Using Plasma Etching to Access the Polymer Density Distribution and Diffusivity of Gel Particles

In this paper we examine the polymer density distribution of gel particles and its effect on solvent diffusivity through the polymer network. In order to access the inner particle regions, external polymer layers were removed by plasma etching, thus reducing them from the outside. Higher polymer densities after erosion showed internal heterogeneity, with the density increasing towards the center of the particles. An exponential decay polymer density model is proposed, and the spatial relaxation length measured. The diffusion of solvent through the particles, before and after the plasma oxidation, revealed a correlation between the diffusion coefficient and the internal density.

The Use of Ion Milling for Surface Preparation for EBSD Analysis

An electron backscattered diffraction (EBSD) method provides information about the crystallographic structure of materials. However, a surface subjected to analysis needs to be well-prepared. This usually requires following a time-consuming procedure of mechanical polishing. The alternative methods of surface preparation for EBSD are performed via electropolishing or focus ion beam (FIB). In the present study, plasma etching using a glow discharge optical emission spectrometer (GD-OES) was applied for surface preparation for EBSD analysis. The obtained results revealed that plasma etching through GD-OES can be successfully used for surface preparation for EBSD analysis. However, it was also found that the plasma etching is sensitive for the alloy microstructure, i.e., the presence of intermetallic phases and precipitates such as carbides possess a different sputtering rate, resulting in non-uniform plasma etching. Preparation of the cross-section of oxidized CM247 revealed a similar problem with non-uniformity of plasma etching. The carbides and oxide scale possess a lower sputtering rate than the metallic matrix, which caused formation of relief. Based on obtained results, possible resolutions to suppress the effect of different sputtering rates are proposed.

Tunable Pore Size from Sub-Nanometer to a Few Nanometers in Large-Area Graphene Nanoporous Atomically Thin Membranes

Membranes are key components in chemical purification, biological separation, and water desalination. Traditional polymeric membranes are subjected to a ubiquitous trade-off between permeance and selectivity, which significantly hinders the separation performance. Nanoporous atomically thin membranes (NATMs), such as graphene NATMs, have the potential to break this trade-off. Owing to their uniqueness of two-dimensional structure and potential nanopore structure controllability, NATMs are expected to have outstanding selectivity through molecular sieving while achieving ultimate permeance at the same time. However, a drastic selectivity discrepancy exists between the proof-of-concept demonstrations and scalable separation applications in graphene membranes. In this paper, we offer a possible solution to narrow this discrepancy by tuning the pore density and pore size separately with two successive plasma treatments. We demonstrate that by narrowing the pore size distribution, the selectivity of graphene membranes can be greatly increased. Low-energy argon plasma is first applied to nucleate high density of defects in graphene. Controlled oxygen plasma is then utilized to selectively enlarge the defects into nanopores with desired sizes. This method is scalable, and the fabricated 1 cm2 graphene NATMs with sub-nanometer pores can separate KCl and Allura Red with a selectivity of 104 and a permeance of 1.1 × 10-6 m s-1. The pores in NATMs can be further tuned from gas-selective sub-nanometer pores to a few nanometer size. The fabricated NATMs show a selectivity of 35 between CO2 and N2. With longer enlargement time, a selectivity of 21.2 between a lysozyme and bovine serum albumin can also be achieved with roughly four times higher permeance than that of a commercial dialysis membrane. This research offers a solution to realize NATMs of tunable pore size with a narrow pore size distribution for different separation processes from sub-nanometer in gas separation or desalination to a few nanometers in dialysis.

Development of Energy-Efficient Superhydrophobic Polypropylene Fabric by Oxygen Plasma Etching and Thermal Aging

This study developed a human-friendly energy-efficient superhydrophobic polypropylene (PP) fabric by oxygen plasma etching and short-term thermal aging without additional chemicals. The effect of the microroughness on the superhydrophobicity was examined by adjusting the weave density. After the PP fabric was treated with oxygen plasma etching for 15 min and thermal aging at 120 °C for 1 h (E15H120 1 h), the static contact and shedding angles were 162.7° ± 2.4° and 5.2° ± 0.7° and the energy consumption was 136.4 ± 7.0 Wh. Oxygen plasma etching for 15 min and thermal aging at 120 °C for 24 h (E15H120 24 h) resulted in a static contact and shedding angle of 180.0° ± 0.0° and 1.8° ± 0.2° and energy consumption of 3628.5 ± 82.6 Wh. E15H120 1 h showed a lower shedding angle but had a higher sliding angle of 90°. E15H120 24 h exhibited shedding and sliding angles of less than 10°. Regardless of the thermal aging time, superhydrophobicity was higher in high-density fabrics than in low-density fabrics. The superhydrophobic PP fabric had a similar water vapor transmission rate and air permeability with the untreated PP fabric, and it showed a self-heading property after washing followed by tumble drying and hot pressing.

