Si Ion Beam Research Articles

A high sensitivity microbeam RBS setup for heavy elements implantation profiles analysis

This work presents a new setup that integrates heavy ion RBS with microbeam technology combined with high detection solid angle for the measurement of the depth profile and areal distribution of heavy elements in silicon using a Si microbeam. Focussed 2.4 MeV Si2+ ions were scanned over the frontal or lateral surface of silicon wafers to measure both the areal concentrations and depth profiles of all elements heavier than silicon. Tests were done on samples with Pt concentration range of 4 × 10 12–2 × 10 14 at/cm 3 that was diffused via the Pt-Silicide surface layer process from one lateral surface into the 400 µm thick Si wafers. It is important to note that employing a Si ion beam instead of the conventional He ion beam serves the purpose of not only increasing the backscattering cross section, as in well-established heavy element RBS, but also reducing pileup by eliminating scattering from the Si substrate, which is essential for sensitive analysis. This allows a significant increase in microbeam currents without increasing the count rate in large area detectors. A set of two large area PIN diodes (10x10 mm) were used in an optimized configuration resulting in 1,04 sr detection solid angle. Additionally, an appropriate microbeam collimator was used to shield the PIN diodes from events caused by forward scattering and scattering of the Si ion beam halo from different components in the reaction chamber. Lateral scans of the silicon wafer were performed by focussed Si ions, with ∼10 µm spot size and of the nA range beam currents. The RBS intensity maps containing the Pt depth profile were obtained with a sensitivity of 6.7 × 109 at/cm2.

60 MeV Si ion beam irradiation induced modifications in the structural and optical properties of Li doped NiO thin films

Li doped NiO films grown on FTO substrates through spin coating technique were irradiated using 60 MeV Si ions. The films were investigated via several approaches including grazing incidence X-ray diffraction, attenuated total reflectance-Fourier transform infrared spectroscopy, atomic force microscopy, micro-Raman and UV–visible spectroscopy. The crystalline nature of films declines with the initial face-centered cubic structure for 1x1014 ions cm−2 owing to the energy loss of Si ions in a Li doped NiO (Li:NiO) lattice during the generation of defects. The crystallite size of samples was evaluated using Scherrer’s equation. The vibrational modes were investigated via micro-Raman analysis. AFM topography was recorded for pristine and Si ion irradiated films. The ion fluence of Si ion in the used energy range lowers the transmittance Li:NiO films as compared to the pristine.

Embedded Si nanoclusters in α-alumina synthesized by ion implantation: An investigation using depth dependent Doppler broadening spectroscopy

Embedded Si nanoclusters in optically transparent host materials have shown potential applications in opto-electronic devices. Ion implantation followed by annealing at higher temperatures is considered a promising way to produce embedded nanoclusters in variety of host materials. In the present work, α-alumina crystals were irradiated with Si ion beam (50 keV) with varying total dose (1 × 1016, 5 × 1016 and 1 × 1017 ions/cm2). The ion implantation and vacancy defect profiles in alumina have been calculated using computer code SRIM. The irradiated samples were annealed at 500 and 1000 °C in a reducing atmosphere for 30 min. Depth dependent Doppler broadening measurements using high purity Germanium (HPGe) detector coupled to a slow positron beam were carried out on as-irradiated as well as annealed samples. The line shape (S- and W-) parameters showing contribution from valence (low momentum) and core (high momentum) electrons were evaluated from the positron implantation energy dependent Doppler broadened spectra. The S-E profiles of as irradiated samples indicated the formation of open volume defects in the damaged region. On annealing, S-E profiles are modified in the damaged region that is attributed to the formation of vacancy clusters and Si nanoclusters as confirmed through S-W correlation plots. The S-E profiles have been fitted using variable energy positron fit (VEPFIT) to evaluate the characteristic S-parameter corresponding to the damaged region. It is observed that ∼90% of implanted positrons in the damaged region are confined to the Si nanoclusters due to their high affinity toward Si as compared to host material, α-alumina. The present study confirms that positrons are confined in embedded nanoclusters and acts as a self seeking probe for their characterization.

