Argon Ion Beam Etching Research Articles

TiO2 nanocone photoanodes by Ar ion-beam etching and physics-based electrochemical impedance spectroscopy

TiO2 nanocone (NC) arrays were produced by argon ion beam etching of nanotube (NT) arrays prepared by Ti anodizing. The anti-reflection performance of NC arrays was enhanced by anodizing a 1 μm-thick Ti film deposited on a p-type silicon substrate. The NC morphology was maintained upon heat treatment up to 400 °C, where the anatase phase was formed. Higher temperature treatments resulted in agglomeration and the formation of the rutile phase. The photoelectrochemical performances of the NC and NT arrays on Ti/Si substrates and the NTs on the Ti disk, both annealed at 400 °C, were compared. The photocurrent curves of the samples on Ti/Si were qualitatively different from NT on Ti. Impedance spectroscopy revealed that the response is dominantly from the p-Si substrates, which can be almost ideally described by the diffusion-recombination governed by the minority electronic carriers. NT on Ti can be characterized by the transmission line model for nanoporous electrodes where the transverse and interfacial capacitances are described by Havriliak-Negami capacitance functions with fixed exponents of either 1 and ½ at high- and low-frequency limits. The model then powerfully deconvolutes TiO2 response from the limited information at the low frequencies for NT and NC on Ti/Si, which can be related to the photoelectrochemical performance. Mott-Schottky analysis of well-defined capacitance parameters from the Havriliak-Negami function allows the physics-based description of the spatially and energetically distributed dopant defects in nanostructured materials.

Large Dense Periodic Arrays of Vertically Aligned Sharp Silicon Nanocones

Convex cylindrical silicon nanostructures, also referred to as silicon nanocones, find their value in many applications ranging from photovoltaics to nanofluidics, nanophotonics, and nanoelectronic applications. To fabricate silicon nanocones, both bottom-up and top-down methods can be used. The top-down method presented in this work relies on pre-shaping of silicon nanowires by ion beam etching followed by self-limited thermal oxidation. The combination of pre-shaping and oxidation obtains high-density, high aspect ratio, periodic, and vertically aligned sharp single-crystalline silicon nanocones at the wafer-scale. The homogeneity of the presented nanocones is unprecedented and may give rise to applications where numerical modeling and experiments are combined without assumptions about morphology of the nanocone. The silicon nanocones are organized in a square periodic lattice, with 250 nm pitch giving arrays containing 1.6 billion structures per square centimeter. The nanocone arrays were several mm2 in size and located centimeters apart across a 100-mm-diameter single-crystalline silicon (100) substrate. For single nanocones, tip radii of curvature < 3 nm were measured. The silicon nanocones were vertically aligned, baring a height variation of < 5 nm (< 1%) for seven adjacent nanocones, whereas the height inhomogeneity is < 80 nm (< 16%) across the full wafer scale. The height inhomogeneity can be explained by inhomogeneity present in the radii of the initial columnar polymer mask. The presented method might also be applicable to silicon micro- and nanowires derived through other top-down or bottom-up methods because of the combination of ion beam etching pre-shaping and thermal oxidation sharpening.Graphic abstractA novel method is presented where argon ion beam etching and thermal oxidation sharpening are combined to tailor a high-density single-crystalline silicon nanowire array into a vertically aligned single-crystalline silicon nanocones array with < 3 nm apex radius of curvature tips, at the wafer scale.

SEM observation of novel characteristic of the dentin bond interfaces of universal adhesives

