Kurash Ibrahim

Influences of Structural Properties on Stability of Fullerenols

Influences of structural properties on the stability of fullerenols are studied using experimental techniques including laser-induced dissociation associated with a time-of-flight measurement, synchrotron radiation XPS, and FT-IR spectroscopy. Stabilities of a family of fullerenols (C60(OH)42, C60(OH)44, C60(OH)30, C60(OH)30, C60(OH)32, and C60(OH)36) as functions of structural parameters-the hydroxyl number, intensity of the impure group, and the ratio of the carbonyl to hydroxyl groups-are investigated. It is found that the molecular stability largely depends on the quantity of impure groups, especially the highly oxygenated carbons in fullerenols, but less on the hydroxyl number. This is different from the previous consideration that the stability of fullerenols largely depends on the hydroxyl number. Previously, to gain the larger solubility required by practical applications, it was suggested to increase the number of the hydroxyl groups. This idea needs to be restudied, because in highly hydroxylated fullerenol molecules, the coinstantaneous formation of a large amount of impure groups is observed. The use of C60(OH) n>36 in practical applications should proceed with caution, since these could lead to unstable open-cage structures. The results reveal a way of controlling the formation of impure groups to gain fullerenols of high stability.

Epitaxial Growth and Air-Stability of Monolayer Antimonene on PdTe2

Monolayer antimonene is fabricated on PdTe2 by an epitaxial method. Monolayer antimonene is theoretically predicted to have a large bandgap for nanoelectronic devices. Air-exposure experiments indicate amazing chemical stability, which is great for device fabrication. A method to fabricate high-quality monolayer antimonene with several great properties for novel electronic and optoelectronic applications is provided.

Structural determination of titanium-oxide nanoparticles by x-ray absorption spectroscopy

To understand and improve the applications of titanium-oxide nanoparticles, it is extremely important to perform a detailed investigation of the surface and the interior structural properties of nanocrystalline materials, such as rutile and anatase with diameter of few nanometers. Here, x-ray absorption spectroscopy has been used to identify the local Ti environment and characterize the related electronic structure. We combine experimental results at the Ti K edge in both bulk and nanocrystal samples to determine the lattice distortion via the characteristic pre-edge features and the variation in the multiple-scattering region of the x-ray absorption near-edge structure spectra. The correlation between peak intensities and surface-to-volume ratio of nanoparticles is also discussed.

Carrier-transport, photoluminescence, and electroluminescence properties comparison of a series of terbium complexes with different structures

A series of terbium complexes with different structures revealed different carrier-transport and photophysical properties. Complex A [tris(1-phenyl-3-methyl-4-isobutyl-5-pyrazolone)-bis(triphenyl phosphine oxide), Tb(PMIP)3(TPPO)2] had overly strong electron-transport properties, complex B [Tb(PMIP)3(EtOH)(H2O)] mainly revealed hole-transport properties, and complex C [tris(1-phenyl-3-methyl-4-(2-ethylbutyryl)-5-pyrazolone) triphenyl phosphine oxide, Tb(eb-PMP)3(TPPO)] showed both electron- and hole-transport properties. Their PL intensity ratio was A−B−C = 2.6:1:1.2. The eletroluminescence (EL) performances (brightness and peak power efficiency) achieved from complexes A, B, and C were 9600 cd/m2 and 5.21 lm/W, 2800 cd/m2 and 2.61 lm/W, and 12000 cd/m2 and 11.3 lm/W, from device configurations of ITO/TPD−B−A−AlQ−Mg0.9Ag0.1−Ag (20:20:50:30:200:80 nm), ITO/TPD−B−BCP−AlQ−Mg0.9Ag0.1)−Ag (40:30:20:20:200:80 nm), and ITO/NPB−C−BCP−AlQ−Mg0.9Ag0.1−Ag (10:50:20:40:200:80 nm), respectively. Results indicated that ...

