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The suitability of GaN PCSSs (photoconductive semiconductor switches) as high voltage switches (&gt, 50 kV) was studied using a variety of commercially available semi-insulating GaN wafers as the base material. Analysis revealed that the wafers’ physical properties were noticeably diverse, mainly depending on the producer. High Voltage PCSSs were fabricated in both vertical and lateral geometry with various contacts, ohmic (Ti/Al/Ni/Au or Ni/Au), with and without a conductive n-GaN or p-type layer grown by metal-organic chemical vapor deposition. Inductively coupled plasma (ICP) reactive ion etching (RIE) was used to form a mesa structure to reduce field enhancements allowing for a higher field to be applied before electrical breakdown. The length of the active region was also varied from a 3 mm gap spacing to a 600 µm gap spacing. The shorter gap spacing supports higher electric fields since the number of macro defects within the device’s active region is reduced. Such defects are common in hydride vapor phase epitaxy grown samples and are likely one of the chief causes for electrical breakdown at field levels below the bulk breakdown field of GaN. Finally, the switching behavior of PCSS devices was tested using a pulsed, high voltage testbed and triggered by an Nd:YAG laser. The best GaN PCSS fabricated using a 600 µm gap spacing, and a mesa structure demonstrated a breakdown field strength as high as ~260 kV/cm.

Lithium niobate on insulator (LNOI), regarded as an important candidate platform for optical integration due to its excellent nonlinear, electro-optic and other physical properties, has become a research hotspot. Light source, as an essential component for integrated optical system, is urgently needed. In this paper, we reported the realization of 1550-nm band on-chip LNOI microlasers based on erbium-doped LNOI ring cavities with loaded quality factors higher than one million, which were fabricated by using electron beam lithography and inductively coupled plasma reactive ion etching processes. These microlasers demonstrated a low pump threshold of ~20 {\mu}W and stable performance under the pump of a 980-nm band continuous laser. Comb-like laser spectra spanning from 1510 nm to 1580 nm were observed in high pump power regime, which lays the foundation of the realization of pulsed laser and frequency combs on rare-earth ion doped LNOI platform. This work has effectively promoted the development of on-chip integrated active LNOI devices., Comment: 4 pages,4 figures

Nano-mold is an essential tool for nano-imprinting. However, large-area nano-mold fabrication relies on expensive equipment or complicated processing. Silicon nano-molds were achieved by proximity ultraviolet lithography and reactive ion etching (RIE). By optimizing the parameters in the processes of exposure, development, and RIE, silicon nano-mold with nano-scale ridges were fabricated with high-precision. The achieved minimum width of nano-ridges was 263 nm. This method is capable of fabricating silicon nano-mold covering four-inch wafer, which is simple, efficient and free from costly equipment.

In this study, we report a method to fabricate molds and flexible stamps with 2D photonic crystal structures. This includes self-assembly of polystyrene particles into monolayer, oxygen reactive ion etching, thin film (chromium (Cr)) deposition, and polydimethylsiloxane replication. By tuning the thickness of Cr layer, reusable master molds with nano bumps or nano concaves could be prepared selectively. We showed that the replicated flexible stamps out of these molds exhibited structural colors. Characteristics of the colors depended on viewing angle, brightness of background and light source. And the colors even faded out when the background is white or when the stamp was bent. By using this feature, possible strategies for anti-counterfeiting applications have been suggested in this study. Since the molds are reusable and the fabrication method is simple and cost-effective, this study is expected to contribute to nano devices for industries in future.

Multicolor holograms have numerous applications, including in art, data storage, security, and advanced displays. In recent years, there has been much interest concerning multicolor holograms based on metasurfaces [1] . Wen et al [2] demonstrated multicolor holograms using dielectric nanoparticles, with the nanoparticle size defining its resonant wavelength and its position defining its phase via the detour phase concept [3] . While this approach worked, it required good control over nanoparticle size and shape, achieved using inductively coupled reactive ion etching (ICP-RIE). This motivates the development of multicolor metasurface holograms that are also based on detour phase, but using other nanostructure types. Here we show that arrays of nanoholes in aluminum films enable the realization of multicolor holograms. We design nanohole arrays that serve as color (i.e. red/green/blue) filters with high transmission and low cross-talk. We then design two multicolor holograms based on these filters and simulate their performance, demonstrating that they show good fidelity to the desired holographic images. Our device is based on aluminum and silicon dioxide, giving it the advantage of CMOS compatibility.

The power conversion efficiency (PCE) of perovskite/silicon tandem solar cells (PSTSCs) is expected to increase with optimized light management. In this work, we report on PSTSCs containing nanostructures enabling PCEs exceeding 26%. A hexagonal sinusoidal nanostructure with 750nm period was used. The structure was transferred into silicon by nanoimprint lithography and reactive ion etching. Perovskite top cells were deposited by spin-coating resulting in a full coverage of the nanostructure. PSTSC comprising these nanostructures yielded a steady-state PCE of 26.1% and a short-circuit current density of 19.5mA·cm−2.