ObjectiveThe aim of this study was to observe the resin/dentin interfaces of universal adhesives by using scanning electron microscopy (SEM), and to compare their morphologies with conventional etch & rinse (ER) and self-etch (SE) adhesive systems. MethodsTwo three-step and one two-step ER adhesives and two two-step and two single-step SE adhesives were used for comparison with seven universal adhesives in ER mode and SE mode, respectively. Bonded surfaces with bovine teeth were longitudinally sectioned and mirror-polished. Half of the samples were treated with HCl and NaOCl solutions. The interfaces were subjected to argon ion beam etching and then observed by scanning electron microscopy. ResultsThe thickness of the adhesive layer (AL) of most of the seven universal adhesives and single-step SE adhesives was similar. Universal adhesives in SE mode formed a hybrid smear layer as a high-density zone between the AL and dentin. The thickness of the hybrid layer (HL) of the universal adhesives in ER mode was ∼1–2μm, with a high-density zone (reaction layer [RL]) below the HL. ConclusionThe morphological features of most universal adhesives in SE mode and single-step SE adhesives are similar. Although resin–dentin interfaces of universal adhesives in ER mode resemble those of ER adhesives, universal adhesives have a distinctive feature, an RL. SignificanceThe RL might be a sign of chemical bonding even when using universal adhesives in ER mode.

In-Depth Spectroscopy and New Heights for Organic Solar Cells

In this issue of Joule, Lami et al. describe a method that enables UV photoemission spectroscopy (UPS) in the transverse dimension of polymeric semiconductor layers with nanometer-scale resolution. The approach is based on the use of Argon gas cluster ion beam (GCIB) etching instead of monoatomic ion bean bombardment. The use of GCIB reduces surface damage, enabling in depth UPS. The method is applied to the study of critical electronic levels and photovoltage in organic solar cells.

Influence of argon ion beam etching and thermal treatment on polycrystalline and single crystal gold electrodes Au(100) and Au(111)

The effect of argon ion beam etching and subsequent annealing on the surface morphology and electrochemical response of poly- and monocrystalline gold electrodes was studied with the help of scanning electron microscopy, cyclic voltammetry and measurements of under-potential deposition of lead. While the samples were cleaned and restructured by the argon ion beam the following thermal treatment produced stable and very smooth highly ordered surfaces. The specific behaviour of polycrystalline and monocrystalline gold surfaces is discussed.

Large-scale fabrication of highly ordered sub-20\u2009nm noble metal nanoparticles on silica substrates without metallic adhesion layers

Periodic noble metal nanoparticles offer a wide spectrum of applications including chemical and biological sensors, optical devices, and model catalysts due to their extraordinary properties. For sensing purposes and catalytic studies, substrates made of glass or fused-silica are normally required as supports, without the use of metallic adhesion layers. However, precise patterning of such uniform arrays of silica-supported noble metal nanoparticles, especially at sub-100 nm in diameter, is challenging without adhesion layers. In this paper, we report a robust method to large-scale fabricate highly ordered sub-20 nm noble metal nanoparticles, i.e., gold and platinum, supported on silica substrates without adhesion layers, combining displacement Talbot lithography (DTL) with dry-etching techniques. Periodic photoresist nanocolumns at diameters of ~110 nm are patterned on metal-coated oxidized silicon wafers using DTL, and subsequently transferred at a 1:1 ratio into anti-reflection layer coating (BARC) nanocolumns with the formation of nano-sharp tips, using nitrogen plasma etching. These BARC nanocolumns are then used as a mask for etching the deposited metal layer using inclined argon ion-beam etching. We find that increasing the etching time results in cone-shaped silica features with metal nanoparticles on the tips at diameters ranging from 100 nm to sub-30 nm, over large areas of 3×3 cm2. Moreover, subsequent annealing these sub-30 nm metal nanoparticle arrays at high-temperature results in sub-20 nm metal nanoparticle arrays with ~1010 uniform particles.

Large-Area Low-Cost Plasmonic Perfect Absorber Chemical Sensor Fabricated by Laser Interference Lithography

We employ laser interference lithography as a reliable and low-cost fabrication method to create nanowire and nanosquare arrays in photopolymers for manufacturing plasmonic perfect absorber sensors over homogeneous areas as large as 5.7 cm2. Subsequently, we transfer the fabricated patterns into a palladium layer by using argon ion beam etching. Geometry and periodicity of our large-area metallic nanostructures are precisely controlled by adjusting the interference conditions during single- and double-exposure processes, resulting in active nanostructures over large areas with spectrally selective perfect absorption of light from the visible to the near-infrared wavelength range. In addition, we demonstrate the method’s applicability for hydrogen detection schemes by measuring the hydrogen sensing performance of our polarization independent palladium-based perfect absorbers. Since palladium changes its optical and structural properties reversibly upon hydrogenation, exposure of the sample to hydrogen caus...

