Low-energy Nitrogen Ion Implantation Research Articles

Spatially selective p-type doping for constructing lateral WS2 p-n homojunction via low-energy nitrogen ion implantation

The construction of lateral p-n junctions is very important and challenging in two-dimensional (2D) semiconductor manufacturing process. Previous researches have demonstrated that vertical p-n junction can be prepared simply by vertical stacking of 2D materials. However, interface pollution and large area scalability are challenges that are difficult to overcome with vertical stacking technology. Constructing 2D lateral p-n homojunction is an effective strategy to address these issues. Spatially selective p-type doping of 2D semiconductors is expected to construct lateral p-n homojunction. In this work, we have developed a low-energy ion implantation system that reduces the implanted energy to 300 eV. Low-energy implantation can form a shallow implantation depth, which is more suitable for modulating the electrical and optical properties of 2D materials. Hence, we utilize low-energy ion implantation to directly dope nitrogen ions into few-layer WS2 and successfully realize a precise regulation for WS2 with its conductivity type transforming from n-type to bipolar or even p-type conduction. Furthermore, the universality of this method is demonstrated by extending it to other 2D semiconductors, including WSe2, SnS2 and MoS2. Based on this method, a lateral WS2 p-n homojunction is fabricated, which exhibits significant rectification characteristics. A photodetector based on p-n junction with photovoltaic effect is also prepared, and the open circuit voltage can reach to 0.39 V. This work provides an effective way for controllable doping of 2D semiconductors.

Gradient self-organized dislocation in expanded austenite layer during low temperature nitriding

Abstract A typical nitrogen expanded austenite layer is formed by plasma-based low-energy nitrogen ion implantation (PBLEII) on AISI 304L austenitic stainless steel at a moderate temperature of 380° C. The dislocation self-organization structure in the nitrogen expanded austenite layer is characterized as an evolution from partial and Lomer-Cottrell dislocations in the inner layer near the interface to multilayer stacking faults in the outer nitrided layer. The self-organized dislocation density and forms are essentially dependent on the plastic deformation, strain-gradient, and nitrogen-related stacking fault energies, respectively, due to the constrained expansion in the nitrided layer. As the nitrogen concentration in the austenitic matrix increases, the stacking fault energy gradually decreases, resulting in the transformation of the defect from Lamer-Cottrell dislocations to a multilayer stacking faults. The appropriate stress, which is associated with orderly stress relief during dislocation self-organization, preserves the integrity of the nitrided layer with a combinedly improved in wear and corrosion resistance. Nitriding-induced dislocation self-organization is basically explored as the formation mechanism of the nitrogen expanded austenite layer, contributing to development of the specific low-temperature nitriding austenitic steel.

Isolation, Mutagenesis, and Organic Acid Secretion of a Highly Efficient Phosphate-Solubilizing Fungus.

The highly effective phosphate-solubilizing microorganisms are significant for making full use of the potential phosphorus resources in the soil and alleviating the shortage of phosphorus resources. In this study, a phosphate-solubilizing fungus was isolated from wheat and cotton rhizosphere soils in the lower reaches of the Yellow River in China and was identified as Penicillium oxalicum by morphological and ITS sequencing analysis. In order to obtain a fungus with more efficient phosphorus solubilization ability, we tested three positive mutant strains (P1, P2, and P3) and three negative mutant strains (N1, N2, and N3) through low-energy nitrogen ion implantation mutagenesis. Compared with the parental strain, the phosphate-solubilizing capacity of P1, P2, and P3 was enhanced by 56.88%, 42.26%, and 32.15%, respectively, and that of N1, N2, and N3 was weakened by 47.53%, 35.27%, and 30.86%, respectively. Compared with the parental strain, the total amount of organic acids secreted significantly increased in the three positive mutant strains and decreased in the negative mutant strains; the pH of culture medium was significantly lower in the positive mutant strains and higher in the negative mutant strains. The capacity of phosphate-solubilizing fungus to secrete organic acids and reduce the growth-medium pH was closely related to its phosphate-solubilizing ability. The changes in the amount of organic acids secreted by mutants can alter their acidification and phosphate-solubilizing capacity. In conclusion, this study offers a theoretical basis and strain materials for the exploration and application of phosphate-solubilizing fungi.

