Redeposition Effect Research Articles

Controllable Fabrication of Gallium Ion Beam on Quartz Nanogrooves.

Nanogrooves with high aspect ratios possess small size effects and high-precision optical control capabilities, as well as high specific surface area and catalytic performance, demonstrating significant application value in the fields of optics, semiconductor processes, and biosensing. However, existing manufacturing methods face issues such as complexity, high costs, low efficiency, and low precision, especially in the difficulty of fabricating nanogrooves with high resolution on the nanoscale. This study proposes a method based on focused ion beam technology and a layer-by-layer etching process, successfully preparing V-shaped and rectangular nanogrooves on a silicon dioxide substrate. Combining with cellular automaton algorithm, the ion sputtering flux and redeposition model was simulated. By converting three-dimensional grooves to discrete rectangular slices through a continuous etching process and utilizing the sputtering and redeposition effects of gallium ion beams, high-aspect-ratio V-shaped grooves with up to 9.6:1 and rectangular grooves with nearly vertical sidewalls were achieved. In addition, the morphology and composition of the V-shaped groove sidewall were analyzed in detail using transmission electron microscopy (TEM) and tomography techniques. The influence of the etching process parameters (ion current, dwell time, scan times, and pixel overlap ratio) on groove size was analyzed, and the optimized process parameters were obtained.

Prolonged pattern coarsening in ion irradiated swinging Si substrates

Low energy ion beams are regarded as an effective means to spatio-temporally pattern a wide variety of surfaces that exhibit intriguing motifs. In this work, an unconventional technique of surface patterning has been demonstrated by studying the topographical evolution of a Si(100) surface in the presence of azimuthal sample swinging (Δϕ=20∘) under 500 eV Ar+irradiation with a polar incidence angle of 67°. A prolonged wavelength coarsening is also noticed for the swinging sample. Ripple anticoarsening is observed for static sample at high fluences. The linear and nonlinear growth regimes are found to bear a direct consequence of this unconventional geometry. Furthermore, two-dimensional slope distributions of the surface morphologies clearly indicate reduced asymmetries in the surface structures. The present geometry brings in an additional factor of differential exposure and redeposition effects in addition to the near-surface mass redistribution, the former being inconceivable in the static configuration. This study establishes the role of this unconventional yet simple method to precisely modify and control surface asymmetries and influence regime shifts.

Absolute doubly differential angular sputtering yields for 20 keV Kr+ on polycrystalline Cu

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness.

Evaluation of Pt particles redeposition effect on gas transport in Nafion membrane

During the operation of proton exchange membrane fuel cell, Pt particles in the catalytic layer inevitably dissolve into the membrane, which affects the performance of fuel cell. In this work, molecular dynamics is employed to investigate the effect of the redeposition of Pt particles on gas diffusion and solvation characteristics in the hydration membrane. Gas diffusion, hydrophilic cluster and its connectivity are analyzed. The interaction between Pt particles, Nafion membrane and water molecules is discussed. The influence of Pt particles on the thermal conduction of membrane is also evaluated. The results demonstrate that the presence of Pt particles affects the solvation effect of membrane, leading to a weak water cluster connectivity of membrane, which in turn leads to a poor gas diffusion performance. In addition, the thermal conductivity gradually deteriorates during the redeposition of Pt particles.

Effects of metal redeposition in plasma sputtering

Ion sputtering, whereby atoms on target surfaces are bombarded by energetic ions, is a key process in the film-coating industry. However, its detailed mechanism has not yet been clarified and remains an empirical operation. This article demonstrates that the redeposition of metal on the target surface significantly enhances the sputtering rate. Although the effect differs depending on the metal species, significant enhancement in the sputtering rate occurs in glow-discharge plasma sputtering––a maximum increase of approximately 2.4 times was observed under experimental conditions. The experimental data agree well with the model equation, which superimposes two processes: sputtering by the desorbed redeposited metal and reduction of the enthalpy of sublimation by the adsorbed redeposited metal. The results of this study demonstrate that the metal redeposition effect is a key mechanism missing in the plasma sputtering process and that taking redeposition into account frees us from its empirical use. These findings are expected to address several of the existing questions related to sputtering, enabling the development of a wide variety of applications.

