CaF2 is a promising luminescent host material for a wide range of applications, due to its high transparency, non-hygroscopy, low refractive index, low density, low backscattering efficiency, and abundance in nature. This paper reports the photoluminescence (PL) and cathodoluminescence (CL) characteristics of rare-earth-doped CaF2 nanoparticles and their composite monoliths with epoxy with visible emissions. The CaF2 nanoparticles of ca. 36,108 and 305 nm were prepared by a facile solution-mixing process and subsequent hydrothermal treatment. As the particle size decreases, the luminescence intensity increases for single-doped particles, while oppositely decreases for codoped particles because of energy transfer. Further, Eu2+- and Tb3+-codoped CaF2 nanoparticles exhibit red emission, providing an efficient path for red emission through an energy transfer by Tb3+ bridging without direct Eu3+ doping. The effects of size and concentration are found to be pronounced in CL than PL, as the charge transfer between Eu2+ and Eu3+ reduces the concentration quenching in CL. The luminescence emission characteristics of epoxy/CaF2 monoliths are different from those of particles due to the interactions with the epoxy molecules, and thus the energy transfer is hindered in PL while not in CL, enabling them for high-energy irradiation applications. (C) 2020 Elsevier B.V. All rights reserved.

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We studied ionization-induced changes in the bonding of highly oriented pyrolytic graphite (HOPG) from sp2 (graphitic) to sp3 (amorphous or diamondlike) using MeV ion beams with varying degrees of surface energy deposition via ionization (electronic stopping power). This study allows us to better understand phase changes in ionizing environments as a function of electronic stopping power, as well as possibly provide a path to precise functionalization of materials such as graphene. Coupons of HOPG were bombarded with He, Si, and C ions at energies designed to produce ionization from 32 to 277 eV/A, and the surfaces were examined using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and 3D laser microscopy. As expected, we observed the transformation of graphitic sp2 bonding to amorphous or diamondlike sp3 bonds, with the extent generally dependent on the amount of ionization energy deposited, a transformation which may be explained by ion-induced excitation followed by rapid thermal quenching. Significant amount of surface disruption and cracking, however, indicated that the results could have been significantly affected by thermal swelling and damage to the material.

In this work we have studied changes in the optical properties of silica after high dose spot-by-spot implantation of 1.450 MeV Au, 0.785 MeV Ag, and high temperature annealing, and the effect of the sequence of annealing and implantation. Using a 2 mm diameter aperture, each spot was implanted to desired dose before moving the spot by 0.5 mm increments laterally across the sample so that a 1 cm2 area was uniformly implanted. Total implantation fluences of Au, Ag, and (sequentially) Au + Ag were varied from 1.5 x 1016 /cm2 to 1.4 x 1017 /cm2, and the implanted area was studied before and after annealing using optical absorption photospectrometry and by Rutherford backscattering spectrometry (RBS). We found that a secondary implantation by Ag ions (after Au implantation & nanoparticle formation) facilitates substrate healing upon a second annealing step, returning the index of refraction to the value near to that of a pristine substrate, and Au nanoparticle absorption to that predicted by Mie theory. Changing the processing order of annealing (annealing after both Au and Ag implantations were completed, rather than between the Au and Ag implantations) eliminated Ag nanocluster formation, returned the substrate index of refraction to its pristine value, and caused Au nanocluster formation to initiate at lower annealing temperatures.

We selected appropriate projects requiring ion beam materials analysis and surface modification of materials by ion beams as undergraduate capstone projects at the Fayetteville State University Department of Chemistry and Physics. we partnered with the Army Research Laboratory to facilitate completion of these projects using their laboratory facilities. Projects highlighted in this presentation are: A) changes in the surface hardness of silica implanted by MeV ions, B) a study of carbon "grafoil" surfaces C) measurement of heavy element content on the surface of polymeric toys; and D) changes in the optical absorption properties of silica implanted with MeV metallic ions. Students were successful in completing their course requirements and learning about ion beam accelerators, analysis and surface modification by ion beams, as well as learning about many other complementary techniques.

Solvothermally synthesized rare-earth-doped superlong BaSiF6nanowires with high aspect ratios with subnanosecond decay time.

a Department of Chemistry and Physics, Fayetteville State University, Fayetteville, NC 28301, USA. E-mail: zluo@uncfsu.edu b College of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, P. R. China c Centre for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA d Oak Ridge Institute for Science and Education, Oak Ridge Associated Universities, Oak Ridge, TN 37830, USA

A scintillator can convert high-energy radiations to visible lights, enabling real-time detection and imaging of the radiations. So far, research on scintillators on the nanometer scale is limited [1-3]. In an electron microscope, cathodoluminescence (CL) spectroscopy can be used to study the scintillation since it can provide the luminescence from a small specimen region using a defined beam of high-energy electrons. In this work, we synthesized scintillator nanofibers for studying their CL properties using an electron probe microanalyzer (EPMA).