Influence of electronic excitations on structural, optical and electrical properties of undoped and antimony doped tin oxide thin films

Study reports on the influence of swift heavy ion irradiation (SHII) induced electronic excitations (EEs) on structural, optical and electrical properties of undoped SnO2 (TO) and antimony doped SnO2 (ATO) thin films. EEs in the thin films were induced by 70MeV Si ion irradiation. It is noticed from the structural analysis that the crystallinity of TO and ATO almost remains unchanged upon Si ion beam irradiation. However, morphological studies by atomic force microscopy and scanning electron microscopy show surface modification upon irradiation. Interestingly, transport measurements show that the pristine ATO film possesses high conductivity which further increases upon irradiation for a fluence of 1×1012ions/cm2, followed with drastic decrease in conductivity and carrier concentration at higher fluences of irradiation. Band gap modification in TO and ATO films are also reported with irradiation fluence and found to be in agreement with quantum confinement (QC) model for TO; while with Burstein-Moss shift (BMS) model for ATO films. However, the modifications at higher fluence can be ascribed to the band tail states due to very high disorder in the lattice as revealed by very high value of Urbach energy in corroboration with transmittance investigations, which also exhibits a significant decrease in transmittance in both films at irradiation fluence ≥1×1013ions/cm2.

The surface layers structure of differently oriented single titanium nickelide crystals subjected to ion implantation

The structure of the surface and near-surface layers of titanium nickelide (NiTi) single crystals having [111]В2 and [001]В2 orientation relative to the direction of Si-ion beam treatment was investigated. It was found that the orientation effects of selective sputtering and the channeling control the thickness of the oxide and amorphous layers, the depth of penetration of ions and impurities, the distribution of Ni with depth. Different scenarios of deformation microstructure evolution are observed in the near-surface layers of NiTi crystals having of ‘soft’ orientation [111] В2 and ‘rigid’ orientation [001] В2.

Influence of Si ion implantation on structure and morphology of g-C3N4

Effect of Si ion implantation on structural and morphological features of graphite-like carbon nitride (g-C3N4) was investigated. g-C3N4 was prepared by using a simple atmospheric thermal decomposition process. The g-C3N4 pellets were irradiated with a Si ion beam of energy 200keV with different fluencies. Structural, morphological and elemental, and phase analysis of the implanted samples in comparison with the pristine samples was carried out by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques, respectively. The observations revealed that Si ion implantation results in a negligible change in the crystallite size and alteration of the network-like to the sheet-like morphology of g-C3N4 and Si ions in the g-C3N4 network.

Electron-DDCS Measurements of Water by C and Si Ion beams

SynopsisDouble differential distributions of electron emission from H2O target under the impact of C6+ and Si13+ ions with energy 4 MeV/u have been measured. The state-of-the art CDW-EIS model provided a good agreement with the data for C-ions whereas a substantial deviation is found for the Si ions. The derived single differential cross sections and total cross sections were also compared with different models.

Thermoluminescence of sol–gel derived Y2O3:Nd3+ nanophosphor exposed to 100 MeV Si8+ ions and gamma rays

Nanocrystalline Nd3+ doped Y2O3 was synthesized by sol–gel technique. Crystallite size calculated by Scherrer relation was found to be in the range 28–30nm. Fourier transform infrared spectroscopy (FTIR) revealed YO, OH stretching and CO bending bonds. Pellets of Y2O3:Nd3+ were irradiated with 100MeV swift Si8+ ions and γ-rays for the fluence/dose in the range 3×1011–3×1013ionscm−2 and 1.0_14kGy respectively. A prominent thermoluminescence (TL) glow with peak at 527K and a weak one with peak at 600K were observed in Si8+ ion irradiated samples while, a prominent TL glow with peak at 393K besides a shoulder at 434K and a weak one with peak at 581K were observed in γ-irradiated phosphors. The relative TL efficiency of Y2O3:Nd3+ of 100MeV Si ion beam to γ-rays of 60Co and is found to be 0.059. The TL kinetic parameters were calculated using Chen’s peak shape method and the results obtained are discussed. Y2O3:Nd3+ was observed for its use in space dosimetry application.

Thermoelectric properties of Zn4Sb3/CeFe(4−)Co Sb12 nano-layered superlattices modified by MeV Si ion beam

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 5 nm thick. The total thickness of the multilayer system is 275 nm. The superlattices were then bombarded by 5 MeV 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.

MeV Si ion modifications on the thermoelectric generators from Si/Si + Ge superlattice nano-layered films

Abstract The performance of thermoelectric materials and devices is characterized by a dimensionless figure of merit, ZT = S 2 σT / 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 300 nm and 317 nm 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 5 MeV 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 5 MeV Si ion beam bombardment fluences, one can fabricate TEG systems with figures of merits substantially higher than the values previously reported.

