Nitrogen Plasma Based Ion Implantation Research Articles

The Influence of High-Temperature Nitrogen Plasma-Based Ion Implantation on Niobium Creep Behavior

Niobium has been considered for applications in the aerospace sector, but its use at high temperatures is restricted, due to the great affinity of refractory metals with oxygen, which results in the formation of oxide layers and a decrease in their mechanical resistances. In the present work, Nb samples were submitted to High-Temperature Nitrogen Plasma-Based Ion Implantation (HT-NPBII). The process runs at a working pressure between 3 and 4 mbar and negative high voltage pulses of 7 kV/30 μs/300 Hz were applied to samples heated to 1000°C, at treatment times of 1 h, 4 h, and 8 h, respectively. Microstructural and mechanical characterizations of the treated samples revealed the formation of a layer of Nb2N, with 3.0 μm thickness and increase in the surface hardness from 225 HV for the untreated material up to about 2498 HV, for samples treated during 8 h. Creep tests were performed at 500°C and with loads varying from 25 to 40 MPa. Results indicated a decrease in the secondary creep rate for treated specimens when compared to the untreated ones. This behavior can be attributed to the formation of a nitride layer on the surface of Nb that acts as barrier to avoid the oxygen diffusion into the material under high temperature conditions.

The Surface Treatment of Niobium Superconducting Reentrant Cavities by Means of High Temperature Nitrogen Plasma Based Ion Implantation

High Temperature Nitrogen Plasma Based Ion Implantation (HT-NPBII) has been used to treat the surface of niobium superconducting reentrant cavities, which are part of parametric transducers in a resonant-mass gravitational wave detector. The aim is to enhance the corresponding electrical quality factors (Q-factors) which are closely related with the increase of the sensitivity of the system. In this experiment, the cavities are immersed in plasma and bombarded by energetic nitrogen ions, which are implanted into the surfaces of these heated substrates. The heating temperature of the cavities is controlled during the treatment and its level directly affects the N implantation depth profile due to the diffusion process. Additional tailoring of the nitrogen doping can be performed by the adjustment of the intensity and the duty cycle of the high negative voltage pulses used for ion implantation. For implantations performed at 5 kV /20 µs /300 Hz/ 700 °C, nitrogen atoms occupy interstitial spaces in the crystal lattice of niobium. The treatment of niobium superconducting cavities under these parameters caused the enhancement of two orders of magnitude of respective Q-factors. A set of characterization techniques was performed herein in order to help with the understanding of the underlying mechanism behind this phenomenon.

Evaluation of the resistance to oxidation of niobium treated by high temperature nitrogen Plasma Based Ion Implantation

Niobium is a technological material used in very distinct applications. Most of them as an alloying element, making part of superconducting radio frequency cavities, nuclear reactor components, missiles, rockets, aviation and space-system engineering. Nevertheless, although refractory, pure niobium presents as the main drawback the poor oxidation resistance in moderate and high temperatures. Different treatment methods have been used to mitigate this issue, as is the case of cementation, conventional nitridation, CVD and PVD processes. The evaluation of the resistance to oxidation of Nb treated by high temperature nitrogen plasma based ion implantation (HTPBII) has been described herein. The implanted nitrogen in this case easily diffuses to inner layers of niobium heated up to 1250°C during treatment, reaching depths of about 7μm, while its atomic concentration of about 25% remains stable for almost the whole treated surface. This allows the formation of thick nitride layers. The produced interstitial nitrides have outstanding properties as the high hardness and strength, like ceramics, and high thermal and electrical conductivities, like metals. In addition, these refractory nitrides also present good chemical resistance and superior resistance against oxidation. The investigation performed herein includes a series of characterization performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The oxidation of the ion-implanted niobium was retarded in comparison with the untreated counterpart in about 130°C. Isothermal analysis revealed reduced oxidation rate when treatment time was extended from 4h to 8h.

Characterization of a NiTi SMA wire treated by nitrogen plasma based ion implantation (PBII)

NiTi SMA wire with Ni-free surface is desirable as construction materials for a range of biomaterials to actuators associated to shape memory and superelastic properties. In biomaterials a potential problem with NiTi implant devices is the release of Ni in the human body. This work analyzes the effects of nitrogen plasma based ion implantation (PBII) technique in a wire of NiTi with shape memory effect associated to a Ni-free surface. The samples were treated for 60 min at 741 °C, with 16 kV high voltage pulses. Results of the thermo-mechanical properties of the PBII treated samples showed that there is no effect of the PBII treatment on the shape memory effect when compared to NiTi samples with no PBII treatment, which is desirable for applications addressing Ni-free surface and shape memory effect. Although it was noted that the stress-strain test causes cracks perpendicular to the stress direction on the treated surface.

