Charge Configuration Memory Devices: Energy Efficiency and Switching Speed.

Current trends in data processing have given impetus for an intense search of new concepts of memory devices with emphasis on efficiency, speed, and scalability. A promising new approach to memory storage is based on resistance switching between charge-ordered domain states in the layered dichalcogenide 1T-TaS2. Here we investigate the energy efficiency scaling of such charge configuration memory (CCM) devices as a function of device size and data write time τW as well as other parameters that have bearing on efficient device operation. We find that switching energy efficiency scales approximately linearly with both quantities over multiple decades, departing from linearity only when τW approaches the ∼0.5 ps intrinsic switching limit. Compared to current state of the art memory devices, CCM devices are found to be much faster and significantly more energy efficient, demonstrated here with two-terminal switching using 2.2 fJ, 16 ps electrical pulses.

High-efficiency diffraction gratings for EUV and soft x-rays using spin-on-carbon underlayers.

We report on the fabrication and characterization of high-resolution gratings with high efficiency in the extreme ultraviolet (EUV) and soft x-ray ranges using spin-on-carbon (SOC) underlayers. We demonstrate the fabrication of diffraction gratings down to 20 nm half-pitch (HP) on Si3N4membranes with a bilayer of hydrogen silsesquioxane (HSQ) and spin-on-carbon and show their performance as a grating mask for extreme ultraviolet interference lithography (EUV-IL). High-resolution patterning of HSQ is possible only for thin films due to pattern collapse. The combination of this high-resolution resist with SOC circumvents this problem and enables the fabrication of high aspect ratio nanostructures. Rigorous coupled-wave analysis shows that the bilayer gratings exhibit higher diffraction efficiency than what is feasible with a grating made of HSQ. We also demonstrate a simple and accurate method to experimentally measure the diffraction efficiency of high-resolution gratings by measuring the relative ratio of the dose-to-clear curves of the photoresist. The measured diffraction efficiencies are in good agreement with the theoretically predicted values. Furthermore, we verify our calculations and measurements by printing line/space patterns in chemically amplified resists down to 10 nm HP with both HSQ and bilayer grating masks using EUV-IL. The improved diffraction efficiency of the bilayers is expected to have applications not only in gratings for interference lithography, but also in Fresnel zone plates and gratings for spectroscopy in the EUV and soft x-ray ranges.

Anisotropic Etching of Pyramidal Silica Reliefs with Metal Masks and Hydrofluoric Acid.

This work describes the fabrication of anisotropically etched, faceted pyramidal structures in amorphous layers of silicon dioxide or glass. Anisotropic and crystal-oriented etching of silicon is well known. Anisotropic etching behavior in completely amorphous layers of silicon dioxide in combination with purely isotropic hydrofluoric acid as etchant is an unexpected phenomenon. The work presents practical exploitations of this new process for self-perfecting pyramidal structures. It can be used for textured silica or glass surfaces. The reason for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. The lateral etch rate under the metal significantly exceeds the vertical etch rate of the non-metallized area by a factor of about 6-43 for liquid and 59 for vapor-based processes. The ratio between lateral and vertical etch rate, thus the sidewall inclination, can be controlled by etchant concentration and selected metal. The described process allows for direct fabrication of shallow angle pyramids, which for example can enhance the coupling efficiency of light emitting diodes or solar cells, can be exploited for producing dedicated silicon dioxide atomic force microscopy tips with a radius in the 50 nm range, or can potentially be used for surface plasmonics.

Nano-confinement of block copolymers in high accuracy topographical guiding patterns: modelling the emergence of defectivity due to incommensurability.

Extreme ultraviolet interference lithography (EUV-IL) is used to manufacture topographical guiding patterns to direct the self-assembly of block copolymers. High-accuracy silicon oxide-like patterns with trenches ranging from 68 nm to 117 nm width are fabricated by exposing a hydrogen silsesquioxane (HSQ) resist layer using EUV-IL. We investigate how the accuracy, the low line width roughness and the low line edge roughness of the resulting patterns allow achieving DSA line/space patterns of a PS-b-PMMA (polystyrene-block-poly methyl methacrylate) block copolymer of 11 nm half-pitch with low defectivity. We conduct an in-depth study of the dependence of the DSA pattern morphology on the trench width and on how the neutral brush covers the guiding pattern. We identify the relation between trench width and the emergence of defects with nanometer precision. Based on these studies, we develop a model that extends available free energy models, which allows us to predict the patterning process window.

Three-Dimensional Microfluidic Capillary Device for Rapid and Multiplexed Immunoassays in Whole Blood.