CuO/Cu based superhydrophobic and self-cleaning surfaces

CuO/Cu based superhydrophobic surfaces with ordered micro/nanostructures have been prepared via a solution-immersion process combining with photolithography and argon ion beam etching. CuO nanoneedles grow only inside microholes on copper substrate due to delaying effect of both residual photoresist and carbon layer produced during Ar etching. The hierarchical structures and surfaces show a water contact angle of 152⁰, a contact angle hysteresis of 3⁰, and a low water adhesion force of 15 μN, indicating a good superhydrophobicity. The obtained surfaces also keep itself clean from carbon black, chalk dust and water, enabling a great potential in self-cleaning and anti-fouling applications.

Large-area fabrication of TiN nanoantenna arrays for refractory plasmonics in the mid-infrared by femtosecond direct laser writing and interference lithography [Invited

Robust plasmonic nanoantennas at mid-infrared wavelengths are essential components for a variety of nanophotonic applications ranging from thermography to energy conversion. Titanium nitride (TiN) is a promising candidate for such cases due to its high thermal stability and metallic character. Here, we employ direct laser writing as well as interference lithography to fabricate large-area nanoantenna arrays of TiN on sapphire and silicon substrates. Our lithographic tools allow for fast and homogeneous preparation of nanoantenna geometries on a polymer layer, which is then selectively transferred to TiN by subsequent argon ion beam etching followed by a chemical wet etching process. The antennas are protected by an additional Al2O3 layer which allows for high-temperature annealing in argon flow without loss of the plasmonic properties. Tailoring of the TiN antenna geometry enables precise tuning of the plasmon resonances from the near to the mid-infrared spectral range. Due to the advantageous properties of TiN combined with our versatile large-area and low-cost fabrication process, such refractory nanoantennas will enable a multitude of high-temperature plasmonic applications such as thermophotovoltaics in the future.

Single and multilayered materials processing by argon ion beam etching: study of ion angle incidence and defect formation

Ion beam etching (IBE) is a very promising technique in microelectronics because of its capability to etch small patterns with a high resolution and inert materials. In this study, the angular incidence of an argon ion beam on the etch rate and uniformity is discussed in the case of several materials often used in microelectronics. The capability of the IBE technique to etch multilayered stack samples with positive anisotropic profiles was demonstrated on TiNiAu, TiNiCuAu, BST and PZT. Two typical defects involved in IBE processing (fences and not etched pattern foots) due to shadow masking and redeposition effect, are explained and solutions are presented to avoid them. Deep IBE was performed on GaN with an etch depth as high as 10 μm, using a 8 μm thick SiO2 mask. The etching of other mask materials, such as TiN, was investigated in order to improve the selectivity. Using a TiN mask, a selectivity to GaN as high as 5 is reported. Finally, the etch rate enhancement needed for deep etching was studied.

Fabrication of Square-Centimeter Plasmonic Nanoantenna Arrays by Femtosecond Direct Laser Writing Lithography: Effects of Collective Excitations on SEIRA Enhancement

We demonstrate the use of femtosecond direct laser writing lithography for a fast and homogeneous large-area fabrication of plasmonic nanoantennas on a substrate by creating a patterned polymer as an etch mask on a metal layer. Subsequent argon ion beam etching provides plasmonic nanoantennas with feature sizes below the diffraction limit of the laser light. They exhibit tunable high-quality plasmon resonances in the mid-infrared spectral range, which are ideally suited for surface-enhanced infrared absorption (SEIRA). In the present work, we demonstrate reliable, fast, and low-cost fabrication of a wide variety of antenna arrays and examine particularly the influence of plasmonic coupling between neighboring antennas on the SEIRA enhancement effect. Specifically, we measure the enhanced infrared vibrational bands of a 5 nm thick 4,4′-bis(N-carbazolyl)-1,1′-biphenyl layer evaporated on arrays with different longitudinal and transversal spacings between antennas. An optimum SEIRA enhancement per antenna of...