Universal Transfer Printing of Micelle-Templated Nanoparticles Using Plasma-Functionalized Graphene

Nanostructure incorporation into devices plays a key role in improving performance, yet processes for preparing two-dimensional (2D) arrays of colloidal nanoparticles tend not to be universally applicable, particularly for soft and oxygen-sensitive substrates for organic and perovskite-based electronics. Here, we show a method of transferring reverse micelle-deposited (RMD) nanoparticles (perovskite and metal oxide) on top of an organic layer, using a functionalized graphene carrier layer for transfer printing. As the technique can be applied universally to RMD nanoparticles, we used magnetic (γ-Fe₂O₃) and luminescent (methylammonium lead bromide (MAPbBr₃)) nanoparticles to validate the transfer-printing methodology. The strong photoluminescence from the MAPbBr₃ under UV illumination and high intrinsic field of the γ-Fe₂O₃ as measured by magnetic force microscopy (MFM), coupled with Raman measurements of the graphene layer, confirm that all components survive the transfer-printing process with little loss of properties. Such an approach to introducing uniform 2D arrays of nanoparticles onto sensitive substrates opens up new avenues to tune the device interfacial properties.

DNA Origami for Silicon Patterning

Desoxyribonucleic acid (DNA) origami architectures are a promising tool for ultimate lithography because of their ability to generate nanostructures with a minimum feature size down to 2 nm. In this paper, we developed a method for silicon (Si) nanopatterning to face up current limitations for high-resolution patterning with standard microelectronic processes. For the first time, a 2 nm-thick 2D DNA origami mask, with specific design composed of three different square holes (with a size of 10 and 20 nm), is used for positive pattern transfer into a Si substrate using a 15 nm-thick silicon dioxide (SiO₂) layer as an intermediate hard mask. First, the origami mask is transferred onto the SiO₂ underlayer, by an HF vapor-etching process. Then, the Si underlayer is etched using an HBr/O₂ plasma. Each hole is transferred in the SiO₂ layer and the 20 nm-sized holes are transferred into the final stack (Si). The resulting patterns exhibited a lateral resolution in the range of 20 nm and a depth of 40 nm. Patterns are fully characterized by atomic force microscopy, scanning electron microscopy, focused ion beam-transmission electron microscopy, and ellipsometry measurements.

Tensegrity Modelling and the High Toughness of Spider Dragline Silk

This work establishes a tensegrity model of spider dragline silk. Tensegrity systems are ubiquitous in nature, being able to capture the mechanics of biological shapes through simple and effective modes of deformation via extension and contraction. Guided by quantitative microstructural characterization via air plasma etching and low voltage scanning electron microscopy, we report that this model is able to capture experimentally observed phenomena such as the Poisson effect, tensile stress-strain response, and fibre toughness. This is achieved by accounting for spider silks' hierarchical organization into microfibrils with radially variable properties. Each fibril is described as a chain of polypeptide tensegrity units formed by crystalline granules operating under compression, which are connected to each other by amorphous links acting under tension. Our results demonstrate, for the first time, that a radial variability in the ductility of tensegrity chains is responsible for high fibre toughness, a defining and desirable feature of spider silk. Based on this model, a discussion about the use of graded tensegrity structures for the optimal design of next-generation biomimetic fibres is presented.

One-Step Large-Scale Nanotexturing of Nonplanar PTFE Surfaces to Induce Bactericidal and Anti-inflammatory Properties

Here we demonstrate a simple and scalable nanotexturing method for both planar (films) and nonplanar (tubes) polytetrafluoroethylene (PTFE) surfaces using a commercial desktop oxygen plasma etcher. The simple process can generate semiordered nanopillar structures on both tubular and planar samples with high radial and axial uniformity. We found that the resulting surfaces exhibit good in vitro bactericidal and in vivo anti-inflammatory properties. When tested against Staphylococcus aureus, the nanotextured surfaces showed significantly decreased live bacteria coverage and increased dead bacteria coverage, demonstrating significant bactericidal functionality. Moreover, the etched planar PTFE films exhibited better healing and inflammatory responses in the subcutis of C57BL/6 mice over 7 and 21 days, evidenced by a thinner inflammatory band, lower collagen deposition, and decreased macrophage infiltration. Our results suggest the possibility of using this simple process to generate large scale biomimetic nanotextured surfaces with good antibiofouling properties to enhance the functionality of many implantable and other biomedical devices.

