Implantation Parameters Research Articles

A new concept of oxidation protection of Ni-base alloys by using the halogen effect

The Ni-base alloys with Al-contents of less than 10 wt% are widely used in high temperature technology due to their beneficial mechanical properties. However, their oxidation resistance may be insufficient at temperatures above 1000°C. Oxidation of these Ni-base alloys does not form a pure continuous Al2O3 protective scale on the surface, but rather a complex layer structure. This structure is characterized by inward growing oxides showing a discontinuous alumina scale. A new method for the formation of a dense protective alumina scale on the surface is now presented. The method is based on the halogen effect, which was successfully applied for TiAl-alloys. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. The fluorine treatment is performed by ion implantation. The implantation parameters are defined by using Monte Carlo simulations. Following these results fluorine implantations of the Ni-base alloy IN 738 are performed to meet the required fluorine content near the surface. After oxidation at 1050°C a thin continuous external alumina scale is formed on the surface, whereas the untreated alloy shows a mixed oxide scale with significant inward growing oxides. The results offer a new and innovative way to protect the Ni-base alloys against oxidation.

A description of stress driven bubble growth of helium implanted tungsten

Low energy (<100 keV) helium implantation of tungsten has been shown to result in the formation of unusual surface morphologies over a large temperature range (700–2100 °C). Simulation of these macroscopic phenomena requires a multiscale approach to modeling helium transport in both space and time. We present here a multiscale helium transport model by coupling spatially-resolved kinetic rate theory (KRT) with kinetic Monte Carlo (KMC) simulation to model helium bubble nucleation and growth. The KRT-based HEROS Code establishes defect concentrations as well as stable helium bubble nuclei as a function of implantation parameters and position from the implanted surface and the KMC-based Mc-HEROS Code models the growth of helium bubbles due to migration and coalescence. Temperature- and stress-gradients can act as driving forces, resulting in biased bubble migration. The Mc-HEROS Code was modified to simulate the impact of stress gradients on bubble migration and coalescence. In this work, we report on bubble growth and gas release of helium implanted tungsten W/O stress gradients. First, surface pore densities and size distributions are compared with available experimental results for stress-free helium implantation conditions. Next, the impact of stress gradients on helium bubble evolution is simulated. The influence of stress fields on bubble and surface pore evolution are compared with stress-free simulations. It is shown that near surface stress gradients accelerate helium bubbles towards the free surface, but do not increasing average bubble diameters significantly.

Surface characterization and wear behavior of ion implanted NiTi shape memory alloy

The aim of this study was investigation of changes in the modified near-surface layer on the NiTi shape memory alloy, caused by ion implantation as well as their influence on the mechanical and shape memory properties of this material. Surface of NiTi has been modified by nitrogen ion beam at several fluences 1 × 10 17 cm −2, 1 × 10 18 cm −2 and 2 × 10 18 cm −2 at the energy 50 keV. The effect of implantation parameters on surface characteristics and wear properties was investigated using dry-sliding-wear test, depth sensing indentation test and scanning profilometry method. The experimental results have shown how the ion implantation treatment can change the original surface: reducing Ni content in the surface, increasing the surface hardness (furthermore, the hardness improvement extended to the regions much deeper than the implanted layer), and improving the sliding wear resistance. The experimental results of surface treatment conditions and mechanical properties of the modified NiTi alloys are compared, analyzed and discussed in this paper.

