Active control of metamaterial properties is critical for advanced terahertz (THz) applications. However, the tunability of THz properties, such as the resonance frequency and phase of the wave, remains challenging. Here, a new device design is provided for extensively tuning the resonance properties of THz metamaterials. Unlike previous approaches, the design is intended to control the electrical interconnections between the metallic unit structures of metamaterials. This strategy is referred to as the molecularization of the meta-atoms and is accomplished by placing graphene bridges between the metallic unit structures whose conductivity is modulated by an electrolyte gating. Because of the scalable nature of the molecularization, the resonance frequency of the terahertz metamaterials can be tuned as a function of the number of meta-atoms constituting a unit metamolecule. At the same time, the voltage-controlled molecularization allows delicate control over the phase shift of the transmitted THz, without changing the high transmission of the materials significantly.
Utilization of discontinuous pn-oragnic heterojunction is introduced as a versatile method to improve charge transport in organic thin film transistors (OTFTs). The method is demonstrated by depositing n-type dioctyl perylene tetracarboxylic diimide (PTCDI-C8) discontinuously onto base p-type pentacene OTFTs. A more pronounced impact of the discontinuous upper layer is obtained on the transistor performances when thinner base layers are employed; a >100-fold enhancement in hole mobility and a >20 V shift in threshold voltage are achieved after applying PTCDI-C8 discontinuously onto 2 nm thick pentacene thin films. Local surface potential measurements (Kelvin-probe force microscopy) and temperature-dependent transport measurements (77–300 K) reveal that the interfacial dipole formed at the pn-heterostructures effectively dopes the base pentacene films p-type and leads to a reduction in transport activation energy.
We present nonvolatile transistor memory devices that rely on the formation of electric double layer (EDL) at the semiconductor-electrolyte interface. The two critical functional components of the devices are the ion gel electrolyte and gold nanoparticles (NPs). The ion gel electrolyte contains ionic species for EDL formation that allow inducing charges in the semiconductor-electrolyte interface. The gold NPs inserted between the ion gel and the channel layer serve as trapping sites to the induced charges to store the electrical input signals. Two different types of gold NPs were used: one prepared using direct thermal evaporation and the other prepared using a colloidal process. The organic ligands attached onto the colloidal gold NPs prevented the escape of the trapped charges from the particles and thus enhanced the retention characteristics of the programmed/erased signals. The low-voltage-driven EDL formation resulted in a programmed/erased memory signal ratio larger than 10 from the nonvolatile indium-gallium-zinc oxide transistor memory devices at voltages below 10 V, which could be held for >10 s. The utility of the electrolytes to operate memory devices demonstrated herein should provide an alternative strategy to realize cheap, portable electronic devices powered with thin-film batteries.
In article number 1802760, Moon Sung Kang, Hojin Lee, and co-workers present a new device design for extensively tuning the terahertz metamaterial resonances by controlling the electrical interconnection between meta-atoms. This strategy is referred to as the molecularization of the meta-atoms and allows delicate control of the resonance frequency and phase shift of the transmitted THz waves by using graphene and an ion-gel gating system on flexible thin-film substrates.
Background: Ingestion of 210 Po laden seafood accounts for a substantial amount of the effective dose of 210 Po. Among seafood items, mollusks, especially domestically produced oysters and mussels, are highly enriched in 210 Po and are consumed in large quantities in Korea. Materials and Methods: Oysters and mussels around the Korean coasts were collected from major farm areas in November 2013. Samples were spiked with an aliquot of 209 Po as a yield tracer, and they were digested with 6 mol•L-1 HNO3 and H2O2. The 210 Po and 209 Po were spontaneously deposited onto a silver disc in an acidic solution of 0.5 mol•L-1 HCl and measured using an alpha spectrometer. The activity concentrations of 210 Pb and 210 Po were decay corrected to the sampling date, accounting for the possible in-growth and decay of 210 Po. Results and Discussion: 210 Po activity concentrations in oysters were in a range from 41.3 to 206 Bq•(kg-ww)-1 and mussels in a range from 42.9 to 46.7 Bq•(kg-ww)-1. The 210 Po activity concentration of oysters in the turbid Western coast was higher than the Southern coast. The 210 Po activity concentration of the oysters was positively correlated (R 2 = 0.89) with those of the suspended particulate matter in the surface water. The calculated annual effective dose of 210 Po from oysters and mussels consumed by the Korean population was 21-104 and 5.01-5.46 μSv•y-1. The combined effective dose due to the consumption of oysters and mussels appears to account for about 35 ± 19% of that arising from seafood consumption in the Korean population. Conclusion: The annual effective dose of 210 Po for oysters in the Korean population was found to be higher than other countries. The total annual effective dose of 210 Po due to consumption of oysters and mussels consumed in Korea was found to be 76 ± 42 µSv •y-1 , accounting for 28 ± 16% of the total effective dose of 210 Po from food in Korea.
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