Nanomembranes Research Articles

A lithography-free approach to create Si nanomembranes on flexible substrates

We demonstrate a lithography-free approach to create a crystalline Si nanomembrane (NM) on a flexible polydimethylsiloxane (PDMS) substrate, and to induce uniaxially tensile strain in the Si NM by mechanically stretching its host PDMS substrate. We start from a commercial silicon-on-insulator (SOI) wafer, remove the buried oxide (BOX) layer using hydrofluoric acid (HF), and transfer the weakly bonded Si NM onto a PDMS substrate by stamping. Flat and smooth Si NMs are created on PDMS substrates by this method, and the typical area of each crack-free region is larger than 100 μm × 100 μm. The root mean square (RMS) roughness of the crack-free regions of a transferred Si NM, as determined by atomic force microscopy (AFM), is typically 0.4–0.5 nm. Using x-ray diffraction (XRD) characterization, we confirm that the Si NM transferred on a PDMS substrate exhibits high crystalline quality that is compatible for device fabrication. We introduce tensile strain in the Si NM by stretching the PDMS substrate where the Si NM is hosted using a home-made mechanical tool. Raman spectroscopy analysis reveals that uniaxial tensile strain up to 1.0% is introduced along the <110> direction of the Si(001) NM. This work suggests that Si NMs created by this lithography-free approach are promising for applications in electronics and optoelectronics.

Advanced nano membrane for an alkaline Fuel Cell

Structural and optical properties were studied as a function of Nano membrane after prepared, for tests. Nano membrane was deposited by the spray coating method on substrates (glass) of thickness 100 mm. The X-ray diffraction spectra of (CNTs, WO3) were studied. AFM tests are good information about the roughness, It had been designed electrolysis cell and fuel cell. Studies have been performed on electrochemical parameters.

Faeces – Urine separation via settling and displacement: Prototype tests for a novel non-sewered sanitation system

The development of novel, non-sewered sanitation systems like the Nano Membrane Toilet requires thorough investigation of processes that may seem well-understood. For example, unlike the settling of primary sludge, the separation of solids from liquids in a small-volume container at the scale of a household toilet has not been studied before. In two sets of experiments, the settling of real faeces and toilet paper in settling columns and the settling of synthetic faeces in a conical tank are investigated to understand the factors affecting the liquid quality for downstream treatment processes. Toilet paper is found to be a major inhibitor to settling of solids. While a lower overflow point results in better phase separation through displacement of liquid, a higher overflow point and frequent removal of solids may be more advantageous for the liquid quality.

Breaking the absorption limit of Si toward SWIR wavelength range via strain engineering.

Silicon has been widely used in the microelectronics industry. However, its photonic applications are restricted to visible and partial near-infrared spectral range owing to its fundamental optical bandgap (1.12 eV). With recent advances in strain engineering, material properties, including optical bandgap, can be tailored considerably. This paper reports the strain-induced shrinkage in the Si bandgap, providing photosensing well beyond its fundamental absorption limit in Si nanomembrane (NM) photodetectors (PDs). The Si-NM PD pixels were mechanically stretched (biaxially) by a maximum strain of ~3.5% through pneumatic pressure-induced bulging, enhancing photoresponsivity and extending the Si absorption limit up to 1550 nm, which is the essential wavelength range of the lidar sensors for obstacle detection in self-driving vehicles. The development of deformable three-dimensional optoelectronics via gas pressure-induced bulging also facilitated the realization of unique device designs with concave and convex hemispherical architectures, which mimics the electronic prototypes of biological eyes.

Theoretical Analysis of Strain‐Optoelectronic Properties in Externally Deformed Ge/GeSi Quantum Well Nanomembranes via Neutral Plane Modulation