Microtransplantation of Dopaminergic Cell Suspensions: Further Characterization and Optimization of Grafting Parameters

Intracerebral transplantation of dopaminergic (DA) cells is currently further explored as a potential restorative therapy for Parkinson's disease (PD). However, before they can be considered for a more widespread clinical use a number of critical issues have to be resolved, including an optimized transplantation protocol. This study has been performed in a rat 6-hydroxydopamine model of PD and is based on the microtransplantation approach. The results demonstrate a reduced survival (threefold) for a single cell suspension of E14 rat ventral mesencephalon compared to a fragment suspension when a metal cannula is used for implantation. However, fragment suspensions result in a more variable graft survival and ectopically placed cells along the implantation tract. When a glass capillary is used for implantation, the survival of the single cell suspension (so-called "micrograft") improved by fourfold (vs. single cells/metal cannula) and is superior to the combination of the metal cannula and fragment suspension (+40%). The micrografts show a reduced variability in DA neuron survival as well as fewer ectopically placed cells. Moreover, the implantation time can significantly be reduced from 19 to 7 min in micrografted animals without a compromise in DA graft survival and functional behavioral outcome. Using the microtransplantation approach graft size can be tailored effectively by varying the density of the final cell suspension at least between 11,000 and 320,000 cells/microl, resulting in comparable survival of tyrosine hydroxylase (TH)-positive neurons in the range of 2-4%. With this approach no more than 100 surviving TH-positive neurons are necessary to produce functional effects in the amphetamine-induced rotation test. Interestingly, we found that DA micrografts into lesion striatum present 20% higher survival rates of TH neurons in comparison to the intact striatum. In summary, these results provide further evidence for the usefulness of the microtransplantation approach and allow for a more precise and tailored adaptation of the implantation parameters for further studies on DA, and possibly also other neural-, glial-, and stem cell-derived grafts.

The halogen effect for Ni-base alloys – A new method for increasing the oxidation protection at high temperatures

A new method for oxidation protection of Ni-base alloys is presented. The method is based on the halogen effect. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. Ion implantation has been chosen for fluorine treatment. The implantation parameters are defined by using the T-DYN simulation software. Based on these results fluorine implantations of the Ni-base alloy IN 738 are performed to meet the required fluorine content near the surface. The fluorine depth profiles are analyzed by using the PIGE-technique. After oxidation at 1050°C a dense protecting external alumina scale is formed on the surface.

Regular surface patterns by local swelling induced by He implantation into silicon through nanosphere lithography masks

Nanopatterning of silicon surfaces by means of He+ ion implantation through self-organized colloidal masks is reported for the first time. Nanosphere lithography (NSL) masks with mask openings of 46–230nm width were deposited on Si(100) wafers. He+ ions were implanted through these masks in order to induce a local cavity formation and Si surface swelling. The surface morphology and the subsurface structure were studied using atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM), respectively, as a function of mask and implantation parameters. It is demonstrated that regular arrays of both individual hillocks and trough-like circular rings can be generated.

A new concept of oxidation protection of Ni-base alloys by using the halogen effect

The Ni-base alloys with Al-contents of less than 10 wt% are widely used in high temperature technology due to their beneficial mechanical properties. However, their oxidation resistance may be insufficient at temperatures above 1000°C. Oxidation of these Ni-base alloys does not form a pure continuous Al2O3 protective scale on the surface, but rather a complex layer structure. This structure is characterized by inward growing oxides showing a discontinuous alumina scale. A new method for the formation of a dense protective alumina scale on the surface is now presented. The method is based on the halogen effect, which was successfully applied for TiAl-alloys. Thermodynamic calculations show the preferred formation of gaseous Al-halogenides within a certain region of fluorine partial pressures. The fluorine treatment is performed by ion implantation. The implantation parameters are defined by using Monte Carlo simulations. Following these results fluorine implantations of the Ni-base alloy IN 738 are performed to meet the required fluorine content near the surface. After oxidation at 1050°C a thin continuous external alumina scale is formed on the surface, whereas the untreated alloy shows a mixed oxide scale with significant inward growing oxides. The results offer a new and innovative way to protect the Ni-base alloys against oxidation.

