High-dose Implantation Research Articles

The effects of ion irradiation on the micromechanical fracture strength and hardness of a self-passivating tungsten alloy

An ultra-fine grained self-passivating tungsten alloy (W88-Cr10-Ti2 in wt.%) has been implanted with iodine ions to average doses of 0.7 and 7 dpa, as well as with helium ions to an average concentration of 650 appm. Pile-up corrected Berkovich nanoindentation reveals significant irradiation hardening, with a maximum hardening of 1.9 GPa (17.5%) observed. The brittle fracture strength of the material in all implantation conditions was measured through un-notched cantilever bending at the microscopic scale. All cantilever beams failed catastrophically in an intergranular fashion. A statistically confirmed small decrease in strength is observed after low dose implantation (−6%), whilst the high dose implantation results in a significant increase in fracture strength (+9%), further increased by additional helium implantation (+16%). The use of iodine ions as the implantation ion type is justified through a comparison of the hardening behaviour of pure tungsten under tungsten and iodine implantation.

Fabrication of chemiresistive gas sensors based on multistep reduced graphene oxide for low parts per million monitoring of sulfur dioxide at room temperature

The proposed multistep reduction of graphene oxide includes two-step reduction process. The graphene oxide is reduced by hydrazine hydrate followed by further reduction with low energy nitrogen ion beam implantation technique. From the Raman spectra, reduction of graphene oxide samples has been estimated on the basis of Tuinstra and Koenig relation. FT-IR studies have shown the removal of oxygen functional groups such as epoxy, hydroxyl and carboxylic on reduction. Ion implantation has enhanced electrical conductivity and specific surface area of graphene oxide on reduction. Besides reduction, the second step has modified the surface morphology of the samples making them more appropriate for gas adsorption. The sample with higher implantation dose (1015ions/cm2) exhibits promising potential for room temperature chemiresistive SO2 gas sensor at ppm levels as low as 5ppm with reasonable response, selectivity and stability.

Formation and properties of high-dose nitrogen implanted epitaxially grown Gd2O3 on silicon

The effects of nitrogen incorporation by high-dose ion implantation in epitaxial Gd2O3 films on Si(111) followed by annealing have been investigated. Nitrogen incorporation is believed to occur by filling the oxygen vacancies or by removing hydroxyl group ions in gadolinium oxide (Gd2O3). The nitrogen content in the oxide layer has been altered by changing the implantation dose. The impact of nitrogen incorporation on Gd-O bonding is studied using X-ray photoelectron spectroscopy. A shift in the Gd and O peak positions indicate the presence of nitrogen in the layer. Raman spectroscopy reveals heavy structural changes. The newly appearing structure is crystalline, but not in agreement with either the known bixbyite (Gd2O3) or rocksalt (GdN) structure. Electron microscopic investigations reveal the formation of cracks and small areas with lower densities or even voids. That structure exhibits similarities with transmission electron microscopy images of gadolinium nitride (GdN) layers. The electronic band gap of Gd2O3 estimated from O1s plasmon energy loss measurements was found to decrease significantly by the incorporation of nitrogen. Reduction in the valence band and conduction band offset is obtained as a function of implantation dose.

Nanostructured multielement (TiHfZrNbVTa)N coatings before and after implantation of N+ ions (1018 cm−2): Their structure and mechanical properties

Multielement high entropy alloy (HEA) nitride (TiHfZrNbVTa)N coatings were deposited by vacuum arc and their structural and mechanical stability after implantation of high doses of N+ ions, 1018cm−2, were investigated. The crystal structure and phase composition were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy, while depth-resolved nanoindentation tests were used to determine the evolution of hardness and elastic modulus along the implantation depth. XRD patterns show that coatings exhibit a main phase with fcc structure, which preferred orientation varies from (111) to (200), depending on the deposition conditions. First-principles calculations reveal that the presence of Nb atoms could favor the formation of solid solution with fcc structure in multielement HEA nitride. TEM results showed that amorphous and nanostructured phases were formed in the implanted coating sub-surface layer (∼100nm depth). Concentration of nitrogen reached 90at% in the near-surface layer after implantation, and decreased at higher depth. Nanohardness of the as-deposited coatings varied from 27 to 38GPa depending on the deposition conditions. Ion implantation led to a significant decrease of the nanohardness to 12GPa in the implanted region, while it reaches 24GPa at larger depths. However, the H/E ratio is ⩾0.1 in the sub-surface layer due to N+ implantation, which is expected to have beneficial effect on the wear properties.