Simulation of lithium flow, redeposition, and vapor shielding in liquid lithium divertor of T-15MD tokamak with SOLPS 4.3 code

The erosion module of the SOLPS 4.3 code package for the liquid Li divertor target is developed to include the thermal sputtering, evaporation, and prompt redeposition effects. Eroded Li atoms are treated within a fully kinetic approach. Simulations for the T-15MD tokamak with liquid Li divertor targets are performed for various operational regimes. The main parameters characterizing the divertor operation are identified. The Li shielding effect is found significant at the input power P SOL > 15 MW. The target conditions remain reasonable in terms of both the erosion rate and target temperature but core plasma dilution with Li remains a problem. The Li flow patterns in the scrape-of-layer (SOL) are analyzed in detail. About 80% of eroded Li is redeposited back on the target. The energy dissipated per an eroded Li particle, E sh, is calculated and its values are in the range of 100–200 eV. These values are 2–4 times lower than those obtained from a simple 0D estimation of E sh. Therefore, relying on simple 0D models for the analysis of Li divertor performance may cause an overestimation of the shielding efficiency.

Effect of re-depositions and fiber exposure on the adhesive bond strength of CFRP after UV excimer laser treatment

Adhesive bonding of CFRP is one major approach to join this class of compound materials with other components, e.g., metals. The necessity to clean CFRP parts after fabrication and generate a bond-ready interface without damaging the implemented fibers demands a gentle and highly reproducible surface treatment. Lasers operating in the UV region are one promising technique for that topic. Yet, the factors influencing the adhesion properties of laser-treated CFRP are not sufficiently understood. The present paper describes the influence of nanosecond-pulsed laser parameters on CFRP treatment effects in context of adhesive bonding properties. A special focus was given on the distribution and avoidance of re-deposition effects by laser parameter selection. Furthermore, the effect of laser-induced fiber exposure was analyzed. Re-deposition and fiber exposure were complementarily discussed with chemical analyses of the surface composition after laser treatment in the context of bond strength studies under Mode I loading. It was found that both effects, i.e., re-deposition on the treated surface and laser-induced fiber exposure by overtreatment, result in lower strength values compared to an “optimized” treatment exhibiting none of the descripted conditions.

Comparative study regarding the sputtering yield of nanocolumnar tungsten surfaces under Ar+ irradiation

Nanostructured tungsten has been proposed as a promising option for plasma facing materials in future fusion reactors, because compared to conventional tungsten it shows advantages such as a better radiation resistance and, in particular, a retardation of tungsten-fuzz growth. Besides these aspects, the sputtering yield of nanostructured tungsten under ion bombardment is of interest, since it would affect the atomic density of tungsten emitted into the fusion plasma, which leads to radiative heat losses. In this work, we present a multiscale approach for investigating the sputtering yield of nanocolumnar tungsten surfaces under 1 keV and 2 keV ${\mathrm{Ar}}^{+}$ irradiation. Our results cover experiments and also computational simulations, which operate either on the basis of the binary collision approximation and ray tracing or use a full molecular dynamics implementation. In our studied case, both computational approaches can predict the sputtering yield of nanocolumnar tungsten surfaces very well. In comparison to flat W, we observe a much reduced dependence on the ion incidence angle, similar as reported for conventional rough surfaces in literature. However, an additional global reduction of the sputtering yield was identified, which can be attributed to geometrical redeposition effects between the separated nanocolumns. These results support the applicability of nanocolumnar tungsten as a first wall coating.

Study of silicon dioxide focused ion beam sputtering using electron microscopy imaging and level set simulation

Sputtering silicon dioxide by the ion beam of gallium ions was studied to obtain the angular dependence of the sputtering yield and estimate the secondary sputtering yield of the redeposited material. For this purpose, rectangular boxes were formed in the SiO2 layer at different incidence angles of the ion beam. The box depths and the distributions of gallium atoms were estimated using the cross-sectional specimens examined by scanning and transmission electron microscopy techniques. The found depth values enabled calculating the sputtering yield angular dependence which was approximated using well-known fitting formulas. It was also demonstrated that for an incidence angle varied from approximately 40°–70° ripple topography is formed on the ion bombarded silicon dioxide. To validate the obtained data characterizing SiO2 sputtering, test symmetrical and asymmetric structures with different aspect ratios were experimentally prepared and simulated using the level set method taking into account the redeposition effect and reflection of incident ions from the sputtered surface. It was established that the performed simulation provides sufficient accuracy in predicting the shape of the focused ion beam fabricated structures in silicon dioxide.

