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Reference Module in Chemistry, Molecular Sciences and Chemical Engineering || Interface Potentials, Intrinsic Defects, and Passivation Mechanisms in Al 2 O 3 , HfO 2 , and TiO 2 Ultrathin Films
摘要： For the tailoring of interface properties in terms of providing active centers for surface reactions, surface passivation, or the adjustment of surface potentials, ultrathin metal oxide surface coatings are of importance. In this contribution we report about the applicability of Al2O3, HfO2, and TiO2 ultrathin films prepared by atomic layer deposition (ALD) regarding the aforementioned items. We have selected these metal oxides because of their wide field of applications. HfO2 is the main competitor for the replacement of SiO2 in microelectronic devices.1,2 Al2O3 ALD films are applied for passivation schemes in silicon-based3 and more recently perovskite solar cells.4 TiO2 is, for example, attractive for resistive switching devices5 and as active or passive layer in energy conversion applications such as solar cells6 or water splitting devices,7,8 to name a few. Here, the use of the ALD technique brings advantages such as: (i) precise thickness control to optimize the trade-off between light absorption (in a range of depletion layer) and charge separation (thinner thickness),7 (ii) high conformity to coat complex structures accompanied by increased light absorption,7 and (iii) capability to control the band-gap narrowing by doping with W7 or N9,10 and hence allow visible light absorption.
关键词： Al2O3,HfO2,TiO2,ultrathin films,interface potentials,intrinsic defects,passivation mechanisms,atomic layer deposition
更新于2025-09-04 15:30:14
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European Microscopy Congress 2016: Proceedings || A micro-combinatorial TEM method for phase mapping of thin two-component films
摘要： The aim is to introduce a new method for the preparation and investigation of thin films of composite materials, specifically focusing on the synthesis and characterization of two-component thin films for optoelectronic applications. The study explores the potential of these materials in enhancing the performance of optoelectronic devices, such as solar cells and LEDs, by improving their efficiency and stability under various environmental conditions.
关键词： LEDs,optoelectronics,solar cells,composite materials,thin films
更新于2025-09-04 15:30:14
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Nucleation-Limited Ferroelectric Orthorhombic Phase Formation in Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> Thin Films
摘要： Various possibilities have been proposed as the cause of the doped- or undoped-HfO2 thin film materials showing unusual ferroelectricity. These assumptions are based on empirical results, yet finding the origin of the unprecedented ferroelectricity within HfO2 has suffered from a serious gap between its theoretical calculation, mostly based on thermodynamic approach and the actual experimental results. To fill the gap, this study proposes to consider the kinetic energy, providing the evidence of the kinetic energy barrier upon a phase transformation from the tetragonal phase to the monoclinic phase affected by the TiN top electrode (capping layer). 10 nm thick Hf0.5Zr0.5O2 thin films are deposited and annealed with or without the TiN capping layer with subsequent annealing at different time and temperature. Arrhenius plot is constructed to obtain the activation energy for the tetragonal-to-monoclinic phase transformation by calculating the amount of the transformed phase using X-ray diffraction pattern. Johnson–Mehl–Avrami and nucleation-limited transformation models are utilized to describe the characteristic nucleation and growth time and calculate the activation energy for the monoclinic phase transformation of the Hf0.5Zr0.5O2 thin film. Both models demonstrate that the TiN capping layer provides a kinetic energy barrier for tetragonal-to-monoclinic phase transformation and enhances the ferroelectric property.
