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Artificial photosynthesis that converts CO2 and H2O into compounds with added value is a viable method for reducing atmospheric CO2 concentration. In this study, we investigated the photocatalytic activity of ultrathin indium tin oxide (ITO) films on rigid and flexible substrates for CO2 reduction in water vapor and batch and flow setups. To explain a viable reaction mechanism for the 2760 ± 10 % μmol.gcat-1.hr-1 production rate achieved in a continuous reaction system, several theoretical models were developed. According to DFT simulation results, oxygen vacancy might be regarded as the main reaction site for CO2 to CO conversion. Moreover, a viable reaction pathway leading to CH4 formation is proposed. The catalyst’s lower rate of CO2 reduction in the batch reactor as compared with the flow reactor was justified via surface affinity simulation. Our findings highlight the significance of the catalyst’s structural design and reaction media configuration for stability and high activity.

Co/CoO multilayers are fabricated by means of radio-frequency magnetron sputtering. For the formation of each multilayer period, a Co layer is initially produced followed by natural oxidation. Platinum is used not only as buffer and capping layers, but also in the form of intermediate ultrathin layers to enhance perpendicular magnetic anisotropy. Three samples are compared with respect to the magnetic anisotropies and exchange bias between 4–300 K based on superconducting quantum interference device magnetometry measurements. Two of the multilayers are identical Co/CoO/Pt ones; one of them, however, is grown on a Co/Pt “magnetic substrate” to induce perpendicular magnetic anisotropy via exchange coupling through an ultrathin Pt intermediate layer. The third multilayer is of the form Co/CoO/Co/Pt. The use of a “magnetic substrate” results in the observation of loops with large remanence when the field applies perpendicular to the film plane. The CoO/Co interfaces lead to a significant exchange bias at low temperatures after field cooling. The largest exchange bias was observed in the film with double Co/CoO/Co interfaces. Consequently, significant perpendicular anisotropy coexists with large exchange bias, especially at low temperatures. Such samples can be potentially useful for applications related to spintronics and magnetic storage.

The interest in ultrathin silver (Ag) films has increased due to their high surface plasmon resonance for coatings of only a few nm. Low roughness ultrathin films of 1 to 9 nm have been deposited on different substrates, such as polyethylene terephthalate (PET) and optical glass, using radio frequency (RF) magnetron sputtering. Films show good surface plasmon resonance up to 7 nm thickness, as revealed by the ultraviolet-visible (UV-Vis) spectra. The roughness of the films, investigated by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM), is small, and one can conclude that depositions are smooth and homogeneous. The bandgap values decrease with film thickness. The refractive index of the films, calculated from ellipsometry measurements, leads to values of under 1 visible domain, with minima in the wavelength range of 400–600 nm. The results are useful for obtaining lower roughness ultrathin Ag films with good surface plasmon resonance for photonic applications.

Materials 15(1), 46 (2022). doi:10.3390/ma15010046, Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich Co$_x$Fe$_{3−x}$O$_4$ films with different stoichiometry (x=1.1 and x=1.4) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/Fe$_3$O$_4$ bilayers deposited before on Nb-doped SrTiO$_3$(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of Co$^{3+}$ cations in the low-spin state on octahedral sites for the Co$_{1.4}$Fe$_{1.6}$O$_4$ film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements., Published by MDPI, Basel

Superconducting nanofilms are tunable systems that can host a 3D-2D dimensional crossover, leading to the Berezinskii-Kosterlitz-Thouless (BKT) superconducting transition approaching the 2D regime. Reducing further the dimensionality, from 2D to quasi-1D, superconducting nanostructures with disorder can generate quantum and thermal phase slips (PS) of the order parameter. Both BKT and PS are complex phase fluctuation phenomena of difficult experimental detection. Here, we have characterized superconducting NbN nanofilms thinner than 15 nm, on different substrates, by temperature dependent resistivity and current-voltage (I-V) characteristics. Our measurements have evidenced clear features related to the emergence of BKT transition and PS events. The contemporary observation in the same system of BKT transition and PS events and their tunable evolution in temperature and thickness, has been explained as due to the nano-conducting paths forming in a granular NbN system. In one of the investigated samples we have been able to trace and characterize the continuous evolution in temperature from quantum to thermal PS. Our analysis has established that the detected complex phase phenomena are strongly related to the interplay between the typical size of the nano-conductive paths and the superconducting coherence length., 22 pages, 14 figures

Synergistic methodological strategies based on the fields of microbial biotechnology and materials science open up an enormous range of possibilities for the sustainable production of advanced materials with predictable properties. This study shows how naturally produced polyhydroxyalkanoate (PHA) particles are introduced into bacterial cellulose (BC) driven by their bacterial producers. Thanks to an extensive knowledge of the internal structure of BC, it was possible to control the colonization process, i.e. loading and localization of PHA. A subsequent acid treatment favored the PHA-BC bonding at the position reached by the bacteria. These biodegradable films showed improved mechanical and barrier properties even with respect to reference plastic films 8 times thicker, reaching a Young's modulus 4.25 times higher and an oxygen permeability 3 times lower than those of polyethylene terephthalate (PET) films. Owing to the versatility of the method, a wide variety of materials can be developed for very diverse fields of application., Authors want to acknowledge the European Union's Horizon 2020 Research and Innovation Program under the grant agreement no. 870294 (Mix-Up). Authors also received financial support from the CSIC Interdisciplinary Thematic Platform (PTI+) Sustainable Plastics towards a Circular Economy (PTI-Susplast+), and the Community of Madrid (P2018/NMT4389) and the Spanish Ministry of Science and Innovation under the research grant BIOCIR (PID2020-112766RB-C21), DECOMPACK (PID2020-112766RB-C22) and the Juan de la Cierva aid of Cristina Campano (FJC2019-040298-I).

Fabrication of ultrathin films of dielectric (with particular reference to materials with high dielectric constants) materials has significance in many advanced technological applications including hard protective coatings, sensors, and next generation logic devices. Current state-of-the-art in microelectronics for fabricating these thin films is a combination of atomic layer deposition and photolithography. As feature size decreases and aspect ratios increase, conformality of the films becomes paramount. Here, we show a polymer brush template assisted deposition of highly conformal, ultrathin (sub 5 nm) high-κ dielectric metal oxide films (hafnium oxide and zirconium oxide) on topographically patterned silicon nitride substrates. This technique, using hydroxyl terminated poly-4-vinyl pyridine (P4VP-OH) as the polymer brush, allows for conformal deposition with uniform thickness along the trenches and sidewalls of the substrate. Metal salts are infiltrated into the grafted monolayer polymer brush films via solution deposition. Tailoring specific polymer interfacial chemistries for ion infiltration combined with subsequent oxygen plasma treatment enabled the fabrication of high-quality sub 5 nm metal oxide films.

We provide a theoretical background for electric-field-assisted thermally activated writing and deleting of magnetic skyrmions in ultrathin transition-metal films. We apply an atomistic spin model, which includes the exchange interaction, the Dzyaloshinskii-Moriya interaction, and the magnetocrystalline anisotropy energy. The strengths of the magnetic interactions are taken from density functional theory (DFT) calculations for a Pd/Fe bilayer on the Ir(111) surface. We systematically vary all magnetic interactions up to $\pm10$~\% reating the magnetoelectric effect in linear response. The critical magnetic fields marking the onset of the skyrmion phase and the field-polarized phase shift considerably upon varying the interaction constants due to the electric field. Based on harmonic transition state theory, we calculate the transition rates for skyrmion nucleation and annihilation, which are in good agreement with experimental values for Pd/Fe/Ir(111). The field-dependent variation of energy barriers and preexponential factors leads to large changes of the transition rates, which are accompanied by changes in skyrmion radii. Finally, we simulate the electric-field-dependent writing and deleting of magnetic skyrmions in Pd/Fe/Ir(111) based on the master equation and transition rates obtained using the magnetic interactions calculated via DFT for electric fields of ${\cal E}= \pm 0.5$~V/{\AA}. The magnetic-field-dependent skyrmion probability follows a Fermi-Dirac distribution function of the free energy difference of the skyrmion state and the ferromagnetic (FM) state. The probability function for the opposite electric field directions is in striking agreement with experimental results [Romming {\it et al.}, Science {\bf 341}, 636 (2013)]., Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via Project No. 414321830 (HE3292/11-1), the Icelandic Research Fund (Grants No. 217750 and No. 184949), the University of Iceland Research Fund (Grant No. 15673), the Russian Science Foundation (Grant No. 19-72-10138), and the Swedish Research Council (Grant No. 2020-05110).

