Tungsten Ion Implantation Research Articles

A High‐Speed Photodetector Fabricated with Tungsten‐Doped MoS2 by Ion Implantation

AbstractMolybdenum disulfide (MoS2) is a promising 2D semiconductor material for its unique characteristics such as tunable bandgap, high electrical conductivity, and strong light–matter interaction. Presently, many efforts have been made to modulate its properties, such as surface engineering, strain introduction, doping, and so on. Recently, it has been proved that substitutional metal doping is an effective approach to tune the energy bandgap of the aimed material and improve the performance of the device. Conventional metal doping methods will inevitably introduce impurities or defects and cannot control doping regions. Ion implantation is widely used in traditional semiconductor modification processes due to its high efficiency, controllability, and homogeneity. But it is rarely applied to 2D materials because of the damage caused during the implantation process. Here, the SiO2 substrate is implanted by tungsten ion implantation and then the tungsten doping of MoS2 is successfully achieved by chemical vapor deposition (CVD) growth process, while avoiding direct implantation damage to it. The W‐doped MoS2 photodetectors show a high‐speed response with a rise/fall time of 210 ms/160 ms. This work provides a novel doping strategy for metal doping of 2D materials and opens a new avenue to modify 2D materials properties.

Influence of the presence of deuterium on displacement damage in tungsten

The influence of the presence of deuterium on displacement damage in tungsten is studied by implanting 20 MeV tungsten ions into displacement-damaged tungsten already containing 1.7 at.% deuterium. SDTrimSP calculations reveal that for the tungsten implantation fluence used, on average each D atom is recoiled once and hence mobile deuterium should be present simultaneously while displacing tungsten atoms. Nuclear reaction analysis after the tungsten implantation shows that no deuterium is lost from the sample and the depth profile is unchanged. However, deuterium must have been de-trapped and is effectively re-trapped again because temperature programmed desorption spectroscopy reveals that deuterium is redistributed from the low temperature de-trapping peak to the high temperature de-trapping peak. Rate equation modelling can describe the measured deuterium desorption with the same de-trapping energies as for the initial material but with increased trap densities only. Decorating the samples after the additional tungsten ion implantation again with a low energy deuterium plasma shows increased deuterium retention beyond the saturation value that is known for initially deuterium free, displacement-damaged tungsten by nearly a factor of two. Both observations together indicate that deuterium is stabilizing the defects created within the collision cascade.

Nanoparticle Formation by Tungsten Ion Implantation in Glassy Carbon

Nanoparticle Formation by Tungsten Ion Implantation in Glassy Carbon

Hardening of self ion implanted tungsten and tungsten 5-wt% rhenium

Tungsten is one of the most promising materials for high temperature components in any future nuclear fusion tokamak. In this study tungsten-ion implantation has been used to simulate the damage caused by neutrons in pure tungsten and tungsten 5wt% rhenium. This damaged layer is only 300nm deep so conventional mechanical tests cannot be used to investigate it. Nanoindentation has been used to measure the change in hardness as a function of six damage levels (0dpa, 0.07dpa, 0.4dpa, 1.2dpa, 13dpa and 33dpa). In pure tungsten the hardness increase is seen to saturate by 0.4dpa at ≈0.8GPa. Transmission electron microscopy of the damage structure sees a similar saturation of the loop volume number density at the same damage level. In the tungsten 5wt% rhenium the increase in hardness is constant between 0.07 and 1.2dpa, ≈0.85GPa. The loop volume number density as measured using TEM is also shows little change in this region. At a damage level of 33dpa the hardness increase is 2.88GPa; this corresponds with the formation of small 3–5nm rhenium clusters as observed using atom probe tomography.

The Tungsten Density Distribution and Tribological Performance Analysis of Carburized Medium Carbon Steel with Tungsten Ion Implantation

This research studies the effect of implanted tungsten ion on the wear mechanism after ionized tungsten was implanted into material surface as tungsten could improve surface hardening ability and increase wear-resistant property. washer-on-disk wear tests were used to study the change of average friction coefficient and total wear rate. Auger electron spectra (AES) analysis, surface profiler and Vickers hardness tester were utilized to realize the relation among hardness distribution, tungsten ion distribution, and hardened surface. From AES, it indicates that the tungsten had high density distribution when tungsten content is at the depth of 0.25 µm and 0.92 µm, among which the depth of 0.25 µm has the highest density distribution. Vickers hardness test shows that 10 gw load can obtain the highest Hv. The decrease and increase of Vickers hardness value is because tungsten is unevenly distributed. The friction coefficient decreases along with the increase of load under constant rotating speed. The friction coefficient of high rotating speed is smaller than that of low rotating speed. The total wear rate is in proportional to the load under the same turning speed.