Nanograting (NG) is a new method for externally doping the surface of Si substrates only by creating nano-size indents. This geometry-induced doping (G-doping) occurs due to quantum effects ruling the patterned region. Our experimental investigations verified that the Fermi level difference at the patterned region depends on the depth of NG indents and, consequently, affects the electronic, magnetic, and optical properties of the NG region. Here, several Si substrates were patterned with different NG depths using laser interference lithography and a consecutive series of reactive ion etching. Four NG regions with 10, 20, 30, and 40 nm were patterned on p-type, n-type, p+ type, and n+ type Si substrates, and 8 samples were cut separately for statistical analysis of the results. The Fermi level difference of these NG regions was characterized by Kelvin probe showing that the Fermi level difference raised for NG-regions with maximum increase for indents of 10 nm depth but declined by increasing the NG depth to 40 nm both in p-type and n-type substrates. Highest decline observed for p-type substrates but negligible increase in n+ type and p+ type substrates. XPS and SEM analyses performed to verify the surface quality and microstructure of NG-junctions.

Porous silicon (PS) can be used as a loading template in sensing or as a matrix to develop nanoparticle arrays. We present a comprehensive study of PS morphology and optical properties before and after the pore opening process, including the determination of thickness, pore size, and pore density of PS layers, its surface wettability, and reflectivity. The PS samples were fabricated by electrochemical anodization of monocrystalline silicon wafer in 5–20 wt.% hydrofluoric acid (HF) solution at a current density in the range of 20–200 mA/cm2 . Anodization was followed by the pore opening process, i.e., the removal of a parasitic superficial layer with a “bottleneck” structure by reactive ion etching (RIE). The results illustrate that “bottleneck”-free PS allows to achieve a high pore density using a low HF concentration and a reduced current density. We established that this structure demonstrates higher hydrophobicity in comparison to the samples before RIE. The applicability of the developed “bottleneck”-free PS was tested via filling the pores with silver nanoparticles, indicating its potential use as a template for the fabrication of nanoparticle arrays.

Terahertz time-domain spectroscopy and Fourier-transform infrared spectroscopy were developed as the method for the investigation of high-frequency characteristics of two-dimensional electron gas and GaN:C buffer layers in AlGaN/AlN/GaN heterostructures grown on a semi-insulating SiC substrate. The reflectance and transmittance spectra of the selected heterostructure layers were studied after the top layers were removed by a reactive ion etching. Results were numerically analyzed using the transfer matrix method taking into account the high-frequency electron conductivity via a Drude model and complex dielectric permittivity of each epitaxial layer via a one-phonon-resonance approximation. Good agreement between the experiment and theory was achieved revealing the temperature dependent electron effective mass in AlGaN/AlN/GaN high electron mobility transistor structures and the small damping factors of optical phonons due to high crystal quality of the epitaxial layers fabricated on the SiC substrate.

This study reports a simple imprinting method for the fabrication of biomimetic moth-eye antireflective polymethyl methacrylate (PMMA) nanostructures on the surface of the substrate. The antireflection structured silicon was obtained by Reactive Ion Etching (RIE) method. By using the antireflection structured silicon substrate as the imprinting stamp, the biomimetic moth-eye polymer structures showed tapered holes, whose depth and periodicity were around 780 nm and 580 nm, respectively. The reflectance of the resulting PMMA structures was reduced from 10% to less than 1% in the wavelength range from 300 nm to 1600 nm. This simple methodology can be scaled up via self-loading and nanoimprinting, which may have a promising application in optoelectronic devices and solar cells.

Nanometer-scale devices are fabricated using numerous fabrication techniques since the last couple of decades. However, the advancement in nanotechnology gives new horizons to the researcher to develop nanometer-scale devices in a controlled manner while also providing high accuracy and precision with cost and time-effectiveness. This article focuses on the production of free-standing nano-scale thick Si3N4 films using Reactive Ion Etch technique. Although there are many reports in the literature on the required conditions to etch Si3N4, unfortunately, there are not many technical reports that illustrate the step-by-step fabrication and characterization together with the detailed optimization steps. Here in this study, the thinning of a membrane is achieved using CF4/Ar in controlled RF power conditions and a well-defined protocol is given with several preliminary optimization steps. By doing so, free-standing locally thinned Si3N4 membranes of about 20 nm thickness are successfully realized in a precise manner. Further assessments are given an offer to the readers of interest the ways to characterize the samples with the required cautions. The detailed procedure given here would potentially provide practical aspects for the researchers working in the field of nanofabrication.

The effects of both HBr/O2 and Cl2/O2 mixing ratios in HBr+Cl2+O2 gas mixture on plasma parameters, steady-state densities of active species and Si etching kinetics were studied under the typical conditions of reactive ion etching process: total gas pressure (p = 10 mTorr), input power (W = 500 W), bias power (Wdc = 200 W). The data on internal plasma parameters and plasma chemistry were obtained using a combination of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. It was found that the variation in HBr/O2 mixing ratio at constant Cl2 fraction in a feed gas is characterized by the stronger impact on the steady-state plasma composition through both electron-impact and atom-molecular reaction kinetics as well as allows one to obtain the wider change in the total halogen atom density. It was shown that changes in both HBr/O2 and Cl2/O2 mixing ratios toward O2-rich plasmas lowers the Si etching rate that exhibits no evident correlations with total halogen atom flux and ion energy flux. The model-based analysis of Si etching kinetics allowed one to conclude that the effective reaction probability for Si + Cl/Br heterogeneous reaction depends on the flux of oxidative species – oxygen atoms and OH radicals. The reasons may be 1) the oxidation of silicon resulting in higher reaction threshold energy; and 2) the decreasing fraction of free adsorption sites for Cl/Br atoms due to the oxidation of reaction products into the lower volatile SiBrxOy and SiClxOy compounds.