Для анализа содержания озона в воздухе были изготовлены тонкопленочные полупроводниковые сенсоры на основе оксида палладия. Пленки оксида палладия получены методом термического окисления в воздухе слоев металла толщиной ~ 20–30 нм при различных температурах. Оксидные пленки исследованы методами электронной микроскопии и дифракции быстрых электронов. Изучены их оптические, электрофизические свойства и газовая чувствительность к озону. Установлена оптимальная температура окислительного отжига пленок, которая обеспечивает их однородный фазовый состав, с одной стороны, и отсутствие электрических шумов придетектировании газов, с другой стороны. Предложен и обоснован механизм появления электрических шумов в ультратонких пленках, который связан с их фрагментированием в процессе окислительного отжига. Показана высокая чувствительность таких пленок к примесям озона в воздухе.

Ultrathin MoO3 semiconductor nanostructures have garnered significant interest as a promising nanomaterial for transparent nano- and optoelectronics, owing to their exceptional reactivity. Due to the shortage of knowledge about the electronic and optoelectronic properties of MoO3/n-Si via an ALD system of few nanometers, we utilized the preparation of an ultrathin MoO3 film at temperatures of 100, 150, 200, and 250 °C. The effect of the depositing temperatures on using bis(tbutylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum source for highly stable UV photodetectors were reported. The ON–OFF and the photodetector dynamic behaviors of these samples under different applied voltages of 0, 0.5, 1, 2, 3, 4, and 5 V were collected. This study shows that the ultrasmooth and homogenous films of less than a 0.30 nm roughness deposited at 200 °C were used efficiently for high-performance UV photodetector behaviors with a high sheet carrier concentration of 7.6 × 1010 cm−2 and external quantum efficiency of 1.72 × 1011. The electronic parameters were analyzed based on thermionic emission theory, where Cheung and Nord’s methods were utilized to determine the photodetector electronic parameters, such as the ideality factor (n), barrier height (Φ0), and series resistance (Rs). The n-factor values were higher in the low voltage region of the I–V diagram, potentially due to series resistance causing a voltage drop across the interfacial thin film and charge accumulation at the interface states between the MoO3 and Si surfaces.

Microscopy and diffraction measurements are presented of ultrathin binary alloy films of ruthenium and molybdenum that are obtained by standard sputter deposition. For compositions close to Ru50Mo50, we find the films to be amorphous. The amorphicity of the films is accompanied by a significant reduction of the roughness with respect to the roughness of equally thick films of either ruthenium or molybdenum. We ascribe this to the absence of the grain structure that is characteristic of the polycrystalline films of the separate elements.

In this work, we present a comprehensive study on real-time monitoring the growth of epitaxial CoxFe3−xO4 thin films grown on SrTiO3(001) substrates via reactive molecular beam epitaxy. The growth process was monitored during evaporation by means of time resolved operando hard X-ray photoelectron spectroscopy (HAXPES). We prepared ultrathin ferrite films using different oxygen partial pressures, showing pure metallic, light oxidic, and cobalt ferrite-like growth. Additional X-ray diffraction measurements confirm HAXPES results.

Metal-oxide nanomaterials, which differ fundamentally from their bulk analogues, are attracting considerable interest owing to their unique electronic properties and thermodynamic stability. In this regard, we show a comprehensive study which spans from the design of well-ordered 2D ZnO ultrathin films supported on Pt(111) and Cu(111) surfaces to the in situ/operando investigations of chemical reactions (CO oxidation and CO2 hydrogenation) with catalytic interest. We propose a model that describes the 2D morphology and its structure. Besides, the in situ/operando investigations of the catalytic CO oxidation and CO2 hydrogenation allows the understanding of their reaction mechanistic.

9 pags., 8 figs., 2 tabs., CoFeO thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523 K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron Mössbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state. Annealing also induced cobalt segregation to the surface of the thicker films. The measured Mössbauer spectra at low temperature were indicative of cobalt ferrite, the both films showing very similar hyperfine patterns. Annealing in oxygen or vacuum affected the cationic distribution, which was closer to that expected for an inverse spinel in the case of annealing in an oxygen atmosphere., This work is supported by the Spanish Ministry of Science and Innovation through Projects RTI2018-095303-B-C51, RTI2018-095303- B-C53, MAT2017-86450-C4-1-R, RTI2018-095303-A-C52, through the Ramón Cajal Contract RYC-2017-23320 and RTI2018-095303-C52 (MCIU/AIE/FEDER,EU), by the Regional Government of Madrid through project S2018-NMT-4321 and by the PROM Programme - International scholarship exchange of Ph.D. students and academics; and by the European Commission through the H2020 Project no. 720853 (AMPHIBIAN)

Materials 15(19), 6911 (2022). doi:10.3390/ma15196911, In this work, we investigated the influence of oxygen plasma on the growth of nickel cobaltite (NiCo$_2$O$_4$) thin films compared to growth in a molecular oxygen atmosphere. The films were grown on MgO(001), MgAl$_2$O$_4$(001) and SrTiO$_3$(001) substrates by oxygen plasma (atmosphere of activated oxygen)-assisted and reactive molecular beam epitaxy (molecular oxygen atmosphere). Soft X-ray photoelectron spectroscopy showed that only the use of oxygen plasma led to a spectrum characteristic of (NiCo$_2$O$_4$). Low energy electron diffraction measurements were conducted to obtain information on the structure of the film surfaces. The results proved the formation of a spinel surface structure for films grown with oxygen plasma, while the formation of a rock salt structure was observed for growth with molecular oxygen. To determine the film thickness, X-ray reflectivity measurements were performed. If oxygen plasma were used to grow (NiCo$_2$O$_4$) films, this would result in lower film thicknesses compared to growth using molecular oxygen although the cation flux was kept constant during deposition. Additional X-ray diffraction experiments delivered structural information about the bulk structure of the film. All films had a rock salt bulk structure after exposure to ambient conditions. Angle-resolved hard X-ray photoelectron spectroscopy revealed a homogeneous depth distribution of cations of the grown film, but no typical (NiCo$_2$O$_4$) spectrum anymore. Thus, on the one hand, (NiCo$_2$O$_4$) films with a spinel structure prepared using activated oxygen were not stable under ambient conditions. The structure of these films was transformed into NiCo oxide with a rock salt structure. On the other hand, it was not possible to form (NiCo$_2$O$_4$) films using molecular oxygen. These films had a rock salt structure that was stable under ambient conditions., Published by MDPI, Basel

Ultrathin metallic films are important functional materials for optical and microelectronic devices. Dedicated characterization with high spatial resolution and sufficient field of view is key to the understanding of the relation between microstructure and optical and electrical properties of such thin films. Here, we have applied on-axis transmission Kikuchi diffraction (TKD) and scanning precession electron diffraction (SPED) to study the microstructure of 10 nm thick polycrystalline gold films. The study compares the results obtained from the same specimen region by the two techniques and provides insights on the limits of each diffraction technique. We compare the physical spatial resolution of on-axis TKD and SPED and discuss challenges due to the larger probe size in scanning electron microscopy (SEM). Moreover, we present an improvement for the physical spatial resolution (PSR) of on-axis TKD through acquisition in immersion mode. We show how this method extends the capabilities of SEM-based microstructure characterization of ultrathin films and achieve PSR comparable to semi-automated SPED.