Alveolar Ridge Augmentation With Titanium Mesh and a Combination of Autogenous Bone and Anorganic Bovine Bone: A 2‐Year Prospective Study

Recently, the use of bovine bone mineral (BBM) in combination with autogenous bone for alveolar ridge augmentation before implant placement has increased in favor because of concerns over morbidity associated with extraoral donor sites. The aim of this prospective study was to evaluate the clinical and radiographic parameters of implants placed in augmented ridges using a 70:30 mixture of autogenous bone and BBM in association with micro-mesh over a 2-year period. Sixteen partially edentulous patients requiring bone augmentation were consecutively treated for 19 reconstructive procedures and delayed implant placement (44 implants) after 8 to 9 months of submerged mesh healing. Clinical examinations were performed and radiographs of the implants were taken 6 months after prosthetic loading and once a year during a 2-year follow-up. Only one (5.3%) of the 19 micro-meshes became exposed after 2 months and was removed. Computed tomography scans of the alveolar ridge pre- and postreconstruction demonstrated mean vertical augmentation of 3.71 +/- 1.24 mm and mean horizontal augmentation of 4.16 +/- 0.59 mm. All of the implants were retained after 2 years, yielding a 100% survival rate. The mean bone resorption around the implants was 1.37 +/- 0.32 mm during the observation period. Only three implants demonstrated bone resorption >2 mm, whereas 41 implants were considered clinically successful, resulting in a success rate of 93.1%. This 2-year prospective study demonstrated that implants placed into augmented bone using this technique exhibited peri-implant stability with high survival (100%) and success (93.1%) rates.

Boron activation and diffusion in silicon and strained silicon-on-insulator by rapid thermal and flash lamp annealings

We present experimental results on the activation and diffusion behaviors of boron in silicon-on-insulator and strained silicon-on-insulator using standard rapid thermal processing treatments as well as flash lamp annealing. After boron implantation at different doses and at a low energy of 1 keV, samples were annealed to activate the dopants, and secondary ion mass spectrometry and Hall measurements were carried out to determine boron diffusion and the amount of activated dopants, respectively. In contrast to rapid thermal annealing, flash lamp annealing enables the activation without significant diffusion of dopants. In addition, we investigated the effect of coating the samples with antireflection layers to increase the absorbed energy during flash annealing. As a result, the activation was increased significantly to values comparable with the activation obtained with standard annealing. Furthermore, the relation between the observed boron diffusion and activation as a function of the implantation and annealing parameters is discussed in terms of the kinetics of the defects involved in these processes.

Influence of alloy compositions on the halogen effect in TiAl alloys

F-implantation concentration profile simulations were carried out and the influence of the ion fluence, implantation energy as well as the alloy composition were investigated. For alloys with Al contents between 40 and 50 at% the conditions to get the halogen effect were assessed by thermodynamic calculations. According to the thermodynamic predictions the implantation parameters were kept constant in this composition range. The implanted alloys were exposed in laboratory air over 4000 h. With the implantation parameters used (20 keV and 1 x 10 17 F/cm 2 ), the halogen effect was found to be efficient over 4000 h. The oxide growth kinetic constants were measured and vary between 1.2 and 2.7 x 10 -13 g 2 / cm 4 /s.

Video-Based Measuring of Quality Parameters for Tricuspid Xenograft Heart Valve Implants

Defective heart valves are often replaced by implants in open-heart surgery. Both mechanical and biological implants are available. Among biological implants, xenograft ones-i.e., valves grafted from animals such as pigs, are widely used. Good implants should exhibit certain typical anatomical and functional characteristics to successfully replace the native tissue. Here, we describe a video-based system for measuring quality parameters of xenograft heart valve implants, including the area of the orifice and the fluttering of the valves' leaflets, i.e., their flaps (or cusps). Our system employs automatic methods that provide a precise and reproducible way to infer the quality of an implant. The automatic analysis of both a valve's orifice and the fluttering of its leaflets offers a more comprehensive quality assessment than current, mostly manual methods. We focus on valves with three leaflets, i.e., aortic, pulmonary, and tricuspid valves.