Structure evolution and mechanical properties of Ta–Nb–Ti–W–N multielement films

In this study, the multielement films (Ta50·5Nb16·7Ti8·8W24·0)N, (Ta25·4Nb13·4Ti20·9W40·3)N and (Ta9·3Nb4·7Ti22·6W63·4)N are prepared by combining magnetron sputtering deposition and nitrogen plasma based ion implantation (N-PBII). The composition, structure and mechanical properties of the films are investigated. X-ray diffraction patterns show that the alloy films Ta50·5Nb16·7Ti8·8W24·0, Ta25·4Nb13·4Ti20·9W40·3 and Ta9·3Nb4·7Ti22·6W63·4 are composed of hcp+bcc, two types of bcc and a single bcc solid solution respectively, whereas all the Ta–Nb–Ti–W films are composed of bcc and fcc structures after N-PBII treatment. The lattice constant increases for both the bcc and fcc phases, while it decreases for the Ta and Nb concentrations in the films. The hardness and modulus of the Ta–Nb–Ti–W–N films are improved with increasing nitrogen implantation dose. The wear rate of the Ta25·4Nb13·4Ti20·9W40·3 with nitrogen implantation for 1 h is decreased two times than the Ta25·4Nb13·4Ti20·9W40·3 alloy films.

Detailed surface analyses and improved mechanical and tribological properties of niobium treated by high temperature nitrogen plasma based ion implantation

Transition metal nitrides, as is the case of NbN, exhibit an attractive mixture of physical, chemical and mechanical properties and can be used to overcome a severe constraint of pure niobium, that is the high oxidation rate for temperature above 400°C. In this work nitrogen ions were implanted into niobium by means of plasma based ion implantation (PBII) and high temperature PBII (HTPBII) in order to produce NbN on the surface of the material. In the case of HTPBII the treatment was performed in the temperature of 1000°C and 1250°C. In the process, negative pulses of 10kV/20μs/500Hz were applied to Nb samples for 1h. The depth of the modified layer reached up to 4.5μm due to the diffusion of nitrogen atoms implanted into the material. X-ray diffraction spectra showed the presence of ɛ-NbN, β-Nb2N and γ-Nb4N3 phases. Wear rate was reduced from 1.5×10−2mm3/Nm up to 2.6×10−6mm3/Nm for treated samples at high temperature in comparison with pristine samples, while friction coefficient was reduced from 0.8 to 0.25. Hardness was significantly increased. Surface topography was measured by optical profilometry. Surface roughness increases with the sample temperature but it remains lower than the one obtained by conventional PBII, very probably due to the heating method, which was performed by electron bombardment.

Chemical state and phase structure of (TaNbTiW)N films prepared by combined magnetron sputtering and PBII

(TaNbTiW)N films with thickness of ∼1000nm are prepared on titanium alloy substrate by combined magnetron sputtering deposition and nitrogen plasma based ion implantation (N-PBII). Chemical state of the elements and phase structure of the films are investigated using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The bonds of TaN, NbN, TiNO and TaO are detected in the (TaNbTiW)N films, however both WN and WO are not found. The initial alloy film has a BCC structure, while the films with N-PBII treatment are composed of BCC and FCC structures. The hardness and elastic modulus of the films can be improved by increasing nitrogen implantation dose and reach maximum values of 9.0GPa and 154.1GPa, respectively.

Characteristics of multi-element (ZrTaNbTiW)N films prepared by magnetron sputtering and plasma based ion implantation

Multi-element (ZrTaNbTiW)N films are prepared by multi-target magnetron sputtering deposition and nitrogen plasma based ion implantation (PBII). The composition, structure and mechanical properties of the films are investigated. X-ray photoelectron spectroscopy (XPS) confirms the formation of a mixture of ZrN, TiN, TaN, Nb–N, ZrO2, Ta, Nb and W in the nitride film. X-ray diffraction (XRD) shows that the (ZrTaNbTiW) alloy film exhibits an amorphous phase, while the (ZrTaNbTiW)N nitride films are composed of BCC and FCC structures. The hardness and modulus of the films are improved significantly after nitrogen PBII and reach maximum values of 13.5 and 178.9GPa, respectively.

