Single photon sources are fundamental building blocks for quantum communication and computing technologies. In this work, we present a device geometry consisting of gold pillars embedded in a van der Waals heterostructure of graphene, hexagonal boron nitride, and tungsten diselenide. The gold pillars serve to both generate strain and inject charge carriers, allowing us to simultaneously demonstrate the positional control and electrical pumping of a single photon emitter. Moreover, increasing the thickness of the hexagonal boron nitride tunnel barriers restricts electroluminescence but enables electrical control of the emission energy of the site-controlled single photon emitters, with measured energy shifts reaching 40 meV.

The phase diagram of an interacting two-dimensional electron system in a high magnetic field is enriched by the varying form of the effective Coulomb interaction, which depends strongly on the Landau level index. While the fractional quantum Hall states that dominate in the lower-energy Landau levels have been explored experimentally in a variety of two-dimensional systems, much less work has been done to explore electron solids owing to their subtle transport signatures and extreme sensitivity to disorder. Here, we use chemical potential measurements to map the phase diagram of electron solid states in N=2, N=3, and N=4 Landau levels in monolayer graphene. Direct comparison between our data and theoretical calculations reveals a cascade of density-tuned phase transitions between electron bubble phases up to two, three, or four electrons per bubble in the N=2, 3, and 4 Landau levels, respectively. Finite-temperature measurements are consistent with melting of the solids for T≈1 K.

A two-dimensional (2D) atomic crystalline transition metal dichalcogenides has shown immense features, aiming for future nanoelectronic devices comparable to conventional silicon (Si). 2D molybdenum ditelluride (MoTe₂) has a small bandgap, appears close to that of Si, and is more favorable than other typical 2D semiconductors. In this study, we demonstrate laser-induced p-type doping in a selective region of n-type semiconducting MoTe₂ field effect transistors (FET) with an advance in using the hexagonal boron nitride as passivation layer from protecting the structure phase change from laser doping. A single nanoflake MoTe₂-based FET, exhibiting initial n-type and converting to p-type in clear four-step doping, changing charge transport behavior in a selective surface region by laser doping. The device shows high electron mobility of about 23.4 cm²V^-1s^-1 in an intrinsic n-type channel and hole mobility of about 0.61 cm²V^-1s^-1 with a high on/off ratio. The device was measured in the range of temperature 77-300 K to observe the consistency of the MoTe₂-based FET in intrinsic and laser-dopped region. In addition, we measured the device as a complementary metal-oxide-semiconductor (CMOS) inverter by switching the charge-carrier polarity of the MoTe₂ FET. This fabrication process of selective laser doping can potentially be used for larger-scale MoTe₂ CMOS circuit applications.

A water soluble cationic fluorescent probe(TPEDPyMe) was designed and synthesized by attaching two pyridinium moieties onto the tetraphenylethene(TPE) core.The molecular structure of TPEDPyMe was characterized by multiple spectroscopic techniques,and its fluorescence property was examined.As its maternal compound,TPEDPyMe exhibited typical aggregation-induced emission(AIE) behavior,and the emission peaked at around 630 nm in aqueous solution.TPEDPyMe was used as a fluorescent probe to detect ctDNA in tris-HCl buffer solution at a pH value of 7.2.It was found that the fluorescence intensity of the TPEDPyMe in the buffer solution was boosted up to 20 folds when the concentration of ctDNA increased from 0 μg/mL to 500 μg/mL.Meanwhile,the emission peaks blue-shifted from 627 nm to 576 nm.In the concentration region from 0 μg/mL to 50 μg/mL,the change in fluorescence intensity was linearly proportional to the concentration of ctDNA.In this region,the Stern-Volmer constant or KSV was calculated to be 1.4 × 102,showing a desirable sensitivity of TPEDPyMe to ctDNA.Moreover,when the concentration of ctDNA increased from 0 μg/mL to 500 μg/mL,the emission peak shifted from 633 nm to 578 nm.This phenomenon implies that the TPEDPyMe can be used as a dual-responsive fluorescent label for probing ctDNA,which is of great significance in biosensor technologies.In summary,the present results indicate that TPEDPyMe is a promising fluorescent probe for the detection of DNA species and more detailed investigation is going on in the laboratory.

Abstract New aromatic diyne monomers of 1,4‐diethynyl‐2,5‐(dihexyloxy)benzene ( 1 ), 1,6‐diethynyl‐2‐(hexyloxy)naphthalene ( 2 ), and 9,9‐bis(4‐ethynylphenyl)fluorene ( 3 ) are synthesized. Their homopolymerizations and copolymerizations with 1‐octyne ( 4 ) or phenylacetylene ( 5 ) are effected by TaBr 5 –Ph 4 Sn and CpCo(CO) 2 – hν , giving soluble hyperbranched polyarylenes with high molecular weights ( M w up to ∼ 2.9 × 10 5 ) in high yields (up to 99%). The structures and properties of the polymers are characterized and evaluated by IR, NMR, UV, PL, and TGA analysis. The polymers show excellent thermal stability ( T d > 400 °C) and carbonize when pyrolyzed at 900 °C. Upon photoexcitation, the polymers emit deep blue light in the vicinity of ∼400 nm with fluorescence quantum yields up to 92%. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4249–4263, 2007

