京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第22238号 / 理博第4552号 / 新制||理||1654(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 松田 祐司, 教授 石田 憲二, 教授 寺嶋 孝仁 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The continued miniaturization of interconnects results in performance and reliability issues for integrated circuit (IC) chips. As the critical dimension of Cu interconnects approaches dimensions near the mean free path of the metal (39.9 nm at room temperature), a rise in resistivity is observed. This phenomenon, termed resistivity size effect, is the result of electron scattering at grain boundaries and surfaces. Cobalt (Co) and ruthenium (Ru) are considered promising candidates to replace Cu as an interconnect metal because these metals exhibit a lower product of mean free path times bulk resistivity when compared with Cu. Additionally, given that electron scattering from grain boundaries is a major contributor to the resistivity-size effect in nanoscale interconnects, we investigate the electrodeposition of epitaxial Co, Ru, and Cu and demonstrate the capability of electrodeposition to fabricate epitaxial, single crystal metal films. Co, Ru, and Cu have a misfit strain that is tensile, zero, and compressive with the epitaxial Ru(0001) seed layer, respectively. This allowed for the study of every kind of misfit relationship that is possible in epitaxial film growth. Ultimately, the successful electrodeposition of Co and Cu epitaxial to a single crystal, conductive seed layer suggests the plausibility of electrodeposited, single crystal interconnects in future IC chips. Co electrodeposited as an epitaxial, single crystal film onto the Ru(0001) seed layers to finite thicknesses relevant for interconnect fabrication. Electrodeposition onto polycrystalline Ru seed layers, however, resulted in the growth of a rough, polycrystalline Co film with faceted growth. Despite a large misfit strain of 7.9%, the epitaxial electrodeposition of planar Co was achieved up to a thickness 75x beyond the calculated critical thickness for defect formation before a transition to island growth was observed. Thus, the importance of a conductive, single crystal seed layer, preferably with a minimal misfit strain with the depositing layer, is demonstrated. Metallic Ru was found to electrodeposit onto Ru(0001) as a porous layer comprised of (0001) oriented Ru crystallites. The presence of a porous Ru deposit was found to be independent of the seed layer, Ru metal ion source, and deposition mode used. An optimization of the deposition electrolyte to improve Ru atomic mobility is necessary to achieve the epitaxial electrodeposition of single crystal Ru. Finally, Cu demonstrated epitaxial growth on the Ru(0001) seed layer, with an out-of-plane epitaxial orientation relationship of Cu(111) | Ru(0001). The hexagonal close packed Ru(0001) seed layer allows Cu to deposit with two equivalent in-plane orientations; thus, the electrodeposited Cu film was determined to be a bicrystal, not a single crystal. While epitaxial deposition of Cu was achieved, a seed layer that permits only one orientation of Cu is required for a significant reduction in electron grain boundary scattering, hence, resistivity.

This diploma thesis is focused on deposition Ga and GaN structures on graphene fabricated by method of mechanical exfoliation. For mechanical exfoliation was used new method with using DGL Gel-Film with kinetically controlled adhesion. Ga is deposited by Molecular beam epitaxy with using eusion cell in UHV conditions. GaN was obtained by post-nitridation of Ga islands. These structures were investigated with optical microscope, SEM, Raman spectroscopy and photoluminiscence.

In this work we studied gallium on graphene. Depositions were done by Molecular beam epitaxy. We observed Raman enhancement and peak shifts by individual Ga islands. Simulation confirmed our assumption, that the enhancement is based on plasmonics effect that is also the main contribution of Surface-enhanced Raman spectroscopy. Another result is hydrogenation of graphene before deposition does have an effect on Ga structure and reduces diffusion length of Ga atoms.

