Improving Charge-Imbalanced Problem of Quantum Dot Light-Emitting Diodes with TPBi/ZnO Electron Transport Layer.

To solve charge-imbalanced problem caused by excessive electron injection into the emitting layer (EML) of quantum dot light emitting diodes (QLEDs) with ZnO electron transport layer (ETL), we proposed QLEDs with TPBi((2,2',2''-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)))/ZnO ETL layered design. Spin coated TPBi demonstrated lower value of the lowest unoccupied molecular orbital (LUMO) than conduction band maximum (CBM) of ZnO, resulting in effective prevention of excessive injection of electrons into the EML even under excessive stress conditions. Experimental results demonstrated that QLEDs with TPBi/ZnO ETL not only could minimize charge imbalanced problem under high current density operation, but also could increase the maximum luminance of QLEDs by up to 156% (i.e., from 10,320 to 16,081 cd/m²). In addition, the new design with TPBi resulted in low roll-off phenomenon in external quantum efficiency (EQE)-current density characteristics.

Ultra-low Doping on Two-Dimensional Transition Metal Dichalcogenides using DNA Nanostructure Doped by a Combination of Lanthanide and Metal Ions.

Here, we propose a novel DNA-based doping method on MoS2 and WSe2 films, which enables ultra-low n- and p-doping control and allows for proper adjustments in device performance. This is achieved by selecting and/or combining different types of divalent metal and trivalent lanthanide (Ln) ions on DNA nanostructures, using the newly proposed concept of Co-DNA (DNA functionalized by both divalent metal and trivalent Ln ions). The available n-doping range on the MoS2 by Ln-DNA is between 6 × 10(9) and 2.6 × 10(10 ) cm(-2). The p-doping change on WSe2 by Ln-DNA is adjusted between -1.0 × 10(10) and -2.4 × 10(10 ) cm(-2). In Eu(3+) or Gd(3+)-Co-DNA doping, a light p-doping is observed on MoS2 and WSe2 (~10(10 ) cm(-2)). However, in the devices doped by Tb(3+) or Er(3+)-Co-DNA, a light n-doping (~10(10 ) cm(-2)) occurs. A significant increase in on-current is also observed on the MoS2 and WSe2 devices, which are, respectively, doped by Tb(3+)- and Gd(3+)-Co-DNA, due to the reduction of effective barrier heights by the doping. In terms of optoelectronic device performance, the Tb(3+) or Er(3+)-Co-DNA (n-doping) and the Eu(3+) or Gd(3+)-Co-DNA (p-doping) improve the MoS2 and WSe2 photodetectors, respectively. We also show an excellent absorbing property by Tb(3+) ions on the TMD photodetectors.

n- and p-Type doping phenomenon by artificial DNA and M-DNA on two-dimensional transition metal dichalcogenides.

Deoxyribonucleic acid (DNA) and two-dimensional (2D) transition metal dichalcogenide (TMD) nanotechnology holds great potential for the development of extremely small devices with increasingly complex functionality. However, most current research related to DNA is limited to crystal growth and synthesis. In addition, since controllable doping methods like ion implantation can cause fatal crystal damage to 2D TMD materials, it is very hard to achieve a low-level doping concentration (nondegenerate regime) on TMD in the present state of technology. Here, we report a nondegenerate doping phenomenon for TMD materials (MoS2 and WSe2, which represent n- and p-channel materials, respectively) using DNA and slightly modified DNA by metal ions (Zn(2+), Ni(2+), Co(2+), and Cu(2+)), named as M-DNA. This study is an example of interdisciplinary convergence research between DNA nanotechnology and TMD-based 2D device technology. The phosphate backbone (PO4(-)) in DNA attracts and holds hole carriers in the TMD region, n-doping the TMD films. Conversely, M-DNA nanostructures, which are functionalized by intercalating metal ions, have positive dipole moments and consequently reduce the electron carrier density of TMD materials, resulting in p-doping phenomenon. N-doping by DNA occurs at ∼6.4 × 10(10) cm(-2) on MoS2 and ∼7.3 × 10(9) cm(-2) on WSe2, which is uniform across the TMD area. p-Doping which is uniformly achieved by M-DNA occurs between 2.3 × 10(10) and 5.5 × 10(10) cm(-2) on MoS2 and between 2.4 × 10(10) and 5.0 × 10(10) cm(-2) on WSe2. These doping levels are in the nondegenerate regime, allowing for the proper design of performance parameters of TMD-based electronic and optoelectronic devices (VTH, on-/off-currents, field-effect mobility, photoresponsivity, and detectivity). In addition, by controlling the metal ions used, the p-doping level of TMD materials, which also influences their performance parameters, can be controlled. This interdisciplinary convergence research will allow for the successful integration of future layered semiconductor devices requiring extremely small and very complicated structures.