Fluorides are promising host materials for optical applications. This paper reports the photoluminescent (PL) and cathodoluminescent (CL) characteristics of barium hexafluorogermanate BaGeF6 nanowires codoped with Ce3+, Tb3+ and Sm3+ rare earth ions, produced by a solvothermal route. The synthesized BaGeF6 nanowires exhibit uniform morphology and size distribution. X-ray diffraction divulges the one-dimensional growth of crystalline BaGeF6 structure, with the absence of any impurity phases. Visible luminescence is recorded from the nanowires in green and red regions, when the nanowires are codoped with Ce3+/Tb3+, and Ce3+/Tb3+/Sm3+, respectively, under a UV excitation source. The PL emission from the codoped BaGeF6 nanowires, when excited by a 254 nm source, originates from the efficient energy transfer bridges between Ce3+, Tb3+ and Sm3+ ions. The decay time of the visible luminescent emission from the nanowires is in the order of subnanoseconds, being one of the shortest decay time records from inorganic scintillators. The CL emission from the BaGeF6 nanowires in the tunable visible range reveals their potential use for the detection of high-energy radiation. The PL emissions are sensitive to H2O2 at low concentrations, enabling their high-sensitivity detection of H2O2 using BaGeF6 nanowires. A comparison with BaSiF6 nanowires is made in terms of decay time and its sensitivity towards H2O2.

A zirconium metal-organic framework (MOF), PCN-111, has been synthesized by using an elongated ditopic carboxylate linker, 4,4'-(buta-1,3-diyne-1,4-diyl)dibenzoate. Single crystal X-ray diffraction characterization indicates that the noninterpenetrated microporous structure of PCN-111 is isoreticular to UIO MOFs with 12 connected Zr6O4(OH)4(CO2)12 clusters and a fcu topology. It was successfully activated through a solvent exchange with acetone followed by controlled evacuation and its gas sorption was reported. By using 77 K nitrogen adsorption isotherm and strictly applying three consistency criteria, the BET surface area for PCN-111 was calculated to be 4825 m2 g-1. Pore size distribution analysis suggests that the sizes of cavities contributing to nitrogen adsorption are predominately in the range of 15 to 20 Å, which are in good agreement with the two polyhedral cages (15.6 and 20.2 Å, respectively) in the single crystal X-ray solved structure. Owing to its relatively high crystal density (0.42 g cm-3), the volumetric surface area for PCN-111 was calculated to be 2026 m2 cm-3. The value is among the highest of all the reported ultrahigh surface area MOF materials. The exceptionally high microporosity of PCN-111 has also been validated by comparison with the simulated nitrogen adsorption isotherm derived from multipurpose simulation code MUSIC.

The linear and non-linear optical properties of silica may be tailored by the introduction of a random distribution of nanocrystallites of an immiscible metal within a near-surface region. The size, size distribution, and spatial distribution of these crystallites must be controllable in order to optimize the functional properties for device applications. In this paper, we present a novel fabrication technique that offers such control. Energetic metal ions are implanted in silica at room temperature. Subsequent heat treatment leads to diffusion of the implanted atoms, nucleation and growth of metal crystallites, and Ostwald ripening of the resulting clusters. We have observed the kinetics and effective activation energies describing the multiple processes involved, for the cases of Au, Ag or Cu implanted at MeV energies, at various fluences, and then annealed at fixed temperatures in the range 500°C-1000°C. Effective activation energies found for nanocrystal nucleation and growth at temperatures below 800°C (e.g. 64 meV for Ag) are replaced above this temperature range by much higher activation energies (e.g. 400 meV for Ag). We may attribute this to the depletion of un-attached mobile metal atoms (so that ripening of clusters will be limited by energy barriers for escape of such mobile atoms from small crystallites), and/or the annealing of implant-caused stress in the silica structure at high temperatures, that creates new channels for thermal diffusion of metal atoms within the silica host.

