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Nano-crystalline graphite (NCG) structures on insulating layers have been grown via implantation of kilo-electron-volt (keV) energetic carbon clusters (Cn) on sapphire (Al2O3) and post-implantation thermal annealing conditions. The clusters were produced using a source of negative ion using Cesium sputtering (SNICS) with graphite and carbon nanotubes (CNT) as cathode materials. The Graphite cathode exhibited high currents for most of the cluster sizes. However, the CNT cathodes showed higher yields for relative heavy clusters (n = 16, 18, and 20). Also, carbon clusters as large as n ~ 56 were observed from the SNICS source. The Sapphire substrates were implanted with carbon cluster (Cn, n = 18) ions at 11 keV (~611 eV per carbon atom) with fluences of 1.1 × 1015 C18-clusters/cm2 (~2 × 1016 carbon atoms/cm2). Ion impact craters and surface build-ups were observed. Further, we have studied the carbon bonding characteristics by Raman Spectroscopy (RS) on as-implanted and annealed implanted samples. We have observed well-developed disorder (D), graphite (G), and 2D peaks from the optimized samples, indicating the formation of nano-crystalline graphite (NCG) structures on the surface. The ratio of D and G peaks in the RS spectra suggests that the nano-crystalline cluster diameter or in-plane correlation length is about 10–16.5 nm. The Crystal size approaches a maximum value with increasing post-implantation thermal annealing temperature. We have studied the growth of NCG by X-ray Photoelectron Spectroscopy (XPS) for the chemical bonding and distribution. The average sizes of crystalline NCGs were also estimated using Grazing Angle X-ray Diffraction (GAXRD) Spectrometry. The surface morphology of the implanted samples was investigated using Atomic Force Microscopy (AFM).

Ternary Fe-Co-Si B20 phase structure was formed by implanting Fe and Co ions consecutively into Si(100) substrate at 50 keV energy, each with a fluence of 1.0 × 1017 atoms/cm2 and post-thermal vacuum annealing at 500 oC for 60 minutes. An in-situ magnetic field was used to enhance the formation of the ternary phase in the Si substrate during the implantation process. The magnetic field of 0.05 T was applied perpendicular to the incoming ion beam direction and parallel to the substrate surface to form elongated clusters in the transverse direction of the sample. Prior to the implantation of ions, the implant ions depth profiles were simulated using a dynamic ion-solid interaction code (TRIDYN). The TRIDYN simulation predicted a saturation in the peak concentration of the Fe and Co ions at a fluence of 1.0 × 1017 atoms/cm2. XPS measurement at the peak concentration depth (40 nm) showed the presence of Fe (23 %) and Co (32 %) in the Si matrix. XRD characterization confirmed the presence of stable Fe-Co-Si B20 phase structure in the annealed samples implanted with the in-situ magnetic field.

We investigate the conditions under which electron irradiation at 2 keV of single-wall carbon nanotube (SWCNT) bundles produces an increase in the Raman D peak. We find that irradiation of SWCNTs that are preheated in situ at 600 °C for 1 h in ultrahigh vacuum before irradiation does not result in an increase in the D peak. Irradiation of SWCNTs that are preheated in vacuum and then exposed to air or gases results in an increase in the D peak, suggesting that adsorbates play a role in the increase in the D peak. Small diameter SWCNTs that are not preheated or preheated and then exposed to air show a significant increase in the D and G bands after irradiation. X-ray photoelectron spectroscopy shows no chemical shifts in the C 1s peak of SWCNTs that have been irradiated versus SWCNTs that have not been irradiated, suggesting that chemisorption of adsorbates is not responsible for the increase in the D peak.

The compositional phases of ion beam synthesized Fe–Si structures at two high fluences (0.50 × 1017 atoms/cm2 and 2.16 × 1017 atoms/cm2) were analyzed using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The distribution of Fe implanted in Si was simulated using a dynamic simulation code (TRIDYN) incorporating target sputtering effects. The Fe depth profiles in the Si matrix were confirmed with Rutherford backscattering spectrometry (RBS) and XPS depth profiling using Ar-ion etching. Based on XPS binding energy shift and spectral asymmetry, the distribution of stable Fe–Si phases in the substrate was analyzed as a function of depth. Results indicate Fe implantation with a fluence of 0.50 × 1017 atoms/cm2 and subsequent thermal annealing produce mainly the β-FeSi2 phase in the whole thickness of the implanted region. But for the samples with a higher fluence Fe implantation, multiple phases are formed. Significant amount of Fe3Si phase are found at depth intervals of 14 nm and 28 nm from the surface. Initially, as-implanted samples show amorphous Fe3Si formation and further thermal annealing at 500 °C for 60 min formed crystalline Fe3Si structures at the same depth intervals. In addition, thermal annealing at 800 °C for 60 min restructures the Fe3Si clusters to form FeSi2 and FeSi phases.

