causes the spectral shift of the resonance wavelength. In particular, most organic molecules have a higher refractive index than buffer solution, thus as the concentration of these molecules rises, the local refractive index increases, thereby redshifting the resonance wavelength. The spectral shift of resonance results in the change of the transmission, refl ection, or absorption spectrum, which can be monitored by inexpensive spectrometry. [1][2][3][4][9][10][11][12] However, strong induced electric current in these plasmonic resonators also leads to signifi cant ohmic loss, [6][7][8] which gives rise to the broadening of the resonance spectrum with low-quality factor ( Q -factor) and thus degrade the performance of the sensor characterized by a fi gure of merit (FOM*). Over the years, numerous efforts have been made to improve the performance of plasmon-based sensor, for example, using high Q-factor Fano resonance induced by coupling of surface plasmon polariton and LSPR [ 11 ] and reducing the substrate effect by lifting the LSPR resonators. [ 13 ] Among the efforts, it has been demonstrated that the metamaterial perfect absorbers (MPAs) can be used to signifi cantly increase the Q -factor and thus improve the FOM*. [ 12,14 ] The MPA is a recently developed branch of metamaterial which exhibits nearly unity absorption within certain frequency range. [15][16][17][18][19][20] The optically thin MPA possesses characteristic features of angular-independence, high Q -factor and strong fi eld localization that have inspired a wide range of applications including electromagnetic (EM) wave absorption, [ 17,21,22 ] spatial [ 20 ] and spectral [ 19 ] modulation of light, [ 23 ] selective thermal emission, [ 23 ] thermal detecting, [ 24 ] and refractive index sensing for gas [ 25 ] and liquid [ 12,14 ] targets. The MPA is typically comprised of three layers: a metallic resonator's layer, e.g., cross-type resonators, [ 23,26 ] split-ring resonators, [ 17 ] or metallic nanoparticles, [ 27 ] and a highly refl ective layer, e.g., metallic fi lm [ 17,23,26,27 ] or metallic mesh grid, [ 17 ] separated by a subwavelength-thick dielectric fi lm (spacer). The impedance matching between MPA and free space, and high attenuation of light inside the MPA result in the perfect absorption. [ 17 ] In the sensing application, the spectral shift of perfect absorption peak is attributed to the refractive index change of gas [ 25 ] or liquid. [ 12,14 ] However, the gas or liquid used as the sensing target has been so far only on the surface of the MPA-basedIn most plasmon resonance based sensor to date, only the surface of the sensor is accessible to the gas or liquid as the sensing target. In this work, an interferometric, lithographically fabricated, large-area, mushroom-capped plasmonic perfect absorber whose dielectric spacer is partially removed by a reactive-ion-etch process, thereby enabling the liquid to permeate into the sensitive region to a refractive index change, is demonstrated. Findings of this paper demonstrate experimentall...

Organic radicals display unique physical structures and could become next generation functional materials. However, design and synthesis of stable neutral radicals with a significant polyradical character has been an enormous challenge for chemists. In this work, we synthesized a series of stable 3,6-linked, kinetically blocked fluorenyl radical oligomers up to hexamer (FR-n, n = 1-6). Their ground-state geometric and electronic structures were systematically studied by various experimental methods including X-ray crystallographic analysis, variable temperature nuclear magnetic resonance, electron spin resonance, and superconducting quantum interference device measurements, supported by density functional theory and ab initio calculations. Moderate antiferromagnetic coupling between the fluorenyl radicals was observed, and moderate to large diradical and polyradical characters were calculated from dimer onward. Furthermore, their photophysical properties were estimated by steady-state, transient absorption, and two-photon absorption measurements, and their electrochemical properties were investigated by cyclic voltammetry/differential pulse voltammetry and spectro-electrochemical measurements. A clear chain length dependence of their optical, electrochemical, and magnetic properties was found for the oligomers with an odd or even number of spin centers, respectively.

Compositions as well as morphologies and structures of particles are vital factors that define their properties and applications. However, the morphology and structure changes associated with the composition change of metal-organic frameworks (MOFs) are barely studied. Herein, we report the morphology and structure changes of MOF particles associated with the ratio of two organic linkers incorporated within MOF particles, when they are constructed from the reactions of In(NO3)3 in the presence of isophthalic acid (H2IPA) and/or 1,4-benzenedicarboxylic acid (H2BDC). Two tendencies—the tendency of BDC and In(3+) to form porous crystalline hexagonal rods, and the tendency of IPA and In(3+) to form non-porous amorphous spherical particles—compete during the formation of MOF particles. Eventually, the incorporated ratio of BDC and IPA within the MOF particles, and thus their morphology and porosity, are controlled by altering the relative amounts of H2BDC and H2IPA used during the reactions.

To understand how disorder within conjugated polymer aggregates influences the polaron generation process, we investigated poly(3-hexylthiophene) (P3HT) and a congeneric random copolymer incorporating 33 mol % substituent-free thiophene units (RP33). Steady-state absorption and fluorescence spectra showed that increasing the intrachain torsional disorder in aggregates increases the energy and breadth of the density of states (DOS). By extracting polaron dynamics in the transient absorption spectra, we found that an activation energy barrier of 0.05 eV is imposed on the charge separation process in P3HT, whereas that in RP33 is essentially barrierless. We also found that a significant amount of excitons in P3HT are deactivated by traps, while no trapped excitons are generated in RP33. This efficient polaron generation in RP33 was attributed to the excess energy and enhanced interchain delocalization of precursor states provided by the intrachain torsional disorder and the close-packing structure in the absence of hexyl substituents.

In the era of hyperconnected contemporary society, hardware and information security become more dependent on advanced cryptographic primitives. A physically unclonable function (PUF), originally implemented by an algorithmic means as software-based security, is considered as an immediate security solution. Nanomaterial-based PUFs have recently received considerable attention but have often limitations on unclonability and scalability for practical applications. Here, we report that heteronanostructures of vertically orientated molybdenum disulfide (MoS 2 ) nanoflakes and titanium dioxide (TiO 2 ) aggregates can be used for a versatile PUF. The band alignment of heteronanostructured MoS 2 /TiO 2 results in photogenerated electron transfer and turns off the bright state of emitters, offering an entropy source. After von Neumann debiasing, extracted cryptographic keys show a large encoding capacity and reliable PUF performance, including randomness, uniqueness, reproducibility, low false rates, and long-term stability. The unique hybridization of the most common semiconductor nanomaterials could not only offer inherent asymmetry not to be cloned for a PUF but also guarantee scalable nanomanufacturing strategies to augment cryptosystems.