Fabrication Of Nanostructures Research Articles

Pillar Growth by Focused Electron Beam-Induced Deposition Using a Bimetallic Precursor as Model System: High-Energy Fragmentation vs. Low-Energy Decomposition.

Electron-induced fragmentation of the HFeCo3(CO)12 precursor allows direct-write fabrication of 3D nanostructures with metallic contents of up to >95 at %. While microstructure and composition determine the physical and functional properties of focused electron beam-induced deposits, they also provide fundamental insights into the decomposition process of precursors, as elaborated in this study based on EDX and TEM. The results provide solid information suggesting that different dominant fragmentation channels are active in single-spot growth processes for pillar formation. The use of the single source precursor provides a unique insight into high- and low-energy fragmentation channels being active in the same deposit formation process.

Reconfigurable generation of chiral optical fields with multiple selective degrees of freedom.

Chiral optical fields caused by vortex beams possessing orbital angular momentum (OAM) can be used to fabricate helically structured materials and identify chiral molecules, in which the materials or molecules are associated with the character of the irradiated light. However, previously reported chiral optical fields can control only some of the parameters including the number of fringes, size, ellipticity, orientation, and local intensity distribution, which may hamper their applications. Thus, in this work, we propose both theoretically and experimentally an approach to fabricate chiral optical fields with five separately controllable degrees of freedom by overlapping two anisotropic vortices whose wavefronts have a nonlinear phase variation with the azimuthal angle. The local intensity distribution, number of fringes, size, orientation, and ellipticity of the chiral optical field can be dynamically controlled by adjusting the nonlinear coefficient, topological charges, axicon parameter, rotation angle, and stretching factor of the anisotropic vortices. Furthermore, the OAM density was investigated and proven to be continuously enhanced with the variation of the field's local intensity distribution, which gives the proposed approach the ability to continuously manipulate the OAM density of chiral optical fields. This work, supporting chiral optical fields by five separately controllable parameters, may make the applications of chiral optical fields in the fields of nanostructure fabrication and optical tweezers more flexible.

Modeling the co-assembly of binary nanoparticles

In this work, we present a binary assembly model that can predict the co-assembly structure and spatial frequency spectra of monodispersed nanoparticles with two different particle sizes. The approach relies on an iterative algorithm based on geometric constraints, which can simulate the assembly patterns of particles with two distinct diameters, size distributions, and at various mixture ratios on a planar surface. The two-dimensional spatial-frequency spectra of the modeled assembles can be analyzed using fast Fourier transform analysis to examine their frequency content. The simulated co-assembly structures and spectra are compared with assembled nanoparticles fabricated using transfer coating method are in qualitative agreement with the experimental results. The co-assembly model can also be used to predict the peak spatial frequency and the full-width at half-maximum bandwidth, which can lead to the design of the structure spectra by selection of different monodispersed particles. This work can find applications in fabrication of non-periodic nanostructures for functional surfaces, light extraction structures, and broadband nanophotonics.

Near-zero-adhesion-enabled intact wafer-scale resist-transfer printing for high-fidelity nanofabrication on arbitrary substrates

There is an urgent need for novel processes that can integrate different functional nanostructures onto specific substrates, so as to meet the fast-growing need for broad applications in nanoelectronics, nanophotonics, and flexible optoelectronics. Existing direct-lithography methods are difficult to use on flexible, nonplanar, and biocompatible surfaces. Therefore, this fabrication is usually accomplished by nanotransfer printing. However, large-scale integration of multiscale nanostructures with unconventional substrates remains challenging because fabrication yields and quality are often limited by the resolution, uniformity, adhesivity, and integrity of the nanostructures formed by direct transfer. Here, we proposed a resist-based transfer strategy enabled by near-zero adhesion, which was achieved by molecular modification to attain a critical surface energy interval. This approach enabled the intact transfer of wafer-scale, ultrathin-resist nanofilms onto arbitrary substrates with mitigated cracking and wrinkling, thereby facilitating the in situ fabrication of nanostructures for functional devices. Applying this approach, fabrication of three-dimensional-stacked multilayer structures with enhanced functionalities, nanoplasmonic structures with ∼10 nm resolution, and MoS2-based devices with excellent performance was demonstrated on specific substrates. These results collectively demonstrated the high stability, reliability, and throughput of our strategy for optical and electronic device applications.

