Unimplanted Samples Research Articles

Conductivity modification of ZnO film by low energy Fe10+ ion implantation

In this paper we report the structural, optical and electrical behaviours of ZnO films implanted with 300keV Fe10+ ions. From UV–vis spectroscopy it is observed that the band gap of the films decreases after implantation. Photoluminescence yield seems to increase in the implanted samples. From Hall measurements it is observed that the unimplanted sample shows n-type conductivity for the entire temperature range (100–300K), whereas after implantation the samples show p-type conductivity for ≤200K. The DC resistivity of the implanted samples is found to be lower than that of the unimplanted sample. We have found that the magnetoresistance of our samples is positive in the temperature range 200–300K, but it becomes negative below 200K.

Electrochemical behavior of the Ti6Al4V alloy implanted by nitrogen PIII

Plasma surface treatments have been used very often to enhance the surface properties of metallic materials. In this work, Ti6Al4V titanium alloy was treated by nitrogen plasma immersion ion implantation (NPIII) in order to obtain improvements in its surface properties, such as corrosion resistance evaluated here. The microstructure and corrosion behavior of the implanted and unimplanted samples were evaluated, using, XRD, GDOES and potentiodynamic polarization and impedance electrochemical spectroscopy tests in 0.6M NaCl solution. It was verified that the NPIII created resistant layers to corrosive attacks. In corrosion tests by polarization, the implanted samples showed corrosion current density reduction of about 10 times compared to the Ti6Al4V alloy without treatment. Besides that, it was also observed a reduction of the passive current density of one order of the magnitude. In all the studied cases, the polarization curves were shifted to more positive values of potentials, indicating a lower tendency of these PIII treated surfaces to corrosion. The implantation process produced a thin TiN surface layer followed by Ti2N and then a layer with nitrogen in solid solution, all detected by GDOES combined with X-ray diffraction. These layers promoted an excellent polarization resistance of the Ti6Al4V surfaces on impedance spectroscopy tests also. This better performance in these tests can be correlated with the formation of continuous nitride layer, which could retard chloride ions ingress into the substrate.

Irradiation enhanced paramagnetism on graphene nanoflakes

We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 10^11- 10^17 ions/cm2. The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 10^15 /cm^2. However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and X-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5K

Si related defects in the VUV in silicon multi-energy implanted Type III silica

Some effects on the vacuum ultraviolet optical bands (6–8 eV) produced by implanted Si, using multi-energies ranging from 320 to 35 keV energies to produce a layer of constant concentration in (Type III) silica, approximately 600 nm thick, have been measured. Based on two methods of analyzing the spectra as a function of implanted layer concentration; first, by subtracting the spectrum of an un-implanted sample from each spectrum of the implanted samples and second, subtracting the spectrum of one concentration from the spectrum of the next largest concentration, we have identified band maxima. In the case of the first subtraction the maxima are at ∼7.54, 7.7, and 7.92 eV. In the case of the second subtraction the maxima are at ∼7.5, 7.85, and 7.95 eV. These difference spectra show that the various states have differing rates of increase with increase in Si concentration. The absorption between 6 and 7 eV increases with increasing Si concentration indicating that there is/are a band or bands in this region of the spectra. Because all of the bands that are resolved increase with increasing Si concentration we attribute these bands to Si related electronic states. An estimate of the oscillator strengths of these bands is made by comparison of their peak absorption with that of the E′ optical band at 5.83 eV, f = 0.14 ± 0.05, in the same samples. This comparison shows that all of the resolved bands between 6 and 8 eV have oscillator strengths equal to or larger than the E′ state, consistent with our assignment of the bands to Si related states. By comparing to the spectra from the Si implanted samples, the bands produced by radiation damage in an Ar implanted sample are between 7.3 and 8 eV bands are attributed to Si related states.

Effect of CH4 Ion Implantation in Pure Aluminium

In this paper, aluminium samples with 99.96% purity were exposed to ion beam, extracted from CH4 plasma. Implantation of ions were performed for 50 keV energy and various doses ranging from 1 × 1017 to 6 × 1017 ions/cm2. Morphology of surfaces, roughness and its evolution during variation of ion dose has been studied by atomic force microscopy (AFM). Microstructure of the modified surfaces after ion implantation has been obtained by X-ray diffraction technique and Raman spectroscopy. Formation of aluminium carbide (Al4C3) was confirmed by XRD results at implantation doses of 3 × 1017 and 6 × 1017 ions/cm2. In addition, it was observed that when the ion dose is increased, orientation of aluminium planes change from (2 2 0) to (2 0 0). Corrosion test was performed and compared for implanted and un-implanted samples. The results showed that corrosion resistivity increase by accumulation of ion dose.

