Delta(δ)‐doping of semiconductor nanowires

The electronic sub‐band structure of single δ‐layers in GaAs nanowires have been determined via the self‐consistent solution of the Poisson–Schrödinger equations in the effective mass approximation. The spread and sheet density of the δ‐layer were varied systematically between 1–12 nm and 10¹²–10¹³ cm^–2, respectively. A V‐shaped potential is obtained for a δ‐layer of 8 nm with a sheet density of 8 × 10¹² cm^–2at the core resulting in strong confinement with just one sub‐band falling below the Fermi level, but complete depletion occurs for smaller spreads and/or sheet densities. In contrast a W‐like potential is obtained across the diameter with three sub‐bands below the Fermi level when the same δ‐layer is positioned half way between the core and surface due to weaker quantum confinement. Finally, δ‐doping at the surface results in a flat‐band potential extending from the core up to the surface and a thinner tunnel barrier suitable for the formation of low‐resistance ohmic contacts and higher carrier mobilities since the charge distribution has a maximum at the core in all of the aforementioned cases. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐association,tautomerism and E–Z isomerization of isatin–phenylsemicarbazones – spectral study and theoretical calculations

The self‐association and tautomerism of (E)‐isatin‐3‐4‐phenyl(semicarbazone) Ia and (E)‐N‐methylisatin‐3‐4‐phenyl(semicarbazone) IIa were investigated in solvents of various polarity. In weakly interacting non‐polar solvents, such as CHCl₃ and benzene, phenylsemicarbazone concentrations above 1×10^?5 mol dm^?3 result in the formation of dimers or higher aggregates of E‐isomers Ia and IIa . This aggregate formation prevents room temperature E–Z isomerization of Ia and IIa to more stable Z‐isomers. In contrast to the situation in non‐polar solvents, E–Z isomerization from the monomeric form of phenylsemicarbazone Ia and IIa E‐isomers occurs in highly interactive polar solvents including MeOH and DMF only at temperatures above 70 °C. Moreover, decrease in phenylsemicarbazone concentration below 1×10^?4 mol dm^?3 in these highly solute–solvent interacting systems leads to aggregate dissociation, and a new hydrazonol tautomeric form with a high degree of conjugation predominates in these solutions. Theoretical calculations confirm obtained experimental results. Copyright © 2013 John Wiley & Sons, Ltd.     

Self‐association in {2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]‐thienyl}alkanols: an NMR,IR, and single‐crystal X‐ray study

syn‐2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. Single‐crystal X‐ray diffraction study of the 3,4‐ethylenedioxythiophene (EDOT) derivative shows that it exists as a centrosymmetric head‐to‐tail, syn dimer in the solid state. The IR spectra of the solids display only a broad OH absorption around 3300 cm^?1, corresponding to a hydrogen‐bonded species. ¹H Nuclear Overhauser Effect Spectroscopy (NOESY) NMR experiments in benzene reveal interactions between the tert‐butyl groups and the H2 and H6 protons of the pyridyl group. Two approaches have been used to determine association constants of the EDOT derivative by NMR titration, based on the concentration dependence of (i) the syn/anti ratio and (ii) the OH proton shift of the syn rotamer. Reasonably concordant results are obtained from 298 to 323 K (3.6 and 3.9 M^?1, respectively, at 298 K). Similar values are obtained from the syn OH proton shift variation for the 3,4‐methylenedioxythiophene (MDOT) derivative. Concentration‐dependent variation of the anti OH proton shift in the latter suggests that the anti isomer associates in the form of an open, singly hydrogen‐bonded dimer, with a much smaller association constant than the syn rotamer. Self‐association constants for 3‐pyridyl‐EDOT‐alkanols with smaller substituents vary by a factor of 4 from (i‐Pr)₂ up to (CD₃)₂, while the hetero‐association constants for the same compounds with pyridine vary slightly less. Copyright © 2007 John Wiley & Sons, Ltd.     

