Nanomembranes Research Articles

Breakthroughs in Photonics 2012: Breakthroughs in Nanomembranes and Nanomembrane Lasers

Crystalline semiconductor nanomembranes (NMs) offer unprecedented opportunities for unique electronic and photonic devices for vertically stacked high-density photonic/electronic integration, high-performance flexible electronics, and adaptive flexible/conformal photonics. We present here major progresses reported over the last year, in the area of semiconductor NM photonics, with focuses on the innovative membrane laser devices and structures for silicon photonics and flexible optoelectronics.

Feather keratin hydrolysates obtained from microbial keratinases: effect on hair fiber

BackgroundHair is composed mainly of keratin protein and a small amount of lipid. Protein hydrolysates, in particular those with low molecular weight distribution have been known to protect hair against chemical and environmental damage. Many types of protein hydrolysates from plants and animals have been used in hair and personal care such as keratin hydrolysates obtained from nails, horns and wool. Most of these hydrolysates are obtained by chemical hydrolysis and hydrothermal methods, but recently hydrolyzed hair keratin, feather keratin peptides, and feather meal peptides have been obtained by enzymatic hydrolysis using Bacillus spp in submerged fermentation.ResultsKeratin peptides were obtained by enzymatic hydrolysis of keratinases using Bacillus subtilis AMR. The microorganism was grown on a feather medium, pH 8.0 (1% feathers) and supplemented with 0.01% of yeast extract, for 5 days, at 28°C with agitation. The supernatant containing the hydrolysates was colleted by centrifugation and ultra filtered in an AMICON system using nano–membranes (Millipore – YC05). The Proteins and peptides were analyzed using HPTLC and MALDI-TOF-MS. Commercial preparations of keratin hydrolysates were used as a comparative standard. After five days the feather had been degraded (90-95%) by the peptidases and keratinases of the microorganism. MALDI-TOF mass spectrometry showed multiple peaks that correspond to peptides in the range of 800 to 1079 Daltons and the commercial hydrolysate was in the range of 900 to 1400 Da. HPTLC showed lower molecular mass peptides and amino acids in the enzymatic hydrolysate when compared with the commercial hydrolysate . A mild shampoo and a rinse off conditioner were formulated with the enzymatic hydrolysate and applied to hair fibers to evaluate the hydration, with and without heat, using a Corneometer® CM 825. The hydration was more efficient with heat, suggesting a more complete incorporation of hydrolysates into the fibers. Scanning Electron Microscopy showed deposits of organic matter in the junction of the cuticles that probably collaborates to the sealing of the cuticles, increasing the brightness and softness.ConclusionsThese results show that the enzymatic method to produce keratin peptides for hair care products is an attractive and eco- friendly method with a great potential in the cosmetic industry.

Semiconductor nanomembranes for integrated silicon photonics and flexible Photonics

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We review here nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration and hybrid organic/inorganic flexible photonics.

Ordering of Epitaxial Quantum Dots on Nanomembranes

Semiconductor nanomembranes (NMs) provide fascinating opportunities to create unique structures and electronic devices owing to their mechanical flexibility. A fascinating question is whether the growth mediated by such flexibility can lead to the formation of ordered epitaxial surface nanostructures. By using computational modeling, we investigate the energetics of ordering of SiGe quantum dots (QDs) on both Si(001) and Si(111) NMs. We calculate the interaction energies for quantum dots grown on one side and on both sides of the NM and assembled in a square lattice for the Si(001) surface and in a hexagonal lattice for the Si(111) surface. Our calculations show that for QDs grown on the Si(001) NM the interaction energy possesses a minimum at a well-defined spacing only when the QDs are positioned on both sides in a square array and aligned along the [110] direction. The predicted QD ordering, spacing, and other features are in excellent agreement with recent experimental results. For QDs grown on the Si(111) NM, our calculations predict that ordered QDs can be achieved for both one-side and both-side growth, albeit with different QD spacings. The present work suggests that semiconductor NMs are a fascinating template for the self-assembled growth of ordered QDs.

Substrate-Free Self-Assembly Approach toward Large-Area Nanomembranes

Free-standing two-dimensional nanostrucutures, such as graphene and semiconductor nanomembranes (NMs) featuring their integration with flexible polymer substrates, address applications in which electronic devices need to be stretchable or conformally positioned to nonplanar surfaces. We report a surfactant-directed surface assembly approach to producing large-area NMs at the water-air interface. The NMs were produced by employing the surfactants as templates as well as incorporating them in the crystal structures. By using excess amount of sodium dodecylsulfate (SDS), a tightly packed monolayer of dodecylsulfate (DS) ion was formed and directed the crystallization of submillimeter-sized zinc hydroxy dodecylsulfate (ZHDS) single-crystalline NMs over the entire water surface. This free-standing NM can be readily transferred to an arbitrary substrate and converted to ZnO via heat treatment. A flexible thin-film transistor was also fabricated using the transferred NMs and demonstrated reasonably good n-type transport properties. This approach circumvented the needs of single-crystalline substrates for making large-area NMs from materials that do not possess a laminate structure. It is a low-cost and large-scale synthesis technique and has great potential in developing NMs and flexible devices from various functional materials that are not feasible by conventional selective etching or delamination approaches.