The formation of ultrathin films of Rh-based porous metal–organic polyhedra (Rh-MOPs) by the Langmuir–Blodgett method has been explored. Homogeneous and dense monolayer films were formed at the air–water interface either using two different coordinatively alkyl-functionalized Rh-MOPs (HRhMOP(diz)12 and HRhMOP(oiz)12) or by in situ incorporation of aliphatic chains to the axial sites of dirhodium paddlewheels of another Rh-MOP (OHRhMOP) at the air–liquid interface. All these Rh-MOP monolayers were successively deposited onto different substrates in order to obtain multilayer films with controllable thicknesses. Aliphatic chains were partially removed from HRhMOP(diz)12 films post-synthetically by a simple acid treatment, resulting in a relevant modification of the film hydrophobicity. Moreover, the CO2/N2 separation performance of Rh-MOP-supported membranes was also evaluated, proving that they can be used as selective layers for efficient CO2 separation., This work was funded by MCIN/AEI/10.13039/501100011033 and ERDF “A way of making Europe” (grant PID2019-105881RB-I00). The authors also acknowledge the support from the Spanish MINECO (project RTI2018-095622-B-I00) and the Catalan AGAUR (project 2017 SGR 238). It was also funded by the CERCA Programme/Generalitat de Catalunya and through a fellowship (LCF/BQ/PR20/11770011) from “la Caixa” Foundation (ID 100010434). ICN2 is supported by the Severo Ochoa programme from the Spanish MINECO (grant no. SEV-2017-0706). I.T. and M.P.-M. gratefully acknowledge their DGA PhD fellowship from Government of Aragon. The microscopy work was carried out in the Laboratorio de Microscopias Avanzadas at the Instituto de Nanociencia y Materiales de Aragon (LMA-INMA). This work benefited from the use of the SasView application, originally developed under NSF award DMR-0520547. SasView contains code developed with funding from the European Union’s Horizon 2020 research and innovation programme under the SINE2020 project, grant agreement no. 654000. The authors thank the synchrotron SOLEIL for beamtime provision under projects 20190435 and 20191874.

Ultrathin Cu(In,Ga)Se-2 (CIGS) absorber layers of 550 nm were grown on Ag/AlOx stacks. The addition of the stack resulted in solar cells with improved fill factor, open circuit voltage and short circuit current density. The efficiency was increased from 7% to almost 12%. Photoluminescence (PL) and time resolved PL were improved, which was attributed to the passivating properties of AlOx. A current increase of almost 2 mA/cm(2) was measured, due to increased light scattering and surface roughness. With time of flight-secondary ion mass spectroscopy, the elemental profiles were measured. It was found that the Ag is incorporated through the whole CIGS layer. Secondary electron microscopic images of the Mo back revealed residuals of the Ag/AlOx stack, which was confirmed by energy dispersive X-ray spectroscopy measurements. It is assumed to induce the increased surface roughness and scattering properties. At the front, large stains are visible for the cells with the Ag/AlOx back contact. An ammonia sulfide etching step was therefore applied on the bare absorber improving the efficiency further to 11.7%. It shows the potential of utilizing an Ag/AlOx stack at the back to improve both electrical and optical properties of ultrathin CIGS solar cells. This research was funded by European Union H2020 research and innovation program grant number 715027.

The structure and growth mechanism of TiO2 ultrathin films on Cu(001) were investigated by experimental and theoretical studies. Multiple experimental techniques, including photoemission spectroscopies and scanning probe microscopy, were used to carefully characterize the chemical, electronic, and morphological structure of the metal oxide layer. A complete and flat TiO2 bilayer with a lepidocrocite-like structure is observed at the earliest stages of its growth on the Cu(001) surface under controlled experimental conditions. The employed multitechnique approach reveals that a transition between two different structures of the TiO2 film, that is, the quasi-hexagonal and lepidocrocite-like structure, occurs as a function of the coverage passing from one to two monolayers. Ab initio calculations indicate that the lepidocrocite-like structure is thermodynamically more stable on Cu(001) than the quasi-hexagonal one, thus supporting the observed transition.

Electrostatically defined perovskite oxide heterostructures, in which carriers are confined by the modulation of the A-site ion charge, offer new possibilities of tuning the magnetic properties of manganite oxides. We investigate the preferential orientation of ferromagnetic and antiferromagnetic moments in ultrathin La0.7Sr0.3MnO3 layers embedded in antiferromagnetic SrMnO3 as they undergo a metal-to-insulator transition with decreasing thickness. Our results evince the role of orbital occupation, metallicity, and competition of different magnetic phases, in absence of spurious effects occurring in thin films as a result of symmetry breaking at La0.7Sr0.3MnO3 interfaces and of incorporation of oxygen vacancies.

The Dzyaloshinskii-Moriya interaction in ultrathin magnetic films gives birth to chiral magnetic domain walls, which have a potential for applications in spintronics and magnetic storage. This thesis aims for a better description of chiral domain-walls under an external in-plane magnetic field used to affect their static and dynamic behaviors. The first chapter gives an overview of existing theoretical and experimental works concerning chiral domain walls. The second chapter describes the methods used by the author to measure the velocity of domain walls in three different samples of ultrathin magnetic films with perpendicular anisotropy. A new semi-analytical model, dubbed the "small-circle" and detailed in chapter three, was developed to address the determination of the domain wall structure. The fourth chapter presents the experimental results of our study of domain wall velocity under out-of-plane and in-plane field, as well as the universal analysis allowing to extract pinning parameters and the value of the Dzyaloshinskii-Moriya interaction. Finally, chapter five shows that our experiments allow to measure the strength and length-scale of the interaction between domain walls and the underlying pinning disorder., L'interaction Dzyaloshinskii-Moriya dans les couches magnétiques ultraminces est à l'origine de parois de domaines magnétiques chirales, qui présentent un fort intérêt pour la spintronique et le stockage magnétique. Cette thèse cherche à obtenir une meilleure description des parois magnétiques chirales soumises à un champ planaire permettant de modifier leur comportement statique et dynamique. Le premier chapitre de la thèse fait le point sur les théories existantes et les derniers résultats expérimentaux concernant la dynamique de parois chirales. Le deuxième chapitre décrit les méthodes utilisées pour mesurer la vitesse des parois de domaines dans trois échantillons de couches magnétiques ultraminces à anisotropie perpendiculaire. Pour accéder à la structure des parois nous avons développé un nouveau modèle micromagnétique, dit du petit cercle, qui est présenté dans le chapitre trois. Le chapitre quatre présente nos résultats expérimentaux de dynamique de parois, ainsi que l'analyse universelle permettant d'en extraire les paramètres macroscopiques décrivant le désordre et la valeur de l'interaction Dzyaloshinskii-Moriya. Enfin, le cinquième chapitre présente nos conclusions sur l'interaction entre la structure des parois de domaine et son ancrage par l'échantillon.

