Direct Etching Research Articles

Interfacial Assembly of Amphiphilic Tiles for Reconfigurable Photonic Surfaces.

Nature has created photonic structures in cells and assembled them to make photonic layers for a living. Inspired from nature, we design amphiphilic photonic tiles and assemble them at air-water interface to compose highly reconfigurable photonic layers. The photonic tiles are prepared by photolithographically defining the shape of the disc using a photocurable dispersion of repulsive particles. The tiles are further treated by directional dry etching to selectively render top and side surfaces of the discs hydrophobic. The amphiphilic photonic tiles deform the air-water interface by gravity, which causes a strong attractive force driven by capillarity. Therefore, the tiles form two-dimensional (2D) dense-packing, which rapidly adapts dynamic fluctuation and shape change of the interface, providing highly reconfigurable photonic layers. In addition, the assembly can be transferred into target solid surfaces through the Langmuir-Blodgett method to make photonic coatings. Moreover, the amphiphilic tiles can be assembled on the surface of water drops, forming a photonic shell on liquid marbles which resembles photonic structures in nature. We believe that our strategy based on a 2D tile assembly at the free interface will provide a simple yet useful means to create photonic layers on various purposes.

Evaporation-Induced Hierarchical Assembly of Rigid Silicon Nanopillars Fabricated by a Scalable Two-Level Colloidal Lithography Approach.

Periodic arrays of silicon nanowires/nanopillars are of great technological importance in developing novel electrical, optical, biosensing, and electromechanical devices. Here, we report a novel two-level colloidal lithography technology for making periodic arrays of single-crystalline silicon nanopillars (or nanocolumns) over large areas. Spin-coated monolayer silica colloidal crystals with unusual nonclose-packed structures are utilized as first-level etching masks in generating ordered polymer posts whose sizes can be much smaller than the templating silica microspheres. These polymer posts can then be used as second-level structural templates in fabricating highly ordered silicon nanopillars with broadly tunable geometries by employing metal-assisted chemical etching. As the silicon nanopillars are produced by direct wet etching on the surface of a single-crystalline silicon wafer, they are relatively free of volume defects and thus their bending strength approaches the predicted theoretical maximum. Most importantly, the unique nonclose-packed structure of the original colloidal template and the close-to-ideal mechanical property enables the formation of unusual open-structured hierarchical assemblies of rigid silicon nanopillars during water evaporation. Both experiments and numerical finite-difference time-domain modeling confirm the importance of high aspect ratios of the templated silicon nanopillars in achieving superior broadband antireflection properties. The large fraction of entrapped air in the hierarchically assembled silicon nanopillars further facilitates to accomplish superhydrophobic surface states, promising for developing self-cleaning antireflection coatings for many important optoelectronic applications.

Highly micro- and mesoporous oxycarbide derived materials from HF etching of silicon oxycarbide materials

Abstract Highly micro-mesoporous silicon oxycarbide-derived carbon materials (SiOC-DC) with elevated specific surface area up to 895 m 2 g -1 and high pore volumes of mesopores (0.3 cm 3 g -1 ) and micropores (0.2 cm 3 g -1 ) have been obtained by direct etching of SiOC with HF. Initial organic-inorganic hybrids were synthesized by the sol-gel method employing triethoxysilane and polydimethylsiloxane (PDMS) of different molecular weights (550, 1750 and 4200 gmol -1 ). These hybrids were pyrolyzed from 1100 to 1400 °C. Short PDMS chains (550 gmol -1 ) within the hybrid structure rendered dense SiOC materials after pyrolysis, however long PDMS chains (1750 and 4200 gmol -1 ) produced highly micro-mesoporous SiOC materials up to 1300 °C. The etching of SiOC employing HF produced the selective removing of silica nano-domains and as a result highly micro-mesoporous SiOC-DC materials were created. In dense SiOC the HF attack is favored at the highest temperatures (1400 °C) when the SiOC is more phase separated. On the other hand, in porous SiOC there is an agreement between the pyrolysis temperature and the porosity and, therefore the SiOC materials are etched easier at 1200 °C. SiOC-DC materials are composed by a porous glassy network enriched with carbon (graphene-like carbon and turbostratic carbon) and SiC which present an incipient crystallization.