Direct Exposure of Dry Enzymes to Atmospheric Pressure Non-Equilibrium Plasmas: The Case of Tyrosinase

The direct interaction of atmospheric pressure non-equilibrium plasmas with tyrosinase (Tyr) was investigated under typical conditions used in surface processing. Specifically, Tyr dry deposits were exposed to dielectric barrier discharges (DBDs) fed with helium, helium/oxygen, and helium/ethylene mixtures, and effects on enzyme functionality were evaluated. First of all, results show that DBDs have a measurable impact on Tyr only when experiments were carried out using very low enzyme amounts. An appreciable decrease in Tyr activity was observed upon exposure to oxygen-containing DBD. Nevertheless, the combined use of X-ray photoelectron spectroscopy and white-light vertical scanning interferometry revealed that, in this reactive environment, Tyr deposits displayed remarkable etching resistance, reasonably conferred by plasma-induced changes in their surface chemical composition as well as by their coffee-ring structure. Ethylene-containing DBDs were used to coat tyrosinase with a hydrocarbon polymer film, in order to obtain its immobilization. In particular, it was found that Tyr activity can be fully retained by properly adjusting thin film deposition conditions. All these findings enlighten a high stability of dry enzymes in various plasma environments and open new opportunities for the use of atmospheric pressure non-equilibrium plasmas in enzyme immobilization strategies.

Enhancing the Sensitivity of Nanoplasmonic Thin Films for Ethanol Vapor Detection

Nanoplasmonic thin films, composed of noble metal nanoparticles (gold) embedded in an oxide matrix, have been a subject of considerable interest for Localized Surface Plasmon Resonance (LSPR) sensing. Ethanol is one of the promising materials for fuel cells, and there is an urgent need of a new generation of safe optical sensors for its detection. In this work, we propose the development of sensitive plasmonic platforms to detect molecular analytes (ethanol) through changes of the LSPR band. The thin films were deposited by sputtering followed by a heat treatment to promote the growth of the gold nanoparticles. To enhance the sensitivity of the thin films and the signal-to-noise ratio (SNR) of the transmittance–LSPR sensing system, physical plasma etching was used, resulting in a six-fold increase of the exposed gold nanoparticle area. The transmittance signal at the LSPR peak position increased nine-fold after plasma treatment, and the quality of the signal increased six times (SNR up to 16.5). The optimized thin films seem to be promising candidates to be used for ethanol vapor detection. This conclusion is based not only on the current sensitivity response but also on its enhancement resulting from the optimization routines of thin films’ architectures, which are still under investigation.

Towards Long-Term Photostability of Nickel Hydroxide/BiVO4 Photoanodes for Oxygen Evolution Catalysts via In Situ Catalyst Tuning

Increasing long-term photostability of BiVO₄ photoelectrode is an important issue for solar water splitting. The NiOOH oxygen evolution catalyst (OEC) has fast water oxidation kinetics compared to the FeOOH OEC. However, it generally shows a lower photoresponse and poor stability because of the more substantial interface recombination at the NiOOH/BiVO₄ junction. Herein, we utilize a plasma etching approach to reduce both interface/surface recombination at NiOOH/BiVO₄ and NiOOH/electrolyte junctions. Further, adding Fe²⁺ into the borate buffer electrolyte alleviates the active but unstable character of etched-NiOOH/BiVO₄ , leading to an outstanding oxygen evolution over 200 h. The improved charge transfer and photostability can be attributed to the active defects and a mixture of NiOOH/NiO/Ni in OEC induced by plasma etching. Metallic Ni acts as the ion source for the in situ generation of the NiFe OEC over long-term durability.