The objective of this PhD work isto study the role of shear on the rupture of ultra-thin polymer films, by coupling a numerical study to an experimental one. First, a numerical method adapted to the resolution of the thin film equation was set up taking into account the capillary and van der Waals forces. This method was validated by comparing the dynamics obtained to theoretical predictions. With the addition of shear, two regimes have then been evidenced as a function of the shear rate: in the case of low shear rates the rupture is delayed, while at higher shear rates it is suppressed. The use of spatio-temporal diagrams allowed the characterization of the interface deformation. The transition from the delayed to the suppressed rupture regime is similar to a phase transition. The experimental study at low shear rate allowed to confirm this delayed rupture, but also showedafter the rupture an increased dewetting speed. This study will allow a better understanding of the rupture phenomena occurring during nanolayer coextrusion., L’objectif de ce travail de thèse est d’étudier le rôle du cisaillement sur la rupture de films ultra-minces de polymères, en couplant une étude numérique à une étude expérimentale. Tout d’abord, une méthode numérique adaptée à la résolution de l'équation des films minces a été mise en place en prenant en compte les forces capillaires et de van der Waals, et validée en comparant la dynamique obtenue à des prédictions théoriques. Un terme de cisaillement a ensuite été rajouté, et deux régimes ont pu être mis en évidence en fonction du taux de cisaillement : dans le cas de faibles taux de cisaillement la rupture est retardée, à plus haut taux de cisaillement elle est supprimée. L’utilisation de diagrammes spatio-temporels a permis de caractériser la déformation de l’interface. Le passage du régime de rupture retardé à celui de rupture supprimée présente une évolution analogue à une transition de phase. L’étude expérimentale à faible taux de cisaillement a permis de confirmer ce retard de rupture, mais également de montrer après la rupture une vitesse de démouillage augmentée. Cette étude permettra de mieux appréhender les phénomènes de rupture de couches survenant lors de la coextrusion multinanocouches.

Tip-enhanced Raman scattering (TERS) in ångström-scale plasmonic cavities has drawn increasing attention. However, Raman scattering at vanishing cavity distances remains unexplored. Here, we show the evolution of TERS in transition from the tunneling regime to atomic point contact (APC). A stable APC is reversibly formed in the junction between an Ag tip and ultrathin ZnO or NaCl films on the Ag(111) surface at 10 K. An abrupt increase of the TERS intensity occurs upon APC formation for ZnO, but not for NaCl. This remarkable observation is rationalized by a difference in hybridization between the Ag tip and these films, which determines the contribution of charge transfer enhancement in the fused plasmonic junction. The strong hybridization between the Ag tip and ZnO is corroborated by the appearance of a new vibrational mode upon APC formation, whereas it is not observed for the chemically inert NaCl.

This work emphasizes the development of a green synthetic approach for growing ultrathin film PtxPd(1-x) alloy catalysts for formic acid oxidation (FAO) by surface limited redox replacement of underpotentially deposited H sacrificial layer. Up to three-monolayers-thick PtxPd(1-x) films with different composition are generated on Au electrodes and characterized for composition and surface roughness using XPS and electrochemical methods, respectively. XPS results show close correlation between solution molar ratio and atomic composition, with slightly higher Pt fraction in the deposited films. The accordingly deposited Pt42Pd58 films demonstrated remarkable specific and mass activities of up to 35 mAcm&minus, 2 and 45 Amg&minus, 1 respectively, lasting for more than 1500 cycles in FAO tests. This performance, found to be better twice or more than that of pure Pt counterparts, renders the Pt42Pd58 films comparable with the frontrunner FAO catalysts. In addition, the best alloy catalyst establishes a nearly hysteresis-free FAO CV curve a lot earlier than its Pt counterpart and thus supports the direct FAO pathway for longer. Overall, the combination of high Pd activity and CO tolerance with the remarkable Pt stability results in highly active and durable FAO catalysts. Finally, this facile and cost-effective synthetic approach allows for scaling the catalyst production and is thus appropriate for foreseeable commercialization.

PtSe$_2$ ultrathin films are used as the channel of back-gated field-effect transistors (FETs) that are investigated at different temperatures and under super-continuous white laser irradiation. The temperature-dependent behavior confirms the semiconducting nature of multilayer PtSe$_2$, with p-type conduction, a hole field-effect mobility up to 40 cm2/(Vs) and significant gate modulation. Electrical conduction measured along different directions shows isotropic transport. A reduction of PtSe$_2$ channel conductance is observed under exposure to light. Such negative photoconductivity is explained by a photogating effect caused by photo-charge accumulation in SiO$_2$ and at the Si/SiO$_2$ interface., Comment: 9 pages, 3 figures

This diploma thesis studies magneto-optical (MO) response of epitaxial thin films of Co-doped ceria. Thin films were characterized by XPS, LEED, STM, spectroscopic ellipsometry and measurement of MO activity. The work focuses on studying MO response of the films depending on film thickness, cobalt concentration, oxidation state of cerium and chemical state of cobalt. Spectra of MO response consist of low energy region where the MO activity is mediated by transitions from defect induced states to conduction band and high energy region where a peak of MO activity appears which we attribute to transitions from valence band to conduction band. In this work we qualitatively explain the effects of the physico- chemical states of the thin films on the structure of the obtained MO spectra, mainly on the appearance of the MO activity in the low energy region, and on the changes of the position of the MO peak. Compared to other preparation methods the epitaxial thin films allow achieving a shift of the MO peak in the direction of higher photon energy.

Данная работа посвящена выращиванию методом молекулярно-лучевой эпитаксии (МЛЭ) тонких слоев фторида кальция на кремниевых подложках CaF2/Si(111) и исследованию их кристаллической структуры и топографии методами дифракции быстрых электронов (ДБЭ) на отражение и атомно-силовой микроскопии (АСМ). В ходе исследований были выращены и получены физические свойства 120 нм и 2 нм пленок CaF2, рассмотрен потенциал использования фторида кальция в двумерной наноэлектронике., This work is devoted to the growth of thin layers of calcium fluoride on silicon substrates CaF2/Si(111) using molecular beam epitaxy (MBE) and the study of their crystal structure and topography by reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). After the growth, the physical properties of 120 nm and 2 nm CaF2 films were studied, and the potential of calcium fluoride films for using in two-dimensional nanoelectronics was considered.

Ultrathin ferromagnets with frustrated exchange and the Dzyaloshinskii-Moriya interaction can support topological solitons such as skyrmions and antiskyrmions, which are metastable and can be considered particle-antiparticle counterparts. When spin-orbit torques are applied, the motion of an isolated antiskyrmion driven beyond its Walker limit can generate skyrmion-antiskyrmion pairs. Here, we use atomistic spin dynamics simulations to shed light on the scattering processes involved in this pair generation. Under certain conditions a proliferation of these particles and antiparticles can appear with a growth rate and production asymmetry that depend on the strength of the chiral interactions and the dissipative component of the spin-orbit torques. These features are largely determined by scattering processes between antiskyrmions, which can be elastic or result in bound states or annihilation., 7 pages, 6 figures