In der vorliegenden Arbeit wurden Röntgentechniken benutzt um die Struktur von dünnen (etwa 40 nm) CrSi2-Schichten, die unter UHV-Bedingungen mittels reaktive Koabscheidung und template-Verfahren auf Si(001) hergestellt wurden, zu charakterisieren. Die Ergebnisse wurden mit TEM-, SEM- und RBS-Untersuchungen korreliert und ergänzt. Die XRD-Analysen zeigen, dass die beiden Abscheideverfahren immer zur Bildung der CrSi2-Phase führen, wobei die Kristallite mit einer bevorzugten Orientierungsbeziehung CrSi2(001)[100] || Si(001)[110] wachsen. Im ersten Teil der Arbeit wurde die Cr-Si-Koabscheidung benutzt um die Prozessparameter zu bestimmen, die zum Wachstum epitaktischer Schichten führen können. Die Strukturuntersuchungen zeigen, dass nur bei einer Substrattemperatur von 700°C nahezu geschlossene Schichten mit Kristalliten, welche lateral eine Größe bis zu 300 nm haben und neben der bevorzugten noch andere Orientierungen zum Substrat aufweisen, entstehen. Als zweite Herstellungsmethode wurde das template-Verfahren verwendet, wo die Cr-Si-Koabscheidung auf ein vorher in-situ präpariertes ultradünnes CrSi2-template erfolgt. Die Morphologie und die Stärke der bevorzugten Orientierung der CrSi2-Schichten sind stark von der template-Dicke abhängig. Die Abscheidung auf CrSi2-templates, welche aus einer Cr-Schicht mit nominaler Dicker von 0,35 nm bis 0,52 nm entstehen, führt zum Wachstum weitgehend geschlossener, homogener und epitaktischer CrSi2-Schichten. Ein Modell, das den Einfluss der template-Dicke auf die Qualität der CrSi2-Schichten erklären kann, wird vorgeschlagen.

This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)

This thesis is devoted to the fabrication, optical characterization and switching behaviour of the prototypical chalcogenide-based phase-change material Ge2Sb2Te5, which is employed in non-volatile optical and electrical data storage devices. While common studies on conventional memory applications of Ge2Sb2Te5 are based on reversible amorphous to polycrystalline phase transitions, this thesis particularly focuses on the use of Ge2Sb2Te5 thin films of epitaxial, single-crystalline like nature aiming to gain deeper insights into structure-property correlations and novel switching pathways. The first part of this thesis deals with the growth of epitaxial Ge2Sb2Te5 thin films on Si(111) substrates by pulsed laser deposition with strong emphasis on controlling the degree of structural order in the thin films resulting from the distribution of intrinsic vacancies in the crystalline state of the material. As a result, highly vacancy-ordered epitaxial Ge2Sb2Te5 thin films in the thermodynamically stable as well as in the metastable crystalline phase are obtained, possessing a pronounced nanostructuring due to periodically spaced Van-der-Waals gaps or vacancy layers. Besides that, epitaxial Ge2Sb2Te5 thin films with complete disordered vacancy distributions are realized. Based on the achieved single-phase quality of the epitaxial thin films, a classification of the optical property contrast of different crystalline Ge2Sb2Te5 phases with respect to their vacancy ordering is presented. Beyond that, the impact of vicinal substrate surfaces on the phase, structure as well as on surface pattern formation in epitaxial Ge2Sb2Te5 thin films is investigated. The second part of this thesis employs epitaxial Ge2Sb2Te5 thin films as a model system to follow ns-laser induced structural modifications ranging from reversible crystalline to amorphous phase transitions to interface assisted epitaxial recrystallization processes. In particular, by applying single ns-laser pulses to the thin films, the transition from the vacancy ordered stable to the vacancy disordered metastable crystalline structure of Ge2Sb2Te5 via a transient molten phase is realized while the epitaxial nature of the thin films is preserved. This transition mechanism provides access to ultrafast crystal growth dynamics in an epitaxial phase-change material thin film model system offering the advantage of high crystalline quality and application-relevant sizing. By introducing a method that combines time-resolved reflectivity measurements with high resolution scanning transmission electron microscopy, crystal growth velocities upon fast cooling after single ns-laser pulse irradiation are determined. As a result, an increase in crystal growth velocity from 0.4 to 1.7 m/s with increasing laser fluence is observed with the maximum rate of 1.7 m/s as the upper detectable limit of the studied material.