A Comparative Study of Gallium-, Xenon-, and Helium-Focused Ion Beams for the Milling of GaN.

The milling profiles of single-crystal gallium nitride (GaN) when subjected to focused ion beams (FIBs) using gallium (Ga), xenon (Xe), and helium (He) ion sources were investigated. An experimental analysis via annular dark-field scanning transmission electron microscopy (ADF-STEM) and high-resolution transmission electron microscopy (HRTEM) revealed that Ga-FIB milling yields trenches with higher aspect ratios compared to Xe-FIB milling for the selected ion beam parameters (30 kV, 42 pA), while He-FIB induces local lattice disorder. Molecular dynamics (MD) simulations were employed to investigate the milling process, confirming that probe size critically influences trench aspect ratios. Interestingly, the MD simulations also showed that Xe-FIB generates higher aspect ratios than Ga-FIB with the same probe size, indicating that Xe-FIB could also be an effective option for nanoscale patterning. Atomic defects such as vacancies and interstitials in GaN from He-FIB milling were suggested by the MD simulations, supporting the lattice disorder observed via HRTEM. This combined experimental and simulation approach has enhanced our understanding of FIB milling dynamics and will benefit the fabrication of nanostructures via the FIB technique.

Highly Controllable Fabrication of Gold Composite Nanostructures by Multiple Electroplating for High‐Performance Electrochemical and Raman Scattering Measurements

Morphology‐controlled nanostructures are important functional materials in multidisciplinary research fields, such as sensing, imaging, catalysis, and energy harvesting. However, existing nanofabrication methods have limitations in terms of controllability, diversity, cost, and efficiency. Here, a novel nanofabrication approach is proposed to construct Au nanostructures with high controllability, cost‐efficiency, and high‐performance sensing and energy harvesting. The fabrication incorporates electric field‐assisted hydrothermal growth of zinc oxide nanorods (ZnO NRs) with two‐step gold electroplating. The ZnO NRs serve as a dissolvable template during the electroplating formation of gold nanostructures for eventually synthesizing pure gold nanostructures on electrodes. The synthesized gold nanostructures take unique composite shape of nanospheres (hundreds of nanometers) covered with tinier nanostructures (tens of nanometers) like floccules, grains, lamellas, or rods, which are highly controlled by regulating electroplating parameters. The gold composite nanostructures provide high‐performance sensing and energy harvesting, such as enhanced electrochemical sensing interface (electric double‐layer impedance decrease up to 97.1%), excellent surface‐enhanced Raman scattering (SERS enhancement factor up to ), and preferable visible–near‐infrared light harvesting (absorptivity near to 90%). For the first time, the application of tumor cell photothermal therapy with nanostructured electrodes and in situ bimodal monitoring of single‐cell impedance and SERS‐based molecular expression during therapy is demonstrated.

Fabrication and utilization of ternary cubical nanostructure modified activated carbon cloth electrodes for capacitive deionization system

