Sulfur-induced corrosion of Au(111) studied by real-time STM

The interaction of sulfur with gold surfaces has attracted considerable interest due to numerous technological applications such as the formation of self-assembled monolayers (SAMs), use as a corrosion inhibitor, and as a chemical sensor. In this work, the interaction of sulfur with Au(111) at two different temperatures (300 K and 420 K) was studied by real-time scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). In the low coverage regime (< 0.1 monolayer), S modifies the surface stress leading to a lateral expansion of the Au surface layer. An ordered ({radical}3 x {radical}3)R30{sup o} sulfur adlayer develops as the coverage reaches {approx}0.3 ML. With further increasing S coverage the Au(111) surface undergoes a dynamic rearrangement while forming a two-dimensional AuS phase: gold surface atoms are removed from regular terrace sites and incorporated into the growing gold sulfide phase resulting in the appearance of pits and irregularly shaped AuS islands. Gold sulfide prepared at room temperature exhibits short-range order; an incommensurate, long-range ordered AuS phase develops upon annealing at 450-525 K. Higher temperatures lead to decomposition of the AuS corrosion film. Formation of an ordered AuS phase via rapid step retraction rather than etch pit formation is observed during S-interaction with Au(111) surfaces at 420 K. Our results shed new light on the S-Au(111) interaction

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

Dislocation nucleation in bcc Ta single crystals studied by nanoindentation

The study of dislocation nucleation in closed-packed metals by nanoindentation has recently attracted much interest. Here, we address the peculiarities of the incipient plasticity in body centered cubic (bcc) metals using low index Ta single-crystals as a model system. The combination of nanoindentation with high-resolution atomic force microscopy provides us with experimental atomic-scale information on the process of dislocation nucleation and multiplication. Our results reveal a unique deformation behavior of bcc Ta at the onset of plasticity which is distinctly different from that of closed-packed metals. Most noticeable, we observe only one rather than a sequence of discontinuities in the load-displacement curves. This and other differences are discussed in context of the characteristic plastic deformation behavior of bcc metals

Massachusetts Adult Tobacco Survey: Tobacco Use and Attitudes After Seven Years of The Massachusetts Tobacco Control Program, Technical Report & Tables 1993 — 2000

The Massachusetts Tobacco Control Program was launched in October of 1993. At that time, the Center for Survey Research conducted the Massachusetts Tobacco Survey (MTS), a comprehensive survey of adults and teens living in Massachusetts. The purpose of the survey was to collect baseline data on the prevalence of tobacco use among adults and teens in the Commonwealth and on issues related to the likelihood of smoking cessation or initiation. The survey also assessed the prevalence of restrictive smoking policies, and attitudes about tobacco control measures. The baseline data serve as a standard against which the impact of various programs sponsored by the Department of Public Health can be assessed. Technical details about the MTS and reports of the results are available from the Massachusetts Department of Public Health. In January, 1995 the Department of Public Health contracted with the Center for Survey Research to carry out a second survey monitoring tobacco use and related attitudes and behaviors among adults in the Commonwealth. This second survey, known as the Massachusetts Adult Tobacco Survey (MATS), has been carried out monthly since March of 1995. Data are aggregated at the end of each calendar year. MATS is similar to the MTS in that initial screening interviews are carried out with a household member who provides demographic and smoking status information about other adults in the household. One member of the household is then randomly selected for extended interview. The annual sample for this survey is smaller than that used for the MTS and does not include teens. It also differs from the MTS in that smokers were not over-sampled, nor were members of minority groups. The sample was geographically stratified as was the MTS. (More details on the sampling design are presented in Chapter I.) Technical Reports are available for the 1993 MTS survey, and for the 1995 through 1999 MATS surveys. Please refer to those reports for descriptions of the respective surveys and a more general discussion of the use of the telephone survey for data collection. This report presents methodological details of the 2000 MATS. It contains an appendix of tables of major results for data collected each year. Nontechnical reports describing the major results are available from the Massachusetts Department of Public Health

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

Selective Thermal Reduction of Single-layer MoO3 nanostructures on Au(111)

MoO{sub 3} is an interesting oxide prototype because its catalytic activity is sensitive to the presence and nature of defects. In this work, we demonstrate that we can control the number of defects in single-layer MoO{sub 3} nanostructures grown on Au(111) by a simple thermal reduction treatment. X-ray photoelectron spectroscopy demonstrates the formation of Mo{sup 5+} species and oxygen vacancies during annealing at 650 K. The percentage of Mo{sup 5+} increases with the duration of annealing, until a stable composition containing 50% Mo{sup 6+} and 50% Mo{sup 5+} is obtained. Surprisingly, the formation of lower oxidation states such as Mo{sup 4+} was not observed. The reduced MoO{sub x} islands remain one layer high, based on scanning tunneling microscope (STM) images. The two-dimensional nature of the reduced oxide nanocrystals may be due to a large barrier for structural reorganization and, thus, may account for the absence of Mo oxidation states lower than +5. Based on scanning tunneling microscopy images and density functional calculations, we propose that the formation of Mo{sup 5+} ions during annealing is not associated with formation of oxygen point defects, but can be attributed to the formation of extended one-dimensional shear defects. These reduced structures are useful for studying the dependence of reactivity on defect type, and present exciting possibilities for chemical sensors and other applications

