Highly efficient blue OLEDs based on diphenylaminofluorenylstyrenes end-capped with heterocyclic aromatics

In this paper, we have designed four diphenylaminofluorenylstyrene derivatives end-capped with heterocyclic aromatic groups, such as 9-phenylcabazole, 4-dibenzofuran, 2-benzoxazole, 2-quinoxaline, respectively. These materials showed blue to red fluorescence with maximum emission wavelengths of 476–611 nm, respectively, which were dependent on the structural and electronic nature of end-capping groups. To explore the electroluminescent properties of these materials, multilayer OLEDs were fabricated in the following sequence: ITO/DNTPD (40 nm)/NPB (20 nm)/2% doped in MADN (20 nm)/Alq₃ (40 nm)/Liq. (1 nm)/Al. Among those, a device exhibited a highly efficient blue emission with the maximum luminance of 14,480 cd/m² at 9 V, the luminous efficiency of 5.38 cd/A at 20 mA/cm², power efficiency of 2.77 lm/W at 20 mA/cm², and CIE_x,y coordinates of (0.147, 0.152) at 8 V, respectively.     

Study on the ITO work function and hole injection barrier at the interface of ITO/a-Si:H(p) in amorphous/crystalline silicon heterojunction solar cells

For this study we focused on the front contact barrier height of HIT (ITO/a-Si:H(p)/a-Si:H(i)/c-Si(n)) solar cell. The ITO films with low resistivity of 1.425 × 10^?4 Ω cm were deposited by pulsed DC magnetron sputtering as a function of substrate temperature (T_s). There were improvement in Φ_ITO from 4.15 to 4.30 eV and delta hole injection barrier from 0 to 0.129 eV for the HIT solar cell. The results show that the high values of Φ_ITO and the delta hole injection barrier at the front interface of ITO/p-layer lead to an increase of open circuit voltage (V_oc), fill factor (FF) and efficiency (η). The performance of HIT device was improved with the increase of T_s and the best photo voltage parameters of the device were found to be V_oc = 635 mV, FF = 0.737 and η = 14.33% for T_s = 200 °C.     

Organic light-emitting devices based on solution-processible quinolato-complex supramolecules

This paper discusses a new type of supramolecular material tris{5-N-[3-(9H-carbazol-9-yl)propyl]-N-(4-methylphenyl)aminesulfonyl-8-hydroxyquinolato} aluminum(III), Al(SCarq)₃, which we synthesized using three 5-N-[3-(9H-carbazol-9-yl)propyl]-N-(4-methylphenyl)aminesulfonyl-8-hydroxyquinoline as bidentate ligands. The peak photoluminescence in the solid phase appears at 488 nm. In cyclic voltammetric measurement, two oxidation peaks, which were obtained at ?5.6 and ?5.9 eV, correspond to HOMO sites of carbazoyl and aluminum quinolates, respectively. In the investigation of solid morphological thin film, the flat surface was investigated using an atomic force microscope. The root mean square (rms) and mean roughness (R_a) were respectively measured to be 0.427 and 0.343 nm. For the fabrication of organic light-emitting devices (OLEDs) using spin-coating techniques, the turn-on voltage and maximum luminescence of the optimized electroluminescence device, glass/ITO (20 nm)/PEDOT:PSS (75 nm)/Al(SCarq)₃ (85 nm)/BCP (8 nm)/LiF (1 nm)/Al (200 nm), were respectively 9.6 V and 35.0 cd m^?2. Due to the electroplex formation between the carbazole (electron-donor) and the aluminum quinolates (electron-acceptor) moieties under an applied DC bias, the chromaticity of electroluminescence shifted to green-yellow with 1931 CIE_x,y (0.40, 0.47).     

Luminescent properties and excitation mechanism of ZnSe quantum dots embedded in ZnS Matrix

In this paper, we report alternative-current thin film electroluminescence structure with ZnSe quantum dots embedded in ZnS matrix as light-emitting center, i.e., ITO/SiO_x (100 nm)/[ZnS (10 nm)/ZnSe (1 nm)]₃₀/SiO_x (100 nm)/Al. Blue emissions at 390 and 477 nm are obtained in its alternative-current electroluminescent spectra. By studying its luminescent spectroscopy and brightness oscillogram of the device, we found that blue emission came from defect states at ZnSe/ZnS interface and the excitation mechanism was hot-electron impact.     