Microstructure and Surface Properties of Silver after High Dose Nitrogen Ion Implantation

In this paper the effect of nitrogen ion implantation at the energy of 50 keV and doses in the range between 1017 and 2 × 1018 ions/cm2 on silver surface has been discussed. X-ray diffraction (XRD) analysis was used to characterize microstructure of implanted layer. The XRD results confirmed that by such implantation AgN3 has been produced. Silver trinitride with orthorhombic structure was formed on cubic structure of silver surface. RMS roughness of implanted samples have been obtained using atomic force microscopy (AFM) analysis and compared with un-implanted sample. Microhardness properties of implanted samples measured by Vickers test. The results show that by increasing the ion dose up to 1 × 1018 ions/cm2 hardness enhances. Finally, reflection changes at the UV–Vis-NIR region measured by diffuse reflectance accessory of a spectrophotometer. The results of spectrophotometry analysis show reduction in diffused reflection spectrum of nitrogen implanted samples.

Improvement in Oxidation Resistance of Ferritic Stainless Steel by Carbon Ion Implantation

The oxidation characteristics of ferritic stainless steel (Crofer22APU), a potential candidate for interconnects in solid oxide fuel cells, were studied. Carbon was introduced on the surface by ion implantation, and both the carbon-implanted and unimplanted samples were subjected to oxidation at 800°C for 500 h. Ion implantation produced a carbon-rich amorphous region at the top surface. Fast diffusion induced by ion implantation promoted the formation of spinel oxides. The carbon-implanted samples showed significantly less mass gain than the unimplanted samples.

Thermal degradation analysis of deuterium-ion-implanted V25Cr40Ti35 using synchrotron radiation photoelectron spectroscopy

The thermal degradation of a native oxide layer on the hydrogen storage alloy V25Cr40Ti35 and the thermal desorption property of deuterium molecules were studied by synchrotron radiation soft X-ray photoelectron spectroscopy and thermal desorption mass spectrometry. Photoelectron spectra of O-1s, C-1s, V-2p, Cr-2p, and Ti-2p were observed for an as-received sample and a deuterium-ion-implanted one. Although the oxide layer changed dramatically by thermal annealing between 373 K and 473 K for the un-implanted sample, the change of the deuterium-ion-implanted sample was lying between 473 K and 573 K corresponding to D2 desorption. The implantation of deuterium resulted in the stabilization of the surface oxide layer by approximately 100 deg.

Optical and Structural Properties of Ion-implanted InGaZnO Thin Films Studied with Spectroscopic Ellipsometry and Transmission Electron Microscopy

Amorphous InGaZnO (IGZO) thin films were grown using RF sputtering deposition at room temperature and their corresponding dielectric functions were measured. In order to reduce defects and increase carrier concentrations, we examined the effect of forming gas annealing and ion implantation. The band gap energy increased with increasing forming gas annealing temperature. We implanted the IGZO thin films with F- ions in order to decrease oxygen vacancies. For comparison, we also implanted InO- ions. Transmission electron microscopy showed that the amorphous phase undergoes transformation to a nanocrystalline phase due to annealing. We also observed InGaZnO4 nanocrystals having an In–(Ga/Zn) superlattice structure. As the annealing temperature increased, the optical gap energy increased due to crystallization. After annealing, we observed an oxygen-vacancy-related 1.9 eV peak for both unimplanted and InO-implanted samples. However, F- ion implantation substantially reduced the amplitude of the 1.9 eV peak, which disappeared completely at a F fluence of 5×1015 cm-2. We observed other defect-related peaks at 3.6 and 4.2 eV after annealing, which also disappeared after F implantation.

Ion energy and dose dependence of strain relaxation for thin SiGe buffer layers using Si + implantation

We systematically investigated ion energy and dose dependencies of strain relaxation for SiGe buffer layers using Si + ion implantation. It was found that for the SiGe grown on Si substrates implanted at the energy of 25 keV and with a dose of 5 × 10 14 cm − 2, relaxation ratio was highly enhanced with very smooth surface. The obtained ratio was 65% higher than that of unimplanted samples. However, strain relaxation ratios were seen to reduce as ion energy increased or ion dose increased. This result indicated that the End-of-Range (EOR) defects generated by ion implantation and post annealing were responsible for strain relaxation and that the depth of the EOR defects from the SiGe/Si heterointerface was very crucial for strain relaxation of the SiGe layers.