Obwohl Biomaterialien schon seit langer Zeit genutzt werden, ist die systematische Biomaterialwissenschaft ein noch recht junger Wissenschaftsbereich mit einer 60- bis 70jährigen Geschichte. Seide wird seit Jahrtausenden für Textilien verwendet und insbesondere Spinnenseide wurde schon vor Jahrhunderten von Polynesiern bei der Fischerei sowie in der Antike als Wundauflage und als Nahtmaterial verwendet. Aus heutiger Sicht ist die Biomaterialwissenschaft ein Zusammenwirken verschiedener Fachbereiche und das Verständnis der physikalischen und chemischen Wechselwirkungen zwischen komplexen biologischen Systemen und synthetischen oder modifizierten natürlichen Materialien nimmt einen hohen Stellenwert ein. Die Biokompatibilität spielt hierbei eine große Rolle. Doch es bedarf einer genauen Betrachtung, die abhängig vom jeweiligen Anwendungsgebiet (z.B. Hartgewebe, Weichgewebe, Herz-Kreislauf-System) des Biomaterials ist. Biokompatibilität kann in zwei Bereiche – die Strukturkompatibilität und die Oberflächenkompatibilität – gegliedert werden. Bei der Strukturkompatibilität wird z.B. die Struktur, Form und Mechanik eines Implantats an das Verhalten des Gewebes im Wirtsorganismus betrachtet. Werden die chemischen, physikalischen, biologischen und morphologischen Oberflächeneigenschaften eines Materials an das Wirtsgewebe angepasst, spricht man von Oberflächenkompatibilität. Die Oberflächeneigenschaften eines Biomaterials sind somit entscheidend für seine Biokompatibilität und Wechselwirkung mit dem Wirtssystem. Durch seine gute Verfügbarkeit und gute Biokompatibilität ist das rekombinante Spinnenseidenprotein eADF4(C16) ein interessantes Material zur Steuerung und Modifizierung der Oberflächeneigenschaften von Biomaterialien. Spinnenseide ist nicht hämolytisch oder zytotoxisch und auch die beim Abbau der Seidenproteine entstehenden Produkte (Peptide und Aminosäuren) sind nicht toxisch und können vom Körper resorbiert werden. Es tritt keine Immunantwort auf und Zellen zeigen nur eine geringe Interaktion mit glatten eADF4(C16)-Filmen und ihren Oberflächen. eADF4(C16) ist daher gut als Beschichtungsmaterial für Implantate (z.B. Silikonbrustimplantate) oder auch Katheter geeignet. In der vorliegenden Arbeit wurde ein Prozess entwickelt, um glatte Polymeroberflächen, wie z.B. von Kathetern (aus Silikon, Polyurethan (PU) und Polytetrafluoroethylen (PTFE)), mit eADF4(C16) zu beschichten. Die Beschichtungen, die sich durch ihre Schichtdicke von < 100 nm von bisher untersuchten Silikonimplantatbeschichtungen aus Spinnenseide mit einer Schichtdicke im Mikrometerbereich unterscheiden, wurden hinsichtlich ihrer Stabilität, Biokompatibilität und ihrer Zelladhäsionseigenschaften untersucht. Die in dieser Arbeit verwendeten polymeren Biomaterialien (PTFE, PU und Silikon) haben hydrophobe Oberflächen und wurden vor dem Tauchbeschichtungsprozess im Sauerstoffplasma hydrophilisiert. Um die Haftung der eADF4(C16)-Beschichtung auf der plasmabehandelten Oberfläche zur erhöhen, wurde eine Vermittlerschicht aus dem polykationischen Polymer Polyethylenimin (PEI) bzw. dem positiv geladenen rekombinanten Spinnenseidenprotein eADF4(k16) auf die hydrophilisierte Polymeroberflächen aufgebracht. Die Beschichtungen zeigen keine Delamination bei Biegebelastung und die Oberflächenkontaktwinkel liegen für diese Beschichtungen deutlich unter dem für gegossene eADF4(C16)-Filme mit einer Dicke von 1 bis 2 µm. Sinkt die Schichtdicke eines Films oder einer Beschichtung, so steigt auch die spezifische Oberfläche je Volumen. Erreicht ein Material Abmessungen von < 100 nm in mindestens einer Dimension, so spricht man von Nanomaterialien, die im Vergleich zum bulkMaterial verschiedene Eigenschaften aufweisen. Es konnte gezeigt werden, dass sich die Oberflächeneigenschaften (hier: Oberflächenkontaktwinkel) abhängig von der Schichtdicke ändern. Zusätzlich wurden die strukturellen Eigenschaften (beta-Faltblattanteil) schichtdickenabhängig untersucht. Betrachtet man die Aminosäuresequenz von eADF4(C16), so lässt sich das Protein als eine sich wiederholende Abfolge eines alaninreichen hydrophoben und eines glycinreichen hydrophilen Blockes beschreiben und kann aus polymerwissenschaftlicher Sicht als AB-Multiblockcopolymer beschrieben werden. Auf Basis der gesammelten Daten über die Schichtdickenabhängigkeit des beta-Faltblattanteils und der Oberflächeneigenschaften zusammen mit den bereits beschriebenen Multiblockcopolymereigenschaften des Proteins wurde ein schichtdickenabhängiges Assemblierungs- und Phasenseparationsmodell von der nur einige Nanometer dicken Proteinlage bis zum bulkMaterial vorgeschlagen. Zusätzlich wurde die Bioabbaubarkeit dünner eADF4(C16)-Beschichtungen untersucht. Die eADF4(k16)/eADF4(C16)-Beschichtungen auf Silikonkathetern zeigten eine sehr gute Stabilität in Puffer und wiesen in Wundheilungsumgebung eine langsame Bioabbaubarkeit sowie eine gute Stabilität der Beschichtungen gegenüber mechanischer Belastung auf. Neben der Beschichtungsstabilität spielt auch die Zellinteraktion mit den Beschichtungsoberflächen eine bedeutende Rolle für die Biokompatibilität des Materials und seine spezifische Anwendung. Auf mit eADF4(C16) beschichteten Katheteroberflächen war eine geringe Zelladhäsion von BALB/3T3 Fibroblasten, B50 neuronalen Zellen, HaCaT Keratinocyten sowie C2C12 Myoblasten zu beobachten. Dünne eADF4(C16) Beschichtungen bieten somit für biomedizinische Anwendungen, in denen keine Wirtsreaktion auftreten soll und Zellen nicht mit der Oberfläche interagieren sollen, eine gute Möglichkeit zur Einstellung der Oberflächeneigenschaften bei gleichzeitig geringem Materialeinsatz. Zusätzlich wurden mit eADF4(C2) funktionalisierte bakterielle Nanopartikeln (MamC-C2 Magnetosomen) untersucht. Magnetosomen werden von magnetotaktischen Bakterien zur Orientierung entlang der Feldlinien des Erdmagnetfeldes gebildet. Im Modellorganismus Magnetospirillum gryphiswaldense bestehen sie aus einem Magnetitkern und einer Phospholipid-Doppelschicht (Magnetosomen-Membran). Im Fall von MamC-C2 Magnetosomen ist eine zweifache Wiederholung des C-Moduls des Spinnenseidenproteins eADF4(C16) über das Ankerprotein MamC in der Biomembran verankert und bildet mit dieser zusammen eine den Partikel kolloidal stabilisierende Hülle. QCM-D Experimente haben gezeigt, dass eine intermolekulare Wechselwirkung zwischen MamC-C2 Magnetosomen und eADF4(C16) besteht und MamC-C2 Magnetosomen als Nukleationskeime für die Assemblierung von eADF4(C16)-Fibrillen dienen können.

The growth of ultrathin layers of VOx (< 12 monolayers) on Pt(111) and the activity of these layers in catalytic methanol oxidation at 10−4 mbar have been studied with low-energy electron diffraction, Auger electron spectroscopy, rate measurements, and with photoemission electron microscopy. Reactive deposition of V in O2 at 670 K obeys a Stranski–Krastanov growth mode with a (√3 × √3)R30° structure representing the limiting case for epitaxial growth of 3D-VOx. The activity of VOx/Pt(111) in catalytic methanol oxidation is very low and no redistribution dynamics is observed lifting the initial spatial homogeneity of the VOx layer. Under reaction conditions, part of the surface vanadium diffuses into the Pt subsurface region. Exposure to O2 causes part of the V to diffuse back to the surface, but only up to one monolayer of VOx can be stabilized in this way at 10−4 mbar.