For indirect‐bandgap germanium (Ge), strain‐engineering provides a controllable means to transform Ge into direct‐bandgap material with strongly enhanced light emission efficiency. Flexible electronics offer a powerful platform for introducing external strain into semiconductor nanomembranes (NMs) through deformation with flexible substrates. So far, the Ge/GexSi1−x alloy quantum well (QW) NMs have not been sufficiently investigated to comprehend how the external deformation tunes the wavelength and light‐emitting properties. Herein, a theoretical model based on the elasticity theory and k·p method is established to analyze the strain‐optoelectronic properties of the externally deformed Ge/GexSi1−x QW NMs via neutral plane (NP) modulation in both embedded and sticked form. Calculated results reveal that the elastic strain is linearly distributed, inducing tilt of the band edge similar to the electric field. Considering the fracture limit of the material, the NP layout determines the critical bending curvature that the NM can achieve. Large tunable range of wavelength Δλ of 1615 nm and enhanced transverse electric (TE)/transverse magnetic (TM) peak gain of 949/3778 cm−1 are predicted for r = 1000 nm (the distance between NP and QW) under the bending limit. Further calculations conclude that larger r allow for smaller bending curvature to achieve wider range of wavelength and more enhanced optical gain.

High-Ge-Content SiGe Alloy Single Crystals Using the Nanomembrane Platform.

The growth of single crystals of Ge-rich SiGe alloys in an extended composition range is demonstrated using the nanomembrane (NM) platform and III-V growth substrates. Thin films of high-Ge-content SiGe films are grown on GaAs(001) to below the kinetic critical thickness and released from the growth substrate by selectively etching a release layer to relax the strain. The resulting crystalline nanomembranes at the natural lattice constant of the alloy are transferred to a new host and epitaxially overgrown at similar compositions to make a thicker single crystal. Straightforward critical-thickness calculations demonstrate that a very wide range of group IV alloys, including those involving Sn, can be fabricated using the NM platform and the proper choice of III-V substrate. Motivations for making new group IV alloys center on band gap engineering for the development of novel group IV optoelectronic structures and devices.

Dynamic Nano Clusters of Water on Waters Catholyte and Anolyte: Electrolysis with Nano Membranes

The electrolysis is a base of many industrial processes like galvanotechnics and galvanoplastics. It is also used for hydrogen, and oxygen production. Different products such as H2, NaOH, HCl, heavy water (D2O) and others could be obtained as well depending on the manufacturing conditions. They can influence significantly the vital processes in living organisms either activating or diminishing their rate [1,2]. The catholyte and anolyte waters are produced in the cathode and anode parts of the electrolysis cell. The catholyte is alkaline and has a negative oxidation reduction potential (ORP). The anolyte is acidic and of positive ORP. The value for ORP is in milivolts (mV). It was demonstrated that the catholyte stimulated the metabolitic processes and immune system, and had an anti-oxidant action. Recent investigation of catholyte water on Graffi tumor in hamsters has demonstrated its antitumor effect [3]. The anolyte however has demonstrated strong biocidal and antiinflamatory action [4,5] Cha, Chun-Nam et al. [6]. In spite of many investigations carried out all over the world no satisfactory explanation of these properties has been suggested until now. In the report a model of the number of water molecules related to the energy of hydrogen bonds is described.

Single-Cell Response to the Rigidity of Semiconductor Nanomembranes on Compliant Substrates.

Single-crystalline semiconductor nanomembranes (NMs) bonded to compliant substrates are increasingly used for biomedical research and in health care. Nevertheless, there is a limited understanding of how individual cells sense the unique mechanical properties of these substrates and adjust their behavior in response to them. In this work, we performed proliferation assays, cytoskeleton analysis, and focal adhesion (FA) studies for NIH-3T3 fibroblasts on 220 and 20 nm single-crystalline Si on polydimethylsiloxane (PDMS) substrates with an elastic modulus of ∼31 kPa. We also characterized cell response on bulk Si as a reference. Our in vitro studies show that varying the thickness of the NM between 20 and 220 nm affects the proliferation rate of the cells, their cytoskeleton, fiber organization, spread area, and degree of FA. For example, cultured cells on 220 nm Si/PMDS exhibit the same response as on bulk Si, that is, they are well-spread with a pentagonal (or dendritic) shape and show a good organization of stress fibers and FAs. On the other hand, the cells on 20 nm Si/PDMS are spherical, with fiber organization and FAs in undetectable levels. We explained the results of our in vitro studies through a shear-lag mechanical model. The calculated FA-substrate contact stiffnesses for fibroblasts on bulk Si and 220 nm Si/PDMS closely match, and they are significantly higher than the stiffness of the integrin clutches and the plaque. Conversely, focal contacts with 20 nm Si/PDMS have comparable lateral compliance to adhesion-mediating intracellular organisms. In conclusion, our work relies on recent advances in NM technology to fill a critical knowledge gap about how individual cells sense and react to the mechanical properties of NM-based substrates. Our findings will have a major impact on the design of flexible electronic materials for applications in biomedical science and health care.

