Chunyu Tan

Range distributions of ion‐implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe

Depth profiles of ion‐implanted fluorine in Hg1−xCdxTe, CdTe, and Pb1−xSnxTe have been measured by use of the 19F(p,αγ)16O resonance nuclear reaction at 872.1 keV with width Γ=4.2 keV. In order to obtain the true range distribution of implanted fluorine from the experimental excitation yield curve, a convolution calculation method is presented, from which the range distribution parameters such as the average projected range RP, the projected range straggling ΔRP and the skewness of the projected range distribution SK were obtained. These experimental range parameters were compared with those obtained by a theoretical calculation and by use of the trim89 program, and shows that for all the materials studied here the experimental RP values agree with the theoretical and the trim values very well but the experimental range straggling ΔRP are larger than those obtained by the theoretical calculation and the trim89. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.

Laser ablation of Si, Ge, ZrO2 and Cu in air

Si, Ge, ZrO2 and Cu were irradiated by air by 1.06 mu m 10 ns laser pulses with a high intensity of 6.4*109 W cm-2. Detailed scanning electron microscopy (SEM) and ablation crater profile measurements were made. The results indicated that the ablation rates of these materials under intense pulsed laser irradiation are quite high. The refractory oxide ZrO2 has the highest material removal rate. Evidence of liquid material flushed out of the ablation craters was observed for all the materials studied with the exception of Cu. Gas dynamic velocities of transient thermal vaporization were calculated using self-similar solutions of the gas dynamic equations. Using these parameters, material removal rates were calculated and the results compared with the experimentally measured values. Possible ablation mechanisms of these materials under the irradiation conditions used in the present work were discussed.

Laser ablation of copper and aluminium in air

The ablation behavior of copper alloy and aluminium irradiated in air by 1.06 μm, 10 ns pulsed laser with power density of 6.4×109W/cm2 was studied using scanning electron microscopy (SEM), MCS-RBS and X-ray microanalysis. Evidence of bulk vaporization via bubble formation was observed for the copper alloy under the laser irradiation. Silver-enrichment microregions were found in the ablation crater created by the laser shots on the copper alloy sample. Material removal rates of these materials were determined by crater shape-profile measurement. Using self-similar solutions of the gas-dynamic equations, gas-dynamic parameters of the vaporization waves are obtained. These parameters are used to calculate material removal rates and impulse coupling coefficients of these materials under the pulsed laser irradiation. The calculated mass removal rates and the coupling coefficients are compared with the corresponding experimentally determined values. The surface kinetic energy of the irradiated area on the Al sample is estimated. Possible mechanisms for laser ablation of the materials under study are discussed.

Depth profiles of implanted 18F, 79Br, and 132Xe in silicon in the energy range 85–600 keV

Abstract The RBS technique and 19 F(p, αγ) 16 O resonance nuclear reaction at 872.1 keV, with Γ = 4.2 keV, were used to measure the depth profiles of implanted 79 Br, 132 Xe and 19 F in silicon samples. A special convolution procedure was used to extract the depth profiles from the RBS spectra and the experimental excitation yield curves. The range parameters, R p and Δ R p obtained in thi experiment were compared with theoretical calculations.

Depth profiles of ion‐implanted fluorine in tin‐oxide films prepared by atmospheric‐pressure chemical vapor deposition

Depth profiles of fluorine in 19F+‐implanted tin‐oxide films have been accurately measured using 19F(p,αγ)16O resonance nuclear reactions at ER=872.1 keV and ER=340.46 keV. A proper deconvolution calculation method was used to extract the true range distribution of implanted fluorine from the experimental excitation yield curves. The range distribution parameters, RP and ΔRp, were thereby obtained and were compared with those obtained by Monte Carlo simulations. The experimental Rp values agree with the Monte Carlo simulation values very well, while the experimental ΔRp values are larger than those obtained theoretically. This phenomenon may be attributed to the enhanced diffusion during the ion implantation.