UiO-66 derived N-doped carbon nanoparticles coated by PANI for simultaneous adsorption and reduction of hexavalent chromium from waste water

Recently, metal organic frameworks (MOFs) have been regarded as a type of uniformly and stably precursor and efficient self-sacrificial template to prepare hierarchical porous carbon related nano-structured functional materials. Herein, we report the use of the zirconium MOFs (UiO-66) as a precursor to prepare N-doped carbon nanoparticles (NC) with high specific surface area (1609.1 m2/g) by direct carbonization and etching processes. Then, polyaniline (PANI) was growth on the NC by in-situ polymerization, showing a superb efficiency and stability for hexavalent chromium (Cr(VI)) removal. Due to the synergistic effect of adsorption and reduction of the obtained PANI@NC nanocomposites, the maximum adsorption capacity was 198.04 mg/g. The effects of different adsorbents, pH, adsorbent dosage, co-existing ions, concentration of Cr(VI) were studied on the Cr(VI) adsorption. The kinetics of adsorption of Cr(VI) followed the Pseudo-second-order model and the adsorption isotherm data fitted well to the Langmuir isothermal model. Importantly, excellent stability of PANI@NC nanocomposites was demonstrated after five cycles. The results of this research indicate that PANI@NC nanocomposites were the promising adsorbent for removal of Cr(VI) from waste water.

Biomimetic non-uniform nanostructures reduce broadband reflectivity in transparent substrates

Abstract

Top-down fabrication of high-uniformity nanodiamonds by self-assembled block copolymer masks

Nanodiamonds hosting colour centres are a promising material platform for various quantum technologies. The fabrication of non-aggregated and uniformly-sized nanodiamonds with systematic integration of single quantum emitters has so far been lacking. Here, we present a top-down fabrication method to produce 30.0 ± 5.4 nm uniformly-sized single-crystal nanodiamonds by block copolymer self-assembled nanomask patterning together with directional and isotropic reactive ion etching. We show detected emission from bright single nitrogen vacancy centres hosted in the fabricated nanodiamonds. The lithographically precise patterning of large areas of diamond by self-assembled masks and their release into uniformly sized nanodiamonds open up new possibilities for quantum information processing and sensing.

Modelling of Direct Laser Patterning of Self Assembled Monolayers (SAMs) on Cobalt-Chromium Alloy

The implantation of biomedical devices is often accompanied with complications such as post-operative infections, lack of tissue integration, and biofilm formation. A strategy that will limit these complications by administering a focused multi-therapeutic treatment is needed. The direct laser patterning of self-assembled monolayers (SAMs) onto the implant can be used to modify the surface and provide a platform for multi-therapeutic treatment. Conventionally, surface patterning of SAMs requires a uniform surface, but most bio-implants are irregularly shaped. Laser patterning is able to bypass this problem and modify the surface of an implant of irregular shape with precision. Effective optimization of patterning process is needed to minimize experimental trials and error for the development of laser assisted patterns. In this abstract, we report the development of a model to simulate the direct laser patterning process on Cobalt-Chromium (Co-Cr) Alloy. COMSOL Multiphysics 4.3b was used to create the 3D model. Governing equations associated with heat transfer in solids were used with the heat source being the heat provided by the laser. The model calculated the resulting temperature gradient on the cobalt chromium surface giving an indication of SAM desorption based on the surface temperature of the metal. Temperature profiles as simulated by the model indicated a laser etch diameter of approximately 11µm. Experimental results of direct laser etching of SAMs on cobalt chromium alloy gave a laser etch of 12µm. The close proximity of the predicted and experimental diameter confirms the validation of the developed model.

Highly Sensitive and Selective Nanogap-Enhanced SERS Sensing Platform.