Electronic structure of antimonene grown on Sb2Te3 (111) and Bi2Te3 substrates

We explore the formation of single bilayer Sb(111) ultrathin film (Antimonene) on Bi2Te3 and Sb2Te3 substrates for the first time, which is theoretically predicated to be a robust trivial semiconductor but can be tuned to a 2D TI by reducing the buckling height. From angle-resolved photoemission spectroscopy measurements, the antimonene can be well grown on the two surfaces and shows clear band dispersion. The electronic structure of the antimonene shows similar character on the two surfaces, but due to the interfacial strain effect, the bands of antimonene on Bi2Te3 are flatter than on Sb2Te3, which attributes to Bi2Te3 substrate lattice constants lager than Sb2Te3. At the same time, the charge transfer effect is also observed through core level shift, which influences the band dispersion simultaneously.

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.

Highly efficient charge transfer from a trans-ruthenium bipyridine complex to nanocrystalline TiO2 particles

trans-Di(isothiocyanato)-[N-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) ruthenium(II) acts as a very efficient charge-transfer sensitizer for nanocrystalline TiO2 films. The incident photon-to-electron conversion efficiency (IPCE) for the dye-coated TiO2 film exceeded 80% in the wavelength domain between 400 and 600 nm. A sandwich-type regenerative solar cell fabricated from a 10 μm thick TiO2 film sensitized with this dye generated a short-circuit photocurrent of 19.6 mA cm−2 and an open-circuit photovoltage of 720 mV in simulated AM1.5 solar light (924 W m−2) with an overall power conversion efficiency of 8.6%.

Electronic structure of BiFe 1-x Mn x O 3 thin films investigated by X-ray absorption spectroscopy

Multiferroic polycrystalline BiFe1-xMnxO3 (0 ≤ x ≤ 0.3) thin films have been prepared on the Pt(111)/Ti/SiO2/Si(100) substrates by pulsed laser deposition method. The influence of Mn substitution on the electronic structure and magnetic properties has been studied. X-ray diffraction spectroscopy shows that Mn substitution slightly modulates crystal structure of the BiFe1-xMnxO3 system within the same structural phase. According to Fe L edge X ray absorption spectroscopy, Fe ions are found to be formally trivalent for doping amount x in BiFe1-xMnxO3. The enhanced magnetization by increasing Mn content is attributed to an alternation degree of hybridization between Fe 3d-O 2p and Mn 3d-O 2p orbitals, basing on the carefully examined Fe L and O K edge X-ray absorption spectroscopy. The crystal structural and the electronic structural results show a causal relation between them by demonstrating intrinsic mutual dependence between respective variations.

Intrinsically patterned two-dimensional materials for selective adsorption of molecules and nanoclusters

Two-dimensional (2D) materials have been studied extensively as monolayers, vertical or lateral heterostructures. To achieve functionalization, monolayers are often patterned using soft lithography and selectively decorated with molecules. Here we demonstrate the growth of a family of 2D materials that are intrinsically patterned. We demonstrate that a monolayer of PtSe2 can be grown on a Pt substrate in the form of a triangular pattern of alternating 1T and 1H phases. Moreover, we show that, in a monolayer of CuSe grown on a Cu substrate, strain relaxation leads to periodic patterns of triangular nanopores with uniform size. Adsorption of different species at preferred pattern sites is also achieved, demonstrating that these materials can serve as templates for selective self-assembly of molecules or nanoclusters, as well as for the functionalization of the same substrate with two different species.

Hydrogen Impurity Defects in Rutile TiO2

Hydrogen-related defects play crucial roles in determining physical properties of their host oxides. In this work, we report our systematic experimental and theoretical (based on density functional theory) studies of the defect states formed in hydrogenated-rutile TiO2 in gaseous H2 and atomic H. In gas-hydrogenated TiO2, the incorporated hydrogen tends to occupy the oxygen vacancy site and negatively charged. The incorporated hydrogen takes the interstitial position in atom-hydrogenated TiO2, forming a weak O-H bond with the closest oxygen ion, and becomes positive. Both states of hydrogen affect the electronic structure of TiO2 mainly through changes of Ti 3d and O 2p states instead of the direct contributions of hydrogen. The resulted electronic structures of the hydrogenated TiO2 are manifested in modifications of the electrical and optical properties that will be useful for the design of new materials capable for green energy economy.