Retrieval of currents of multiply charged ions emitted from laser-produced carbon plasma

The emission of ions from laser-produced carbon plasmas is investigated by a deconvolution of ion collector signals. The deconvolution is based on the use of Kelly and Dreyfus function expressing the time-resolved ion current to recover hidden peaks in an ion collector signal. The parameters of recovered C ^q+ (1?≤?q?≤?6) currents make possible the quantification of properties of laser-produced plasmas. The drift and peak velocities of C ^q+ ions, the abundance of ions and the plasma temperature are presented in the dependence on focused laser beam energy. The carbon plasma was generated employing either single 9-ns pulses of second harmonics (532 nm) of Nd:YAG laser or pulses repeated at a stable repetition rate of 30 Hz.     

Scanning near-field cathodoluminescence microscopy of an Si+ implanted and thermally annealed SiO2 layer

A scanning near-field cathodoluminescence microscope (SNCLM) is successfully used to image the cathodoluminescence of an Si⁺ implanted and thermally annealed submicronic SiO₂ layer. Owing to the subwavelength resolution of the system a “cross-sectional” cathodoluminescence image was obtained. The intensity image profile shows that sample luminescence results from the whole SiO₂ layer confirming a preceding electroluminescence study. Sample luminescence is attributed to point defects generated into the whole SiO₂ layer during Si⁺ ion implantation and thermal annealing.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Reflectivity modification of polymethylmethacrylate by silicon ion implantation

The effect of silicon ion implantation on the optical reflection of bulk polymethylmethacrylate (PMMA) was examined in the visible and near UV. A low-energy (30 and 50 keV) Si⁺ beam at fluences in the range from 10¹³ to 10¹⁷ cm⁻² was used for ion implantation of PMMA. The results show that a significant enhancement of the reflectivity from Si⁺-implanted PMMA occurs at appropriate implantation energy and fluence. The structural modifications of PMMA by the silicon ion implantation were characterized by means of photoluminescence and Raman spectroscopy. Formation of hydrogenated amorphous carbon (HAC) layer beneath the surface of the samples was established and the corresponding HAC domain size was estimated.     

Au5+ ion implantation induced structural phase transitions probed through structural,microstructural and phonon properties in BiFeO3 ceramics,using synergistic ion beam energy

Implanted Au⁵⁺-ion-induced modification in structural and phonon properties of phase pure BiFeO₃ (BFO) ceramics prepared by sol–gel method was investigated. These BFO samples were implanted by 15.8?MeV ions of Au⁵⁺ at various ion fluence ranging from 1?×?10¹⁴ to 5?×?10¹⁵?ions/cm². Effect of Au⁵⁺ ions’ implantation is explained in terms of structural phase transition coupled with amorphization/recrystallization due to ion implantation probed through XRD, SEM, EDX and Raman spectroscopy. XRD patterns show broad diffuse contributions due to amorphization in implanted samples. SEM images show grains collapsing and mounds’ formation over the surface due to mass transport. The peaks of the Raman spectra were broadened and also the peak intensities were decreased for the samples irradiated with 15.8?MeV Au⁵⁺ ions at a fluence of 5?×?10¹⁵?ion/cm². The percentage increase/decrease in amorphization and recrystallization has been estimated from Raman and XRD data, which support the synergistic effects being operative due to comparable nuclear and electronic energy losses at 15.8?MeV Au⁵⁺ ion implantation. Effect of thermal treatment on implanted samples is also probed and discussed.     

Time evolution of the infrared laser ablation plasma plume of SiO

The spatio-temporal evolution of the silicon monoxide SiO plasma produced by a high-power CO₂ pulsed laser has been investigated using optical emission spectroscopy (OES) and imaging methods. The formed plasma was found to be strongly ionized, yielding Si⁺, O⁺, Si²⁺, O²⁺ and Si³⁺ species, rich in neutral silicon and oxygen atoms, and very weak molecular bands of SiO time-integrated and time-resolved two-dimensional OES plasma profiles were recorded as a function of emitted wavelength and distance from the target. The temporal behavior of specific emission lines of Si, Si⁺, O⁺, Si²⁺ and O²⁺ was characterized. The results show a faster decay of O²⁺ and Si²⁺ than that of O⁺, Si⁺ and Si. The Stark broadening of isolated single-ionized silicon emission lines was employed for deducing the electron density during the plasma expansion. The relative intensities of two Si²⁺ lines were used to calculate the time evolution of the plasma temperature.     