Tantalum oxide film prepared by reactive magnetron sputtering deposition for all-solid-state electrochromic device

Inorganic-solid-state electrolyte tantalum oxide thin films were deposited by reactive DC magnetron sputtering to improve the leakage and deterioration of traditional liquid electrolytes in electrochromic devices. O₂ at 1–20 sccm flow rates was used to deposit the tantalum oxide films with various compositions and microstructures. The results indicate that the tantalum oxide thin films were amorphous, near-stoichiometric, porous with a loose fibrous structure, and highly transparent. The maximum charge capacity was obtained at an oxygen flow rate of 3 sccm and 50 W. The transmission change of the Ta₂O₅ film deposited on a WO₃/ITO/glass substrate between colored and bleached states at a wavelength of 550 nm was 56.7%. The all-solid-state electrochromic device was fabricated as a multilayer structure of glass/ITO/WO₃/Ta₂O₅/NiO_x/ITO/glass. The optical transmittance difference of the device increased with increasing applied voltage. The maximum change was 66.5% at an applied voltage of ± 5 V.     

Current-induced butterfly shaped domains and magnetization switching in magnetic tunnel junctions

Patterned magnetic tunnel junctions (MTJs) with the layer structure of Ta (5 nm)/Ni₇₉Fe₂₁ (5 nm)/Cu (20 nm)/Ni₇₉Fe₂₁ (5 nm)/Ir₂₂Mn₇₈ (10 nm)/Co₇₅Fe₂₅ (4 nm)/Al (0.8 nm)-oxide/Co₇₅Fe₂₅ (4 nm)/Ni₇₉Fe₂₁ (20 nm)/Ta (5 nm) were fabricated using magnetron sputtering deposition and lithography. High tunnelling magnetoresistance ratios of 22 and 50% were obtained at room temperature before and after annealing, respectively. The evolution of leaf shaped images was observed via Lorentz transmission electron microscopy (LTEM) on the MTJs, which were deposited on a patterned and carbon-coated transmission electron microscopy grid. These leaf-like LTEM images correspond to a butterfly shaped domain structure that was confirmed by a micromagnetics simulation. When a large DC current or bias voltage was applied across the MTJ, the butterfly-like vortex domain structures could be induced to form in the free layer of the MTJ, resulting in a significant decrease of magnetization in the free layer. The existence of these butterfly shaped domains could be one of the major causes of the bias voltage dependence of the TMR ratio.     

Synthesis and luminescence of a new phosphorescent iridium(III) pyrazine complex

The synthesis and luminescent study of a new iridium pyrazine complex are reported. The iridium complex [Ir(MDPP)2(acac)] (MDPP=5-methyl-2,3-diphenylpyrazine, acac=acetylacetone) shows strong ¹MLCT (singlet metal-to-ligand charge-transfer) and ³MLCT (triplet metal to ligand charge-transfer) absorption at 386 and 507 nm, respectively. Organic light emitting device (OLED) with a configuration of ITO / NPB (30 nm) / NPB: 7% (wt.) Ir(MDPP)₂(acac) (25 nm) / BCP (10 nm) / Alq₃(30 nm) / Mg : Ag (mass ratio 10 : 1)120 nm / Ag(10 nm) exhibits an external quantum efficiency of 6.02% (power efficiency 9.89 lm W^− 1 ) and a maximum brightness of 78,924 cd m^− 2. The device also shows high color purity with a maximum peak at 576 nm without any shoulder.     

Magnetic exchange coupling in bilayers of two epitaxial ferromagnetic oxides

Despite a decade of research effort on La_0.7Sr_0.3MnO₃/SrRuO₃ (LSMO/SRO) bilayers (BLs), a full knowledge on the magnetic properties and integration of these BLs on silicon substrate is not yet in sight. In this paper, we report on the magnetic exchange coupling observed from the above two ferromagnetic oxide thin film BLs, prepared through a novel approach, called ‘domain matching epitaxy’. LSMO (100 nm)/SRO (45 nm) and LSMO (31 nm)/SRO (45 nm) bilayers have been epitaxially integrated with Si (1 0 0). Notably, in the former sample, positive exchange bias is observed – an indication of antiferromagnetic exchange coupling and is found to be absent in the latter. Furthermore, in the former sample, the cross-over from antiferromagnetic to ferromagnetic interface exchange coupling is noticed by varying the cooling field. We have verified that this coupling is of magnetic origin, not due to electrostatic interaction by inserting a thin (∼10 nm) SrTiO₃ layer between LSMO and SRO. We believe that in addition to the formation of interface domain walls, the strong interplay among Zeeman, anisotropic and exchange energies could play a dominant role. Our results would have important implications for devices comprising of magnetic exchange coupled systems.     