Area dependence and influence of crystal inhomogeneity on superconducting properties of Bi2212 mesa structures

The rapid increase in applications of terahertz waves requires new techniques to obtain continuous wave terahertz sources. Mesa structures fabricated from high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi2212) single crystal have been observed as an intense, coherent, continuous electromagnetic wave source in the terahertz (THz) frequency region. However, in order to produce coherent radiation with high applicable power, we need large mesa structures that enter a collective electromagnetic state in which their oscillations are largely synchronized in phase. On the other hand, large mesa structures cause a heating problem. In this study, we report on the critical current density dependence of mesa area and the crystal inhomogeneity to understand heating problems in large area mesas for terahertz radiation. Since the doping dependence of Bi2212 is an important parameter, the as-grown Bi2212 crystals were heat-treated at various temperatures under vacuum conditions. We have fabricated triple mesa structures from Bi2212 single crystal using e-beam lithography and argon ion beam etching techniques with same area and with different area on the same chip. We investigated and compared characteristics of triple mesas which are on the same chip and next to each other. In this way, we searched the crystal inhomogeneity in triple mesa structures and studied the critical current density dependence of mesa area to obtain high emission power for the THz radiation. Our experimental results clearly show that the Josephson critical current density is decreasing when the area of mesa is increasing.

Low-temperature diffusion bonding of pure aluminum

1 keV argon ion beam was employed to remove the oxide film of pure aluminum before diffusion bonding. A sound joint of pure aluminum was obtained by ion activation-assisted diffusion bonding at the low temperature of \(350~{}^{\circ}\mathrm{C}\), while the high-quality joining of pure aluminum was infeasible by conventional diffusion bonding at the temperature lower than \(500~{}^{\circ}\mathrm{C}\). The residual oxide film ratios of joints decreased with the increase of ion cleaning time. When the specimens were cleaned for 120 min, the joint with the maximum tensile strength of 62.3 MPa and the elongation of 14.1 % was obtained. The argon ion beam etching surface treatment provides a new route for the low-temperature diffusion bonding. The reliable diffusion bonded joint of pure aluminum indicates that low-temperature diffusion bonding is feasible for bulk materials, especially for materials with the outstanding plasticity.

Depth profiling of NbxO/W multilayers: effect of primary ion beam species (O2+, Ar+ and Cs+)

Depth profiling of NbxO/W multilayered samples was carried out using O2+, Cs+ or Ar+ beams of different energies (2 keV, 1 keV and 0.5 keV). The obtained depth profiles showed that sputtering with O2+ or Ar+ beams can reveal the distribution of light elements, while sputtering with Cs+ cannot show correctly their distribution if lower energy of 0.5 keV is applied. SRIM simulations show that changes in primary energy of sputter ions have much stronger effect on deposited energy incl. vacancy/ion and sputter yields than for oxygen and argon ion beam etching. It is suggested that O2+ or Ar+ sputter sources should be used when both light and heavy species are present in nano‐scale multilayered targets. Copyright © 2012 John Wiley &amp; Sons, Ltd.

The influence of residual gas on boron carbide thin films prepared by magnetron sputtering

Boron carbide (B4C) thin films were prepared by magnetron sputtering and residual gas impurities in the films were analyzed by X-ray photoelectron spectroscopy. The impurities, mainly oxygen, decrease with improving vacuum. By using argon ion beam etching of the films, the atomic concentration was measured as a function of etching depth. The binding energy spectra were analyzed using wavelet transform and curve fitting, showing that most of the oxygen impurity is in the form of boron oxides, and that the impurities are physically trapped among columnar structures in the film. In order to improve the base vacuum before coating the film, a range of methods were used, including argon gas filling on the target surface and titanium pre-sputtering. The experimental results show that the latter is an efficient and feasible method. Based on the titanium pre-sputtering technology, the optical performance of W/B4C multilayer was improved so much.