Atomic layer deposition synthesized ZnO nanomembranes: A facile route towards stable supercapacitor electrode for high capacitance

ZnO nanomembranes (NMs) are successfully fabricated by atomic layer deposition for electrochemical supercapacitor applications. The structure and morphology of ZnO NMs are investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. In order to prove their potential applications in supercapacitors, the electrochemical performance of ZnO NMs is characterized in the aqueous electrolytes (i.e., KOH, KCl, and Na2SO4). Experimental results indicate that 6 M KOH electrolyte is the most promising one, and the largest capacitance of 846 F g−1 is achieved in this electrolyte with remarkable stability. In addition, ZnO NM with 100 ALD cycles demonstrates advanced performance in all three aqueous electrolytes, mainly due to the effective ion adsorption/desorption or extraction/insertion in the electrode. The 180-min flashing of a red LED powered by ZnO NMs supercapacitors suggests great potentials of NMs electrodes in practical applications.

Investigation of Thermal Properties of β-Ga2O3 Nanomembranes on Diamond Heterostructure Using Raman Thermometry

The β-Ga2O3 nanomembrane (NM)/diamond heterostructure is one of the promising ultra-wide bandgap heterostructures that offers numerous complementary advantages from both materials. In this work, we have investigated the thermal properties of the β-Ga2O3 NM/diamond heterostructure with three different thicknesses of β-Ga2O3 nanomembranes (NMs), namely 100 nm, 1000 nm, and 4000 nm thick β-Ga2O3 NMs using Raman thermometry. The thermal property—temperature relationships of these β-Ga2O3 NM/diamond heterostructures, such as thermal conductivity and interfacial thermal boundary conductance were determined under different temperature conditions (from 100 K to 500 K with a 40 K interval). The result provides benchmark knowledge about the thermal conductivity of β-Ga2O3 NMs over a wide temperature range for the design of novel β-Ga2O3-based power electronics and optoelectronics.

Planning and communicating prototype tests for the Nano Membrane Toilet: A critical review and proposed strategy.

Urban sanitation in growing cities of the Global South presents particular challenges. This led to the Bill & Melinda Gates Foundation's Reinvent The Toilet Challenge, which sparked the development of various non-sewered sanitation technologies like the Nano Membrane Toilet. Complex disruptive technologies like this entail an extensive product development process, including various types of prototype tests. While there is an abundance of literature discussing how to build prototypes, and the optimal number of tests, there has been little focus on how to plan and conduct tests, especially in a development endeavour of this complexity. Four approaches to testing are reviewed, and their strengths and weaknesses compared. A visualised testing strategy is proposed that encompasses the entire product development process and can be used to plan and communicate prototype tests for the Nano Membrane Toilet to ultimately achieve compliance with international standards.

Planning and communicating prototype tests for the Nano Membrane Toilet: A critical review and proposed visual tool

Urban sanitation in growing cities of the Global South presents particular challenges, like the speed of their growth, the high population density, and, often, the lack of existing wastewater infrastructure. This led to the Bill & Melinda Gates Foundation’s Reinvent The Toilet Challenge, a call to develop novel, non-sewered sanitation technologies, which sparked the development of various inventions, like the Nano Membrane Toilet. Complex technologies like this entail an extensive product development process, including various iterations of prototype tests. While there is an abundance of literature discussing how to build prototypes, and the optimal number of tests, there has been little focus on how to plan, communicate, and conduct tests, especially in a product development endeavour of this complexity. Multiple aspects of testing prototypes are reviewed. A visual test planning tool is proposed that encompasses the entire product development process and can be used to plan and communicate prototype tests for the Nano Membrane Toilet to ultimately achieve compliance with international standards.