Superconducting microwave resonators are important components of superconducting quantum information and astronomy detector systems. In this paper, we show how to modify the microwave resonator performance after fabrication through surface engineering. In particular, we focus on titanium nitride (TiN)/silicon (Si) resonators because they have shown potential for achieving high-quality factors $(\text{Q}_{i}\text{s})$ . Depending on the type of surface treatment, chemical- or plasma-based, we found $\text{Q}_{i}\text{s}$ that vary by approximately a factor of 18. We used inductively coupled plasma (ICP) combined with reactive ion etching (RIE) for the plasma surface treatment. We found that the microwave resonator performance depends on the type of plasma environment, such as single gas (oxygen) or gas mixtures [argon/hydrogen (Ar/H2), argon/octafluorocyclobutane (Ar/C4F8), and argon/sulfur hexafluoride (Ar/SF6)], and the plasma processing conditions, such as treatment time, ICP power, and RIE power. Of the plasma surface treatments, the Ar/SF6 environments with no or low ICP power showed the highest potential to improve $Q_{i}$ . The processing conditions determined the chemistry and roughness of the Si and TiN surfaces, TiN film thickness, and the overall TiN/Si resonator structure (edge and sidewall). Our results can be used as a guideline for optimizing the microwave resonator performance using surface treatments.

Gold (Au) is a noble metal that has been widely researched due to its high catalytic performance-to-cost ratio. The catalysis could be improved by fabrication of nanostructured arrays on Au thin film with a large area. In the present paper, a facile NSL-RIE approach comprising of nanosphere lithography followed by oxygen plasma reactive ion etching has been developed to fabricate ordered Au nano-ring arrays with almost 100% substrate coverage. The preferential etching of {1 1 1} lattice planes of Au gives rise to the formation of a number of Au nano-pyramids across the entire surface of the nano-ring arrays. The sharp tips along with the Au atoms around the edges of these nano-pyramids provide active sites that perform strong catalysis. Meanwhile, Moire fringes are observed over the etched Au surface which is caused by the rotation of the partial Au lattice with respect to the original Au lattice. This lattice distortion provides high surface energy allowing the significant improvement of the catalysis of Au nano-ring arrays. The direct evidence is proven by the enhanced electrochemical properties of the as-produced Au nano-ring array, which has high efficiency in ethanol oxidation reactions (EORs) with low energy input requirement. Electrochemical testing with varying physical parameters shows that the detecting limit of ethanol is ∼5.0 mM and strong signals come with high concentrations of mobile charge carriers at extreme pH values. Long continuous CV scans reveal that in alkaline medium, C1 pathway could become increasingly preferential over C2 pathway, and thus making the Au nano-ring array structure useful in the field of direct ethanol fuel cell.

Here, we report a straightforward approach to fabricate antifogging antireflective dual-function nanostructured coatings, where antireflective nanograsses were etched into antifogging polymer coatings by self-masking reactive ion etching (RIE). The transmittance of coatings increases with the etching time, and the maximum transmittance reaches up to 98.9% in 180 s. The effective refractive index of grass-like nanostructure was calculated to be 1.15 and its optical property was simulated via the finite difference time domain (FDTD) model. The antifogging property of polymer coatings remains unchanged after RIE, which results from the hygroscopicity of polymer matrix. This strategy surpasses traditional design concepts of antifogging polymer coatings by combining excellent antireflective and antifogging properties on the same outermost layer, which demonstrates that it is probable to achieve multifunction on a single layer of a single composition.

In this work, we investigate the impact of successively removing the passivation layers of ISFET sensors implemented in a standard CMOS process to improve sensing performance. Reactive ion etching is used as a post-processing technique of the CMOS chips for uniform and accurate etching. The removal of the passivation layers addresses common issues with commercial implementation of ISFET sensors, including pH sensitivity, capacitive attenuation, trapped charge, drift and noise. The process for removing the three standard layers (polyimide, Si3N4 and SiO2) is tailored to minimise the surface roughness of the sensing layer throughout an array of more than 4000 ISFET sensors. By careful calibration of the plasma recipe we perform material-wise etch steps at the top and middle of the nitride layer and top of the oxide layer. The characterisation of the ISFET array proves that the location of the trapped charge in the passivation layers is mainly at the interface of the layers. Etching to the top of the oxide layer is shown to induce an improvement of 80% in the offset range throughout the array and an increase in SNR of almost 40 dB compared to the non-processed configuration. The performance enhancement demonstrates the benefit of a controlled industry-standard etch process on CMOS ISFET array system-on-chips.

We study the surface morphology, mass loss and wetting of fluorinated ethylene propylene surfaces which have been treated using reactive ion etching. We find that etching with argon gas alone results in a network structure, while oxygen combined with argon results in pyramidal hair-like structures, and by adding CF4 globules are found. We demonstrate that small alterations in the preparation allows one to create samples with either homogeneous nanostructures exhibiting large contact angles and very low hysteresis or more irregular structures which exhibits pinning sites that allow very large contact angle hysteresis. The advancing and receding contact angles are estimated based on the tilting plate method, and the pinning force measured for the samples is investigated for large droplets. The results reported here indicate that surface structure and contact angle hysteresis of fluorinated polymers can be manipulated for applications where either large or small contact angle hysteresis is needed.