Cubical nanostructure zinc tin oxide (ZTO) was in-situ deposited on activated carbon cloth (ACC) substrate via a co-precipitation method. The amount and size of ZTO on the ACC substrate were varied by changing the different overall metal ion (Sn4+ and Zn2+) concentrations. The surface morphology and crystalline analysis revealed the well distributed cubic shape perovskite ZTO on the ACC substrates. The ZTO-deposited ACC electrodes showed superior electrochemical performances with higher specific capacitance and better ion transfer activity than pristine ACC. ZTO deposited ACC substrates were used as electrodes in a capacitive deionization system. ACC substrate coated with 0.01 M Sn and Zn metal concentrations achieved the best desalination efficiency of 52%, salt adsorption capacity of 45.0 ± 2 mg/g and faster salt adsorption rate of 0.14 mg/g/s compared to the other tested electrodes using 500 ppm NaCl solution. Further desalination of real groundwater (1000 ppm) achieved with ions adsorption improvement of 36% for Na+, 48% for Ca2+, 60% for Mg2+, and 46% for Cl- compared to the pristine ACC. Additionally, compared to the pristine ACC, the ZTO-coated electrode enhanced the ions adsorption rate and reduced energy consumption by 40%. Post surface characterization of used pristine ACC displayed substantial scaling of the minerals from the ground water but ZTO-II electrodes exhibited better stability with less scaling. The outcomes of this study provide a stepping stone for the modification and utilization of electrodes for the real brackish water in the CDI system.

Picosecond Pulsed Laser Deposition of Metals and Metal Oxides.

In this work, we present the fabrication of thin films/nanostructures of metals and metal oxides using picosecond laser ablation. Two sets of experiments were performed: the depositions were carried out in vacuum and in air at atmospheric pressure. The subjects of investigation were the noble metals Au and Pt and the metal oxides ZnO and TiO2. We studied and compared the phase composition, microstructure, morphology, and physicochemical state of the as-deposited samples' surfaces in vacuum and in air. It was found that picosecond laser ablation performed in vacuum led to the fabrication of thin films with embedded and differently sized nanoparticles. The implementation of the same process in air at atmospheric pressure resulted in the fabrication of porous nanostructures composed of nanoparticles. The ablation of pure Pt metal in air led to the production of nanoparticles with an oxide shell. In addition, more defects were formed on the metal oxide surface when the samples were deposited in vacuum. Furthermore, the laser ablation process of pure Au metal in a picosecond regime in vacuum and in air was theoretically investigated using molecular dynamics simulation.

Facile Synthesis of Ge@TiO2 Nanotube Hybrid Nanostructure Anode Materials for Li-Ion Batteries.

Utilizing nanostructures of Li-alloying anode materials (e.g., Si, Ge, Sn, etc.) has been proposed as a key strategy to improve the electrochemical performance. However, the main challenge lies in the costly and complex nanostructure synthesis processes. Notably, the nanostructure growth processes are mainly supported by Li-inactive templates, which later need to be removed, and the template removal process results in the destruction of the desired nanostructures. In this report, we demonstrated the use of a Li-active, self-organized TiO2 nanotube template to fabricate germanium (Ge)-based nanostructured anodes. This has been achieved as follows: first, TiO2 nanotubes are fabricated via electrochemical anodization of titanium foil. Then, the nanotubes are coated with a Ge film in the second step via electrodeposition. Besides the effective nanostructure growth using a Li-active template, the implemented electrochemical synthesis methods are cost-effective, accessible, and scalable. Furthermore, the electrochemical methods allow the fabrication of nanostructures with well-controlled structures, morphology, and compositions. Accordingly, a Ge-coated TiO2 nanotube (Ge@TiO2) nanocomposite anode has been successfully fabricated, and its electrochemical performance has been tested for Li-ion batteries. The study has shown the important roles of TiO2 nanotube arrays in improving the performance by providing strong mechanical support to buffer the volume expansion and offering a high surface area to enhance Ge-active mass loading. Moreover, the direct contact of the nanotubes with a Ti current collector facilitates one-dimensional (1D) electron transport and avoids the need of adding inactive binders or conductive additives.

Controlling 1D Nanostructures and Handedness by Polar Residue Chirality of Amphiphilic Peptides.