Surface modification of NiTi by plasma based ion implantation for application in harsh environments

The substitution of conventional components for NiTi in distinct devices such as actuators, valves, connectors, stents, orthodontic arc-wires, e.g., usually demands some kind of treatment to be performed on the surface of the alloy. A typical case is of biomaterials made of NiTi, in which the main drawback is the Ni out-diffusion, an issue that has been satisfactorily addressed by plasma based ion implantation (PBII). Even though PBII can tailor selective surface properties of diverse materials, usually, only thin modified layers are attained. When NiTi alloys are to be used in the harsh space environment, as is the case of devices designed to remotely release the solar panels and antenna arrays of satellites, e.g., superior mechanical and tribological properties are demanded. For this case the thickness of the modified layer must be larger than the one commonly achieved by conventional PBII. In this paper, new nitrogen PBII set up was used to treat samples of NiTi in moderate temperature of 450°C, with negative voltage pulses of 7kV/250Hz/20μs, in a process lasting 1h. A rich nitrogen atomic concentration of 85at.% was achieved on the near surface and nitrogen diffused at least for 11μm depth. Tribological properties as well as corrosion resistance were evaluated.

Roughness studies of NiTi shape memory alloy treated by nitrogen plasma based ion implantation at high temperatures

The NiTi shape memory alloys (SMA) are employed in various applications, thanks to its specific mechanical properties. However, for many applications, it is interesting to improve its surface mechanical resistance to tribological or chemical attacks. This work aims to analyze the effects of nitrogen plasma based ion implantation (PBII) technique on the surface of NiTi produced by electron beam melting (EBM). The samples were treated for 120min (550°C and 770°C) and 360min (550°C), with 16kV high voltage pulses. The surfaces were analysed by X-ray diffraction (XRD), white light interferometry (WLI) and glow discharge optical emission spectrometry (GDOES). In addition to martensitic and austenitic NiTi, the XRD analysis shows the appearance of titanium nitride TiN and Ni3Ti phase in the PBII treated samples. Whereas the untreated specimen presents a RMS roughness RRMS around 16nm, the PBII treatments were shown to increase it, from 44nm, at 550°C, to 82nm at 770°C. The nitrogen incorporation ranges from 150nm (at 550°C, whatever the duration), up to more than 500nm (770°C) thanks to temperature activated diffusion. The increase of RRMS may be explained by the sputtering effect but it may be linked to the presence of a buried oxi-nitride phase grown by diffusion at higher temperature.

Nitrogen plasma-based ion implantation of poly(tetrafluoroethylene): Effect of the main parameters on the surface properties

The surface of poly(tetrafluoroethylene) (PTFE or Teflon) was treated by nitrogen plasma-based ion implantation. Accelerating voltages between 15 and 30 kV, fluences between 1 × 10 17 and 3 × 10 17 cm −2 and fluence rates between 3 × 10 13 and 7 × 10 13 cm −2 s −1 were applied. The effects of these main parameters were examined on the evolution of surface chemical composition, mean roughness, abrasive wear, wettability and surface electrical resistance. The aim was to obtain relationships, enabling to control the surface properties examined. The F/C atomic ratio determined by XPS strongly decreased, correlating inversely with voltage. The mean surface roughness characterized by topography measurements, increased, correlating directly with fluence and inversely with voltage. The wear volume obtained by multipass scratch tests did not show clear relationship with the main process parameters, however, it increased upon treatment with the increase of surface roughness and O/C atomic ratio. The water contact angle increased at low voltages and high fluences, due to preferential increase of roughness, and decreased at high voltages and low fluences, owing to intense defluorination and incorporation of N and O. The electrical resistance of the PBII-treated surfaces decreased by several orders of magnitude, showing a significant inverse correlation with fluence. It continued to decrease for samples exposed to air, primarily after treatments performed with low fluences, due to post-treatment type oxidation.