(Invited) Progress in Buried Grid Technology for Improvements in on-Resistance of High Voltage SiC Devices

Silicon Carbide (SiC) is regarded as the material of choice for high voltage (>1kV) power devices due to its material properties, mature fabrication technology, and availability of 150mm diameter wafer material. SiC power devices like Schottky barrier diodes (SBDs) and MOSFETs with voltage ratings of 1700V and current handling capabilities of 50A and more are commercially available from several vendors. Commercial SiC SBDs are based on the merged p-n junction and Schottky (MPS) concept or the junction barrier controlled Schottky (JBS) concept. Commercial MOSFETs utilize the VDMOS concept having a vertical device design with lateral channel and the UMOS concept with vertical channel at trench sidewalls. Common for these device concepts is that the electric field at device areas like Schottky contacts and MOS interfaces is relatively high and limits often the device performance. This leads to that the full potential of SiC devices cannot be realized. For example, in planar surface p-grid JBS diode structures the protection of the Schottky areas from high electric field is not sufficient and result in high leakage currents limiting the SOA in terms of junction and operation temperature. In addition, the edge termination is realized at the top surface of the SiC material and has to be carefully designed to not exceed the limitations of passivation and packaging materials. Buried grid technology is suggested to decrease the electric field at field sensitive device areas and to move areas of high electric field into the SiC bulk. It was demonstrated for SiC JBS diodes that buried grid technology gives more than three orders of magnitude lower leakage currents even at high temperature operation due to the superior shielding effect. The drawback is that the introduction of the buried grid increases the total resistance and therefore increases the forward voltage drop at rated current and the conduction losses. In this paper, we review our work on improving the on-state characteristics of buried grid SiC devices. The work is mainly done for buried grid JBS-diodes (BG-JBS), but can be applied also to buried grid MOSFETs (BG-MOSFET). For the BG-SiC devices, a p-grid is fabricated either by aluminum implantation followed by high temperature anneal or trench etching with subsequent epitaxial re-growth and planarization to fill up etched trenches with p-type material. As a final step, the p-grid is buried by another re-growth step of a thin n-layer. The epitaxial grid approach is done with Ascatron’s 3D-SiC core technology based on embedded epitaxial growth techniques, replacing high dose ion implantation at elevated temperatures and high temperature anneal by epitaxial growth in trenches. For cost-effective fabrication, this process should be performed in multi-wafer reactors. For devices with blocking capability of up to 1700V, we typically employ floating ring type edge termination formed simultaneously with the active area p-grid. For higher voltages than 1700V we suggest to use a JTE type edge termination formed by ion implantation in the same layer as the p-grid. Hence, the edge termination is also buried in the SiC bulk. By carefully designing the drift and re-growth layers as well as the epitaxial or implanted p-grid, the fabrication process can be optimized in terms of trade-off between current handling capability in forward and blocking behavior and leakage current in reverse. In addition, the size and spacing of the p-areas are critical parameters to optimize the BG-SiC device performance to realize maximum current handling capability at forward voltage similar or below surface grid devices and minimum leakage current especially for high temperature operation. To reduce the forward voltage, we employed relatively high n-doping in the channel regions between the p-islands and optimized the drift and re-grown top layer doping. Due to the superior material quality, epitaxial grown BG-structures result in increased bipolar injection at high current densities and thus give improved surge current capabilities. In addition, epitaxial p-n junctions show lower leakage currents than implanted ones.