Systematic Measurement of Lineal Energy Distributions for Proton, He and Si Ion Beams Over a Wide Energy Range Using a Wall-less Tissue Equivalent Proportional Counter

The frequency distributions of the lineal energy, y, of 160 MeV proton, 150 MeV/u helium, and 490 MeV/u silicon ion beams were measured using a wall-less tissue equivalent proportional counter (TEPC) with a site size of 0.72 µm. The measured frequency distributions of y as well as the dose-mean values, y(D), agree with the corresponding data calculated using the microdosimetric function of the particle and heavy ion transport code system PHITS. The values of y(D) increase in the range of LET below ~10 keV µm(-1) because of discrete energy deposition by delta rays, while the relation is reversed above ~10 keV µm(-1) as the amount of energy escaping via delta rays increases. These results indicate that care should be taken with the difference between y(D) and LET when estimating the ionization density that usually relates to relative biological effectiveness (RBE) of energetic heavy ions.

Atomic collisions involving C60 and collective excitation

Here we review and discuss some of our recent investigations on collective excitation in a free C60 molecule and its influence on the atomic collisions. In particular, emphasis has been given for collisions with fast highly charged ions. It is demonstrated, from the charge-state-dependence studies of recoil-ion spectra, that the plasmon excitation plays a dominant role in the single and double ionization process. The observed linear charge-state-dependence is in contrast to the expected behavior predicted by ion-atom collisions models. This behavior was observed for different projectiles and at different energies. The time-of-flight recoil-ion mass spectroscopy experiments involve 1–5 MeV/u C, O, F and Si ion beams with different charge states, ranging between 4+ and 14+. In addition, the influence of the collective excitation on the electron capture process was also investigated. The wake-field induced Stark-mixing and splitting of sub-levels of projectile-ions following electron capture from C60 carries signature of the collective plasmon excitation. For the electron capture studies X-ray spectroscopic technique was used for collisions with bare and dressed S and Cl ion beams. The results on the TOF data on fullerene target obtained in last few years will be summarized.

Synergetic effects of dual-beam implantation on the microstructural development in silicon

We report a synergy effect on the microstructural development of silicon specimens as a result of dual-beam high temperature irradiation/implantation. In situ transmission electron microscopy experiments using two different experimental setups have been used, where the primary 50 keV Co{sup +} ion implantation beam was supplemented with either a 300 keV electron beam or a 500 keV Si{sup +} ion beam. In both cases, the secondary beam intensity was such that both beams created comparable overall primary damage. Completely different microstructural response has been found in these two cases. An intensive electron irradiation was found to sharply accelerate the evolution of dislocation structure, only weakly affecting the disilicide kinetics. On the contrary, the Si ion beam weakly affected the kinetics of either dislocation loops or coherent CoSi{sub 2} precipitates, but drastically increased the number density of thermodynamically unstable semicoherent precipitates. Possible microstructural reasons for the observed effects and the implications for both dislocation loop and cobalt disilicide nucleation mechanisms in high-temperature implanted TEM samples are discussed and supported by detailed molecular dynamics calculations of annealing of cascade remnants produced by the energetic silicon recoils.

MeV Si ion beam implantation as an effective patterning tool for the localized formation of porous silicon

Porous silicon (PS), in the form of single layer and multilayer structures, is a low-cost nanomaterial with applications in a wide range of fields. Hence, there is an increasing interest on the fabrication of laterally patterned PS structures. In biophysics for example, PS is a promising material for the development of low cost optical biochips, due to its remarkable biocompatibility and adjustable surface chemistry and optical properties. However, conventional lithography processes have shown to be not suitable for the proper patterning of PS. In this work, implantation of MeV Si ions is proposed as an effective tool for the localized formation of PS in the micrometer range. As previously reported by other groups, irradiation of silicon with H and He keV ions can inhibit the formation of PS. In the case of heavier ions, its higher damage efficiency allows for lower implantation doses to achieve PS growth inhibition, which allows shorter process times, and at the same time provides good lateral resolution below the micrometric range. Besides, the usage of ions of the same elementary nature as the target material avoids inconvenient side effects that may be ascribed to the implanted species. Two dimensional PS patterns with feature size of few micrometers have been successfully fabricated. Fluorescence and scanning electron microscopy reveal the proper transfer of different mask motifs into a PS/silicon patterned structure. Patterns present well defined lateral contrast and flat surface with no significant height variations, mandatory features for the development of PS based biochips. A resistivity increase has been observed on irradiated samples which could explain the inhibition of PS formation. This effect is attributed to dopant deactivation by the ion beam, since backscattering channeling measurements show no significant lattice damage.

