Zhuoyu Ji

Solid-state fluorescence enhancement of organic dyes by photonic crystals

Photonic crystal (PC) films were fabricated by self-assembly of colloidal crystals using a vertical deposition method at invariant temperature and humidity. Organic dyes, whose emission wavelengths overlap the photonic stopbands of selected PCs, were deposited on the surface of PC films by thermal evaporation under vacuum. The fluorescence of organic dyes deposited on PCs is obviously enhanced in comparison with that on aluminium films and glass surfaces. There were 41-fold and 20-fold fluorescence enhancements when Rhodamine B base was deposited on the surface of a yellow PC film, compared with that on glass surface and aluminium film respectively, where PCs were utilized as a Bragg reflection mirror. The results show that the PCs are more effective and selective reflection mirrors than aluminium, and have potential applications in optoelectronic and lighting devices.

A non-planar organic molecule with non-volatile electrical bistability for nano-scale data storage

A new non-planar organic molecule with electron donor and acceptor capabilities was synthesized for nano-scale data storage. Macroscopic I–V characteristics of organic crystalline thin films indicate that the non-planar molecule possesses good electrical bistability. Nano-scale recording dots with an average diameter of 2.5 nm were realized by scanning tunneling microscopy.

Low-Voltage Organic Field-Effect Transistor With PMMA/

This paper reports on the application of a bilayer polymethylmethacrylate (PMMA)/ZrO2 dielectric in copper ph-thalocyanine (CuPc) organic field-effect transistors (OFETs). By depositing a PMMA layer on ZrO2, the leakage of the dielectric is reduced by one order of magnitude compared to single- layer ZrO2. A high-quality interface is obtained between the organic semiconductor and the combined insulators. By integrating the advantages of polymer and high-fe dielectrics, the device achieves both high mobility and low threshold voltage. The typical field-effect mobility, threshold voltage, on/off current ratio, and subthreshold slope of OFETs with bilayer dielectric are 5.6 times 10-2 cm2/V ldr s, 0.8 V, 1.2 times 103, and 2.1 V/dec, respectively. By using the bilayer dielectrics, the hysteresis observed in the devices with single-layer ZrO2 is no longer present.

\hbox{ZrO}_{2}

Applying a bidirectional sweeping gate voltage, the white-light illuminated copper phthalocyanine thin-film transistors (CuPc-TFTs) show obvious hysteresis effect and the hysteresis window is 32 V. This effect is dominated by the additional carriers generated by photoirradiation. Although small hysteresis exists in CuPc-TFTs without illumination, light makes the hysteresis more obvious. Thus, CuPc-TFTs are promising to realize light detection and/or light memory in a single organic device for future low-cost, ultrahigh-density organic photoelectric integration.

Bilayer Dielectric

In this letter, a contact-length-dependent contact resistance model for top-gate staggered organic thin-film transistors (OTFTs) is proposed. The presented model can well describe the contact resistance increase as the distance by which the gate electrode overlaps the source and drain contact (contact length) decrease. Based on the contact resistance model, the contact-length-dependent cutoff frequency of OTFTs is described, and an optimized contact length can be obtained for high-frequency OTFT applications.

Light-induced hysteresis characteristics of copper phthalocyanine organic thin-film transistors

Contact resistance has great impact on the performance of oxide thin film transistors (TFTs) and their applications. In this letter, temperature, gate voltage, and electrode dependences of the contact resistance were investigated in amorphous InGaZnO (a-IGZO) TFTs. We found that gate voltage dependent contact resistance made a large contribution to or even dominated the “field effect” of oxide TFTs. After separating the influence of contact resistance, the intrinsic temperature dependent field effect mobility of the a-IGZO TFTs was obtained. Furthermore, the experimental data of the contact resistance can be well described by an optimized transmission line model, and the height of the Schottky barrier in the interface between the metal electrode and a-IGZO semiconductor was found to be related to the gate voltage and account for the contact resistances dependence on the gate voltage.

Contact-Length-Dependent Contact Resistance of Top-Gate Staggered Organic Thin-Film Transistors

In this letter, an improved transmission line model is proposed to investigate contact resistance (CR) in bottom-gate bottom-contact organic thin-film transistors (OTFTs). With the modified model, the CR decreases with the increase of gate voltage, which is a good agreement to experimental results. Further, the CR dependence to thickness, width, and edge angle of drain/source electrode contact has been discussed in detail. The simulation result provides a possible way to improve the performance of bottom-contact OTFTs.

Analysis of the contact resistance in amorphous InGaZnO thin film transistors

We propose an approach for nanopore-based DNA sequencing using characteristic transverse differential conductance. Molecular dynamics and electron transport simulations show that thetransverse diff ...

Modified Transmission Line Model for Bottom-Contact Organic Transistors

A disorder based analytical carrier density for graphene is presented here. The carrier density, a basic property of all semiconductors, is obtained based on exponential distribution describing the potential fluctuations induced by impurities and shows good agreement with numerical results. The quantum capacitance is subsequently derived from the carrier density, with a good agreement with experimental measurements. A method for extracting the gate coupling function is also proposed, which relates the internal surface potential with the external applied gate voltage. The essential properties of graphene device physics, such as the temperature, material disorder, and surface potential dependences, are captured in these analytical equations.

Differential conductance as a promising approach for rapid DNA sequencing with nanopore-embedded electrodes

In this letter, an organic memory cell based on tris(8-hydroxyquinolinato)aluminum doped with gold nanoparticles is reported. The device can achieve good resistive switching properties, such as a high on/off current ratio of about 104, and good retention (4 h at 0.1 V). The device remains in either state even after the power has been turned off and shows a good stability under stress test. The current-voltage characteristics are comprehensively investigated, and a possible mechanism is proposed and well fitted with the experiment data. The results show that the organic memory devices have promising potentials for future flexible electronic systems.