Self‐Assembly of Drug–Drug Conjugates as Drug Self‐Delivery System for Tumor‐Specific pH‐Triggered Release

An acid‐labile doxorubicin dimer (D‐DOX) is designed as drug–drug conjugate for tumor intracellular pH‐triggered release, by conjugating doxorubicin (DOX) with adipic acid dihydrazide (ADH). The dimer‐based surfactants modified with polyethylene glycol (PEG), DOX‐ADH‐DOX‐PEG or are synthesized by mono‐PEGylation and bi‐PEGylation, respectively. Then the prodrug nanoparticles are fabricated with different drug contents via dialyzing the mixture solution of D‐DOX and the PEGylated surfactants in dimethyl sulfoxide (DMSO) with different mass ratios against water. It is found that the smaller prodrug nanoparticles (142–163 nm) could be obtained with the mono‐PEGylated surfactant, than those of 157–225 nm with the bi‐PEGylated surfactant. Furthermore, the mono‐PEGylated surfactant results in a higher drug content of 51% due to their lower PEG contents. All prodrug nanoparticles could release DOX completely within 36 h at pH 5.0, with the premature drug leakage of less than 10% at pH 7.4. The 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assays demonstrate the proposed drug self‐delivery system possessed an enhanced anticancer efficacy against HepG2 cells than the free DOX.     

Zinc Oxide–Porphyrin Hybrid Rhombuses: Catalytically Active Microstructures via Self‐Assembly

A novel self‐assembled organic–inorganic hybrid structure consisting of zinc oxide and two oppositely charged porphyrins, showing significantly enhanced photocatalytic activity, is presented. Electrostatic self‐assembly of the cationic tetra‐(N‐methyl‐4‐pyridyl)porphyrin (TMPyP) with preformed assemblies of ZnO nanorods and the anionic tetra‐(4‐sulfonatophenyl)porphyrin (TPPS) in ethanol results in porphyrin microrhombuses decorated with ZnO nanorods. The structure formation is followed spectroscopically. The shape of the microrhombuses and the number of attached ZnO nanoparticles can be tuned through the porphyrin ratio TMPyP/TPPS. An enhanced and selective catalytic activity is found, giving insight into the degradation mechanism. Due to the tool‐box principle and its versatility, the concept may have great impact in fields such as solar‐energy conversion and optoelectronics.     

A 3‐state defect model for light‐induced degradation in boron‐doped float‐zone silicon

We report on a light‐induced bulk defect activation and subsequent deactivation in boron doped float‐zone silicon that can be described by a 3‐state model. During treatment at elevated temperature and illumination, a sample first converts from an initial high lifetime state into a degraded low lifetime state and then shows a recovery reaction leading to a third high lifetime state that is then stable under degradation conditions. Furthermore, it is shown that reverse reactions into the initial state appear to be possible both from the degraded as well as the regenerated state. An injection dependent analysis of lifetime data yields a defect capture cross section ratio of ～20 suggesting a positively charged defect. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Effect of solvent evaporation on the self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) and on the film morphology during electrospray deposition

A high‐voltage rectangular pulse was applied to the electro‐spray deposition (ESD) to control the evaporation‐induced self‐assembly of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT). Two groups of P3HT thin films were deposited by a series of high‐voltage rectangular pulses. Compared with the ESD driven by a constant voltage, the pulse‐driven ESD enables to probe the effect of solvent evaporation on the self‐assembly of P3HT molecules. The droplet size and the evaporation of residual solvent in the droplet determine the film morphology. Ultraviolet–visible absorption spectroscopy was used to identify the ordering of P3HT molecules in the films. The self‐assembly of P3HT molecules took place during the solvent evaporation which can be controlled by a combination of the pulse amplitude and the pulse interval. With an appropriate combination of the amplitude and the interval, the ESD produced a P3HT thin film with high chain ordering.

     

4‐Alkyl‐2,2,6,6‐tetramethyl‐1,4,2,6‐oxaazadisilinanes: synthesis,structure, and conformational analysis

4‐Alkyl‐2,2,6,6‐tetramethyl‐1,4,2,6‐oxaazadisilinanes RN[CH₂Si(Me)₂]₂O [R = Me ( 1 ), i‐Pr ( 2 )] were synthesized by two methods which provided good yields up to 84%. Low temperature NMR study of compounds ( 1 ) and ( 2 ) revealed a frozen ring inversion with the energy barriers of 8.5 and 7.7 kcal/mol at 163 and 143 K, respectively, which is substantially lower than that for their carbon analog, N‐methylmorpholine. DFT calculations performed on the example of molecule ( 1 ) showed that N? Me_ax conformer to exist in the sofa conformation with the coplanar fragment C? Si? O? Si? C, and its N? Me_eq conformer in a flattened chair conformation. Copyright © 2009 John Wiley & Sons, Ltd.     