Ellipsometric models for vertically inhomogeneous composite structures

AbstractThe optical properties of thin films usually depend on the preparation conditions. For example, the microstructure of ion implantation‐caused damage, the grain size of deposited polycrystalline materials, or the porosity of chemically etched silicon largely depend on the parameters of ion implantation, deposition, and etching, respectively. Generally, as a first approach, these materials can be considered as a mixture of components described by reference dielectric function data from the literature using the effective medium approximation (EMA). Interface roughness and vertical inhomogeneity can be described by the volume fraction of components changing as a function of depth. The EMA models are robust, and provide useful information like damage depth profiles of ion implanted materials, crystallinity and surface roughness of deposited materials, or porosity of chemically etched porous silicon. The requirement for EMA is that the size of the components must be smaller than the wavelength of the measuring light, but large enough to retain their bulk dielectric properties. If the component sizes are large, diffraction and scattering has to be taken into account. For example, surface roughness is routinely modeled by EMA, but in case of rough surfaces with large correlation length EMA may become invalid as approaching small wavelengths in the UV part of the spectrum. If component sizes decrease, it may not be possible to describe the components using bulk reference data, because of size effects or strain. For example, fine grained polycrystalline silicon or highly porous silicon can not be modeled by the usual mixture of single‐crystalline silicon (c‐Si) and amorphous silicon (a‐Si) for polycrystalline silicon, or mixing c‐Si and voids for porous silicon, but a component representing an intermediate structure between c‐Si and a‐Si has to be used to describe the vanishing long‐range order. A less robust but more detailed analysis is provided by parametrization of the dielectric function of the layer or the components in an EMA composition using model dielectric functions, critical point (CP) models, oscillator models, or empirical dispersion equations. In these cases, cross‐correlation, parameter‐coupling, selection of sensitive parameters, local minima, and regression in a multi‐parameter space are crucial issues to be handled properly. Consideration of the optical penetration depth (OPD) is also important, when measuring vertically inhomogeneous semiconductor materials. Obviously, CP analysis in semiconductors is most sensitive around the CP photon energies, but the OPD is the smallest just at this region of the spectrum. In silicon, the OPDs at the E1 and E2 CP energies are about 10 nm and 5 nm, respectively. Consequently, CP analysis of structures below this depth is not possible using ex situ measurement of silicon. This work shows approaches and examples to model multi‐component materials created using different methods including ion implantation, deposition, and electrochemical etching. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

What treatment margins should we achieve with Iodine-125 prostate brachytherapy?

Purpose: Low-dose-rate prostate brachytherapy achieves a very high and very effective intraprostatic dose. Implant quality parameters concentrate on the dose received by the prostate (D90, V100) and do not take into account the dose to the CTV or the periprostatic tissue at risk for microscopic disease. Surgical pathologic studies have confirmed that the majority of extracapsular disease extends <2 mm outside the prostate. We report the implant quality parameters, D90 and V100, of the CTV (prostate+2 mm, prostate+3 mm and prostate+5 mm) for 117 men treated with Iodine-125 prostate brachytherapy, and examine these parameters for 4 local failures occurring in an experience of 960 implants.

Development of a Testing Methodology to Quantify Bone Load Transfer Patterns for Multiple Stemmed Implants in a Single Bone With an Application in the Distal Ulna