Characterization and simulation of sputtering etched profile by focused gallium ion beam on GaN substrate

With the continuous development of manufacturing technology of micro/nano devices based on GaN, focused gallium ion beam has become a momentous method for machining complex GaN structures. Therefore, this study focuses on the characterization and simulation of sputtering etched profile by Ga FIB on GaN substrate. First, the profile characterization experiments are carried out to analyze the influence of ion dose, dwelling time, and scan area, and the results reflect that the sputtering etched regularity on GaN substrate differs from that on Si substrate, especially in redeposition effect, milling rate, and droplet phenomenon. In addition, the forming mechanism of droplet phenomenon is discussed, and the milling experiments are conducted to research the droplets avoidance method, which shows that the appearance of droplets is impacted by ion dose and dwelling time. Finally, the sputtering yield of GaN under focused gallium ion beam is measured and sorted, and the simulation program is developed based on continuous cellular automaton (CCA) model. This work can provide a guidance for the further application of GaN-based materials.

Modeling of the impurity-induced silicon nanocone growth by low energy helium plasma irradiation

The formation mechanism of nanocone structure on silicon (Si) surface irradiated by helium plasma has been investigated by experiments and simulations. Impurity (molybdenum) aggregated as shields on Si was found to be a key factor to form a high density of nanocone in our previous study. Here to concrete this theory, a simulation work has been developed with SURO code based on the impurity concentration measurement of the nanocones by using electron dispersive x-ray spectroscopy. The formation process of the nanocone from a flat surface was presented. The modeling structure under an inclining ion incident direction was in good agreement with the experimental result. Moreover, the redeposition effect was proposed as another important process of nanocone formation based on results from the comparison of the cone diameter and sputtering yield between cases with and without the redeposition effect.

Purification of a Thermostable β-mannanase from Paenibacillus Thiaminolyticus - characterization and its Potential Use as a Detergent Additive

Endo-1, 4- β- D-mannanase (EC 3.2.1.78) is a glycoside hydrolase involved in random cleavage of β-1, 4- D-manno-pyranosyl linkages within mannans and heteromannans and generates branched and linear oligosaccharides. A β-mannanase was purified from a thermotolerant bacterium Paenibacillus thiaminolyticus isolated from a soil sample. Enzyme was purified to homogeneity with specific activity of 8812 U/mg protein. Sodium dodecyl sulfate (SDS) and native poly-acryl amide gel electrophoresis indicated that the purified mannanase is a monomeric protein with a molecular mass of 38 kDa. The purified enzyme was found to be maximally active at temperature and pH of 60°C and 7.0, respectively. It was stable at 55°C for 24 h and maintained more than 50 % activity up to 3 h at 60°C. The enzyme was very stable in the pH range of 5.0-9.0. Purified β-mannanase demonstrated high stability after 1 h of pre-incubation with most of the tested organic solvents. Enzyme retained significant stability in the presence of various detergent additives, commercially available detergents and dish washing liquids. The high compatibility and substantial stability in the presence of nonionic detergents and dishwashing liquids confirmed its utility as an additive to dish washing liquids and laundry detergents. Enzyme exhibited efficacious de-staining of heteromannan based stains of chocolate ice cream and salad dressing in the wash performance test for detergent application. It also exhibited anti-soil redeposition effect on cotton swatches treated with tennis court clay and heteromannans.

Characterization of multilayer coatings of aluminium, tungsten and molybdenum on steel substrate using laser-induced breakdown spectroscopy

Laser induced breakdown spectroscopy (LIBS) has been applied for the depth profiling of multilayer metallic coating structure which is simulated to the ITER-like wall materials in fusion devices such as EAST tokamak. The coatings were produced by magnetron sputtering and characterized by LIBS using a Nd:YAG laser at 1064 nm with pulse duration of 5 ns. The light from the resulting plasma was analyzed as a function of both number of laser pulse (N) and elemental spectral line intensity. The depth profile of the multilayer coating was determined by three different spectral signal processing methods; intensity background subtraction, intensity normalization and linear Pearson correlation. The intensity normalization method provides the best outcomes/solutions for thickness measurement and analysis of interfaces of multilayer coatings among other methods. The evolution of spectral intensity representing different materials was properly examined for 90 consecutive laser shots at the same spot. The ablation behaviour of the coating materials was analyzed in terms of ablation rate under the laser pulse of various fluences. In a much deep crater, some factors originating from laser ablation, such as material re-deposition and plasma shielding effect were analyzed. As a comparison, the depth, shape and diameter of craters were also measured using SEM and a profilometer. The influence of laser power density on the ablation rate and crater profile was investigated. The elemental composition, inside the crater, was verified by the EDX technique. The results indicate that LIBS has a potential power for in-situ depth profiling of multilayer coatings on the wall of the EAST.

