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Huang, Hanchen

Publications and source records attributed to Huang, Hanchen.

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Low-temperature bonding with spaced nanorods and eutectic alloys

Bonded surfaces are formed by adhering first nanorods and second nanorods to respective first and second surfaces. The first shell is formed on the first nanorods and the second shell is formed on the second nanorods, wherein at least one of the first nanorods and second nanorods, and the first shell and the second shell are formed of distinct metals. The surfaces are then exposed to at least one condition that causes the distinct metals to form an alloy, such as eutectic alloy having a melting point below the temperature at which the alloy is formed, thereby bonding the surfaces upon which solidification of the alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Theory of Growing Crystalline Nanorods

Energy harvesting and storage benefit from and depend on the design of nanomaterials such nanorods. Without design, the nanorods can take numerous configurations that correspond to local minima of energy. Focusing on the science of nanorod growth, the PI has developed a theoretical framework of nanorod growth, and designed and experimentally grown small and well-separated nanorods using physical vapor deposition. Building on the framework, this project in the next three years will focus on: (1) Identifying atomic mechanisms of step bunching and dissociation; (2) Analytically formulating the competition of monolayer and multiple-layer steps to derive closed-form expressions of monolayer and multiple-layer step populations and nanorod diameters; (3) Designing nanorods by using the scientific insights from the closed-form theory (as well as atomistic simulations); and (4) Exploring technological benefits of the scientific advancements. This research relies on the synergy of analytical formulations, atomistic simulations (density-functional-theory or DFT based ab initio, classical molecular dynamics, lattice kinetic Monte Carlo), and experiments; the prototype material is face-centered-cubic Cu. If successful, the proposed research will result in a scientific theory of nanorod growth, which in turn enables discoveries of new nanorods and subsequently innovations of energy technologies. As one example, the enabled discovery of small and well-separated metallic nanorods has subsequently led to the innovation of a technology - metallic glue in ambient. This technology has been covered in ~200 news reports in 20-30 countries during the first two months of 2016; examples of new agencies include Fortune Magazine, Popular Mechanics, Yahoo News, and Fox News.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Simultaneous Thermal Stability and Ultrahigh Sensitivity of Heterojunction SERS Substrates

This paper reports the design of Ag-Al 2 O 3 -Ag heterojunctions based on Ag nanorods (AgNRs) and their applications as thermally stable and ultrasensitive substrates of surface-enhanced Raman scattering (SERS). Specifically, an ultrathin Al 2 O 3 capping layer of 10 nm on top of AgNRs serves to slow down the surface diffusion of Ag at high temperatures. Then, an additional Ag layer on top of the capping layer creates AgNRs-Al 2 O 3 -Ag heterojunctions, which lead to giant enhancement of electromagnetic fields within the Al 2 O 3 gap regions that could boost the SERS enhancement. As a result of this design, the SERS substrates are thermally stable up to 200 °C, which has been increased by more than 100 °C compared with bare AgNRs, and their sensitivity is about 400% that of pure AgNRs. This easy yet effective capping approach offers a pathway to fabricate ultrasensitive, thermally stable and easily prepared SERS sensors, and to extend SERS applications for high-temperature detections, such as monitoring in situ the molecule reorientation process upon annealing. Such simultaneous achievement of thermal stability and SERS sensitivity represents a great advance in the design of SERS sensors and will inspire the fabrication of novel hetero-nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A theory of growing crystalline nanorods – Mode Ⅰ

Nanorods grow in two possible modes during physical vapor deposition (PVD). In mode I, monolayer surface steps dictate the diameter of nanorods. In mode II, multiple-layer surface steps dictate the diameter, which is the smallest possible under physical vapor deposition [5,10]. Here this paper reports closed-form theories of terrace lengths and nanorod diameter during the growth in mode I, as a function of deposition conditions. The accompanying lattice kinetic Monte Carlo simulations verify these theories. This study reveals that (1) quasi-steady growth exists for each set of nanorod growth conditions, and (2) the characteristic length scales, including terrace lengths and nanorod diameter at the quasi-steady state, depend on the deposition conditions – deposition rate F, substrate temperature T, and incidence angle θ – only as a function of l 2D /tan θ, with l2D = 2($\frac{v_{2D}}{F cos θ}$)$^\frac{1}{3}$ as a diffusion-limited length scale and v 2D as the atomic diffusion jump rate over monolayer surface steps.

