Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)

The metastable orthorhombic phase of Hf0.5Zr0.5O2 (HZO) can be stabilized in thin films on La0.67Sr0.33MnO3 (LSMO) buffered (001)-oriented SrTiO3 (STO) by an intriguing epitaxy that results in (111)-HZO oriented growth...

Confocal Microscopy in Conjunction With Haemocytometry to Evaluate the Imperative Physical Characteristics of Multicellular Tumor Spheroids

Background: Tumor tissues resist penetration of therapeutic molecules. Multicellular tumor spheroids (MCTSs) were used as an in vitro tumor model. The aim of this study was to determine the growth of MCTSs with the age of spheroids, which could be applied and compared with in vivo drug uptake and penetration. Method: Spheroids were generated by liquid overlay techniques, and their diameter was measured by confocal microscopy for up to two weeks. The trypan blue exclusion method was used to count dead and live cells separately via a hemocytometer. Results: The pentaphysical characteristics of spheroids, including diameter, cell number, volume per cell, viability status, and estimated shell of viable and core of dead cells, were determined. The growth of spheroids was linear over the first week but declined in the 2nd week, which may be due to an overconcentration of dead cells and degraded products inside the spheroids, hence lowering the ratio of live cells in spheroids. Compaction of spheroids occurs from day 3 to day 7, with the mature spheroids having a low amount of extracellular space compared to intracellular volume. Conclusion: Age-oriented growth of MCTSs provides a rationale to predict less rapid penetration as spheroids get older and could be correlated with in vivo tumors to predict pharmaceutical and therapeutic intervention.

Growth and Structural Properties of Rare Earth Nitride Thin Films

<p>In this thesis aspects of the growth of rare earth nitride thin films and characterisation of the resulting structural, electronic and magnetic properties of the film are investigated. The rare earth nitrides are a class of materials which combine interesting electronic and magnetic properties with potential applications in novel spintronic device structures. We study the formation of a preferential orientation in polycrystalline thin films of GdN deposited by electron-beam physical vapour deposition. X-ray diffraction is used to characterise the crystalline structure of films of varying thickness to identify a preference to grow along the [111] crystal direction, understood in terms of an evolutionary selection process. Variations in the film microstructure as a result of growth parameter variation are also correlated to electronic and magnetic properties. Investigation of the epitaxial growth of SmN on AlN surfaces revealed a novel growth orientation transition, controllable only via the growth temperature. Epitaxial integration of rare earth nitrides with III-nitride surfaces has previously only resulted in (111)-oriented growth on the (0001) surface as is expected from matching of the close-packed planes in the different crystal structures. High growth temperatures (≥800 ℃) induce (001)-oriented growth of SmN on the same (0001) AlN surface. This unexpected cube-on-hexagon geometry is confirmed through ex situ x-ray and in situ electron diffraction, the latter for which a computational simulation tool was developed to model and understand. The viability of using Sm as a temporary capping layer for rare earth nitride thin film samples is investigated. Capping layers are required to passivate samples due to their high reactivity, limiting the range of ex situ characterisation techniques that can be performed on them. Elemental Sm is relatively volatile raising the possibility of removing a Sm cap in situ using moderate annealing temperatures (400 °C to 600 ℃). The ability to remove the capping layer would allow in situ characterisation techniques to be performed in ultra high vacuum systems not directly connected to the growth system. In situ electron diffraction is used to characterise the growth and thermal annealing of Sm grown on top of epitaxial GdN layers, and the effects of the thermal removal process on the structural, electronic and magnetic properties of the GdN layer are investigated.</p>

Growth and Structural Properties of Rare Earth Nitride Thin Films

<p>In this thesis aspects of the growth of rare earth nitride thin films and characterisation of the resulting structural, electronic and magnetic properties of the film are investigated. The rare earth nitrides are a class of materials which combine interesting electronic and magnetic properties with potential applications in novel spintronic device structures. We study the formation of a preferential orientation in polycrystalline thin films of GdN deposited by electron-beam physical vapour deposition. X-ray diffraction is used to characterise the crystalline structure of films of varying thickness to identify a preference to grow along the [111] crystal direction, understood in terms of an evolutionary selection process. Variations in the film microstructure as a result of growth parameter variation are also correlated to electronic and magnetic properties. Investigation of the epitaxial growth of SmN on AlN surfaces revealed a novel growth orientation transition, controllable only via the growth temperature. Epitaxial integration of rare earth nitrides with III-nitride surfaces has previously only resulted in (111)-oriented growth on the (0001) surface as is expected from matching of the close-packed planes in the different crystal structures. High growth temperatures (≥800 ℃) induce (001)-oriented growth of SmN on the same (0001) AlN surface. This unexpected cube-on-hexagon geometry is confirmed through ex situ x-ray and in situ electron diffraction, the latter for which a computational simulation tool was developed to model and understand. The viability of using Sm as a temporary capping layer for rare earth nitride thin film samples is investigated. Capping layers are required to passivate samples due to their high reactivity, limiting the range of ex situ characterisation techniques that can be performed on them. Elemental Sm is relatively volatile raising the possibility of removing a Sm cap in situ using moderate annealing temperatures (400 °C to 600 ℃). The ability to remove the capping layer would allow in situ characterisation techniques to be performed in ultra high vacuum systems not directly connected to the growth system. In situ electron diffraction is used to characterise the growth and thermal annealing of Sm grown on top of epitaxial GdN layers, and the effects of the thermal removal process on the structural, electronic and magnetic properties of the GdN layer are investigated.</p>

