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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The influence of projectile ion induced chemistry on surface pattern formation

We report the critical role of projectile induced chemical inhomogeneity on surface nanostructure formation. Experimental inconsistency is common for low energy ion beam induced nanostructure formation in the presence of uncontrolled and complex contamination. To explore the precise role of contamination on such structure formation during low energy ion bombardment, a simple and clean experimental study is performed by selecting mono-element semiconductors as the target and chemically inert or reactive ion beams as the projectile as well as the source of controlled contamination. It is shown by Atomic Force Microscopy, Cross-sectional Transmission Electron Microscopy, and Electron Energy Loss Spectroscopy measurements that bombardment of nitrogen-like reactive ions on Silicon and Germanium surfaces forms a chemical compound at impact zones. Continuous bombardment of the same ions generates surface instability due to unequal sputtering and non-uniform re-arrangement of the elemental atom and compound. This instability leads to ripple formation during ion bombardment. For Argon-like chemically inert ion bombardment, the chemical inhomogeneity induced boost is absent; as a result, no ripples are observed in the same ion energy and fluence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

The Role of Ligand–Ligand Interactions in Multimodal Ligand Conformational Equilibria and Surface Pattern Formation

Multimodal chromatography uses multiple modes of interaction such as charge, hydrophobic, or hydrogen bonding to separate proteins. Recently, we used molecular dynamics (MD) simulations to show that ligands immobilized on surfaces can interact and associate with neighboring ligands to form hydrophobic and charge patches, which may have important implications for the nature of protein–surface interactions. Here, we study interfacial systems of increasing complexity—from a single immobilized multimodal ligand to high density surfaces—to better understand how ligand behavior is affected by the presence of a surface and the presence of other ligands in the vicinity, and how this behavior scales to larger systems. Furthermore, we find that tethering a ligand to a surface restricts its conformations to a subset of those observed in free solution, yet the ligand maintains flexibility in the plane of the surface and can form contacts with neighboring ligands. We find that although the formation of a contact between two neighboring ligands is slightly unfavorable, three neighboring ligands exhibit a preference for the formation of a fully connected cluster. To explore how these trends in ligand association extend to a larger surface with high density of ligands, we performed coarse-grained Monte Carlo (MC) simulations of a 132-ligand surface using ligand interactions parametrized based on free energies obtained from the three-ligand MD simulations. Despite their simplicity, the coarse-grained simulations qualitatively capture the cluster size distribution of ligands observed in detailed MD simulations. Quantitative differences between the two suggest opportunities for improvements in the coarse-grained energy function for efficient predictions of cluster and pattern formations. Our approach presents a promising route to the engineering of multimodal patterns for future chromatographic resin design.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Rapid prototyping of microchannels with surface patterns for fabrication of polymer fibers

Microfluidic technology has provided innovative solutions to numerous problems, but the cost of designing and fabricating microfluidic channels is impeding its expansion. In this study, Shrinky-Dink thermoplastic sheets are used to create multilayered complex templates for microfluidic channels. We also used inkjet and laserjet printers to raise a predetermined microchannel geometry by depositing several layers of ink for each feature consecutively. We achieved feature heights over 100 μm, which were measured and compared with surface profilometry. Templates closest to the target geometry were then used to create microfluidic devices from soft-lithography with the molds as a template. These microfluidic devices were, futhermore used to fabricate polymer microfibers using the microfluidic focusing approach to demonstrate the potential that this process has for microfluidic applications. Finally, an economic analysis was conducted to compare the price of common microfluidic template manufacturing methods. We showed that multilayer microchannels can be created significantly quicker and cheaper than current methods for design prototyping and point-of-care applications in the biomedical area.

42 ENGINEERING↗
DOE OSTI2015

Nanostructure surface patterning of GaN thin films and application to AlGaN/AlN multiple quantum wells: A way towards light extraction efficiency enhancement of III-nitride based light emitting diodes

Enhanced light extraction efficiency was demonstrated on nanostructure patterned GaN and AlGaN/AlN Multiple-Quantum-Well (MQW) structures using mass production techniques including natural lithography and interference lithography with feature size as small as 100 nm. Periodic nanostructures showed higher light extraction efficiency and modified emission profile compared to non-periodic structures based on integral reflection and angular-resolved transmission measurement. Light extraction mechanism of macroscopic and microscopic nanopatterning is discussed, and the advantage of using periodic nanostructure patterning is provided. An enhanced photoluminescence emission intensity was observed on nanostructure patterned AlGaN/AlN MQW compared to as-grown structure, demonstrating a large-scale and mass-producible pathway to higher light extraction efficiency in deep-ultra-violet light-emitting diodes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Strain-induced growth instability and nanoscale surface patterning in perovskite thin films

