The influence of lanthanum doping on the physical and electrical properties of BTV ferroelectric thin films

In this study, the ferroelectricity of as-deposited Bi_3.9La_0.1Ti_2.9V_0.1O₁₂ (BLTV), Bi_3.9Ti_2.9V_0.1O₁₂ (BTV), and Bi₄Ti₃O₁₂ (BIT) thin films was prepared and compared by rf magnetron sputtering technology. For the BLTV, BTV, and BIT thin films deposited on Pt/Ti/SiO₂/Si and SiO₂/Si substrate, the physical and electrical characteristics of lanthanum doped BTV (BLTV) were better than those of BIT and BTV thin films. Regarding the physical properties, the micro-structure of as-deposited BTV and BLTV thin films were obtained and compared by XRD patterns and SEM images. The BLTV and BTV thin films were also exhibited clear the ferroelectricity. The remanent polarization (P _r ) of as-deposited BLTV thin films was 11 μC/cm² as the measured frequency of 100 kHz. It was higher than those of BTV thin films. Finally, the polarization of BLTV thin film capacitor decreased by 9%, while that of the BTV decreased by 15% after the fatigue test with 10⁹ switching cycles.     

Magnetic properties of electroless-deposited Ni and Ni-NiO core-shell nano-arrays

Ni and Ni-NiO core-shell nano-arrays were fabricated by means of electroless deposition, where the latter was covered by a NiO shell of ∼10 nm by annealing the former at 350 °C for 30 min in an atmospheric condition. HRTEM showed that the NiO shell was developed at the expense of Ni at the array's surface. Ferromagnetic ordering of the Ni-NiO arrays was found to be suppressed compared with those of the less oxidized reference Ni arrays. This is attributed to the screening effect of the NiO shell, and weak ferromagnetism of inner Ni arrays resulted from the development of the NiO. X-ray absorption spectrum reveals that the reference Ni is partially oxidized. Also, X-ray magnetic circular dichroism suggests that the magnetic suppression of the Ni-NiO arrays is associated with a reduced spin moment.     

Influence of terminal substituent on non-linear S-shaped oligomers consisting of azobenzene moieties at the peripheral arm: Synthesis,characterisation and phase transition behaviour

A series of symmetrical S-shaped mesogens based on 4,4′-bis-(6-bromohexyloxy)biphenyl as a central unit containing two 2-{6-[4-(4-substitutedphenylazo)phenoxy]hexyloxy}phenol as side-chain groups has been successfully synthesised. The terminal substituent was varied from halogen (X = F, Cl, Br and I) to non-halogen (X = C₂H₅ and OC₂H₅). The oligomers with C₂H₅ and OC₂H₅ substituents exhibit predominantly the monotropic nematic (N) phase. The OC₂H₅-containing derivatives possess long-range stability of N phase than its C₂H₅-containing analogue in which it has small range of N phase stability. As for halogen-containing analogues, oligomer with F exhibits monotropic N phase whilst oligomers with Cl and Br exhibit monotropic N and smectic A (SmA) phases. In addition, homologue with Br shows additional phase which is smectic B (SmB) phase upon further cooling. However, the oligomers in which F, Cl and Br were substituted by I exhibits purely monotropic SmA and SmB phases. X-ray diffraction measurements reveal that the smectic phase is inclined to the monolayer structure.     

Large memory window in the vanadium doped Bi4Ti3O12 thin films

We report the enhancement of ferroelectric properties in vanadium-doped Bi₄Ti₃O₁₂ (BIT) thin films prepared by rf magnetron sputtering method for MFM and MFIS structures. The optimal sputtering parameters of the as-deposited Bi_3.9Ti_2.9V_0.08O₁₂ (BTV) ferroelectric films for different depositing times were obtained. Compared to the undoped BIT, vanadium doped BIT (BTV) showed better physical and electrical characteristics. The as-deposited BTV showed a remanent polarization (2P _r ) of 23 μC/cm², higher than the value of 16 μC/cm² for BIT, as the measured frequency was 100 kHz. For BTV thin films in the MFIS structure, the leakage current density and the memory window decreased, the change ratio of capacitance critically increased as the depositing time increased from 30 to 120 min. Regarding the measured physical properties, the micro-structure and thickness of as-deposited undoped and vanadium doped BIT thin films were obtained and compared by XRD patterns and SEM images.     

Star-like fluorene based polyamines: non-conjugated building blocks for light-harvesting materials

We report herein a series of novel tetramines (2-6) built using the fluorene core. The design features a diamine conjugated by a fluorene core and two non-conjugated triarylamines dangling through the bridge methine moiety. These polyamines are amorphous in nature and display moderate emission properties that are either dependent on the nature of the arylamine segments or reminescent of the fluorene backbone. The phenyl, naphthyl, fluorenyl and carbazolyl amine based materials are blue emissive while the pyrenylamine based compound emits yellow-green color. We demonstrate a possibility of using blue-emitting fluorene derivatives (2 and 4) blended with poly(N-vinylcarbazole) (PVK) to fabricate organic light emitting diodes (OLEDs). Emissions in the EL devices purely originated from the fluorene derivatives alone (blue) are contaminated with those of complex species (electromer/electroplex) formed by intermolecular interactions.     