The Effect of Subsequent Stress-Induced Martensite Aging on the Viscoelastic Properties of Aged NiTiHf Polycrystals

This study investigated the effect of stress-induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H-phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress-induced martensite aging at 428 K for 12 h results in the appearance of a two-way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress-induced martensite aging is associated with the oriented growth of thermal-induced martensite. After stress-induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress-induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them.

Controlled Epitaxial Growth and Atomically Sharp Interface of Graphene/Ferromagnetic Heterostructure via Ambient Pressure Chemical Vapor Deposition

The strong spin filtering effect can be produced by C-Ni atomic orbital hybridization in lattice-matched graphene/Ni (111) heterostructures, which provides an ideal platform to improve the tunnel magnetoresistance (TMR) of magnetic tunnel junctions (MTJs). However, large-area, high-quality graphene/ferromagnetic epitaxial interfaces are mainly limited by the single-crystal size of the Ni (111) substrate and well-oriented graphene domains. In this work, based on the preparation of a 2-inch single-crystal Ni (111) film on an Al2O3 (0001) wafer, we successfully achieve the production of a full-coverage, high-quality graphene monolayer on a Ni (111) substrate with an atomically sharp interface via ambient pressure chemical vapor deposition (APCVD). The high crystallinity and strong coupling of the well-oriented epitaxial graphene/Ni (111) interface are systematically investigated and carefully demonstrated. Through the analysis of the growth model, it is shown that the oriented growth induced by the Ni (111) crystal, the optimized graphene nucleation and the subsurface carbon density jointly contribute to the resulting high-quality graphene/Ni (111) heterostructure. Our work provides a convenient approach for the controllable fabrication of a large-area homogeneous graphene/ferromagnetic interface, which would benefit interface engineering of graphene-based MTJs and future chip-level 2D spintronic applications.

Structure and Magnetization of Strontium Hexaferrite (SrFe12O19) Films Prepared by Pulsed Laser Deposition

M-type strontium hexaferrite (SrM) thin films show excellent magnetic properties and uniaxial magnetic anisotropy. We systematically investigated the magnetism of SrM films prepared by pulsed-laser deposition on different substrates [Al2O3 (11¯02), SrTiO3 (100), ZnO (0001), and LiNbO3 (0001)] at vacuum (10−4 Pa) and a substrate temperature of 800°C. Prepared films were annealed in air at a temperature of 1,000°C for 2 hours. This investigation determined the effect of annealing and different substrates on the morphology, strain, and hysteresis loops of the films. The prepared films were characterized using x-ray diffractometry, Raman spectroscopy, scanning electron microscopy, and superconducting quantum interference device (SQUID) magnetometry. X-ray diffraction analyses confirmed c-oriented growth along the out-of-plane direction in most films. We found that annealing causes enhanced crystallization in films and a significant increase in coercivity. The highest coercivity of ∼11 KOe was measured for the film deposited on the Al2O3 (11¯02) substrate.

2D Organic–Inorganic Hybrid Perovskite Quantum Well Materials and Their Dramatical X-ray Optoelectronic Properties

Two-dimensional organic–inorganic hybrid perovskites (2D OIHPs) have attracted extensive attention in the field of X-ray detection due to their excellent stability compared to traditional three-dimensional OIHPs and the strong optoelectronic response to X-ray along the quantum wells. In this review, the nucleation and growth process as well as intermolecular forces for controlling out-of-plane growth are summarized along with the oriented growth mechanism. The optoelectronic properties in 2D OIHP under irradiation of X-ray are also discussed. Finally, conclusions and outlook for orientation 2D OIHP quantum wells and their challenges in application of direct X-ray detection are given. This review will provide a basic understanding on the strategy of designing 2D OIHP thick films as promising X-ray photoconductors, which may inspire the development of next-generation X-ray detectors.