Nitrogen ion implantation on the mechanical properties of AISI 420 martensitic stainless steel

Abstract Nitrogen ions with different energy of 30 keV and 50 keV and dose of 5 × 1016, 5 × 1017 and 1 × 1018 cm− 2 were implanted into the surface of AISI 420 martensitic stainless steel. The micro topography, roughness, friction coefficient, wear loss, hardness, as well as the chemical composition were investigated. Mounds and craters were found on the ion implanted surfaces, indicating increases in the roughness. However, very little changes in friction coefficient were detected after implantation. Nitrogen ions implantation on AISI 420 significantly improved the nanohardness, and the value of 16.2 GPa at the depth of 17.3 nm was about 2.3 times as hard as the untreated samples at the same depth when the implant energy and dose were 50 keV and 5 × 1016 cm− 2, respectively. The wear loss of the implanted samples was less than that of untreated ones, and an optional dose of 5 × 1017 cm− 2 could be used for the wear resistance improvement. XPS results demonstrated that chromium nitrides were produced during ion implantation, which possibly contributes to the improvements of the hardness and wear resistance. The N 1s core spectra showed that nitrogen oxides was found in the samples with higher implantation dose, which had counteraction for the improvements of the hardness.

Effects of high-dose hydrogen implantation on defect formation and dopant diffusion in silver implanted ZnO crystals

This work reports on the effects of a deep high-dose hydrogen ion implant on damage accumulation, defect retention, and silver diffusion in silver implanted ZnO crystals. Single-crystal ZnO samples were implanted with Ag ions in a region ∼150 nm within the surface, and some of these samples were additionally implanted with hydrogen ions to a dose of 2 × 1016 cm−2, close to the depth ∼250 nm. Rutherford backscattering/ion channeling measurements show that crystal damage caused by Ag ion implantation and the amount of defects retained in the near surface region following post-implantation annealing were found to diminish in the case with the H implantation. On the other hand, the additional H ion implantation resulted in a reduction of substitutional Ag atoms upon post-implantation annealing. Furthermore, the presence of H also modified the diffusion properties of Ag atoms in ZnO. We discuss these findings in the context of the effects of nano-cavities on formation and annihilation of point defects as well as on impurity diffusion and trapping in ZnO crystals.

Detection and reduction of tungsten contamination in ion implantation processes

AbstractIn this paper, we review the results of some studies addressing the problem of tungsten contamination in implantation processes. For some tests, the implanter was contaminated by implantation of wafers with an exposed tungsten layer, resulting in critical contamination conditions. First, DLTS (deep level transient spectroscopy) measurements were calibrated to measure tungsten contamination in ion‐implanted samples. DLTS measurements of tungsten‐implanted samples showed that the tungsten concentration increases linearly with the dose up to a rather low dose (5×1010 cm–2). Tungsten deactivation was observed when the dose was further increased. Under these conditions, ToF‐SIMS revealed tungsten at the wafer surface, showing that deactivation was due to surface segregation. DLTS calibration could therefore be obtained in the linear dose regime only. This calibration was used to evaluate the tungsten contamination in arsenic implantations. Ordinary operating conditions and critical contamination conditions of the equipment were compared. A moderate tungsten contamination was observed in samples implanted under ordinary operating conditions. This contamination was easily suppressed by a thin screen oxide. On the contrary, implantations in critical conditions of the equipment resulted in a relevant tungsten contamination, which could be reduced but not suppressed even by a relatively thick screen oxide (up to 150 Å). A decontamination process consisting of high dose implantations of dummy wafers was tested for its efficiency to remove tungsten and titanium contamination. This process was found to be much more effective for titanium than for tungsten. Finally, DLTS proved to be much more sensitive that TXRF (total reflection X‐ray fluorescence) in detecting tungsten contamination. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evolution of embedded lithium nanoclusters in lithium implanted alumina

High dose of ion implantation followed by annealing is considered a feasible way to generate thermally stable nanoclusters inside a transparent host matrix. Low energy (50 keV) Li ions have been implanted into single crystals of alumina with different fluence (1 × 1015–1 × 1017 ions/cm2). The samples have been annealed at temperatures ranging from 500 to 1100 °C in air in step of 100 °C. Depth dependent Doppler broadening measurements have been carried out using high purity germanium detector coupled to a variable energy slow positron beam. Fractional area in the central and wing regions of Doppler broadened annihilation radiation spectrum, namely, S- and W- parameters, were evaluated from each spectrum. Any variation in positron annihilation probability with valence and core electrons which occurs on trapping of positrons at a defect site is reflected in these parameters. The effect of ion fluence and annealing temperature on evolution of defects and formation of embedded Li nanoclusters have been studied by indexing the variation in line shape S- (W-) parameter as a function of positron implantation depth. These studies supplemented by theoretical calculations confirm that with annealing up to 700 °C, vacancy clusters are created due to the aggregation of vacancies wherein Li nanoclusters are formed. On annealing at higher temperature, there is evidence for the breakdown of these Li clusters leaving behind vacancy clusters in the samples.