Picosecond fluorescence studies by intracavity gain spectroscopy in a modelocked dye laser

This article presents measurements which combine modelocking technique with intracavity spectroscopy. To test this approach, a sample (10^–5 m ethanolic solution of 1,4-dihydroxyanthranquinone) was inserted in a modelocked Ar⁺ ion laser and probed by intracavity pulses of a synchronously pumped dye laser. The probing of the sample results in an amplification of the dye laser output. Maximum output was measured if the pulses of the dye laser temporally overlapped with those of the Ar⁺ ion laser inside the sample. Under this condition, the spectral laser intensity was shaped by the spectrum of stimulated fluorescence which originated from a molecular vibronic state populated by pump laser excitation.Presented at LASERION '91, June 12–14, 1991, München (Germany)     

High resolution laser spectroscopy of metallic atoms and molecules: Storage of singly and doubly charged ions transferred from externally generated laser plasmas

A radio-frequency (RF) ion trap has been constructed for high resolution laser spectroscopy of metallic ions. Ions in externally generated laser plasma have been directly introduced into the RF ion trap. An Nd:YAG laser is used to vaporize and ionize sample metals placed behind a ring electrode. Both hyperbolic and cylindrical electrodes are successfully used for confinement of the ions. Trapped ions are detected either with a quadrupole mass spectrometer or with a photomultiplier for the measurement of laser-induced fluorescence. Metallic ions such as Ca⁺, Ba⁺, La⁺, Nd⁺, Tm⁺, Lu⁺, and Ta⁺ have been confined for the time range of several to 20 minutes in the presence of He buffer gas, and a doubly charged ion Ba²⁺ for several seconds. Some ions like Nd⁺, Lu⁺, Hf⁺, and Ta⁺ are found to be highly reactive with background gaseous molecules.     

Effect of high doses on the Si <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> x-ray emission spectra of silicon implanted with iron ions under steady-state conditions

The effect of high doses on p-and n-type silicon samples implanted with Fe⁺ ions under steady-state conditions (implantation energy, 100 keV; ion current density, 0.6–0.8 μA/cm²; irradiation dose, 10¹⁴–10¹⁶ ions/cm²) is investigated using Si L _{2, 3} x-ray emission spectroscopy (the 3d3s → 2p electronic transition). An analysis of the Si L x-ray emission spectra of the silicon samples is performed by comparison with the spectra of reference materials and the spectra of silicon samples implanted with Fe⁺ ions in a pulsed mode. The Si L x-ray emission spectra are simulated by the molecular dynamics and full-potential linearized augmented-plane-wave (FLAPW) methods. It is revealed that the effect of high doses under steady-state conditions of Fe⁺ ion implantation into the semiconductor crystal matrix exhibits specific features: the disordering of the structure and partial amorphization of the sample from the surface deep into the bulk are more pronounced than those observed under conditions of pulsed ion implantation, although virtually no recrystallization of the sample at the threshold dose occurs. The most probable origins and mechanisms of the effect of high doses on the samples under investigation are discussed.     

Photoluminescence studies of Si nanocrystals

Summary We report room temperature time-resolved photoluminescence (PL) and temperature dependence of continuous wave (cw) PL studies of high fluence (from 3·10¹⁶ to 3·10¹⁷ cm⁻²) Si⁺-implanted thermal SiO₂ layers after annealing at high temperature (T=1000°C). Such measurements were related to TEM analysis of samples. Nancocrystals were observed at TEM only a samples implanted at higher fluence. In these samples a near infrared PL signal peaked at approximately 1.5 eV with decay time of about 100 μs is present. Besides, in all samples a light emission is present in the green region of the spectrum. The intensity of the emission shows large variations with ion fluence, and is characterized by 0.4, 2 and 7 ns decay times. Paper presented at the III INSEL (Incontro Nazionale sul Silicio Emettitore di Luce) Torino, 12–13 October 1995.     