Ion Beam Assisted Deposition (IBAD) was used to process a thermoelectric materials system, with high volume fraction and high thermoelectric figure of merit, based on the interaction of composites of two metal nanocrystals in silica substrate prepared by a multilayer structure having alternate layers of metal/material mixture. The alternate layers component of this work either has gold or silver content. The deposited layered structure was bombarded during deposition by 500 eV to 10keV argon ions in order to produce nanoclusters in each layer. Using the IBAD method we obtained a much larger volume fraction, compared to our previous work, and a resulting thermal conductivity as low as 1.2 (W/m.k), electrical conductivity nearly as high as 90,000 (1/Ohm.m), square of Seebeck Coefficient as high as 1.37 x 10-7 (V/k)2 at 350K, which translates to a Figure of Merit as high as 3.6.

The ternary chalcogenides AgBiTe2 and AgSbTe2 belong to the family of semiconductors with disordered NaCl cubic structure in which Ag and Sb occupy metal sublattices. Both compounds are very interesting due to their thermoelectric properties. We have grown single-layer AgBiTe and AgSbTe thin films on silicon (Si) and fused silica (Suprasil) substrates using electron beam deposition. High-energy (MeV) Si-ion bombardment was performed on the thin-film samples at five different fluences between 5 × 1013 ions/cm2 and 7 × 1015 ions/cm2. We have measured the thermoelectric efficiency (figure of merit, ZT) of the fabricated thermoelectric devices by measuring the cross-plane thermal conductivity using the third-harmonic (3ω) method, the cross-plane Seebeck coefficient, and the in-plane electrical conductivity using the van der Pauw method before and after MeV Si-ion bombardment. Rutherford backscattering spectrometry and the Rutherford Universal Manipulation Program (RUMP) simulation package were used to analyze the elemental composition and thickness of the deposited materials on the substrates. The RUMP simulation gave thicknesses for the AgBiTe and AgSbTe thin films of 270 nm and 188 nm, respectively. The figure of merit for AgBiTe started to decrease from the value of 0.37 for the virgin sample after bombardment. We saw similar decreasing behavior for the AgSbTe thin-film system. The figure of merit for AgSbTe started to decrease from the value of 0.88 for the virgin sample after bombardment. MeV Si-ion bombardment caused changes in the thermoelectric properties of the thin films.

This paper reviews gas cluster ion beam (GCIB) technology, including the generation of cluster beams, fundamental characteristics of cluster ion to solid surface interactions, emerging industrial applications, and identification of some of the significant events which occurred as the technology has evolved into what it is today. More than 20 years have passed since the author (I.Y) first began to explore feasibility of processing by gas cluster ion beams at the Ion Beam Engineering Experimental Laboratory of Kyoto University. Processes employing ions of gaseous material clusters comprised of a few hundred to many thousand atoms are now being developed into a new field of ion beam technology. Cluster-surface collisions produce important non-linear effects which are being applied to shallow junction formation, to etching and smoothing of semiconductors, metals, and dielectrics, to assisted formation of thin films with nano-scale accuracy, and to other surface modification applications. HISTORICAL MILESTONES IN GCIB TECHNOLOGY In 1950, Becker et al first studied cluster formation for thermonuclear fuel applications using gaseous materials passed through supersonic nozzles wchichi were cooled by liquid nitrogen and helium shrouds [1]. The supersonic expansion approach was successful in producing cryogenic beams containing large numbers of clusters. This original work opened the way to employ gas clusters for materials processing. During the late 1970's and 1980's, an ionized cluster beam (ICB) technique which employed metal vapor clusters from heated Knudsen cells for thin film formation was studied at Kyoto University and elsewhere. Kyoto University investigations of metal vapor clusters ended when collaborative work with W.L.Brown at Bell Laboratories showed the cluster ion intensities within the metal vapor streams to be too low for most practical purposes [2,3]. Subsequent work at the Kyoto University Ion Beam Engineering Experimental Laboratory then focused upon cluster beam formation employing gas expansion through simple supersonic nozzles. Initial research on gas cluster beam formation showed that supersonic nozzles having converging-diverging shapes operating at room temperature could produce intense beams of gas clusters. This then led to research and development of gas cluster ion beam (GCIB) techniques [4] and to investigations of new ion-solid interactions produced by gas cluster ion impacts. These studies demonstrated that GCIB produces unique ion/solid interactions and offers new atomic and molecular ion beam process opportunities in areas of implantation, sputtering, and ion beam assisted deposition. Most of the original technical results through to the year 2000 have been summarized in a monograph. [5]. Over the first 10 years of GCIB studies, low energy surface interaction effects, lateral sputtering phenomena and high chemical reaction effects were observed experimentally and were www.cambridge.org © in this web service Cambridge University Press Cambridge University Press 978-1-107-40865-4 Ion-Beam-Based Nanofabrication: Materials Research Society Symposium Proceedings: Volume 1020 Editors: Daryush ILA, John Baglin, Naoki Kishimoto and Paul K. Chu Excerpt More information