Synthesis and sintering of tin-doped indium oxide nanoparticles with uniform size

The urea-based hydrothermal (UBH) method can synthesize indium tin oxide (ITO) nanopowders with good monodispersity and size uniformity. However, the resulting formation of high pressure CO₂ gas by the hydrolysis of urea during the hydrothermal process is unsafe. The pressure generated by the UBH method can be lowered by connecting the hydrothermal reactor to a vessel containing sodium hydroxide solution to quickly absorb CO₂ gas. ITO nanoparticles with particle sizes of 90 ± 3 nm and 40 ± 3 nm can be produced. The size of the as-prepared nanoparticles is readily controlled by adjusting the precursor concentration. Using properly mixed nanoparticles with a volume ratio of V_40 nm:V_90 nm = 30:70 as the raw materials, ITO can be sintered to a high and consistent density of 99.3–99.5% of the theoretical density.     

Enhanced photoluminescence features of Eu3+-modified di-ureasil-zirconium oxocluster organic–inorganic hybrids

In this work, a series of transparent di-ureasil hybrids containing different amounts of methacrylic acid modified zirconium tetrapropoxide (ZrMcOH) nanoclusters (5–85 mol%) and incorporating EuCl₃ and [Eu(tta)₃(H₂O)₂] (tta = thenoyltrifluoroacetonate) complex were prepared. These hybrids are multi-wavelength emitters due to the convolution of the host intrinsic emission (electron–hole recombinations occurring in siliceous and urea cross-linkages) Eu³⁺ intra-4f⁶ transitions. The ZrMcOH incorporation deviates the maximum excitation wavelength of the hybrid host intrinsic emission from the UV (365 nm) to the blue (420 nm) and enhances the absolute emission quantum yield from 6.0 ± 0.6% to 9.0 ± 0.9%, and contributes to an increase in the ⁵D₀ lifetime values, quantum efficiency due to a decrease in the non-radiative transition probability and OH groups coordinated to the Eu³⁺ ions.     

Potentiometric urea biosensor based on multi-walled carbon nanotubes (MWCNTs)/silica composite material

A novel potentiometric urea biosensor has been fabricated with urease (Urs) immobilized multi-walled carbon nanotubes (MWCNTs) embedded in silica matrix deposited on the surface of indium tin oxide (ITO) coated glass plate. The enzyme Urs was covalently linked with the exposed free –COOH groups of functionalized MWCNTs (F-MWCNTs), which are subsequently incorporated within the silica matrix by sol–gel method. The Urs/MWCNTs/SiO₂/ITO composite modified electrode was characterized by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and UV–visible spectroscopy. The morphologies and electrochemical performance of the modified Urs/MWCNTs/SiO₂/ITO electrode have been investigated by scanning electron microscopy (SEM) and potentiometric method, respectively. The synergistic effect of silica matrix, F-MWCNTs and biocompatibility of Urs/MWCNTs/SiO₂ made the biosensor to have the excellent electro catalytic activity and high stability. The resulting biosensor exhibits a good response performance to urea detection with a wide linear range from 2.18 × 10^? 5 to 1.07 × 10^? 3 M urea. The biosensor shows a short response time of 10–25 s and a high sensitivity of 23 mV/decade/cm².     

Enhancement of external quantum efficiency and reduction of roll-off in blue phosphorescent organic light emitt diodes using TCTA inter-layer

The improved external quantum efficiency (EQE) and reduced roll-off properties of blue phosphorescent organic light-emitting diodes (PHOLEDs), were fabricated with structure, ITO/NPB (400 Å)/TCTA (200 Å)/mCP:FIrpic (7%)(300 Å)/TPBi (300 Å)/Liq (20 Å)/Al (800 Å) by incorporating an 4,4′,4′′-tris(carbazol-9-yl)-triphenylamine (TCTA) interlayer. We compared the properties of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) as the electron transport layer (ETL) with a typical structure of hole transport layer (HTL)/emissive layer (EML)/ETL in OLEDs and utilized inter-layer in the optimized structure to enhance EQE to 52% at 5.5 V, also stabilize the roll-off of 23%. The use of inter-layer in blue PHOLEDs exhibits a current efficiency of 10.04 cd/A, an EQE of 6.20% at 5.5 V and the highest luminance of 10310 cd/m² at 9.5 V. We have identified the properties of electroluminescence through the inter-layer in blue PHOLEDs which can be divided into singlet excitons and triplet excitons which emit fluorescence of N,N′-bis(1-naphthalenyl)-N,N′-bis-phenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) at 420 nm and phosphorescence of Iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C²′] picolinate (FIrpic) at 470 nm, 494 nm, respectively.     