Made available in DSpace on 2019-10-06T15:41:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-25 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Optical waveguide amplifiers have seen a growing interest in the last years due to their applications in telecommunication. This paper reports a notable increase of the relative gain of Yb3+/Er3+ codoped Bi2O3–GeO2 waveguides by introducing disorder in the form of silicon nanostructure as scattering centers. A photoluminescence enhancement of about 10 times for the 520 nm and 1530 nm emission bands is observed in the waveguides when the silicon nanostructures are introduced. Increase of the Yb3+/Er3+ effective absorption, due to the scattering provided by the silicon nanostructures, and decrease of [Bi+], caused by the introduction of silicon, are proposed as likely causes for the luminescence and gain enhancement. The pedestal waveguides were fabricated by RF-sputtering followed by optical lithography and reactive ion etching. RF-sputtering of silicon together with Yb/Er and Bi2O3–GeO2 glass, followed by heat treatment, produced Yb3+/Er3+ codoped Bi2O3–GeO2 waveguides with silicon nanostructures of size 25–30 nm. The resulting relative gain reached 5.5 dB/cm at 1542 nm representing an enhancement of 50% with respect to waveguides without silicon nanostructures. This strategy of introducing appropriate disorder may open an avenue for designing and manufacture of novel photonic devices in this emerging field of integrated optics. Centro de Lasers e Aplicações Instituto de Pesquisas Energéticas e Nucleares CNEN-IPEN/SP, Av. Prof. Lineu Prestes 2242 Escola Politécnica Universidade de São Paulo Faculdade de Tecnologia de São Paulo CEETEPS/UNESP Faculdade de Tecnologia de São Paulo CEETEPS/UNESP FAPESP: 2013/26113-6 CNPq: 465.763/2014 FAPESP: PV-2017/05854-9

Microfluidic chemotaxis analysis requires stable and reproducible formation of chemical gradient with low batch-to-batch variation. Dimensional uniformity of a junction channel plays a key role in diffusion-based gradient generation. Conventional methods for the analysis of bacterial chemotaxis are limited in stability and reproducibility of the chemical gradient. Here, we report a microfabrication method employing plasma enhanced chemical vapor deposition for silicon oxide deposition and consecutive reactive ion etching processes to reduce the experimental errors of chemotaxis analysis occurring from dimensional inaccuracy of the junction channel. This approach produces precise dimensional junction channels with below 1% variation. Thus, we confirm the reproducibility of chemotaxis analysis and obtain the chemotaxis index of Pseudomonas aeruginosa PAO1 with bacterial chemoeffectors.

This paper presents the fabrication and measurements of a vertical out-of-plane microprobe electrode array with individual interconnects through the substrate using a silicon through-glass via (TGV) with transparent properties. The TGV was fabricated using a low-resistance silicon (LRS) via and the glass reflow process. The microprobe structure was formed by multiple deep reactive ion etching and reactive ion etching processes using one-step photolithography and a single etch mask. The height and pitch of the microprobe are designed to be 90 μm and 210 μm, respectively. Cr and Au conductive layers were deposited and patterned on the silicon microprobe structure. A parylene-C thin film was used as an insulating layer and it was etched only at the tip-end through the self-alignment fabrication process using a thick photoresist to expose the conductive part. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. The single via resistance was measured to be 1.26 ± 0.041 Ω. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured by the cyclic voltammetry method for each electrode. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Further, the electrode impedance was measured and the equivalent circuit analysis was constructed using the Zview impedance modeling software. Experiments were conducted to measure the impedance of 16 microprobe electrodes, and it was confirmed that the impedance did not exceed 1 MΩ at 1 kHz. Then, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. Also, the light transmittance experiment was conducted to measure the transparency of the TGV structure fabricated through the glass reflow process.

The fabrication of silicon nanohole (SiNH) using a combination of electron beam lithography (EBL) and reactive ion etching (RIE) processes is reported. The optimum exposure dose of EBL process was found to be in the range of 210-240 µC/cm2 due to small enlargement of hole diameter after pattern development process. The anisotropic etching and isotropic etching was achieved at low and high reaction pressures, respectively. As expected, the etching rate increase with time and RF power. A relatively smooth and well-defined NH has been obtained at RF power of 100 W and reaction pressure of 0.08 Torr, which is suitable to be applied for optical waveguide.

Capacitively coupled plasma reactive ion etching of silicon by injecting nitrogen trifluoride (NF3) gas was conducted, and the etching process was studied with a residual gas analyzer and an optical emission spectroscopy. During the etching of silicon by the NF3 plasma, the currents of F+ and SiF+3 ions were obtained from the residual gas analyzer. At the same time, the line intensity of fluorine was measured using optical emission spectroscopy. The ion currents of F+ and SiF+3 and the line intensity of fluorine were highest for etching at high pressure. With the results of this study, the general characteristics of reactive ion etching of silicon by using NF3 plasma were confirmed. In addition, by simply changing the flow rate of NF3, a high NF3 flow rate was found to result in a high etch rate because of the reduced residence time.

