Abstract: An innovative biomimetic method has been developed to synthesize layered nanocomposite coatings using silica and sugar-derived carbon to mimic the formation of a natural seashell structure. The layered nanocomposites are fabricated through alternate coatings of condensed silica and sugar. Sugar-derived carbon is a cost-effective material as well as environmentally friendly. Pyrolysis of sugar will form polycyclic aromatic carbon sheets, i.e., carbon black. The resulting final nanocomposite coatings can survive temperatures of more than 1150 °C and potentially up to 1650 °C. These coatings have strong mechanical properties, with hardness of more than 11 GPa and elastic modulus of 120 GPa, which are 80% greater than those of pure silica. The layered coatings have many applications, such as shielding in the form of mechanical barriers, body armor, and space debris shields. Graphical abstract: [Figure not available: see fulltext.]
Abstract: Here, we report the high pressure phase and morphology behavior of ordered anatase titanium dioxide (TiO2) nanocrystal arrays. One-dimensional TiO2 nanorods and nanorices were synthesized and self-assembled into ordered mesostructures. Their phase and morphological transitions at both atomic scale and mesoscale under pressure were studied using in situ synchrotron wide- and small-angle x-ray scattering (WAXS and SAXS) techniques. At the atomic scale, synchrotron WAXS reveals a pressure-induced irreversible amorphization up to 35 GPa in both samples but with different onset pressures. On the mesoscale, no clear phase transformations were observed up to 20 GPa by synchrotron SAXS. Intriguingly, sintering of TiO2 nanorods at mesoscale into nano-squares or nano-rectangles, as well as nanorices into nanowires, were observed for the first time by transmission electron microscopy. Such pressure-induced nanoparticle phase-amorphization and morphological changes provide valuable insights for design and engineering structurally stable nanomaterials. Impact statement: The high pressure behavior of nanocrystals (NCs) continues to be of interest, as previous studies have demonstrated that an externally applied pressure can serve as an efficient tool to induce structural phase transitions of NC assemblies at both the atomic scale and mesoscale without altering any chemistry by manipulating NC interatomic and interparticle distances. In addition, the high pressure generated deviatoric stress has been proven to be able to force adjacent NCs to connect and fuse into new crystalline nanostructures. Although the atomic structural evolution of TiO2 NCs under pressure has been widely investigated in the past decades, open questions remain regarding the mesoscale phase transition and morphology of TiO2 NC assemblies as a function of pressure. Therefore, in this work, systemic high pressure experiments on ordered arrays of TiO2 nanorods and nanorices were conducted by employing wide/small angle x-ray scattering techniques. The sintering of TiO2 assemblies at mesoscale into various nanostructures under pressure were revealed by transmission electron microscopy. Overall, this high pressure work fills the current gap in research on the mesoscale phase behavior of TiO2 assemblies. The observed morphology tunability attained by applying pressure opens new pathways for engineering nanomaterials and optimizing their collective properties through mechanical compression stresses. Graphical abstract: [Figure not available: see fulltext.].
Pulsed-power generators using the magnetic loading technique are able to produce well-controlled continuous ramp compression of condensed matter for high-pressure equation-of-state studies. X-ray diffraction (XRD) data from dynamically compressed samples provide direct measurements of the elastic compression of the crystal lattice, onset of plastic flow, strength-strain rate dependence, structural phase transitions, and density of crystal defects such as dislocations. Here, we present a cost effective, compact X-ray source for XRD measurements on pulsed-power-driven ramp-loaded samples. This combination of magnetically-driven ramp compression of materials with single, short-pulse XRD diagnostic will be a powerful capability for the dynamic materials community. The success in fielding this new XRD diagnostic dramatically improves our predictive capability and understanding of rate-dependent behavior at or near phase transition. As Sandia plans the next-generation pulse-power driver platform, a key element needed to deliver new state-of-the-art experiments will be having the necessary diagnostic tools to probe new regimes and phenomena. These diagnostics need to be as versatile, compact, and portable as they are powerful. The development of a platform-independent XRD diagnostic gives Sandia researchers a new window to study the microstructure and phase dynamics of materials under load. This project has paved the way for phase transition research in a variety of materials with mission interest.
Self-assembly of anisotropic plasmonic nanomaterials into ordered superstructures has become popular in nanoscience because of their unique anisotropic optical and electronic properties. Gold nanorods (GNRs) are a well-defined functional building block for fabrication of these superstructures. They possess important anisotropic plasmonic characteristics that result from strong local electric field and are responsive to visible and near-IR light. There are recent examples of assembling the GNRs into ordered arrays or superstructures through processes such as solvent evaporation and interfacial assembly. In this Minireview, recent progress in the development of the self-assembled GNR arrays is described, with focus on the formation of oriented GNR arrays on substrates. Key driving forces are discussed, and different strategies and self-assembly processes of forming oriented GNR arrays are presented. The applications of the oriented GNR arrays in optoelectronic devices are also overviewed, especially surface enhanced Raman scattering (SERS).