Amorphization of Si (100) under O implantation studied by spectroscopic ellipsometry

The amorphization of crystalline Si (100) under 125 keV O⁺ ion implantation is investigated in the fluence range 1×10¹⁴ ions/cm² to 1×10¹⁶ ions/cm². The microstructure of the O⁺ implanted Si is modeled from ellipsometric data using a two phase, multilayer model within Bruggeman effective medium approximation (BEMA). The transition from the crystalline to the amorphous phase is found to be smooth and progressive. From a detailed analysis of the moments of the dielectric spectra and laser Raman spectroscopy, we infer that the amorphization occurs through a progressive disruption of long-range order caused by the overlap of amorphous nanozones. The dielectric spectrum of the fully amorphous phase is characterized using the Forouhi-Bloomer interband model.     

Continuous-wave laser oscillation at 1.06 µm in silicon ion-implanted Nd:YVO<Subscript>4</Subscript> planar waveguide

This work, for the first time to our knowledge, reports continuous-wave laser oscillation at 1.06 μm in Nd:YVO₄ planar waveguide formed by 3.0 MeV Si⁺ ion implantation at a dose of 1 × 10¹⁵ ions/cm² at room temperature. The effective refractive indices of the waveguide propagation modes were measured by using a prism-coupling method after the annealing at 240°C for 60 min in air. The performance of the waveguide laser has been studied in terms of the threshold pump power and slope efficiency. The laser outputs show a very high stability operating in cw regime at room temperature.     

Femtosecond ionization and fragmentation of free silicon nanoparticles

Femtosecond-laser spectroscopy is used to study the photoionization and photofragmentation of large neutral silicon clusters in a beam. Silicon clusters Si_n with sizes up to n≈6000, corresponding to nanoparticles with diameters up to 6 nm, are generated in a laser vaporization source. Nanosecond- and femtosecond-laser ionization are employed to characterize the free silicon nanoparticles. Excitation with intense femtosecond-laser pulses leads to prompt formation of doubly and triply charged Si_n clusters. Additionally, strong fragmentation of charged clusters occurs by Coulomb explosion, resulting in high released kinetic energies. Multiply charged atoms up to Si⁴⁺ with initial kinetic energies in the range of 500 eV are observed for laser intensities of about 10¹³ W/cm². Pump–probe spectroscopy yields decay times of the intermediate resonances of the nanoparticles. Received: 22 January 2000 / Published online: 7 August 2000     

Ionizing Dose Effect of Thermal Oxides Implanted with Si^＋ Ions

Total ionizing dose effects of Si^＋ ion implanted thermal oxides are studied by 10keV x-ray irradiation. Photoluminescence （PL） method is engaged to investigate nanostructures of samples. Ar^＋ implanted samples are also studied by the same way to provide a comparison. The results show that Si^＋ implantation following with high temperature annealing can significantly reduce the radiation induced flatband shift, which is caused by net posi- tive charge accumulation in oxides. This reduction is attributed to the formation of Si nanoscale structures. Ar^＋ implantation is also found to reduce the radiation induced flatband shift, while it is different that the reduction with Si^＋ implantation shows little dependence on implant dose of Ar^＋ ions. This is explained by possible increase of recombination centres.     

Sequence of structural-phase states during implantation of C+, N+, and Si+ ions into molybdenum

The sequence of structural-phase changes in the surface layer of molybdenum during pulsed implantation of N⁺, C⁺, and Si⁺ ions has been studied. At radiation doses 5·10¹⁶ cm^–2 we detected qualitatively similar structural-phase transformations with the formation of highly dispersed secondary-phase particles (nitrides, carbides, and silicides), dislocations, point defects, and clusters of defects. At radiation doses (1–2)·10¹⁷ cm^–2 implantation of C⁺ and Si⁺ ions causes amorphization of the surface layer; nitrogen implantation is accompanied by the formation of continuous layers of the nitride phase on the surface.Siberian Physicotechnical Institute at the V. D. Kuznetsov State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 3–9, February, 1994.     

