Employing the Au(111) surface as substrate for the synthesis of two-dimensional metal oxide and metal sulfide structures

Novel properties of a material arise by reducing the length scale from macroscopic to the nanometer scale. This effect can be exploited to engineer materials with unique electronic, catalytic, optical and mechanical properties. The goal is to develop materials with unique properties that meet the design requirements for a particular technology. In this thesis, I will demonstrate that we are able to synthesize novel, nanocrystalline monolayer structures of MoO3, TiS2, MoS2 and AuS on Au(111). In the course of this thesis I will demonstrate that the Au(111) surface is anything but a static, inert surface. I will discuss various levels of interaction between the Au(111) surface and various adsorbates and adsorbed monolayer structures. Specifically, I will discuss the role of surface stress, the enhanced reactivity of under-coordinated Au atoms such as step edge atoms or surface atoms, and surface alloying. We will see that: the surface stress of Au(111) is modified by small amounts of adsorbed sulfur causing a lifting of the herringbone reconstruction; high sulfur coverages lead to the corrosion of Au(111) surfaces and formation of a 2D AuS phase; the step edges of Au(111) are reactive sites for decomposition of Mo(CO)6; place exchange with physical vapour deposited Mo occurs at the elbow sites of the herringbone reconstruction; Mo deposited on Au(111) at elevated temperatures leads to formation of a substitutional surface alloy; bond lengths and bond angles within nanocrystalline MoO3 structures on Au(111) are distorted to fit the symmetry of the underlying gold substrate; the orientation of triangular TiS2 nanocrystals on Au(111) is affected by a strain field interaction; Au clusters exhibit a high reactivity towards SO2 decomposition. This list of examples demonstrates that the Au(111) surface can be a very dynamic rather than a static substrate

Structure of incommensurate gold sulfide monolayer on Au(111)

We develop an atomic-scale model for an ordered incommensurate gold sulfide (AuS) adlayer which has previously been demonstrated to exist on the Au(111) surface, following sulfur deposition and annealing to 450 K. Our model reproduces experimental scanning tunneling microscopy images. Using state-of-the-art Wannier-function-based techniques, we analyze the nature of bonding in this structure and provide an interpretation of the unusual stoichiometry of the gold sulfide layer. The proposed structure and its chemistry have implications for related S-Au interfaces, as in those involved in self-assembled monolayers of thiols on Au substrates

Synthesis of TiO2 nanoparticles on the Au(111) surface

The growth of titanium oxide nanoparticles on reconstructed Au(111) surfaces was investigated by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Ti was deposited by physical vapor deposition at 300 K. Regular arrays of titanium nanoparticles form by preferential nucleation of Ti at the elbow sites of the herringbone reconstruction. Titanium oxide clusters were synthesized by subsequent exposure to O{sub 2} at 300 K. Two- and three-dimensional titanium oxide nanocrystallites form during annealing in the temperature range from 600 to 900 K. At the same time, the Au(111) surface assumes a serrated, <110> oriented step-edge morphology, suggesting step-edge pinning by titanium oxide nanoparticles. The oxidation state of these titanium oxide nanoparticles varies with annealing temperature. Specifically, annealing to 900 K results in the formation of stoichiometric TiO{sub 2} nanocrystals as judged by the observed XPS binding energies. Nano-dispersed TiO{sub 2} on Au(111) is an ideal system to test the various models explaining the enhanced catalytic reactivity of supported Au nanoparticles

Ultra-low-density digitally architected carbon with a strutted tube-in-tube structure

Porous materials with engineered stretching-dominated lattice designs, which offer attractive mechanical properties with ultra-light weight and large surface area for wide-ranging applications, have recently achieved near-ideal linear scaling between stiffness and density. Here, rather than optimizing the microlattice topology, we explore a different approach to strengthen low-density structural materials by designing tube-in-tube beam structures. We develop a process to transform fully dense, three-dimensional printed polymeric beams into graphitic carbon hollow tube-in-tube sandwich morphologies, where, similar to grass stems, the inner and outer tubes are connected through a network of struts. Compression tests and computational modelling show that this change in beam morphology dramatically slows down the decrease in stiffness with decreasing density. In situ pillar compression experiments further demonstrate large deformation recovery after 30-50% compression and high specific damping merit index. Our strutted tube-in-tube design opens up the space and realizes highly desirable high modulus-low density and high modulus-high damping material structures

Ultralight, ultrastiff mechanical metamaterials

The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material

ALD Functionalized Nanoporous Gold: Thermal Stability, Mechanical Properties, and Catalytic Activity

Nanoporous metals have many technologically promising applications but their tendency to coarsen limits their long-term stability and excludes high temperature applications. Here, we demonstrate that atomic layer deposition (ALD) can be used to stabilize and functionalize nanoporous metals. Specifically, we studied the effect of nanometer-thick alumina and titania ALD films on thermal stability, mechanical properties, and catalytic activity of nanoporous gold (np-Au). Our results demonstrate that even only one-nm-thick oxide films can stabilize the nanoscale morphology of np-Au up to 1000 C, while simultaneously making the material stronger and stiffer. The catalytic activity of np-Au can be drastically increased by TiO{sub 2} ALD coatings. Our results open the door to high temperature sensor, actuator, and catalysis applications and functionalized electrodes for energy storage and harvesting applications

