Survey of Materials for Nanoskiving and Influence of the Cutting Process on the Nanostructures Produced

This paper examines the factors that influence the quality of nanostructures fabricated by sectioning thin films with an ultramicrotome (“nanoskiving”). It surveys different materials (metals, ceramics, semiconductors, and conjugated polymers), deposition techniques (evaporation, sputter deposition, electroless deposition, chemical-vapor deposition, solution-phase synthesis, and spin-coating), and geometries (nanowires or two-dimensional arrays of rings and crescents). It then correlates the extent of fragmentation of the nanostructures with the composition of the thin films, the methods used to deposit them, and the parameters used for sectioning. There are four major conclusions. (i) Films of soft and compliant metals (those that have bulk values of hardness less than or equal to those of palladium, or ≤500 MPa) tend to remain intact upon sectioning, whereas hard and stiff metals (those that have values of hardness greater than or equal to those of platinum, or ≥500 MPa) tend to fragment. (ii) All conjugated polymers tested form intact nanostructures. (iii) The extent of fragmentation is lowest when the direction of cutting is perpendicular to the exposed edge of the embedded film. (iv) The speed of cutting−from 0.1 to 8 mm/s−has no effect on the frequency of defects. Defects generated during sectioning include scoring from defects in the knife, delamination of the film from the matrix, and compression of the matrix. The materials tested were: aluminum, titanium, nickel, copper, palladium, silver, platinum, gold, lead, bismuth, germanium, silicon dioxide ($\textrm{SiO}_2$), alumina ($\textrm{Al}_2\textrm{O}_3$), tin-doped indium oxide (ITO), lead sulfide nanocrystals, the semiconducting polymers poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV), poly(3-hexylthiophene) (P3HT), and poly(benzimidazobenzophenanthroline ladder) (BBL), and the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).Chemistry and Chemical Biolog

Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications

This Review discusses nanoskiving—a simple and inexpensive method of nanofabrication, which minimizes requirements for access to cleanrooms and associated facilities, and which makes it possible to fabricate nanostructures from materials, and of geometries, to which more familiar methods of nanofabrication are not applicable. Nanoskiving requires three steps: 1) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate; 2) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and 3) sectioning the epoxy block into slabs with an ultramicrotome. These slabs, which can be 30 nm–10 μm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films. Electronic applications of structures produced by this method include nanoelectrodes for electrochemistry, chemoresistive nanowires, and heterostructures of organic semiconductors. Optical applications include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.Chemistry and Chemical Biolog

Multifunctional Nanocomposites based on Bacterial Cellulose

Cellulose is biodegradable, renewable, and abundant in nature thus cellulose (or paper)-based products can be inexpensively produced and recycled. Among cellulosic materials, bacterial nanocellulose (BNC) draws a special research attention due to the inherent three-dimensional nanofibrous structure, excellent mechanical flexibility, high purity and well-defined surface chemistry, and cost-efficient, scalable and environment-friendly synthesis. BNC can be biosynthesized by Gluconacetobacter xylinus, which is the most characterized BNC producer among various microorganisms. BNC is composed of highly pure cellulose nanofibrils, produced from well-defined dextrose through biochemical steps and subsequent self-assembling of the secreted cellulose fibrils which has the dimension ranges from 25 to 100 nm in diameter from bacteria in the culture medium. During the biosynthesis of BNC, shape-controlled hydrogels with well-defined network structure pore diameters below 10 µm can be easily achieved. For all the above-mentioned reasons, BNC is a highly promising platform material for the fabrication of functional composites through in situ growth or adsorption of pre-synthesized nanostructures on the nanoscale cellulose fibers. In this work, we have designed and demonstrated novel strategies to realize BNC-based functional nanocomposites with applications in sensing, water purification and energy storage. We have demonstrated a BNC film-based surface enhanced Raman scattering (SERS) substrate which has 3D porous structure and ultrafine fibers with uniform and dense adsorption of plasmonic nanostructures, resulting large SERS enhancement and excellent uniformity of SERS activity. For the first time, we have demonstrated a novel, highly scalable, cost-effective and green strategy to realize functional BNC-based foams/membranes. Functional materials such as graphene oxide (GO), polydopamine (PDA) can be efficiently incorporated within BNC matrix during its growth. Owing to the intercalation of functional materials within the layered BNC matrix, the functional composites showed excellent mechanical robustness and flexibility, which is crucial for efficient, large-scale applications, either as a foam or as a membrane. Specifically, we have designed and developed a bilayered hybrid biofoam comprised of BNC and RGO and a completely biodegradable bilayered foam based on BNC and PDA for highly efficient solar steam generation, which can be a sustainable solution to alleviate global water crisis. An innovative water filtration membrane based on BNC and RGO which harvests sunlight to kill microorganisms has been developed to provide a novel anti-biofouling approach. We have also demonstrated a robust filtration membrane based on BNC loaded with GO and PdNPs, which exhibited excellent dye degradation performance for highly efficient wastewater treatment. Furthermore, the in situ fabrication approach has been extended to polymeric materials such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to realize hybrid flexible supercapacitor electrodes based on RGO, BNC and PEDOT:PSS. The fabrication strategies and materials design demonstrated in this work can be easily extended to realize various BNC-based nanocomposites with applications in water purification, energy harvesting, sensing, catalysis, and life sciences

