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Reflection high energy electron diffraction (RHEED) information is critical for the growth of thin films; however, only a small percentage of the data from RHEED videos is typically used. The use of full videos in machine learning can require dimension reduction techniques. In this paper, three dimension reduction techniques, principal component analysis (PCA), non-negative matrix factorization (NMF), and kmeans clustering, are compared to investigate their benefits to the analysis of RHEED data. Three different heterostructures with different growth modes, all deposited on Ti-terminated strontium titanate by pulsed laser deposition, were used for the analysis: lanthanum aluminate with layer-by-layer growth, lithium cobalt oxide with island growth, and strontium ruthenate with a transition from layer-by-layer to step-flow growth. A phase shift in intensity fluctuations of different RHEED spots was discovered and discussed in terms of their sensitivity to the film growth characterization. The diffraction spots that were more sensitive to the growth were differentiated from the spots that are affected by the substrate as a function of film thickness. It was concluded that NMF provides the analysis that is easiest to interpret without the loss of detailed physical information due to its non-negativity constraint and lack of forced orthogonality such as in PCA. Analysis of the full RHEED videos enables a more detailed understanding of growth characteristics and control of growth processes as aided by dimension reduction. [ABSTRACT FROM AUTHOR]

In the field of atomically thin 2D materials, oxides are relatively unexplored in spite of the large number of layered oxide structures amenable to exfoliation. There is an increasing interest in ultrathin film oxide nanostructures from applied points of view. In this Perspective paper, recent progress in understanding the fundamental properties of 2D oxides is discussed. Two families of 2D oxides are considered: (1) van der Waals bonded layered materials in which the transition metal is in its highest valence state (represented by V 2 O 5 and MoO 3) and (2) layered materials with ionic bonding between positive alkali cation layers and negatively charged transition metal oxide layers (LiCoO 2). The chemical exfoliation process and its combination with mechanical exfoliation are presented for the latter. Structural phase stability of the resulting nanoflakes, the role of cation size, and the importance of defects in oxides are discussed. Effects of two-dimensionality on phonons, electronic band structures, and electronic screening are placed in the context of what is known on other 2D materials, such as transition metal dichalcogenides. The electronic structure is discussed at the level of many-body-perturbation theory using the quasiparticle self-consistent G W method, the accuracy of which is critically evaluated including effects of electron–hole interactions on screening and electron–phonon coupling. The predicted occurrence of a two-dimensional electron gas on Li-covered surfaces of LiCoO 2 and its relation to topological aspects of the band structure and bonding is presented as an example of the essential role of the surface in ultrathin materials. Finally, some case studies of the electronic transport and the use of these oxides in nanoscale field-effect transistors are presented. [ABSTRACT FROM AUTHOR]

Thermal depoling is investigated with impedance spectroscopy as a function of temperature and frequency for unmodified and Zn'Sc modified compositions around the morphotropic phase boundary (MPB) in the high temperature material (1-x)BiScO3-xPbTiO3 (BSPT). By tracking the shape and width of the fundamental resonance peaks and phase angle during impedance analysis, it was shown that the depoling temperature (Td), usually considered a single temperature, can actually be characterized as occurring over a range with an onset temperature (Tdonset) and a final temperature (Tdfinal). When this technique is applied to the rhombohedral compositions near the MPB of BSPT, it is seen that the peak narrowing in phase angle closely correlates to the rhombohedral-tetragonal phase transition decreasing from 350 °C to 300 °C when increasing from 58% to 62% PT. The Td onset and the subsequent correlation to the phase transition are investigated further through aliovalent substitution of 1%, 2%, and 5% ZnSc in BS-PT. The Tdonset for the rhombohedral compositions displays enhancement over the unmodified compositions at ~12 °C/1% ZnSc. [ABSTRACT FROM AUTHOR]

Thermal depoling is investigated with impedance spectroscopy as a function of temperature and frequency for unmodified and Zn'Sc modified compositions around the morphotropic phase boundary (MPB) in the high temperature material (1-x)BiScO3-xPbTiO3 (BSPT). By tracking the shape and width of the fundamental resonance peaks and phase angle during impedance analysis, it was shown that the depoling temperature (Td), usually considered a single temperature, can actually be characterized as occurring over a range with an onset temperature (Tdonset) and a final temperature (Tdfinal). When this technique is applied to the rhombohedral compositions near the MPB of BSPT, it is seen that the peak narrowing in phase angle closely correlates to the rhombohedral-tetragonal phase transition decreasing from 350 °C to 300 °C when increasing from 58% to 62% PT. The Td onset and the subsequent correlation to the phase transition are investigated further through aliovalent substitution of 1%, 2%, and 5% ZnSc in BS-PT. The Tdonset for the rhombohedral compositions displays enhancement over the unmodified compositions at ~12 °C/1% ZnSc. [ABSTRACT FROM AUTHOR]