The roles of nano-SiO2 particles on the tribological behavior of short carbon fiber reinforced PEEK

In the present work, the roles of low-loading (1 vol.%) nano-SiO₂ particles (13 nm) on the tribological behavior of short carbon fiber (SCF)/PTFE/graphite (micro-sized) filled PEEK were investigated. Tribological tests were carried out at room temperature in extremely wide pressure and sliding velocity ranges, i.e. from 1 MPa to 7 MPa and from 1 m/s to 2 m/s, respectively. Under all conditions studied, the nanopartilces remarkably reduce the friction coefficients. With respect to the wear rates, however, the roles of the nanoparticles show a strong dependence on the sliding conditions. Under 1 MPa, the abrasiveness exerted by possible nano-SiO₂ agglomerates seems to accelerate SCF destructions. Under pressures higher than 2 MPa, however, the nanoparticles remarkably reduce the wear rate. This effect is more pronounced under high pressures and especially at high sliding velocities. The protection of SCF/matrix interface by the nanoparticles is supposed to be the main reason for the enhancement of the wear resistance.     

Improved efficiency of sol–gel synthesized mesoporous anatase nanopowders in photocatalytic degradation of metoprolol

The structural and morphological properties of mesoporous anatase nanopowders, synthesized by sol–gel method, have been modified by varying the duration of calcination, in order to obtain more efficient photocatalyst than Degussa P25 in the degradation of relatively large pollutant molecules (>1 nm in size). According to X-ray diffraction analysis, the crystallite size was increased from 13 to 17.5 nm with the increase of calcination time from 1 to 7 h. The analysis of nitrogen sorption experimental data revealed that all samples were mesoporous, with a mean pore diameters in the range of ∼5–9 nm. The corrugated pore structure model was employed to evaluate pore structure tortuosity. Nanopowder properties have been related to the photocatalytic activity, tested in the degradation of metoprolol tartrate salt, selective β₁-blocker used in a variety of cardiovascular diseases, with molecular size of 0.610 nm × 1.347 nm. The study has demonstrated that samples calcined for 4 and 5 h have displayed higher photocatalytic performance than Degussa P25, whereas the sample calcined for 3 h has shown comparable activity.     

Microstructural,electrical and optical properties of indium tin oxide (ITO) nanoparticles synthesized by co-precipitation method

In the present study, the synthesis of Tin doped indium oxide (ITO) nanopowder at different compositions (In/Sn = 0, 5, 10, 15 at %) was carried out by co-precipitation method. The decomposition of precipitated indium tin acetylacetonate precursor to form In₂O₃–SnO₂ (Sn_1?xIn_xO₂) at 400 °C was confirmed by the thermal and FTIR studies. The changes in strain and grain size of the synthesized particle with respect to dopant concentration were determined from the X-ray diffraction (XRD) analysis. Transmission electron microscopy (TEM) images support to confirm the grain size. The optical properties on ITO nanoparticles were analyzed with UV–visible spectroscopy, and band gap was found to vary from 3.62 to 3.89 eV with Sn dopant concentration. This variation was ascribed to the quantum confinement effect.     

Time-resolved photoluminescence from Si-in-SiNx/Si-in-SiC quantum well-dot structures

Si-in-SiN_x/Si-in-SiC quantum well-dot structures, with Si quantum dots slightly larger than 1.0 nm embedded in both amorphous SiN_x and SiC sublayers, were grown at nearly room temperature by using PECVD. Time-resolved photoluminescence for three samples in a period of 100/30 nm, 60/10 nm and 20/10 nm, respectively, has been measured at emission lengths ranging from 430 nm to 490 nm, and fitted with a stretched-exponential function. Typical decay time was at the order of one nanosecond, which could be attributed to the core-state emission. The matrix materials forming the well provide a non-uniform potential background which induces a modulation to the carrier diffusion process, thus resulting in an emission-wavelength dependent decay time. When confinement effect from the well comes into play as in the sample of smaller well width, the decay time can be below 1.0 ns and indifferent to the varied emission wavelength, and the carrier diffusion is dominated by hopping. These quantum well-dot systems of strong and fast decaying light emission in blue–violet colors might find potential utilization in GHz optical connection and other photoelectronic devices.     

