A Comparison of Site Manager Competencies and Attributes in Ireland with those of the Site Superintendent in the United States

The construction industry is one of the oldest internationalized economic sectors dating back more than 100 years. The role of construction site manager or superintendent is one of the most important contributing to project success. In 2013 the authors utilized mixed methods research to determine which Site Manager competencies and attributes were most important for project success in Ireland. These data were compared to a 2010 research project in the United States which used a similar survey to identify construction Superintendents’ competencies and attributes required forsuccess. Forty-two competencies and attributes were identified and ranked in order of importance. Comparing data gathered in both studies indicates that there is no statistically significant difference in the ranking of 31 of the competencies and attributes required for construction site manager and superintendent success. The number one ranked competency for Superintendent success in the United States and Site Manager Success in Ireland is the “Ability to Plan Ahead”. Having a “Strong Work Ethic” was ranked number three in both countries. Five competencies and attributes were significantly more important for a superintendent’s success in the United States, and sixcompetencies and attributes were significantly more important for a Site Managers’ success in Ireland

Monolayer MoS2 strained to 1.3% with a microelectromechanical system

We report on a modified transfer technique for atomically thin materials integrated onto microelectromechanical systems (MEMS) for studying strain physics and creating strain-based devices. Our method tolerates the non-planar structures and fragility of MEMS, while still providing precise positioning and crack free transfer of flakes. Further, our method used the transfer polymer to anchor the 2D crystal to the MEMS, which reduces the fabrication time, increases the yield, and allowed us to exploit the strong mechanical coupling between 2D crystal and polymer to strain the atomically thin system. We successfully strained single atomic layers of molybdenum disulfide (MoS2) with MEMS devices for the first time and achieved greater than 1.3% strain, marking a major milestone for incorporating 2D materials with MEMS We used the established strain response of MoS2 Raman and Photoluminescence spectra to deduce the strain in our crystals and provide a consistency check. We found good comparison between our experiment and literature.Published versio

Voltage gated inter-cation selective ion channels from graphene nanopores

With the ability to selectively control ionic flux, biological protein ion channels perform a fundamental role in many physiological processes. For practical applications that require the functionality of a biological ion channel, graphene provides a promising solid-state alternative, due to its atomic thinness and mechanical strength. Here, we demonstrate that nanopores introduced into graphene membranes, as large as 50 nm in diameter, exhibit inter-cation selectivity with a ~20x preference for K+ over divalent cations and can be modulated by an applied gate voltage. Liquid atomic force microscopy of the graphene devices reveals surface nanobubbles near the pore to be responsible for the observed selective behavior. Molecular dynamics simulations indicate that translocation of ions across the pore likely occurs via a thin water layer at the edge of the pore and the nanobubble. Our results demonstrate a significant improvement in the inter-cation selectivity displayed by a solid-state nanopore device and by utilizing the pores in a de-wetted state, offers an approach to fabricating selective graphene membranes that does not rely on the fabrication of sub-nm pores

Adhesion of 2D MoS2_2 to Graphite and Metal Substrates Measured by a Blister Test

Using a blister test, we measured the work of separation between MoS$_2$ membranes from metal, semiconductor, and graphite substrates. We found a work of separation ranging from 0.11 +- 0.05 J/m^2 for chromium to 0.39 +- 0.1 J/m^2 for graphite substrates. In addition, we measured the work of adhesion of MoS$_2$ membranes over these substrates and observed a dramatic difference between the work of separation and adhesion which we attribute to adhesion hysteresis. Due to the prominent role that adhesive forces play in the fabrication and functionality of devices made from 2D materials, an experimental determination of the work of separation and adhesion as provided here will help guide their development

Adhesion, Stiffness and Instability in Atomically Thin MoS2 Bubbles

We measured the work of separation of single and few-layer MoS2 membranes from a SiOx substrate using a mechanical blister test, and found a value of 220 +- 35 mJ/m^2. Our measurements were also used to determine the 2D Young's modulus of a single MoS2 layer to be 160 +- 40 N/m. We then studied the delamination mechanics of pressurized MoS2 bubles, demonstrating both stable and unstable transitions between the bubbles' laminated and delaminated states as the bubbles were inflated. When they were deflated, we observed edge pinning and a snap-in transition which are not accounted for by the previously reported models. We attribute this result to adhesion hysteresis and use our results to estimate the work of adhesion of our membranes to be 42 +- 20 mJ/m^2

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum, and find a linear tuning rate of the optical band gap of 99 meV/%. This method is then used to study the PL spectra of bilayer and trilayer devices under strain, and to find the shift rates and Gr\"uneisen parameters of two Raman modes in monolayer MoS2. Finally, we use this result to show that we can apply biaxial strains as large as 5.6% across micron sized areas, and report evidence for the strain tuning of higher level optical transitions.Comment: Nano Lett., Article ASA

Transient thermal characterization of suspended monolayer MoS2_2

We measure the thermal time constants of suspended single layer molybdenum disulfide drums by their thermomechanical response to a high-frequency modulated laser. From this measurement the thermal diffusivity of single layer MoS$_2$ is found to be 1.14 $\times$ 10$^{-5}$ m$^2$/s on average. Using a model for the thermal time constants and a model assuming continuum heat transport, we extract thermal conductivities at room temperature between 10 to 40 W/(m$\cdot$K). Significant device-to-device variation in the thermal diffusivity is observed. Based on statistical analysis we conclude that these variations in thermal diffusivity are caused by microscopic defects that have a large impact on phonon scattering, but do not affect the resonance frequency and damping of the membrane's lowest eigenmode. By combining the experimental thermal diffusivity with literature values of the thermal conductivity, a method is presented to determine the specific heat of suspended 2D materials, which is estimated to be 255 $\pm$ 104 J/(kg$\cdot$K) for single layer MoS$_2$