A single phase polycrystalline β-FeSi2 layer has been synthesized at the near surface region by implantation in Si(1 0 0) of a high fluence (∼1017 atoms/cm2) of 50 keV Fe ions and subsequent thermal annealing in vacuum at 800 °C. The depth profile of the implanted Fe atoms in Si(1 0 0) were simulated by the widely used transportation of ions in matter (TRIM) computer code as well as by the dynamic transportation of ions in matter code (T-DYN). The simulated depth profile predictions for this heavy ion implantation process were experimentally verified using Rutherford Backscattering Spectrometry (RBS) and X-ray Photoelectron Spectroscopy (XPS) in combination with Ar-ion etching. The formation of the β-FeSi2 phase was monitored by X-ray diffraction measurements. The T-DYN simulations show better agreement with the experimental Fe depth profile results than the static TRIM simulations. The experimental and T-DYN simulated results show an asymmetric distribution of Fe concentrated more toward the surface region of the Si substrate.

Chemical and electronic properties of ion beam synthesized Fe-Si binary structures are studied using X-ray photoelectron spectroscopy binding energy analysis. Ferromagnetic Fe-Si (Fe3Si) binary structure formation is enhanced in the ion-beam synthesis process by applying an in situ external magnetic field parallel to the Si substrate during the Fe implantation. Core-level analysis shows features corresponding to chemical environments of different Fe-Si phases. Fe 2p3/2 and Fe 3s peaks were analyzed, considering peak position, symmetry, and splitting. The ferromagnetic Fe3Si phase shows a highly asymmetric 2p3/2 peak at 706.6 eV and peak splitting in the 3s peak due to the exchange interaction with unfilled 3d electrons in the valance band. In contrast, the Si core-level did not show any significant features leading to the identification of Fe-Si binary compounds. The Si 2p peak showed a constant 0.2 eV peak shift toward the high-energy side compared to the elemental Si. Further valance band spectra reveal distinct features to help identify the Fe3Si phase. In general, core and valance band features of Fe-Si binary compounds provided definitive information about Fe3Si phase identification and its electronic structure with direct evidence of the exchange interaction, which occurs between core levels, valance band, and the unfilled 3d shell.Chemical and electronic properties of ion beam synthesized Fe-Si binary structures are studied using X-ray photoelectron spectroscopy binding energy analysis. Ferromagnetic Fe-Si (Fe3Si) binary structure formation is enhanced in the ion-beam synthesis process by applying an in situ external magnetic field parallel to the Si substrate during the Fe implantation. Core-level analysis shows features corresponding to chemical environments of different Fe-Si phases. Fe 2p3/2 and Fe 3s peaks were analyzed, considering peak position, symmetry, and splitting. The ferromagnetic Fe3Si phase shows a highly asymmetric 2p3/2 peak at 706.6 eV and peak splitting in the 3s peak due to the exchange interaction with unfilled 3d electrons in the valance band. In contrast, the Si core-level did not show any significant features leading to the identification of Fe-Si binary compounds. The Si 2p peak showed a constant 0.2 eV peak shift toward the high-energy side compared to the elemental Si. Further valance band spectra reveal...

Transition-metal doped Indium Phosphide (InP) has been studied over several decades for utilization in optoelectronics applications. Recently, interesting magnetic properties have been reported for metal clusters formed at different depths surrounded by a high quality InP lattice. In this work, we have reported accumulation of Ni atoms at various depths in InP via implantation of Ni- followed by H– and subsequently thermal annealing. Prior to the ion implantations, the ion implant depth profile was simulated using an ion-solid interaction code SDTrimSP, incorporating dynamic changes in the target matrix during ion implantation. Initially, 50 keV Ni- ions are implanted with a fluence of 2 × 1015 atoms cm-2, with a simulated peak deposition profile approximately 42 nm from the surface. 50 keV H- ions are then implanted with a fluence of 1.5 × 1016 atoms cm-2. The simulation result indicates that the H- creates damages with a peak defect center ~400 nm below the sample surface. The sample has been annealed at 50°C in an Ar rich environment for approximately 1hr. During the annealing, H vacates the lattice, and the formed nano-cavities act as trapping sites and a gettering effect for Ni diffusion into the substrate. The distribution of Ni atoms in InP samples are estimated by utilizing Rutherford Backscattering Spectrometry and X-ray Photoelectron Spectroscopy based depth profiling while sputtering the sample with Ar-ion beams. In the sample annealed after H implantation, the Ni was found to migrate to deeper depths of 125 nm than the initial end of range of 70 nm.