Spectroscopic characterizations of Er doped LaPO4 submicron phosphors prepared by homogeneous precipitation method

Hexagonal shaped LaPO₄ submicron particles doped with various concentrations of Er were successfully prepared by homogenous precipitation method using metal nitrates and ammonium phosphate. Particles of approximate particle size 125 nm and size distribution of 85 nm are obtained with good crystallinity. After heat treatment at 1200 °C for 2 h, the particles are characterized for their various optical properties such as absorption, emission, fluorescence decay and optical band gap. Optical absorption and emission data are numerically analyzed with the help of Judd–Ofelt model to evaluate various radiative spectral properties such as radiative decay rates, radiative quantum yield, emission cross-section and fluorescence branching ratios of various emission transitions. Though the radiative quantum yield of 1554 nm emission approaches the theoretical limit of 100%, the experimentally measured quantum yield is only 11% at 12 W/cm² at 980 nm excitation power density in 2% Er doped LaPO₄.     

Study of annealing time on sol–gel indium tin oxide films on glass

Indium and tin salt-based precursors maintaining In:Sn atomic ratio as 90:10 were utilized for the development of sol–gel dip coated indium tin oxide films (ITO) on SiO₂ coated (∼ 200 nm thickness) soda lime silica glass substrate. The gel films were initially cured in air at ∼ 450 °C to obtain oxide films of physical thickness ∼ 250 nm. These were then annealed in 95% Ar–5% H₂ atmosphere at ∼ 500 °C. The annealing time was varied from 0.5 h to 5 h. Variation of annealing time did not show any considerable change of transmittance in the visible region. Thermal emissivity (ε_d, 0.67–0.79) of the films were evaluated from their hemispherical spectral reflectance. These passed through a minima with increasing annealing time as the reflectivity of the films in the mid-IR passed through a maxima. The microstructure of the films revealed systematic growth of the ITO grains. XRD and XPS studies revealed the presence of both In and Sn metals in addition to the metal oxides. The energy dispersive X-ray (EDX) analysis showed little lowering of tin content in the films with increasing annealing time.     

Synthesis and functionalization of SiO2 coated Fe3O4 nanoparticles with amine groups based on self-assembly

The purpose of this research was to synthesize amino modified Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetic iron-oxide nanoparticles (NPs) were prepared via co-precipitation. The NPs were then modified with a thin layer of amorphous silica. The particle surface was then terminated with amine groups. The results showed that smaller particles can be synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g^? 1 for uncoated Fe₃O₄ NPs and it increased to about 208 m² g^?1 for 3-aminopropyltriethoxysilane (APTS) coated Fe₃O₄/SiO₂ NPs. The total thickness and the structure of core-shell was measured and studied by transmission electron microscopy (TEM). For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of (80–100) emu g^?1 and coercivity of (80–120) Oe for particles between (35–96) nm, respectively. The Fe₃O₄/SiO₂ NPs with 50 nm as particle size, demonstrated a magnetization value of 30 emu g^?1. The stable magnetic fluid contained well-dispersed Fe₃O₄/SiO₂/APTS nanoshells which indicated monodispersity and fast magnetic response.     

Lithium storage capability of CuGeO3 nanorods

Copper metagermanate (CuGeO₃) nanorods were synthesized through a low temperature hydrothermal method at 180 °C. The as-synthesized CuGeO₃ nanorods show a well crystallined nanostructure with diameters in the range from 40 to 70 nm, and a length from 250 to 350 nm. Electrochemical measurements demonstrate that the CuGeO₃ nanorods exhibit a first charge capacity of 924 mAh g^?1 and 690 mAh g^?1 after 50 cycles, which is remarkably improved than the pure nanosize GeO₂ electrode. This investigation indicates that CuGeO₃ nanorods could be utilized as a high capacity anode material in lithium-ion batteries by reducing particle size and metal oxide addition. The lithium storage mechanisms for the improved capacity retention were also studied.