Analysis of surface morphological change in PET films induced by tungsten ion implantation

Surface morphological changes and metal nanograin formation of polyethylene terephthalate films with tungsten ion implantation were studied. Tungsten ions were accelerated with a voltage of 40 kV and implanted at fluences from 5 × 10 16 to 2 × 10 17 cm −2 using a metal vapor vacuum arc implanter. Scanning electron micrographs at the highest fluence show semi-spherical hills, indicating formation of tungsten nanograins on the polymer. The tungsten nanograin formation in the polymer film is confirmed by cross-sectional observation using transmission electron microscopy. Depth profiles of tungsten atoms obtained from energy dispersive X-ray spectra indicate densification and sputtering of the polymer surface layer during implantation. These results indicate that surface morphological change is related with the effects of a critical fluence and tungsten nanograin formation.

Characterization of effects and model of voids induced by high current density tungsten ion implantation

Tungsten ions of low energy and high current densities were implanted into H13 steel to investigate the void effects of heavy ion implantation. The voids induced by ion implantation were examined by high voltage electron microscopy (HVEM). The abnormal tungsten concentration depth profile was characterized by Rutherford backscattering spectroscopy (RBS). Experimental results of wear and hardness indicated that the formation of voids had a great influence on the surface mechanical properties of H13 steel. A new spikes model can be used to qualitatively explain the voids formation and their effects.

Effect of void formation during MEVVA tungsten ion implantation on the microstructure and surface properties of H13 die steel

H13 die steel was implanted with tungsten using a metal vapour vacuum arc (MEVVA) ion source. When the pulsed beam current density of tungsten ions increased to 6mA.cm−2, some voids appeared in the high voltage electron microscope (HVEM) micrograph, which would disappear at an annealing temperature of 600 degrees C. HVEM and x-ray diffraction were used for observing the phase structure of the annealed and un-annealed H13 steel after the steel was implanted. Results of wear and hardness tests indicated that whether the voids appear significantly influences the hardness and wear of H13 steel. Reasons for the formation of voids and the relation between the surface mechanical property and voids are discussed in terms of collision theory.

THE VOID EFFECT OF MEVVA W ION IMPLANTATION ON THE TRIBOLOGICAL PROPERTIES OF H13 STEEL

H13 steel samples were implanted with tungsten using a metal vapor vacuum arc (MEVVA) ion source, with an implantation dose of 1×1017 cm -2, an extraction acceleration of 30 kV and pulsed ion beam fluxes of between 0.3 mA·cm -2 and 6 mA·cm -2. The surface mechanical properties and microstructure for the W-implanted samples was characterized by the Rutherford backscattering spectroscope (RBS) and a high voltage electron microscope (HVEM). Experimental results of wear and hardness indicated that the hardness and wear of H13 steel increased when the voids were produced by tungsten ion implantation with a high pulsed current density. Forming causes for voids and their influence on the tungsten concentration depth profile in the implanted H13 steel and the surface mechanical properties were discussed in terms of spike theory.

Characterization of surface mechanical properties and microstructure of H13 steel implanted by pulsed tungsten

H13 steel samples were implanted with tungsten and the improvement in surface mechanical properties was investigated. The tungsten ion implantation was done using a metal vapor vacuum arc (MEVVA) ion source, with an ion current density of 15 μA cm −2. The implantation of tungsten showed a superior wear resistance surface. The relationship between surface mechanical property and microstructure for the tungsten-implanted samples was characterized by Rutherford backscattering spectroscopy (RBS), grazing-angle X-ray diffraction (GAXRD) and X-ray photoelectron spectroscopy (XPS). The tungsten carbides and tungsten oxides were observed in the doped region. The experimental results have shown that the formation of WC and WO 3 improved the wear resistance of H13 steel.

