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Author: Heather M. A. Patton Publisher: ISBN: Category : Languages : en Pages : 63
Book Description
In this project, the author explored the possibility of growing high quality Heusler alloy thin films from multiphase targets. Bulk targets were found to be partially formed, i.e. not of homogeneous L21 structure, through x-ray diffraction measurements. Pulsed laser deposition is a technique that can provide a congruent transfer of material from the target to the substrate, even in some cases where the target is not of a single crystalline phase. It was the objective of this work to determine whether L21 structured thin films of Co2MnAs[subscript x]Ge(1[subscript x]) could be grown from multiphase targets. Measurements have been carried out to study the magnetic and structural properties of the Heusler alloys Co2MnAs[subscript x]Ge(1−[subscript x]). The optimization parameters that were investigated were substrate type, growth temperature, laser parameters, film thickness, and other common deposition parameters. Temperature-dependent magneto-optic Kerr effect (MOKE) techniques were used to study the qualitative magnetic properties. Alternating current (AC) susceptibility (using a MOKE technique) measurements were made as a function of temperature to view the second-order transition and obtain the Curie temperatures. Frequency dependent AC susceptibility was measured to determine the frequency dependence of the AC susceptibility for Co2MnAs[subscript x]Ge(1−[subscript x]).
Author: Heather M. A. Patton Publisher: ISBN: Category : Languages : en Pages : 63
Book Description
In this project, the author explored the possibility of growing high quality Heusler alloy thin films from multiphase targets. Bulk targets were found to be partially formed, i.e. not of homogeneous L21 structure, through x-ray diffraction measurements. Pulsed laser deposition is a technique that can provide a congruent transfer of material from the target to the substrate, even in some cases where the target is not of a single crystalline phase. It was the objective of this work to determine whether L21 structured thin films of Co2MnAs[subscript x]Ge(1[subscript x]) could be grown from multiphase targets. Measurements have been carried out to study the magnetic and structural properties of the Heusler alloys Co2MnAs[subscript x]Ge(1−[subscript x]). The optimization parameters that were investigated were substrate type, growth temperature, laser parameters, film thickness, and other common deposition parameters. Temperature-dependent magneto-optic Kerr effect (MOKE) techniques were used to study the qualitative magnetic properties. Alternating current (AC) susceptibility (using a MOKE technique) measurements were made as a function of temperature to view the second-order transition and obtain the Curie temperatures. Frequency dependent AC susceptibility was measured to determine the frequency dependence of the AC susceptibility for Co2MnAs[subscript x]Ge(1−[subscript x]).
Author: Xiaojun Zhang Publisher: ISBN: Category : Languages : en Pages : 79
Book Description
Pulsed laser deposition (PLD) is a physical vapor deposition technique for thin film fabrication. Compared with other techniques, pulsed laser deposition technique has advantages such as stoichiometry, flexibility, versatility, lower deposition temperature, ability to grow metastable materials. Because of these advantages, pulsed laser deposition has been widely used in materials research. In this dissertation, pulsed laser deposition has been used to grow thin films for solid oxide fuel cell, light-emitting diode, and solar cell applications. Firstly, yttria-stabilized zirconia (YSZ) and cerium dioxide (CeO2) thin films are deposited in oxygen-deficient environments; their properties are compared to those deposited in oxygen-rich environments. Oxygen-deficient films are highly (001)-oriented, which corresponds to a surface that is expected to be forbidden based on Tasker's theoretical calculation of stoichiometric ionic crystals. A model considering non-stoichiometry-induced surface relaxation and surface atomic density is proposed to explain the orientation phenomenon observed under oxygen-deficient deposition conditions. This model is consistent with previous experimental results for indium tin oxide (ITO), SnO2 and NiO thin films deposited under similar conditions. Detailed studies of the preferred orientation of these oxygen-deficient ionic crystals are of direct relevance to the fabrication of films for use in solid oxide fuel cells. Secondly, undoped, Cu-doped, Se-enriched, Cu2Se-doped, Ag-doped, Ag2Se-doped, and nitrogen-doped ZnSe films have been grown on fused quartz substrates by pulsed laser deposition. It is found that adding a small amount (~2 mol%) of Cu2Se can significantly improve crystallinity and (111) texturing of ZnSe films. While the other films are highly resistive, Cu2Se-doped ZnSe films are p-type conducting with hole concentrations of ~ cm-3 and resistivity of ~0.098 ohm*cm (compared