P-n nanostructure formation effect of low-energy N2+ ions on n-GaAs surface

The electronic structure and chemical composition of the n-GaAs surface after implantation of N2+ ions with energy Ei = 3000 eV and fluence Q ∼ 3 × 1015 cm−2 were studied by synchrotron-based X-ray photoelectron spectroscopy to clarify effects of low-energy nitrogen ion implantation on A3B5 semiconductor surfaces. Conversion of the conductivity type and creation of a p-n structure on the n-GaAs surface were revealed under N2+ ion irradiation. The conductivity type transformation was shown to occur due to pure mechanical action of nitrogen ions, resulting in formation of Ga anti-site acceptors. The ∼ 10 nm-thick p-layer obtained consisted of concentrated GaAs1-xNx (x ∼ 0.1) alloy whose bandgap width is known to be essentially narrower compared to the pristine GaAs semiconductor. Therefore, the structure formed is a nano-heterosctructure incorporating the semiconductor alloy whose properties are considered to be attractive for infrared applications. The obtained GaAsN electron binding energies (EB (N1s) = 397.0 eV, EB (Ga3d) = 19.42 eV and EB (As3d) = 41.25 eV) can be used for identification of the GaAsN alloy phase. An approach to 3D p-n structures formation was suggested using nitrogen ion beam without wet lithography.

Effect of Low-Energy Nitrogen Ion Implantation on Friction and Wear Properties of Ion-Plated TiC Coating

To further improve the performance of the coated tools, we investigated the effects of low-energy nitrogen ion implantation on surface structure and wear resistance for TiC coatings deposited by ion plating. In this experiment, an implantation energy of 40 keV and a dose of 2 × 1017 to 1 × 1018 (ions/cm2) were used to implant N ions into the TiC coatings. The results indicate that the surface roughness of the coating increases first and then decreases with the increase of ion implantation dose. After ion implantation, the surface of the coating will soften and reduce the hardness, and the production of TiN phase will gradually increase the hardness. Nitrogen ion implantation can reduce the friction coefficient of the TiC coating and improve the friction performance. In terms of wear resistance, the coating with an implant dose of 1×1018 ions/cm2 has the greatest improvement in wear resistance. Tribological analysis shows that the improvement in the performance of TiC coatings implanted with N ions is mainly due to the effect of the lubricating implanted layer. The implanted layer mainly exists in the form of amorphous TiC, TiN phase, and sp2C–C phase.

Indirect overgrowth as a synthesis route for superior diamond nano sensors

The negatively charged nitrogen-vacancy (hbox {NV}^{-}) center shows excellent spin properties and sensing capabilities on the nanoscale even at room temperature. Shallow implanted hbox {NV}^{-} centers can effectively be protected from surface noise by chemical vapor deposition (CVD) diamond overgrowth, i.e. burying them homogeneously deeper in the crystal. However, the origin of the substantial losses in hbox {NV}^{-} centers after overgrowth remains an open question. Here, we use shallow hbox {NV}^{-} centers to exclude surface etching and identify the passivation reaction of NV to NVH centers during the growth as the most likely reason. Indirect overgrowth featuring low energy (2.5–5 keV) nitrogen ion implantation and CVD diamond growth before the essential annealing step reduces this passivation phenomenon significantly. Furthermore, we find higher nitrogen doses to slow down the NV–NVH conversion kinetics, which gives insight into the sub-surface diffusion of hydrogen in diamond during growth. Finally, nano sensors fabricated by indirect overgrowth combine tremendously enhanced T_2 and T_2^* times with an outstanding degree of depth-confinement which is not possible by implanting with higher energies alone. Our results improve the understanding of CVD diamond overgrowth and pave the way towards reliable and advanced engineering of shallow hbox {NV}^{-} centers for future quantum sensing devices.