Wear properties of tungsten-implanted polyimide

Amorphous carbon layers have been fabricated in polyimide (C 22H 10N 2O 5) films using high-dose tungsten ion implantation, and their wear properties have been investigated. The width of the tracks formed by alumina balls in sliding tests decreased with increasing implantation dosage. This means that the deformation of the films during the test decreased owing to surface hardening. The surface of a sample implanted at 5 × 10 17 cm −2 was the hardest, and the coefficient of friction and the depth of the tracks were at a minimum at an implantation dosage of 1 × 10 17 cm −2. The average values of the coefficient of friction were 0.35 (non-implanted), 0.33 (1 × 10 15 cm −2), 0.25 (1 × 10 16 cm −2), 0.22 (1 × 10 17 cm −2) and 0.30 (5 × 10 17 cm −2). Scanning electron microscopy observation shows that small fragments were formed in the track, and especially in the sample implanted at a dosage of 5 × 10 17 cm −2, where abrasive wear occurred.

Tungsten ion implantation into copper by use of metal arc-plasma electro-magnetically accelerated to several km s −1

A coaxial plasma gun was designed for the injection of W into Cu, by employment of the high speed of W ions attained by electro-magnetic acceleration. Under acceleration at 5 kV, W atoms could be injected into a Cu substrate at depths up to about 30 μm, whereas under acceleration at 4 kV no injection was observed. The injected W was observed to have nonuniform spatial distribution provably forming clusters or small groups of particles. Under acceleration at 5 kV, the first plasma to arrive at the substrate has a velocity of 10 km s −1, which is much higher than that of initial plasma under acceleration at 4 kV. Immediately after the initial plasma, the relationship between the velocities of the respective plasmas reverses, so that average velocity at 5 kV is lower than that at 4 kV. Maximum plasma velocity plays a major role in the injection of W; i.e. the depth of W injection may depend on the velocity of initially generated plasma. The subsequent plasma forms a W layer on the surface of the substrate.

Structural and mechanical properties of amorphous-carbon films produced by high-fluence metallic ion implantation into polyimide

Metal-doped amorphous-carbon layers were fabricated by high-dose tungsten ion implantation into polyimide (C 22H 10N 2O 5) films, and the chemical states, structure and friction properties were investigated. The tungsten ion implantation was performed with an acceleration voltage of 70 kV using a MEVVA-type ion implanter. The dose of the implantation ranged from 1×10 15 to 5×10 17 cm −2. The X-ray photoelectron spectroscopy (XPS) study showed the formation of WC bonds in the implanted layer and tungsten atoms exposed on the surface due to sputtering, along with the formation of WO bonds in the specimen implanted at 5×10 17 cm −2. The cross-sectional transmission electron spectroscopy (TEM) observation shows neither metallic particles nor domains of compounds formed in the specimens implanted with tungsten ions. The friction coefficient measurement with a pin-on-disk tribometer at an applied load of 5 N under atmospheric room temperature showed a large effect due to tungsten implantation. The friction coefficient decreased with an increase in fluence, the minimum value being 0.14 for a specimen implanted at 1×10 16 cm −2. In this specimen, the wear volume was also minimized.

Microstructural modifications of aluminium surfaces ion implanted with W and its effect on corrosion and passivation

Tungsten ion implantation into aluminium is shown to improve corrosion resistance. The microstructural changes induced by W implantation, the role of W concentration and the influence of beam energy in producing an amorphous phase were investigated. A fully amorphous phase is observed at near 9 at% W. At all accelerating energies the presence of an amorphous phase is concentration dependent. A crystalline phase was also observed at lower W concentrations (Al 5W) which by post-implanting annealing generated the formation of a different phase, Al 12W, that required diffusion at 425 °C. Passivation in the presence of the crystalline phases was not as favourable as in the amorphous superficial alloys.

Tungsten ion implantation of aluminum for improved resistance to pitting corrosion — Electrochemical testing results

The greatly accelerated localized corrosion of aluminum in salt solutions has been observed and combated for many years. The susceptibility to pitting attack has been linked to the presence of chloride ions in the solution. Alloying additions to aluminum for improved corrosion resistance are restricted due to its limited solubility for passivating species such as chromium and molybdenum. However, many recent attempts to produce non-equilibrium alloys with these and other species, both through sputtering techniques and by rapid solidification, have met with very promising pitting resistance enhancements. The most dramatic increase in passivity is demonstrated by a thin co-sputtered film of Al and 9 atomic percent W, in which the pitting potential is increased by 2600 m V relative to pure Al. Recent efforts to extrapolate the promising W-Al thin film results to a bulk aluminum alloy using tungsten ion implantation are discussed here.