with previous reports of ~ cm-3 and 0.75 ohm*cm, respectively). The successful heavy p-type doping of ZnSe films is attributed to substitution of Zn atoms with Cu while limiting selenium-vacancy-associated compensating defects with additional selenium. Nitrogen doping has turned ZnSe films more favorable to wurtzite structures. Two newly observed Raman peaks at 555 cm-1 and 602 cm-1 are assigned to N local vibrational modes of hexagonal ZnSe structures. The nitrogen-doped ZnSe films are not conductive, which might be due to compensating defects arising from the presence of native defects or other impurities. This work is of importance to solve doping difficulties and contact problems of wide-bandgap semiconductors. Finally, batch growth of thin films by pulsed laser deposition has been tried. Using the natural temperature gradient, films with different deposition temperatures have been fabricated together. With change of deposition temperatures, ZnSe films are shown to have problems associated with crystalline defects, selenium loss, or phase separation. ZnSe films with improved crystallinity and no phase separation have been achieved using a 16 mol% Se enriched target. Multi-plume pulsed laser deposition has been proposed and discussed. With directionality of PLD plumes and non-uniformity of PLD films, this system is supposed to be more suitable for high-throughput compound thin film fabrication, which makes it very promising for efficient materials optimization and exploration. High-throughput fabrication of compound thin films has been successfully achieved using this system.
Author: Antti Hakola Publisher: LAP Lambert Academic Publishing ISBN: 9783847300397 Category : Languages : en Pages : 148
Book Description
Ferromagnetic shape-memory (FSM) compounds are actively studied materials due to their large shape changes in an external magnetic field. This makes it possible to realize novel actuators and sensors. For the fabrication of micromechanical components and even microscopic machines, the material should be in thin-film form, and pulsed laser deposition (PLD) is an effective technique to reach this goal. In this thesis, FSM Ni-Mn-Ga films with a thickness of a few hundred nanometers were deposited on different substrates and methods were developed to release the film from its substrate. For efficient ablation, the intensity distribution of the laser beam on the target should be smooth with steep edges. In this work, such a distribution was realized with the help of diffractive optics. Diffractive optics was also applied to directly produce almost propagation-invariant laser beams, so-called Bessel-Gauss beams in laser resonators. Furthermore, Bessel-like laser beams were created as a result of self-focusing in a certain liquid crystal. Such diffraction-free laser beams can be used in precise laser ablation and accurate patterning of small structures in thin films.
Author: Yilu Li Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 97
Book Description
Pulsed ultraviolet light from a XeF excimer laser was used to grow thin films of zinc oxide and tin dioxide on (111) p-type silicon wafers within a versatile high vacuum laser deposition system. This pulsed laser deposition system was self-designed and self-built. Parameters such as pressure, target temperature, and distance from the target to the substrate can be adjusted in the system. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, Raman spectroscopy and ellipsometry were used to analyze the structures and properties of ZnO and SnO2 thin films. The critical temperature required to fabricate a crystalline ZnO thin film by pulsed laser deposition was found and has been confirmed. For the SnO2 thin film, the critical temperature required to generate a crystalline structure could not be found because of the temperature limit of the substrate heater used in the experiment. In SnO2 thin films, thermal annealing has been used to convert into crystalline structure with (110), (101) and (211) orientations. After fabricating the amorphous SnO2 thin films, they were put into an oven with specific temperatures to anneal them. The minimum annealing temperature range was found for converting the amorphous SnO2 thin films into SnO2 thin films with a crystalline structure. Thermal annealing has also been applied to some amorphous ZnO thin films which were fabricated under the critical temperature required to produce crystalline ZnO thin films. The minimum annealing temperature range for amorphous ZnO thin films was found and only one orientation (002) shown after annealing. Laser annealing technology has also been applied for converting both amorphous ZnO and SnO2 thin films, and results show that this method was not well suited for this attempt. ZnO thin films and SnO2 thin films with a crystalline structure have inportant widely used in industry, for example, application in devices such as solar cells and UV or blue-light-emitting devices. The aim of this research is to help improving the manufacturing process of ZnO and SnO2 thin films.