Simple extraction and membrane purification process in isolation of steviosides with improved organoleptic activity

In recent years there has been increasing demand for natural non-nutritive high intensity sweeteners with low-calorie value as an alternative to sucrose. Extracts of the leaves of Stevia rebaudiana (Bertoni), have been known for their sweet taste. Steviosides and rebaudioside-A are the two major diterpenoid glucosides components present in the leaf extracts of the stevia, these glycosides are 300 times sweeter than sugar and also exhibits wide therapeutic activity. The conventional methods of isolation of steviosides involve long extraction and purification procedures; therefore optimization of product yields is a challenging problem. The present study, establishes a new improvised process of extraction of steviosides from the stevia leaves in which the dry treated leaves were grounded, defatted, and extracted through pressurized hot water extractor (PHWE), followed by purification and concentration of the sweet glycosides through ultra (UF) and nano (NF) membrane filtration in obtaining high (98.2%) purity steviosides. This process established “green” method for isolation of high quality steviol glycosides, with improved final yield is 10.1% from 11% of crude leaf extract and observed the improved organoleptic and biological activity (antioxidant). Thus the method confirms a simple, inexpensive and eco-friendly process in obtaining pure steviosides.

Free standing GaN nano membrane by laser lift-off method

ABSTRACTIn this work, we present a method able to fabricate thin GaN nanomembranes fit for device applications. Starting from commercial GaN on sapphire substrates, MBE was used to deposit a sacrificial layer, which comprises of a superlattice of InN/InGaN, after which thin a GaN film of hundreds of nanometers thickness was grown on top. Pulsed laser irridiation with photon energy of 2.3eV gives rise to the controlled decomposition of the sacrificial intermediate layer, which can be followed by easy separation of the top GaN membrane from the substrate. This process can be used to manufacture GaN membranes with low defect density and a wider range of thickness. We demonstrated that large area, free-standing GaN membranes, with a thickness from 200nm and up, could be made using this method, and the high crystal quality of the lift-off GaN layers is well preserved in this process.

Batik Industry Synthetic Wastewater Treatment Using Nanofiltration Membrane

Abstract This study illustrates that the application of nano membrane process is an environmental and economical friendly technique for reactive dyes filtration in batik industries in local areas. Batik industry is the biggest cottage textile industry in the South East of Asia, specifically in Malaysia. Many local families earn their living through this industry. It is a well-known fact in the textile industry that dyeing processes consume a large amount of water thus generating harmful wastewater. The most used dyes in Batik are Remazol and Vinyl Sulphone fibre reactive dyes, based on process conditions (cold bath, pH and others). The locals use traditional methods for producing batik thus releasing untreated wastewaters that contain dyes, waxes, heavy metals with high COD and TSS contents. These effluents are known to be the one of most difficult to treat due to the recalcitrant nature of dyes.

Electrical properties of stacking electrodes for flexible crystalline semiconductor photonic devices

We report here electrical properties of low-temperature-stacked electrodes for large-area flexible photonic devices, based on single-crystalline InP nanomembrane (NM) transfer and stacking processes. Au, Al and ITO electrodes were investigated. An excellent ohmic contact was demonstrated on the stacked InP NM–ITO electrode, with a measured contact resistivity of 0.45 Ω cm2. Two types of flexible InP solar cells were also fabricated and characterized, based on the stacked InP NM–ITO and InP NM–Al contacts, respectively. The efficiency of solar cells with ITO as back contact is five times higher than that with Al as back contact. Such low-temperature energy-efficient NM transfer and electrode-stacking techniques can be applied to a wide range of flexible thin film photonic devices.

Defect-Free Single-Crystal SiGe: A New Material from Nanomembrane Strain Engineering

Many important materials cannot be grown as single crystals in bulk form because strain destroys long-range crystallinity. Among them, alloys of group IV semiconductors, specifically SiGe alloys, have significant technological value. Using nanomembrane strain engineering methods, we demonstrate the fabrication of fully elastically relaxed Si(1-x)Ge(x) nanomembranes (NMs) for use as growth substrates for new materials. To do so, we grow defect-free, uniformly and elastically strained SiGe layers on Si substrates and release the SiGe layers to allow them to relax this strain completely as free-standing NMs. These SiGe NMs are transferred to new hosts and bonded there. We confirm the high structural quality of these new materials and demonstrate their use as substrates for technologically relevant epitaxial films by growing strained-Si layers and thick, lattice-matched SiGe alloy layers on them.