关键词： ferroelectric thin films,hafnium zirconium oxide,activation energy,nucleation-limited transformation,nucleation and growth transformation kinetics
更新于2025-09-04 15:30:14
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Conductive Fused Porphyrin Tapes on Sensitive Substrates by a Chemical Vapor Deposition Approach
摘要： Oxidative polymerization of nickel(II) 5,15-diphenyl porphyrin and nickel(II) 5,15-bis(di-3,5-tert-butylphenyl) porphyrin by an oxidative chemical vapor deposition (oCVD) approach yields multiply fused porphyrin oligomers in thin film form. The oCVD technique enables the formation, deposition and p-doping of conjugated poly(porphyrins) coatings in a single step without the use of solvents or post-treatments. The decisive reactions and side reactions during the oCVD process are evidenced by high-resolution mass spectrometry. Due to the highly conjugated structure of the fused porphyrin tapes the thin films exhibit an electrical conductivity of 3.6×10–2 S·cm–1 and strong absorption in the visible to near-infrared spectral region. The formation of smooth conjugated poly(porphyrins) thin films, even on sensitive substrates, is demonstrated by their successful deposition and patterning on glass, silicon and printer paper. The ability to form conductive poly(porphyrins) thin films could enable the design of a new category of optoelectronic devices using the oCVD approach.
关键词： Porphyrins,Oxidative Coupling,Chemical Vapor Deposition,Thin Films,Polymerization
更新于2025-09-04 15:30:14
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Preparation, characterization and electrical behaviors of PEDOT:PSS-Au/Ag nanocomposite thin films: an ecofriendly approach
摘要： Structure, morphology and electrical behaviors of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) or PEDOT:PSS thin films are investigated in the presence of protein-mediated green chemically synthesized positively charged gold and silver nanoparticles. The pure and PEDOT:PSS nanocomposite thin films are prepared by spin coating method. The presence of both nanoparticle and polymer is confirmed from X-ray diffraction, whereas composite formation is confirmed from Raman and FTIR spectroscopy. Atomic force microscopy (AFM) images show the surface morphologies of both pure and composite films, whereas average film thicknesses are obtained from AFM and X-ray reflectivity analysis. The presence of electrostatic interaction between the positively charged metallic nanoparticles and negatively charged PSS chains leads to the electrostatic shielding between cationic PEDOT and anionic PSS, which favors better charge transfer through PEDOT–PEDOT conducting paths. The increase in electrical conductivity is visualized from the current–voltage (I–V) curves, which show that the conductivity is relatively higher in the presence of silver than gold nanoparticles in the composite thin films. The conductivity of nanocomposite films is approximately five to six times enhanced in comparison with the pristine PEDOT:PSS thin films.
关键词： FTIR spectroscopy,PEDOT:PSS-Au/Ag thin films,AFM,UV–Vis,Nanocomposites,Conductivity
更新于2025-09-04 15:30:14
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Transport properties of Cu-AlF3-W and Cu-AlF3-Cu heterojunctions using STS measurements and a DFT-NEGF approach
摘要： To understand and to analyze the transport properties of different metal-insulator systems, we developed an experimental study of the electronic transport properties of AlF3 thin films deposited over a Cu(1 0 0) substrate, and a theoretical study to model systems composed by an AlF3 molecule between two metallic Cu(1 0 0)-W(1 0 0) and Cu(1 0 0)-Cu(1 0 0) electrodes with different geometries. The left common electrode is always a Cu(1 0 0) layer, meanwhile the right changing electrode, W(1 0 0) or Cu(1 0 0), in some cases is represented as a layer and in others as having a tip ending. Tunnelling current against voltage (I-V) characteristic curves have been obtained by Scanning Tunneling Spectroscopy (STS) measurements and computed using density functional theory (DFT) with the non equilibrium Green function method (NEGF) within a bias voltage range from ?2.5 to 5.0 V. The theoretical curves show low current values, in the order of 10?12 to 10?9, in good agreement with the I-V experimental curves in the same range. This reveals that breakdown response currents begin at higher voltages than 5.0 V. The transmission spectrum, total (DOS) and partial (PDOS) density of states are also presented being the transmission variations addressed in terms of the DOS.