Feedback from MRI Based Post Implant Dosimetry Shifts the Dominant Challenge from Under-Dosed to High Dose Implants

Feedback from MRI Based Post Implant Dosimetry Shifts the Dominant Challenge from Under-Dosed to High Dose Implants

(Invited) An Overview of Doping Studies in MoS2

The advent of 2D materials in recent years has brought the potential for new device applications at ever decreasing transistor design nodes. Transition metal dichalcogenides have received much of that attention, with much of the focus on MoS2 thanks to its desirable bandgap. Studies have shown the advantages of MoS2 devices in key performance metrics such as a high ION/IOFF ratio and a subthreshold swing that approaches or potentially exceeds the fundamental 60 mV/dec limit. However, the contact resistance remains prohibitively high, and questions remain regarding the ability to dope these materials. Numerous routes for doping MoS2 have been reported, including surface charge transfer via molecular adsorption, cation substitution during growth, chalcogenide substitution via immersion in solution, and plasma-assisted doping. The effectiveness of these doping methods is displayed by reductions in contact resistance, increases in drive current, and in some instances a change from n-type to p-type behavior. This talk will review these recent reports on MoS2 doping. Recent experiments have begun to explore the possibility of doping MoS2 by ion-implantation, which is a legacy doping technique that is often avoided with 2D materials due to their ultra-thin nature. These experiments utilize ultra low implant energies of 200 eV which places the species of interest (Cl+ and Ar+) completely within the 3-5 layers of MoS2 being investigated. Cl is potentially a donor in MoS2 whereas Ar was used to determine the effect of the implant damage on the electrical properties. These studies focused on room temperature implants at doses between 1 x 1013/cm2 and 1 x 1015/cm2. Preliminary structural studies utilizing angle-resolved XPS indicate a Cl peak is around 1 nm deep into the MoS2, in rough agreement with Monte Carlo TRIM calculations. STM studies have revealed a number of defects present after implantation, including sub-surface defects that may be sulfur vacancies as well as surface sulfur vacancies. The density of these defects track with the dose. Relative to the pristine surface, STS studies have shown little change in tunneling current associated with the sub-surface defects, but enhanced tunneling current associated with the sulfur vacancies. It was observed that as the dose increases the oxidation of the surface as measured by XPS after exposure to the air increases. Additionally, we are performing transmission line measurements to observe the electrical effect of the implantation. Using lithography, transmission line masks were patterned onto individual exfoliated flakes. Photoresist was used as a mask to protect the channel and the implantation preceded contact metal (Ni/Au) deposition. Thus, only the contact area was implanted. Prior to implantation, primarily non-linear IDS-VDS curves are observed for few-layer (<=10 layers) MoS2 flakes with no applied back-gate voltage. After implantation at lower doses, linear IDS-VDS curves are observed implying more ohmic contacts. This is prior to annealing implying the electrical nature of the implant damage is contributing to better contacts. However the effect is greater for Cl+ implants than Ar+ implants implying that the effect is not strictly a damage-related phenomenon. At higher doses the contacts went back to being non-ohmic and this may be associated with the aforementioned oxidation after higher dose implantation. The dose dependence of the role of implant doping on contact resistivity will be discussed as well as the results from post implant annealing to facilitate dopant activation.

Magnetic and structural changes in the near-surface epitaxial Y2.95La0.05Fe5O12 films after high-dose ion implantation.

The method of magnetic force microscopy was used to study the domain structure of various-thickness epitaxial Y2.95La0.05Fe5O12 iron-yttrium garnet films modified by high-dose implantation of N+ nitrogen ions. The results of multi-crystal x-ray diffractometry were analyzed, and a possible defect structure of garnets prior to and after implantation was identified. It was established that the reduction of magnetic losses observed after high-dose ion implantation is accompanied by the essential ordering of magnetic domains on the surface of implanted films. There is a direct dependence of electromagnetic properties on the dose of implanted atoms followed by a considerable sputtering and amorphization of the near-surface film layer and formation of a well-defined electromagnetic structure.