Hollow Porous Gold Nanoshells with Controlled Nanojunctions for Highly Tunable Plasmon Resonances and Intense Field Enhancements for Surface-Enhanced Raman Scattering

Plasmonic metal nanostructures with nanogaps have attracted great interest owing to their controllable optical properties and intense electromagnetic fields that can be useful for a variety of applications, but precise and reliable control of nanogaps in three-dimensional nanostructures remains a great challenge. Here, we report the control of nanojunctions of hollow porous gold nanoshell (HPAuNS) structures by a facile oxygen plasma-etching process and the influence of changes in nanocrevices of the interparticle junction on the optical and sensing characteristics of HPAuNSs. We demonstrate a high tunability of the localized surface plasmon resonance (LSPR) peaks and surface-enhanced Raman scattering (SERS) detection of rhodamine 6G (R6G) using HPAuNS structures with different nanojunctions by varying the degree of gold sintering. As the neck region of the nanojunction is further sintered, the main LSPR peak shifts from 785 to 1350 nm with broadening because the charge transfer plasmon mode becomes more dominant than the dipolar plasmon mode, resulting from the increase of conductance at the interparticle junctions. In addition, it is demonstrated that an increase in the sharpness of the nanojunction neck can enhance the SERS enhancement factor of the HPAuNS by up to 4.8-fold. This enhancement can be ascribed to the more intense local electromagnetic fields at the sharper nanocrevices of interparticle junctions. The delicate change of nanojunction structures in HPAuNSs can significantly affect their optical spectrum and electromagnetic field intensity, which are critical for their practical use in a SERS-based analytical sensor as well as multiple-wavelength compatible applications.

Large-Area Nanopatterning Based on Field Alignment by the Microscale Metal Mask for the Etching Process

Recently, researchers have dedicated efforts toward producing large-area nanostructures using advanced lithography techniques and state-of-the-art etching methods. However, these processes involve challenges such as the diffraction limit and an unintended etching profile. In this work, we demonstrate large-area nanopatterning on a silicon substrate using the microscale metal mask by meticulous optimization of the etching process. Around the vertex of a microscale metal mask, a locally induced electric field is generated by a bias voltage applied on a silicon mold. We utilize this field to change the trajectory of reactive ions and their effect flux, thus providing a controllable bowing effect. The results are analyzed by both numerical simulations and experiments. Based on the field alignment by the metal mask for the etching (FAME) process, we demonstrate the fabrication of 378 nm-size nanostructure patterns which translate to a size reduction of 63% from 1 μm-size mask patterns on a wafer by optimization of the processes. This is much higher than the undercut (∼37%) usually achieved by a typical non-Bosch process under similar etching conditions. The optimized nanostructure is used as a mold for the transfer printing of nanostructure arrays on a flexible substrate to demonstrate that it enables the functionality of FAME-processed nanostructures.

Integrated N-Co/Carbon Nanofiber Cathode for Highly Efficient Zinc-Air Batteries

In order to reduce the charge-transfer resistance, ohmic resistance, and ionic and electronic resistances arising from the polymer binder, designing and constructing self-standing and binder-free porous electrodes are very significant for energy storage and conversion devices. Herein, self-standing and binder-free porous N-Co carbon nanofiber (N-Co/CNF) cathodes are prepared for zinc-air batteries (ZABs) by an in situ electrospinning/plasma-etching method. The morphology and activity of the prepared electrodes are investigated by several characterization techniques. The prepared specimens exhibit a multilayered CNF structure, and a new CoN compound is produced after plasma-etching treatment. The N-Co/CNF-300-10 cathode demonstrates excellent electrocatalytic performance toward oxygen reduction reaction, with an onset potential and a half-wave potential of 0.995 and 0.853 V (vs reversible hydrogen electrode), respectively, which is comparable to that of 20% Pt/C. The N-Co/CNF-300-10 cathode acting as a self-standing electrode for ZABs exhibits a maximum discharge power density as high as 229 mW cm^-2 and a specific capacity of 659.6 mA h g_Zn^-1, which are much higher than those of the commercial catalysts, benefiting from the self-standing porous structure, N-doping, and more defects and active sites induced by plasma-etching. It provides an effective way to construct a self-standing porous electrode with controllable compositions for rechargeable metal-air batteries.