This paper reports a highly sensitive and selective surface-enhanced Raman spectroscopy (SERS) sensing platform. We used a simple fabrication method to generate plasmonic hotspots through a direct maskless plasma etching of a polymer surface and the surface tension-driven assembly of high aspect ratio Ag/polymer nanopillars. These collapsed plasmonic nanopillars produced an enhanced near-field interaction via coupled localized surface plasmon resonance. The high density of the small nanogaps yielded a high plasmonic detection performance, with an average SERS enhancement factor of 1.5 × 107. More importantly, we demonstrated that the encapsulation of plasmonic nanostructures within nanofiltration membranes allowed the selective filtration of small molecules based on the degree of membrane swelling in organic solvents and molecular size. Nanofiltration membrane-encapsulated SERS substrates do not require pretreatments. Therefore, they provide a simple and fast detection of toxic molecules using portable Raman spectroscopy.

Fabrication and characterization of SiO2 microcantilevers by direct laser writing and wet chemical etching methods for relative humidity sensing

In the present work, SiO2 microcantilevers (MCs) of various lengths (50–330 μm, width – 37 μm, thickness – 0.98 μm) were fabricated using Direct Laser Writing (DLW) and wet chemical etching methods. An effective method to avoid “stiction” while releasing these MCs by wet chemical etching of underlying Si is presented. It is shown that introducing a sharp convex tip at the free end of the MC along with post-etch rinsing in boiling DI water, substantially reduces the stiction. Successfully released MCs were characterized using a 3D optical microscope (3D OM) and Nano Vibration Analyzer (NVA), for initial bending and resonance frequency measurements, respectively. 3D OM measurements revealed that released MCs are bending upwards (i.e. away from the wafer) and the peak deflection (zmax) value increases with increasing MC length (L). This is attributed to the presence of gradient residual stress (σmax) in SiO2 film and from zmax vs. L2 plot σmax was estimated to be 15.14 (± 0.32) MPa. The resonance frequency of the MCs was measured using NVA and found to be lower than the analytically estimated values, especially at smaller lengths. It is explained on the basis of the increase in the effective length of MCs due to undercutting. Finally, relative humidity (RH) sensitivity of the released MCs is demonstrated in dynamic mode, without any functionalization.

Flexible control over optical reflection property of metallic surfaces via pulse laser

The control of fundamental optical properties, such as transmission and reflection, over metallic surfaces plays a significant role in multiple fields like solar cells and aerospace. The direct laser etching in air can perform a variety of flexible control abilities in optical functional metal surfaces. In this paper, the authors use the aluminum alloy as an example of widely metal materials and propose two kinds of controlling strategies: large-range controlling strategy and small-range precise controlling strategy. The former changes the process repeat number of femtosecond lasers or the scanning speed of nanosecond lasers. The latter combines the femtosecond laser and the nanosecond laser. The results show that when the process repeat number of femtosecond lasers is changed from 30 to 1, the height of the induced micropillars on the surface of Al alloy is changed from 80 to 6 μm. As a result, the reflectivity of samples will change from ∼16% to ∼87%. The nanosecond laser-induced micro-/nanostructures achieve the reflectivity changing from ∼18% to ∼79% when the scanning speed changes from 10 to 400 mm/s in a spectrum range of 250–2000 nm. What is more, after being fabricated in the way of two-step controlling strategy, the reflectivity raises from ∼30% to ∼40% when the scanning speed of nanosecond lasers changes from 10 to 200 mm/s, while the reflectivity of samples fabricated simply by nanosecond laser changes from ∼18% to ∼66% when the scanning speed changes in the same range and other parameters are kept the same. In addition, the authors demonstrated that the two-step precise controlling strategy is applicable to a variety of metals such as copper, stainless steel, and titanium.