Following the demand for three-dimensional (3D) micromachined structures, additive and subtractive processes were developed for fabrication of real 3D shapes in metals, alloys and monocrystalline Si (c-Si). As a primary structuring step for well-defined 3D structuring of the photoresist, grayscale lithography by laser direct writing was used. For additive fabrication of 3D microstructures, structured photoresist was used as molds. They were sputtered and subsequently electroplated by a metal (Cu) and an alloy (NiCo). The derived electroplated structures were demolded from the photoresist using an organic stripper. These metal structures are satisfactory replicas of the photoresist pattern. For subtractive pattern transfer of 3D structures into c-Si, reactive ion etching (RIE) was used to transfer the 3D photoresist structure into c-Si with 1:1 pattern transferability. The process parameters of RIE were optimized to obtain a selectivity of 1 and an anisotropy factor close to 1. Whereas conventional X-ray lithography (LIGA) and nanoimprint lithography result in 2.5D patterns, these techniques allow the fabrication of almost any arbitrary 3D shapes with high accuracy. In many cases, 3D structures (‘free forms’) are required, e.g. for molding of optical components such as spheres (or aspheres), channels for lab-on-a-chip and pillars for biological applications. Moreover, 3D structures on Si could be used as optical gratings and sensors.

An active matrix light emitting diode (LED) micro-display system was demonstrated with GaN-on-Si epilayers and a custom-designed CMOS backplane using an Au-free Cu/Sn-based metal bonding method. The blue micro-LED array consists of $64\times36$ pixels with a pitch size of $40\,\,\mu \text{m}\,\,\times 40\,\,\mu \text{m}$ and a pixel density of 635 pixels/in (ppi). The Si substrate for the LED growth was removed by reactive ion etching (RIE) using SF6-based gas after flip-chip bonding. Crack-free and smooth GaN layers in the display area were exposed. Images and videos with 4-bit grayscale could be clearly rendered, and light crosstalk was significantly suppressed compared to its counterpart using the GaN-on-sapphire epilayers. The demonstration suggests the tremendous potential of the low-cost and large-scale GaN-on-Si epilayers and cost-effective Au-free Cu/Sn-based bonding scheme for micro-display applications.

For various lighting and monolithic sensor systems application, vertically aligned three-dimensional (3D) gallium nitride (GaN)- and indium gallium nitride (InGaN)/GaN-based LED nanowire arrays with sub-200 nm feature sizes (down to 35 nm) were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the lithographic opening and well-controlled surface functionalization prior to the polystyrene nanosphere (PN) deposition, vertical GaN nanowire arrays with an area density of 9.74 × 108 cm–2 and an aspect ratio of >10 could be realized in a specified large area of 1.5 × 1.5 mm2. Optoelectrical characteristics of the nanoLEDs were further investigated in cathodoluminescence (CL) measurements, in which multiquantum well (MQW) shows a clear CL-emission at a wavelength of 465 nm. Thus, using NSLL to manufacture low-cost but highly ordered 3D GaN-based nanowir...

Nanoporous materials have attracted great attention due to the large ratio of surface over volume. Similarly, nanomaterials with big surface roughness have also high surface/volume ratio. The present work investigates the electrochemical behavior of a nanowire electrode with a big surface roughness. An on-chip individually addressable suspended gold nanowire (width: 340 nm, thickness: 90 nm, and length: 5.5 μm) electrode with an arithmetic mean surface roughness of 15.02 ± 2.95 nm was fabricated by using the electron beam lithography and reactive ion etching technique. The Cyclic Voltammograms (CV) of the suspended Au nanowire electrode in both the potassium ferricyanide and the sulfuric acid electrolytes show noticeably different characteristics from that of the control Au thin film electrode. The suspended nanowire shows an excellent room-temperature cyclic reliability, with only ±3% variation in the integrated capacitance after 600 cycles at the scanning rate of 0.1 Vs-1. The facile on-chip fabrication, large effective surface area, and excellent cyclic stability make the suspended gold nanowire electrode an ideal candidate for many emerging applications such as electrochemical catalysts, biosensors, and detectors.

Silicon nanowire (SiNW) biosensors have received a special attention from the research community due to its ability to detect a range of species. The nano feature size of the SiNW has been exploited to fabricate small, low-cost, robust, portable, real-time read-out biosensors. These sensors are manufactured by two methods – top-down or bottom-up. Instead of the bottom-up method, the top-down approach is widely used due to its compatibility with complementary metal-oxide semiconductor (CMOS) process and scope of mass production. However, in the top-down method, the post fabrication microfluidic channel integration to access the SiNW test site remains complex and challenging. Since the nanosensor is expected to operate in a bio environment, it is essential to passivate the metal electrodes while pathways have to be made to access the test site. In this paper, we present a relatively easier method to access the SiNW test site without employing complex microfluidic channels while achieving leakage free passivation of metal electrodes and preserving the integrity of the nanosensor. This is accomplished in the last step of the manufacturing process by employing a lithography mask and reactive ion etching (RIE). HfO2 integrated crystalline silicon nanosensors are manufactured using novel top-down front end of line (FEOL) sidewall transfer lithography (STL) process. HfO2 acts as an etch stop layer while performing RIE in the last step to access the sensor test site. The 100 mm wafer scale results of 20 nm × 60 nm × 6 μm (H x W x L) p-type nanosensors shows an average Ion/Ioff ≥ 105 with maximum turn-on voltage of −4 V and uniform subthreshold slope of 70 mV/dec. In comparison with sensors encapsulated with SiO2, the HfO2 integrated nanosensors were found to improve the threshold voltage variation by 50%. Based on this work, the HfO2 integrated SiNW demonstrates good stability for biosensing application.

