Chun-Yen Peng

Nanoscale structure and mechanism for enhanced electromechanical response of highly Strained BiFeO3 thin films.

Author(s): Damodaran, Anoop R; Liang, Chen-Wei; He, Qing; Peng, Chun-Yen; Chang, Li; Chu, Ying-Hao; Martin, Lane W | Abstract: The presence of a variety of structural variants in BiFeO3 thin films give rise to exotic electric-field-induced responses and resulting electromechanical responses as large as 5%. Using high-resolution X-ray diffraction and scanning-probe-microscopy-based studies the numerous phases present at the phase boundaries are identified and an intermediate monoclinic phase, in addition to the previously observed rhombohedral- and tetragonal-like phases, is discovered. Copyright

Growth of nonpolar (112¯0) ZnO films on LaAlO3 (001) substrates

Nonpolar (112¯0) ZnO films were grown on LaAlO3 (001) single crystal substrates at temperature from 300 to 750 °C by pulsed laser deposition method. The films were examined using x-ray diffraction, reflection high energy electron diffraction, and photoluminescence measurements for the crystallinity. The surface morphology of ZnO films from atomic force microscopy exhibits L-shaped domains. Cross-sectional transmission electron microscopy with selected area diffraction reveals two types of a-plane ZnO domains perpendicular to each other with in-plane orientation relationships of [0001]ZnO∥[11¯0]LAO and [11¯00]ZnO∥[11¯0]LAO.

Indium-rich InAlN films on GaN/sapphire by molecular beam epitaxy

Here, we report the results of characterization of indium (In)-rich InAlN films on GaN/Sapphire (0001) substrates grown by molecular beam epitaxy. The high-quality ~123 nm thick InAlN films with 85% In content without phase separation were assessed with x-ray diffraction and transmission electron microscopy (TEM) with x-ray energy dispersive spectroscopy. High-resolution TEM analysis reveals the relaxation at InAlN/GaN interface with misfit dislocations of 1.59 nm spacing. Finally, optical and electrical properties of the InAlN films are presented from absorption spectroscopy and Hall measurements.

Defects in m-plane ZnO epitaxial films grown on (112) LaAlO3 substrate

The crystallographic orientations of m-plane ZnO on (112) LaAlO3 (LAO) substrate are [1¯21¯0]ZnO∥[111¯]LAO and [0001]ZnO∥[1¯10]LAO. The defects in m-plane ZnO have been systematically investigated using cross section and plan-view transmission electron microscopy (TEM). High-resolution TEM observations in cross section show misfit dislocations and basal stacking faults (BSFs) at the ZnO/LAO interface. In the films, threading dislocations (TDs) with 1/3⟨112¯0⟩ Burgers vectors are distributed on the basal plane, and BSFs have 1/6⟨202¯3⟩ displacement vector. The densities of dislocations and BSFs are estimated to be 5.1×1010 cm−2 and 4.3×105 cm−1, respectively. In addition to TDs and BSFs, plan-view TEM examination also reveals that stacking mismatch boundaries mainly lie along the m-planes and they connect with planar defect segments along the r-planes.

The cooling effect on structural, electrical, and optical properties of epitaxial a-plane ZnO:Al on r-plane sapphire grown by pulsed laser deposition

Here, the unambiguous effect of cooling rate on structural, electrical, and optical properties of a-plane ZnO:Al on r-plane sapphire grown by pulsed laser deposition at 700 °C is reported. A high cooling rate (∼100 °C/min) can result in stripe morphology along m-direction and significant deformation on the epitaxial films of a-plane ZnO:Al with deteriorated crystallinity and significantly lowered resistivity. Also, photoluminescence spectra exhibit high intensities of excess violet and green emissions with low intensity of near band edge luminescence. Comparison with pure a-plane ZnO films is also presented.

Defects in semipolar

The microstructure of semipolar [Formula: see text] ZnO deposited on (112) LaAlO3/(La,Sr)(Al,Ta)O3 was investigated by transmission electron microscopy. The ZnO shows an in-plane epitaxial relationship of [Formula: see text] with oxygen-face sense polarity. The misfit strain along [Formula: see text] and [Formula: see text] is relieved through the formation of misfit dislocations with the Burgers vectors [Formula: see text] and [Formula: see text], respectively. The line defects in the semipolar ZnO are predominantly perfect dislocations, and the dislocation density decreases with increasing ZnO thickness as a result of dislocation reactions. Planar defects were observed to lie in the M-plane and extend along 〈0001〉, whereas basal stacking faults were rarely found.

(1 1\bar {2}\bar {2})

The microstructure of semipolar [Formula: see text] ZnO deposited on (112) LaAlO3/(La,Sr)(Al,Ta)O3 was investigated by transmission electron microscopy. The ZnO shows an in-plane epitaxial relationship of [Formula: see text] with oxygen-face sense polarity. The misfit strain along [Formula: see text] and [Formula: see text] is relieved through the formation of misfit dislocations with the Burgers vectors [Formula: see text] and [Formula: see text], respectively. The line defects in the semipolar ZnO are predominantly perfect dislocations, and the dislocation density decreases with increasing ZnO thickness as a result of dislocation reactions. Planar defects were observed to lie in the M-plane and extend along 〈0001〉, whereas basal stacking faults were rarely found.

ZnO grown on (112) LaAlO3/(La,Sr)(Al,Ta)O3 substrate by pulsed laser deposition

The effect of growth temperature on a-plane ZnO formation on r-plane sapphire has been systematically investigated by employing in situ high pressure reflection high-energy electron diffraction, atomic force microscopy, and high-resolution x-ray diffraction. For film growth above and below 600 °C, it is shown that there is a significant difference in growth rate and surface morphology due to the differences in the growth mode. Stripelike morphologies were observed on the surface of a-plane ZnO grown at low temperature (LT) because of differences in the growth rate along the c-axis and the growth rate normal to the c-axis. Furthermore, annealing of films grown at low temperature results in more pronounced stripe morphology and in improvement of crystallinity.

Defects in semipolar (11(2)over-bar(2)over-bar) ZnO grown on (112) LaAlO3/(La, Sr) (Al, Ta)O-3 substrate by pulsed laser deposition

The defects in (134¯0)ZnO epitaxial film grown on (114)LaAlO3 (LAO) have been systematically investigated by using transmission electron microscopy. At the ZnO/LAO interface, the Burgers vectors of misfit dislocations are identified to be 1/3[1¯21¯0] and 1/2[0001]. Threading dislocations with the Burgers vectors of 1/3⟨112¯0⟩ and ⟨0001⟩ are distributed on the basal plane. In (134¯0)ZnO film, the predominant planar defects are basal stacking faults (BSFs) with 1/6⟨202¯3⟩ displacement vectors. The densities of dislocations and BSFs are about 3.8 × 1010 cm−2 and 3.1 × 105 cm−1, respectively.

Effect of growth temperature on a-plane ZnO formation on r-plane sapphire

The defects in (134¯0)ZnO epitaxial film grown on (114)LaAlO3 (LAO) have been systematically investigated by using transmission electron microscopy. At the ZnO/LAO interface, the Burgers vectors of misfit dislocations are identified to be 1/3[1¯21¯0] and 1/2[0001]. Threading dislocations with the Burgers vectors of 1/3⟨112¯0⟩ and ⟨0001⟩ are distributed on the basal plane. In (134¯0)ZnO film, the predominant planar defects are basal stacking faults (BSFs) with 1/6⟨202¯3⟩ displacement vectors. The densities of dislocations and BSFs are about 3.8 × 1010 cm−2 and 3.1 × 105 cm−1, respectively.