Laser ablated carbon nanodots for light emission

The synthesis of fluorescent carbon dots-like nanostructures (CNDs) obtained through the laser ablation of a carbon solid target in liquid environment is reported. The ablation process was induced in acetone with laser pulses of 1064, 532, and 355 nm under different irradiation times. Close-spherical amorphous CNDs with sizes between 5 and 20 nm, whose abundance strongly depends on the ablation parameters were investigated using electron microscopy and was confirmed using absorption and emission spectroscopies. The π- π* electronic transition at 3. 76 eV dominates the absorption for all the CNDs species synthesized under different irradiation conditions. The light emission is most efficient due to excitation at 3.54 eV with the photoluminescence intensity centered at 3. 23 eV. The light emission from the CNDs is most efficient due to ablation at 355 nm. The emission wavelength of the CNDs can be tuned from the near-UV to the green wavelength region by controlling the ablation time and modifying the ablation and excitation laser wavelength

Redistribution of Nickel Ions Embedded within Indium Phosphide Via Low Energy Dual Ion Implantations

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

Simultaneous measurement of the average ion-induced electron emission yield and the mean charge for isotachic ions in carbon foils

Article discussing the simultaneous measurement of the average ion-induced electron emission yield and the mean charge for isotachic ions in carbon foils

Mechanism for etching of exfoliated graphene on substrates by low-energy electron irradiation from helium plasma electron sources

Article investigating the mechanism for etching of exfoliated graphene multilayers on SiO₂ by low-energy (50 eV) electron irradiation using He plasma systems for electron sources

Experimental evidence for a discrete transition to channeling for 1.0-MeV protons in Si〈100〉

This article discusses experimental evidence for a discrete transition to channeling for 1.0-MeV protons in Si〈100〉

Introduced Mammalian Predators Induce Behavioural Changes in Parental Care in an Endemic New Zealand Bird

The introduction of predatory mammals to oceanic islands has led to the extinction of many endemic birds. Although introduced predators should favour changes that reduce predation risk in surviving bird species, the ability of island birds to respond to such novel changes remains unstudied. We tested whether novel predation risk imposed by introduced mammalian predators has altered the parental behaviour of the endemic New Zealand bellbird (Anthornis melanura). We examined parental behaviour of bellbirds at three woodland sites in New Zealand that differed in predation risk: 1) a mainland site with exotic predators present (high predation risk), 2) a mainland site with exotic predators experimentally removed (low risk recently) and, 3) an off-shore island where exotic predators were never introduced (low risk always). We also compared parental behaviour of bellbirds with two closely related Tasmanian honeyeaters (Phylidonyris spp.) that evolved with native nest predators (high risk always). Increased nest predation risk has been postulated to favour reduced parental activity, and we tested whether island bellbirds responded to variation in predation risk. We found that females spent more time on the nest per incubating bout with increased risk of predation, a strategy that minimised activity at the nest during incubation. Parental activity during the nestling period, measured as number of feeding visits/hr, also decreased with increasing nest predation risk across sites, and was lowest among the honeyeaters in Tasmania that evolved with native predators. These results demonstrate that some island birds are able to respond to increased risk of predation by novel predators in ways that appear adaptive. We suggest that conservation efforts may be more effective if they take advantage of the ability of island birds to respond to novel predators, especially when the elimination of exotic predators is not possible

Sputtering by Multiply-Charged Ions, and Preferential Sputtering of Isotopic Mixtures

Collector-type experiments have been conducted to investigate two different aspects of sputtering induced by keV ions. The first study looked for possible ejection mechanisms related to the primary charge state of the projectile. Targets of CsI and LiNbO₃ were bombarded with 48 keV Arq+, and a Au target was bombarded with 60 keV Arq+, for q = 4, 8, and 11. The collectors were analyzed using heavy-ion Rutherford backscattering spectroscopy to determine the differential angular sputtering yields; these and the corresponding total yields were examined for variations as a function of projectile charge state. For the Au target, no significant changes were seen, but for the insulating targets slight (~10%) enhancements were observed in the total yields as the projectile charge state was increased from 4+ to 11+. In the second investigation, artificial ⁹²Mo/¹⁰⁰Mo targets were bombarded with 5 and 10 keV beams of Ar⁺ and Xe⁺ to study the isotopic fractionation of sputtered neutrals as a function of emission angle and projectile fluence. Using secondary ion mass spectroscopy to measure the isotope ratio on the collectors, material ejected into normal directions at low bombarding fluences (~ 10¹⁵ ions cm⁻²) was found to be enriched in the light isotope by as much as ~70‰ compared to steady state. Similar results were found for secondary Mo ions sputtered by 14.5 keV O⁻. For low-fluence 5 keV Xe⁺ bombardment, the light-isotope enrichment at oblique angles was ~20‰ less than the corresponding enrichment in the normal direction. No angular dependence could be resolved for 5 keV Ar⁺ projectiles at the lowest fluence. The above fractionation decreased to steady-state values after bombarding fluences of a few times 10¹⁶ ions cm⁻², with the angular dependence becoming more pronounced. The fractionation and total sputtering yield were found to be strongly correlated, indicating that the above effects may have been related to the presence of a modified target surface layer. The observed effects are consistent with other secondary ion measurements and multiple-interaction computer simulations, and are considerably larger than predicted by existing analytic theory.</p

University Scholars Day

This paper discusses research on modeling and optimization of deflection slits for fast-pulsing of a low energy ion beam. The authors also investigate simulated slit configurations that reduce the length of the fields along the beam axis, thus optimizing the pulsing mechanism

University Scholars Day

Presentation for the 2006 University Scholars Day at the University of North Texas discussing research on modeling and optimization of deflection slits for fast-pulsing of a low energy ion beam

The angular distribution of atoms sputtered from a Ga-In eutectic alloy target

Angular distributions of sputtered atoms have been obtained for 3, 25, and 50 keV Ar+ bombardment of a liquid Ga-In eutectic alloy target. Sputtered material was collected on graphite foils which were subsequently analyzed by Rutherford backscattering spectroscopy, and the resulting distributions were fit by a functional form, N (θ) α. cos^nθ. For each energy, the angular distribution of sputtered In atoms was overcosine, with n_(In) ≈ 1.8 ±0.1. The distributions of the sputtered Ga atoms were sharper, varying from n_(Ga) ≈ 3.2 ± 0.2 at 25 and 50 keV, to n_(Ga) = 4.9 ± 0.3 at 3 keV. A comparison of the sputtered flux composition with the alloy surface composition profile gives F_1, the fraction of sputtered atoms originating from the first atomic layer. The fraction was found to be f_1 = 0.87 ± 0.01 for 25 and 50 keV bombardment, and increased to 0.94 ± 0.01 at 3 keV. The variations of n_(ga), and F_1 with projectile energy may be the result of a decrease in the average recoil-atom energy for the 3 keV bombardment. The large values found for F_1 support a prediction that the sputtered-atom escape depth is determined by the elastic-collision mean free path of recoil atoms