We report on a novel and simple pattern transfer process into Si via fullerene-based spin-on-carbon (SOC) hard masks in this work. Electron beam lithography and extreme ultraviolet interference lithography techniques are used to pattern high-resolution and dense lines on a resist/SOC bilayer. The patterns are subsequently transferred by a low-pressure O2 plasma etching (SOC) and reactive ion etching process with a gas mixture of SF6 and C4F8 (Si). Si sidewall trimming can be controlled by modifying the Si etching rate, achieving Si fins with dimension down to 15 nm half-pitch with aspect ratio as high as of 7:1.

We developed a novel approach to characterize the electrochemical reaction of solid oxide fuel cell. The method constrained electrode-electrolyte interface geometry and thereby limited reaction area for charge transfer. Reactive ion etch (RIE) and sputtering techniques were used and the well-defined geometry of interfaces was realized as patterned strips. The number of strips of the pattern shape was fully consistent with the value of charge transfer impedance. The confined interface structure also helped maintain open circuit voltage for 10 h. This new approach proposes an alternative to quantitatively analyze different electrode materials for SOFC operation while excluding consideration for structural variables.

The advent of recent technologies in the nanoscience arena requires new and improved methods for the fabrication of multiscale features (e.g., from micro- to nanometer scales). Specifically, biological applications generally demand the use of transparent substrates to allow for the optical monitoring of processes of interest in cells and other biological materials. Whereas wet etching methods commonly fail to produce essential nanometer scale features, plasma-based dry etching can produce features down to tens of nanometers. However, dry etching methods routinely require extreme conditions and extra steps to obtain features without residual materials such as sidewall deposits (veils). This work presents the development of a gold etching process with gases that are commonly used to etch glass. Our method can etch gold films using reactive ion etching (RIE) at room temperature and mild pressure in a trifluoromethane (CHF3)/oxygen (O2) environment, producing features down to 50 nm. Aspect ratios of 2 are obt...

Solar-blind deep-ultraviolet (DUV) photodetectors have attracted wide attention because of their extensive military and civil applications. The ternary oxide Zn 2GeO4 is an ideal material with a wide bandgap (Eg = 4.69 eV). In this work, DUV photodetectors based on a ternary Zn2GeO4 nanowire (NW) network were fabricated on SiO2/Si substrates. Reactive ion etching of the SiO2/Si wafer was used to grow the NW network to avoid contamination of the Au catalyst during synthesis of the Zn2GeO4 NW network via high-temperature chemical vapor deposition . Photodetectors based the Zn 2GeO4 NW revealed fast response and recovery times, which is attributed to the unique cross-junction barrier-dominated conductance of the NW network. Results showed that the ternary oxide-based NW network is an ideal building block for nanoscale solar-blind photodetectors with superior performance.

The capability to develop novel nanomaterials with properly tailored optical properties is of great interest for many nanophotonic applications. In the present work, 2D-ordered plasmonic nanoarrays with different morphologies, as nanoprism, nanoparticle, nanohole and semi-nanoshell arrays, are realized by nanosphere lithography, combining metal depositions, reactive ion etching and thermal treatments. By controlling the processing parameters, the plasmonic properties of the nanoarrays can be tailored, engineering the optical functionalities of the plasmonic nanosystems. Some selected examples are presented to show the potentialities of the synthesized nanoarrays in different fields: to realize ultra-fast and tunable nonlinear optical materials, to enhance the quantum efficiency of nearby rare-earth emitters and to develop high-sensitivity, label-free biosensors. The versatility of the fabrication technique gives the possibility to design different configurations and many other applications can be envisaged for these plasmonic nanoarrays in advanced nanophotonic devices.

The end-cap removal of carbon nanotubes (CNTs) refers to the structural modification method that makes inner-core spaces and voids between walls accessible. Specifically, the accommodation of alkali metal cations in those hidden surfaces for electrochemical energy storage has been a challenging task. Here we present open-ended vertically aligned CNTs (VA-CNTs) as an ideal structure for Li+ accommodation, which were produced by chemical vapor deposition, followed by CF4 reactive ion etching. A model study suggests a link between Li+ capacity and the surface area, more specifically, allows us to estimate the amount of additional Li+ accommodation, which is 2.3 times increased after end-cap removal. The relatively high capacity (889 mAh/g) has confirmed that open-ended VA-CNTs are highly active for Li+ intercalation as well as exposing interior surfaces, which can be compared to the control (338 mAh/g). The microstructural change observation combined with spectroscopic studies reveals that poor Li+ reversibi...

Dry and maskless texturing process of mono-crystalline silicon wafers using CF4/O2 plasma in a reactive ion etching (RIE) system has been developed with the aim of obtaining optimized surface texture characterized by low optical reflection loss for photovoltaic applications. In this study c-Si has been successfully subjected to plasma etching at unusual process conditions, specifically high value of substrate temperature (15 °C) coupled with high value of process pressure (40 Pa). Different c-Si surface textures are produced at different etch durations. Specifically, pyramid-like morphology appears at very short etch time and crater-like nanostructures form at longer etch time, whereas the former gives the lowest average reflectance (

Silicon nanopillar (Si NP) arrays with the axial p-n junction were formed and investigated. A method to fabricate Si NP ordered arrays by means of electron beam lithography using the negative electron resist and reactive ion etching is presented. The effect of strong resonance light scattering – change of the color of separate Si NPs - was demonstrated. One or several minima were registered in the measured reflection spectra. Thereat, the position of reflection minimum was changed with a change in Si NP diameter. A shift of the minimum position towards the longer wavelength spectral region with an increase in Si NP diameter was observed. A shift of the position of minima to the shorter wavelength spectral region with a decrease in Si NP pitch in microarrays with the same Si NP diameter was observed. The quantitative divergence in the position of reflection minima in Si NPs with calculated dependencies for Mie resonances was found. High photosensitivity of Si NP arrays with axial p-n junction to visible and near IR light was discovered. So, these structures may be used for selective photonic sensors.