Poly-4-vinylphenol and poly(melamine-co-formaldehyde)-based graphene passivation method for flexible, wearable and transparent electronics.

Next generation graphene-based electronics essentially need a dielectric layer with several requirements such as high flexibility, high transparency, and low process temperature. Here, we propose and investigate a flexible and transparent poly-4-vinylphenol and poly(melamine-co-formaldehyde) (PVP/PMF) insulating layer to achieve intrinsic graphene and an excellent gate dielectric layer at sub 200 °C. Chemical and electrical effects of PVP/PMF layer on graphene as well as its dielectric property are systematically investigated through various measurements by adjusting the ratio of PVP to PMF and annealing temperature. The optimized PVP/PMF insulating layer not only removes the native -OH functional groups which work as electron-withdrawing agents on graphene (Dirac point close to zero) but also shows an excellent dielectric property (low hysteresis voltage). Finally, a flexible, wearable, and transparent (95.8%) graphene transistor with Dirac point close to zero is demonstrated on polyethylene terephthalate (PET) substrate by exploiting PVP/PMF layer which can be scaled down to 20 nm.

Selective formation of a latticed nanostructure with the precise alignment of DNA-templated gold nanowires.

A very efficient method is introduced to selectively align and uniformly separate λ-DNA molecules and thus DNA-templated gold nanowires (AuNW's) using a combination of molecular combing and surface-patterning techniques. By the method presented in this work, it is possible to obtain parallel and latticed nanostructures consisting of DNA molecules and thus DNA-templated AuNW's aligned at 400 nm intervals. DNA-templated AuNW's are uniformly formed with an average height of 2.5 nm. This method is expected to hold potential for the integration of nanosized building blocks applicable to nanodevice construction.

Fabrication of highly uniform conductive polypyrrole nanowires with DNA template.

Deoxyribonucleic acid (DNA) is considered as one of the alternative materials for electronic device applications; however, DNA has critical limitation to electronic device applications due to its low electrical conductivity and unreliability. Therefore, it is required for electronic devices to prepare the well defined conductive polymer nanowires with DNA as a template. Polypyrrole (PPy) is an attractive polymer due to its high conductivity and environmental stability in bulk; although it is well known that ammonium persulfate (APS) used for the polymerization of pyrrole causes the deformation of DNA molecules. We minimized the damage of immobilized DNA strands on (3-aminopropyl) triethoxysilane (APTES) modified silicon wafer during APS polymerization. Atomic force microscopy (AFM) images from different APS treatment times and from using the vortex process obviously showed the effect on the synthesis of individual and continuous polypyrrole nanowires (PPy NWs). The PPy NWs at various pyrrole concentrations had similar height; however, the higher concentration gave more residues. Fourier transform-infrared spectroscopy (FT-IR) spectroscopy provided the strong evidence that PPy NWs were successfully synthesized on the DNA strands.

Electrical characteristics and doping mechanism of DNA molecules doped with iodine solutions.

This study examined the electrical characteristics of deoxyribonucleic acid (DNA) molecules doped with iodine solution and their chemical state changes before and after doping. The experiments were progressed in each lambda (A), poly(dA)-poly(dT) and poly(dG)-poly(dC) DNA under the same conditions. The authors prepared 20 nm gap Au/Ti electrodes fabricated by e-beam lithography. DNA solutions were dropped on the nano gap of the electrodes and DNA films were formed by drying in a vacuum. DNA films were doped with an iodine solution dissolved in methanol. The authors measured the electrical conductivity of DNA molecules as the number of iodine doping times in 10(-2) torr vacuum. As increase of the iodine solution doping number, the electrical conductivity of three sorts of DNA molecules was remarkably improved respectively. X-ray photoelectron spectroscopy (XPS) was performed to inspect the electrical conduction mechanism that holes on DNA nitrogen region were generated by transferring electrons to iodine molecules.

Formation of lambda-DNA's in parallel- and crossed-line arrays by molecular combing and scanning-probe lithography.

With the combination of a molecular combing technique and scanning-probe lithographic patterning, lambda-DNA's were stretched and aligned to form line array structures on patterned organic monolayer surfaces. The pattern was generated by anodizing a silicon surface using scanning-probe lithography to implant a polar organic layer in the middle of a nonpolar layer. The molecule in the polar layer, (aminopropyl)triethoxysilane (APS), has a -NH(3)(+) terminal group, which interacts strongly with phosphate backbone of DNA and provides a site for selective attachment of DNA. When parallel lines of APS were patterned, followed by combing along the lines, a single DNA was attached from the very top of each line and stretched along the line all the way to the bottom. The DNA-APS interaction was strong enough to withstand the second combing applied perpendicular to the first one. Thereby, the crossed-line array of DNA's was formed on the crossed-line array pattern of APS on a silicon substrate.