ENERGY SPECTRA OF HE+ IONS PENETRATING THICK BIOLOGICAL TARGETS

Abstract Energy spectra of 500 keV–1MeV He+ ion penetrating 50 μ m – 100 μ m thick seed coat of maize, fruit peel of grape and of tomato, are measured. The results indicate that these thick biological targets, as seen by the penetrating ions, are inhomogeneous, and there are open paths, along which the incident ions can penetrate the targets easily. While most of the incident ions are stopped in the targets, some of the penetrating ions only lose a small fraction of their initial incident energy. The penetration energy spectra show a pure electronic stopping feature. Transmission electron microscope (TEM) micrographs taken from these samples with thickness of 30 μ m indicate that 150 keV electron beam from the TEM can penetrate the thick samples to give very good images with clear contrast. The electronic structures of β−1,4 glucosan molecular chains, which is deemed as the most important constituent of the cell walls of seed coats and peels of fruits, are calculated to show the possible open-path directions which exist in biological samples.

Self-assembly growth of single-wall carbon nanotubes

Abstract The growth of single-wall carbon nanotubes through adduction of small carbon clusters is studied using a molecular-dynamics simulation method. The perfection of the tubes grown depends on the collisional direction, the growth temperature, and the cluster species involved. Narrow single-wall carbon nanotubes can grow without existence of catalysts under controlled conditions. C2, colliding with the side wall of the tubes, can be assembled into the network forming localized defects during annealing.

Fusion of two C60 molecules and fragmentation of the fusion product caused by C60C60 collisions

Abstract Molecular fusion of two C60 molecules in C60C60 collisions and the stability of the reaction products are studied using molecular dynamics simulations. It shows that the shape of the fusion product depends on the collision energy and the classical impact parameter between the mass centres of the two colliding partners. At impact parameter b = 0, two C60 molecules, colliding at energy E0 = 50 eV in the laboratory frame, coalesce to form a very stable dumbbell-shaped C120 cluster, which never fragments. When the incident energy increases to 400 eV, the two C60 molecules fuse to form a common larger C120 cluster, completely losing the geometry of the original C60 cages. However, the C120 formed in this case is highly deformed and the intrinsic ‘heat’ energy stored in it is increasing gradually until the ‘temperature’ of the cluster goes high enough to result in a fragmentation process, which starts with a sequential evaporation of C-dimers, C-trimers, individually C atoms and other small C clusters. Collisions of C60 molecules at larger impact parameters cause rotating motion of the coalescence products. All these coalescence reactions induced by the collisions of C60 molecules are shown to have deep inelastic behaviour.

Electronic stopping powers of Au, Ag, Cu, Pd and Co metals for 19F ions at low velocity

Abstract Electronic stopping cross sections for 80–350 keV 19 F ions in Au, Ag, Cu, Pd and Co films were obtained by range measurement. Depth profiles of 19 F in these materials were measured by 19 F( p , αγ ) 16 O resonance nuclear reaction. A proper deconvolution program was used to extract the depth distribution parameters from the experimental excitation yield curves. The electronic stopping powers were derived through fitting the projected ranges simulated by TRIM/XLL code to the experimentally determined projected ranges. It is shown that the electronic stopping cross sections obtained in this work agree well with those calculated by using TRIM96 as well as previous experimental data and can be described by the four-parameter formulae.

An investigation of range distribution parameters of implanted 19F ions in tantalum

Abstract Depth profiles of fluorine in 19 F + implanted tantalum have been accurately measured using the 19 F(p,αγ) 16 O resonance nuclear reaction at E R = 872.1 keV . In order to extract the range distribution of implanted fluorine from the experimental excitation yield curve, a proper convolution calculated method is presented, from which the range distribution parameters, such as the average projected range R p , the projected range straggling Δ R p , and the skewness of the range distribution SK, were obtained.