A Facile, Low-Cost Plasma Etching Method for Achieving Size Controlled Non-Close-Packed Monolayer Arrays of Polystyrene Nano-Spheres

Monolayer nano-sphere arrays attract great research interest as they can be used as templates to fabricate various nano-structures. Plasma etching, and in particular high-frequency plasma etching, is the most commonly used method to obtain non-close-packed monolayer arrays. However, the method is still limited in terms of cost and efficiency. In this study, we demonstrate that a low frequency (40 kHz) plasma etching system can be used to fabricate non-close-packed monolayer arrays of polystyrene (PS) nano-spheres with smooth surfaces and that the etching rate is nearly doubled compared to that of the high-frequency systems. The study reveals that the low-frequency plasma etching process is dominated by a thermal evaporation etching mechanism, which is different from the atom-scale dissociation mechanism that underlines the high-frequency plasma etching. It is found that the polystyrene nano-sphere size can be precisely controlled by either adjusting the etching time or power. Through introducing oxygen as the assisting gas in the low frequency plasma etching system, we achieved a coalesced polystyrene nano-sphere array and used it as a template for metal-assisted chemical etching. We demonstrate that the method can significantly improve the aspect ratio of the silicon nanowires to over 200 due to the improved flexure rigidity.

Conversion of a Patterned Organic Resist into a High Performance Inorganic Hard Mask for High Resolution Pattern Transfer

Polyphthalaldehyde is a self-developing resist material for electron beam and thermal scanning probe lithography (t-SPL). Removing the resist in situ (during the lithography process itself) simplifies processing and enables direct pattern inspection, however, at the price of a low etch resistance of the resist. To convert the material into a etch resistant hard mask, we study the selective cyclic infiltration of trimethyl-aluminum (TMA)/water into polyphthalaldehyde. It is found that TMA diffuses homogeneously through the resist, leading to material expansion and formation of aluminum oxide concurrent to the exposure to water and the degradation of the polyphthalaldehyde polymer. The plasma etch resistance of the infiltrated resist is significantly improved, as well as its stability. Using a silicon substrate coated with 13 nm silicon nitride and 7 nm cross-linked polystyrene, high resolution polyphthalaldehyde patterning is performed using t-SPL. After TMA/H₂O infiltration, it is demonstrated that pattern transfer into silicon can be achieved with good fidelity for structures as small as 10 nm, enabling >10× amplification and low surface roughness. The presented results demonstrate a simplified use of polyphthalaldehyde resist, targeting feature scales at nanometer range, and suggest that trimethyl-aluminum infiltration can be applied to other resist-based lithography techniques.

Isotropic Atomic Layer Etching of ZnO Using Acetylacetone and O2 Plasma

Atomic layer etching (ALE) provides Ångström-level control over material removal and holds potential for addressing the challenges in nanomanufacturing faced by conventional etching techniques. Recent research has led to the development of two main classes of ALE: ion-driven plasma processes yielding anisotropic (or directional) etch profiles and thermally driven processes for isotropic material removal. In this work, we extend the possibilities to obtain isotropic etching by introducing a plasma-based ALE process for ZnO which is radical-driven and utilizes acetylacetone (Hacac) and O₂ plasma as reactants. In situ spectroscopic ellipsometry measurements indicate self-limiting half-reactions with etch rates ranging from 0.5 to 1.3 Å/cycle at temperatures between 100 and 250 °C. The ALE process was demonstrated on planar and three-dimensional substrates consisting of a regular array of semiconductor nanowires (NWs) conformally covered using atomic layer deposition of ZnO. Transmission electron microscopy studies conducted on the ZnO-covered NWs before and after ALE proved the isotropic nature and the damage-free characteristics of the process. In situ infrared spectroscopy measurements were used to elucidate the self-limiting nature of the ALE half-reactions and the reaction mechanism. During the Hacac etching reaction that is assumed to produce Zn(acac)₂, carbonaceous species adsorbed on the ZnO surface are suggested as the cause of the self-limiting behavior. The subsequent O₂ plasma step resets the surface for the next ALE cycle. High etch selectivities (∼80:1) over SiO₂ and HfO₂ were demonstrated. Preliminary results indicate that the etching process can be extended to other oxides such as Al₂O₃.