Structural Transformations in Austenitic Stainless Steel Induced by Deuterium Implantation: Irradiation at 295K.

Deuterium thermal desorption spectra were investigated on the samples of austenitic steel 18Cr10NiTi pre-implanted at 295 K with deuterium ions in the dose range from 8 × 1014 to 2.7 × 1018 D/cm2. The kinetics of structural transformation development in the steel layer was traced from deuterium thermodesorption spectra as a function of deuterium concentration. Three characteristic regions with different low rates of deuterium amount desorption as the implantation dose increases were revealed: I—the linear region of low implantation doses (up to 1 × 1017 D/cm2); II—the nonlinear region of medium implantation doses (1 × 1017 to 8 × 1017 D/cm2); III—the linear region of high implantation doses (8 × 1017 to 2.7 × 1018 D/cm2). During the process of deuterium ion irradiation, the coefficient of deuterium retention in steel varies in discrete steps. Each of the discrete regions of deuterium retention coefficient variation corresponds to different implanted-matter states formed during deuterium ion implantation. The low-dose region is characterized by formation of deuterium-vacancy complexes and solid-solution phase state of deuterium in the steel. The total concentration of the accumulated deuterium in this region varies between 2.5 and 3 at.%. The medium-dose region is characterized by the radiation-induced action on the steel in the presence of deuterium with the resulting formation of the energy-stable nanosized crystalline structure of steel, having a developed network of intercrystalline boundaries. The basis for this developed network of intercrystalline boundaries is provided by the amorphous state, which manifests itself in the thermodesorption spectra as a widely temperature-scale extended region of deuterium desorption (structure formation with a varying activation energy). The total concentration of the accumulated deuterium in the region of medium implantation doses makes 7 to 8 at.%. The resulting structure shows stability against the action of deuterium ion implantation. This manifests itself in a nearly complete ceasing of deuterium accumulation from a newly implanted dose (radiation-resistant structure).

Non-cultured adipose-derived cells promote the bone augmentation induced by low-dose BMP2

Event Abstract Back to Event Non-cultured adipose-derived cells promote the bone augmentation induced by low-dose BMP2 Kazuhiro Egashira1*, Yoshinori Y. Sumita1*, Takashi T. Shirairi1* and Izumi I. Asahina1* 1 Nagasaki University Graduate School of Biomedical Sciences, Department of Regenerative Surgery, Japan BMP2 has been shown to induce bone formation in a variety of indications on bone engineering, and is now recognized as one of most effective materials that can confer osteoinducibility to bone substitutes. However, direct implantation of high doses of BMP2 is known to induce substantial swelling that may cause the obstruction of airway when applied to oral and cervical areas. On the other hand, recent studies have shown adipose-tissue contains on the order of 100- to 500-fold more MSCs than do bone-marrow after initial harvest. Therefore, non-cultured adipose-derived cells (NC-ADCs) including high densities of stem/progenitor cells may possess a stronger bone regenerative capability and effectively reduce the amounts of BMP2 required to induce bone formation. Our aim is to investigate whether NC-ADCs can promote the bone augmentation induced by low-dose BMP2. For experiments, human ADCs were isolated by enzymatically dissociation after surgical removal of buccal fat-pad. Then, NC-ADCs were obtained after centrifugation to separate the mature adipocytes. After characteristics analyses in vitro, 3x106 NC-ADCs were mixed with β-TCP granules that absorbed low-dose BMP2, and were transplanted to onlay-placement on mice cranium. Other four groups were transplanted as experimental controls. After 2 and 4 weeks, the specimens were harvested and observed histologically. As findings, remarkable augmented bone-area were observed at 2 weeks of transplantation when NC-ADCs were transplanted with low-dose BMP2. Furthermore, ectopic bone formation could be clearly recognized in those specimens at 4 weeks. This suggests NC-ADCs can facilitate the clinical use of BMP2 for bone engineering. Keywords: Bone Regeneration, stem cell, in vivo tissue engineering Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Regenerative medicine: biomaterials for control of tissue induction Citation: Egashira K, Sumita YY, Shirairi TT and Asahina II (2016). Non-cultured adipose-derived cells promote the bone augmentation induced by low-dose BMP2. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.01031 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. * Correspondence: Dr. Kazuhiro Egashira, Nagasaki University Graduate School of Biomedical Sciences, Department of Regenerative Surgery, Nagasaki, Japan, Email1 Dr. Yoshinori Y Sumita, Nagasaki University Graduate School of Biomedical Sciences, Department of Regenerative Surgery, Nagasaki, Japan, y-sumita@nagasaki-u.ac.jp Dr. Takashi T Shirairi, Nagasaki University Graduate School of Biomedical Sciences, Department of Regenerative Surgery, Nagasaki, Japan, shiraishi@nagasaki-u.ac.jp Dr. Izumi I Asahina, Nagasaki University Graduate School of Biomedical Sciences, Department of Regenerative Surgery, Nagasaki, Japan, asahina@nagasaki-u.ac.jp Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Kazuhiro Egashira Yoshinori Y Sumita Takashi T Shirairi Izumi I Asahina Google Kazuhiro Egashira Yoshinori Y Sumita Takashi T Shirairi Izumi I Asahina Google Scholar Kazuhiro Egashira Yoshinori Y Sumita Takashi T Shirairi Izumi I Asahina PubMed Kazuhiro Egashira Yoshinori Y Sumita Takashi T Shirairi Izumi I Asahina Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Thermal annealing of C ion irradiation defects in nuclear graphite studied by positron annihilation

