Julia W. P. Hsu

Bio: Julia W. P. Hsu is an academic researcher from Washington University in St. Louis. The author has contributed to research in topics: Substrate (chemistry) & Self-assembled monolayer. The author has an hindex of 2, co-authored 3 publications receiving 26 citations.

Electron Beam-Induced Damage of Alkanethiolate Self-Assembled Monolayers Adsorbed on GaAs (001): A Static SIMS Investigation†

Abstract: We have investigated the reaction pathways involved in the electron-beam-induced damage of −CH3, −OH, and −COOH terminated alkanethiolate self-assembled monolayers (SAMs) adsorbed on GaAs (001) using time-of-flight secondary ion mass spectrometry. Upon electron beam exposure, the monolayers dehydrogenate, leading to the formation of C═C bonds, cross-links, and polycyclic aromatic hydrocarbons (PAHs). We also observe C−S bond scission. The data suggest that the electron beam damage is not uniform along the alkanethiol backbone. Upon electron beam exposure, we observe the loss of CO2 and H2O from the −COOH and −OH terminated SAMs, respectively, indicating that the terminal groups decompose. Although the SAM degradation mechanism is similar to that previously reported for alkanethiolate SAMs adsorbed on metals, there are some important differences. First, the electron dose required to form C═C bonds and PAHs is much smaller than for SAMs adsorbed on metals. Second, although we observe C−S bond scission, we d...

Electron-Beam-Induced Damage of Alkanethiolate Self-Assembled Monolayers (SAMs): Dependence on Monolayer Structure and Substrate Conductivity

Abstract: We report the first studies of the relative importance of substrate conductivity and monolayer structure on the electron-beam-induced damage of alkanethiolate self-assembled monolayers (SAMs) adsorbed on Au and GaAs(001) using time-of-flight secondary-ion mass spectrometry. The results clearly show that the extent of damage observed is strongly dependent on the electrical conductivity of the substrate; at a given electron dose, the amount of degradation is greatest for SAMs adsorbed on the least conductive substrate, semi-insulating GaAs(001). This is because there is a buildup of static charge at the substrate/SAM interface, whereas for an electrically conductive substrate, electrons can be conducted away from the surface, leading to less electron-beam-induced damage. The monolayer structure also greatly affects the amount of electron beam damage. Disordered SAMs, such as nonanethiol adsorbed on Au, undergo more degradation at a given electron dose than ordered SAMs, such as octadecanethiol (ODT) adsorbe...

RF/Microwave Properties of Nanotubes and Nanowires: LDRD Project 105876 Final Report

Abstract: LDRD Project 105876 was a research project whose primary goal was to discover the currently unknown science underlying the basic linear and nonlinear electrodynamic response of nanotubes and nanowires in a manner that will support future efforts aimed at converting forefront nanoscience into innovative new high-frequency nanodevices. The project involved experimental and theoretical efforts to discover and understand high frequency (MHz through tens of GHz) electrodynamic response properties of nanomaterials, emphasizing nanowires of silicon, zinc oxide, and carbon nanotubes. While there is much research on DC electrical properties of nanowires, electrodynamic characteristics still represent a major new frontier in nanotechnology. We generated world-leading insight into how the low dimensionality of these nanomaterials yields sometimes desirable and sometimes problematic high-frequency properties that are outside standard model electron dynamics. In the cases of silicon nanowires and carbon nanotubes, evidence of strong disorder or glass-like charge dynamics was measured, indicating that these materials still suffer from serious inhomogeneities that limit there high frequency performance. Zinc oxide nanowires were found to obey conventional Drude dynamics. In all cases, a significant practical problem involving large impedance mismatch between the high intrinsic impedance of all nanowires and nanotubes and high-frequency test equipment had to be overcome.