Peptide assemblies are promising nanomaterials, with their properties and technological applications being highly hinged on their supramolecular architectures. Here, how changing the chirality of the terminal charged residues of an amphiphilic hexapeptide sequence Ac-I4 K2 -NH2 gives rise to distinct nanostructures and supramolecular handedness is reported. Microscopic imaging and neutron scattering measurements show thin nanofibrils, thick nanofibrils, and wide nanotubes self-assembled from four stereoisomers. Spectroscopic and solid-state nuclear magnetic resonance (NMR) analyses reveal that these isomeric peptides adopt similar anti-parallel β-sheet secondary structures. Further theoretical calculations demonstrate that the chiral alterations of the two C-terminal lysine residues cause the formation of diverse single β-strand conformations, and the final self-assembled nanostructures and handedness are determined by the twisting direction and degree of single β-strands. This work not only lays a useful foundation for the fabrication of diverse peptide nanostructures by manipulating the chirality of specific residues but also provides a framework for predicting the supramolecular structures and handedness of peptide assemblies from single molecule conformations.

Fabrication of Nanogroove Arrays on Acrylic Film Using Micro-Embossing Technique.

The fabrication of nanostructures is of great importance in producing biomedical devices. Significantly, the nanostructure of the polymeric film has a significant impact on the physical and biophysical behavior of the biomolecules. This study presents an efficient nanofabrication method of nanogroove structures on an acrylic film by the micro-embossing process. In this method, a master mold was made from a thermos oxide silicon substrate using photolithography and etching techniques. An isotropic optical polymethyl methacrylate (PMMA) film is used in the experiment. The acrylic film is known for its excellent optical properties in products such as optical lenses, medical devices, and various general purpose engineering plastics. Then, the micro-embossing process was realized to fabricate nanogroove patterns on an acrylic film by using a micro-embossing machine. However, the morphology of the nanopatterns on an acrylic film was characterized by using an atomic force microscope to measure the dimensions of the nanogroove patterns. The impact of embossing temperature on the morphology of nanogroove patterns on acrylic film is experimentally investigated. The results show that when the embossing temperature is too small, the pattern is not fully formed, and slipping occurs in nanopatterns on the acrylic film. On the other hand, the effect of increasing the embossing temperature on the morphology of nanogrooves agrees with the master mold, and the crests between the nanogrooves form straight edges. It should be noted that the micro-embossing temperature also strongly influences the transferability of nanopatterns on an acrylic film. The technique has great potential for rapidly fabricating nanostructure patterns on acrylic film.

Bioinspired fabrication of zinc hydroxide-based nanostructure from lignocellulosic biomass Litchi chinensis leaves and its efficacy evaluation on antibacterial, antioxidant, and anticancer activity

Zinc-based nanostructures are known for their numerous potential biomedical applications. In this context, the biosynthesis of nanostructures using plant extracts has become a more sustainable and promising alternative to effectively replace conventional chemical methods while avoiding their toxic impact. In this study, following a low-temperature calcination process, a green synthesis of Zn-hydroxide-based nanostructure has been performed using an aqueous extract derived from the leaves of Litchi chinensis, which is employed as a lignocellulose waste biomass known to possess a variety of phytocompounds. The biogenic preparation of Zn-hydroxide based nanostructures is enabled by bioactive compounds present in the leaf extract, which act as reducing and capping agents. In order to evaluate its physicochemical characteristics, the produced Zn-hydroxide-based nanostructure has been subjected to several characterization techniques. Further, the multifunctional properties of the prepared Zn-hydroxide-based nanostructure have been evaluated for antioxidant, antimicrobial, and anticancer activity. The prepared nanostructure showed antibacterial efficacy against Bacillus subtilis and demonstrated its anti-biofilm activity as evaluated through the Congo red method. In addition, the antioxidant activity of the prepared nanostructure has been found to be dose-dependent, wherein 91.52 % scavenging activity could be recorded at 200 μg/ml, with an IC50 value of 45.22 μg/ml, indicating the prepared nanostructure has a high radical scavenging activity. Besides, the in vitro cytotoxicity investigation against HepG2 cell lines explored that the as-prepared nanostructure exhibited a higher cytotoxic effect and 73.21 % cell inhibition could be noticed at 25.6 μg/ml with an IC50 of 2.58 μg/ml. On the contrary, it was found to be significantly lower in the case of HEK-293 cell lines, wherein ~47.64 % inhibition could be noticed at the same concentration. These findings might be further extended to develop unique biologically derived nanostructures that can be extensively evaluated for various biomedical purposes.