In order to investigate the thermal behaviour of radiation induced point defects in nuclear graphite, ETU10 graphite was implanted with 350 keV C+ ion to doses of 1015 and 1016 cm-2. The point defects introduced by the implantation were characterized by Positron Annihilation Doppler Broadening (PADB) and their thermal behaviour was studied during “in situ” annealing at Delft Variable Energy Positron beam (VEP). The annealing was performed for 5 minutes at temperatures ranging from 300 K (as implanted) to 1500 K in steps of 100 K. For both doses, an annealing stage at around 450 K is observed followed by a second stage around 700 K. For the high dose implantation vacancy complexes are found which are stable up to a temperature around 1400K.

Hardening silicon-on-insulator nMOSFETs by multiple-step Si+ implantation

A novel technique is proposed to improve total irradiation dose (TID) hardness of buried oxides in a 0.13μm silicon-on-insulator (SOI) technology. Multiple-step Si ion implantation is implemented to avoid silicon film amorphization. Each implant step introduces silicon ion implantation of a lower dose into buried oxides which creates an amorphous/crystalline (a/c) interface inside the silicon layer. Rapid thermal annealing (RTA) removes implant-induced lattice damages by silicon recrystallization reflected in a/c interface moving towards the top silicon surface. The thermal process prevents top silicon layers from total amorphization arising in the technique of single high dose implantation method. X-ray Diffraction (XRD) spectrum confirms the existence of the a/c interface and determines the single implant dose. Experimental results on pseudo-MOS and H-gate partially-depleted SOI n-type MOSFETs show radiation tolerance up to 1.0Mrad(Si) though introduced metastable electron traps lead to I–V hysteresis and bias instabilities.

Synthesis of porous silicon with silver nanoparticles by low-energy ion implantation

In this paper, a new technique is proposed for synthesis of porous silicon (PSi) layers with silver nanoparticles based on the method of low-energy high-dose metal ion implantation into Si. In order to demonstrate this technique, the implantation at room temperature of a polished Si wafer by Ag+ ions with the ion energy of 30 keV, ion dose of 1.5 × 1017 ion/cm2, and ion current density of 8 µA/cm2 is carried out. Using methods of high resolution scanning electron and atomic-force microscopy, electron probe microanalysis, and Raman scattering, it is shown that ion implantation results in the formation, on the surface of irradiated Si, of a thin amorphous layer of PSi with the average pore size of 150–180 nm, a pore depth of about 100 nm, and wall thickness between pores of about 30–60 nm. Moreover, the PSi structure contains Ag nanoparticles 5–15 nm in size. It is established that, during the ion implantation, the sputtering of the Si surface by Ag+ ions takes place, which was not observed previously. Based on the data obtained, it is concluded that, in contrast to chemical techniques, the proposed physical technique for PSi formation can be integrated into the modern advanced process of fabricating and improving electronic circuits based on industrial ion implantation.

