a b s t r a c tThe humidity-sensing properties of ZnO nanowires synthesized by carbothermal catalyst-free vapor solid (VS) technique were studied. The morphology and the crystal structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The humidity adsorption and desorption kinetics of the synthesized ZnO nanowires were investigated via quartz crystal microbalance (QCM) measurements. The observed positive frequency shift of ZnO nanowires when loaded on the QCM crystal under varying relative humidity conditions can be explained in terms of visco-elastic variations in their mechanical stiffness.
a b s t r a c t 4-[(3-Methylphenyl)(phenyl)amino]benzoic acid (MPPBA) was synthesized in order to facilitate the hole-injection in Organic Light Emitting Diodes (OLED). MPPBA was applied to form self-assembled monolayer (SAM) on indium tin oxide (ITO) anode to align energy-level at the interface between organic semiconductor material (TPD) and inorganic anode (ITO) in OLED devices. The modified surface was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). KPFM was used to measure the surface potential and work function between the tip and the ITO surface modified by SAM technique using MPPBA. The OLED devices (ITO/MPPBA/TPD/Alq 3 /Al) fabricated with SAM-modified ITO substrates showed lower turn-on voltages and enhanced diode current compare to the OLED devices fabricated with bare ITO substrates.Crown
a b s t r a c t 5-[(3-Methylphenyl)(phenyl)amino]isophthalic acid (5-MePIFA) and 5-(diphenyl)amino]isophthalic acid (5-DPIFA) organic molecules were synthesized to form self-assembled monolayer on indium tin oxide (ITO) anode to enhance hole transport from ITO to organic hole transport layers such as TPD. The modified surface was characterized by scanning tunneling microscopy (STM). The change in the surface potential was measured by Kelvin probe force microscopy (KPFM). Our Kelvin probe force microscopy (KPFM) measurements showed that the surface potentials increased more than 100 mV with reference to bare indium tin-oxide. The results show that the threshold voltage on OLEDs with modified ITO is lowered significantly compared to OLEDs with unmodified ITO. The hole mobility of TPD has been estimated using space-charge-limited current measurements (SCLC).
We have investigated the effect of two different self-assembled monolayers (SAMs) on electrical characteristics of bilayer graphene (BLG)/n-Si Schottky diodes. Novel 4 bis(diphenylamino)-1, 1 :3terphenyl-5 carboxylic acids (TPA) and 4,4-di-9H-carbazol-9-yl-1,1 :3 1 -terphenyl-5 carboxylic acid (CAR) aromatic SAMs have been used to modify n-Si surfaces. Cyclic voltammetry (CV) and Kelvin probe force microscopy (KPFM) results have been evaluated to verify the modification of n-Si surface. The current-voltage (I-V) characteristics of bare and SAMs modified devices show rectification behaviour verifying a Schottky junction at the interface. The ideality factors (n) from ln(I)-V dependences were determined as 2.13, 1.96 and 2.07 for BLG/n-Si, BLG/TPA/n-Si and BLG/CAR/n-Si Schottky diodes, respectively. In addition, Schottky barrier height (SBH) and series resistance (R s ) of SAMs modified diodes were decreased compared to bare diode due to the formation of a compatible interface between graphene and Si as well as -interaction between aromatic SAMs and graphene. The CAR-based device exhibits better diode characteristic compared to the TPA-based device. Computational simulations show that the BLG/CAR system exhibits smaller energy-level-differences than the BLG/TPA, which supports the experimental findings of a lower Schottky barrier and series resistance in BLG/CAR diode.
Au/n-Si/Graphene/Au Schottky diodes were fabricated by transferring atmospheric pressure chemical vapor deposited (APCVD) graphene on silicon substrates. Graphene/n-Si interface properties were improved by using 5-[(3-methylphenyl)(phenyl) amino]isophthalic acid (MePIFA) and 5-(diphenyl)amino]isophthalic acid (DPIFA) aromatic self-assembled monolayer (SAM) molecules. The surface morphologies of modified and non-modified films were investigated by atomic force microscopy and scanning electron microscopy. The surface potential characteristics were obtained by Kelvin-probe force microscopy and found as 0.158 V, 0.188 V and 0,383 V as a result of SAMs modification. The ideality factors of n-Si/Graphene, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes were found as 1.07, 1.13 and 1.15, respectively. Due to the chain length of aromatic organic MePIFA and DPIFA molecules, also the barrier height φ B values of the devices were decreased. While the barrier height of n-Si/Graphene diode was obtained as 0.931 eV, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes have barrier height of 0.820 and 0.720 eV, respectively. Graphene is a one-atom thick sheet of sp 2 bonded carbon atoms that are arranged in a honeycomb crystal lattice with exceptional properties. At room temperature electron mobility reached 2.5 × 10 5 cm 2 /V.s. 1 Young's modulus of 1 TPa and intrinsic strength of 130 GPa are very close to that were predicted by theory.2 Very high thermal conductivity (above 3000 WmK −1 ), 3 low optical absorption (∼2.3%), 4 ability to sustain high electric current densities 5 and be suitable to chemical functionalization [6][7][8] are other important properties of graphene that attract great attention. When graphene is transferred onto semiconductors such as GaAs, GaN, SiC and Si; it forms Schottky junctions.9-12 More efficient and stable solar cells and Schottky barrier devices will be achieved by the development of surface improvement, doping and functionalization. 13,14 The electrical transport performance of the fabricated Schottky diode is directly based on interface properties between substrate and graphene layer. 15Chemical Vapor Deposition (CVD) is promising technique for large area and high quality graphene growth. 16 In this technique, carbon precursors (methane, ethylene) are deposited carbon atoms onto the surfaces of various transition metals such as Nickel and Copper under high temperatures and form graphene. [16][17][18] Self-assembled monolayers (SAMs) are well-oriented molecular structures that are formed by the adsorption of an active surfactant on a substrate surface. Aromatic SAMs were used to modify anode/hole transport layer interface in order to achieve preferable barrier alignment and charge carrier injection. 19,20 Additionally, SAM modification of graphene also leads to electronic passivation of graphene edges and defects, thus might be responsible for a strong doping at the interface due to high acidity of the protons. 21 Although there have been various studies to enhance Schottky diodes depend...
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