Subnanometre ligand-shell asymmetry leads to Janus-like nanoparticle membranes

Abstract: Self-assembly of nanoparticles at fluid interfaces has emerged as a simple yet efficient way to create two-dimensional membranes with tunable properties. In these membranes, inorganic nanoparticles are coated with a shell of organic ligands that interlock as spacers and provide tensile strength. Although curvature due to gradients in lipid-bilayer composition and protein scaffolding is a key feature of many biological membranes, creating gradients in nanoparticle membranes has been difficult. Here, we show by X-ray scattering that nanoparticle membranes formed at air/water interfaces exhibit a small but significant ∼6 A difference in average ligand-shell thickness between their two sides. This affects surface-enhanced Raman scattering and can be used to fold detached free-standing membranes into tubes by exposure to electron beams. Molecular dynamics simulations elucidate the roles of ligand coverage and mobility in producing and maintaining this asymmetry. Understanding this Janus-like membrane asymmetry opens up new avenues for designing nanoparticle superstructures.

Mechanical characterization of carbon nanomembranes from self-assembled monolayers

Abstract: This paper reports on the mechanical characterization of carbon nanomembranes (CNMs) with a thickness of 1 nm that are fabricated by electron-induced crosslinking of aromatic self-assembled monolayers (SAMs). A novel type of in situ bulge test employing an atomic force microscope (AFM) is utilized to investigate their mechanical properties. A series of biphenyl-based molecules with different types of terminal and/or anchor groups were used to prepare the CNMs, such as 4'-[(3-trimethoxysilyl)propoxy]-[1,1'-biphenyl]-4-carbonitrile (CBPS), 1,1'-biphenyl-4-thiol (BPT) and 4-nitro-1,1'-biphenyl-4-thiol (NBPT). The elastic properties, viscoelastic behaviors and ultimate tensile strength of these biphenyl-based CNMs are investigated and discussed.

Strain patterning and direct measurement of Poisson's ratio in nanoparticle monolayer sheets.

Abstract: Close-packed monolayers self-assembled from ligated nanoparticles can form 10 nm thin sheets that stretch over micrometer-wide holes. Employing electron and focused ion beams, we show that one can locally tailor the strain in such sheets while they remain clamped around their perimeter, making it possible to imprint strain fields by design. Furthermore, using the nanoparticles themselves to track imposed strain gradients allows for the first direct measurement of Poisson’s ratio in these two-dimensional materials.

Relative Thermal Stability of Thiolate- and Selenolate-Bonded Aromatic Monolayers on the Au(111) Substrate

Abstract: The thermal stability of self-assembled monolayers (SAMs) is of fundamental importance for the majority of their applications. It strongly depends on the type of chemical group used for bonding the molecules forming the SAMs to the selected substrate. Here, we compare the impact of using S and Se bonding groups on the thermal stability of aromatic model SAMs based on naphthalene, containing a polar substituent, and formed on a Au(111) substrate. Using a combination of secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) while heating the samples, we show that the thermal stability of S-bonded SAMs is higher although the bonding between Se and the Au substrate is stronger. This seeming contradiction is found to result from a higher stability of the S–C compared to the Se–C bond. The latter forms the weakest link in the SAMs with Se anchor and, thus, controls its thermal stability. These conclusions are supported by state-of-the art dispersion-corrected density functional theory...

Thiol Terminated 1,4-Benzenedimethanethiol Self-Assembled Monolayers on Au(111) and InP(110) from Vapor Phase

Abstract: We present results of a clean vacuum evaporative adsorption method of assembly of the conjugated dithiol molecule 1,4-benzenedimethanethiol on the surfaces of gold and indium phosphide. Measurements of direct recoil spectroscopy with time-of-flight analysis show in both cases formation of a self-assembled monolayer (SAM) with S atoms available at the SAM-vacuum interface. Investigation of the adsorption kinetics shows that a lying-down phase is formed at low exposures, which precedes the standing up SAM phase. The standing up SAM formation requires exposures of the order of a mega Langmuir. A study of the SAM stability with temperature shows that the S terminated layer survives up to ∼370 K, above this temperature a reordering of the layer takes place where S atoms are no longer available at the vacuum interface. Final desorption occurs around 450 K for Au and around 500K for InP.