Effect of trap states on the electrical doping of organic semiconductors

We demonstrate that direct charge transfer (CT) from trap states of host molecules to the p-dopant molecules raises the doping effect of organic semiconductors (OS). Electrons of the trap states in 4,4′-N,N′-dicarbazolyl-biphenyl (CBP) (E_HOMO = 6.1 eV) are directly transferred to the p-dopant, 2,2′-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6-TCNNQ) (ELUMO = 5.4 eV). This doping process enhances the conductivity of doped OS by different ways from the ordinary doping mechanism of generating free hole carriers and filling trap states of doped OS. Trap density and trap energy are analysed by impedance spectroscopy and it is shown that the direct charge transfer from deep trap states of host to dopants enhances the hole mobility of doped OS and the I–V characteristics of hole only devices.     

New hybrid method for simultaneous improvement of tensile and impact properties of carbon fiber reinforced composites

For weight savings of automobiles to improve fuel efficiency, tensile and impact strengths of carbon fiber reinforced composites (CFRC) are important properties required for substitution of metallic or ceramic automotive parts by CFRC parts. Effect of surface treatments of carbon fiber (CF) such as plasma, nitric acid, and liquid nitrogen treatments on interfacial bonding and mechanical properties of CF reinforced thermoplastic composites was investigated and nitric acid treatment was the best method to improve the interfacial affinity between the used CF and thermoplastic polymer matrix since the treatment induced acidic functional groups on the surface and increased surface roughness simultaneously. A new hybrid fabrication method was suggested by applying a bi-component two-layer structure to the film insert molding to improve tensile and impact strengths of CFRC simultaneously. Compared with tensile and impact strengths of the base polymer, those of the new hybrid composites filled with rubber particles and CF were improved by about 41.3% and 105.7%, respectively. In particular, tensile and impact strengths of the composite specimen prepared by the hybrid fabrication method were improved by about 15.0% and 36.0%, respectively when compared with those of the composite specimen prepared by the conventional melt mixing.     

High-performance supercapacitors based on defect-engineered carbon nanotubes

Defect-engineered carbon nanotubes (CNTs) were prepared by KOH activation and subsequent nitrogen doping. Controlled KOH activation of the CNTs enlarged the specific surface area to 988 m² g⁻¹, which is about 4.5 times greater than that of pristine CNTs. In addition, a hierarchical pore structure and a rough surface developed at high degrees of activation, which are advantageous features for fast ion diffusion. The subsequent nitrogen doping changed the band structure of the CNTs, resulting in improved electrical properties. Symmetric supercapacitors fabricated using these nitrogen-doped and activated CNTs (NA-CNTs) successfully worked across a wide potential range (0–3.5 V) and exhibited a high capacitance of 98 F g⁻¹ at a current density of 1 A g⁻¹. Furthermore, a low equivalent series resistance (2.2 Ω) was achieved owing to the tailored nanostructure and electrical properties of the electrode materials. Over the voltage range from 0 to 3.5 V, supercapacitors based on NA-CNTs exhibited a high specific energy of 59 Wh kg⁻¹ and a specific power of 1750 W kg⁻¹. In addition, a specific power of 52,500 W kg⁻¹ with a 3-s charge/discharge rate was achieved with a specific energy of 26 Wh kg⁻¹. Moreover, the supercapacitors showed stable performance over 10,000 charge/discharge cycles.     

Orientation dependence of secondary recrystallisation in silicon–iron

Experiments and analyses have been carried out to reach a better understanding of the mechanism of Goss texture formation during the secondary recrystallisation of silicon steel processed by the single cold reduction route. A new experimental approach demonstrated the effect of misorientation on the growth rates of secondary grains and it is shown that these rates are controlled by the proportion of matrix grains having Σ9 CSL relationships to growing secondary grains. It is considered that the Σ9 boundaries have lower energy than general grain boundaries and so are less strongly inhibited by Zener drag. The relative infrequency of Σ9 boundaries around the periphery of secondary grains is seen as evidence for their sacrificial behaviour. Other experiments involving growth of randomly oriented nuclei provide independent support for the important role of Σ9 boundaries during secondary recrystallisation in this steel.     

Impact of two circular plates one of which is floating on a thin layer of liquid

The paper deals with the axisymmetric unsteady problem of the collision of two circular plates, one of which is located initially on the surface of a shallow liquid layer and another is falling down on it. The presence of air between the colliding plates is taken into account. Both the air and the liquid are assumed ideal and incompressible and their flows potential. The flows in the liquid layer and between the plates are assumed one-dimensional with corrections for three-dimensional effects close to the plate edges. The present study is focused on the stage of strong interaction between the plates, during which the floating plate is accelerated and the hydrodynamic pressure in the liquid layer takes its maximum value. A simplified model of this interaction is suggested. Velocities of the plates and the hydrodynamic pressure on the bottom of the liquid layer are analytically estimated and compared with experimental results. The model provides the maximum of the hydrodynamic pressure, which can be used at the design stage. It is shown that the air flow between the moving plates is of major importance to explain the low amplitude of the measured hydrodynamic pressures.     