Lead Pipe Scale Analysis Using Broad-Beam Argon Ion Milling to Elucidate Drinking Water Corrosion

Herein, we characterized lead pipe scale removed from a drinking water distribution system using argon ion beam etching and a variety of solids analysis approaches. Specifically, pipe scale cross sections and solids were analyzed using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, and acid digestion followed by inductively coupled plasma mass spectrometry analyses. The pipe scale consisted of at least five layers that contained Pb(II) and Pb(IV) minerals, and magnesium, aluminum, manganese, iron, and silicon solids. The outer layer was enriched with crystalline amorphous manganese and iron, giving it a dark orange to red color. The middle layers consisted of hydrocerussite and plattnerite, and the bottom layer consisted primarily of litharge. Over the litharge layer, hydrocerussite crystals were grown vertically away from the pipe wall, which included formations of plattnerite. Significant amounts of trace contaminant vanadium, likely in the form of vanadinite, and copper accumulated in the scale as well.

Fabrication of metallic oxide nanowires

Micron length nanowires with varying widths were patterned in half-metallic La 2/3Sr 1/3MnO 3 (LSMO) thin films of different thicknesses, using a thin negative-tone electron beam lithography (EBL) process. Patterns were realized in the high resolution hydrogen silsesquioxane (HSQ) inorganic resist and successfully transferred to the manganite via an energetic argon ion beam etching (IBE). We have obtained wires with widths down to 65 nm and length up to 4 μm that exhibit transport properties comparable with those of unpatterned thin films.

Design and fabrication of a negative microlens array

An operation model of a negative microlens array is demonstrated. The array consists of two kinds of materials with different refractive indices. First of all, a positive microlens array with 256×256 elements serving as a pattern is fabricated by argon ion beam etching on the quartz. The diameter and average corona height of the element are 28 and 0.638 μm, respectively. The spacing between two neighboring elements is 2 μm. In the second phase, after being coated by epoxy, the positive microlens array pattern is spun and baked, leading to a complex negative microlens array. Surface stylus measurement shows that the surface of the positive quartz microlens array is smooth and uniform. Focal length measurement of the negative microlens array indicates that the focal length region with −731±3 μm is in good agreement with the theoretical calculation value of −729 μm.

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ thin film microelectrodes investigated by impedance spectroscopy

The electrochemical properties of geometrically well-defined Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) microelectrodes have been investigated by impedance spectroscopy. The microelectrodes of 20–100 μm diameter and 100 nm thickness were prepared by pulsed laser deposition (PLD), photolithography and argon ion beam etching. The oxygen reduction reaction at these model electrodes is limited by interfacial processes, i.e. by the oxygen surface exchange and/or by the transfer of oxide ions across the electrode/electrolyte boundary, whereas the resistance associated with the transport of oxide ions through the bulk of the thin film electrode is negligible. The experiments revealed an extremely low absolute value of the electrochemical surface exchange resistance of only 0.09 (± 0.03) Ω cm 2 at 750 °C in air, which is more than a factor of 50 lower than the corresponding value measured for La 0.6Sr 0.4Co 0.8Fe 0.2O 3− δ (LSCF) microelectrodes of the same geometry. The dependence of this and other electrochemical quantities such as the chemical bulk capacitance or the BSCF/YSZ interfacial resistance on temperature has been studied between 500 and 750 °C.

Ion beam etching of high resolution structures in Ta 2O 5 for grating-assisted directional coupler applications

An investigation on thin Ta 2O 5 films patterning using argon ion beam etching (IBE) is presented. The etch rates are characterised by varying the angle of incidence of the beam onto the substrate. Ta 2O 5 gratings with a period of 2.2 μm (1.1 μm linewidth) and 0.25 μm thickness are fabricated using an angle of incidence of 0°. The resulting Ta 2O 5 grating cross sectional profiles are analysed using AFM and SEM imaging. A fabrication method is thus demonstrated which could be used to implement wavelength selective gratings in applications such as grating-assisted directional couplers (GADCs).