In this study, we demonstrate whole blood immunoassays using a microfluidic device optimized for conducting rapid and multiplexed fluorescence-linked immunoassays. The device is capable of handling whole blood samples without any preparatory treatment. The three-dimensional channels in poly(methyl methacrylate) are designed to passively load bodily fluids and, due to their linearly tapered profile, facilitate size-dependent immobilization of biofunctionalized particles. The channel geometry is optimized to allow for the unimpeded flow of cellular constituents such as red blood cells (RBCs). Additionally, to make the device easier to operate, the biofunctionalized particles are pretrapped in a first step, and the channel is dried under vacuum, after which it can be loaded with the biological sample. This novel approach and design eliminated the need for traditionally laborious steps such as filtering, incubation, and washing steps, thereby substantially simplifying the immunoassay procedures. Moreover, by leveraging the shallow device dimensions, we show that sample loading to read-out is possible within 5 min. Our results also show that the presence of RBCs does not compromise the sensitivity of the assays when compared to those performed in a pure buffer solution. This highlights the practical adaptability of the device for simple and rapid whole-blood assays. Lastly, we demonstrate the device's multiplexing capability by pretrapping particles of different sizes, each functionalized with a different antigen, thus enabling the performance of multiplexed on-chip whole-blood immunoassays, showcasing the device's versatility and effectiveness toward low-cost, simple, and multiplexed sensing of biomarkers and pathogens directly in whole blood.

EUV-induced hydrogen desorption as a step towards large-scale silicon quantum device patterning.

Atomically precise hydrogen desorption lithography using scanning tunnelling microscopy (STM) has enabled the development of single-atom, quantum-electronic devices on a laboratory scale. Scaling up this technology to mass-produce these devices requires bridging the gap between the precision of STM and the processes used in next-generation semiconductor manufacturing. Here, we demonstrate the ability to remove hydrogen from a monohydride Si(001):H surface using extreme ultraviolet (EUV) light. We quantify the desorption characteristics using various techniques, including STM, X-ray photoelectron spectroscopy (XPS), and photoemission electron microscopy (XPEEM). Our results show that desorption is induced by secondary electrons from valence band excitations, consistent with an exactly solvable non-linear differential equation and compatible with the current 13.5 nm (~92 eV) EUV standard for photolithography; the data imply useful exposure times of order minutes for the 300 W sources characteristic of EUV infrastructure. This is an important step towards the EUV patterning of silicon surfaces without traditional resists, by offering the possibility for parallel processing in the fabrication of classical and quantum devices through deterministic doping.

Tailoring p-Type Behavior in ZnO Quantum Dots through Enhanced Sol-Gel Synthesis: Mechanistic Insights into Zinc Vacancies.

The synthesis and control of properties of p-type ZnO is crucial for a variety of optoelectronic and spintronic applications; however, it remains challenging due to the control of intrinsic midgap (defect) states. In this study, we demonstrate a synthetic route to yield colloidal ZnO quantum dots (QD) via an enhanced sol-gel process that effectively eliminates the residual intermediate reaction molecules, which would otherwise weaken the excitonic emission. This process supports the creation of ZnO with p-type properties or compensation of inherited n-type defects, primarily due to zinc vacancies under oxygen-rich conditions. The in-depth analysis of carrier recombination in the midgap across several time scales reveals microsecond carrier lifetimes at room temperature which are expected to occur via zinc vacancy defects, supporting the promoted p-type character of the synthesized ZnO QDs.

Resistless EUV lithography: Photon-induced oxide patterning on silicon.

In this work, we show the feasibility of extreme ultraviolet (EUV) patterning on an HF-treated silicon (100) surface in the absence of a photoresist. EUV lithography is the leading lithography technique in semiconductor manufacturing due to its high resolution and throughput, but future progress in resolution can be hampered because of the inherent limitations of the resists. We show that EUV photons can induce surface reactions on a partially hydrogen-terminated silicon surface and assist the growth of an oxide layer, which serves as an etch mask. This mechanism is different from the hydrogen desorption in scanning tunneling microscopy-based lithography. We achieve silicon dioxide/silicon gratings with 75-nanometer half-pitch and 31-nanometer height, demonstrating the efficacy of the method and the feasibility of patterning with EUV lithography without the use of a photoresist. Further development of the resistless EUV lithography method can be a viable approach to nanometer-scale lithography by overcoming the inherent resolution and roughness limitations of photoresist materials.

The Extent of Platinum-Induced Hydrogen Spillover on Cerium Dioxide.

Hydrogen spillover from metal nanoparticles to oxides is an essential process in hydrogenation catalysis and other applications such as hydrogen storage. It is important to understand how far this process is reaching over the surface of the oxide. Here, we present a combination of advanced sample fabrication of a model system and in situ X-ray photoelectron spectroscopy to disentangle local and far-reaching effects of hydrogen spillover in a platinum-ceria catalyst. At low temperatures (25-100 °C and 1 mbar H2) surface O-H formed by hydrogen spillover on the whole ceria surface extending microns away from the platinum, leading to a reduction of Ce4+ to Ce3+. This process and structures were strongly temperature dependent. At temperatures above 150 °C (at 1 mbar H2), O-H partially disappeared from the surface due to its decreasing thermodynamic stability. This resulted in a ceria reoxidation. Higher hydrogen pressures are likely to shift these transition temperatures upward due to the increasing chemical potential. The findings reveal that on a catalyst containing a structure capable to promote spillover, hydrogen can affect the whole catalyst surface and be involved in catalysis and restructuring.