Single-step fabrication of single-junction c-Si nano-structured solar cells by optimization of plasma etching parameters

The production cost of photovoltaic solar cells could be reduced by minimizing the number of fabrication steps, e.g., eliminating separate stages of assembling p-layer, n-layer and anti-reflection coating layer. The uniqueness of the present work remains in the single step growth of the n-layer and the simultaneous anti-reflection coating layer via plasma etching of the p-type crystalline silicon (p–c-Si) wafers by low pressure inductively coupled plasma (ICP) CVD system. Chemical and physical etching of the p–c-Si wafer by high density of atomic H and ionic Ar/H species in the (Ar + H2) plasma create surface-roughness that introduce reduced surface reflectance. Further, ejection of Si moieties from the wafer surface produces SiHX (x = 1–4) radicals in the plasma, which in turn instigate re-deposition at the dangling c-Si bond sites and produce variety of silicon nanostructures (Si-NSs). The etching and sequential redeposition effects occur differently on varying gas ratio of Ar/H2, changing plasma pressure and etching temperature. At optimized low pressure (∼100 mTorr) in the plasma crystalline silicon nano-pillar like structures of uniform diameter, length and alignment are produced, from which multiple internal reflections result efficient light trapping and a significantly low reflection loss. Further, the plasma deposited Si nanostructures on the etched p-type c-Si wafer surface changes to n-type in electronic configuration, grown via p-to-n type conductivity conversation (PTNCC) process, initiated by alteration in BH1 bonds to BH2 and/or BH3 configurations. The p-n junction solar cells spontaneously grown via PTNCC mechanism demonstrates a proof-of-concept conversion efficiency, η ∼4.22%, using ITO layer at the front and silver (Ag) paste as the back electrodes.

Formation mechanism and compensation methods of profile error in focused ion beam milling of three-dimensional optical microstructures

The formation mechanism and compensation methods of the profile error in focused ion beam (FIB) bitmap milling of three-dimensional (3D) optical microstructure are studied in this paper. The processing parameters such as ion beam currents, dwell times, and beam overlap ratios on the profile error have an optimized parameters combination of 21 nA, 10 μs, and 50%, and the shape accuracy processed under the conditions is 0.44 μm of P–V and 0.142 μm of RMS, respectively. Inappropriate processing parameters lower either shape accuracy or processing efficiency. By means of an accurate simulation model of the FIB machined 3D profiles, the intrinsic formation mechanism of the profile error can be attributed to ion beam diameters, redeposition effect, and sputter yields, and these factors are inevitable in FIB milling of 3D microstructures. In situ modification and iterative optimization are proposed to compensate the FIB milling error, which both can improve the shape accuracy more than 50%. The in situ modification method needs to load the original bitmap and modified bitmap separately, which is less convenient than the iterative optimization method that only need loading one bitmap file. However, the in situ modification is better than the iterative optimization at decreasing the RMS value of the profile error which indicates the global profiles error of the processed microstructures.

Fabrication of refractive silicon microlens array with a large focal number and accurate lens profile

In this paper, we demonstrate the fabrication of refractive silicon microlens array with a large focal number and almost perfect spherical lens shape. Through a modified thermal reflow, photoresist microlens array of a large focal number is fabricated, which is then transferred into the silicon substrate by ion beam milling. To reach an accurate spherical lens profile, we both theoretically and experimentally study the practical factors that harm the pattern transfer fidelity, which mainly include the etching selectivity and faceting effect. Other secondary etching effects, such as the trenching effect and re-deposition effect, are also discussed. Based on these studies, a silicon microlens array with a focal number of 1.35 has been successfully obtained, with the profile error controlled well-below 0.121 μm, less than λ/6 within the whole infrared wavelength band. Besides, the fabricated microlens array exhibits a good uniformity and fine surface smoothness. The fabricated silicon microlens arrays can be applied in minatured infrared and terahertz imaging devices, or used as the master mould for soft lithography.