Damage formation in Ge during Ar and He implantation at 15 K

Ar⁺ and He⁺ ions were implanted into Ge samples with (1 0 0), (1 1 0), (1 1 1) and (1 1 2) orientations at 15 K with fluences ranging from 1×10¹¹ to 1×10¹⁴ cm⁻² for the Ar⁺ ions and fluences ranging from 1×10¹² to 6×10¹⁵ cm⁻² for the He⁺ ions. The Rutherford backscattering (RBS) technique in the channelling orientation was used to study the damage built-up in situ. Implantation and RBS measurements were performed without changing the target temperature. The samples were mounted on a four axis goniometer cooled by a close cycle He cryostat. The implantations were performed with the surface being tilt 7° off the ion beam direction to prevent channelling effects. After each 300 keV Ar⁺ and 40 keV He⁺ implantation, RBS analysis was performed with 1.4 MeV He⁺ ions.For both the implantation ions, there is about no difference between the values found for the damage efficiency per ion for the four different orientations. This together with the high value (around 5 times higher than that found in Si), gives rise to the assumption of amorphous pocket formation per incident ion, i.e. direct impact amorphization, already at low implantation fluences. At higher fluences, when collision cascades overlap, there is a growth of the already amorphized regions.     

The generation,detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate

The generation, detection and measurement of laser-induced carbon plasma ions and their implantation effects on brass substrate have been investigated. Thomson parabola technique was employed to measure the energy and flux of carbon ions. The magnetic field of strength 80?mT was applied on the graphite plasma plume to provide an appropriate trajectory to the generated ions. The energy of carbon ions is 678?KeV for laser fluence of 5.1?J/cm² which was kept constant for all exposures. The flux of ions varies from 32?×?10¹¹ to 72?×?10¹⁴?ions/cm² for varying numbers of laser pulses from 3000 to 12,000. In order to explore the ion irradiation effects on brass, four brass substrates were irradiated by carbon ions of different flux. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) are used to analyze the surface morphology and crystallographic structure of ion-implanted brass, respectively. SEM analysis reveals the formation and growth of nano-/micro-sized cavities, pores and pits for the various ion flux for varying numbers of laser pulses from 3000 to 12,000. By increasing ion flux by increasing the number of pulses up to 9000 shots, the dendritic structures initiate to grow along with cavities and pores. At the maximum ion flux for 12,000 shots, the unequiaxed dendritic structures become distinct and the distance between the dendrites is decreased, whereas cavities, pores and pits are completely finished. The XRD analysis reveals that a new phase of ZnC (0012) is formed in the brass substrate after ion implantation. Universal tensile testing machine and Vickers microhardness tester are used to explore the yield stress, ultimate tensile strength and microhardness of ion-implanted brass substrate. The mechanical properties monotonically increase by increasing the ion flux. Variations in mechanical properties are correlated with surface and structural modifications of brass.     

The behaviour of mosaic blocks and electrical properties of polysilicon under ion implantation

Abstract

The change in microstrains ε, block sizes L and in the temperature dependences of conductivity of polysilicon with the grain size 30-40nm at N⁺, Ne⁺, P⁺ ion irradiation has been studied. It is shown that ε increases while L practically is not changing up to amorphization. The change in conductivity is governed by an increase in the density of states near the Fermi level and depends both on the damage rate for the given ions and their chemical activity.     

Optimum ion implantation and annealing conditions for stimulating secondary negative ion emission

The type, energy, ion dose, and heating temperature required to ensure a stable minimum work function of a surface in one experimental cycle (at least 2–3 min) are determined. Secondary ion mass spectrograms are recorded using Cs⁺, Ba⁺, and Ar⁺ ions. Cu, Al, and Mo samples are studied. The optimum ion implantation conditions and the activation temperature that provide a stable minimum work function of the sample surfaces are found. The samples implanted by Ba⁺ ions withstand higher temperature and current loads than the samples implanted by Cs⁺ ions. However, the work function in the case of Cs⁺ ions decreases stronger (to 1.9 eV). It is shown that neutral sputtered particles do not leave the surface at eφ ≤ 1.85–1.90 eV.     

预注入对Si1-xCx合金形成的影响

室温下在单晶Si中注入(0.6—1.5)at%的C原子,部分样品在C离子注入之前在其中注入²⁹Si⁺离子产生损伤,然后在相同条件下利用高温退火固相外延了Si_1-xC_x合金,研究了预注入对Si_1-xC_x合金形成的影响.如果注入C离子的剂量小于引起Si非晶化的剂量,在950℃退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇,难于形成Si_1-xC关键词： 离子注入 固相外延 1-xC_x合金')" href="#">Si_1-xC_x合金