2D Raman band splitting in graphene: charge screening and lifting of the K-point Kohn anomaly

Pristine graphene encapsulated in hexagonal boron nitride has transport properties rivalling suspended graphene, while being protected from contamination and mechanical damage. For high quality devices, it is important to avoid and monitor accidental doping and charge fluctuations. The 2D Raman double peak in intrinsic graphene can be used to optically determine charge density, with decreasing peak split corresponding to increasing charge density. We find strong correlations between the 2D 1 and 2D 2 split vs 2D line widths, intensities, and peak positions. Charge density fluctuations can be measured with orders of magnitude higher precision than previously accomplished using the G-band shift with charge. The two 2D intrinsic peaks can be associated with the “inner” and “outer” Raman scattering processes, with the counterintuitive assignment of the phonon closer to the K point in the KM direction (outer process) as the higher energy peak. Even low charge screening lifts the phonon Kohn anomaly near the K point for graphene encapsulated in hBN, and shifts the dominant intensity from the lower to the higher energy peak.This work was supported by the United States National Science Foundation (DMR 1411008, DMR 1308659). J.C. thanks the Department of Defence (DoD), Air Force Office of Scientific Research for its support through the National Defence Science and Engineering Graduate (NDSEG) Fellowship, 32 CFR 168a. The authors would like to thank Cory Dean and Carlos Forsythe for the graphene encapsulated hBN sample. (DMR 1411008 - United States National Science Foundation; DMR 1308659 - United States National Science Foundation; 32 CFR 168a - Department of Defence (DoD), Air Force Office of Scientific Research through the National Defence Science and Engineering Graduate (NDSEG) Fellowship

Physical mechanisms controlling the strength and deformation behavior of unfrozen and frozen Manchester fine sand

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1994.Includes bibliographical references (v. 4, leaves 721-743).by Christopher Wayne Swan.Sc.D

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

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

Designing Value into Engineering Learning Through Service Activities Using a Blueprint Model

Both course-based service-learning (S-L) and extracurricular community service activities, together referred to as Learning Through Service, provide the opportunity for rich learning, personal growth, and tangible beneficial outcomes for students, community partners, and faculty. However, to fully realize this potential careful planning and design of the Learning Through Service (LTS) effort are required. This paper describes a framework with nine important elements to consider for LTS program design: (1) stakeholders, (2) value propositions, (3) relationships, (4) channels, (5) key activities, (6) resources, (7) partnerships, (8) value stream returns, and (9) value stream costs/outlays. This LTS development framework is based on the Business Canvas Model used in developing and evaluating the business viability of an innovative product or service. For LTS, the stated program design attributes were identified based on the personal LTS experience of the research team and input from additional experts. These nine elements can be effectively presented as a blueprint for an LTS program. Thoughtful planning in each of these areas will help ensure that the program goals are met and provide optimal benefits for all of the stakeholders. These elements also help to identify where management and assessment efforts are best targeted. Specific examples for each of the nine attributes from thirty-four different LTS programs are presented. Some of these LTS programs were in the planning phases and missing elements that could make the programs more meaningful, such as student reflection or engaging community partners as equals. Together, the model and examples provide guidance for others who are interested in designing a new LTS program, or improving an existing one.</div

2010 Status of the Lake Ontario Lower Trophic Levels

This report presents data on the status of lower trophic level components of the Lake Ontario ecosystem (zooplankton, phytoplankton, nutrients) in 2010 and compares the 2010 data with available time series. Lower trophic levels are indicators of ecosystem health [as identified by the Lake Ontario Pelagic Community Health Indicator Committee (EPA 1993) and presented in the biennial State of the Lake Ecosystem Conference (SOLEC) reports] and determine the lake’s ability to support the prey fish upon which both wild and stocked salmonids depend. Understanding the production potential of lower trophic levels is also integral to ecosystem-based management. Continued evaluation of lower trophic levels is particularly important for fisheries management, as the observed declines in alewife and Chinook salmon in Lake Huron in 2003 may have been partly the result of changes in lower trophic levels (Barbiero et al. 2009)

Identifying the science and technology dimensions of emerging public policy issues through horizon scanning

Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security.Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security