Structural and phonon properties of InN synthesized by ion implantation in SiO2

Ion-implantation is a powerful technique for the formation of compound semiconductor nanocrystal precipitates in a host medium. The aim is to elaborate quantum dots for device technology purposes. High dose (5.2×1016ions/cm2) implantations of Indium (In) and Nitrogen (N) ions have been performed in a 206nm thick SiO2 layer thermally grown on <111> silicon. The implantation energies have been chosen from 12 to 180keV to produce 5–10at.% profiles overlapping at a mean depth of about 100nm. Thermal treatments between 500°C and 900°C for different annealing times lead to the formation of InN nanometric precipitates and to cure the oxide defects. In addition, the In2O3 and metallic indium phases have been observed. Their sizes, crystalline structures and depth distributions have been studied as a function of annealing temperature using grazing incidence X-ray diffraction, transmission electron microscopy, Rutherford back scattering spectrometry and Raman spectroscopy.

Cubic silicon carbide as a potential photovoltaic material

In this work we present a significant advancement in cubic silicon carbide (3C-SiC) growth in terms of crystal quality and domain size, and indicate its potential use in photovoltaics. To date, the use of 3C-SiC for photovoltaics has not been considered due to the band gap of 2.3eV being too large for conventional solar cells. Doping of 3C-SiC with boron introduces an energy level of 0.7eV above the valence band. Such energy level may form an intermediate band (IB) in the band gap. This IB concept has been presented in the literature to act as an energy ladder that allows absorption of sub-bandgap photons to generate extra electron–hole pairs and increase the efficiency of a solar cell. The main challenge with this concept is to find a materials system that could realize such efficient photovoltaic behavior. The 3C-SiC bandgap and boron energy level fits nicely into the concept, but has not been explored for an IB behavior.For a long time crystalline 3C-SiC has been challenging to grow due to its metastable nature. The material mainly consists of a large number of small domains if the 3C polytype is maintained. In our work a crystal growth process was realized by a new approach that is a combination of initial nucleation and step-flow growth. In the process, the domains that form initially extend laterally to make larger 3C-SiC domains, thus leading to a pronounced improvement in crystalline quality of 3C-SiC. In order to explore the feasibility of IB in 3C-SiC using boron, we have explored two routes of introducing boron impurities; ion implantation on un-doped samples and epitaxial growth on un-doped samples using pre-doped source material. The results show that 3C-SiC doped with boron is an optically active material, and thus is interesting to be further studied for IB behavior.For the ion implanted samples the crystal quality was maintained even after high implantation doses and subsequent annealing. The same was true for the samples grown with pre-doped source material, even with a high concentration of boron impurities.We present optical emission and absorption properties of as-grown and boron implanted 3C-SiC. The low-temperature photoluminescence spectra indicate the formation of optically active deep boron centers, which may be utilized for achieving an IB behavior at sufficiently high dopant concentrations. We also discuss the potential of boron doped 3C-SiC base material in a broader range of applications, such as in photovoltaics, biomarkers and hydrogen generation by splitting water.

Formation of InAs nanoclusters in silicon by high-dose ion implantation: Experimental data and simulation results

A physicomathematical model and dedicated software are developed for simulating high-dose implantation of two types of atoms to form InAs nanoclusters in a silicon matrix. The model is based on solving a set of convection–diffusion–reaction equations. The synthesis of InAs nanoclusters produced by highdose implantation of As+ and In+ ions into crystalline silicon is numerically simulated. Using the methods of transmission electron microscopy and Raman scattering, it is found that InAs nanoclusters are crystalline and have a mean diameter of 7 nm. After As implantation (170 keV, 3.2 × 1016 cm−2) and In implantation (250 keV, 2.8 × 1016 cm−2) into silicon at 500°C, the nanoclusters are distributed with a density of 2.87 × 1011 cm−2. From experimental data and theoretical results, the coefficients of radiation-stimulated diffusion of In and As in silicon, as well as the fraction of the implant in the bound state (i.e., entering into InAs nanoclusters), are determined. Experimental data are compared with simulation results.