Hyperspectral Imaging of Structure and Composition in Atomically Thin Heterostructures

Havener, Robin W.,Kim, Cheol-Joo,Brown, Lola,Kevek, Joshua W.,Sleppy, Joel D.,McEuen, Paul L.,Park, Jiwoong American Chemical Society 2013 Nano letters Vol.13 No.8

<P>Precise vertical stacking and lateral stitching of two-dimensional (2D) materials, such as graphene and hexagonal boron nitride (h-BN), can be used to create ultrathin heterostructures with complex functionalities, but this diversity of behaviors also makes these new materials difficult to characterize. We report a DUV–vis-NIR hyperspectral microscope that provides imaging and spectroscopy at energies of up to 6.2 eV, allowing comprehensive, all-optical mapping of chemical composition in graphene/h-BN lateral heterojunctions and interlayer rotations in twisted bilayer graphene (tBLG). With the addition of transmission electron microscopy, we obtain quantitative structure–property relationships, confirming the formation of interfaces in graphene/h-BN lateral heterojunctions that are abrupt on a micrometer scale, and a one-to-one relationship between twist angle and interlayer optical resonances in tBLG. Furthermore, we perform similar hyperspectral imaging of samples that are supported on a nontransparent silicon/SiO<SUB>2</SUB> substrate, enabling facile fabrication of atomically thin heterostructure devices with known composition and structure.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2013/nalefd.2013.13.issue-8/nl402062j/production/images/medium/nl-2013-02062j_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl402062j'>ACS Electronic Supporting Info</A></P>

Van Hove Singularities and Excitonic Effects in the Optical Conductivity of Twisted Bilayer Graphene

Havener, Robin W.,Liang, Yufeng,Brown, Lola,Yang, Li,Park, Jiwoong American Chemical Society 2014 NANO LETTERS Vol.14 No.6

<P>We report a systematic study of the optical conductivity of twisted bilayer graphene (tBLG) across a large energy range (1.2–5.6 eV) for various twist angles, combined with first-principles calculations. At previously unexplored high energies, our data show signatures of multiple van Hove singularities (vHSs) in the tBLG bands as well as the nonlinearity of the single layer graphene bands and their electron–hole asymmetry. Our data also suggest that excitonic effects play a vital role in the optical spectra of tBLG. Including electron–hole interactions in first-principles calculations is essential to reproduce the shape of the conductivity spectra, and we find evidence of coherent interactions between the states associated with the multiple vHSs in tBLG.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-6/nl500823k/production/images/medium/nl-2014-00823k_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl500823k'>ACS Electronic Supporting Info</A></P>

Laser-based imaging of individual carbon nanostructures

Havener, Robin W.,Tsen, Adam W.,Choi, Hee Cheul,Park, Jiwoong Nature Publishing Group 2011 NPG Asia Materials Vol.3 No.-

그래핀의 대면적 이미지 특성 분석

권강혁,김나영,원동관,조승민,박지웅,Kwon, Kanghyuk,Kim, Nayoung,Havener, Robin W.,Won, Donggwan,Cho, Seungmin,Park, Jiwoong 한국광학회 2013 한국광학회지 Vol.24 No.3

라만 분광기는 그래핀의 특성을 분석하기 위한 필수적인 방법이다. 상용 마이크로 라만 분광기는 작은 면적에 대해 유용하게 사용되고 있으나 작은 면적 측정으로 인하여 산업적으로는 시료 측정 등에 제한적으로 사용되고 있다. 본 논문에서는 그래핀의 대면적 이미지 얻을 수 있는 라만 분광기에 대해 제안하였다. 이 이미지를 이용하여 그래핀의 유무 및 결함에 대한 정보를 빠르게 얻었다. 이를 이용하여, 실시간으로 그래핀에 대한 결함 유무, 층 수에 대한 균일도를 확인할 수 있으며, 양산 그래핀에 대한 품질 평가에 활용할 수 있을 것이다. A Raman spectrometer is essential for analyzing the characteristics of graphene. The commercial micro-Raman spectrometer is useful for measuring small areas, but due to the small measuring area, it has limited use in industry, as a sampling measure. This paper suggests a Raman spectrometer able to get a large area image of graphene. By using this image, we can get information on defects and on the presence of graphene. Therefore, this equipment can be used for quality assessment for production of graphene.

Polycrystalline Graphene with Single Crystalline Electronic Structure

Brown, Lola,Lochocki, Edward B.,Avila, José,Kim, Cheol-Joo,Ogawa, Yui,Havener, Robin W.,Kim, Dong-Ki,Monkman, Eric J.,Shai, Daniel E.,Wei, Haofei I.,Levendorf, Mark P.,Asensio, Marí,a,Shen American Chemical Society 2014 NANO LETTERS Vol.14 No.10

<P>We report the scalable growth of aligned graphene and hexagonal boron nitride on commercial copper foils, where each film originates from multiple nucleations yet exhibits a single orientation. Thorough characterization of our graphene reveals uniform crystallographic and electronic structures on length scales ranging from nanometers to tens of centimeters. As we demonstrate with artificial twisted graphene bilayers, these inexpensive and versatile films are ideal building blocks for large-scale layered heterostructures with angle-tunable optoelectronic properties.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-10/nl502445j/production/images/medium/nl-2014-02445j_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl502445j'>ACS Electronic Supporting Info</A></P>