Silicon solar cells with nitrogen-rich SiNx/Si interfacial passivation by low-energy nitrogen-ion implantation

We investigated low energy nitrogen ion implantation into the SiNx/Si interfacial layer of silicon solar cells using various energies and fluences, followed by a thermal annealing process. The low energy implanted nitrogen ions penetrated into the SiNx antireflection layer and reached the Si emitter layer. However, ions could not pass through the Ag electrode contact layer and were unable to form the contact passivation layer. A low energy nitrogen ion implanted cell showed the formation of a rich nitrogen layer in the SiNx/Si interfacial area and an increase in electrical performance. With increasing nitrogen ion implantation energy, cells were damaged and suffered decreasing efficiency compared to a reference cell. Increasing the fluence of nitrogen ions also caused a decrease in cell efficiency. After a low temperature annealing process, the cell efficiency recovered almost to the pre-implantation point of the reference cells and showed a similar recovery in their photoreflectance and quantum efficiency. The low-energy nitrogen ion implantation showed the improved cell efficiency of 17.28% for the energy of 12 keV with a fluence of 1 × 1013 cm-2.

Formation of buried superconducting Mo2N by nitrogen-ion-implantation.

Nitrogen ion implantation is a useful technique to put nitrogen ions into lattices. In this work, nitrogen ion implantation into epitaxial Mo films is performed to create a buried superconducting γ-Mo2N. Atomically flat epitaxial (110) Mo films are grown on (0001) Al2O3. By impinging nitrogen ions, where the beam energy is fixed to 20 keV, we observe (111) γ-Mo2N diffraction and the formation of a γ-Mo2N layer from X-ray reflectivity. Magnetization and transport measurements clearly support a superconducting layer in the implanted film. Our strategy shows that formation of a buried superconducting layer can be achieved through ion implantation and self-annealing.

Effect of nitrogen ion implantation in semi insulating 6H-SiC and recrystallization probed by Raman scattering

The study is intended to investigate the low energy nitrogen ion implantation induced behavior and re-crystallization in semi-insulating 6H-SiC from surface to 5 µm, by Raman spectroscopy. The nature of defects accumulation related to the SiC bond breakages and re-crystallization on vacuum annealing were analyzed from the A1(LO) phonon mode and probed at successive depth from the surface. Variations on the asymmetrical A1(LO) peaks of as-implanted samples were made to order upon annealing, and the mode regained. The peak intensity variation of A1(LO) mode indicated the disorder accumulation. The identified damage depth was in good agreement with Stopping and Ranges of Ions in Matter (SRIM). The changes in Si-Si, deformed-Si-C, C-C vibrations and crystalline-SiC were used to explain the defect role in the implanted and annealed samples.

Lithographically engineered shallow nitrogen-vacancy centers in diamond for external nuclear spin sensing

The simultaneous control of the number and position of negatively charged nitrogen-vacancy (NV) centers in diamond was achieved. While single near-surface NV centers are known to exhibit outstanding capabilities in external spin sensing, trade-off relationships among the accuracy of the number and position, and the coherence of NV centers have made the use of such engineered NV centers difficult. Namely, low-energy nitrogen implantation with lithographic techniques enables the nanoscale position control but results in degradation of the creation yield and the coherence property. In this paper, we show that low-energy nitrogen ion implantation to a 12C (99.95%)-enriched homoepitaxial diamond layer using nanomask is applicable to create shallow NV centers with a sufficiently long coherence time for external spin sensing, at a high creation yield. Furthermore, the NV centers were arranged in a regular array so that 40% lattice sites contain single NV centers. The XY8-k measurements using the individual NV centers reveal that the created NV centers have depths from 2 to 12 nm, which is comparable to the stopping range of nitrogen ions implanted at 2.5 keV. We show that the position-controlled NV centers are capable of external spin sensing with a ultra-high spatial resolution.

The Effect of Low Energy Nitrogen Ion Implantation on Graphene Nanosheets

Herein, we report the effect 50 keV nitrogen ion implantation at varying fluence on the optical properties of graphene nanosheets (number of layers < 5). Initially, graphene nanosheets synthesized by the direct liquid exfoliation of graphite layers were deposited on a cleaned Si-substrate by drop cast method. These graphene nanosheets are implanted with 50 keV nitrogen-ion beam at six different fluences. Raman spectroscopic results show that the D, D′ and G peak get broadened up to the nitrogen ion fluence of 1 × 1015 ions/cm2, while 2D peak of graphene nanosheets disappeared for nitrogen-ions have fluence more than 1014 ions/cm2. However, further increase of fluence causes the indistinguishable superimposition of D, D′ and G peaks. Surface contact potential value analysis for ion implanted graphene nanosheets shows the increase in defect concentration from 1.15 × 1012 to 1.98 × 1014 defects/cm2 with increasing the nitrogen ion fluence, which resembles the Fermi level shift towards conduction band. XRD spectra confirmed that the crystallinity of graphene nanosheets was found to tamper with increasing fluence. These results revealed that the limit of nitrogen ion implantation resistant on the vibrational behaviors for graphene nanosheets was 1015 ions/cm2 that opens up the scope of application of graphene nanosheets in device fabrication for ion-active environment and space applications.

