CINT science highlights from the 4 scientific thrusts: Nanoscale Electronics and Mechanics (NEM), Nanophotonics and Optical Nanomaterials (NPON), Soft, Biological and Composite Nanomaterials (SBCN), Theory and Simulation of Nanoscale Phenomena (TSNP)
Nanoscale Electronics and Mechanics (NEM)
A conventional material makes emerging materials even newer
Scientific Achievement: Heterostructuring germanium (Ge) thin film and atomically thin molybdenum disulfide (MoS2) delivers novel characteristics distinguished from those of Ge and MoS2.
Significance: The novel heterostructure composed of conventional materials and two-dimensional (2D) materials provides novel ways of controlling physical properties of 2D materials and preparing crystalline building blocks for flexible devices.
Research Details: Heterostructuring is utilized for exploring emergent phenomena and obtaining novel functionality beyond that of homogeneous materials.Two-dimensional (2D) materials are of particular interest due to their exotic characteristics. However, controlling properties of 2D materials is still far behind from the standards of conventional semiconductors due to difficulty in doping and alloying in 2D materials. A heterostructure composed of 2D materials and conventional materials provides novel insights of materials preparation and realization of functionality. Because 2D materials do not have surface dangling bonds, conventional epitaxy cannot be directly applied to prepare 2D/conventional material heterostructures. In this study, we demonstrate crystalline germanium thin film on monolayer molybdenum disulfide, a representative 2D material, via chemical vapor deposition. The Ge/MoS2 heterostructure shows remarkable difference of electrical characteristics from the constituents, Ge and MoS2. In the heterostructure, nominally n-type MoS2 was converted to lightly p-doped, and undoped Ge was highly conducting without doping. The density functional theory calculations revealed that charge transfer between Ge and MoS2 induces the significant changes of electrical properties of Ge and MoS2.
Publications: Yung-Chen Lin, Ismail Bilgin, Towfiq Ahmed, Renjie Chen, Doug Pete, Swastik Kar, Jian-Xin Zhu, Gautam Gupta, Aditya Mohite, Jinkyoung Yoo, "Charge transfer in crystalline germanium/monolayer MoS2 heterostructures prepared by chemical vapor deposition", Nanoscale, 2016, 8, 18675, DOI: 10.1039/C6NR03621J. READ THE ARTICLE.
Nanophotonics and Optical Nanomaterials (NPON)
A New Fano Metasurface with Record Narrow Resonances
Scientific Achievement: Using broken symmetry concepts, we created all-dielectric metasurfaces based on semiconductors that show record high quality factors (Q~600).
Significance: Among the highest Q resonances for metasurfaces using a relatively simple design. These Fano metasurfaces could lead to new types of optical devices such as nanolasers, detectors, modulators and sources of entangled photons.
Research Details: We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality factor Fano resonances. The approach utilizes symmetry breaking of highly symmetric resonator geometries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple “bright” dipole modes to “dark” dipole modes whose radiative decay is suppressed by local field effects in the array. The approach is widely scalable from the near-infrared to radio frequencies. The investigation first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieves a quality factor of ∼1300 at ∼10.8 μm. The work also presents two experimental demonstrations operating in the near- infrared (∼1 μm): a silicon-based implementation that achieves a quality factor of ∼350; and a gallium arsenide-based structure that achieves a quality factor of ∼600, the highest near-infrared quality factor experimentally demonstrated to date with this kind of metasurface. Importantly, large electromagnetic field enhancements appear within the resonators at the Fano resonant frequencies. Combining high quality factor, high field enhancement resonances with nonlinear and active/gain materials such as gallium arsenide has the potential to lead to new classes of active optical devices.
Publication: Salvatore Campione, Sheng Liu, Lorena I. Basilio, Larry K. Warne, William L. Langston, Ting S. Luk, Joel R. Wendt, John L. Reno, Gordon A. Keeler, Igal Brener, and Michael B. Sinclair, ACS Photonics 2016, 3 (12), pp 2362–2367, DOI: 10.1021/acsphotonics.6b00556. READ THE ARTICLE.
Soft, Biological and Composite Nanomaterials (SBCN)
Mimicking supramolecular energy transfer in green bacteria-inspired polymer nanocomposites
Scientific Achievement: An artificial light-harvesting (LH) system composed of block copolymer-based membrane nanocomposites demonstrates three-dimensional, supramolecular energy transfer. The system structurally and functionally mimics green bacterial LH systems.
Significance: Supramolecular energy transfer is realized using solution-processable polymer membrane materials via self-assembly. Artificial polymer-based LH system exhibits advantages to biological LH systems, namely; control of composition, flexibility and stability while maintaing bio-like efficiency.
Research Details: Polymer nanocomposites that structurally and functionally mimic chlorosome LH antenna of green bacteria created using amphiphilic block copolymer as monolayer forming membrane. Multi-membrane energy transfer demonstrated from artificial chlorosome donors to supported polymer membrane acceptors (estimated energy transfer ~55%).
Theory and Simulation of Nanoscale Phenomena (TSNP)
Cluster Dynamics in Associating Polymers
Scientific Achievement: Atomistic molecular dynamics simulations and quasi-elastic neutron scattering showed that dynamics in acid-containing polymers are heterogeneous, and that acid clusters exchange acid groups on the 1 ns time scale.
Significance: This study revealed the life time of acid clusters within the polymer matrix. Knowledge of the cluster life time, which controls the transport, mechanical, and viscoelastic properties of polymers with associating groups, will guide future design of these polymers.
Research Details: An important step toward manipulating the transport, mechanical, and viscoelastic properties in associating polymers is to know the lifetime of polar or ionic aggregates within the nonpolar polymer matrix. We combined quasi-elastic neutron scattering (QENS) and atomistic molecular dynamics simulations to study the dynamics (picosecond to nanosecond) of precise acrylic acid-containing polyethylenes. The agreement between experiment and simulation is excellent. The acid groups in these polymers form nanoscale-size aggregates which affect both the structure and dynamics. Two dynamic processes were observed. The faster dynamic processes which occur at the picosecond timescales are related to spatially restricted local motions. The slower dynamic processes are associated with the structural relaxation of the polymer backbone. Additionally, the dynamics of specific hydrogen atom positions along the backbone correlate structural heterogeneity imposed by the associating acid groups with a mobility gradient along the polymer backbone. Analysis of the simulations shows that the acid aggregates exchange acid groups within ~1 ns when the spacer length between pendent acid groups is 9, 15, or 21 carbons. This study provides validation of simulation force fields and advances the understanding of heterogeneous chain dynamics in associating polymers.
Publication: L. R. Middleton, J. D. Tarver, J. Cordaro, M. Tyagi, C. L. Soles, A. L. Frischknecht, and K. I. Winey, “Heterogeneous Chain Dynamics and Aggregate Lifetimes in Precise Acid-Containing Polyethylenes: Experiments and Simulations,” Macromolecules, 2016, 49, 9176, DOI: 10.1021/acs.macromol.6b01918. READ THE ARTICLE.