Optimal parameters for many orthopaedic implants, such as stem length and material, are unknown. Geometry and mechanical properties of bone can vary greatly amongst cadaveric specimens, requiring a large number of specimens to test design variations. This study aimed to develop an experimental methodology to measure bone strains as a function of multiple implant stem designs in a single specimen, and evaluate its efficacy in the distal ulna. Eight fresh-frozen cadaveric ulnae were each instrumented with 12 uniaxial strain gauges on the medial and lateral surfaces of the bone. The proximal portion of each ulna was cemented in a custom-designed jig that allowed a medially directed force to be applied to the distal articular surface. An implant with a finely threaded stem was cemented into the canal by an experienced upper extremity orthopaedic surgeon. Six loads (5-30 N) were applied sequentially to the lateral surface of the prosthetic head using a materials testing machine. Testing was repeated after breaking the stem-cement bond, and after removing and reinserting the stem several times into the threaded cement mantle. Near the end of the testing period, the initial stem was reinserted and data were collected to determine if there was any change in bone properties or testing setup over time. Finally, a smooth stem was inserted for comparison to the threaded stem. Strain varied linearly with load (R(2)> or =0.99) for all testing scenarios. Bending strains were not affected by breaking the stem-cement bond (P=0.7), testing durations up to 18 h (P=0.7), nor the presence of threads when compared to a smooth stem (P>0.4). Furthermore, for all gauges, there was no interaction between the effect of the threads and level of applied load (P>0.1). This methodology should prove to be useful to compare stem designs of varying lengths and materials in the same bone, allowing for a direct comparison between implant designs for the ulna and other bones subjected primarily to bending loads. Furthermore, it will minimize the need for large numbers of specimens to test multiple implant designs. The ultimate goal of using this protocol is to optimize implant stem properties, such as length and material, with respect to load transfer.

Formation of dislocation loops in silicon by ion irradiation for silicon light emitting diodes

We have studied the influence of the ion species, ion energy, fluence, irradiation temperature and post-implantation annealing on the formation of shallow dislocation loops in silicon, for fabrication of silicon light emitting diodes. The substrates used were (100) Si, implanted with 20–80keV boron at room temperature and 75–175keV silicon at 100 and 200°C. The implanted fluences were from 5×1014 to 1×1015 ions/cm2. After irradiation the samples were processed for 15s to 20min at 950°C by rapid thermal annealing. Structural analysis of the samples was done by transmission electron microscopy and Rutherford backscattering spectrometry. In all irradiations the silicon substrates were not amorphized, and that resulted in the formation of extrinsic perfect and faulted dislocation loops with Burgers vectors a/2〈110〉 and a/3〈111〉, respectively, sitting in {111} habit planes. It was demonstrated that by varying the ion implantation parameters and post-irradiation annealing, it is possible to form various shapes, concentration and distribution of dislocation loops in silicon.

Research on metastable electron traps in the modified SOI materials induced by Si ion implantation

Silicon-On-Insulator (SOI) materials were modified by Si ion implantation with different doses, as reported in this letter. The electrical performance was studied and the effect of a modification technique on the SOI materials was investigated. The characteristic, obtained by pseudo-metal-oxide-semiconductor (pseudo-MOS) method, showed that the drain ID current versus gate voltage VG(ID−VG) curves shifted along the axis of VG with the change of Si ion implantation doses. The results of electron paramagnetic resonance (EPR), x-ray photoelectron spectroscopy (XPS), and electronic test suggested that the parameters of implantation affect the electrical performance and that the metastable electron traps are introduced into the buried oxide layers of SOI materials.

Study of the magnetic properties on Mn and As co-implanted GaAs

The interest on diluted magnetic semiconductor (DMS), like GaMnAs, has increased during the last years due to potential applications, mainly on spintronic device. The magnetic anisotropy and the interacting effects between the magnetic nanostructures are fundamental topics to be studied. In this work we present some results on Mn and As co-implanted GaAs. Samples with three different implantation energies of Mn were prepared, keeping the As implantation energy fixed and the Mn and As dose of 2×10 16 cm −2. Annealing was done using rapid thermal annealing (RTA) at 750 °C for 20 and 50 s. Using a superconducting quantum interference device (SQUID) and magnetic anisotropy values reported in the literature, we have obtained information about nanocluster size distribution. Our studies indicated that the nanocluster size distribution depends on the implantation parameters and the annealing time. Differently from previous studies reported in similar samples, we have observed room-temperature hysteresis in all samples, with coercive field values typical of nanoparticle systems.