Deposition of polycrystalline Si thin films on glass substrates by direct negative Si ion beam deposition

Polycrystalline Si (Poly-Si) thin films were deposited on a glass substrate by direct negative Si (Si −) ion beam deposition. The glass substrate temperature was kept constant at 500 °C for all depositions. Prior to deposition, the ion energy spread and ion-to-atom arrival ratio were evaluated as a function of the ion beam energy. The Si − ion energy spread was less than 10% regardless of the ion energy, while the ion-to-atom arrival ratio increased proportionally from 1.3 to 1.6 according to the ion beam energy. Atomic force microscopy images showed that a relatively rough surface was obtained at 50 eV of Si − ion energy and it is also concluded that the Si − ion beam irradiation at 50 eV is effective to deposit Si thin film with small grains as shown in Fig. 3.

Crystallographic characteristics and fine structures of semiconducting transition metal silicides

Silicide-based photonic materials have attracted a great deal of research interest due to their compatibility with the well-developed silicon technology. Extensive efforts have been made for the synthesis and characterisation of these materials. This paper covers some aspects of the microstructural and crystallographic characteristics of ion beam synthesised silicides such as the semiconducting iron and ruthenium silicides, using transmission electron microscopy. A previously predicted new orientation relationship has been found to exist between the Si substrate and ion beam synthesised βFeSi 2 nanocrystals, which are free of 90° rotational order domain boundaries.

Surface erosion induced by heavy ion backscattering analysis

Material removal induced by HIBS (Heavy Ion Backscattering Spectrometry) analysis has been investigated. For this purpose the thickness of thin metal films deposited on graphite was measured as a function of fluence of the Si and Ti projectile ion beam. Steady state erosion rates are in fair agreement with surface sputtering rates calculated by SRIM. For some layers however, the first few monolayers are removed at a much faster rate. A comparison with standard He RBS is made and consequences for the applicability of HIBS are discussed.

Si Ion Implantation-Induced Defect Photoluminescence in Silica Films

Dry and wet oxidation silica films doped with silicon ions were prepared using metal vapor vacuum arc (MEVVA) ion source implanter. The does of Si ion beams were kept constant at 3×1016 /cm2 and the energy varied from 42KeV to 70KeV. Five photoluminescence (PL) bands at the wavelength of 560nm, 580nm, 620nm, 650nm and 730nm have been observed at room temperature in all samples. The results of XRD showed none of Si nanocrystals were formed in the as-implanted silica films and originations of the PL bands were defects introduced by implantation. The 560nm PL band originated from oxygen surplus defect small peroxy radical (SPR), whereas the PL bands which ranges from the wavelength of 620nm to 730nm were attributed to non bridge oxygen hole center (NBOHC). Elevating implantation energy resulted in intensity increasing of 560nm PL band of dry oxidation samples but had inverse effects on wet oxidation samples. Influence mechanism of implantation energy on the defect photoluminescence was discussed in this article.

Study of erbium-doped silicon nanocrystals in silica

Er-doped SiO2 and Er-doped Si-NCs embedded in a SiO2 matrix were produced by Er and/or Si ion beam implantation of a Si (100) substrate. The composition and distribution of implanted Er varies in samples either with or without Si implants. HAADF and EELS detail in samples with Si implants, the Si and Er distribution is identical, and within a band of ~110 nm width at ~75 nm below the SiO2 surface. Intense PL emission at 1.54 μm confirms formation of ErSi2, for the majority of aggregates, is unlikely. The present investigation details most Si-NCs are surrounded by Er2O3, or possess this phase within.

Enhanced electron field emission of carbon nanotubes by Si ion beam irradiation

The electron field emission of carbon nanotubes (CNTs) has been enhanced by Si ion beam irradiation. The defects generated by ion beam irradiation and the absorbed molecules on the CNTs were responsible for the enhancement of electron field emission. This investigation provides a possible way to improve the electron field emission properties of CNTs and understand the mechanism of electron field emission enhancement of CNTs.