The ePetri dish, an on-chip cell imaging platform based on subpixel perspective sweeping microscopy (SPSM)

We report a chip-scale lensless wide-field-of-view microscopy imaging technique, subpixel perspective sweeping microscopy, which can render microscopy images of growing or confluent cell cultures autonomously. We demonstrate that this technology can be used to build smart Petri dish platforms, termed ePetri, for cell culture experiments. This technique leverages the recent broad and cheap availability of high performance image sensor chips to provide a low-cost and automated microscopy solution. Unlike the two major classes of lensless microscopy methods, optofluidic microscopy and digital in-line holography microscopy, this new approach is fully capable of working with cell cultures or any samples in which cells may be contiguously connected. With our prototype, we demonstrate the ability to image samples of area 6 mm × 4 mm at 660-nm resolution. As a further demonstration, we showed that the method can be applied to image color stained cell culture sample and to image and track cell culture growth directly within an incubator. Finally, we showed that this method can track embryonic stem cell differentiations over the entire sensor surface. Smart Petri dish based on this technology can significantly streamline and improve cell culture experiments by cutting down on human labor and contamination risks

Deformation Behavior of Nanoporous Metals

Nanoporous open-cell foams are a rapidly growing class of high-porosity materials (porosity {ge} 70%). The research in this field is driven by the desire to create functional materials with unique physical, chemical and mechanical properties where the material properties emerge from both morphology and the material itself. An example is the development of nanoporous metallic materials for photonic and plasmonic applications which has recently attracted much interest. The general strategy is to take advantage of various size effects to introduce novel properties. These size effects arise from confinement of the material by pores and ligaments, and can range from electromagnetic resonances to length scale effects in plasticity. In this chapter we will focus on the mechanical properties of low density nanoporous metals and how these properties are affected by length scale effects and bonding characteristics. A thorough understanding of the mechanical behavior will open the door to further improve and fine-tune the mechanical properties of these sometimes very delicate materials, and thus will be crucial for integrating nanoporous metals into products. Cellular solids with pore sizes above 1 micron have been the subject of intense research for many years, and various scaling relations describing the mechanical properties have been developed.[4] In general, it has been found that the most important parameter in controlling their mechanical properties is the relative density, that is, the density of the foam divided by that of solid from which the foam is made. Other factors include the mechanical properties of the solid material and the foam morphology such as ligament shape and connectivity. The characteristic internal length scale of the structure as determined by pores and ligaments, on the other hand, usually has only little effect on the mechanical properties. This changes at the submicron length scale where the surface-to-volume ratio becomes large and the effect of free surfaces can no longer be neglected. As the material becomes more and more constraint by the presence of free surfaces, length scale effects on plasticity become more and more important and bulk properties can no longer be used to describe the material properties. Even the elastic properties may be affected as the reduced coordination of surface atoms and the concomitant redistribution of electrons may soften or stiffen the material. If, and to what extend, such length scale effects control the mechanical behavior of nanoporous materials depends strongly on the material and the characteristic length scale associated with its plastic deformation. For example, ductile materials such as metals which deform via dislocation-mediated processes can be expected to exhibit pronounced length scale effects in the sub-micron regime where free surfaces start to constrain efficient dislocation multiplication. In this chapter we will limit our discussion to our own area of expertise which is the mechanical behavior of nanoporous open-cell gold foams as a typical example of nanoporous metal foams. Throughout this chapter we will review our current understanding of the mechanical properties of nanoporous open-cell foams including both experimental and theoretical studies

Breaking the Screen: Interaction Across Touchscreen Boundaries in Virtual Reality for Mobile Knowledge Workers.

Virtual Reality (VR) has the potential to transform knowledge work. One advantage of VR knowledge work is that it allows extending 2D displays into the third dimension, enabling new operations, such as selecting overlapping objects or displaying additional layers of information. On the other hand, mobile knowledge workers often work on established mobile devices, such as tablets, limiting interaction with those devices to a small input space. This challenge of a constrained input space is intensified in situations when VR knowledge work is situated in cramped environments, such as airplanes and touchdown spaces. In this paper, we investigate the feasibility of interacting jointly between an immersive VR head-mounted display and a tablet within the context of knowledge work. Specifically, we 1) design, implement and study how to interact with information that reaches beyond a single physical touchscreen in VR; 2) design and evaluate a set of interaction concepts; and 3) build example applications and gather user feedback on those applications.Comment: 10 pages, 8 figures, ISMAR 202

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