Generally, the electrical performance of these materials depends strongly on the number and location of defects within the deposited layers, interfaces and the local environment, and changes induced by biasing them with an electric field over an extended time.\u00a0 It is vital to be able to investigate defects on the scale of the defects themselves.\u00a0 \u00a0Typical measurements instead average over an area that includes many defects and possibly multiple interfaces.\u00a0 \u00a0Our lab specializes in challenging and creative uses of atomic force microscopy (AFM), along with standard electrical transport measurements.\u00a0 Kelvin Probe Force Microscopy (KPFM) is a mode of operation of the AFM allowing direct measurement of surface potentials with spatial resolution of a few tens of nanometers, correlated with high resolution topographic images.\u00a0 Under the right conditions, KPFM can be used to measure the density of states in a material.\u00a0 We are developing a technique<\/a> to study the real-time motion of charges in thin films, which can measure the filling and emptying of trap states, which is particularly important to understand in materials where traps dominate the transport.<\/p>\n Organic semiconductors are particularly exciting for their applications with low cost, flexible electronics.\u00a0 Imagine rolling up your “computer”\u00a0 into the width of a pencil, covering parking lots with awnings filled with solar cells, or having a display on the contact lens in your eye.\u00a0 Commercial OLED displays use these materials, and the recently released foldable phones make use of their flexibility.\u00a0 While the optical properties of these materials hold tremendous promise with low cost fabrication techniques, the electrical properties are often dominated by traps, interfaces, and can be unstable over time.\u00a0 We work in collaboration with the Arango Lab<\/a> at Mount Holyoke to explore a range of materials relevant to the photovoltaics fabricated in their lab.\u00a0 These materials include P3HT, full name poly(3-hexylthiophene-2,5-diyl), a frequently studied hole majority carrier organic semiconductor, and PDI-CN2, a perylene diimide, which is an electron majority carrier.\u00a0 Check out Xinrui (Anna) Zhu’s APS March Meeting 2020 talk on evidence for an accumulation layer at the donor-acceptor interface in organic solar cells here<\/a>.<\/p>\n Nanocrystal (aka “colloidal”) Quantum Dots (QDs) are roughly spherical nanoscale chunks of crystalline material with a diameter of generally less than 10nm.\u00a0 When materials are restricted to this size range, their electronic properties change dramatically due to quantum confinement.\u00a0 A quantum dot is the real-life implementation of the “particle in a box” that undergraduates solve in their quantum mechanics class.\u00a0 The quantum confinement leads to quantized energy levels.\u00a0 The narrower the diameter, the larger the energy level spacing.\u00a0 This results in different wavelength emission of light (redder for larger QDs, bluer for smaller QDs), such that by changing only the diameter of the QD, one can control the wavelength of light.\u00a0 QLED televisions are a commercial application of this technology, along with fluorescent labels for microscopy.\u00a0 Our collaborators in the Arango Lab\u00a0<\/a>study PbS QDs in solar cells.<\/p>\n Perhaps unsurprisingly, the electronic properties of QDs are highly dependent on their immediate environment.\u00a0 A single trapped charge can impact the electrical and optical properties.\u00a0 Presently, the optical properties of QDs are better studied than the electronic properties of arrays of the QDs.\u00a0 We are presently focusing on the electrical properties of PbS quantum dots.<\/p>\n Materials like graphene form strong bonds in two-dimensions, while weakly interacting between layers through van der Waals forces (e.g. graphite).\u00a0 Since the discovery in 2004 that single layers of graphene could be controlled in the research lab,\u00a0<\/em>many researchers have been studying the unique properties of this class of materials that arise due to the quantum mechanical confinement to two dimensions.\u00a0 Our lab is presently interested in the properties of semiconductor MoS2<\/sub>, in collaboration with Jing Kong’s<\/a> lab at MIT, as part of the NSF funded Center for Integrated Quantum Materials<\/a>.\u00a0 Check out Christina McGahan’s APS March Meeting 2020 talk on comparative electrical scanning probe measurements on doped monolayer MoS2 here<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":" Motivation Traditional silicon electronics have allowed us to follow the trend predicted by Moore’s Law, doubling process power roughly every two years.\u00a0 If we are to continue this trend, we need alternative electronics.\u00a0 Additionally, non-traditional semiconductors can provide other desirable properties like printability and flexibility, lower cost, and lower weight.\u00a0 Potential applications include printed large-area…<\/p>\n","protected":false},"author":1030,"featured_media":676,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"class_list":["post-177","page","type-page","status-publish","has-post-thumbnail","hentry"],"_links":{"self":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/177","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/users\/1030"}],"replies":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/comments?post=177"}],"version-history":[{"count":47,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/177\/revisions"}],"predecessor-version":[{"id":873,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/pages\/177\/revisions\/873"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/media\/676"}],"wp:attachment":[{"href":"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-json\/wp\/v2\/media?parent=177"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-content\/uploads\/sites\/483\/2019\/06\/biosensor-300x169.jpg\")
Types of Materials Studied in the Lab<\/h3>\n
Organic semiconductors<\/h4>\n
Nanocrystal Quantum Dots<\/h4>\n
![\"\"](\"https:\/\/commons.mtholyoke.edu\/aidalalab\/wp-content\/uploads\/sites\/483\/2019\/06\/BawendiVials3-300x73.jpg\")
2D Atomic Layered Materials<\/h4>\n