We have deposited five periodic SiO2/SiO2 + Ag multi-nano-layered films on fused silica substrates using physical vapor deposition technique. The co-deposited SiO2:Ag layers were 2.7-5 nm and SiO2 buffer layers were 1-15 nm thick. Total thickness was between 30 and 105 nm. Different concentrations of Ag, ranging from 1.5 to 50 molecular% with respect to SiO2 were deposited to determine relevant rates of nanocluster formation and occurrence of interaction between nanoclusters. Using interferometry as well as in situ thickness monitoring, we measured the thickness of the layers. The concentration of Ag in SiO2 was measured with Rutherford Backscattering Spectrometry (RBS). To nucleate Ag nanoclusters, 5 MeV cross plane Si ion bombardments were performed with fluence varying between 5 x 10(14) and 1 x 10(16) ions/cm(2) values. Optical absorption spectra were recorded in the range of 200-900 nm in order to monitor the Ag nanocluster formation in the thin films. Thermal annealing treatment at different temperatures was applied as second method to form varying size of nanoclusters. The physical properties of formed super lattice were criticized for thermoelectric applications. (C) 2014 Elsevier B.V. All rights reserved.

A thermoelectric system based on the interaction of composites of two metal nanocrystals in silica substrate prepared by a multilayer structure having alternate layers of metal/material mixture is discussed in detail in this paper. The alternate layers component of this work has two metal content, gold and silver. The layered structure irradiated with ionizing radiation to produce nanoclusters in these layers one on the top of each metal nanocrystal containing nanolayer with no silica buffer layer. The differing metal content serves to quench the nanoclusters to isolate nanoclusters along the 5.0MeV Si beam irradiation track, as described in our past 16 years publications [1], [2], [3], [4], [5]. The result is a thermoelectric material with high electrical conductivity, low thermal conductivity, high Seebeck coefficient thus a high figure of merit as high as 3.1, as described in this work.

The performance of thermoelectric materials and devices is characterized by a dimensionless figure of merit, ZT=S2σT/K, where, S and σ denote, respectively, the Seebeck coefficient and electrical conductivity, T is the absolute temperature in Kelvin and K represents the thermal conductivity. The figure of merit may be improved by means of raising either S or σ or by lowering K. In our laboratory, we have fabricated and characterized the performance of a large variety of thermoelectric generators (TEG). Two TEG groups comprised of 50 and 100 alternating layers of Si/Si+Ge multi-nanolayered superlattice films have been fabricated and thoroughly characterized. Ion beam assisted deposition (IBAD) was utilized to assemble the alternating sandwiched layers, resulting in total thickness of 300nm and 317nm for 50 and 100 layer devices, respectively. Rutherford Backscattering Spectroscopy (RBS) was employed in order to monitor the precise quantity of Si and Ge utilized in the construction of specific multilayer thin films. The material layers were subsequently impregnated with quantum dots and/or quantum clusters, in order to concurrently reduce the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and raise the cross plane electrical conductivity. The quantum dots/clusters were implanted via the 5MeV Si ion bombardment which was performed using a Pelletron high energy ion beam accelerator. We have achieved remarkable results for the thermoelectric and optical properties of the Si/Si+Ge multilayer thin film TEG systems. We have demonstrated that with optimal setting of the 5MeV Si ion beam bombardment fluences, one can fabricate TEG systems with figures of merits substantially higher than the values previously reported.

We prepared multilayers of superlattice thin film system with 50 periodic alternating nano-layers of semiconducting half-Heusler β-Zn4Sb3 and skutterudite CeFe2Co2Sb12 compound thin films using ion beam assisted deposition (IBAD) with Au layers deposited on both sides as metal contacts. The deposited multilayer thin films have alternating layers about 5nm thick. The total thickness of the multilayer system is 275nm. The superlattices were then bombarded by 5MeV Si ion at six different fluences to form nano-cluster structures. The film thicknesses and composition were monitored by Rutherford backscattering spectrometry (RBS) before and after MeV ion bombardment. We have measured the thermoelectric efficiency, Figure of Merit ZT, of the fabricated device by measuring the cross plane thermal conductivity by the 3rd harmonic (3ω) method, the cross plane Seebeck coefficient, and the electrical conductivity using the van der Pauw method before and after the MeV ion bombardments. We reached the remarkable thermoelectric Figure of Merit results at optimal fluences.

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.