Nanoparticle (NP) high pressure behavior has been extensively studied over the years. In this review, we summarize recent progress on the studies of pressure induced NP phase behavior, property, and applications. This review starts with a brief overview of high pressure characterization techniques, coupled with synchrotron X-ray scattering, Raman, fluorescence, and absorption. Then, we survey the pressure induced phase transition of NP atomic crystal structure including size dependent phase transition, amorphization, and threshold pressures using several typical NP material systems as examples. Next, we discuss the pressure induced phase transition of NP mesoscale structures including topics on pressure induced interparticle separation distance, NP coupling, and NP coalescence. Pressure induced new properties and applications in different NP systems are highlighted. Finally, outlooks with future directions are discussed.
Pressure-driven assembly of ligand-grafted gold nanoparticle superlattices is a promising approach for fabricating gold nanostructures, such as nanowires and nanosheets. Optimizing this fabrication method will require extending our understanding of superlattice mechanics to regimes of high pressures. We use molecular dynamics simulations to characterize the response of alkanethiol-grafted gold nanoparticle superlattices to applied hydrostatic pressures up to 15 GPa. At low applied pressures, intrinsic voids govern the mechanics of compaction. As applied pressures increase, the void collapse and ligand compression depend significantly on the ligand length. These microstructural observations correlate directly with trends in bulk modulus and elastic constants. For short ligands, core-core contact between gold nanoparticles is observed at high pressures, which augurs irreversible response and eventual sintering. This presintering behavior was unexpected under hydrostatic loading and is observed only for the shortest ligands.
Semiconductor nanomaterials with controlled morphologies and architectures are of critical importance for high-performance optoelectronic devices. However, the fabrication of such nanomaterials on polymer-based flexible electrodes is particularly challenging due to degradation of the flexible electrodes at a high temperature. Here we report the fabrication of nickel oxide nanopillar arrays (NiOx NaPAs) on a flexible electrode by vapor deposition, which enables highly efficient perovskite solar cells (PSCs). The NiOx NaPAs exhibit an enhanced light transmittance for light harvesting, prohibit exciton recombination, promote irradiation-generated hole transport and collection, and facilitate the formation of large perovskite grains. These advantageous features result in a high efficiency of 20% and 17% for the rigid and flexible PSCs, respectively. Additionally, the NaPAs show no cracking after 500 times of bending, consistent with the mechanic simulation results. This robust fabrication opens a new opportunity for the fabrication of a large area of high-performance flexible optoelectronic devices.
Due to remarkable electronic property, optical transparency, and mechanical flexibility, monolayer molybdenum disulfide (MoS 2 ) has been demonstrated to be promising for electronic and optoelectronic devices. To date, the growth of high-quality and large-scale monolayer MoS 2 has been one of the main challenges for practical applications. Here we present a MoS 2 -OH bilayer-mediated method that can fabricate inch-sized monolayer MoS 2 on arbitrary substrates. This approach relies on a layer of hydroxide groups (aOH) that are preferentially attached to the (001) surface of MoS 2 to form a MoS 2 -OH bilayer structure for growth of large-area monolayer MoS 2 during the growth process. Specifically, the hydroxide layer impedes vertical growth of MoS 2 layers along the [001] zone axis, promoting the monolayer growth of MoS 2 , constrains growth of the MoS 2 monolayer only in the lateral direction into larger area, and effectively reduces sulfur vacancies and defects according to density functional theory calculations. Finally, the hydroxide groups advantageously prevent the MoS 2 from interface oxidation in air, rendering high-quality MoS 2 monolayers with carrier mobility up to ∼30 cm 2 V -1 s -1 . Using this approach, inch-sized uniform monolayer MoS 2 has been fabricated on the sapphire and mica and high-quality monolayer MoS 2 of single-crystalline domains exceeding 200 μm has been grown on various substrates including amorphous SiO 2 and quartz and crystalline Si, SiC, Si 3 N 4 , and graphene This method provides a new opportunity for the monolayer growth of other two-dimensional transition metal dichalcogenides such as WS 2 and MoSe 2 .
We report there has been widespread recent interest in self-assembly and synthesis of porphyrin and its derivatives-based ordered arrays aiming to emulate natural light-harvesting processes and energy storage. However, technologies that leverage the structural advantages of individual porphyrins have not been fully realized and have been limited by available synthesis methods. This article provides general perspectives on porphyrin and derivative chemistry, and discussions on surfactant-assisted cooperative self-assembly using amphiphilic surfactants and functional porphyrins and derivatives. The cooperative self-assembly amplifies the intrinsic advantages of individual porphyrins by engineering them into well-defined one-dimensional–three-dimensional (1D–3D) nanostructures. Surfactant-assisted self-assembly of amphiphilic surfactants and porphyrins has been utilized to form well-defined “micelle-like” nanostructures. Lastly, driven by intermolecular interactions, subsequent nucleation and growth confined within these nanostructures lead to the formation of 1D–3D ordered optically and electrically active nanomaterials with structure and function on multiple length scales.