Mutation breeding of ethanol-producing yeast Saccharomyces cerevisiae by low-energy nitrogen ion implantation and UV rays

Mutation breeding of ethanol-producing yeast Saccharomyces cerevisiae by low-energy nitrogen ion implantation and UV rays

Shallow nitrogen ion implantation: Evolution of chemical state and defect structure in titanium

Evolution of chemical states and defect structure in titanium during low energy nitrogen ion implantation by Plasma Immersion Ion Implantation (PIII) process is studied. The underlying process of chemical state evolution is investigated using secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The implantation induced defect structure evolution as a function of dose is elucidated using variable energy positron annihilation Doppler broadening spectroscopy (PAS) and the results were corroborated with chemical state. Formation of 3 layers of defect state was modeled to fit PAS results.

CrN precipitation and elemental segregation during the decay of expanded austenite

Nitrogen insertion into austenitic stainless steel at elevated temperatures leads to anomalous fast nitrogen diffusion and the formation of an expanded fcc phase which is known as expanded austenite. In situ x-ray diffraction measurements during low energy nitrogen ion implantation into steel AISI 304 at 475 °C and short annealing at 575 °C were performed in conjunction with transmission electron microscopy investigations. They show the time dependent decay of this expanded phase with coalescing and growing CrN precipitates. There is elemental segregation associated with this decay where Fe is absent very early from the Cr–N containing precipitates. Ni is segregating towards the Fe-rich matrix more slowly. At the same time, the microstructure—decayed phase vs expanded austenite—is visible in SIMS cluster analysis.

Corrosion-fatigue properties of plasma-based low-energy nitrogen ion implanted AISI 304 L austenitic stainless steel in borate buffer solution

Abstract AISI 304 L austenitic stainless steel was modified by using the plasma-based low-energy nitrogen ion implantation (PBLEII) at a process temperature of 400 °C for a processing time of 4 h in order to improve the corrosion-fatigue resistance of the austenitic stainless steel. A single high-nitrogen face-centered-cubic phase (γN) layer with a maximal nitrogen concentration of about 25 at.% was formed on the nitrogen-modified austenitic stainless steel. Compared with the original austenitic stainless steel, the γN phase layer on the austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with a pH value of 8.4. The corrosion-fatigue properties of the γN phase layer on the austenitic stainless steel were examined by the push–pull fatigue experiments with a ratio R of tensile and compression of − 1 in the borate buffer solution. The γN phase layer has an increased corrosion-fatigue strength up to 230 MPa from 180 MPa of the original austenitic stainless steel with an apparent increase of about 28%. The corrosion-fatigue crack initiation in the γN phase layer was found as a controllable stage in the fracture process at the interface between the γN phase layer and the austenitic stainless steel matrix with the arc corrosion-fatigue source. Some tiny corrosion-fatigue striations were obtained on the corrosion-fracture surfaces of the γN phase layer. The high density of slip bands and dislocations in the γN phase layer was able to prevent the crack initiation and propagation, leading to improvement of the corrosion-fatigue properties in the borate buffer solution.

Novel ultraviolet emitting low energy nitrogen ion implanted magnesium ion incorporated nanocrystalline calcium phosphate

The effect of low energy nitrogen ion (N+) implantation on microwave synthesized magnesium ion incorporated hydroxyapatite (HAp-Ca10(PO4)6(OH)2) was analyzed with fluences of 1×1014, 1×1015 and 1×1016 ions/cm2. The implant enhanced surface roughness, pore size (35%) and bioactivity along with a considerable decrease in the crystallite size (21%) and resistivity. Enhanced photoluminescence (PL) at 352nm was observed at 1×1014 ions/cm2. The surface turned to hydrophilic and hydrophobic at lower fluence (<1×1014 ions/cm2) and higher fluence (>1×1016 ions/cm2) respectively. Ion implantation is a cost-effective and rapid technique to modify the surface of magnesium ion incorporated HAp. The ion implanted sample has multifunctional properties and could be used for biomedical, biosensing applications and also utilized as a novel environmental friendly, rare-earth free ultraviolet phosphor material.