In this thesis, complex spin structures driven by frustration of magnetic interactions are studied in ultrathin Co and Mn films. Therefore, density functional theory (DFT) calculations using the full potential linearized augmented planewave method are mapped onto an atomistic spin model. On this basis, spindynamics simulations are performed to analyse the properties of non-collinear spin structures such as domain walls (DWs), skyrmions and antiskyrmions. The obtained results are compared to spin-polarized scanning tunnelling microscopy (SP-STM) measurements performed by experimental collaborators. For the prominent Pt/Co/Ir interface, additive effects have been proposed in magnetic multilayer systems to enhance the Dzyaloshinskii-Moriya interaction (DMI); however, here it is shown that this phenomenon does not occur in atomic Pt/Co bilayers (BLs) on Ir(111). Even though an enhancement of the DMI from Co/Ir(111) to Pt/Co/Ir(111) is observed, the interfacial DMI appears more complex and a frustration of DMI is predicted – an effect which has been neglected so far. It results in a dependence of the rotational sense on the period of spin spirals and demonstrates that DMI calculations can give wrong results when unsuitable non-collinear spin structures are considered. Furthermore, the exchange interaction of Co/Ir(111) is tuned with 4d top layers from weakly to strongly ferromagnetic. Replacing Ir(111) by its 4d equivalent Rh(111), the spin-orbit coupling dependent interactions can be controlled. Exceptionally large frustration is found for Rh/Co/Ir(111). This stabilizes atomic-scale non-collinear spin structures such as DWs and skyrmions without an external magnetic field. SP-STM measurements confirm this prediction and reveal a large non-collinear magnetoresistance at the Fermi energy. This effect is explained by a spin mixing of a majority dxz and a minority pz state in the Rh/Co BL and allows for the detection of skyrmions and DWs with non-magnetic tips. Antiferromagnetic (AFM) materials are promising for spintronic applications and the prototypical AFM Mn holds a wide spectrum of magnetic and structural properties. Although a seemingly simple c(2 × 2) AFM ground state in a Mn double layer on W(001) has been suggested by SP-STM measurements, the presented DFT calculations highlight a dead magnetic layer in the Mn subsurface driven by strong frustration effects. This is confirmed by excellent agreement of theory and experiment. In Mn/Re(0001), experimental collaborators have discovered the row-wise antiferromagnetic (RW-AFM) and the 3Q state in STM measurements. Calculations point out strong frustration of exchange and DMI, but also of higher order exchange interactions due to hybridization of Mn and Re(0001). The coupling of the RW-AFM state to the lattice in Mn-fcc is explained by the interplay of dipolar and pseudo-dipolar interactions, whereas a distortion of the 3Q state in Mn-hcp towards the RW-AFM is predicted by DFT.

Conductive metal-organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu-CAT-1 is described. ispartof: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION vol:57 issue:46 pages:15086-15090 ispartof: location:Germany status: published

Hydrogen-related technologies are rapidly developing, driven by the necessity of efficient and high-density energy storage. This poses new challenges to the detection of dangerous gases, in particular the realization of cheap, sensitive, and fast hydrogen sensors. Several materials are being studied for this application, but most present critical bottlenecks, such as high operational temperature, low sensitivity, slow response time, and/or complex fabrication procedures. Here, we demonstrate that WO3 in the form of single-crystal, ultrathin films with a Pt catalyst allows high-performance sensing of H2 gas at room temperature. Thanks to the high electrical resistance in the pristine state, this material is able to detect hydrogen concentrations down to 1 ppm near room temperature. Moreover, the high surface-to-volume ratio of WO3 ultrathin films determines fast sensor response and recovery, with characteristic times as low as 1 s when the concentration exceeds 100 ppm. By modeling the hydrogen (de)intercalation dynamics with a kinetic model, we extract the energy barriers of the relevant processes and relate the doping mechanism to the formation of oxygen vacancies. Our results reveal the potential of single-crystal WO3 ultrathin films toward the development of sub-ppm hydrogen detectors working at room temperature.

The presence of interfaces and geometrical confinement can have a strong influence on the structure and morphology of thin films of semicrystalline polymers. Using surface-sensitive grazing incidence wide angle X-ray scattering and atomic force microscopy to investigate the vertical structure of thin films of poly(3-hexylthiophene) crystallized from the melt, we show that highly oriented crystallites are induced at the air/polymer interface and not as sometimes assumed at the interface to the substrate. These crystallites are oriented with their crystallographic a-axis perpendicular to the plane of the film. While the corresponding orientation dominates in thinner films, for sufficiently thick films (>60 nm) a layer containing unoriented crystals is present below the surface layer. Due to the anisotropic charge transport properties, the observed effects are expected to be of special relevance for potential applications of semiconductor polymers in the field of organic photovoltaics for which vertical transport in thicker films plays an important role.

The presence of interfaces and geometrical confinement can have a strong influence on the structure and morphology of thin films of semicrystalline polymers. Using surface-sensitive grazing incidence wide angle X-ray scattering and atomic force microscopy to investigate the vertical structure of thin films of poly(3-hexylthiophene) crystallized from the melt, we show that highly oriented crystallites are induced at the air/polymer interface and not as sometimes assumed at the interface to the substrate. These crystallites are oriented with their crystallographic a-axis perpendicular to the plane of the film. While the corresponding orientation dominates in thinner films, for sufficiently thick films (>60 nm) a layer containing unoriented crystals is present below the surface layer. Due to the anisotropic charge transport properties, the observed effects are expected to be of special relevance for potential applications of semiconductor polymers in the field of organic photovoltaics for which vertical transport in thicker films plays an important role.

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response., J.M. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant, agreement No. 654682. A.A. and A.I. acknowledge financial support from the Spanish Ministry Ministerio de Economia y Competitividad (MINECO) (code: MAT2015-63704-P (MINECO/FEDER, UE)) and the Eusko Jaurlaritza (Basque Government) (code: IT-654-13). A.C. would like to acknowledge the financial support of the EPSRC (EP/M014142/1). A.N., T.A.E., and C.M. acknowledge financial support from MINECO (codes: MAT2014-59187-R, MAT2015-66443-C02-1-R, and MAT2014-53437-C2-1P, respectively). N.S. is in addition grateful for support from a European Research Council ERC Starting Independent Research Fellowship under the grant agreement No. 279587.

International audience; Germanene is a single layer allotrope of Ge, with a honeycomb structure similar to graphene. This report concerns the electrochemical formation of germanene in a pH 4.5 solution. The studies were performed using in situ Electrochemical Scanning Tunneling Microscopy (EC-STM), voltammetry, coulometry, surface X-ray diffraction (SXRD) and Raman spectroscopy to study germanene electrodeposition on Au(111) terraces. The deposition of Ge is kinetically slow and stops after 2-3 monolayers. EC-STM revealed a honeycomb (HC) structure with a rhombic unit cell, 0.44 +/- 0.02 nm on a side, very close to that predicted for germanene in the literature. Ideally the HC structure is a continuous sheet, with six Ge atoms around each hole. However, only small domains, surrounded by defects, of this structure were observed in this study. The small coherence length and multiple rotations domains made direct observation with surface X-ray diffraction difficult. Raman spectroscopy was used to investigate the multi-layer Ge deposits. A peak near 290 cm(-1), predicted to correspond to germanene, was observed on one particular area of the sample, while the rest resembled amorphous germanium. Electrochemical studies of germanene showed limited stability when exposed to oxygen.