Roughness Evolution and Charging in Plasma-Based Surface Engineering of Polymeric Substrates: The Effects of Ion Reflection and Secondary Electron Emission

The interaction of plasma with polymeric substrates generates both roughness and charging on the surface of the substrates. This work, toward the comprehension and, finally, the control of plasma-induced surface roughness, delves into the intertwined effects of surface charging, ion reflection, and secondary electron-electron emission (SEEE) on roughness evolution during plasma etching of polymeric substrates. For this purpose, a modeling framework consisting of a surface charging module, a surface etching model, and a profile evolution module is utilized. The case study is etching of a poly(methyl methacrylate) (PMMA) substrate by argon plasma. Starting from an initial surface profile with microscale roughness, the results show that the surface charging contributes to a faster elimination of the roughness compared to the case without charging, especially when ion reflection is taken into account. Ion reflection sustains roughness; without ion reflection, roughness is eliminated. Either with or without ion reflection, the effect of SEEE on the evolution of the rms roughness over etching time is marginal. The mutual interaction of the roughness and the charging potential is revealed through the correlation of the charging potential with a parameter combining rms roughness and skewness of the surface profile. A practical implication of the current study is that the elimination or the reduction of surface charging will result in greater surface roughness of polymeric, and generally dielectric, substrates.

Manipulation of the Superhydrophobicity of Plasma-Etched Polymer Nanostructures

The manipulation of droplet mobility on a nanotextured surface by oxygen plasma is demonstrated by modulating the modes of hydrophobic coatings and controlling the hierarchy of nanostructures. The spin-coating of polytetrafluoroethylene (PTFE) allows for heterogeneous hydrophobization of the high-aspect-ratio nanostructures and provides the nanostructured surface with "sticky hydrophobicity", whereas the self-assembled monolayer coating of perfluorodecyltrichlorosilane (FDTS) results in homogeneous hydrophobization and "slippery superhydrophobicity". While the high droplet adhesion (stickiness) on a nanostructured surface with the spin-coating of PTFE is maintained, the droplet contact angle is enhanced by creating hierarchical nanostructures via the combination of oxygen plasma etching with laser interference lithography to achieve "sticky superhydrophobicity". Similarly, the droplet mobility on a slippery nanostructured surface with the self-assembled monolayer coating of FDTS is also enhanced by employing the hierarchical nanostructures to achieve "slippery superhydrophobicity" with modulated slipperiness.

Rapid Plasma Etching for Fabricating Fused Silica Microchannels

In order to advance the performances of micro chemical and biochemical systems on a chip, the fabrication of microstructures such as channels and pillars is an essential basic technology. However, conventional fabrication methods based on wet etching have limitations in their applications for device engineering. In this study, we report on a new microchannel fabrication process on a fused silica substrate using photoresist and plasma etching based on C₃F₈, CHF₃, and Ar gases. Deep, rectangular microchannels, having vertical angles close to 90°, 10 μm-scale deep and low surface roughness of less than 1 nm, could be fabricated on a fused silica substrate at high etching rates on the order of 5 - 7 nm s^-1. This metal-free fabrication methodology is expected to be a low-cost, easy, and simple technique for a fused silica microstructure applications.

Increased Efficiency of Solar Cells Protected by Hydrophobic and Hydrophilic Anti-Reflecting Nanostructured Glasses

We investigated the fabrication of large-area (cm²) nanostructured glasses for solar cell modules with hydrophobic and hydrophilic properties using soft lithography and colloidal lithography. Both of these techniques entail low-cost and ease of nanofabrication. We explored the use of simple 1D and 2D nanopatterns (nanowires and nanocones) and the effect of introducing disorder in the nanostructures. We observed an increase in the transmitted light for ordered nanostructures with a maximum value of 99% for wavelengths >600 nm when ordered nanocones are fabricated on the two sides of the solar glass. They produced an increment in the efficiency of the packaged solar cell with respect to the glass without nanostructures. On the one hand, the wettability properties showed that the ordering of the nanostructures improved the hydrophobicity of the solar glasses and increased their self-cleaning capacity. On the other hand, the disordered nanostructures improved the hydrophilic properties of solar glasses, increasing their anti-fogging capacity. The results show that by selecting the appropriate nanopattern, the wettability properties (hydrophobic or hydrophilic) can be easily improved without decreasing the efficiency of the solar cell underneath.