Periodic nanostructures on single-crystal copper for SERS substrate fabricated by using AFM dynamic lithography

The fabrication of periodic nanostructures on noble metals as surface enhanced Raman scattering (SERS) substrate is still challenging through facile and cost-effective process. Dynamic lithography under AFM tapping mode has been applied to the fabrication of nanogrooves on single-crystal copper to reduce the feature size. However, there was a lack of fundamental understanding of the effect of the fabrication of periodic nanostructures due to dynamic lithography and then SERS enhancement. To this end, this study aims to investigate the variation of the energy dissipation and the corresponding fabricated nanogrooves at different laser spot positions. It was found that improper laser position was contributed to the increased energy dissipation and irregular nanogrooves were thus obtained with much larger machined depth. On the contrary, at the optimal laser position, the minimal sensitivity was associated with the maximum voltage value on the photodiode. In this case, regular nanogrooves with controlled feature size can be produced for the fabrication of periodic nanostructures. And checkerboard nanodots with a period of 200 nm were fabricated by the combination of arrays of nanogrooves, which indicated advantages of high stability for AFM dynamic lithography. In addition, rhodamine 6G (R6G) was selected as the detecting target to measure SERS spectra of fabricated substrates. Results indicated the Raman enhancement factors can be promoted due to uniform shape of nanogroove and high resolution in horizon dimension.

Theoretical simulated fabrication of nanostructure by interference of four-beam guided mode excited by 193 nm laser

This study proposed a lithography method for fabricating periodic nanostructures using the interference of four-beam TE0 guided modes excited by a 193 nm deep ultraviolet laser. The physical mechanism and normalized electric field intensity distribution of four-beam TE0 guided mode interference were theoretically analyzed and numerically simulated using the finite element method. The simulation results confirmed the ability of this method to fabricate periodic structures with a half-pitch resolution of 30.35 nm (approximately λ/6.36), an aspect ratio of 3.95, and a contrast ratio of 1. The theoretically calculated value of the resolution was consistent with the numerical simulation value. The resolution and aspect ratio of the fabricated nanostructures could be adjusted through changes to the thickness of the resist. Moreover, the shape of the fabricated nanostructures, such as the one-dimensional sub-wavelength grating structure and two-dimensional square array lattice structure, were adjustable via changes to the number and azimuth of the excited TE0 guided modes. The results obtained in this study provide valuable theoretical information for the practical manufacture of ultra-high-resolution lithography.

Electrodeposited Fabrication of CeO2 Branched-like Nanostructure Used for Nonenzymatic Glucose Biosensor

The fabrication of nonenzymatic glucose sensors is essential because of the enhancement in the selectivity and accuracy of these sensors. In this work, we used the electrodeposition approach to prepare a CeO2-based electrode for nonenzymatic glucose detection. A CeO2 branched-like nanostructure was successfully fabricated by electrodeposition on the surface of a Au substrate electrode at room temperature. The effects of cyclic voltammetry, CH3COOH content, and scan cycle number on the formation of the CeO2 branched-like nanostructure were investigated. The fabricated electrodes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The results showed that a CeO2 branched-like nanostructure could be obtained with a CH3COOH content of 1.0 mL and a scan cycle number of 100 in a solution containing 0.015 M Ce(NO3)3, 0.01 M KCl, and 0.02 M CH3COONH4 and with a scan rate of 400 mV/s. The electrochemical characteristics of the sensor were examined by chronoamperometry and cyclic voltammetry. The results showed that the sensitivity of the sensor was 37.72 μA/mM·cm2 and the limit of detection (LOD) of the sensor was 0.093 mM. The findings in this work prove that it is feasible to fabricate CeO2-based sensors for nonenzymatic glucose detection.