Smart actuators and intelligent structures are sought after for aeronautical applications. As a result of high Curie temperature (430 °C) and piezoelectric coefficient (>200 pC/N), BiScO3–PbTiO3 (BS-PT) ceramics are prospective materials for high temperature actuators. This paper reports on the temperature dependent electrical, ferroelectric, and electromechanical properties of liquid phase sintered BS-PT ceramics. Compared to solid state sintered BS-PT, liquid phase sintered BS-PT with Bi2O3 showed improved electrical performance: (1) threefold reduction in loss tangent at elevated temperatures, (2) fivefold increase in dc resistivity at high electrical fields, and (3) 15% increase in high field piezoelectric coefficient. Hysteresis loops of the highly resistive ceramics were saturated and showed no major dependence on the magnitude and the frequency of the applied field. BS-PT ceramics exhibit depoling behavior at temperatures below (>350 °C) the Curie temperature (430 °C). Liquid phase sintering using excess Bi2O3 is shown to be a promising approach to produce superior BS-PT ceramics for high temperature actuators. [ABSTRACT FROM AUTHOR]

Dielectric measurements are reported as a function of temperature for phase transformations in the lead magnesium niobate-lead titanate system (PMN-PT). Data are given for single crystal specimens in the morphotropic phase boundary (MPB) region. Transition temperatures were determined from dielectric loss data. The characteristics for both poled and unpoled crystals are compared. Values of dielectric constant were found to increase after poling at room temperature, and an anomaly was induced at the lower-temperature transition. Details are reported for these properties depending upon composition within the MPB region. At room temperature, the poled crystals had high values for dielectric constant (e.g., 5000–15 000), piezoelectric coefficient (e.g., 1000–4000 pC/N), and electromechanical coupling factor (e.g., >0.9). The temperature dependence of dielectric properties is treated in terms of competing phases at transformations, with a change from continuous to discontinuous behavior with increasing PT content towards the MPB. The effect of poling on the induction of the tetragonal (T) phase, with a lowering of the low temperature to tetragonal (LT→T) phase transformation temperature, is discussed. Piezoelectric crystals with the highest depoling temperature were farthest away from the MPB in the MPB region. This information should be useful for the application of PMN-PT piezoelectric crystals. [ABSTRACT FROM AUTHOR]

This work establishes the level of uncertainty for electrical measurements commonly made on thermoelectric samples. The analysis targets measurement systems based on the four probe method. Sources of uncertainty for both electrical resistivity and Seebeck coefficient were identified and evaluated. Included are reasonable estimates on the magnitude of each source, and cumulative propagation of error. Uncertainty for the Seebeck coefficient includes the cold-finger effect which has been quantified with thermal finite element analysis. The cold-finger effect, which is a result of parasitic heat transfer down the thermocouple probes, leads to an asymmetric over-estimation of the Seebeck coefficient. A silicon germanium thermoelectric sample has been characterized to provide an understanding of the total measurement uncertainty. The electrical resistivity was determined to contain uncertainty of ±7.0% across any measurement temperature. The Seebeck coefficient of the system is +1.0%/-13.1% at high temperature and ±1.0% near room temperature. The power factor has a combined uncertainty of +7.3%/-27.0% at high temperature and ±7.5% near room temperature. These ranges are calculated to be typical values for a general four probe Seebeck and resistivity measurement configuration. [ABSTRACT FROM AUTHOR]

Strain-relaxation in LaAlO3/SrTiO3 heterostructures was systematically investigated with LaAlO3 film thickness in the range 4.9-84 nm. Heterostructures were characterized using reciprocal lattice mapping (RLM), high resolution rocking curve, and x-ray reflectivity. RLM enables the measurement of lattice constant with accuracy of 10-6 nm. Lattice constant, mismatch, and strain are independently determined in both out-of-plane and in-plane directions. Heterostructures are tetragonally distorted over the entire range of film thickness, even in the film with thickness of 84 nm, in which plastic deformation occurred. This strain-relaxation analysis of LaAlO3/SrTiO3 heterostructure contributes, on the experimental basis, to the knowledge of the strained heterostructure interfaces from thin film growth point of view. [ABSTRACT FROM AUTHOR]

0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystals were examined by single crystal x-ray diffraction in the transmission mode, and a superlattice was revealed with a doubling of the unit cell in all three directions, giving a cell volume eight times that of a traditional perovskite unit cell. The significance of the superlattice peaks increased with poling, indicating a structural contribution to ordering. Lack of such observations by electron diffraction in the transmission electron microscope examinations suggests the presence of a bulk effect. [ABSTRACT FROM AUTHOR]