Realization of ultrashallow junctions by plasma immersion ion implantation and laser annealing

To achieve the requirements of the 45nm ITRS technology node and beyond, beamline implantation has reached its limit in terms of low energies. Plasma immersion ion implantation (PIII) is thus an alternative doping technique for the formation of ultrashallow junctions for source/drain extension in silicon devices. In this study, the authors present some results obtained on the PIII prototype called PULSION® designed by the IBS French company. In previous works [F. Torregrosa et al., Proceedings of the 14th International Conference on Ion Implant Technology, 2004 (unpublished); Proceedings of the 16th International Conference on Ion Implant Technology, 2006 (unpublished), p. 6], it has been shown that this machine offers the possibility to reach ultralow energy implantations and then to obtain implantation depths of only a few nanometers. One of the main issues is then to highly activate these junctions with a limited diffusion of dopants. Wafers have been implanted by PULSION® with acceleration voltages from 1to2kV at saturation dose, with or without preamorphization implantation (PAI). Then, they have been annealed by a XeCl excimer laser with a wavelength of 193nm, with energy densities from 275to600mJ∕cm2 and several shots. Electrical and physicochemical characterizations such as secondary-ion-mass spectrometry, four-point probe, and optical noncontact measurements were then performed. In this article, the authors investigate the effects of PAI, implantation parameters, and laser fluence on the junction specifications (depth, sheet resistance, and leakage current).

The Role of Fundamental Material Parameters for the Fluorine Effect in the Oxidation Protection of Titanium Aluminides

AbstractTo improve the insufficient oxidation resistance of Titanium Aluminides at temperatures above 750°C the fluorine effect offers an innovative way. The focus of this paper is to define the fundamental material variables for the fluorine effect related to the macroscopic behaviour (oxidation resistance) and its long time stability. The thermodynamic model predicted the fluorine effect for the TiAl within a corridor of total fluorine amount in terms of partial pressures. To realize the fluorine effect the required F-concentration [in at.-%] within the near surface region had to be found. Using fluorine ion implantation several fluences within 5e15 and 5e17 F cm-2 were implanted with an energy of 20 keV. The implantation depth profiles were calculated by using the Monte Carlo simulation code T-DYN and verified experimentally by using the non-destructive PIGE - technique (Proton Induced Gamma-ray Emission). After oxidation tests at 800°C – 1000°C a value of 2e17 F cm-2 / 20 keV was determined as an optimal implantation parameter set. Following these results the maximal fluorine concentration was identified to be a fundamental material variable for starting the alumina formation with a required fluorine amount of about 40-45 at.-%. However this maximum fluorine concentration showed a rapid decrease to values less than 5 at.-% only after a few hours of oxidation (900°C and 1000°C) followed by a slow decrease. Therefore the maximum fluorine concentration Cmax – now located at the metal/oxide – interface – was identified to be a fundamental parameter for the long time stability. An exponential decay function containing a constant term of about 1 at.-% was found to describe the time behaviour of Cmax for isothermal and cyclic oxidation (900°C, 1000°C). Because the alumina scale on the surface acts as a diffusion barrier for fluorine, the stability of Cmax is strongly influenced by the F-diffusion into the metal. From the F-depth profiles the diffusion coefficient of fluorine into the TiAl at 900°C was determined as a fundamental parameter for the long-term stability of Cmax showing a value of 1.56e-15cm2/s.

Area laser crystallized LTPS TFTs with implanted contacts for active matrix OLED displays

We have developed a four mask low temperature poly-Si (LTPS) TFT process for p- and n-channel devices. Our PECVD deposited amorphous silicon is recrystallized to polycrystalline silicon with single area excimer laser crystallization while formation of drain and source is carried out with self aligned ion beam implantation. We have investigated implantation parameters, suitability of various metallizations as well as laser activation and annealing procedures. To prove the potential capability of our devices, which are suitable for conventional and inverted OLEDs alike, we have produced several functional active matrix backplanes implementing different pixel circuits. Our active matrix backplane process has been customized to drive small molecules as well as polymers, regardless if top or bottom emitting.