Facile template-free route to synthesis visible light respensive hollow TiO2 spheres

The monodisperse hollow TiO2 spheres (HTS) were fabricated by facile template-free route involving direct precipitation and etching reaction. Tetrabutyl titanate was used as titanium precursor to form amorphous TiO2 spheres (ATS) directly in ethanol-acetonitrile mixed solution. Then, the ATS were etched by F− with the protection of PVP to form HTS under hydrothermal reaction conditions. The physical and chemical characterizations of synthesized samples were conducted by SEM, TEM, XRD and UV–vis diffuse reflectance spectroscopy. Result showed that morphology and structure of HTS can be easily controlled by adjusting time of etching reaction. The HTS obtained by etching for 4 h exhibited good hollow structure with unique shell assembled with enriched nanothorns, and it possessed good photocatalytic activity under visible light irradiation.

Deep X-ray lithography system with a uniform and high-accuracy fabrication area established in beamline BL11 at NewSUBARU.

A new lithography system to fabricate high-aspect-ratio 3D microstructures was developed at the NewSUBARU synchrotron radiation facility (University of Hyogo, Japan). The X-ray beam generated by this system has high parallelism (horizontal and vertical divergence angles of 278 µrad and 14 µrad, respectively) and high photon flux (31 mW mm-2 at a beam current of 300 mA). The high photon flux and exposure area of the system were validated and a beam-scan method for a large exposure area with a uniform dose distribution has been proposed. In addition, the deep X-ray lithography performance was characterized using a conventional photosensitive material and the synchrotron-radiation-induced direct etching of polytetrafluoroethylene (PTFE) was demonstrated. An enlargement of the microfabrication area up to 100 mm × 100 mm while contemporarily ensuring high uniformity was achieved.

High-quality graphene transfer via directional etching of metal substrates.

Large-scale applications of graphene require its high-efficiency transfer from growth metal substrates to any other substrates of interest. The wrinkles and folds generated during the transfer process of graphene by the well-known poly(methyl methacrylate) (PMMA)-assisted technique is a critical issue. Here, we report an improvement of this method by applying a directional etching process for the removal of the growth Cu substrates, using a pair of electrodes inserted into the etchant with a constant current to form an electrochemical system. The controlled redox reactions between the Cu and the solution environment result in the etching of Cu in a part-by-part manner strictly from one end to the other. The consistency of the Cu etching direction can avoid the formation of an easily destroyable Cu structure and release the stress concentration that is usually generated during the random etching process, and finally yield significantly improved quality of the transferred graphene film with a lowered density of wrinkles, cracks/folds, adlayers, reduced root-mean-square of surface roughness, and increased performance in sheet resistance and carrier mobility.

Large Area Three‐Dimensional Photonic Crystal Membranes: Single‐Run Fabrication and Applications with Embedded Planar Defects

AbstractThree‐dimensional photonic crystals (3D PhCs) enable light manipulations in all three spatial dimensions, however, real world applications are still faced with challenges in fabrication. Here, a facile fabrication strategy for 3D silicon PhCs with a simple cubic (SC) lattice structure is presented, which exhibits a complete photonic bandgap at near‐infrared wavelengths of around 1100 nm. The fabrication process is composed of standard deep ultra‐violet stepper lithography, followed by a single‐run modified plasma etch process. By applying a direct dry etch release step at the end of the 3D structural etch process, the fabricated 3D PhCs can be released and transferred in the form of a membrane onto other substrates such as glass, polymers, or even substrates with engineered surface. The thickness of the demonstrated membranes is around 2 µm and the size can be up to a few millimeters. A high reflectivity is observed at the stop band frequency, and a planar defect is introduced during the etching process resulting in an optical resonance mode with a small linewidth of around 30 nm. The structure constitutes an optical bandpass filter and can be used as a sensor for organic solvents.

