuAl₂ phases. Moreover, ε-Cu₁₅Si₄, Al-Si and CuZn₂ are formed on the α-Al solid solution in the brazing seam region. Technology parameters of vacuum brazing were: brazing temperature T=590-610 °C, vacuum level 10⁻³ Pa, holding time t=5-10 min.     

9Cr18轴承钢氮等离子体浸没离子注入表面改性工艺及机理的研究

采用不同怕等离子体浸没离子注入工艺对９Ｃｒ１８轴承钢进行了氮离子注入,结果发现,不同条件下的氮离子注入均能显著提高９Ｃｒ１８钢表面的显微硬度和耐磨性,同时耐磨蚀性也明显改善。实验分析结果表明、氮离子注入后试样表面形成了大量的氮化物相,它们在改善材料表面特性中起到了关键的作用。     

Surface charge and adsorption of sodium ions at the controlled porosity glasses/electrolyte interface

Controlled porosity glasses (CPGs) are used as adsorbents, supports or catalysts. Their properties depend on the amount of surface boron and sodium concentration. The surface boron and sodium concentration can be changed by proper thermal treatment. The presented paper deals with the change of charge surface density and pH of point zero charge of the thermally treated CPG. The surface reaction constants according to the site binding theory of the electric double layer were calculated on the basis of the surface charge data. The results of Na⁺ adsorption on the CPGs are presented.     

Surface modification of cp-Ti using femtosecond laser micromachining and the deposition of Ca/P layer

Femtosecond laser processing is employed to create regular patterns and bioactive layer on the surface of pure titanium. Surface morphology and microstructure of the laser-processed layer are characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the processing with varied laser energies builds a surface with three-order roughness from nanometer scale to micrometer scale. Selected area electron diffraction indicates that some kind of TiO layer emerges on the surface after femtosecond laser machining. The bioactivity of TiO layer is further evaluated by soaking it in simulated body fluid (SBF). SEM observation and EDX analysis show that Ca/P layer is rapidly formed on the surface of TiO layer after SBF soaking. It implies that TiO layer with unique three-order roughness has good bioactivity.     

Effect of annealing on magnetic properties and silicide formation at Co/Si interface

The interaction of Co (30 nm) thin films on Si (100) substrate in UHV using solid state mixing technique has been studied. Cobalt was deposited on silicon substrate using electron beam evaporation at a vacuum of 4×10^?8 Torr having a deposition rate of about 0·1 Å/s. Reactivity at Co/Si interface is important for the understanding of silicide formation in thin film system. In the present paper, cobalt silicide films were characterized by atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS) in terms of the surface and interface morphologies and depth profile, respectively. The roughness of the samples was found to increase up to temperature, 300°C and then decreased with further rise in temperature, which was due to the formation of crystalline CoSi₂ phase. The effect of mixing on magnetic properties such as coercivity, remanence etc at interface has been studied using magneto optic Kerr effect (MOKE) techniques at different temperatures. The value of coercivity of pristine sample and 300°C annealed sample was found to be 66 Oe and 40 Oe, respectively, while at high temperature i.e. 748°C, the hysteresis disappears which indicates the formation of CoSi₂ compound.