Fabricating high-quality Fresnel zone plates by efficiently eliminating redeposition based on focused ion beam

Fresnel zone plates (FZPs) are significant optical objects for extreme ultraviolet and x-ray microscopy, both of which are powerful tools due to their high spatial resolution and large penetration depth. Fabrication of FZPs is challenging as it requires high accuracy to achieve the narrow outmost zone and large aspect ratio. The focused ion beam (FIB) has been practically demonstrated as a potential alternative to electron beam lithography for its precision, rapidness, and mask-free essence. However, the common redeposition effect in the FIB process is a major obstacle to distort actual patterns from designed ones, especially for FZPs with outmost zone width of 100 nm and simultaneously aspect ratio beyond 2. We proposed an efficient method noted as single-pixel line-assisted sputtering (SLAS) to eliminate redeposition in situ during FZP fabrication. Through systematically optimizing parameters predominating ion dosages and, particularly, the positions of SLAS, we successfully obtained high-quality FZPs with outmost zone width down to 100 nm, perpendicular side walls, aspect ratio of up to 3 and diameter of 38 μm in 1.5 h. The application of SLAS also provides instructive guidance for other FIB processes to finely modulate the nanostructures.

Study on the effect of re-deposition induced by ion beam etching on MTJ performances

Magnetic tunnel junction (MTJ) as a key spintronics device can be used for the high-sensitivity magnetic field sensor and high-density non-volatile magnetic random access memory (MRAM). To obtain a high tunneling magnetoresistance (TMR), precise control of the etching process for MTJs is an essential step. In order to investigate the effect of the etching angle on the performance of MTJ devices, a series of MTJ pillars are fabricated by etching with the incidence angle of 10°, 20° and 30°. The prepared samples are characterized by the optical microscopy and SEM, and the R-H curves are also measured and then statistically analyzed. The results reveal that the performance of the MTJ is strongly affected by the IBE process, displaying the uniformity of the pillars edge and MTJ performance will improve as well with the increase of the etching angle. Then, a simplified model based on the re-deposition effect of the etching process is established to explain the experimental phenomena. Furthermore, a newly defined material parameter is introduced in this model and obtained with fitting the experimental results. This proves a valuable way to evaluate the quality of the MTJ stack film without the interference of the device fabrication process.

Status and prospects of plasma-assisted atomic layer deposition

Processing at the atomic scale is becoming increasingly critical for state-of-the-art electronic devices for computing and data storage, but also for emerging technologies such as related to the internet-of-things, artificial intelligence, and quantum computing. To this end, strong interest in improving nanoscale fabrication techniques such as atomic layer deposition (ALD) has been present. New ALD processes are being sought continuously and particularly plasma-assisted processes are considered an enabler for a wide range of applications because of their enhanced reactivity. This review provides an update on the status and prospects of plasma-assisted ALD with a focus on the developments since the publication of the review by Profijt et al. [J. Vac. Sci. Technol. A 29, 050801 (2011)]. In the past few years, plasma ALD has obtained a prominent position in the field of ALD with (i) a strong application base as demonstrated by the breakthrough in high-volume manufacturing; (ii) a large number of established processes, out of which several are being enabled by the plasma step; and (iii) a wide range of plasma ALD reactor designs, demonstrating many methods by which plasma species can be applied in ALD processes. In addition, new fundamental insights have been obtained, for instance, with respect to plasma damage, on the effect of ions on the material properties and on the so-called redeposition effect. Regarding new and emerging developments, plasma ALD is expected to take a prominent position in the atomic-scale processing toolbox and will contribute to ongoing developments in area-selective deposition, controlled growth of 2D materials, and atomic layer etching.

Distribution and avoidance of debris on epoxy resin during UV ns-laser scanning processes

In this paper the distribution of debris generated by a nanosecond UV laser (248 nm) on epoxy resin and the prevention of the corresponding re-deposition effects by parameter selection for a ns-laser scanning process were investigated. In order to understand the mechanisms behind the debris generation, in-situ particle measurements were performed during laser treatment. These measurements enabled the determination of the ablation threshold of the epoxy resin as well as the particle density and size distribution in relation to the applied laser parameters. The experiments showed that it is possible to reduce debris on the surface with an adapted selection of pulse overlap with respect to laser fluence. A theoretical model for the parameter selection was developed and tested. Based on this model, the correct choice of laser parameters with reduced laser fluence resulted in a surface without any re-deposited micro-particles.