掺杂浓度及掺杂层厚度对Si均匀掺杂的GaAs量子阱中电子态结构的影响

本文通过自洽地求解薛定鄂方程及泊松方程计算了在温度T=0, 有效质量近似下, Si均匀掺杂的GaAs/AlGaAs量子阱系统的电子态结构. 研究了掺杂浓度及掺杂层厚度对子带能量, 本征包络函数, 自洽势, 电子密度分布, 及费米能量的影响. 发现在给定掺杂浓度下, 子带能量随掺杂层厚度的增加单调递减, 自洽势的势阱变宽变浅, 电子密度分布变宽, 峰值变低; 在给定掺杂层厚度下, 随掺杂浓度的增加子带能量及费米能级单调递增, 自洽势阱变深变陡变窄, 电子密度分布的峰值变高, 集中在中心. 关键词： 掺杂 量子阱 电子结构 半导体GaAs     

Bond cutting in Cs‐doped tris(8‐hydroxyquinoline) aluminium

A series of Cs 4d and Al 2p spectra associated with valence‐band and cut‐off spectra have been used to characterize the interaction between caesium and tris(8‐hydroxyquinoline) aluminium (Alq₃) molecules in a Cs‐doped Alq₃ layer. The Cs 4d and Al 2p spectra were tuned to be very surface sensitive by selecting a photon energy of 120 eV at the National Synchrotron Radiation Research Center, Taiwan. A critical Cs concentration exists, above which a new Al 2p signal appears next to the Al 2p peak of Alq₃ in the lower binding‐energy side. The Al 2p signal was analyzed and assigned as being contributed from a mixture of Alq₂, Alq and Al. Experimental data supported the observation that bond cutting of Alq₃ by the doped Cs atoms occurred at high Cs doping concentration.     

Bond cutting in K‐doped tris(8‐hydroxyquinoline) aluminium

A series of Al 2p, K 2p, O 1s and N 1s core‐level spectra have been used to characterize the interaction between potassium (K) and tris(8‐hydroxyquinoline) aluminium (Alq₃) molecules in the K‐doped Alq₃ layer. All core‐level spectra were tuned to be very surface sensitive in selecting various photon energies provided by the wide‐range beamline at the National Synchrotron Radiation Research Center, Taiwan. A critical K concentration (x = 2.4) exists in the K‐doped Alq₃ layer, below which the K‐doped atoms generate a strained environment near the O and N atoms within 8‐quinolinoline ligands. This creates new O 1s and N 1s components on the lower binding‐energy side. Above the critical K coverage, the K‐doped atoms attach the O atoms in the Al—O—C bonds next to the phenoxide ring and replace Al—O—C bonds by forming K—O—C bonds. An Alq₃ molecule is disassembled into Alq₂ and Kq by bond cutting and bond formation. The Alq₂ molecule can be further dissociated into Alq, or even Al, through subsequent formations of Kq.     

Physical image vs structure relation: part 12 – structure of 2,2,5,5‐tetramethyl‐dihydro‐furan‐3‐one oxime and its protonated forms through isomerization and NMR spectra

The study of an isomeric A / B mixture of the title oxime 1 , by photolytic or thermal E,Z‐isomerization and NMR measurement including ¹H{¹H}‐NOE difference spectra, led to assignment of the E configuration to its predominating form A . The ¹H/¹³C data were interpreted in terms of steric overcrowding of both forms, especially of the thermolabile photoproduct B . Four classical (empirical) NMR methods of elucidating the oxime geometry were critically tested on these results. Unexpected vapor‐phase photoconversion A → B in the window glass‐filtered solar UV and spectroscopic findings on their protonated states were discussed, as well. The kinetically controlled formation of the N‐protonated species (Z)‐ 5 ⁺ was proved experimentally. In addition, some ¹H NMR assignments reported for structurally similar systems were rationalized ( 3 and 4 ) or revised ( 1 and 7–9 ) with the GIAO‐DFT(B3LYP) and/or GIAO‐HF calculational results. Copyright © 2007 John Wiley & Sons, Ltd.     

Correction method for the self‐absorption effects in fluorescence extended X‐ray absorption fine structure on multilayer samples

A novel correction method for self‐absorption effects is proposed for extended X‐ray absorption fine structure (EXAFS) detected in the fluorescence mode on multilayer samples. The effects of refraction and multiple reflection at the interfaces are fully considered in this correction method. The correction is performed in k‐space before any further data analysis, and it can be applied to single‐layer or multilayer samples with flat surfaces and without thickness limit when the model parameters for the samples are known. The validity of this method is verified by the fluorescence EXAFS data collected for a Cr/C multilayer sample measured at different experimental geometries.     