Planning and communicating prototype tests for the Nano Membrane Toilet: A critical review and proposed strategy

Urban sanitation in growing cities of the Global South presents particular challenges. This led to the Bill & Melinda Gates Foundation's Reinvent The Toilet Challenge, which sparked the development of various non-sewered sanitation technologies like the Nano Membrane Toilet. Complex disruptive technologies like this entail an extensive product development process, including various types of prototype tests. While there is an abundance of literature discussing how to build prototypes, and the optimal number of tests, there has been little focus on how to plan and conduct tests, especially in a development endeavour of this complexity. Four approaches to testing are reviewed, and their strengths and weaknesses compared. A visualised testing strategy is proposed that encompasses the entire product development process and can be used to plan and communicate prototype tests for the Nano Membrane Toilet to ultimately achieve compliance with international standards.

Ultrafast and Chemically Stable Transfer of Au Nanomembrane Using a Water-Soluble NaCl Sacrificial Layer for Flexible Solar Cells.

Large-scale industrial application of flexible device has called for development of transfer methods that deliver high yield and stability. Here, we show an ultrafast and chemically stable transfer method by using a water-soluble NaCl sacrificial layer. Extremely thin (10 nm) and large-area (4 in. wafer) free-standing Au nanomembranes (NMs) prepared on silicon substrate were successfully transferred to flexible PDMS substrate by dissolving the NaCl sacrificial layer. This transfer method enables highly transparent and electrically conductive Au NMs on PDMS substrate. To transfer a multilayered optoelectronic device, we fabricated flexible hydrogenated amorphous silicon (a-Si:H) solar cell on a glass substrate and transferred it to a PDMS substrate. There was no degradation of the electrical characteristic of the solar cell after the transfer. This approach enables the integration of high-temperature-processed a-Si:H solar cell onto low-temperature tolerant flexible polymer substrate without chemical contamination or damage.

Prediction of Hyperelastic Material Properties of Nafion117 and Nafion/ZrO2 Nano-Composite Membrane

This paper presents constitutive laws suitable for the prediction of mechanical behaviour of nano-composite membrane compared with the commercial membrane Nafion®117. The uniaxial tensile data of commercial Nafion®117 and Nafion®/ Zr-150 nano-composite membrane utilised for fitting hyperelastic models was determined experimentally. Several material models on mechanical behaviour of nano-composite and commercial Nafion® 117 membrane material was fitted to determined accuracy. In order to observe yield and fracture behaviour, the com-mercial Nafion®117 and Nafion®/ Zr-150 nano-composite membranes were loaded in uniaxial direction at a constant strain rate. To obtain the optimal material constants form six different material models considered in this study, the OriginLab® version 9 was used and the Leven-berg-Marquardt (M) optimization logarithm. Hyperplastic material models including Mooney-Rivlin, Yeoh, Ogden, Humphrey, Martins and Veronda-Westmann were selected to use in an inverse method to fit the experimental uniaxial data of nano-composite material. The hyper-plastic material parameters could then be used to simulate material behaviour of nano mem-brane using finite element analysis (FEA) technique. The procedure discussed in this paper could be used to accurately determine the constitutive parameters of various constitutive models of Polymer Nafion presented.

Atomic-layer-deposited HfO2/Al2O3 laminated dielectrics for bendable Si nanomembrane based MOS capacitors

Flexible metal-oxide-semiconductor capacitors in a vertical structure using the single-crystalline Si nanomembrane (NM) with a HfO2/Al2O3 bilayer gate stack prepared by atomic layer deposition have been fabricated on plastic substrates by flip-transfer printing of Si NM/Ti/Au based trilayer heterostructures (1.3 cm × 0.9 cm × 360 nm). The electrical properties of the bilayer structure exhibit an excellent improved capacitance-voltage (C-V) frequency dispersion feature associated with an inhibited weak inversion hump and significantly larger accumulation capacitance, thus indicating the effectiveness of the passivation utilizing bilayer high-k dielectrics on a Si NM channel compared with monolayer HfO2. A comprehensive electromechanical characterization has been conducted for HfO2/Al2O3 stacked structures to investigate the effect of bending strain on C-V characteristics, leakage current density, and the associated evolution of interface charges. The presented research will be beneficial to realizing high performance thin-film transistors with lower operating voltage and higher driving current required in emerging flexible and stretchable electronics via optimized design of a nanolaminate gate stack and understanding the impact of mechanical strains on the electrical behavior of such MOS devices.

