C. Muntele

Nano-cluster engineering: A combined ion implantation/co-deposition and ionizing radiation

We have used the energy deposited due to the electronic excitation by post-implantation irradiation to induce the nucleation of nano-clusters of Au in silica. We have produced the Au/silica by two methods. (A) MeV Au implantation into silica, (B) producing thin films of a combined Au and silica on a silica substrate, using co-deposition of gold and silica. The process of ion beam assisted nucleation of nano-clusters was used to reduce the threshold implantation dose, or the Au concentration in the silica host, required to produce Au nano-crystals by at least two orders of magnitude. In this presentation, we applied a similar technique, post-irradiation electronic excitation, to films produced by both ion implantation of Au into silica as well as to films produced using co-deposition of gold and silica. By a co-deposition technique, gold and silica (co-deposited at various concentrations) are grown, then post-irradiated. The resultant Au nano-cluster formation was observed and studied using optical spectroscopy, X-ray diffraction, RBS and TEM.

Enhanced tissue adhesion by increased porosity and surface roughness of carbon based biomaterials

Abstract We present recent results using ions of C, O, Si, Fe, Zn and Au at energies between 100 keV and 10 MeV to increase the roughness and porosity of the partially and fully cured precursor phenolic resins. The fully cured phenolic resin is called glassy polymeric carbon (GPC). GPC is chemically inert, biocompatible and useful for medical applications, such as heart valves and other prosthetic devices. Ion implantation enhances biological cell/tissue growth on, and tissue adhesion to, prosthetic devices made from GPC. We have previously shown that increased porosity of GPC is also useful for drug delivery devices. The porosity of the ion implanted partially and fully cured precursor phenolic resins was measured by introducing lithium from a molten LiCl salt into each sample. By using Li(p,2α) nuclear reaction analysis (NRA) we measured the concentration of Li retention in the pre- and post-implanted samples. The surface roughness was measured using optical microscopy. The curing process was monitored using micro-Raman microscopy. We have correlated the NRA measurements of increased pore availability with the observations of increased surface roughness.

Superlattice Multinanolayered Thin Films of SiO2/SiO2 + Ge for Thermoelectric Device Applications

Thermoelectric generators convert heat to electricity. Effective thermoelectric materials and devices have a low thermal conductivity and a high electrical conductivity. The performance of thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and K is the thermal conductivity. We have prepared 100 alternating layers of SiO2/SiO2+ Ge superlattice thin films using ion beam–assisted deposition for the thermoelectric generator device application. The 5 MeV Si ion bombardments were performed using the Center for Irradiation Materials’ Pelletron ion beam accelerator to form quantum dots and/or quantum clusters in the multinanolayer superlattice thin films to decrease the cross-plane thermal conductivity and increase the cross-plane Seebeck coefficient and cross-plane electrical conductivity. The thermoelectric and transport properties have been characterized for SiO2/SiO2+ Ge superlattice thin films.

Ion beam characterization and engineering of strain in semiconductor multi-layers

Abstract The objective of this work is to measure and engineer the strain in III–V compound semiconductor multi-layers using ion beams, which leads to spatial band-gap tuning for the integration of optoelectronics devices. Strained layer superlattices have been of unique interest due to their ability to tune the band gap, which depends on the strain at the interface. Therefore the strain measurements at the interface are of great interest. A large area two-dimensional positions sensitive Δ E − E detector telescope and a fully automated high energy channeling facility have been developed at NSC, New Delhi. An overview of the series of ERDA, RBS, Channeling, HRXRD and ion beam mixing experiments performed in this direction will be discussed in this paper.

Effect of MeV protons on the phase behaviour and thermal stability of polytetrafluoroethylene

Thermomechanical spectroscopy analysis was used to study the influence of accelerated protons on the molecular-topological properties of polytetrafluoroethylene (PTFE). The study showed changes in a wide number of polymer parameters as a result of bombardment with 1, 2 and 4 MeV protons at fluences up to 2 × 1015 protons/cm2. The basic topological process occurring under proton bombardment is amorphicity, as found for γ-irradiation of PTFE. The flow temperature of bombarded PTFE significantly decreases with increasing the fluxes and energy of the accelerated protons. The general process resulting from proton bombardment is cleavage of C-F bonds, leading to formation of “centered” radicals ∼CF2CF · CF2∼ and HF. The thermal stability of bombarded PTFE is below than that of virgin polymer. The rate of thermal destruction noticeably increases and the temperature of the initiation of effective thermal decomposition decreases after bombardment. The gaseous products generated during thermal destruction of the bombarded and virgin PTFE are similar.