Elevated plasma levels of cardiac troponin-I predict left ventricular systolic dysfunction in patients with myotonic dystrophy type 1:A multicentre cohort follow-up study

Objective: High sensitivity plasma cardiac troponin-I (cTnI) is emerging as a strong predictor of cardiac events in a variety of settings. We have explored its utility in patients with myotonic dystrophy type 1 (DM1). Methods: 117 patients with DM1 were recruited from routine outpatient clinics across three health boards. A single measurement of cTnI was made using the ARCHITECT STAT Troponin I assay. Demographic, ECG, echocardiographic and other clinical data were obtained from electronic medical records. Follow up was for a mean of 23 months. Results: Fifty five females and 62 males (mean age 47.7 years) were included. Complete data were available for ECG in 107, echocardiography in 53. Muscle Impairment Rating Scale score was recorded for all patients. A highly significant excess (p = 0.0007) of DM1 patients presented with cTnI levels greater than the 99th centile of the range usually observed in the general population (9 patients; 7.6%). Three patients with elevated troponin were found to have left ventricular systolic dysfunction (LVSD), compared with four of those with normal range cTnI (33.3% versus 3.7%; p = 0.001). Sixty two patients had a cTnI level < 5ng/L, of whom only one had documented evidence of LVSD. Elevated cTnI was not predictive of severe conduction abnormalities on ECG, or presence of a cardiac device, nor did cTnI level correlate with muscle strength expressed by Muscle Impairment Rating Scale score. Conclusions: Plasma cTnI is highly elevated in some ambulatory patients with DM1 and shows promise as a tool to aid cardiac risk stratification, possibly by detecting myocardial involvement. Further studies with larger patient numbers are warranted to assess its utility in this setting

Verwendung der Au(111) Oberflaeche fuer die Synthese von zweidimensionalen Metalloxid- und Metallsulfid-Strukturen

Novel properties of a material arise by reducing the length scale from macroscopic to the nanometer scale. This effect can be exploited to engineer materials with unique electronic, catalytic, optical and mechanical properties. The goal is to develop materials with unique properties that meet the design requirements for a particular technology. In this thesis, I will demonstrate that we are able to synthesize novel, nanocrystalline monolayer structures of MoO3, TiS2, MoS2 and AuS on Au(111). In the course of this thesis I will demonstrate that the Au(111) surface is anything but a static, inert surface. I will discuss various levels of interaction between the Au(111) surface and various adsorbates and adsorbed monolayer structures. Specifically, I will discuss the role of surface stress, the enhanced reactivity of under-coordinated Au atoms such as step edge atoms or surface atoms, and surface alloying. We will see that: the surface stress of Au(111) is modified by small amounts of adsorbed sulfur causing a lifting of the herringbone reconstruction; high sulfur coverages lead to the corrosion of Au(111) surfaces and formation of a 2D AuS phase; the step edges of Au(111) are reactive sites for decomposition of Mo(CO)6; place exchange with physical vapour deposited Mo occurs at the elbow sites of the herringbone reconstruction; Mo deposited on Au(111) at elevated temperatures leads to formation of a substitutional surface alloy; bond lengths and bond angles within nanocrystalline MoO3 structures on Au(111) are distorted to fit the symmetry of the underlying gold substrate; the orientation of triangular TiS2 nanocrystals on Au(111) is affected by a strain field interaction; Au clusters exhibit a high reactivity towards SO2 decomposition. This list of examples demonstrates that the Au(111) surface can be a very dynamic rather than a static substrate

Engineering on-chip nanoporous gold material libraries via precision photothermal treatment.

Libraries of nanostructured materials on a single chip are a promising platform for high throughput and combinatorial studies of structure-property relationships in the fields of physics and biology. Nanoporous gold (np-Au), produced by an alloy corrosion process, is a nanostructured material specifically suited for such studies because of its self-similar thermally induced coarsening behavior. However, traditional heat application techniques for the modification of np-Au are bulk processes that cannot be used to generate a library of different pore sizes on a single chip. Here, laser micro-processing offers an attractive solution to this problem by providing a means to apply energy with high spatial and temporal resolution. In the present study we use finite element multiphysics simulations to predict the effects of laser mode (continuous-wave vs. pulsed) and thermal conductivity of the supporting substrate on the local np-Au film temperatures during photothermal annealing. Based on these results we discuss the mechanisms by which the np-Au network is coarsened. Thermal transport simulations predict that continuous-wave mode laser irradiation of np-Au thin films on a silicon substrate supports the widest range of morphologies that can be created through photothermal annealing of np-Au. Using the guidance provided by simulations, we successfully fabricate an on-chip material library consisting of 81 np-Au samples of 9 different morphologies for use in the parallel study of structure-property relationships