Application of nano-structures requires a knowledge of their fundamental physical (mechanical, electromagnetic, optical, etc.) characteristics. Thermodynamic properties associated with phonon displacements through the nano-samples are particularly interesting. Independent of the type of lattices, the thermodynamics of their subsystems (electrons, excitons, spin waves, etc.) is determined when the subsystem is in thermodynamic equilibrium with phonons. Phonons are collective mechanical oscillations of molecules or atoms and represent the most important system of excitations. Besides, the acoustical characteristics as well as conductive and superconductive properties etc. could not be realistically explained without phonons. All quoted is well known and all applications of phonons in bulk structures have been intensively exploited for more than a century. The fact which must be especially pointed out is that the role of phonons in nanostructures is much more impressive than in bulk structures. The main fact concerning phonon properties in nanostructures is the absence of the so-called acoustic phonons, i.e., phonons whose energy tends to zero when phonon momentum tends to zero. For the exciting of phonons in nanostructures activation energy different from zero is necessary. These unexpected characteristics require revision of all conclusions obtained by bulk theories of phonons. Therefore, the contribution of phonon subsystems to thermodynamic and energy transfering analysis is the first step in a research of nanostructure properties. This paper describes a major aspect of the effort to understand nanostructures, namely the study of phonons and phonon-mediated effects in structures with nanoscale dimensional confinement in one or more spatial dimensions. During the last two decades, there has been a steady effort to understand the optical and acoustic phonons in nanostructures such as the superlattice, quantum wires, nanotubes and quantum dots. The central theme of this paper is the description of the acoustic phonons of the optical type in these nanostructures. As a preliminary to describing the dispersion relations and mode structures for phonons in nanostructures, phonon amplitudes are quantized in terms of the harmonic oscillator approximation, and anharmonic effects leading to phonon decay are described in terms of the dominant phonon decay channels. These elastic and discontinued models are applied to describe the deformation potential and interactions in a variety of nanostructures. Dependence of energy on the wave vector is highly nonlinear and linear approximation of the laws of dispersion of phonons in small size nanostructures makes no sense. Changing the phonon dispersion law due to confinement severely affects the kinetic effects conditioned by the interaction of acoustic phonons with electrons, dotted defects, phonon-phonon interactions. Managing transport properties of acoustic phonons through the modification of their energy spectrum in nanostructures was named phonon engineering. In this paper we will try to observe the difference between the characteristics of different nano-crystalline structures: ultrathin films, composite films, i.e., superlattices, nanorods and quantum dots, we were interested in whether the quantum size effects (quantum confinement), quantum (de) coherence and influence of boundary conditions, strengthen or weaken in nanosamples. Finally, this paper describes how the dimensional confinement of phonons in nanostructures leads to modifications in the electronic, optical, acoustic, superconducting and thermodynamic properties of quantum. Thermal properties of nanostructures have recently attracted a lot of attention. The influence of size effects on thermal conductivity is becoming extremely important for device design and reliability. The problem of thermal management is even more severe for photonic devices such as vertical cavity surface emitting lasers. On the other hand, to improve performance of thermoelectrics, one needs to achieve low thermal conductivity. These are two contradictory demands, but both can be approached with appropriate modification of phonon modes, e.g., phonon engineering. On the basis of the calculated dispersion law and distribution of phonon states in nanoscopis crystals, free energy and entropy will be calculated. Internal energy as well as heat capacitance will also be analyzed. Low-temperature behavior of these quantities will be compared to the corresponding ones of bulk-structures. It was shown that heat capacitances of nano-layered structures in low-temperature region were higher than the same quantities of the corresponding bulk sample. In the middle and the highest temperature region, temperature behavior was inverse: heat capacitance of layered structures was lower than of the corresponding bulk ones. The consequences were discussed with relation to the better superconductive properties of nanomaterials.

Die Herstellung von ultradünnen Germaniumdioxidfilmen auf Metallsubstraten ist erstmals erfolgreich gelungen. Die Filmstruktur konnte mittels oberflächensensitiven Techniken mit atomarer Präzision und chemischer Sensitivität aufgelöst werden. Zur Untersuchung werden STM-Bilder analysiert und durch niederenergetische Elektronenbeugung (LEED), eine dynamischen LEED-Studie und extern ausgeführte Dichtefunktionaltheorieberechnungen (DFT) ergänzt. In dieser Arbeit werden atomar aufgelöste Rastertunnelmikroskopiebilder (STM) von ultradünnen Germaniumdioxid- und Siliziumdioxidfilmen direkt verglichen. Ziel der Analyse ist es, den Einfluss des Metallsubstrats auf die Struktur von Oxidfilmen zu untersuchen. Zu diesem Zweck werden ultradünne Germaniumdioxid-Filme auf Ru(0001), Pt(111) und Au(111) abgeschieden und mit Siliziumdioxid-Filmen auf verschiedenen Substraten verglichen, die in früheren Studien untersucht wurden. Germaniumdioxid und Siliziumdioxid sind eng miteinader verknüpft. Hierbei sind Struktur und chemische Eigenschaften als äquivalent anzusehen. Es wurden drei verschiedene Netzwerkstrukturen aufgeklärt: Monolagen-, Zickzack- und Bilagenfilme. Die einzelnen Bausteine in diesen Filmsystemen bestehen aus verzerrten Tetraedern, in denen ein Germaniumatom von vier Sauerstoffatomen umgeben ist. Benachbarte Tetraeder sind durch Ge-O-Ge-Bindungen miteinander verknüpft und binden im Fall der Monolagenfilme an das darunterliegende Metallsubstrat. In Bilagenfilmen hingegen gibt es keine chemischen Bindungen zum Substrat, wodurch die Filmstruktur flexibler wird. Durch Variation der Herstellungsbedingungen kann man rein kristalline, amorphe oder Phasen mittlerer Ordnung erhalten. Es ist wichtig hervorzuheben, dass der amorphe Germaniumdioxid-Bilagenfilm ein neues amorphes zweidimensionales Material darstellt. The preparation of metal-supported ultrathin films of germanium dioxide, termed also germania, has been successfully achieved for the first time. The structure of the films is elucidated with atomic precision and chemical sensitivity using surface science techniques. The investigation is performed by analyzing STM images and is complemented by low-energy electron diffraction (LEED) patterns, a dynamical LEED study, and external support from density functional theory (DFT) calculations. In this work, we compare side-by-side atomically-resolved scanning tunneling microscopy (STM) images of ultrathin films of germania and silica. The analysis aims to investigate the impact of the metal support on the structure of oxide films. For that purpose, ultrathin germania films are grown on Ru(0001), Pt(111) and Au(111), and compared with previously reported silica ultrathin films supported on different substrates. Germania has been widely associated with silica since they are considered to be structural and chemical equivalent materials. Three main network structures have been characterized: monolayer, zigzag and bilayer films. In all systems, the building block consists of a distorted tetrahedron with a germanium atom surrounded by four oxygen atoms. Adjacent tetrahedra connect to each other through Ge-O-Ge bonds and, in the case of the monolayer films, they also bind to the metal support. Conversely, in bilayer films there are no chemical bonds to the metal substrate, thus providing more flexibility to the film structure. Through a meticulous control of the preparation conditions one can obtain a purely crystalline phase, an amorphous one, or one with intermediate order. It is important to highlight that the amorphous germania bilayer film represents a new 2-dimensional amorphous material.

A literature review on ultrathin films of cellulose is presented. The review focuses on different deposition methods of the films-all the way from simple monocomponent films to more elaborate multicomponent structures-and the use of the film structures in the vast realm of materials science. The common approach of utilizing cellulose thin films as experimental models is therefore omitted. The reader will find that modern usage of cellulose thin films constitutes an exciting emerging area within materials science and it goes far beyond the traditional usage of the films as model systems.

Topological insulators (TI) are one of the critical elements for the new generation of electronics and spintronics devices. Such as charge-to-spin current conversion gates or Dirac fermions based nanometer scale Schottky diodes. When reduced just too a few single layers or exposed to additional doping, TI begins to show a dramatic effect that changes the electronic structure and in consequence dynamics of carriers and phonons. In order to describe those behaviors, I used advanced high-vacuum cluster with MBE to produce ultrathin films of Bi2Te3. The samples were grown on a muscovite mica substrate. The monocrystalline structure of the film was confirmed with both LEED and RHEED measurements, and the complementary studies of electronic structure focused on the analysis of the valence band and core levels. The femtosecond pump-probe spectroscopy has been used to excite the hot carriers and generate coherent optical phonons within Bi2Te3 nanostructures and observe it in the time domain.In this thesis, I reveal an evident modification of the out-of-equilibrium carriers and phonons dynamics when extreme thickness or doping modify the BT layer. Performed experimental optical measurement integrate both bulk and surface electrons, but nonnegligible surface carriers contribution still gives a strong response. This continuous and time-domain investigation provides new insight into physical properties of topological insulators and shows that downscaling the topological insulators properties and their interaction with metallic interfaces have to be taken into account for potential TIs based spintronic devices., Les isolants topologiques (TIs) sont l'un des éléments clefs de la nouvelle génération de composants pour la spintronique. Ils offrent des perspectives de conversion de charge en courant de spin ou de réalisation de diodes Schottky à l'échelle nanométrique à base de fermions Dirac. Lorsque les TIs sont élaborés en couches ultra-minces (

The catalytic model system Rh(111)/VOx/CH3OH + O2 was investigated to study the interactions of metal-oxide-supported catalysts under reaction conditions. Under reaction conditions macroscopic pattern formation causing the development of stripes and circular islands in a self organization process was observed.

