Vladimir Popok

Optical properties of polymethylmethacrilate with implanted silver nanoparticles

AbstractSilvernanoparticleshavebeensynthesisedinpolymethylmethacrilateby30keVAg þ ionimplantationwithdosesfrom3:1 10 15 to7:5 10 16 ion/cm 2 .Despitetheformationofthenanoparticlesinthenearsurfacelayer,thechar-acteristicstrongopticalabsorptionoftheplasmonresonanceinmetallicnanoparticlesatwavelengthsinthevisiblerangewasnotapparent.Onlyweakabsorptionbandsinawidespectralarea,whichshowsomedependenceontheimplantationdose,wereobserved.Thefactorsinfluencingtheexperimentaldataarediscussedandtheopticalextinctionspectraofthemetalnanoparticlesinthepolymeror/andinamorphouscarbonweremodelledusingMietheory.Somequalitativeagreementbetweentheoreticalandexperimentaldatawasachievedbytakingintoaccountthecarbonisationphenomenoninthepolymerduetoradiation-inducedeffects. 2002PublishedbyElsevierScienceB.V. Keywords:Ionimplantation;Nanoparticles;Opticalextinctionandtransmission 1. IntroductionDespitetheintensivestudyofmetalnanopar-ticlesynthesisbyionimplantationindielectrics,such as non-organic glasses and crystals, whichwasstartedin1975withArnold’spublication[1],theformationofnanoparticlesinorganicmatriceswasrealisedonlyatthebeginningoftheeightiesbyKoonetal.intheirexperimentsonimplanta-tion of Fe ions into polymers [2,3]. In general,polymerscontainingmetalnanoparticles,inpar-ticularformedbyimplantation,showencouragingproperties from both the applied (optical fil-ters,magneticor/andopticaldatastorage)andthefundamentalpointofview[4].Avarietyofmetalions was used for implantation into polymers.Present work focuses on polymer-based opticalmaterials containing metallic nanoparticles (Ag,Auetc.)characterisedbyastrongopticalplasmonresonance.Onlyrecentlyweresuchmaterialsfab-ricatedbyAgimplantationintoepoxyresins[5,6]and polymethylmethacrilate (PMMA) [7,8]. Anunusually weak plasmon resonance absorptionwasdetectedinthecaseoftheAg–PMMAcom-posite despite the high concentration of thesynthesisedAgnanoparticles[8].Oneofthesug-gestionsforthereasonoftheweakabsorptionwas

ION BEAM EFFECTS IN POLYMER FILMS : STRUCTURE EVOLUTION OF THE IMPLANTED LAYER

Abstract Thin films of polyethylene, polyamide-6 and cellulose implanted with 100 keV B + , N + and Sb + ions to the fluences of 10 13 –10 17 cm −2 were investigated using RBS and NDP techniques as well as IR, UV-visible and EPR spectroscopies. The peculiarities of the depth distribution of implanted species and the origin of the processes responsible for modification of the structural, optical and paramagnetic properties of polymers are discussed with consideration for two major reactions occurring in the implanted layer: (i) oxidation of the radiation-damaged polymer that predominates at moderate doses; (ii) clusterization of radiation defects with the formation of carbon-enriched domains (“drops”) which can overlap at high ion fluences yielding the network of conjugated carbon structures.

High fluence ion beam modification of polymer surfaces: EPR and XPS studies

Abstract Polyethylene, polyamide-6 and polyimide foils implanted with 100 keV B + , P + and Sb+ ions to a fluence range of 10 15 –10 17 cm −2 have been studied using the electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) methods. The experimental data allow the comparison of the implantation-induced changes both in a given polymer foil under different ion beam regimes and in different polymers under similar ion-bombardment conditions. The high fluence implantation of boron ions, depositing energy mainly via electronic stopping, was found to be accompanied with the effective formation of π-bonded carbon-rich clusters. By contrast, heavier (phosphorus and antimony) ions, which deposit energy predominantly in nuclear collisions, produced a lower concentration of π-radicals and a less carbonised top surface layer. The peculiarities and main trends of the alterations of the polymer structure and composition induced via electronic and nuclear stopping have also been discussed.

Structure evolution of implanted polymers: Buried conductive layer formation

The polarization, temperature and frequency dependence of the conductivity of polyethylene and poliamide-6 films implanted with B+ ions at 60–100 keV to various fluences were investigated. The phenomenon of hysteresis was observed in the d.c. current–voltage dependence for the polymers implanted with moderate fluences. This effect was attributed to the aligning of electric dipoles (attributed to the carbon-rich clusters) in the implanted layer by the applied electric field. The possibility of fabrication of a sandwich structure insulator/conductive layer/insulator combining the ion implantation with the electrochemical deposition of dielectric polymer poly-ortho-phenylenediamine from solution was demonstrated. The spatial characteristics of this structure enable the control of the conductance of the concealed carbonaceous layer by applying an external electric field that opens the way for fabrication of a transistor-like electronic switch.