Oxidation Behavior and Chromium Vaporization of Ion Implanted Crofer22APU

Crofer 22APU, used for interconnects in solid oxide fuel cells (SOFCs), is studied to improve its oxidation resistance and to suppress chromium vaporization from the oxide scales. Carbon and nitrogen were implanted on the plate surface by the ion implantation method. These samples were subjected to oxidation at 800oC for 500 hours. Oxidation kinetics was determined by measuring weight gains at regular time intervals. Experiments to determine chromium volatility from the samples were conducted at 800 {degree sign}C in a tube furnace in flowing air. The chromium vapors were collected on a silicon wafer and Rutherford Backscattering Spectroscopy (RBS) was used to measure the chromium vaporization rates. ASR measurements were also carried out on the samples. AES, SEM/EDS and TEM were used to characterize the initial and oxidized surface of the samples. The ion-implanted samples show significantly less chromium vaporization rate than the unimplanted samples.

Photoluminescence enhancement in Si + implanted PMMA

Silicon ion implantation effects on the optical and photoluminescence (PL) properties of polymethyl–methacrylate (PMMA) have been studied. Low-energy ion implantation ( E = 30–50 keV) was carried out over a range of different ion fluences ( D = 10 13–10 17 cm −2). Visible PL and optical transmission spectra in the range (330–800 nm) have been measured. The existing visible range PL emission in the unimplanted PMMA samples is clearly affected by the Si + ion implantation and the observed modification effect of photoluminescence enhancement (PLE) is essentially dependent on the implantation fluence. For certain fluences, dependent on the ion energy, the overall amplitude of the PL emission has a several times (∼5 times) increase. Optical absorption also gradually increases with the fluence.

Electrical and photoluminescence properties of carbon implanted ZnO bulk single crystals

Carbon-ions, which are expected as an amphoteric impurity, are implanted into ZnO bulk single crystals with a fluence of 1.5×1015cm−2. The carbon-ion implanted ZnO shows the n-type conductivity and the resistivity varies from 6×104Ωcm (for unimplanted samples) to 3×10−2Ωcm (for 800°C-annealed ones). The Rutherford backscattering (RBS) studies show the existence of the displaced zinc atoms. In photoluminescence (PL) measurements, the broad emission at 2.34eV observed in un-implanted and as-implanted samples is related to oxygen vacancy and zinc interstitial. After annealing, the weak PL-emission related to carbon donor is observed at 3.06eV, indicating that the donor level lies at ∼310meV below the conduction band. The carbon-ion implanted ZnO layer with the low resistivity achieved in the present study suggests the possibility of transparent conductive oxide.

Annealing Behavior of Defects in Multiple-Energy Nitrogen Implanted ZnO Bulk Single Crystal

Multiple-energy nitrogen ions (energies:1 to 100 keV and a net concentration:2.24 x 1020 cm-3) are implanted into ZnO bulk single crystals grown by the hydrothermal method. Rutherford backscattering-channeling studies show the presence of displaced Zn atoms (Zni) of about 4 % in as-implanted samples. An A-emission band related to the interstitial oxygen (Oi) is observed at 580 nm in 600 oC-annealed samples, and a new emission appears at 515 nm in 800 oC-annealed samples. It is proposed that the new emission band consists of the superposition of the green band (~525 nm) observed in unimplanted ZnO and the residual A-emission band. In 800 oC-annealed samples, a band to acceptor transition at 3.26 eV is also observed in addition to a donor to acceptor pair transition, suggesting that nitrogen acceptor is located at about 180 meV above the valence band. A thermally stimulated current peak, P1 (165 meV), which has been attributed to a native point defect, observed in unimplanted samples almost disappears in nitrogen-implanted samples annealed at 800 oC.

Analysis of explanted ePTFE cardiovascular grafts (modified BT shunt)

Structural, chemical, mechanical and surface changes were studied in expanded polytetrafluroethylene vascular grafts explanted from children undergoing planned surgical management of congenital heart disease. These grafts were implanted when recipients were aged 7 days to 8 years (median—48 weeks) and they had been in circulation for a period of 10–52 months (median—74 weeks). While no chemical changes were observed in the shunt, on average the tensile strength had decreased by 50%, total elongation by 61% and crystallinity by 3%. No salt deposits were observed on the surface of the graft. Soluble and insoluble proteins were bound to the polymer surface, which had made the surface hydrophilic. The external surface roughness had increased by 254.5 and the internal surface roughness by 2.6 times the initial value. The fine polymer structure had become fused and clumped. The fusing of strands on the polymer surface became more pronounced with longer duration of implantation. In one instance of previously documented graft stenosis, the heat capacity was found to be more than that of the unimplanted sample, indicating an increase in crystallinity. A longer period of study with a larger sample size would likely shed more light on the relation between physico-chemical changes and graft stenosis.