The magnetic susceptibility of 3-4ML ultrathin Fe/W(001) films was measured in situ under ultrahigh vacuum using the surface magneto-optic Kerr effect (SMOKE). Susceptibility measurements indicate that Fe/W(001) is a 2DXY system, and therefore undergoes a finite-size Kosterlitz-Thouless (KT) transition at the critical temperature T_KT. The films were grown using molecular beam epitaxy (MBE) and were characterized using Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). Three distinct categories of susceptibility signals were observed, and are referred to as Type I, II, and III. The primary difference between these signals is the size of the imaginary susceptibility, which likely corresponds to dissipative effects such as domain wall motion. The critical behaviour of the susceptibility in the paramagnetic region is described in the theory by χ(T) ~exp⁡〖〖(B/(T/T_KT-1) 〗^a)〗. A least-squares fit to this paramagnetic region from many independently grown films gives values of a=0.50±0.03 and B=3.48±0.16, which are in quantitative agreement with the KT theory. In comparison to 2nd order phase transitions, a power law fit to the paramagnetic region of the susceptibility yields an effective critical exponent of γ_eff≈3.7±0.7, which does not correspond to any known universality class. Thesis Master of Science (MSc) The magnetic properties of atomically thin iron films, referred to as Fe/W(001), were investigated using the highly sensitive phenomenon known as the surface magneto-optic Kerr effect (SMOKE). Fe/W(001) films were grown using the well-developed technique known as molecular beam epitaxy (MBE), which involved a slow and controlled thermal evaporation of an iron source onto a tungsten substrate. Film thickness and uniformity were verified using Auger electron spectroscopy, and film structure was determined using low energy electron diffraction. Film growth and all subsequent measurements were performed in situ under ultrahigh vacuum (10-10 mbar) to limit surface contamination. Using SMOKE, the magnetic susceptibility of the Fe/W(001) films was measured as a function of temperature to look for evidence of a unique phase transition known as the Kosterlitz-Thouless (KT) transition. Fitting experimental susceptibility data to the theoretical model for the KT transition presented persuasive evidence that Fe/W(001) films undergo a KT transition.

WOS: 000506316400038, In this study, Au/n-Si/p-CZTS/Ag solar cells have been produced by using PLD technique. Ultrathin CZTS films have been grown on n-Si wafer in different thicknesses depending on number of laser pulses. These ultrathin CZTS films were analysed by XRD, AFM and UV-vis spectra. J-V characteristics of Au/n-Si/p-CZTS/Ag solar cells have been determined based on thickness of ultrathin CZTS films under AM 1.5 solar radiation of 80 mW/cm(2). Short circuit current density (mA/cm(2)), fill factor, open circuit voltage (V) and power conversion efficiency (%) of ultrathin CZTS film solar cells have been determined for device produced in this work. The photovoltaic (PV) characteristics of ultrathin CZTS film solar cells has been discussed in detail in this present article and, as a result, the ideal ultrathin CZTS film solar cell structure having the highest efficiency has been determined and concluded., Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [1649B031503748]; Selcuk University, Scientific Research Projects Coordination (BAP)UnitSelcuk University [18401178, 18401124, 15201070], Authors kindly would like to thank, The Scientific and Technological Research Council of Turkey (TUBITAK) for financial support via Grant No. 1649B031503748,; -Selcuk University, High Technology Research and Application Center for supplying with Infrastructure and; -Selcuk University, Scientific Research Projects Coordination (BAP)Unit for grands via projects with references of 18401178, 18401124 and 15201070.

Conductive and transparent ultra-thin Nickel films are grown by RF sputtering on fused silica substrates. The characteristics of Ni films (thickness, refractive index, and extinction coefficient) are obtained by fitting multi-angle spectrophotometric and ellipsometric data. Films thickness inferred by X ray reflection (XRR) measurements is in good accordance with ellipsometric results. XPS analysis reveals that Ni metal phase is present in the film surface together with Ni mixed oxide phases, which explains the high electrical stability of such films.

The electrical transport mechanism of non-percolated copper ultrathin films was studied. For this purpose, resistance behavior was measured during sample growth, aging in vacuum and oxidation in air, and contrasted with a model based on tunnel current and on film’s morphology. In addition, the electrical characterization of chromium and gold ultrathin films was performed and compared with that obtained for copper. All films were grown on muscovite mica through thermal evaporation under high vacuum conditions. Electrical characterization throughout films’ growth, aging and oxidation was performed in situ and in real time. Finally, to address the transport mechanism of non-percolated oxidized copper films, samples were put into a cryostat in which electrical resistance was measured changing the temperature between 35 and 300 K. It was found that the three materials present an almost constant resistance decay during growth. This resistance decrease was studied for copper films by fitting a tunnel transport model which considered islands’ distance as a function of film thickness, indicating a resistance reduction given by coalescing islands. During aging, the resistance of copper and gold ultrathin films increases without reaching a saturation value after 30 min, with a behavior independent of the material or the initial resistance. The theoretical model applied to copper film resistance explains the increment by further formation of 3D structures, mainly conducted by atom diffusion on the substrate. Finally, a change in the resistance behavior is observed during the oxidation of copper ultrathin films, electrical transport is mediated by two mechanisms a semi-conductor type, resembling that of oxidized chromium layers, and a tunnel conduction type, observed in gold films. The first mechanism dominates when temperature is above 200 K, while tunneling is the main process for temperatures below 150 K.

Infrared (IR) spectroscopy is a powerful technique to characterize the chemical structure and dynamics of various types of samples. However, the signal-to-noise-ratio drops rapidly when the sample thickness gets much smaller than penetration depth, which is proportional to wavelength. This poses serious problems in analysis of thin films. In this work, an approach is demonstrated to overcome these problems. It is shown that a standard IR spectroscopy can be successfully employed to study the structure and composition of films as thin as 20 nm, when the layers were grown on porous substrates with a well-developed surface area. In contrast to IR spectra of the films deposited on flat Si substrates, the IR spectra of the same films but deposited on porous ceramic support show distinct bands that enabled reliable chemical analysis. The analysis of Zn-S ultrathin films synthesized by atomic layer deposition (ALD) from diethylzinc (DEZ) and 1,5-pentanedithiol (PDT) as precursors of Zn and S, respectively, served as proof of concept. However, the approach presented in this study can be applied to analysis of any ultrathin film deposited on target substrate and simultaneously on porous support, where the latter sample would be a reference sample dedicated for IR analysis of this film.

Ultrathin transition metal oxide films exhibit unique physical and chemical properties not observed for the corresponding bulk oxides. These properties, originating mainly from the limited thickness and the interaction with the support, make those films similar to other supported 2D materials with bulk counterparts, such as transition metal dichalcogenides. Ultrathin iron oxide (FeO) films, for example, were shown to exhibit unique electronic, catalytic and magnetic properties that depend on the type of the used support. Ag(111) has always been considered a promising substrate for FeO growth, as it has the same surface symmetry, only ~5% lattice mismatch, is considered to be weakly-interacting and relatively resistant to oxidation. The reports on the growth and structure of ultrathin FeO films on Ag(111) are scarce and often contradictory to each other. We attempted to shed more light on this system by growing the films using different preparation procedures and studying their structure using scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). We observed the formation of a previously unreported Moir&eacute, superstructure with 45 &Aring, periodicity, as well as other reconstructed and reconstruction-free surface species. The experimental results obtained by us and other groups indicate that the structure of FeO films on this particular support critically depends on the films&rsquo, preparation conditions. We also performed density functional theory (DFT) calculations on the structure and properties of a conceptual reconstruction-free FeO film on Ag(111). The results indicate that such a film, if successfully grown, should exhibit tunable thickness-dependent properties, being substrate-influenced in the monolayer regime and free-standing-FeO-like when in the bilayer form.