Surface entropy of rare-gas clusters.

Abundances of ArN+ and XeN+ clusters produced in a supersonic expansion source are inverted to find relative dissociation energies. The values around the shell and subshell closings at N=55, 71, and 147 differ from theoretical values derived from ground-state energies of Lennard-Jones clusters. A significant part of the difference can be accounted for by the conformational entropies of surface atoms and vacancies.

Laser annealing of sapphire with implanted copper nanoparticles

Abstract Copper nanoparticles have been synthesized by ion implantation in sapphire at 40 keV to a dose of 1×10 17 ion/cm 2 , at a current density from 2.5 to 12.5 μA/cm 2 . The samples were treated using pulses of a high-power KrF excimer laser (248 nm) in ambient atmosphere. This employed a single (25 ns) pulse fluence of 0.3 J/cm 2 for Cu-implanted sapphires. Number of pulses of the same energy density and at a frequency of 1 Hz were accumulated in the same area on the surface. The formation and modification of metal nanoparticles were assessed via optical reflectance. Generally, changes induced by laser pulses suggest that there are reductions of the size of the nanoparticles without diffusion of metal atoms inward the sapphire. No evidence for oxidization of Cu nanoparticles was founded.

Nanohillock formation by impact of small low-energy clusters with surfaces

Results on nanoscale structuring of different substrates (silicon, pyrolytic graphite, indium-tin-oxide) using clusters from 20 to 100 atoms in size formed from gaseous precursors (O2, N2, Ar) at relatively low impact energy up to 15 keV are presented. Images of the substrate surfaces after cluster collisions obtained using atomic force microscopy (AFM) show the formation of hillocks from a few to 15 nm height with a basal diameter from 50 to 300 nm depending on implantation conditions. The shape and size of the structures are found to be a function of the cluster size and species, implantation energy, impact angle and the type of substrate. A model explaining the hillock formation is discussed.

Pulse and continuous ion beam treatment of polyethylene

Polyethylene (PE) films were treated by a nitrogen ion beam with an energy of 20 keV at a quasicontinuous regime with low current density and at a pulse-periodical regime with high current density. IR ATR spectra and UV spectra showed significant differences in structural changes of PE treated by pulse and continuous treatment at the same average current density. The changes in the molecular structure that are induced by ion beams, i.e. the appearance of aromatic cycles, unsaturated bonds and carbonyl groups in PE, have a similar qualitative character for all types of ion beam regimes. However, the same degree of structural changes is achieved at lower dose in the pulse regime than in the continuous regime. At equal treatment parameters (ion energy, dose treatment, average current density) the pulse regime leads to a higher concentration of unsaturated and oxygen-containing groups then the continuous regime. This effect at the pulse regime can be explained by the high current density in the single pulse, at which a high local temperature is generated in the ion track field of the polymer. Probably this leads to a wave of internal stress, and these effects additionally stimulate structural changes in the polymer at pulsed ion beam treatment.

Degradation Assessment in IGBT Modules Using Four-Point Probing Approach

Four-point probing of electrical parameters on various components of IGBT modules is suggested as an approach for the estimation of degradation in stressed devices. By comparison of these parameters for stressed and new components one can evaluate an overall degradation of the module and find out the wear state of individual components. This knowledge can be applied for preventing early failures and for optimization of the device design. The method is presented by regarding a standard type power module subjected to power cycling.

Design and capabilities of an experimental setup based on magnetron sputtering for formation and deposition of size-selected metal clusters on ultra-clean surfaces

The design and performance of an experimental setup utilizing a magnetron sputtering source for production of beams of ionized size-selected clusters for deposition in ultra-high vacuum is described. For the case of copper cluster formation the influence of different source parameters is studied and analyzed. Size-selected clusters are deposited on substrates and the efficiency of an electrostatic quadrupole mass selector is tested. Height analysis using atomic force microscopy (AFM) demonstrates relative standard size deviations of 7%-10% for the particles of various sizes between 6 nm and 19 nm. Combined analysis by AFM and transmission electron microscopy reveals that the clusters preserve almost spherical shape after the deposition on amorphous carbon substrates. Supported nanoparticles of a few nanometres in diameter have crystalline structure with a face-centered cubic (fcc) lattice.