Homopolycouplings of aryltriynes Ar(C⋮CH)3 and their copolycouplings with monoyne Ar‘C⋮CH are effected by CuCl in air under Glaser-Hay oxidative coupling conditions, giving soluble hyperbranched polyynes (hb-PYs). Hyperbranched poly[tris(4-ethynylphenyl)amine] emits bright blue light (λem = 440 nm) and shows high light refractivity (n = 1.770−1.861). Its peripheral terminal triple bonds can be 100% end-capped by aromatic rings via palladium-catalyzed coupling with aryliodides. The carbon-rich polyynes are readily curable (from ∼150 °C), thermally stable (Td up to ∼550 °C), and pyrolytically carbonizable (Wr up to ∼80% at 900 °C). Complexations with cobalt carbonyls metallify the hb-PYs, and ceramizations of the cobalt−polyyne complexes afford soft ferromagnetic materials with high magnetizability (Ms up to ∼118 emu/g) and low coercivity (Hc down to ∼0.045 kOe).

Abstract Van der Waals heterostructures are an excellent platform for studying intriguing interface phenomena, such as moiré and proximity effects. Many of these phenomena occurring in such heterostructures' interfaces and surfaces have so far been hampered because of their high sensitivity to disorder and interface contamination. Here, it reports a dry polymer‐based assembly technique to fabricate arbitrary designer van der Waals heterostructures with atomically clean surfaces. The key features of the suspended dry pick‐up and flip‐over assembly technique are: 1) the heterostructure surface never comes into contact with polymers, 2) the assemble is entirely solvent‐free, 3) it is entirely performed in a glovebox, and 4) it only requires temperatures below 130 °C. By performing ambient atomic force microscopy and atomically‐resolved scanning tunneling microscopy on example heterostructures, it demonstrates the fabrication of air‐sensitive heterostructures with ultra‐clean interfaces and surfaces. It envisions that, due to the avoidance of polymer melting, this technique is potentially compatible with heterostructure assembly under ultra‐high vacuum conditions, which promises ultimate heterostructure quality.

Abstract Valley Hall effect is observed in asymmetric single‐layer and bilayer graphene systems. In single‐layer graphene systems, asymmetry is introduced by aligning graphene with hexagonal boron nitride (hBN) with a near‐zero twist angle, breaking the sub‐lattice symmetry. Although a similar approach is used in bilayer graphene to break the layer symmetry and thereby observe the valley Hall effect, the bilayer graphene is sandwiched with hBN on both sides in those studies. This study looks at a much simpler, non‐encapsulated structure where hBN is present only at the top of graphene. The crystallographic axes of both hBN and bilayer graphene are aligned. A clear signature of the valley Hall effect through non‐local resistance measurement ( R NL ) is observed. The observed non‐local resistance can be manipulated by applying a displacement field across the heterostructure. Furthermore, the electronic band structure and Berry curvature calculations validate the experimental observations.

The electronic properties of electrode materials play a crucial role in defining their electrochemical behavior in energy conversion and storage devices. The assembly of van der Waals heterostructures and fabrication into mesoscopic devices enable the dependence of an electrochemical response on electronic properties to be systematically interrogated. Here, we evaluate the effect of charge carrier concentration on heterogeneous electron transfer at few-layer MoS₂ electrodes by combining spatially resolved electrochemical measurements with field-effect electrostatic manipulation of band alignment. Steady-state cyclic voltammograms and finite-element simulations reveal a strong modulation of the measured electrochemical response for outer-sphere charge transfer at the electrostatic gate voltage. In addition, spatially resolved voltammetric responses, obtained at a series of locations at the surface of few-layer MoS₂, reveal the governing role of in-plane charge transport on the electrochemical behavior of 2D electrodes, especially under conditions of low carrier densities.

cis,cis-1,2,3,4-Tetraphenylbutadiene (TPBD) exhibits aggregation-induced emission (AIE) in the UV-blue band: the photoluminescence (PL) quantum yield of TPBD aggregates can differ from that of molecularly dissolved species by 2 orders of magnitude (>200). When the isolated molecules in solutions are cooled to extremely low temperature, they also emit intense light comparable to that in the solid state. TPBD thin layer shows on−off fluorescence switching behavior that can be utilized for the sensing of organic vapors. The phenyl substituents in TPBD are twisted in the solid state, and excimer formation is greatly prohibited. The cooling-enhanced emission of the TPBD solution and the fluorescence switching behavior suggest that the aggregation-induced emission is caused by restricted intramolecular rotation of the phenyl groups. The intramolecular phenyl rotations of TPBD can be regarded as rotational relaxations around their equilibrium positions, from which mean relaxation time is defined based on an Arrhenius equation. All the PL behaviors of TPBD can be well explained qualitatively by the magnitude of the relaxation time.