Despite extensive studies on the effects of epitaxial strain on the evolution of the lattice and properties of materials, considerably less work has explored the impact of strain on growth dynamics. In this work, we demonstrate a growth-mode transition from 2D-step flow to self-organized, nanoscale 3D-island formation in PbZr0.2Ti0.8O3/SrRuO3/SrTiO3 (001) heterostructures as the kinetics of the growth process respond to the evolution of strain. With increasing heterostructure thickness and misfit dislocation formation at the buried interface, a periodic, modulated strain field is generated that alters the adatom binding energy and, in turn, leads to a kinetic instability that drives a transition from 2D growth to ordered, 3D-island formation. The results suggest that the periodically varying binding energy can lead to inhomogeneous adsorption kinetics causing preferential growth at certain sites. This, in conjunction with the presence of an Ehrlich-Schwoebel barrier, gives rise to long-range, periodically-ordered arrays of so-called “wedding cake” 3D nanostructures which self-assemble along the [100] and [010].

36 MATERIALS SCIENCE↗
DOE OSTI2022

Novel Patterned Surfaces for Improved Condenser Performance in Power Plants

In this project, we seek to improve the thermoelectric power plant performance through engi-neered nonwetting condenser tube surface designs that can enhance heat transfer performance by: (1) promoting dropwise condensation of the steam on the shell side and eliminating flooding of the surface structure by maintaining low droplet adhesion, thus increasing condensation heat transfer coefficient; (2) deterring fouling and corrosion, thereby reducing fouling resistance and improving heat transfer; (3) possibly reducing drag and increasing convective heat transfer inside coolant tubes; and (4) reducing the number of tubes, coolant water usage, and levelized cost of condenser.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2014

Numerical study of the effects of surface topography and chemistry on the wetting transition using the string method

Droplets on a solid surface patterned with microstructures can exhibit the composite Cassie-Baxter (CB) state or the wetted Wenzel state. The stability of the CB state is determined by the energy barrier separating it from the wetted state. In this work, we study the CB to Wenzel transition using the string method [E et al., J. Chem. Phys. 126, 164103 (2007); W. Ren and E. Vanden-Eijnden, J. Chem. Phys. 138, 134105 (2013)]. We compute the transition states and energy barriers for a three-dimensional droplet on patterned surfaces. The liquid-vapor coexistence is modeled using the mean field theory. Numerical results are obtained for surfaces patterned with straight pillars and nails, respectively. It is found that on both type of surfaces, wetting occurs via infiltration of the liquid in a single groove. The reentrant geometry of nails creates large energy barrier for the wetting of the solid surface compared to straight pillars. We also study the effect of surface chemistry, pillar height, and inter-pillar spacing on the energy barrier and compare it with nails.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Influence of substrate pattern on the adsorption of HP lattice proteins

With the highly simplified hydrophobic-polar model representation of a protein, we can study essential qualitative physics without an unnecessarily large computational overhead. Using Wang-Landau sampling in conjunction with a set of efficient Monte Carlo trial moves, we studied the adsorption of short HP lattice proteins on various simple patterned substrates and in particular for checkered patterned surfaces. In this work, a set of single-site mutated HP proteins is used to investigate the role of hydrophobicity of a protein chain and surface pattern for substrates with various pattern cell sizes relative to the protein’s native configuration. For most cases, we found that the adsorption transition occurs at a lower temperature, while the hydrophobic core formation is less affected. Additionally, the flattening procedure after the HP protein is adsorbed is more sensitive to the change in surface patterns and single-site mutations. These observations stay valid for both strongly and weakly attractive surfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Facile stamp patterning method for superhydrophilic/superhydrophobic surfaces

Patterning techniques are essential to many research fields such as chemistry, biology, medicine, and micro-electromechanical systems. In this letter, we report a simple, fast, and low-cost superhydrophobic patterning method using a superhydrophilic template. The technique is based on the contact stamping of the surface during hydrophobic dip coating. Surface characteristics were measured using scanning electron microscopy and energy-dispersive X-ray spectroscopic analysis. The results showed that the hydrophilic template, which was contacted with the stamp, was not affected by the hydrophobic solution. The resolution study was conducted using a stripe shaped stamp. The patterned line was linearly proportional to the width of the stamp line with a constant narrowing effect. A surface with regions of four different types of wetting was fabricated to demonstrate the patterning performance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Dual-Responsive Macromolecular Surfaces with Binary Patterns

The development of nanopatterned interfaces incorporating multiple stimuli-responsive polymers has great potential for advancing smart sensors and molecular capture devices, yet it remains challenging due to limitations in patterning techniques and “grafting from” methods. Here, we present a binary-patterned surface featuring honeycomb-shaped photothermal polypyrrole (PPy) and thermally responsive poly(ethylene glycol methyl ether acrylate-co-poly(ethylene glycol) methyl ether acrylate) [poly(EGMEA-co-PEGMEA)] brushes within the cavities, fabricated using colloidal lithography and surface-initiated photoinduced electron transfer-reversible addition–fragmentation chain transfer (SI-PET-RAFT) polymerization. The morphology of the surface can be precisely tuned by adjusting the height of each domain. This design integrates unique topographical features with the stimuli-responsiveness of the polymer, enabling the collapse of the copolymer brushes through direct heating or photothermal conversion of PPy under near-IR light. In conclusion, this innovative system offers potential capture-release functionality, providing versatility for diverse applications and enhancing adaptability across different functional scenarios.