—The results of investigating the spectral characteristics of reflection from silicon nanopillar (Si NP) microarrays in the wavelength region from 400 to 1100 nm are presented. The Si nanopillars are formed by electron lithography on a negative resist with subsequent reactive ion etching. The Si nanopillars are etched through a resist mask and SiO2 100 nm thick. In the spectra of reflection from nanopillar microarrays, minima are observed, the position of which depends strongly on the Si nanopillar diameter.

The epitaxial lateral overgrowth of GaN by metal-organic chemical vapor deposition using a nano-cavity patterned sapphire substrate (NCPSS) was investigated. The NCPSS, with a hexagonal non-close-packed nano-cavity pattern on the sapphire substrate, was fabricated by polystyrene sphere coating and size reduction by reactive ion etching, followed by deposition of alumina and thermal oxidation. The coalescence of GaN on the NCPSS was achieved by the formation of relatively large GaN islands and enhanced lateral overgrowth of the GaN islands over several nano-cavity pattern areas. The threading dislocation density (TDD) measured by cathodoluminescence measurement was significantly reduced from 2.4 × 108 cm−2 to 6.9 × 107 cm−2 by using the NCPSS. A dislocation behavior that contributes to the reduction of TDD of the GaN layer was observed by transmission electron microscopy. Raman spectroscopy revealed that the compressive stress in the GaN layer was reduced by 21% due to the embedded nano-cavities. In addition, the diffuse reflectance of GaN on the NCPSS was enhanced by 54% ∼ 62%, which is attributed to the increased probability of light extraction through effective light scattering by nano-cavities.

Inductively coupled plasma reactive ion etching of copper thin films patterned with SiO2 masks was carried out using CH3COOH/Ar gas. The etch rate, etch selectivity to SiO2 mask, and the etch profiles of copper films were examined. The evolution study of the etch profile as a function of gas concentration and etch depth revealed the etch sequence and etch mechanism. In the optimized CH3COOH/Ar gas, the systematic approach on the etch characteristics of copper films was performed by changing the etch parameters including inductively coupled plasma (ICP) rf power, dc-bias voltage to substrate, and process pressure. As the ICP rf power and dc-bias voltage increased and the process pressure decreased, the etch rate increased and the etch profile improved. X-ray photoelectron spectroscopy was used to determine the etch mechanism in CH3COOH/Ar gas. Finally, the etching of copper films in the CH3COOH/Ar was achieved with good etch profile with a high degree of anisotropy.

SrTiO3 (STO) is a highly attractive oxide material due to its flexible tunability of electrical properties. It can be designed to exhibit a high mobility with a tunable carrier concentration by creating oxygen vacancies, or by doping with Nb or La, which substitute the Ti and Sr sites, respectively. Here we show a micro-patterned surface doping of STO by using reactive ion etching (RIE). The creation and pattering of a conductive STO surface were achieved by sequential treatments with Ar and O2 plasma. The patterned conductive surface edge was well defined as confirmed by an electrostatic force microscopy. The electronic characteristics of the RIE treated STO surface were probed by a synchrotron radiation photoemission spectroscopy, which shows the emergence of Ti3+, Ti2+, Ti1+ states and metallic states near the Fermi level. The electrical mobility of the conductive STO surface can be increased up to 12000 cm/V s with a typical sheet carrier concentration around 1013–1014 cm−2. Increasing Ar plasma time elongate the depth of the conductive surface, which reflects the change of magnetoresistance behavior at low temperature. The demonstrated control of the STO surface conductivity along with a large area and high precision patterning method can be widely used for a variety of oxide electronic and spintronic devices.

AlN etching with chloride plasmas is studied. The experimental results show that the etching of AlN under a low pressure Cl2/Ar plasma mixture in moderate DC bias is not possible. The addition of BCl3 gas to Cl2/Ar mixture allows the etching of AlN materials. However the obtained properties of etched AlN is still not in conformity with the technological specification especially for the condition which the etched AlN must be kept only along the sidewall of the InP laser cavity and be removed elsewhere (selective etching). To know more about the effect of the BCl3 addition to the Cl2/Ar plasma mixture, global model of BCl3/Cl2/Ar is developed to quantify the neutral and ion densities as well as the electron density and temperature. The simulation results show that the electron density and low pressure linearly varies with the RF power. The negative ion density decreases with the percentage of BCl3 leading to the diminution of the electronegativity which is represented by negative ion to electron density ratio. The simulation shows that the positive ion to atomic chlorine flux ratio increases with the %BCl3. Such parameters could play an important role in the ion neutral synergy during the etching process.