Flexible β‐Ga2O3 Nanomembrane Schottky Barrier Diodes

AbstractHere, high power flexible Schottky barrier diodes (SBDs) are demonstrated on a plastic substrate using single crystalline β‐Ga2O3 nanomembranes (NMs). In order to realize flexible high power β‐Ga2O3 SBDs, sub‐micron thick freestanding β‐Ga2O3 NMs are created from a bulk β‐Ga2O3 substrate and transfer‐printed onto the plastic substrate via a microtransfer printing method. It is revealed that the material property of β‐Ga2O3 NMs such as crystal structure, electron affinity, and bandgap remains unchanged compared with its bulk properties. Flexible β‐Ga2O3 SBDs exhibit the record high critical breakdown field strength (Ec) of 1.2 MV cm−1 in the flat condition and 1.07 MV cm−1 of Ec under the bending condition. Overall, flexible β‐Ga2O3 SBDs offer great promise for future flexible energy convergence systems and are expected to provide a much larger and more versatile platform to address a broader range of high‐performance flexible applications.

Nanoscale Variable-Area Electronic Devices: Contact Mechanics and Hypersensitive Pressure Application.

Nanomembranes (NMs) are freestanding structures with few-nanometer thickness and lateral dimensions up to the microscale. In nanoelectronics, NMs have been used to promote reliable electrical contacts with distinct nanomaterials, such as molecules, quantum dots, and nanowires, as well as to support the comprehension of the condensed matter down to the nanoscale. Here, we propose a tunable device architecture that is capable of deterministically changing both the contact geometry and the current injection in nanoscale electronic junctions. The device is based on a hybrid arrangement that joins metallic NMs and molecular ensembles, resulting in a versatile, mechanically compliant element. Such a feature allows the devices to accommodate a mechanical stimulus applied over the top electrodes, enlarging the junctions' active area without compromising the molecules. A model derived from the Hertzian mechanics is employed to correlate the contact dynamics with the electronic transport in these novel devices denominated as variable-area transport junctions (VATJs). As a proof of concept, we propose a direct application of the VATJs as compression gauges envisioning the development of hypersensitive pressure pixels. Regarding sensitivity (∼480 kPa-1), the VATJ-based transducers constitute a breakthrough in nanoelectronics, with the prospect of carrying its sister-field of molecular electronics out of the laboratory via integrative, hybrid organic/inorganic nanotechnology.

Infrared tubular microcavity based on rolled-up GeSn/Ge nanomembranes

Germanium-Tin (GeSn) alloys have attracted great amounts of attention as these group IV semiconductors present direct band-gap behavior with high Sn content and are compatible with current complementary metal oxide semiconductor technology. In this work, three dimensional tubular GeSn/Ge micro-resonators with a diameter of around 7.3 μm were demonstrated by rolling up GeSn nanomembranes (NM) grown on a Ge-on-insulator wafer via molecular beam epitaxy. The microstructural properties of the resonators were carefully investigated and the strain distributions of the rolled-up GeSn/Ge microcavities along the radial direction were studied by utilizing micro-Raman spectroscopy with different excitation laser wavelengths. The values of the strains calculated from Raman shifts agree well with the theoretical prediction. Coupled with fiber tapers, as-fabricated devices present a high quality factor of up to 800 in the transmission spectral measurements. The micro-resonators fabricated via rolled-up nanotechnology and GeSn/Ge NMs in this work may have great potential in photonic micro- and nanodevices.

Properties of Omp2a-Based Supported Lipid Bilayers: Comparison with Polymeric Bioinspired Membranes.

Omp2a β-barrel outer membrane protein has been reconstituted into supported lipid bilayers (SLBs) to compare the nanomechanical properties (elastic modulus, adhesion forces, and deformation) and functionality of the resulting bioinspired system with those of Omp2a-based polymeric nanomembranes (NMs). Protein reconstitution into lipid bilayers has been performed using different strategies, the most successful one consisting of a detergent-mediated process into preformed liposomes. The elastic modulus obtained for the lipid bilayer and Omp2a are ∼19 and 10.5 ± 1.7 MPa, respectively. Accordingly, the protein is softer than the lipid bilayer, whereas the latter exhibits less mechanical strength than polymeric NMs. Besides, the function of Omp2a in the SLB is similar to that observed for Omp2a-based polymeric NMs. Results open the door to hybrid bioinspired substrates based on the integration of Omp2a-proteoliposomes and nanoperforated polymeric freestanding NMs.