Search Results - (Author, Cooperation:X. Q. Pan)

2011-02-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

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2011-11-19

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

2016-04-21

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

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2018-09-15

American Physical Society (APS)

1098-0121

1095-3795

Physics

Electronic structure and strongly correlated systems

1089-7550

AIP Digital Archive

Physics

An ultrafast (100 fs) Ti sapphire laser (780 nm) was used for the deposition of SnO2 thin films. The laser-induced plasma generated from the SnO2 target was characterized by optical emission spectroscopy and electrostatic energy analysis. It was found that the ionic versus excited-neutral component ratio in the plasma plume depends strongly on the amount of background oxygen introduced to the deposition chamber. Epitaxial SnO2 films with high quality and a very smooth surface were deposited on the (1¯012) sapphire substrate fabricated at 700 °C with an oxygen background pressure of ∼0.1 mTorr. The films are single crystalline with the rutile structure, resulting from the high similarity in oxygen octahedral configurations between the sapphire (1¯012) surface and the SnO2 (101) surface. Hall effect measurements showed that the electron mobility of the SnO2 film is lower than that of bulk single crystal SnO2, which is caused by the scattering of conduction electrons at the film surface, substrate/film interface, and crystal defects. © 2002 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

Electronic Resource

1089-7550

AIP Digital Archive

Physics

This work demonstrates the correlation between the microstructure of nanocrystalline SnO2 thin films and their electrical transport properties and sensitivities to reducing gases. SnO2 thin films were deposited on the (1¯012) surface of α-Al2O3 (sapphire) using electron beam evaporation of a pure SnO2 ceramic source, followed by postdeposition annealing in synthetic air. SnO2 thin films with randomly oriented nanosized grains were obtained by annealing an amorphous SnO film deposited at room temperature. Films with nanosized SnO2 laminates were obtained by annealing epitaxial α-SnO films deposited at 600 °C. The laminates are oriented with their (101) planes parallel to the substrate surface and have a high density of coherent twin boundaries. Hall measurements indicate that the electron concentration of the film with laminate grains is much lower than for the film with random grains. It is proposed that the high density twin boundaries inside the laminates trap conducting electrons and significantly reduce the electron concentration. As a result, the sensitivity to reducing gases of the laminar film is higher than that of the corresponding film with randomly oriented SnO2 grains. It was also found that the grain size has strong effects on the sensitivity of SnO2 films. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We report the effect of lattice stress relaxation on the microstructures of epitaxial thin films by domain structure studies of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates. X-ray diffraction analysis revealed that the as-grown films are single domain and have a strained lattice due to the lattice mismatch with the substrate. In contrast, plan-view transmission electron microscopy (TEM) images obtained from the same films showed the coexistence of domains with three different crystallographic orientations. The discrepancy is attributed to the lattice stress relaxation occurring on the TEM specimens as the substrate material is eliminated by ion milling or etching, resulting in the formation of elastic domains with different crystallographic orientations. These studies directly reveal a crucial effect of the lattice strain relaxation on the microstructures and properties of epitaxial thin films when the substrate material is removed. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Metallic oxide films of SrRuO3 deposited on (001) SrTiO3 by pulsed laser deposition have been investigated by transmission electron microscopy (TEM) techniques. These films have a single crystalline structure with an extremely smooth surface. A TEM study of cross-sectional samples shows that the film grew epitaxially on the (001) surface of the SrTiO3 substrate. The films grew along the [110] directions with an in-plane orientation relationship of either SrRuO3[1¯10]//SrTiO3 [100] and SrRuO3[001]//SrTiO3[010], or SrRuO3[11¯0]//SrTiO3[010] and SrRuO3[001]//SrTiO3 [100]. Domains with a rotation of 90° around SrRuO3[110] were observed in the dark-field image of plan-view samples. © 1998 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

We studied the structural behavior and electrical transport properties of epitaxial α-SnO thin films grown on the (1¯012) α-Al2O3 (sapphire) substrate. Hall effect measurements revealed that the epitaxial as-deposited SnO film is a p-type semiconductor. In situ x-ray diffraction studies show that the α-SnO phase is metastable and will transform into SnO2 with the rutile type structure when annealed at high temperatures in air. The onset of this phase transformation was observed to begin approximately at 300 °C during heating. Shortly thereafter, rutile SnO2 was observed to coexist with α-SnO and intermediate products such as Sn and Sn3O4. After being annealed at temperatures above 600 °C, the film then fully transformed into the rutile SnO2 phase. Our results show that the α-SnO to SnO2 structural transformation proceeds initially by the localized disproportionate redistribution of internal oxygen at low temperature, followed by the transformation of the remaining SnO phase and intermediate phases into SnO2 via the inward diffusion of external oxygen at higher temperatures. Most of the SnO2 crystallites nucleate epitaxially on α-SnO with the orientation relationship of (101)SnO2//(001)SnO and their growth processes are controlled by the (101)SnO2//(001)SnO interfaces, leading to a (101) texture and a laminar grain shape for SnO2. The relationship between the electrical transport properties and the structural evolution of the film has also been investigated. © 2001 American Institute of Physics.