Plasma based ion implantation of engineering polymers

Abstract An overview of the rapidly developing field of modification of engineering polymers by plasma based ion implantation (PBII) and plasma based ion implantation and deposition (PBII&D) is presented. Furthermore, the applicability and usefulness of the approach of “design of experiments” is demonstrated by the nitrogen PBII treatments of polyamide 6 (PA) and poly(bisphenol A carbonate) (PC). Alterations in surface chemical composition and bonding were studied by XPS. Modifications in surface mechanical and tribological properties were followed by dynamic depth-sensitive nanoindentation and multiple nanoscratch measurements. Changes in wettability, surface energy and its components were evaluated by contact angle studies. Alterations in surface electrical resistance were also determined. Surface compositional changes reflected a relative decrease in the C-content and increase in the N-content for both polymers, while alterations in the peak shapes suggested degradation of the amide group with the formation of imine, protonated amine and urethane-like moieties for PA, and degradation of surface carbonate groups with the formation of imine, tertiary amine and amide-like groups for PC. The hydrophilicity of the surface increased and the surface electrical resistance decreased significantly for both polymers. The volume loss, obtained by the multi-pass scratch test, decreased from the original value expressed as V 0 = 100%, down to V = 11% and 59% for PA and PC, respectively. For PA the incorporation of some N had a favorable effect on the resistance to abrasive wear, but an excessive amount of N decreased this effect. Similarly, for PC a significant increase of the wear resistance could not be reached by the mere increase of the total N-content, but the surface concentration of tertiary amine type N should be maximized. The latter showed positive correlations with the fluence and the fluence rate applied.

Fabrication of nitrogen-doped TiO 2 layer on titanium substrate

In this paper, macropores TiO 2 layer was fabricated on titanium substrates based on plasma based ion implantation (PBII). In order to increase the photodegradation efficiency of fabricated TiO 2 layer, two approaches are used: (1) preparation of macropores on TiO 2 layer to increase the total photodegradation area and (2) nitrogen doping (N-doping) to increase light absorption efficiency. The fabrication process of the N-doped macropores TiO 2 layer comprises four steps: firstly, helium plasma based ion implantation (He-PBII) is employed to generate He bubbles in substrate; secondly, oxygen plasma based ion implantation (O-PBII) and a followed annealing in air are executed to obtain rutile and anatase mixture TiO 2 phases; thirdly, He bubbles are exposed to the surface via an Ar ion sputter process; lastly, the samples are doped by nitrogen PBII (N-PBII). The photodegradation of Rhodamine B solution under Xe lamp indicates that the TiO 2 layer with surface macropores and N-doping has higher light photocatalysis efficiency.

Synthesis of Boron Carbonitride Films by Plasma-Based Ion Implantation

BCN films were prepared with unbalanced magnetron sputtering boron carbide film followed by nitrogen plasma-based ion implantation at different voltages on Si substrate. The implantation voltages vary from 10 kV to 50 kV. The chemical states of B, C and N of the films were studied with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The nano-hardness and elastic modulus of films were measured by Nano-Indenter. The results showed that amorphous BCN films formed in the nitrogen implanted layer. The amorphous peak becomes obvious with increasing of the implanted voltage when the voltage is under of 40 kV. The Nano-Indenter measurement showed that the B-C bond content and the disorder degree affect the hardness and modulus.

A study of interface and adhesion of c-BN film on Si(100) modified by nitrogen plasma based ion implantation technique

Cubic boron nitride (c-BN) films were deposited on Si substrate with poor adhesion using magnetically enhanced active reaction evaporation (ME-ARE). An attempt has been made to enhance the adhesion strength between c-BN film and substrate by nitrogen plasma based ion implantation (PBII) into c-BN film. Nitrogen ion doses range from 5×10 16 to 1×10 17 ions cm −2 at an implant voltage of 50 kV. The nitrogen ion implanted c-BN films were analyzed using FTIR, scratch test, and XPS to investigate the change of structure, adhesion strength of c-BN film, and interfacial mixing between the initial turbostratic BN (t-BN) film layer and substrate caused by nitrogen ion implantation. FTIR spectra showed little change of c-BN phase content in the films under the above implantation conditions but XPS depth elemental profile of N + -implanted boron nitride films displayed a mixed layer consisting of elements from film and substrate formed at interface. A highly optimized dynamic Monte Carlo program TAMIX was used to simulate the PBII process in a good agreement with above measured depth elemental profile. The scratch test showed that the adhesion strength evaluated in terms of the critical load of N + -implanted c-BN film was 1.4 times higher than that of as deposited c-BM film.