Synthesis and phase transition behaviours of laterally substituted liquid crystals containing methylhydroquinone: emerging of smectic C phase for higher homologues

A series of laterally substituted low-molar-mass liquid crystals with molecular geometry were constructed with three phenyl rings bridged through ester central groups as the rigid core and a lateral methyl group as the flexible part of a molecule, with a view to understanding and establishing the effect of molecular structure on liquid crystal behaviour. Low-molar-mass mesogens known as 1,4-bis[(4′-n-alkyloxybenzoyl)oxy]toluene with different number of carbon (n) at the alkyl chain have been prepared. Their molecular structures were proposed via physical measurements and spectroscopic techniques. Mesomorphic properties were studied by using differential scanning calorimetry, optical polarizing microscopy and powder X-ray diffraction techniques. The results showed that the melting points as well as the clearing temperatures decreased upon lengthening of the terminal alkyloxy chain lengths. Members with the shorter chain (n = 2–10) exhibited nematic phase. As for higher homologues, members with n = 12, 14, 16 and 18 showed polymorphism, whereby these compounds displayed both smectic and nematic properties.     

VISCOPLASTIC COLLAPSE OF SHARP-NOTCHED CIRCULAR TUBES UNDER CYCLIC BENDING

This study discusses the experimental result of the viscoplastic response and col- lapse of sharp-notched 316L stainless steel tubes with different notched depths subjected to cyclic bending. The tube bending machine and curvature-ovalization measurement apparatus were used for conducting the symmetric curvature-controlled cyclic bending. To highlight the viscoplastic behavior, three different curvature-rates, 0.0035, 0.035 and 0.35 m-1s-1, were controlled. Ob- servations of a certain curvature-rate reveal that five almost parallel lines corresponding to five different notch-depth （0.2, 0.4, 0.6, 0.8 and 1.0 mm） tubes were presented in the experimental relationship between the cyclic controlled curvature and the number of cycles needed to pro- duce buckling on a log-log scale. However, the slopes for the three different curvature-rates are different. An empirical formulation was proposed to simulate the aforementioned relationship. When comparing with the experimental findings, the simulation was in good agreement with the experimental data.     

Liquid crystalline non-linear S-shaped oligomers consisting of azobenzene and biphenylene units: synthesis,characterisation and influence of central spacer

A series of non-linear S-shaped liquid crystal oligomers wherein the molecule consists of biphenylene moiety as a central core unit and two symmetrical side arms azobenzene moieties joined to catechol as a linkage group have been successfully synthesised and characterised. The members in this series possess different inner spacer with carbon number n ranging from 4 to 9 while the outer spacer length located in azobenzene moieties are remains unaltered. The members with even parity exhibit monotropic phase, whereas homologues with odd parity display enantiotropic phase. The appearance of nematic, smectic A and smectic B phases was validated with texture observation under polarised light and X-ray diffraction (XRD). The XRD study on the S-shaped oligomer indicates that the arrangement of smectic phase exists as an intercalated structure. The S-shaped oligomer shows photoisomerisation properties in solution whereby the trans to cis isomerisation for this molecule is accomplished 1140 s, whereas reverse process under thermal back reaction occurred in 4620 min.     

Analysis of perfluorooctanesulfonate and related fluorochemicals in water and biological tissue samples by liquid chromatography-ion trap mass spectrometry

A method for the determination of perfluorinated compounds (PFCs) in various water and biological tissue samples was developed and validated. The contents of selected PFCs (i.e., perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA) and perfluorodecanoate (PFDA)) in water samples were extracted by the C(18) solid-phase extraction (SPE). The biological tissue samples (frozen-dried fish and oysters) were simply extracted by liquid-solid extraction with MTBE and adding tetrabutylammonium hydrogensulfate (TBA) as an ion-pairing reagent. The analytes were then identified and quantitated by liquid chromatography-ion trap negative electrospray mass spectrometry (LC-ESI ion-trap-MS). Limits of quantitation (LOQ) were established between 0.5 and 6 ng/l in 250 ml of water sample, while 5-50 ng/g (dry weight) for biological tissue sample. Intrabatch and interbatch precision with their accuracy at two concentration levels were also investigated. Precision for these three PFCs, as indicated by RSD, proved to be less than 11 and 17%, respectively. The total contents of PFOA, PFOS and PFDA were detected in concentrations of up to 400 ng/l in various water samples, while up to 1,100 ng/g in fish and oyster samples. PFOA and PFDA was the major PFCs detected in water samples and biological tissue samples, respectively.