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Author: Publisher: ISBN: Category : Languages : en Pages : 43
Book Description
Methods of preparing high-perfection single crystalline films of 3d elements (including Fe, Co) and magnetic rare earths on semiconducting GaAs substrates have been investigated. The use of seed layers of Fe or Co (a few monolayers thick), deposited onto GaAs(001), followed by a Ag(001) film, provided a suitable template for Fe epitaxy. This method avoided interfacial chemical reactions between Fe and the semiconductor, at the expense of introducing coherency strain and tilted epitaxy of the Fe. In the case of rare earths, intermediate seed films of rare earth trifluorides, grown onto GaAs(111(-)) provided a template for growth of c-axis oriented rare earth films and sandwich structures. These methods have enabled the effects of coherency strain on magnetic properties of Fe and rare earths to be investigated. Using an automated X-ray photoelectron diffraction (XPD) system we have investigated the growth and interfacial mixing of several key epitaxial systems including Co/Pt, Co/Ag, NdF3/LaF3 and Pt/GaAs. Interfacial mixing in the interfaces of Co/Pt superlattices was confirmed, resulting in an alloyed region containing the ordered L12 phase: CoPt3. Spin-polarized photoelectron diffraction (SPPD) experiments on MnF2 suggest a new , high-temperature magnetic ordering transition at 380K which is 313K above the Neel temperature.
Author: Publisher: ISBN: Category : Languages : en Pages : 43
Book Description
Methods of preparing high-perfection single crystalline films of 3d elements (including Fe, Co) and magnetic rare earths on semiconducting GaAs substrates have been investigated. The use of seed layers of Fe or Co (a few monolayers thick), deposited onto GaAs(001), followed by a Ag(001) film, provided a suitable template for Fe epitaxy. This method avoided interfacial chemical reactions between Fe and the semiconductor, at the expense of introducing coherency strain and tilted epitaxy of the Fe. In the case of rare earths, intermediate seed films of rare earth trifluorides, grown onto GaAs(111(-)) provided a template for growth of c-axis oriented rare earth films and sandwich structures. These methods have enabled the effects of coherency strain on magnetic properties of Fe and rare earths to be investigated. Using an automated X-ray photoelectron diffraction (XPD) system we have investigated the growth and interfacial mixing of several key epitaxial systems including Co/Pt, Co/Ag, NdF3/LaF3 and Pt/GaAs. Interfacial mixing in the interfaces of Co/Pt superlattices was confirmed, resulting in an alloyed region containing the ordered L12 phase: CoPt3. Spin-polarized photoelectron diffraction (SPPD) experiments on MnF2 suggest a new , high-temperature magnetic ordering transition at 380K which is 313K above the Neel temperature.
Author: Ashish Garg Publisher: ISBN: Category : Languages : en Pages :
Book Description
Epitaxial oxide thin films are used in many technologically important device applications. This work deals with the deposition and characterization of epitaxial WO3 and SrBi2Ta2O9 (SBT) thin films on single crystal oxide substrates. WO3 thin films were chosen as a subject of study because of recent findings of superconductivity at surfaces and twin boundaries in the bulk form of this oxide. Highly epitaxial thin films would be desirable in order to be able to create a device within a film without patterning it, by locally creating superconducting regions (e.g. twins) within an otherwise defect free film by reducing or doping the film with Na. Films were deposited by reactive magnetron sputtering at various temperatures on single crystal SrTiO3 (100) and R-sapphire substrates. X-ray diffraction studies showed that the optimised films were highly (001) oriented, quality of epitaxy improving with decreasing deposition temperature. AFM studies revealed columnar growth of these films. Films were heat treated with Na vapour in order to reduce or dope them with Na. Low temperature measurements of the reduced films did not show existence of any superconductivity. SBT is a ferroelectric oxide and its thin films are attractive candidates for non-volatile ferroelectric random access memory (FRAM) applications. High structural anisotropy leads to a high degree of anisotropy in its ferroelectric properties which makes it essential to study epitaxial SBT films of different orientations. In this study, SBT films of different orientations were deposited on different single crystal substrates by pulsed laser ablation. Highly epitaxial c-axis oriented and smooth SBT films were deposited on SrTiO3 (100) substrates. AFM studies revealed the growth of these films by 3-D Stranski-Krastanov mode. However, these films did not exhibit any ferroelectric activity. Highly epitaxial (116)-oriented films were deposited on SrTiO3 (110) substrates. These films were also very smooth with root mean square (RMS) roughness of 15-20 Å. Films deposited on TiO2 (110) were partially a-/b-axis oriented and showed the formation of c-axis oriented SBT and many impurities. Completely a-/b-axis oriented SBT films were deposited on LaSrAlO4 (110) substrates. Films deposited at non-optimal growth temperatures showed the formation of many impurities. Attempts were also made towards depositing Sr2RuO4 films on LaSrAlO4 (110) substrates, which can act as a bottom electrode for ferroelectric SBT films.