Copolymers↗
DOE OSTI2026

Interplay of Quantum Size Effect and Tensile Strain on Surface Morphology of β-Sn(100) Islands

The quantum size effect (QSE) and strain effect are two key factors influencing the surface morphology of thin films, which can increase film surface roughness through QSE-induced thickness oscillation and strain-induced island formation, respectively. Surface roughness usually manifests in the early stages of film growth and diminishes beyond a critical thickness. In this work, we employ molecular beam epitaxy (MBE) to grow β-Sn(100) islands with varying thickness N on bilayer graphene-terminated 6H-SiC(0001) substrates. Scanning tunneling microscopy and spectroscopy measurements reveal an inverse surface roughness effect that highlights the interplay of QSE and misfit strain in shaping the surface morphology of β-Sn(100) islands. For N ≤ 10, the islands exhibit flat surfaces, while for N ≥ 26, the island surfaces become corrugated and patterned. For the intermediate range, i.e., 12 ≤ N ≤ 24, both flat and patterned surfaces coexist, with the percentage coverage of the patterned surface oscillating as a function of N. By performing density functional theory calculations, we demonstrate that the unusual surface pattern evolution in our MBE-grown β-Sn(100) islands is a result of the interplay between QSE-induced surface roughing and tensile strain-induced smoothening effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Diffusion-assisted growth of periodic patterns on metal surfaces

Periodic patterns formed on various solid surfaces could seriously affect the properties of materials. Understanding the underlying mechanism is a key step to apply and control pattern formation in many fields. In this work, periodic patterns induced by low energy plasma exposures on tungsten surfaces are observed and related new formation mechanisms are developed. Results from experiments and computer simulations demonstrate that atom diffusion accelerated by low energy and high flux exposures is the dominant mechanism for pattern formation. Additionally, a similar pattern formation has been confirmed by plasma exposure experiments on molybdenum. Based on this mechanism, patterns with controllable size and shape have been successfully prepared on tungsten surface by adjusting plasma exposure parameters, which may provide a new understanding of pattern formation and related surface damage in tungsten induced by plasma exposures.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Using Ambient Ion Beams to Write Nanostructured Patterns for Surface Enhanced Raman Spectroscopy

Electrolytic spray deposition was used to pattern surfaces with 2D metallic nanostructures. Spots that contain silver nanoparticles (AgNP) were created by landing solvated silver ions at desired locations using electrically floated masks to focus the metal ions to an area as little as 20 mm in diameter. The AgNPs formed are unprotected and their aggregates can be used for surface-enhanced Raman spectroscopy (SERS). The morphology and SERS activity of the NP structures were controlled by the surface coverage of landed silver ions. The NP structures created could be used as substrates onto which SERS samples were deposited or prepared directly on top of predeposited samples of interest. The evenly distributed hot spots in the micron-sized aggregates had an average SERS enhancement factor of 108. The surfaces showed SERS activity when using lasers of different wavelengths (532, 633, and 785 nm) and were stable in air.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2024

Tuning Surface Adhesion Using Grayscale Electron-beam Lithography

Surface texturing of manufactured products tailors their properties, such as friction, adhesion, biocompatibility, or fluid interactions. However, advancements in this area are largely the result of trial-and-effort testing and generally lack a science-guided framework for determining the surface topography that will optimize performance. The present investigation explores grayscale electron-beam lithography as a means to create multiscale surface patterns to control surface performance. Here, we created and characterized a set of surface textures on a silicon wafer; the textures were superpositions of sine waves of varying wavelengths and amplitudes. First, the multiscale topography of the patterned surface was characterized, using profilometry and atomic force microscopy, to understand its fidelity to the designed-in pattern. The results of this analysis demonstrated how grayscale lithography accurately controlled the lateral size of features but was less precise on the vertical height of the surface, and also introduced inherent roughness below the scale of patterning. Second, a micromechanical tester was used to characterize the adhesion of the surfaces with large-scale polished silicon spheres. The results showed that adhesion could be tailored, with significant contribution from all of the designed-in length scales of topography. The strength of adhesion did not correlate with conventional roughness parameters but could be accurately modeled using simple numerical integration. Taken together, this investigation demonstrates the promise and challenges of grayscale e-beam lithography with multiscale patterns as a method for the tailoring of surface performance.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