A Synthetic Garden of State of the Art Natural Protein Nanoarchitectures Dispersed in Nanofluids

As a significant discovery in the 20th century, carbon nanotubes are attracting particular attention in many unique fields such as electronics, catalysts, hydrogen storage composites, gas sensors, drug delivery, medical diagnostics, therapeutics and nanofluids. In this project, we focus on self-assembled synthetic special natural protein alpha-lactalbumin nanotubes with different (straight, waved, coiled, regularly bent, branched, beaded) shapes, nanospherical particles, nanorods, nanowires, nanopores, polyhedral (hexagonal network, spherical, cubic) nanostructures, nanochannels, nanofibers, nanosheets, nanoleaves, nanowave branched structures, nanobeads, nanoflowers, nanocapsules, novel nano-hybrids consisting of tubes and rods (new core-shell), nanocrystal shapes, apiary or cobweb, branched nanotubes with Y-junctions, nano membrane structures, nano sweep symmetrical shape, nano sponge structures, nano helical homogeneous structures and nano perpendicular and horizontal stable hollow single-walled natural protein nanotubes (NPNTs). These were successfully synthesized by the chemical hydrolysis sol--gel method and partial biochemical enzymatic hydrolysis by cleavage sites (Asp-X and Glu-X) of the milk protein a-lactalbumin by using various organic surfactants, pH controller functions and divalent metallic salt ions as a binding site or ions ligand formation between two bio-based building blocks to form remarkable various new morphologies in appearance of nanoemulsions and clear green nanofluids, for application in the diet nutrition food science and pharmaceutical industry. The characterization by SEM, TEM, XRD and Raman spectroscopy (specific D and G bond in protein nanotubes) confirmed the novelty of these products.

Design of Colloidal Pt Catalysts Encapsulated by Silica Nano Membranes for Enhanced Stability in H2S Streams

Poisoning of platinum catalysts by sulphur compounds is a significant problem that prevents their application in untreated gas streams. We introduce a novel concept to circumvent the poisoning problem by encapsulating individual platinum nano-particles with silica layers that act as selective membranes. Greatly enhanced sulfur tolerance for sufficiently dense illustrates the potential of our approach to design noble metal catalysts that survive in sulphur containing gas streams.

Flexible photonic-crystal Fano filters based on transferred semiconductor nanomembranes

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We report and review here nanophotonic devices based on stacked semiconductor NMs that were built on Si, glass and flexible PET substrates. Photonic-crystal Fano resonance based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Such a low temperature NM stacking process can lead to a paradigm shift on silicon photonic integration and inorganic flexible photonics.

Evaluation of ultra- and nanofiltration for refining soluble products from rice husk xylan

Liquors from water treatments of rice husks (containing soluble xylan-derived products) were processed with NF and UF membranes for concentrating and removing both monosaccharides and non-saccharide compounds. Among the commercial membranes assayed, the best results were achieved with the 4 kDa polymeric tubular ESP04 (PCI Membranes), and the 1 kDa ceramic monolithic Kerasep Nano (Novasep). Several trade-offs were identified both in membrane selection and in operating conditions. The ESP04 polymeric membrane provided the best fractionation, but lower recovery under comparable experimental conditions, while its fluxes were about half of those of the ceramic Kerasep Nano membrane. Increase in transmembrane pressure resulted in improved product recovery, at the expense of a lower purity. Additional data on product refining by coupling membrane processing with extraction and ion exchange are provided.

Development of a Micro fluidic Nanoscale Protein Sensor Device for Improving Vascular Surgical Outcomes

ABSTRACTThe normal physiologic response of vascular surgery is one of acute and intense inflammation and thrombosis. Research to date on improving outcomes after surgery has focused on drugs known to be active with the adrenergic system more specifically statins. Till date there has been no correlation between inflammation post surgery and the effect of perioperative anti-inflammatory drugs on improving surgical outcomes. The goal of this research is to characterize the role perioperative inflammation and thrombosis plays in determining outcomes after surgery. The goal of this particular application is to identify two specific pro-inflammatory protein markers namely C-reactive protein (CRP) and Myloperoxidase (MPO) associated with thrombosis from a wide range of serum samples. This is achieved by integrating the principles of fabrication associated with micro and nanotechnology to develop a sensor device comprising of nano ordered porous alumina membrane embedded in an elastomer (polydimethylsiloxane, PDMS) micro fluidic base. The nano porous membrane is selectively functionalized by a two level masking technique to the binding of CRP and MPO in selected areas. The binding event results in an electrochemical reaction that in turn produces a change in the surface charge. This in turn produces a measurable change to the electrical voltage. This is measured in an in-situ, non-invasive manner from selectively metalized areas of the nano membrane. Energy density analysis yielded unique electrical identifiers for each of the protein markers. Detection sensitivity of the order of 10 ppm was observed.