Zhiyong Pang

Phase-sensitive Bloch surface wave sensor based on variable angle spectroscopic ellipsometry

In this paper, we propose a phase-sensitive Bloch surface wave sensor based on the variable angle spectroscopic ellipsometry and numerically simulate the phase behavior of the sensor. The simulation results show that the dependence of resonant phase is step-like when BSWs are excited. In contrast to the reflectance behavior, even though losses of the dielectric layers are very small, the resonance dip in the reflectivity will be shallow while the step-like change of the reflection phase of the BSW still be remarkable. This means that phase detection is an alternative to reflectivity intensity detection for the sensing applications of the BSWs in this case. Our experimental results indicate that phase detection for the BSW sensors has the potential to achieve the higher sensitivity and the lower limit of detection.

Phase properties of Bloch surface waves and their sensing applications

We study the phase properties of Bloch surface waves (BSWs) on truncated one-dimensional photonic crystals and find an abrupt change of the phase induced by BSWs. The phase of the BSW device shows a prominent response to the refractive index changes of the environment under resonance conditions. Furthermore, we demonstrate that the phase sensitivity of the BSW device is higher by nearly 1 order of magnitude than its amplitude sensitivity in terms of the figure of merit. This means that phase detection can be utilized to enhance the sensitivity of the BSW devices.

Magnetism in Co-doped tris-8-hydroxyquinoline aluminum studied by first-principles calculations

The electronic and magnetic properties of Co-doped tris-8-hydroxyquinoline aluminum (Alq3) are studied by first-principles calculations. Our results indicate that the local magnetic moments in doped Alq3 originate from the localized d states of Co atom. Electron transfer takes place from Co atom to Alq3 molecule, which is mainly localized on the quinolate ligand, resulting in formation of bound magnetic polarons. The indirect ferromagnetic exchange interaction between two bound magnetic polarons antialigning with the same magnetic ion promotes the collective magnetism found in recent experiments.

Structure of Co-Doped Alq3 Thin Films Investigated by Grazing Incidence X-ray Absorption Fine Structure and Fourier Transform Infrared Spectroscopy

The structural properties of Co-doped tris(8-hydroxyquinoline)aluminum (Alq(3)) have been studied by grazing incidence X-ray absorption fine structure (GIXAFS) and Fourier transform infrared spectroscopy (FTIR). GIXAFS analysis suggests that there are multivalent Co-Alq(3) complexes and the doped Co atoms tend to locate at the attraction center with respect to N and O atoms and bond with them. The FTIR spectra indicate that the Co atoms interact with the meridional (mer) isomer of Alq(3) rather than forming inorganic compounds.

Structures and photoluminescence properties of Alq3 1D materials prepared by an extremely facile solution method

Ultra-long crystalline Alq3 1 dimensional (1D) materials were prepared by using an extremely facile solution approach without any surfactant, SDS, anti-solvent, or other reagents. The Alq3 1D materials have smooth surfaces and pentagonal or hexagonal cross-sections. The length of the microrods have α-phase crystalline structures. The prepared Alq3 samples exhibit excellent green-light photoluminescence (PL) performance. The growth mechanism of the Alq3 1D structures were discussed. The limitation conditions of the Alq3 microrods were also studied. In addition, the influence of the volume of CHCl3 on the microrods was discussed. This controllable growth method can potentially be extended to other functional organic nanomaterials.

Magnetic properties of tris(8-hydroxyquinoline)iron: Experimental and theoretical investigation

The magnetic properties of tris(8-hydroxyquinoline)iron (Feq3) are investigated by experiments and first-principles density functional theory. In contrast to the diamagnetic behavior of Alq3, the Feq3 films deposited by vacuum thermal evaporating exhibit paramagnetic behaviors at 5 K. The calculated electronic structure of Feq3 molecule shows clear exchange splitting between the majority and minority spin channels. The total magnetic moment is about 1 μB, which mainly derives from the localized Fe 3d orbital. The paramagnetic behavior observed is ascribed to the small energy difference (1 meV) between ferromagnetic and antiferromagnetic coupling.

Annealing Effect on Transport and Magnetic Properties of La0.67Sr0.33MnO3 Thin Films Grown on Glass Substrates by RF Magnetron Sputtering

The manganite La 0.67 Sr 0.33 MnO 3 (LSMO) thin films were grown on glass substrates in a mixed argon and oxygen atmosphere by using RF magnetron sputtering. The structural characteristics, transport behaviors and magnetic properties of LSMO films were studied by annealing the films in air at 550 and 620°C. The out-of-plane lattice parameter a LSMO contracted after annealing and was close to that of bulk LSMO a bulk , indicating that the internal strain was fully relaxed. Nanocrystalline grains were observed in the annealed films. Enhanced saturation magnetization and metal-to-insulator transition temperature (T MI =268 K) were also obtained. Curie temperatures ( T c ) of the as-grown films was 340 K with the same as that of annealed at 550°C, but dropped to 315 K when the annealing temperature increased to 620°C, which can be attributed to the oxygen release during annealing in atmosphere.

The structure of Mn-doped tris(8-hydroxyquinoline)gallium by extended x-ray absorption fine structure spectroscopy and first principles calculations

Metal-Mqx (M = Al, Ga, Zn, Be, and Ca, x = 2 or 3) complexes play a key role in organic spintronics and organic optoelectronics. However, the accurate structure determination of these complexes has been a challenge for a long time. Here, we report the structure of Mn-Gaq3 investigated by using first-principle density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy. First, the structures of Mn-Gaq3 were predicted by first-principle DFT calculations. Then, all reasonable structures achieved from the calculations were used to fit the EXAFS spectra. By this method, the structure of Mn-Gaq3 is well obtained. We believe this method is also applicable to other metal-Mqx films.

Solid-to-Solid Crystallization of Organic Thin Films: Classical and Nonclassical Pathways

The solid-to-solid crystallization processes of organic molecules have been poorly understood in view of the complexity and the instability of organic crystals. Here, we studied the crystallization of a π-conjugated small molecular semiconductor, bis-(8-hydroxyquinoline) copper (CuQ2), by annealing the thin films at different temperatures. We observed a classical film-to-nanorods crystallization at 80 °C, a coexistence of classical and nonclassical nucleation and particle growth at 120 °C, and a nonclassical crystal growth at 150 °C. We found that the growth of the crystals followed the following processes: particle nucleation, particle growth, particle migration, nondirectional particle attachment, and structure reconstruction. We notice that the growth of CuQ2 particles follows an outside-to-inside process. More interestingly, our experiments suggest that the submicron CuQ2 particles are able to migrate dozens of micrometers at 150 °C.

Room temperature ferromagnetic properties of dysprosium-doped tris(8-hydroxyquinoline) aluminum: experimental and theoretical investigation

Room temperature ferromagnetism was observed in rare earth dysprosium (Dy)-doped tris(8-hydroxyquinoline) aluminum (Alq3) organic small molecular films. The Dy-doped Alq3 films were prepared by co-evaporating pure Alq3 and Dy powders on Si substrates in a vacuum. The maximum room temperature coercive field and the saturation magnetization are about 70 Oe and 9.5 × 10−6 emu, respectively. The structures were studied by the atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR) and synchrotron radiation X-ray absorption fine structure (XAFS). The magnetic properties were investigated by the MicroMag Alternating Gradient Magnetometer (AGM), Quantum Design superconducting quantum interference device (SQUID) and first-principles calculations. The room temperature ferromagnetism is ascribed to the magnetic moments induced by the Dy atom and the large energy difference between ferromagnetic and antiferromagnetic coupling.