Modeling of Inner Surface Modification of a Cylindrical Tube by Plasma-Based Low-Energy Ion Implantation**supported by National Natural Science Foundation of China (Nos. 50725519, 51271048, 51321004)

The inner surface modification process by plasma-based low-energy ion implantation (PBLEII) with an electron cyclotron resonance (ECR) microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications. In this paper, a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias. Using this plasma density distribution as the initial condition, a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time. The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field. The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24, respectively, of which the value is 1 at the central plasma source. After a 5 μs pulse-on time, in the area less than 2 cm from the end of the tube, the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°; both variations reduce the nitrogen ion implantation depth. However, the nitrogen ion implantation dose peaks of about 2×1010 – 7×1010 ions/cm2 in this area are 2 – 4 times higher than that of 1.18×1010 ions/cm2 and 1.63×1010 ions/cm2 on the inner and outer surfaces of the tube. The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation, because the modification effect is mainly determined by the ion implantation dose, just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion. Therefore, a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.

In situ investigation of phase formation during low energy ion nitriding of Ni80Cr20 alloy

The formation of expanded austenite after nitrogen insertion into austenitic stainless steel, CoCr or Ni base alloys is characterised by an unusually high nitrogen content in solid solution representing a diffusion layer. However, the process is still not completely understood. Using in situ X-ray diffraction (XRD) experiments and additional data from SEM, the phase formation and diffusion after low energy nitrogen ion implantation into commercial Ni80Cr20 (Nichrome) are investigated in the temperature range from 350 to 500°C. A compound layer consisting of a phase similar to fct Ni4N is formed on the surface, most likely with a composition of (Ni,Cr)4N, followed by a diffusion zone extending about 1μm into the material. For increasing temperature, the total nitrogen uptake is decreasing. The time evolution shows that a saturation is reached earlier for higher temperatures whereas no saturation has been found for 375°C and 90min. A competition exists between nitrogen loss at the surface and nitrogen supply by the ion beam. This loss process is thermally activated and depends on the surface orientation. Additionally, at 500°C some CrN precipitates are found.

In situ x-ray diffraction investigations during low energy ion nitriding of austenitic stainless steel grade 1.4571

Insertion of nitrogen into austenitic stainless steel leads to anomalously fast nitrogen diffusion and the formation of an expanded face-centred cubic phase which is known to contain a large amount of mechanical stress. In situ x-ray diffraction (XRD) measurements during low energy nitrogen ion implantation into steel 316Ti at 300–550 °C allow a direct view into diffusion and phase formation. While the layer growth is directly observable from the decreasing substrate reflection intensity, the time evolution of the intensities for the expanded phase reflection is much more complex: several mechanisms including at least formation and annealing of defects, twinning, reduction of the crystal symmetry, or grain rotation may be active inside the expanded phase, besides the thermally activated decay of the metastable expanded phase. This locally varying coherence length or scattering intensity from the expanded phase is furthermore a function of temperature and time, additionally complicating the deconvolution of XRD spectra for stress and concentration gradients. As no concise modelling of this coherence length is possible at present, a simple qualitative model assuming a dependence of the scattering intensity on the depth, influence by stress and plastic flow during the nitriding process is proposed for understanding the underlying processes.

Mass Deposition, Etching and Sputtering Effects of Low-Energy N+ Ion Irradiation on Solid Fly Ash

Fly ash is an industrial waste created when coal is burned to generate electrical power. In the present study, we used low-energy nitrogen ion implantation on fly ash to improve its surface properties. Scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were used to study the changes of physical and chemical properties of fly ash after N+ ion implantation, and the mechanism of fly ash modified by ion implantation. In the optimal implantation with energy of 5 keV and dose of 15D0, the ion beam could effectively increase the specific surface area (approximately 150% increase) of the fly ash. Lots of scratches were generated in the surface of the fly ash after N+ ion implantation, therefore it is good for enhancing the specific surface area. Experimental results show that the ion implantation could open the chemical bonds of Si-O, Si-Al and Al-O, and deposit nitrogen ions on the surface of fly ash.