Multifunctional Nanocomposites based on Bacterial Cellulose

Cellulose is biodegradable, renewable, and abundant in nature thus cellulose (or paper)-based products can be inexpensively produced and recycled. Among cellulosic materials, bacterial nanocellulose (BNC) draws a special research attention due to the inherent three-dimensional nanofibrous structure, excellent mechanical flexibility, high purity and well-defined surface chemistry, and cost-efficient, scalable and environment-friendly synthesis. BNC can be biosynthesized by Gluconacetobacter xylinus, which is the most characterized BNC producer among various microorganisms. BNC is composed of highly pure cellulose nanofibrils, produced from well-defined dextrose through biochemical steps and subsequent self-assembling of the secreted cellulose fibrils which has the dimension ranges from 25 to 100 nm in diameter from bacteria in the culture medium. During the biosynthesis of BNC, shape-controlled hydrogels with well-defined network structure pore diameters below 10 µm can be easily achieved. For all the above-mentioned reasons, BNC is a highly promising platform material for the fabrication of functional composites through in situ growth or adsorption of pre-synthesized nanostructures on the nanoscale cellulose fibers. In this work, we have designed and demonstrated novel strategies to realize BNC-based functional nanocomposites with applications in sensing, water purification and energy storage. We have demonstrated a BNC film-based surface enhanced Raman scattering (SERS) substrate which has 3D porous structure and ultrafine fibers with uniform and dense adsorption of plasmonic nanostructures, resulting large SERS enhancement and excellent uniformity of SERS activity. For the first time, we have demonstrated a novel, highly scalable, cost-effective and green strategy to realize functional BNC-based foams/membranes. Functional materials such as graphene oxide (GO), polydopamine (PDA) can be efficiently incorporated within BNC matrix during its growth. Owing to the intercalation of functional materials within the layered BNC matrix, the functional composites showed excellent mechanical robustness and flexibility, which is crucial for efficient, large-scale applications, either as a foam or as a membrane. Specifically, we have designed and developed a bilayered hybrid biofoam comprised of BNC and RGO and a completely biodegradable bilayered foam based on BNC and PDA for highly efficient solar steam generation, which can be a sustainable solution to alleviate global water crisis. An innovative water filtration membrane based on BNC and RGO which harvests sunlight to kill microorganisms has been developed to provide a novel anti-biofouling approach. We have also demonstrated a robust filtration membrane based on BNC loaded with GO and PdNPs, which exhibited excellent dye degradation performance for highly efficient wastewater treatment. Furthermore, the in situ fabrication approach has been extended to polymeric materials such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to realize hybrid flexible supercapacitor electrodes based on RGO, BNC and PEDOT:PSS. The fabrication strategies and materials design demonstrated in this work can be easily extended to realize various BNC-based nanocomposites with applications in water purification, energy harvesting, sensing, catalysis, and life sciences

Electroless Deposition of Nanolayered Metallic Coatings

Electroless metallic coating is referred as the deposition of a substrate material by the process of chemical or autocatalytic reduction of aqueous metal ions deposited to a substrate material without any external supply of power. Electroless nickel alloys are generally considered synonymous to the word “electroless coating” as ~90% of productions in industries are of this alloy coating. Rest of the electroless metallic coatings includes gold, copper, palladium, cobalt, silver, etc. These electroless metallic coatings (other than electroless nickel coatings) are also one of the vibrant areas in the field of materials properties and surface engineering research. From the year 2000 to till date, nearly 1000 SCI indexed research papers were published on this topic. However, no comprehensive studies about the recent progress on this topic were reported elsewhere so far. In this context, the present chapter aims to give a complete overview on various aspects of the rest of the electroless metallic nanocoatings/layer as a whole. More importance will be on the recent developments of the nanocharacteristics and future scopes