영양상태지수(trophic state index)을 이용한 수체 내 식물플랑크톤 제한요인 및 seston 조성의 유추

Havens, Karl E . 한국육수학회 2000 생태와 환경 Vol.33 No.3

This paper describes a simple method that uses differences among Carlson's (1977) trophic state index (TSI) values based on total phosphorus (TP), chlorophyll a (CHL) and Secchi depth (SD) to draw inferences regarding the factors that are limiting to phytoplankton growth and the composition of lake seston. Examples are provided regarding seasonal and spatial patterns in a large subtropical lake (Lake Okeechobee, Florida, USA) and inter- and intro-lake variations from a multilake data set developed from published studies. Once an investigator has collected routine water quality data and established TSI values based on TP, CHL, and SD, a number of inferences can be made. Additional information can be provided where it also is possible to calculate a TSI based on total nitrogen (TN). Where TSI (CHL)<<TSI (TP), some factor other than P is inferred to limit algal growth. If one also finds that TSI (CHL)<<TSI (SD), this is evidence that seston is dominated by very small (abiotic) particles, and that light may be limiting. In contrast, if TSI (CHL)<<TSI (TP) but TSI (CHL)>>TSI (SD), light attenuating particles are large (large filaments or colonies of algae), and the phytoplankton may be limited by zooplankton grazing. Other limiting conditions are inferred by different relationships between the TSI values. Results of this study indicate that the analysis is quite robust, and that it generally gives good agreement with conclusions based on more direct methods (e.g., nutrient-addition bioassays, zooplankton size data, zoo-plankton removal experiments). The TSI approach, when validated periodically with these more costly and time-intensive methods, provides an effective, low cost method for tracking long-term changes in pelagic structure and function with potential value in monitoring lake ecology and responses to management.

Liquid Ripple

나이트헤이븐 ( Haven Shane Knight ) 한국기초조형학회 2018 한국기초조형학회 작품집 Vol.2018 No.1

An Introduction to U.S. Law for Prospective IEP Advocates

Eric Havens 영미어문학회 2006 영미어문학연구 Vol.22 No.1

  This integrative research paper serves as a comprehensive introduction to education law for teachers of English to speakers of other languages. (TESOL) who aspire to advocate for their intensive English programs (IEP). Firstly, background knowledge is amassed about the structural hierarchies of the U.S. educational and legal systems, at both the federal and state levels. Then, immigration law and agency reorganization is discussed. The decline in IEP enrollment is documented, before concluding with the beneficial actions currently being undertaken by IEP professional accrediting associations.<BR>  Intensive English programs (IEPs) in the United States are ceaseless hives of pedagogic activity and action research for teachers of English to speakers of other languages (TESOL). They attract TESOL profess ionals of all virtues and varieties to their halls and classrooms: there are those teacher-researchers dedicated to new discoveries in second language acquisition (SLA), those promoters constantly forming interdepartmental and intercommunity linkages and outreach programs, those continually innovating visionaries devoted to improving the services of computer assisted language learning (CALL) labs, those organizers actively streamlining the system for an efficient and effective program, those advisors who work to bridge the gap between international and mainstream students, and finally, the leaders who inspire and encourage all staff members to achieve and even exceed expectations. IEPs serve a very important role in U.S. universities; however, in recent years they have been in decline. Fortunately, through a keen acumen into the law and the political system, associations exist that are fighting for the rights of IEPs and the international students they serve. This eclectic, integrative, and interdisciplinary research paper seeks to show how an in-depth knowledge of the law and the educational system can help IEPs obtain the benefits they deserve, so that they will no longer be in decline, but will once again be the popular choice for English as a second language (ESL) and English as a global language (EGL) training.<BR>  IEPs can stand independently, or be housed within a parent college or university. Furthermore, IEPs do not exist purely to teach international English language learners (IELLs) English, or merely to make a profit. These goals, the former highly noble and the latter contemptibly base, exist peripherally of the more consequential goal of enabling students to earn post-secondary degrees (Genzel, Simon, & Stevens, 2003). That is, IEPs, consistent with a policy that is neither explicit nor expressed but implied by their historical development, act as gateways to undergraduate or graduate study (Kaplan, 1997). Post-secondary ESL study, unlike foreign language study, is not viewed as an end in itself in an academic sense, but as a means through which academic knowledge may be obtained. Thus, IEPs and TESOL practitioners may suffer from low status and marginalization in the academic milieu (Eskey, 1997). This is one reason that IEPs need advocatesi that is," people and organizations willing to take a stand and defend the immense societal value of IEPs, TESOL professionals, and international students.<BR>  Secondly, in recent years, lEPs have suffered from low enrollment because of increasingly strict immigration regulations, stories of denied student visas, increasingly intense competition from institutions in other countries, rising tuition costs, and the feeling that America, in a disabling state of xenophobia, no longer welcomes IELLs. This is another reason why IEPs and the international students they serve need advocates.<BR>  Advocacy, in addition to maintaining industry-wide standards, is a chief reason why IEPs work closely with such professional accrediting associations as the National Association of Foreign Student Affairs (NAFSA), the Ameri

영양상태지수 ( trophic state index ) 를 이용한 수체 내 식물플랑크톤 제한요인 및 seston 조성의 유추

Karl E. Havens 한국수생태학회(구 한국하천호수학회) 2000 생태와 환경 Vol.33 No.3