Resonance Raman study of He+ ion implanted nanostructured ZnS

AbstractZnS nanocrytsals of size ∼2.5 nm were prepared by chemical precipitation technique. Pressed pellets of nanostructured ZnS were implanted with He+ ions at doses of 5 × 1014, 1 × 1015 and 5 × 1015 ions/cm2. Raman spectra of both unimplanted and He+ ion implanted samples were recorded with ultraviolet (UV) excitation. LO, 2LO, 2TO, (LO + TA) and (2TO − TA) modes of ZnS were observed in the resonance Raman spectra of the unimplanted nanostructured ZnS samples. In addition, a surface mode was observed at 294 cm−1. With the implantation of He+ ions, the 2TO mode disappeared and 2LO mode became prominent and this observation was attributed to the decrease in band gap of ZnS nanocrytsals due to ion implantation. The exciton–LO phonon coupling strength was determined from the intensity ratio of 2LO to LO modes and it was observed that the exciton–LO phonon coupling strength increases with increase in implantation dose. In the present work, we report for the first time the observation of 2TO mode in the resonance Raman spectrum of nanostructured ZnS and also the modification of exciton–LO phonon coupling strength of semiconductor nanoparticles by ion implantation. Copyright © 2008 John Wiley & Sons, Ltd.

Nitrogen Implantation to Improve Electron Channel Mobility in 4H-SiC MOSFET

Normally off 4H-SiC MOSFET devices have been fabricated on a p-type semiconductor and electrically characterized at different temperatures. A gate oxide obtained by nitrogen ion implantation performed before the thermal oxidation of SiC has been implemented in n-channel MOSFET technology. Two samples with a nitrogen concentration at the SiO2/SiC interface of 5 X 1018 and 1.5 X 1019 cm-3 and one unimplanted sample have been manufactured. The sample with the highest N concentration at the interface presents the highest channel mobility and the lowest threshold voltage. For increasing temperature, in all the samples, the threshold voltage decreases, and the electron channel mobility increases. The latter case attains a maximum value of about 40 cm2/V ldr s at 200degC for the sample with the highest N concentration. These trends are explained by the reduction of interface electron traps in the upper half of the band gap toward the conduction band edge. These results demonstrate that N implantation can be effectively used to improve the electrical performances of an n-type surface channel 4H-SiC MOSFET.

Reduction of Traps and Improvement of Carrier Lifetime in SiC Epilayer by Ion Implantation

Reduction in deep level defects and increase of carrier lifetime in 4H-SiC epilayer was observed after carbon ion implantation into the shallow surface layer of 250 nm and subsequent annealing above 1400 °C. The concentration of Z1/2 and EH6/7 traps was determined by deep level transient spectroscopy 4 μm below the implanted layer. After annealing, concentration of both traps decreased from 1013 cm-3 range to below the detection limit. Minority carrier lifetime almost doubled in the implanted samples compared to the unimplanted samples. We suggest that carbon interstitials from the implanted layer in-diffuse into the layer underneath during annealing and annihilate with carbon vacancies. Our results indicate that Z1/2 and EH6/7 traps are most likely carbon vacancy related.

Thermal characterization of Ag and Ag + N ion implanted ultra-high molecular weight polyethylene (UHMWPE)

Most of total hip joints are composed of ultra-high molecular weight polyethylene (UHMWPE ). However, as ultra-high molecular weight polyethylene is too stable in a body, wear debris may accumulate and cause biological response such as bone absorption and loosening of prosthesis. In this study, ultra-high molecular weight polyethylene samples were Ag and Ag+N hybrid ion implanted by using MEVVA ion implantation technique to improve its surface properties. Samples were implanted with a fluence of 1017ion/cm2 and extraction voltage of 30kV. Implanted and unimplanted samples were investigated by thermo-gravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical microscopy (OM) and contact Angle measurement. Thermal characterization results showed that the ion bombardment induced an increase in the % crystallinity, onset and termination degradation temperatures of UHMWPE.

Characterization of Ti + N and Zr ion implanted 316 L stainless steel

In this study, polished 316LSS stainless steel has been implanted with Ti + N and Zr ions at fluence of 2 × 10 17 ions/cm 2 and 1 × 10 17 ions/cm 2, respectively. Ion charge state distributions of Ti + N and Zr were measured by time-of-flight spectrometry, and the mean energies of these ions were determined. The Zr concentration profiles were obtained by Rutherford backscattering spectrometry. The range distribution of ions in implanted and unimplanted samples were evaluated using TRIM and STOPPO programs and the results were compared with the experimental data, which were in good agreement. The influence of the ions on the mechanical behavior of the 316LSS was investigated. The measurements show that after Ti + N implantation; the friction coefficient decreases, the hardness value increases, the wear resistance decreases and after Zr implantation; the friction coefficient decreases, the hardness value increases and the wear resistance increases with respect to an unimplanted sample.