42 ENGINEERING↗
DOE OSTI2017

Degradation Mechanism of Ag Nanorods for Surface Enhanced Raman Spectroscopy

This paper reports a degradation mechanism of silver (Ag) nanorods that are used as substrates for surface enhanced Raman spectroscopy (SERS). The attachment of sulfur and hydrocarbons to the surfaces of Ag nanorods is observed when they are stored in ambient over four months. This attachment is observed to correlate with ~20% decrease in SERS signal. The attachment, and thereby the signal degradation, takes three weeks to complete, and remains stable after the initial decay over the rest of the four month test period. While this degradation mechanism is a limitation to the gross enhancement, the ensuing stability beyond three weeks is encouraging.

42 ENGINEERING↗
DOE OSTI2017

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {$\bar{1}$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$\bar{1}$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$\bar{1}$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Control of Separation and Diameter of Ag Nanorods through Self-organized Seeds

This paper proposes a mechanism of controlling the diameter and separation of metallic nanorods from physical vapor deposition through self-organized seeds and experimentally demonstrates the feasibility using Ag as the prototype metal, In as the seed and Si the substrate. Being non-wetting on Si substrates, deposited In atoms self-organize into islands. Subsequently deposited Ag atoms attach to In islands, rather than to Si substrates, due to preferential bonding and geometrical shadowing. The experimental results show that self-organized In seeds of 5 nm nominal thickness give rise to the best separation and the smallest diameter of Ag nanorods.

Science & Technology - Other Topics↗
DOE OSTI2015

Combined hydrophobicity and mechanical durability through surface nanoengineering

This paper reports combined hydrophobicity and mechanical durability through the nanoscale engineering of surfaces in the form of nanorod-polymer composites. Specifically, the hydrophobicity derives from nanoscale features of mechanically hard ZnO nanorods and the mechanical durability derives from the composite structure of a hard ZnO nanorod core and soft polymer shell. Experimental characterization correlates the morphology of the nanoengineered surfaces with the combined hydrophobicity and mechanical durability, and reveals the responsible mechanisms. Such surfaces may find use in applications, such as boat hulls, that benefit from hydrophobicity and require mechanical durability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Enhanced thermal stability of Ag nanorods through capping

Ag nanorods may serve as sensors in the detection of trace amounts of chemical agents, even single molecules, through surface enhanced Raman spectroscopy (SERS). However, thermal coarsening of Ag nanorods near room temperature limits their applications. This letter proposes the use of a thin oxide capping layer to enhance the thermal stability of Ag nanorods beyond 100 °C. Using electron microscopy characterization and SERS tests, the authors show that the proposed method is effective in stabilizing both morphology and sensitivity of Ag nanorods. The results of this work extend the applicability of Ag nanorods as chemical sensors to higher temperatures.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Control of New Kinetic Barriers and Design of Nanorods

The report will follow a theme of theoretical developments. However, it should be noted that this project has always relied on the synergy of theoretical formulations, atomistic simulations, and experiments; and it will continue to do so. In the following, we start with a background section 1 to briefly introduce the relevant developments by others, and the first foundational element from our own work during earlier project periods. Afterwards, we present the three new foundational elements in sections 2-­4, highlight scientific and technological impacts of the theoretical developments in section 5, and finally present an “accidental” development of a computational tool in section 6.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Pressure effect on stabilities of self-Interstitials in HCP structures

The self-interstitial atoms (SIAs) mediate the evolution of micro-structures which is crucial in understanding the instabilities of hexagonal close packed (HCP) structures. Taken zirconium as a prototype, we investigate the pressure effect on the stabilities of SIAs using first-principles calculations based on density-functional theory. We found that the pressure greatly affects the stability of the SIAs. The SIAs in basal planes are more stable to changes in pressure. The most stable SIA configuration changes from basal octahedral (BO) to octahedral (O) at pressure of 21 GPa. The lowest formation enthalpy configuration switches from BO to S (split-dumbbell) at P = 30 GPa. Our results reveal that it is important to take the pressure effect into account when predicting the micro-structural evolution of HCP structures.

Ab initio calculation↗