Composition dependent self‐regenerative property of perovskite‐type oxides

The self‐regenerative property of LaCo_{1–x –y}Pd_x Zn_y O_3±δ and LaFe_{1–x –y}Pd_x Zn_y O_3±δ solid solutions with monometallic Pd or bimetallic Pd/Zn substituents for Co or Fe is studied under a redox cycle by high angular annular dark‐field scanning transmission electron microscopy (STEM‐HAADF) and energy dispersive X‐ray spectroscopy (EDX) and X‐ray diffraction (XRD). These results reveal that the composition of perovskites determines the self‐regenerative property that occurs largely in LaCo_{1–x –y}Pd_x Zn_y O_3±δ but is limited greatly in LaFe_{1–x –y}Pd_x Zn_y O_3±δ. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Self‐Organization of Anisotropic and Binary Colloids in Thermo‐Switchable 1D Microconfinement

Anisotropic and binary colloids self‐assemble into a variety of novel supracolloidal structures within the thermo‐switchable confinement of molecular microtubes, achieving structuring at multiple length scales and dimensionalities. The multistage self‐assembly strategy involving hard colloidal particles and a soft supramolecular template is generic for colloids with different geometries and materials as well as their binary mixtures. The colloidal architectures can be controlled by colloid shape, size, and concentration. Colloidal cubes align in chains with face‐to‐face arrangement, whereas rod‐like colloids predominantly self‐organize in end‐to‐end configurations with their long axis parallel with the long axis of the microtubes. The 1D microconfinement imposed on binary mixtures of anisotropic and isotropic colloids further increases the diversity of colloid‐in‐tube structures. In cube–sphere mixtures, cubes may act as additional confiners, locking in colloidal sphere chains, while a “colloidal Morse code” is generated where rods and spheres alternate in the case of rod–sphere mixtures. The versatile confined colloidal superstructures including their thermoresponsive assembly and disassembly are relevant for the development of stimulus–responsive materials where controlled release and encapsulation are desired.     

Charge‐transfer‐induced doping at an electron donor (α‐sexithiophene)/acceptor (C60) interface and mobility improvement

We studied various aspects relating to surface charge‐transfer‐induced doping at an organic/organic interface using in situ electrical measurements with a field‐effect transistor (FET) during the formation of the electron donor/acceptor interface. Adsorption of the electron‐accepting molecules (C₆₀) on top of the electron donating molecules (α‐6T) led to an increase in the FET hole mobility in an α‐6T film. Under illumination, the FET hole mobility in the α‐6T film with C₆₀ deposition was significantly increased in comparison with that in the dark due to exciton dissociation at the C₆₀/α‐6T interface, resulting in a large threshold voltage shift. The origin of the mobility increase is explained by the multiple trapping and release (MTR) model in which the mobility is determined by the carrier density. Various phenomena relevant to charge transfer and charge transport at the organic/organic interface are reported and their origins are discussed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Raman imaging and stress quantification in self‐assembled graphene oxide fiber ‘Latin Letters’

To probe the intrinsic stress distribution in terms of spatial Raman shift (ω) and change in the phonon linewidth (Γ), here we analyze self‐assembled graphene oxide fibers (GOF) ‘Latin letters’ by confocal Raman spectroscopy. The self‐assembly of GOF ‘Latin letters’ has been explained through surface tension, π–π stacking, van der Waals interaction at the air–water interface and by systematic time‐dependent investigation using field emission scanning electron microscopy analysis. Intrinsic residual stress due to structural joints and bending is playing a distinct role affecting the E_2g mode (G band) at and away from the physical interface of GOF segments with broadening of phonon linewidth, indicating prominent phonon softening. Linescan across an interface of the GOF ‘letters’ reveals Raman shift to lower wavenumber in all cases but more so in ‘Z’ fiber exhibiting a broader region. Furthermore, intrinsic stress homogeneity is observed for ‘G’ fiber distributed throughout its curvature with negligible shift corresponding to E_2g mode vibration. This article demonstrates the significance of morphology in stress distribution across the self‐assembled and ‘smart‐integrable’ GOF ‘Latin letters’. Copyright © 2016 John Wiley & Sons, Ltd.     

Layer‐by‐layer AuCl3 doping of stacked graphene films

We investigated the effect of layer‐by‐layer AuCl₃ doping on the electrical and optical properties of stacked graphene films. Graphene grown by the chemical‐vapor deposition method on a Cu‐foil was chemically doped by AuCl₃ solution with a concentration of 20 mM. Eight different configurations were prepared and analyzed by using four‐point probe measurements, optical transmittance measurements, scanning electron microscopy, and micro‐Raman spectroscopy to compare the optical and electrical characteristics of the different graphene samples. In our study, the top‐layer doping method was very effective because better performances considering both sheet resistance and optical transmittance were observed from the configurations with the top‐layer doped. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)