Author: Publisher: Elsevier ISBN: 0080532675 Category : Science Languages : en Pages : 673
Book Description
Although there has been steady progress in understanding aspects of epitaxial growth throughout the last 30 years of modern surface science, work in this area has intensified greatly in the last 5 years. A number of factors have contributed to this expansion. One has been the general trend in surface science to tackle problems of increasing complexity as confidence is gained in the methodology, so for example, the role of oxide/metal interfaces in determining the properties of many practical supported catalysts is now being explored in greater detail. A second factor is the recognition of the potential importance of artificial multilayer materials not only in semiconductor devices but also in metal/metal systems because of their novel magnetic properties. Perhaps even more important than either of these application areas, however, is the newly-discovered power of scanning probe microscopies, and most notably scanning tunneling microscopy (STM), to provide the means to study epitaxial growth phenomena on an atomic scale under a wide range of conditions. These techniques have also contributed to revitalised interest in methods of fabricating and exploiting artificial structures (lateral as well as in layers) on a nanometre scale.This volume, on Growth and Properties of Ultrathin Epitaxial Layers, includes a collection of articles which reflects the present state of activity in this field. The emphasis is on metals and oxides rather than semiconductors.
Author: J Matthews Publisher: Elsevier ISBN: 0323152120 Category : Science Languages : en Pages : 401
Book Description
Epitaxial Growth, Part A is a compilation of review articles that describe various aspects of the growth of single-crystal films on single-crystal substrates. The collection contains topics on the historical development of epitaxy, the nucleation of thin films, the structure of the interface between film and substrate, and the generation of defects during film growth. The text also provides descriptions of the methods used to prepare and examine thin films and a list of the overgrowth-substrate combinations studied. Mineralogists, materials engineers and scientists, and physicists will find this book a great source of insight.
Author: Yu Bai (Ph.D.) Publisher: ISBN: Category : Languages : en Pages : 126
Book Description
Epitaxial Ge thin films are being investigated for many important roles in next generation microelectronics. Metal-oxide-semiconductor field effect transistors (MOSFETs) utilizing Ge channels have demonstrated dramatic performance enhancements over Si based technology. Theoretical studies have predicted that tensile strain enhances both electron and hole mobilities of Ge to levels much greater than those in unstrained or compressively-strained Ge and Si. Additionally, high enough levels of tensile strain have been postulated to alter the band structure of Ge to make Ge a direct-band-gap semiconductor. We investigated the physics and fabrication of Ge/III-V compound heterostructures, where the III-V compound material could serve as a tensile-strain-inducing template for subsequent Ge epitaxy. Through experimentation and the use of characterization techniques such as transmission electron microscopy (TEM), photoluminescence (PL), secondary ion mass spectrometry (SIMS) and spreading resistance analysis (SRA), we established correlations between the initial III-V compound surface stoichiometry and the structural, optical, and electronic properties of Ge thin films deposited on GaAs and AlAs templates. We determined that the highest structural quality Ge epitaxy initiates via a bond and exchange mechanism with the surface group III element atoms, whereas group V element atoms do not bond as effectively with Ge and thin film deposition processes that rely on Ge-group V binding processes lead to 'pitting' in Ge thin films. With the developed understanding of the growth mechanisms, we successfully fabricated high quality tensile-strained Ge thin films and quantum dots on InxGaixAs templates. Tensile strain levels as high as 0.58% in Ge thin films and 1.37% in Ge quantum dots were achieved. However, the film deposition methods that facilitated the highest structural quality also led to unintentional doping characteristics that affected the electrical and optical properties of the tensile-strained Ge epitaxial structures. Nevertheless, we designed processing sequences that led to the first demonstration of room temperature, Ge direct band gap luminescence from Ge/III-V compound heterostructures. We parlayed our advancements in Ge/Ill-V compound heterostructure fabrication to demonstrate a novel process for the fabrication of GaAs-on-Insulator (GaAsOI). The combination of GaAs/Ge/GaAs heterostructure establishment, room temperature oxide-oxide bonding methods, and XeF2-based sacrificial etching of Ge, led to the successful fabrication of GaAsOI on a small scale. We tested the implementation of our process on a full wafer scale and determined the process was kinetically limited by the lateral Ge etch process. We adapted the Deal-Grove oxidation model to establish a model to understand the relationships between lateral etch rate, lateral etch distance, release layer thickness, channel displacements, and the radius of curvature of the donor wafer. Our Ge/III-V compound heterostructure research advanced the understanding and stateof- the-art processing of such structures. We established methods and elucidated challenges for future research targeted toward demonstrating novel Ge-based devices and advanced large-diameter engineered substrates.
Author: Bijoya Dhar Publisher: ISBN: Category : Languages : en Pages : 136
Book Description
The growth and characterization of epitaxial thin films see ubiquitous use in both research and applications spanning a number of scientific and industrial fields with overlapping interests in materials science. The central theme of this work centers on leveraging the structural control afforded through the ultrahigh vacuum (UHV) approaches to thin-film epitaxy to derive atomically specific structure-chemistry relationships of key importance to various interface-mediated reactions. The first project was aimed at developing gold (Au) and ceria (CeO2) thin films using advanced surface-science techniques. In that project, a thoroughly wetted Au film on Ta metal substrate has been identified. This model system is necessary due to its potential candidacy as a promising electro-catalyst for oxygen reduction reaction (ORR) in proton exchange membrane fuel cell cathodes. The second film is CeO2(100), grown on a silver (Ag) single crystal substrate. Cerium oxide is a fascinating material with unique properties and has applications in many fields. The (100) plane of ceria is particularly interesting because it is the most active plane among the low index planes. Here in-situ growth of ceria islands on Ag has been reported.
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Author: Zuoming Zhu
Author: Ashish Garg
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Author: Jianwei Dong
Author: Henry Kressel
Author: J Matthews
Author: Yu Bai (Ph.D.)
Author: Reza Loloee
Author: Bijoya Dhar