The quest for increased efficiency of solar cells has driven the research in synthesizing photovoltaic cells involving Si based materials. The efficiency of solar cells involving crystalline Si is stalled around 25% for the last decade. Recently Shi et al. had shown that light trapping can be enhanced by fabricating double layers of Ag nanoparticles in silicon based materials. The light trapping is critically important in a photo devices such as solar cells in order to increase light absorption and efficiency. In the present work, we report enhancement in the absorption of light in Ag ion implanted Si substrates. Multiple low energies Ag ions, ranging from ∼80 keV to ∼30 keV, with different fluences ranging from ∼1 × 1016 to ∼1 × 1017 atoms/cm2 were sequentially implanted into commercially available Si (100) substrates followed by post-thermal annealing to create different sizes of Ag nanoclusters (NC) at different depths in the top 100 nm of the Si. The absorbance of light is increased in Ag implanted Si...

This paper investigates the synthesis of Ag NCs in Si(100) substrate by implanting multiple energies and fluences of Ag ions and subsequent thermal annealing.

The Ion Beam Modification and Analysis Laboratory (IBMAL) at the University of North Texas includes several accelerator facilities with capabilities of producing a variety of ion beams from tens of keV to several MeV in energy. The four accelerators are used for research, graduate and undergraduate education, and industrial applications. The NEC 3MV Pelletron tandem accelerator has three ion sources for negative ions: He Alphatross and two different SNICS-type sputter ion sources. Presently, the tandem accelerator has four high-energy beam transport lines and one low-energy beam transport line directly taken from the negative ion sources for different research experiments. For the low-energy beam line, the ion energy can be varied from ∼20 to 80 keV for ion implantation/modification of materials. The four post-acceleration beam lines include a heavy-ion nuclear microprobe; multi-purpose PIXE, RBS, ERD, NRA, and broad-beam single-event upset; high-energy ion implantation line; and trace-element accelerator mass spectrometry. The NEC 3MV single-ended Pelletron accelerator has an RF ion source mainly for hydrogen, helium and heavier inert gases. We recently installed a capacitive liner to the terminal potential stabilization system for high terminal voltage stability and high-resolution microprobe analysis. The accelerator serves a beam line for standard RBS and RBS/C. Another beamline for high energy focused ion beam application using a magnetic quadrupole lens system is currently under construction. This beam line will also serve for developmental work on an electrostatic lens system. The third accelerator is a 200 kV Cockcroft-Walton accelerator with an RF ion source. The fourth accelerator is a 2.5 MV Van de Graaff accelerator, which was in operation for last several decades is currently planned to be used mainly for educational purpose. Research projects that will be briefly discussed include materials synthesis/modification for photonic, electronic, and magnetic applications, surface sputtering and micro-fabrication of materials, development of high-energy ion microprobe systems, and educational and outreach activities.

The University of North Texas (UNT) Ion Beam Modification and Analysis Laboratory (IBMAL) has four particle accelerators including a National Electrostatics Corporation (NEC) 9SDH-2 3 MV tandem Pelletron, a NEC 9SH 3 MV single-ended Pelletron, and a 200 kV Cockcroft-Walton. A fourth HVEC AK 2.5 MV Van de Graaff accelerator is presently being refurbished as an educational training facility. These accelerators can produce and accelerate almost any ion in the periodic table at energies from a few keV to tens of MeV. They are used to modify materials by ion implantation and to analyze materials by numerous atomic and nuclear physics techniques. The NEC 9SH accelerator was recently installed in the IBMAL and subsequently upgraded with the addition of a capacitive-liner and terminal potential stabilization system to reduce ion energy spread and therefore improve spatial resolution of the probing ion beam to hundreds of nanometers. Research involves materials modification and synthesis by ion implantation for photonic, electronic, and magnetic applications, micro-fabrication by high energy (MeV) ion beam lithography, microanalysis of biomedical and semiconductor materials, development of highenergy ion nanoprobe focusing systems, and educational and outreach activities. An overview of the IBMAL facilities and some of the current research projects are discussed.