Thermoelectric properties of SiO2/SiO2+CoSb multi-nanolayered thin films modified by MeV Si ions

We have fabricated the thermoelectric generator devices from 100 alternating layers of SiO2/SiO2+CoSb superlattice thin films using the ion beam–assisted deposition. Rutherford backscattering spectrometry was used for quantitative elemental analysis of Si, Co, and Sb in the multilayer films. The thin films were then modified by 5-MeV Si ion bombardments using the Alabama A&M University Pelletron ion beam accelerator. Quantum dots and/or clusters were produced in the nanolayered superlattice films to decrease the cross-plane thermal conductivity, increase the cross-plane Seebeck coefficient, and the cross-plane electrical conductivity. We have characterized the thermoelectric generator devices before and after Si ion bombardments using the thermoelectric, optical, and surface characterization techniques. The optical absorption amplitude decreased when the first fluence of 1 × 1012 ions/cm2 was introduced from the value of 2.8 to about 1.9 at 200 nm. The figure of merit reached the maximum value of about 0.005 at the fluence of 1 × 1013 ions/cm2.

Surface engineering of a Zr-based bulk metallic glass with low energy Ar- or Ca-ion implantation

In the present study, low energy ion implantation was employed to engineer the surface of a Zr-based bulk metallic glass (BMG), aiming at improving the biocompatibility and imparting bioactivity to the surface. Ca- or Ar-ions were implanted at 10 or 50 keV at a fluence of 8 × 10(15)ions/cm(2) to (Zr0.55Al0.10Ni0.05Cu0.30)99Y1 (at.%) BMG. The effects of ion implantation on material properties and subsequent cellular responses were investigated. Both Ar- and Ca-ion implantations were suggested to induce atom displacements on the surfaces according to the Monte-Carlo simulation. The change of atomic environment of Zr in the surface regions as implied by the alteration in X-ray absorption measurements at Zr K-edge. X-ray photoelectron spectroscopy revealed that the ion implantation process has modified the surface chemical compositions and indicated the presence of Ca after Ca-ion implantation. The surface nanohardness has been enhanced by implantation of either ion species, with Ca-ion implantation showing more prominent effect. The BMG surfaces were altered to be more hydrophobic after ion implantation, which can be attributed to the reduced amount of hydroxyl groups on the implanted surfaces. Higher numbers of adherent cells were found on Ar- and Ca-ion implanted samples, while more pronounced cell adhesion was observed on Ca-ion implanted substrates. The low energy ion implantation resulted in concurrent modifications in atomic structure, nanohardness, surface chemistry, hydrophobicity, and cell behavior on the surface of the Zr-based BMG, which were proposed to be mutually correlated with each other.

Characterization of gold nanodots arrangements in SiO2/SiO2+Au nanostructured metamaterials

Effective thermoelectric materials have a low thermal conductivity and a high electrical conductivity. For this study, we have prepared a thermoelectric generator device of SiO2/SiO2+Au multi-nano-layered thin film systems using ion beam-assisted deposition followed by 5 MeV Si ion bombardment. The ion bombardment causes the Au atoms to nucleate into metallic nanoclusters. However, as the kinetic energy of the Si ions decreases with the depth of the sample, so does the electronic stopping power responsible for the Au nucleation. This produces variations in the size and spacing of the nanoclusters. Here, we are investigating the effects of the size and arrangement variations within the device on the electrical and thermal transports within the system. We characterized the thin film system, using I–V characterization, conductance measurement, quasi-static capacitance, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy.

Structural Changes in Polymer Films by Fast Ion Implantation

In applications from food wrapping to solar sails, polymers films can be subjected to intense charged panicle bombardment and implantation. ETFE (ethylenetetrafluoroethylene) with high impact resistance is used for pumps, valves, tie wraps, and electrical components. PFA (tetrafluoroethylene‐per‐fluoromethoxyethylene) and FEP (tetrafluoroethylene‐hexa‐fluoropropylene) are sufficiently biocompatible to be used as transcutaneous implants since they resist damage from the ionizing space radiation, they can be used in aerospace engineering applications. PVDC (polyvinyllidene‐chloride) is used for food packaging, and combined with others plastics, improves the oxygen barrier responsible for the food preservation. Fluoropolymers are also known for their radiation dosimetry applications, dependent on the type and energy of the radiation, as well as of the beam intensity.In this work ETFE, PFA, FEP and PVDC were irradiated with ions of keV and MeV energies at several fluences and were analyzed through techniques ...

RBS and PIXE Ion Beam Methods for Characterizing Ni‐Co Alloys

Various electroplating/electroforming processes have been used for years to produce nickel‐cobalt components for applications from space industry to tool refurbishing. The mechanical properties (hardness, strength, etc.) are drastically affected by the nickel to cobalt ratio of the alloy, as well as the amount of organic additives and trace contaminants present in the plating tank. Traditionally, chemical or optical methods were used for characterizing the constituents of the resulting deposit. In this paper we present the usefulness of nuclear methods of analysis based on accelerated ion beams for performing both qualitative and quantitative compositional characterization of such alloys. Samples of electroformed materials were prepared in a nickel sulfamate bath with nickel‐cobalt ratios ranging between 70:30 (or 2.33:1) and 80:20 (or 4:1) atomic percent. The samples were analyzed using PIXE (Proton Induced X‐Ray Emission) with proton beam of 1 MeV and RBS (Rutherford Backscattering Spectrometry) with 6 ...