Electronic Resource

1089-7550

AIP Digital Archive

Physics

SrRuO3 thin films deposited on (001) LaAlO3 substrates by 90° off-axis sputtering at 600 °C were studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both AFM and cross-section TEM investigations show that the films have a rough surface. Plan-view TEM studies demonstrate that the films are composed of all three different types of orientation domains (twins). These domain structures and surface morphology are different from the SrRuO3 film deposited on the (001) SrTiO3 substrate which has an atomically flat surface and is composed of only the [110]-type domains. The reason for these differences was ascribed as the effect of lattice mismatch across the film/substrate interface. It is proposed that a SrRuO3 thin film grows on a (001) SrTiO3 substrate through a two-dimensional nucleation process, while a film on LaAlO3 grows with three steps: the coherent growth of a few monolayers at the initial stage through a two-dimensional nucleation process; the formation of misfit dislocations when the film reaches a critical thickness; and an island-like growth thereafter due to the nonuniform distribution of stress along the film surface. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

PbTiO3/SrTiO3 superlattices were grown on (001) SrTiO3 substrates by reactive molecular beam epitaxy (MBE). Sharp superlattice reflections were observed by x-ray diffraction. High-resolution transmission electron microscopy of a [(PbTiO3)10/(SrTiO3)10]15 superlattice revealed that the PbTiO3/SrTiO3 interface structure is atomically sharp. The superlattice interfaces are fully coherent; no misfit dislocations or other crystal defects were observed in the superlattice by transmission electron microscopy. Selected area electron diffraction patterns indicated that the PbTiO3 layers are oriented with the c axis parallel to the growth direction. The dimensional control and interface abruptness achieved in this model system indicate that MBE is a viable method for constructing oxide multilayers on a scale where enhanced dielectric effects are expected. © 1999 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The microstructure of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates with miscut angle of 1.9° and miscut direction of 12° away from [100] direction was studied using transmission electron microscopy (TEM). Cross-section as well as plan-view TEM studies revealed that these films are single domain with the in-plane epitaxial orientation relationship of SrRuO3[001]//SrTiO3[010] and SrRuO3[1¯10]//SrTiO3[100]. This result is in contrast to the previous studies of the SrRuO3 thin films grown on exactly (001) SrTiO3, which are composed of two types of [110] domains with nearly the same volume fraction. The occurrence of these different domain structures is attributed to the step-flow growth of the film on the substrate surface due to the miscut. © 1998 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

The microstructure and interfacial atomic structure of MgB2 thin films fabricated on the (0001) Al2O3 substrate were characterized by transmission electron microscopy. It was found that the MgB2 films grow epitaxially on the substrate with an orientation relationship with respect to the substrate as: (0001)MgB2(parallel)(0001)Al2O3 and [112¯0]MgB2(parallel)[101¯0]Al2O3. At the film/substrate interface, both MgO and MgAl2O4 phases were observed, which also grow epitaxially on the (0001) Al2O3 substrate. The formation of these intermediate phases is ascribed to the existence of oxygen during the annealing. © 2002 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

Nanocrystalline tin dioxide (SnO2) thin films of different thicknesses were fabricated on the (0001) surface of α-Al2O3 (sapphire) using femtosecond pulsed laser deposition. X-ray diffraction and transmission electron microscopy (TEM) analysis revealed that the microstructure of the films strongly depends on the film thickness. The films with a small thickness (〈30 nm) are composed of nanosized columnar (100) oriented grains (3–5 nm in diameter) which grow epitaxially on the substrate with three different in-plane grain orientations. The (101) oriented grains (25 nm in diameter) appear when the film thickness becomes larger than a critical value (about 60 nm). The volume fraction of the (101) grains increases with film thickness. Cross-section TEM studies indicated that the (101) oriented grains nucleate on the top of the (100) oriented nanosized grains and show abnormal grain growth driven by surface energy minimization. As a result, the electrical transport properties are strongly dependent on the film thickness. © 2001 American Institute of Physics.

Electronic Resource

1077-3118

AIP Digital Archive

Physics

BaRuO3 thin films with hexagonal 4H structure were grown on (001) SrTiO3 by a 90° off-axis rf-sputtering technique. The thin films were epitaxially grown on the (001) surface of SrTiO3, with (202¯3) planes parallel to the surface of the substrate. Within the growth plane, the film consists of four different crystallographic orientations with respect to the substrate, defined by the surface symmetry of the (001) SrTiO3 substrate. BaRuO3 grains of all four orientations show an anisotropic shape elongated along the [1¯21¯0] direction. The reason for the anisotropic growth is that the lattice mismatch between BaRuO3 and SrTiO3 is smaller along the [1¯21¯0] direction of SrTiO3 in comparison to that along its perpendicular direction. Stacking faults and intergrowths of the 9R structure were observed in small local regions of the film. © 2000 American Institute of Physics.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

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[Auszug] Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (Tc) is traditionally accomplished by chemical substitution—as in ...

Electronic Resource

0921-4534

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Physics

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