Author: Publisher: ISBN: Category : Languages : en Pages : 129
Book Description
Hard, wear-resistant coatings of thin film borides based on AlMgB14 have the potential to be applied industrially to improve the tool life of cutting tools and pump vanes and may account for several million dollars in savings as a result of reduced wear on these parts. Past work with this material has shown that it can have a hardness of up to 45GPa and be fabricated into thin films with a similar hardness using pulsed laser deposition. These films have already been shown to be promising for industrial applications. Cutting tools coated with AlMgB14 used to mill titanium alloys have been shown to substantially reduce the wear on the cutting tool and extend its cutting life. However, little research into the thin film fabrication process using pulsed laser deposition to make AlMgB14 has been conducted. In this work, research was conducted into methods to optimize the deposition parameters for the AlMgB14 films. Processing methods to eliminate large particles on the surface of the AlMgB14 films, produce films that were at least 1m thick, reduce the surface roughness of the films, and improve the adhesion of the thin films were investigated. Use of a femtosecond laser source rather than a nanosecond laser source was found to be effective in eliminating large particles considered detrimental to wear reduction properties from the films. Films produced with the femtosecond laser were also found to be deposited at a rate 100 times faster than those produced with the nanosecond laser. However, films produced with the femtosecond laser developed a relatively high RMS surface roughness around 55nm. Attempts to decrease the surface roughness were largely unsuccessful. Neither increasing the surface temperature of the substrate during deposition nor using a double pulse to ablate the material was found to be extremely successful to reduce the surface roughness. Finally, the adhesion of the thin films to M2 tool steel substrates, assessed using the Rockwell C indentation adhesion test, was found to be substantially improved by the deposition of a titanium interlayer, but unaffected by increasing the temperature of the substrates. The titanium was found to improve the adhesion strength of the films because it reacted with both the steel and the AlMgB14 compound to form new compounds. Ultimately, it was concluded that the films with the best properties were produced with a femtosecond pulsed laser and were deposited on top of a titanium interlayer to improve the thin film adhesion.
Author: Michael C. Gao Publisher: Springer ISBN: 3319270133 Category : Technology & Engineering Languages : en Pages : 524
Book Description
This book provides a systematic and comprehensive description of high-entropy alloys (HEAs). The authors summarize key properties of HEAs from the perspective of both fundamental understanding and applications, which are supported by in-depth analyses. The book also contains computational modeling in tackling HEAs, which help elucidate the formation mechanisms and properties of HEAs from various length and time scales.
Author: B.S. Murty Publisher: Elsevier ISBN: 0128160683 Category : Technology & Engineering Languages : en Pages : 390
Book Description
High-Entropy Alloys, Second Edition provides a complete review of the current state of the field of high entropy alloys (HEA). Building upon the first edition, this fully updated release includes new theoretical understandings of these materials, highlighting recent developments on modeling and new classes of HEAs, such as Eutectic HEAs and Dual phase HEAs. Due to their unique properties, high entropy alloys have attracted considerable attention from both academics and technologists. This book presents the fundamental knowledge, the spectrum of various alloy systems and their characteristics, key focus areas, and the future scope of the field in terms of research and technological applications. - Provides an up-to-date, comprehensive understanding on the current status of HEAs in terms of theoretical understanding and modeling efforts - Gives a complete idea on alloy design criteria of various classes of HEAs developed so far - Discusses the microstructure property correlations in HEAs in terms of structural and functional properties - Presents a comparison of HEAs with other multicomponent systems, like intermetallics and bulk metallic glasses
Author: Heather M. A. Patton
Author: Heather M. A. Patton
Author: Xiaojun Zhang
Author: Chrissy Emeny
Author: Antti Hakola
Author: Yilu Li
Author: 
Author: Michael C. Gao
Author: Stephen Skinner
Author: B.S. Murty
Author: American Society for Metals