Unconventional Low-Cost Fabrication and Patterning Techniques for Point of Care Diagnostics

The potential of rapid, quantitative, and sensitive diagnosis has led to many innovative ‘lab on chip’ technologies for point of care diagnostic applications. Because these chips must be designed within strict cost constraints to be widely deployable, recent research in this area has produced extremely novel non-conventional micro- and nano-fabrication innovations. These advances can be leveraged for other biological assays as well, including for custom assay development and academic prototyping. The technologies reviewed here leverage extremely low-cost substrates and easily adoptable ways to pattern both structural and biological materials at high resolution in unprecedented ways. These new approaches offer the promise of more rapid prototyping with less investment in capital equipment as well as greater flexibility in design. Though still in their infancy, these technologies hold potential to improve upon the resolution, sensitivity, flexibility, and cost-savings over more traditional approaches

Direct metallisation of polyetherimide substrates by activation with different metals

This article reports the performance of different metallic ions and nanoparticles (Ag, Cu, Ni, Pd, Cr, Co, Au and Fe) used as seed layers, formed by chemical or optical reduction, for the electroless Cu plating of metal tracks onto polyetherimide (PEI). Plated Cu performance was tested by adhesion, electrical conductivity, plating rate, XPS, SEM, XRD and EDX analysis. The application of Cu and Ag seeds resulted in high quality electroless Cu deposits presenting strong adhesion properties and high conductivity ((2.0 ± 0.5) × 107 S/m and (3.6 ± 0.2) × 107 S/m, respectively) compared with bulk copper (5.96 × 107 S/m). Performance is attributed to the high surface density and uniformity of seed layers. Of the metals, only Ag ions were photoreduced under the conditions applied and were subsequently used to electroless Cu plate high quality track features of 150 μm width. The application of sulphuric acid pre-treatment to PEI prior to Ag ion exchange, improved the photoinitiated track formation process, as demonstrated by a threefold increase to both photoinduced Ag nanoparticle density on the surface and electroless Cu plating rate, as well as improved electroless Cu adhesion to PEI

Polymer-Nanoparticle Hybrid Materials for Plasmonic Hydrogen Detection

Plasmonic metal nanoparticles and polymer materials have independently undergone rapid development during the last two decades. More recently, it has been realized that combining these two systems in a hybrid or nanocomposite material comprised of plasmonically active metal nanoparticles dispersed in a polymer matrix leads to systems that exhibit fascinating properties, and some first attempts had been made to exploit them for optical spectroscopy, solar cells or even pure art. In my thesis, I have applied this concept to tackle the urgent problem of hydrogen safety by developing Pd nanoparticle-based “plasmonic plastic” hybrid materials, and by using them as the active element in optical hydrogen sensors. This is motivated by the fact that hydrogen gas, which constitutes a clean and sustainable energy vector, poses a risk for severe accidents due to its high flammability when mixed with air. Therefore, hydrogen leak detection systems are compulsory in the imminent large-scale dissemination of hydrogen energy technologies. To date, however, there a several unresolved challenges in terms of hydrogen sensor performance, whereof too slow sensor response/recovery times and insufficient resistance towards deactivation by poisoning species are two of the most severe ones. In this thesis, I have therefore applied the plasmonic plastic hybrid material concept to tackle these challenges. In summary, I have (i) developed hysteresis-free plasmonic hydrogen sensors based on PdAu, PdCu and PdAuCu alloy nanoparticles; (ii) demonstrated ultrafast sensor response and stable sensor operation in chemically challenging environments using polymer coatings; (iii) introduced bulk-processed and 3D printed plasmonic plastic hydrogen sensors with fast response and high resistance against poisoning and deactivation

Nanoimprint lithography of Al nanovoids for deep-UV SERS.

Deep-ultraviolet surface-enhanced Raman scattering (UV-SERS) is a promising technique for bioimaging and detection because many biological molecules possess UV absorption lines leading to strongly resonant Raman scattering. Here, Al nanovoid substrates are developed by combining nanoimprint lithography of etched polymer/silica opal films with electron beam evaporation, to give a high-performance sensing platform for UV-SERS. Enhancement by more than 3 orders of magnitude in the UV-SERS performance was obtained from the DNA base adenine, matching well the UV plasmonic optical signatures and simulations, demonstrating its suitability for biodetection.We acknowledge financial support from EPSRC grant EP/G060649/1, EP/I012060/1, EP/J007552/1, ERC grant LINASS 320503.This is the final version of the article. It first appeared from ACS via http://dx.doi.org/10.1021/am505511