Selective Etching of Silicon in Preference to Germanium and Si0.5Ge0.5

The selective etching characteristics of silicon, germanium, and Si_0.5Ge_0.5 subjected to a downstream H₂/CF₄/Ar plasma have been studied using a pair of in situ quartz crystal microbalances (QCMs) and X-ray photoelectron spectroscopy (XPS). At 50 °C and 760 mTorr, Si can be etched in preference to Ge and Si_0.5Ge_0.5, with an essentially infinite Si/Ge etch-rate ratio (ERR), whereas for Si/Si_0.5Ge_0.5, the ERR is infinite at 22 °C and 760 mTorr. XPS data showed that the selectivity is due to the differential suppression of etching by a ∼2 ML thick C_xH_yF_z layer formed by the H₂/CF₄/Ar plasma on Si, Ge, and Si_0.5Ge_0.5. The data are consistent with the less exothermic reaction of fluorine radicals with Ge or Si_0.5Ge_0.5 being strongly suppressed by the C_xH_yF_z layer, whereas, on Si, the C_xH_yF_z layer is not sufficient to completely suppress etching. Replacing H₂ with D₂ in the feed gas resulted in an inverse kinetic isotope effect (IKIE) where the Si and Si_0.5Ge_0.5 etch rates were increased by ∼30 times with retention of significant etch selectivity. The use of D₂/CF₄/Ar instead of H₂/CF₄/Ar resulted in less total carbon deposition on Si and Si_0.5Ge_0.5 and gave less Ge enrichment of Si_0.5Ge_0.5. These results are consistent with the selectivity being due to the differential suppression of etching by an angstrom-scale carbon layer.

Superhydrophobic Copper Surfaces with Anticorrosion Properties Fabricated by Solventless CVD Methods

Due to continuous miniaturization and increasing number of electrical components in electronics, copper interconnections have become critical for the design of 3D integrated circuits. However, corrosion attack on the copper metal can affect the electronic performance of the material. Superhydrophobic coatings are a commonly used strategy to prevent this undesired effect. In this work, a solventless two-steps process was developed to fabricate superhydrophobic copper surfaces using chemical vapor deposition (CVD) methods. The superhydrophobic state was achieved through the design of a hierarchical structure, combining micro-/nanoscale domains. In the first step, O₂- and Ar-plasma etchings were performed on the copper substrate to generate microroughness. Afterward, a conformal copolymer, 1H,1H,2H,2H-perfluorodecyl acrylate-ethylene glycol diacrylate [p(PFDA-co-EGDA)], was deposited on top of the metal via initiated CVD (iCVD) to lower the surface energy of the surface. The copolymer topography exhibited a very characteristic and unique nanoworm-like structure. The combination of the nanofeatures of the polymer with the microroughness of the copper led to achievement of the superhydrophobic state. AFM, SEM, and XPS were used to characterize the evolution in topography and chemical composition during the CVD processes. The modified copper showed water contact angles as high as 163° and hysteresis as low as 1°. The coating withstood exposure to aggressive media for extended periods of time. Tafel analysis was used to compare the corrosion rates between bare and modified copper. Results indicated that iCVD-coated copper corrodes 3 orders of magnitude slower than untreated copper. The surface modification process yielded repeatable and robust superhydrophobic coatings with remarkable anticorrosion properties.

Selective Plasma Etching of Polymeric Substrates for Advanced Applications

In today’s nanoworld, there is a strong need to manipulate and process materials on an atom-by-atom scale with new tools such as reactive plasma, which in some states enables high selectivity of interaction between plasma species and materials. These interactions first involve preferential interactions with precise bonds in materials and later cause etching. This typically occurs based on material stability, which leads to preferential etching of one material over other. This process is especially interesting for polymeric substrates with increasing complexity and a “zoo” of bonds, which are used in numerous applications. In this comprehensive summary, we encompass the complete selective etching of polymers and polymer matrix micro-/nanocomposites with plasma and unravel the mechanisms behind the scenes, which ultimately leads to the enhancement of surface properties and device performance.

Magnetic switching of nanoscale antidot lattices

We investigate the rich magnetic switching properties of nanoscale antidot lattices in the 200 nm regime. In-plane magnetized Fe, Co, and Permalloy (Py) as well as out-of-plane magnetized GdFe antidot films are prepared by a modified nanosphere lithography allowing for non-close packed voids in a magnetic film. We present a magnetometry protocol based on magneto-optical Kerr microscopy elucidating the switching modes using first-order reversal curves. The combination of various magnetometry and magnetic microscopy techniques as well as micromagnetic simulations delivers a thorough understanding of the switching modes. While part of the investigations has been published before, we summarize these results and add significant new insights in the magnetism of exchange-coupled antidot lattices.