Research Highlights
Ying-Yu Wang, Ding-Rui Chen, Jen-Kai Wu, Tian-Hsin Wang, Chiashain Chuang, Ssu-Yen Huang, Wen-Pin Hsieh, Mario Hofmann, Yuan-Huei Chang, Ya-Ping Hsieh*
Nano Lett., https://doi.org/10.1021/acs.nanolett.1c02331 (2021).
We here demonstrate the multifunctional properties of atomically thin heterojunctions that are enabled by strong interfacial interactions and their integration into ultra-high performance, self-powered sensors. Epitaxial alignment between tin diselenide and graphene through direct growth produces thermoelectric and mechanoelectric properties beyond the ability of either component. An unprecedented ZT of 2.43 originated from the synergistic combination of graphene’s high carrier conductivity and SnSe2 mediated thermal conductivity lowering. Moreover, strong interaction at the SnSe2/graphene interface produces stress localization that results in a novel 2D-crack-assisted strain sensing mechanism whose sensitivity (GF=450) is superior to all other 2D materials. Finally, the graphene-assisted growth process, permits the formation of high-quality heterojunctions directly on polymeric substrates for flexible and transparent self-powered sensors that achieve fast and reliable strain sensing from a small temperature gradient. Our work enhances the fundamental understanding of multifunctionality at the atomic scale and provide a route towards structural health monitoring through ubiquitous and smart devices.
Y. H. Chan, Diana Y. Qiu, Felipe H. da Jornada, and Steven G. Louie
Proceedings of National Academy of Sciences
Shift current is a direct current generated from nonlinear light–matter interaction in a noncentrosymmetric crystal and is considered a promising candidate for next-generation photovoltaic devices. The mechanism for shift currents in real materials is, however, still not well understood, especially if electron–hole interactions are included. Here, we employ a first-principles interacting Green’s-function approach on the Keldysh contour with real-time propagation to study photocurrents generated by nonlinear optical processes under continuous wave illumination in real materials. We demonstrate a strong direct current shift current at subbandgap excitation frequencies in monolayer GeS due to strongly bound excitons, as well as a giant excitonic enhancement in the shift current coefficients at above bandgap photon frequencies. Our results suggest that atomically thin two-dimensional materials may be promising building blocks for next-generation shift current devices.
Qian-Rui Huang, Ying-Cheng Li, Tomoki Nishigori, Marusu Katada, Asuka Fujii,* and Jer-Lai Kuo*
The Journal of Physical Chemistry Letters 11, 10067 (2020); https://doi.org/10.1021/acs.jpclett.0c03059.
Complex vibrational features of solvated hydronium ion, H3O+, in 3 μm enable us to look into the vibrational coupling among O-H stretching modes and other degrees of freedom. Two anharmonic coupling schemes have often been engaged to explain observed spectra: coupling with OH bending overtone, known as Fermi resonance (FR), has been proposed to account for the splitting of the OH stretch band at ~3300 cm-1 in H3O+…Ar3, but an additional peak in H3O+…(N2)3 at the similar frequency region has been assigned to a combination band (CB) with the low-frequency intermolecular stretches. While even stronger vibrational coupling is expected in H3O+…(H2O)3, such pronounced peaks are absent. In the present study, vibrational spectra of H3O+…Kr3 and H3O+…(CO)3 are measured to complement the existing spectra. Using ab initio anharmonic algorithms, we are able to assign the observed complex spectral features, to resolve seemingly contradictory notions in the interpretations, and to reveal simple pictures of the interplay between FR and CB.
Qian-Rui Huang, Ryunosuke Shishido, Chih-Kai Lin, Chen-Wei Tsai, Jake A. Tan, Asuka Fujii* and Jer-Lai Kuo*
Angewandte Chemie International Edition, https://doi.org/10.1002/anie.202012665 (2020).
Experimental infrared spectra between 2600 to 3800 cm-1 for a series of asymmetric proton bound dimers with protonated trimethylamine (TMA–H+) as the proton donor were recorded and analyzed. Based on conventional wisdom, the frequency of the N-H+ stretching mode is expected to red shift as the proton affinity of proton acceptors (Ar, N2, CO, C2H2, H2O, CH3OH, and C2H5OH) increases. The observed band, however, shows a peculiar splitting of ≈300 cm-1 with the intensity shifting pattern resembling a two-level system. Theoretical investigation based on ab initio anharmonic algorithms reveals that the observed band splitting and its extraordinarily large gap of ≈300 cm-1 is a result of strong coupling between fundamental of the proton stretching mode and overtone states of the two proton bending modes, that is commonly known as Fermi resonance (FR). We also provide a simple and general theoretical model to link the strong FR coupling to the quasi-two-level system behavior in the observed band intensity. Since the model does not depend on the molecular specification of TMA–H+, the strong coupling we observed here is an intrinsic property associated with proton motions in a wide range of molecular systems.
Dr. Liang-Yan Hsu, Dr. Chia-Chun Chen
(2020)
Liang-Yan Hsu*, Hung-Chi Yen, Ming-Wei Lee, Yae-Lin Sheu, Po-Chun Chen, Hongjie Dai*, Chia-Chun Chen*
Chem, 2020, 6, 3396-3408.
Large-scale inhomogeneous plasmonic metal chips have been demonstrated as a promisingplatform for biochemical sensing, but the origin of their strong fluorescence enhancementsand average gap dependence is a challenging issue due to the complexity of modelingtremendous molecules within inhomogeneous gaps. To address this issue, we bridgedmicroscopic mechanisms and macroscopic observations, developed a kinetic model, andexperimentally investigated the fluorescence enhancement factors of IR800-streptavidinimmobilized on metal nanoisland films (NIFs). Inspired by the kinetic model, we controlledthe distribution of IR800-streptavidin within the valleys of NIFs by regioselectivemodification and achieved the fluorescence intensity enhancement up to 488-fold. Thekinetic model allows us to qualitatively explain the mechanism of fluorescence intensityenhancements and quantitatively predict the trend of experimental enhancement factors,thereby determining the design principles of the plasmonic metal chips. Our studyprovides one key step further toward the sensing applications of large-scale plasmonicmetal chips.
Institute of Atomic and Molecular Sciences Academia Sinica