This thesis deals with the deposition of epitaxial chalcogenide (Ge2Sb2Te5 (GST225), GeTe and Sb2Te3) thin films and superlattice (SL) arrangement based on GeTe-Sb2Te3 using pulsed laser deposition (PLD) technique on (111)-oriented Si substrates. The thin films are characterized using in-situ RHEED, XRD, SEM, AFM and TEM. The epitaxial trigonal GST225 films with out-of-plane c-plane orientation were grown in 2D growth mode. For the first group of the films (substrate-target distance (dts) of ~7.5 cm), the epitaxial window was observed from 200 °C to 300 °C. By varying laser frequency, deposition rate as high as 42 nm/ min can be achieved. The deposition with a slight reduction of dts to ~6 cm (second group) at moderate Ts of 220 °C results in the epitaxial films with heterogeneous vacancy structures (coexisting metastable phases. i.e. with random and ordered vacancies, and stable trigonal phase). Thermal annealing (at 220 °C) leads to a phase transformation towards a pure trigonal phase. The epitaxial Sb2Te3 films with out-of-plane (0001) oriented trigonal structure were grown at Ts from 140 to 280 °C in 2D growth mode. The optimum Ts in terms of deposition rate and film quality was determined to be 240 °C. The epitaxial growth of Sb2Te3 thin films is initiated by the self-organized formation of a Sb/Te single-atomic passivation layer on the Si surface. The growth of GeTe was initialized by the formation of an ultra-thin amorphous layer. The films were predominantly grown in the mix of 2D and 3D growth modes. The deposited films possesses trigonal structure out-of-plane (0001)-orientated on Si(111). By employing a 2D-bonded Sb2Te3 as a seeding layer on Si(111), the epitaxial window of GeTe can be extended especially towards the lower temperature regime, up to 145 °C. Additionally, the surface topography can be significantly improved, indicating that the films are grown in 2D growth mode on the buffered substrate. The epitaxial SLs can be grown starting at Ts = 140 °C. Each layer of the SLs, i.e. Sb2Te3 and GeTe layer, was grown in 2D growth mode. An intermixing of GeTe and Sb2Te3 layers occurred at a higher temperature deposition. Studies on local structure of 140 °C-deposited SL showed that the SL consists of Ge-rich Ge(x+y)Sb(2–y)Tez and Sb2Te3 units intercalated by Van der Waals gaps with the inhomogeneity of layer thickness across the SL. The obtained results demonstrate the feasibility of PLD for deposition of good quality epitaxial chalcogenide thin films and SL structure on Si(111).

A dimensionality controlled metal insulator transition in epitaxial [LaNiO3 (d nm)/LaAlO3(2nm)]10 (100) superlattices (thereafter [d/2]10 SLs) is demonstrated for decreasing LaNiO3 single layer thickness from 4nm down to 1.2 nm. The [4/2]10 SL shows metallic behavior with positive resistivity temperature coefficient, while the [2/2]10 SL shows a metal-insulator transition with crossover from 3D to two-dimensional single-layer dimensionality. Strong localization appears for the [1.2/2]10 SL with the resistivity being dominated by two-dimensional variable range hopping with a localization length of about 0.035 nm.

Magnetic spin structures in epitaxial BiFeO3 single layer and an epitaxial BaTiO3/BiFeO3 multilayer thin film have been studied by means of nuclear resonant scattering of synchrotron radiation. We demonstrate a spin reorientation in the 15 x[BaTiO3/BiFeO3] multilayer compared to the single BiFeO3 thin film. Where as in the BiFeO3 film, the net magnetic moment m→ lies in the (1–10) plane, identical to the bulk, m→ in the multilayer points to different polar and azimuthal directions. This spin reorientation indicates that strain and interfaces play a significant role in tuning the magnetic spin order. Furthermore, large difference in the magnetic field dependence of the magnetoelectric coefficient observed between the BiFeO3 single layer and multilayer can be associated with this magnetic spin reorientation.