Direct etching of perovskite film by electron-beam scanning

In this work patterning method of organic-inorganic hybrid methyl ammonium lead iodide (CH3NH3PbI3) perovskite films is demonstrated. It was estimated that using focused E-beam make possible to etch the perovskite film. Etching took place due to formation of lead-organic volatile compounds. The etching process was strongly depended on grazing angle of incident beam. It was estimated that etching effectively take place when grazing angle was close to 45 °C. Next key factor was an accelerating voltage. Structure changes take place when E-beam accelerating voltage exceeds 1 kV.Change of structure was tracked by X-ray diffractometry and X-ray photoelectron spectroscopy analyses. The surface evaluation was monitored by atomic force microscopy and scanning electron microscopy methods. Bulk composition was estimated by energy dispersive spectrometer.

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.

Glassy Carbon: A Promising Material for Micro- and Nanomanufacturing.

When certain polymers are heat-treated beyond their degradation temperature in the absence of oxygen, they pass through a semi-solid phase, followed by the loss of heteroatoms and the formation of a solid carbon material composed of a three-dimensional graphenic network, known as glassy (or glass-like) carbon. The thermochemical decomposition of polymers, or generally of any organic material, is defined as pyrolysis. Glassy carbon is used in various large-scale industrial applications and has proven its versatility in miniaturized devices. In this article, micro and nano-scale glassy carbon devices manufactured by (i) pyrolysis of specialized pre-patterned polymers and (ii) direct machining or etching of glassy carbon, with their respective applications, are reviewed. The prospects of the use of glassy carbon in the next-generation devices based on the material’s history and development, distinct features compared to other elemental carbon forms, and some large-scale processes that paved the way to the state-of-the-art, are evaluated. Selected support techniques such as the methods used for surface modification, and major characterization tools are briefly discussed. Barring historical aspects, this review mainly covers the advances in glassy carbon device research from the last five years (2013–2018). The goal is to provide a common platform to carbon material scientists, micro/nanomanufacturing experts, and microsystem engineers to stimulate glassy carbon device research.

Electrochemical etching of lightweight nanotips for high quality‐factor quartz tuning fork force sensor: atomic force microscopy applications

Commercially available quartz tuning forks (QTFs) can be transformed into self-sensing and actuating force sensors by micro-assembling a sharp tip on the apex of a tine. Mass of the tip is critical in determining the quality (Q)-factor of the sensor, therefore, fabrication of the lightweight nanotips is a precondition for high Q-factor QTF sensors. The work reports fabrication of very lightweight tungsten nanotips with a two-step electrochemical etching technique which can be used to develop high Q-factor QTF force sensor. First, a tungsten wire with protective coating at one end (1–2 mm) is etched with a trapezoidal waveform to form a lengthy (∼2–5 mm) and slender (diameter ∼10–40 μm) micro-needle. In the second step, sharp tip apex is fabricated with a direct current etching. High Q-factor (6600–8000) QTF force sensors have been developed with the fabricated nanotips. Atomic force microscope scanning of nano-grating and a triblock copolymer surface validates the scanning performance of the developed sensors.

Polymer Masking Method for a High Speed Roll-to-Roll Process

A new polymer masking system with photo-degradable material applicable to high-speed roll-to-roll vacuum deposition processing was studied. Specifically, a process using intense pulsed light to quickly and cleanly remove polymer masks was developed. Poly(methyl methacrylate) (PMMA) and TiO2 were blended together with the positive photoresist to prepare a photo-degradable polymer masking. Infrared spectroscopy confirmed that the positive photoresist moiety, diazonaphtoquinone, was photo-decomposed by white intense pulsed light. The process time required to remove the polymer mask was short enough that this method could be used even in high-speed roll-to-roll processes. It was confirmed that the polymer mask film could be easily removed even at a high process speed by using pressurized gas and adhesive roller tape. The transparent electrode was patterned using a polymer mask and an etching paste, and full solution processed inverted type OPV devices were fabricated. The fabricated OPV by direct etching showed a 94% efficiency compared with that of the reference device.

Fabrication of Integrated PTFE-Filled Waveguide Butler Matrix for Short Millimeter-Wave by SR Direct Etching

Fabrication of Integrated PTFE-Filled Waveguide Butler Matrix for Short Millimeter-Wave by SR Direct Etching