Color centers in silicon carbide have recently attracted broad interest as high bright single photon sources and defect spins with long coherence time at room temperature. There have been several methods to generate silicon vacancy defects with excellent spin properties in silicon carbide, such as electron irradiation and ion implantation. However, little is known about the depth distribution and nanoscale depth control of the shallow defects. Here, a method is presented to precisely control the depths of the ion implantation induced shallow silicon vacancy defects in silicon carbide by using reactive ion etching with little surface damage. After optimizing the major etching parameters, a slow and stable etching rate of about 5.5 ± 0.5 nm min-1 can be obtained. By successive nanoscale plasma etching, the shallow defects are brought close to the surface step by step. The photoluminescence spectrum and optically detected magnetic resonance spectra are measured, which confirm that there were no plasma-induced optical and spin property changes of the defects. By tracing the mean counts of the remaining defects after each etching process, the depth distribution of the defects can be obtained for various implantation conditions. Moreover, the spin coherence time T2* of the generated VSi defects is detected at different etch depths, which greatly decreases when the depth is less than 25 nm. The method of nanoscale depth control of silicon vacancies would pave the way for investigating the surface spin properties and the applications in nanoscale sensing and quantum photonics.

A volcano-shaped nano-patterned sapphire substrate (VNPSS) was fabricated by nanoimprint lithography and wet etching. The edge effects were used to form a ring mask for wet etching. The widths of the SiO2 rings were obtained as 136 and 91 nm by changing the reactive ion etching time. The crystal planes were determined to be {10} and {10} for the etching facets of the outside and inside of the ring, respectively. X-ray diffraction rocking curves indicate that the dislocation density of the GaN epilayer on the VNPSS is lower than that on the nano-patterned sapphire substrate (NPSS). Temperature-dependent photoluminescence results show that the internal quantum efficiency of the GaN-based light emitting diode (LED) on the VNPSS is 24% larger than that on the NPSS, which is due to the improved crystal quality. 3-D finite difference time domain (FDTD) simulations show that the light extraction efficiency (LEE) of the GaN-based LED on the VNPSS is 21% more than that of the LED on the NPSS, which conforms to the LEE enhancement by PL measurement. The use of edge effects provides ideas for preparing complex NPSS patterns with commonly used imprint stamps to further increase crystal quality and LEE.

Phenomena of electrical and optical properties in porous silicon (PSi) remain interested. In this study, we focus on fabrication of PSi on N-type Si(100) surface using photolithography and reactive ion etching (RIE) methods with variations of etching times for10, 20, 30, and 40 min. SEM analysis demonstrated similar Psi in shape and size. Based on the profilometer and the four-point probe (FPP) measurement, the pore depth and the resistivity of Psi increase with the increasing etching time. The pores can be consideredas a defect on the silicon surface which inhibits electron diffusion so that the resistivity will increase.

Generation of diffraction gratings by top-down and bottom-up approaches based on scanning probe lithography is demonstrated. With regard to top-down fabrication, silicon nanostructured diffraction gratings are fabricated through one-dimensional (1D) dip-pen-nanolithography (DPN). Nanodot arrays (two-dimensional simple cubic lattice) of alkanethiol self-assembled monolayers (SAMs) are printed by 1D DPN on an Au-film-coated silicon substrate with lattice distances of 700, 1000, and 1200 nm. Silicon nanocircular pillars of length hundreds of nanometers are generated by sequential Au etching and reactive ion etching (RIE) of the 1D DPN printed sample. The performance of the silicon diffraction gratings as a microspectrometer is demonstrated through red, green, and blue color diffraction with white light incident at 45°. Moreover, arrays of zirconia nanoparticles (NPs) with an average diameter of visible wavelength (φ ≈ 470 nm) on an Au substrate are generated via bottom-up fabrication of the diffraction gratings. Microarrays of hydrophilic alkanethiol SAMs are obtained by polymer pen lithography (PPL). Self-assembly of zirconia NPs occurs after the passivation of hydrophobic alkanethiol SAMs of the PPL-printed sample. Fraunhofer diffraction with a square aperture is observed for the zirconia NP diffraction grating fabricated by the bottom-up approach.

In this paper, we report on the fabrication and high performance of power p-n diodes grown on free-standing (FS) GaN substrate. The key technique to enhance the high breakdown voltage and suppress the surface leakage current is the isolation process. The mesa-structure diode is generally formed by utilizing the inductively coupled plasma reactive ion etching; however, it always induces high surface damages and thus causes a high leakage current. In this paper, we propose a planar structure by employing the oxygen ion implantation to frame the isolation region. By following the crucial process, the fabricated mesa- and planar-type diodes exhibit the turn-on voltages of 3.5 and 3.7 V, specific on-resistance ( $\text{R}_{\mathrm{ ON}}\text{A}$ ) of 0.42 and 0.46 $\text{m}\Omega $ -cm2, and breakdown voltage ( V B) of 2640 and 2880 V, respectively. The corresponding Baliga’s figures of merit (BFOM, i.e., V $_{B}^{2}/\text{R}_{\mathrm{ ON}}\text{A}$ ) are 16.6 and 18 GW/cm2, respectively. The BFOM of 18 GW/cm2 is the highest reported value for FS-GaN diode. From the temperature dependent measurements, the planar-type diode also shows the better leakage current and thermal stability than the mesa-type diode.

The masking properties are studied for polymeric structures based on a triacrylamide derivative of polyfluorochalcone at wet etching in aqueous acidic (H2SO4, H3PO4) and alkaline (NaOH) environments, as well as at reactive ion etching (CF4). The kinetic curves are obtained and the etching rates inherent in the photoresists are estimated. A comparison with commercially available photoresists AZ4562 and SU-8 is performed.