Structural effect of nitrogen plasma-based ion implantation on ultra-high molecular weight polyethylene

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 μs duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp 3/sp 2 bonded carbon in the modified layer was obtained by suitable fitting of the XPS C 1s energy peak, using a four-curve fitting procedure, which recognizes a portion of C–O and CO surface bonding. The XPS results for N 1s peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering.

Structural effect of nitrogen plasma-based ion implantation on ultra-high molecular weight polyethylene

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 μs duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp 3 /sp 2 bonded carbon in the modified layer was obtained by suitable fitting of the XPS C 1s energy peak, using a four-curve fitting procedure, which recognizes a portion of C–O and CO surface bonding. The XPS results for N 1s peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering.

A study of interface and adhesion of c-BN film on Si(1 0 0) modified by nitrogen plasma based ion implantation technique

Cubic boron nitride (c-BN) films were deposited on Si substrate with poor adhesion using magnetically enhanced active reaction evaporation (ME-ARE). An attempt has been made to enhance the adhesion strength between c-BN film and substrate by nitrogen plasma based ion implantation (PBII) into c-BN film. Nitrogen ion doses range from 5×10 16 to 1×10 17 ions cm −2 at an implant voltage of 50 kV. The nitrogen ion implanted c-BN films were analyzed using FTIR, scratch test, and XPS to investigate the change of structure, adhesion strength of c-BN film, and interfacial mixing between the initial turbostratic BN (t-BN) film layer and substrate caused by nitrogen ion implantation. FTIR spectra showed little change of c-BN phase content in the films under the above implantation conditions but XPS depth elemental profile of N +-implanted boron nitride films displayed a mixed layer consisting of elements from film and substrate formed at interface. A highly optimized dynamic Monte Carlo program TAMIX was used to simulate the PBII process in a good agreement with above measured depth elemental profile. The scratch test showed that the adhesion strength evaluated in terms of the critical load of N +-implanted c-BN film was 1.4 times higher than that of as deposited c-BM film.

Effect of nitrogen plasma-based ion implantation on joint prosthetic material

In total hip arthroplasty (THA), Ultra High Molecular Weight Polyethylene (UHMWPE) wear debris generated at the articular surface has been recognized as a long-term cause of loosening and failure of artificial hip joints due to osteolysis. The technique of ion implantation has been used to improve wear resistance of the metal femoral head. The Plasma-Based Ion Implantation (PBII) technique is more suitable for complex shaped implants such as femoral head and femoral prosthesis due to three-dimensional ion implantation effects. The effect of pulse voltage and cooling of the substrate of the PBII process for Co–Cr-based materials were examined in terms of wear resistance by the pin-on-disc wear test. The wear resistance of Co–Cr alloy with high nitrogen-ion implantation dose was superior to the untreated Co–Cr alloy. Their corrosion resistance has also been examined with an anodic polarization measurement. High dose and cooling of PBII process proved to be effective in enhancing corrosion resistance of Co–Cr alloy. In this study, it was confirmed that the improvement of wear and corrosion resistance of Co–Cr alloy modified by PBII, as well as high pulse voltage and cooling of the substrate for PBII were the most effective treatments.

Plasma-based nitrogen implantation of chrome-plated steel

Plasma-based ion implantation (PBII) of nitrogen into chrome plated-steel is discussed with regard to dimensional homogeneity, depth distribution and the possibility of combining different implantation modes. A stainless holder with 60×10 mm 2 trenches at depths of 60, 40, 20 and 10 mm was made. The chromium-plated steel plates were fixed on the bottom of the trenches and treated by PBII under various conditions. The depth profiles and chemical bonds were measured with X-ray photoelectron spectroscopy (XPS) combined with Ar sputtering. The primary results confirmed that nitrogen PBII could introduce a significant amount of nitrogen into the chrome-plated layers in a shorter time than a conventional beam-line implanter. The implanted nitrogen was observed to combine with chromium. The depth profiles of nitrogen were the same for samples set on holder surfaces both facing and reversed to the RF source, which suggested homogeneous implantation in all directions. The PBII treatment was found to be homogenous for the trenches with an aspect ratio less than 4 without sample manipulation. A rapid elevation in temperature occurred during PBII treatment. Control of the target temperature remains as a future challenge.