Bottom-up Filling of Nanosized Trenches with Silver to Fabricate Transparent Conducting Electrodes

Transparent conducting electrodes (TCEs) are essential in many optoelectronic devices including solar cells, sensors, displays, and LEDs. The use of transparent metal oxide layers, in particular Indium tin oxide (ITO), is the most common used approach. However, ITO comes with numerous drawbacks such as the relatively rarity of indium and hence high cost, fragility, strong UV absorption and relative high sheet resistance. An exciting alternative TCE is the use of interconnected metallic nanowires, where their sub-wavelength cross-sections makes them transparent to visible light, where especially silver nanowires are a good candidate because of their high conductivity.Here we show a promising cost-effective method called selective-area electrochemical deposition (SAEC) for the fabrication of these metal nanostructures. SAEC is based on a through-the-mask electrochemical deposition method, where the mask is made using substrate conformal imprint lithography. Next to the inherent low fabrication cost of the electrochemical deposition, it has numerous advantages such as bottom-up growth, scalability, operate at ambient conditions, control over nucleation, and yields high purity deposits. While submicron sized features have been already demonstrated by SAEC, obtaining homogeneous void free filling of features below 100 nm using direct plating is a major challenge because of the terminal effect and the poor control of nucleation of the seed layer.In this work, we have explored the SAEC fabrication of large area silver nanowire grids on ITO substrates and on TOPCon solar cells. We show that the nucleation density of the silver nanoparticles is the key parameter for the successful homogenous void-free filling of the trenches. The nucleation density namely determines the coalescence thickness, which sets a minimum thickness for the silver nanowires in order to be connected. We control the nucleation density of the silver nanoparticles by making use of the double pulse method, where a high overpotential nucleation pulse is applied for controlling the nucleation density. After nucleation, we merge the silver nuclei by applying a low overpotential growth pulse.After the successful filling of the trenches, we have compared the optical and electrical performance of the SAEC fabricated silver nanowire grids to those using conventional thermal or e-beam evaporation followed by lift-off. The SAEC-fabricated TCEs show high transmission (>96%) and extreme low resistance (as low as 3 Ω/sq), resulting into a superior figure of merit (FoM). Due to the bottom-up nature of this technique, arbitrary high aspect ratio nanowires can be achieved and therefore the relationship of decreasing transmission with decreasing sheet resistance is broken.Furthermore, we have also incorporated the silver NW grids in TOPCon cells and compared the performance to similar cells based on ITO. This work represents a low-cost and scalable strategy to fabricate sub 100 nm predefined metal structures, enabling the commercial viable fabrication of nanostructure based transparent conductive electrodes for optoelectronic devices.

Boundary-Directed Epitaxy of Block Copolymers Toward Sub-10 nm Fabrication

The directed self-assembly (DSA) of block copolymers (BCPs) can be used to produce nanometer-scale patterns without the cost and process complexity of state-of-the-art optical nanolithography. Thus, DSA is of potential use in a wide variety of semiconductor technologies, such as finFETs and biosensors. To control the position and orientation of BCP domains and create technologically useful patterns, conventional DSA mechanisms often rely on topographically complex structures or high-resolution chemical patterns that are difficult to fabricate. In comparison, a newly discovered mechanism for the DSA of BCPs – termed “boundary-directed epitaxy” – utilizes the chemical contrast at the boundaries between a substrate and relatively wide chemical stripe.[1] As a result, aligned and high density-multiplied BCP nanopatterns with half-pitch of 6.4 nm have been created using stripes as wide as 100 nm. By obviating the need for high-resolution chemical patterns, boundary-directed epitaxy offers exciting opportunities for the fabrication of sub-10 nm nanostructures.[1] Boundary-directed epitaxy of block copolymers. R.M. Jacobberger, V. Thapar, G.-P. Wu, T.-H. Chang, V. Saraswat, A.J. Way, K.R. Jinkins, Z. Ma, P.F. Nealey, S.-M. Hur, S. Xiong, M.S. Arnold, Nature Communications 11, 4151 (2020), 10.1038/s41467-020-17938-3. Figure 1

Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies

In magnetic tunnel junctions based on iron oxide nanoparticles the disorder and the oxidation state of the surface spin as well as the nanoparticles functionalization play a crucial role in the magnetotransport properties. In this work, we report a systematic study of the effects of vacuum annealing on the structural, magnetic and transport properties of self-assembled ∼10 nm Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K) decomposes the organic coating into amorphous carbon, reducing the electrical resistivity of the assemblies by 4 orders of magnitude. At the same time, the 3.Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing temperature of the sample increases from 573 to 873 K, indicating an important surface oxidation. Although the 2 nm physical gap remains unchanged with the thermal treatment, a monotonous decrease of tunnel barrier width was obtained from the electron transport measurements when the annealing temperature increases, indicating an increment in the number of defects and hot-spots in the gap between the nanoparticles. This is reflected in the reduction of the spin dependent tunneling, which reduces the interparticle magnetoresistance. This work shows new insights about influence of the nanoparticle interfacial composition, as well their the spatial arrangement, on the tunnel transport of self-assemblies, and evidence the importance of optimizing the nanostructure fabrication for increasing the tunneling current without degrading the spin polarized current.

Peptide Hydrogels and Nanostructures Controlling Biological Machinery.

Peptides are versatile building blocks for the fabrication of various nanostructures that result in the formation of hydrogels and nanoparticles. Precise chemical functionalization promotes discrete structure formation, causing controlled bioactivity and physical properties for functional materials development. The conjugation of small molecules on amino acid side chains determines their intermolecular interactions in addition to their intrinsic peptide characteristics. Molecular information affects the peptide structure, formation, and activity. In this Perspective, peptide building blocks, nanostructure formation mechanisms, and the properties of these peptide materials are discussed with the results of recent publications. Bioinstructive and stimuli-responsive peptide materials have immense impacts on the nanomedicine field including drug delivery, cellular engineering, regenerative medicine, and biomedicine.

Nanoscale Si fishbone structures for manipulating heat transport using phononic resonators for thermoelectric applications

Thermoelectric materials have the potential to convert waste heat into electricity, but their thermoelectric efficiency must be improved before they are effective and economically viable. One promising route to improving thermoelectric efficiency in thin-film thermoelectric materials is to reduce the material’s thermal conductivity through nanopatterning the surface. In this work nanoscale phononic resonators are introduced to the surface, and their potential to reduce thermal conductivity is explored via coupled experimental and theoretical techniques. Atomistic modelling is used to predict the dependence of the thermal conductivity on different design parameters and used to guide the design and fabrication of silicon fishbone nanostructures. The nanostructure design incorporates a variation on design parameters such as barb length, width and spacing along the shaft length to enable correlation with changes in thermal conductivity. The thermal characteristics of the nanostructures are investigated experimentally using the spatial resolution of scanning thermal microscopy to correlate changes in thermal conductivity with the changes in the structure parameters. The method developed uses a microheater to establish a temperature gradient along the structure which will be affected by any local variations in thermal conductivity. The impact on the thermal gradient and consequently on the tip temperature is modelled using finite element computer simulations. Experimental changes as small as 7.5% are shown to be detectable in this way. Despite the experimental technique being shown to be able to detect thermal changes far smaller than those predicted by the modelling, no modifications of the thermal conductivity are detected. It is concluded that in order to realise the effects of phononic resonators to reduce thermal conductivity, that much smaller structures with a greater ratio of resonator to shaft will be needed.