Micro/nano-heater integrated cantilevers for micro/nano-lithography applications

This paper describes an array of micro/nano-heater-integrated cantilevers for micro- and nano-lithography applications. In the scanning thermal cantilever, as the electrical current flows through the cantilever with a conductive tip, electrical power is dissipated mainly within the tip area, and this dissipation raises the local temperature around the tip area. When the thermal power is applied to a thin photoresist film, spin-coated on silicon wafers or mask substrates, more than 90% of solvents involved in the photoresist starts to evaporate from the layer. Hence, the exposed areas can resist commercial developers during the development process. Patterning speed has been improved by employing an array of heaters with various sizes. The novel concept of the SPM-based nano-lithography has been successfully demonstrated by application on the fabricated cantilevers and a commercial SPM system.     

Relationship between exciton recombination zone and applied voltage in organic light-emitting diodes

In this paper, the relationship between exciton recombination zone and applied voltage in organic light-emitting diodes (OLEDs) ITO/NPB (40 nm)/Alq₃(w nm)/rubrene(3 nm)/Alq₃(50−w)/Al, in which a 3 nm rubrene as sensing layer is inserted in Alq₃ layer at different depth, is studied. By comparing the electroluminescence (EL) spectra of device driven under different applied voltages, a conclusion can be drawn that the recombination zone shifts logarithmically with increasing applied voltages.     

Simultaneous enhancement of mechanical and microwave absorption properties with a novel in-situ synthesis α-Al2O3 fillers for SiCf/SiC composites

The Al and H₃BO₃ mixed powder was introduced into the PCS/Xylene precursor solution as in-situ synthesis α-Al₂O₃ filler by precursor infiltration and pyrolysis (PIP) method. The in-situ synthesis filler can effectively decrease the open porosity of SiC_f/SiC composites and give rise to multiple scattering of microwave and dipolar polarization. Therefore, the mechanical and microwave absorption properties of SiC_f/SiC composites can be simultaneously enhanced. The effects of in-situ synthesis filler on the morphologies, flexure strength and reflection loss values of SiC_f/SiC composites were investigated. With 2 wt% in-situ synthesis filler, the flexure strength of SiC_f/SiC composite was 305 MPa and the maximum reflection loss (RL_m) can reach ? 54.68 dB with the effective absorption band (EAB) of 3.51 GHz in the X band. With 5 wt% in-situ synthesis filler, the flexure strength of SiC_f/SiC composite was 207 MPa and the RL_m was ? 30.91 dB. Due to the inefficient infiltration process, the RL_m of SiC_f/SiC composites with 10 wt% in-situ synthesis filler was only ? 27.36 dB. Nevertheless, the flexure strength of that composite was 259 MPa, owing to the dense matrix. Additionally, the flexure strength of SiC_f/SiC composite without filler was 148 MPa and the RL_m was ? 26.40 dB.     

Effects of multilayer hydrothermal carbon interphases on mechanical properties and thermal shock resistance of CF/ZrB2-SiCBN

Multilayer hydrothermal carbon coatings (HTCCs) with various thicknesses were constructed on CFs using alternating hydrothermal carbonization and heat treatment approach. Well-established CF/ZrB₂-SiCBN composites with distinct multilayer interphases were processed via slurry injection and precursor infiltration pyrolysis method. The multilayer HTCCs with suitable thickness would be pulled-out stepwise from the matrix, which could absorb the impact energy and toughen the composites effectively. Although the outer HTCC would still react with the matrix to form a strong interface, the moderate interfacial binding force between CF and inner HTCC could effectively transfer the load and assure the fiber debonding when the composites deformed drastically. Moreover, the increasing of coating thickness could alleviate the damage of fibers in oxidation environment and improve the critical thermal shock temperature difference of composites, while the excessive thick coating would weaken the fiber strength and limit toughening abilities of the CFs.     

Effect of alloying chemistry on the lattice constant of austenitic Fe-Mn-Al-C alloys

In summary, the lattice constant of austenitic Fe-Mn-Al-C alloys as a function of composition has been determined. The addition of manganese, aluminum, or carbon increases the lattice constant of austenitic Fe-Mn-C alloys, but the addition of silicon decreases the lattice constant. The effect of aluminum and carbon on the increase in lattice constant are similar, while that of manganese is about one order of magnitude smaller.