关键词： Scanning Tunneling Spectroscopy (STS),Non Equilibrium Green Functions (NEGF),Scanning Tunneling Microscopy (STM),Electronic transport,AlF3 thin films
更新于2025-09-04 15:30:14
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Effects of Al2O3 buffer layer and annealing on the structural and optoelectronic properties of AZO films
摘要： Transparent conductive aluminum-doped ZnO (AZO) films are deposited on glass substrates using radio frequency (rf) magnetron sputtering, with an AZO ceramic target (Al2O3 content is ~ 3 wt%). Before the AZO films is coated, the hydrophilicity of the surface of the glass substrate is increased by oxygen plasma etching. The grey Taguchi method is used to determine the effect of the deposition parameters on the structural and optoelectronic properties of AZO films. In the confirmation runs, using the grey Taguchi method, an improvement of 46.3% in electrical resistivity and of 1.74% in transmittance is observed. The effect of an Al2O3 buffer layer is also determined. When the thickness of the Al2O3 buffer is increased (from 50 nm to 150 nm), the intensity of the (0 0 2) peak for the AZO films increases and the peaks become sharper, the resistivity of the AZO films is decreased and the transmittance is slightly reduced. Annealing at 500 °C in a vacuum (2.0 Pa) for a period of 30 min, increases the performance of the AZO/Al2O3/glass to better than that for AZO/glass samples. Using a Rockwell-C hardness tester, the AZO/Al2O3 (50 nm)/glass film are classified as HF1, which represents good adhesive mechanical strength. The crystallinity of AZO/Al2O3 (50 nm)/glass samples that are annealed at 500 °C for 30 min is improved, the electrical resistivity is 9.70 × 10?4 ? cm and the optical transmittance in the visible region is approximately 85%. The figure of merit shows that the bi-layer films have better optoelectronic performance.
关键词： optoelectronic properties,AZO films,Al2O3 buffer layer,structural properties,annealing
更新于2025-09-04 15:30:14
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Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods
摘要： Silica mono- and bilayer films on Ru(0001) can be physisorbed or chemisorbed, with ordered or vitreous structures, depending on the particular preparation procedures applied. Using the SMART spectro-microscope at BESSY-II with its capabilities for μ-spectroscopy, μ-diffraction, and LEEM imaging with lateral resolution below 5 nm, in situ and in real time and applied to identical areas, we have investigated the formation of these layers, defined and characterized their properties and their connected morphology, and followed their evolution. Two distinct chemisorbed monolayers and three bilayers (physisorbed crystalline and vitreous, and chemisorbed zigzag phases), and some transitions between them, have been studied. We found that, apart from the deposited silicon amount, the most important parameter for steering the evolution to a particular well-defined layer is the oxygen content at the Ru interface. Nucleation and growth of all layers are homogeneous on the scale of our resolution, leading to rather small domains (20 – 40 nm), mostly of the same phase, separated by defect lines. We discuss these and other basic findings in context and point out open questions. We also offer alternative recipes for the preparation of some phases, to obtain more homogeneous layers on a mesoscopic scale.
关键词： Silica films,SMART spectro-microscope,real-time methods,in situ,LEEM,chemisorbed,physisorbed,polymorphs,Ru(0001),μ-spectroscopy,μ-diffraction
更新于2025-09-04 15:30:14
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Effects of Surface Termination and Layer Thickness on Electronic Structures of LaNiO <sub/>3</sub> Thin Films
摘要： We investigate the e?ects of surface termination and layer thickness on the electronic structures of LaNiO3 thin ?lms on SrTiO3 substrate using ?rst-principles density-functional theory calculations. The NiO2-terminated ?lm with one unit cell thickness shows a pseudogap at the Fermi level owing to the negative charge transfer energy, whereas the 1.5-unit-cell-thick LaO-terminated ?lm exhibits an insulating gap of 1.0 eV as a result of the large exchange splitting. The metallic state is quickly restored for thicker ?lms with either NiO2 or LaO termination, resembling that in bulk nickelate. Our results indicate the strong dependence of the electronic properties on layer thickness and provide insightful information into the metal–insulator transition in LaNiO3 thin ?lms.
关键词： surface termination,electronic structures,layer thickness,LaNiO3 thin films,metal–insulator transition
更新于2025-09-04 15:30:14
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Effects of gas residence time of CH <sub/>4</sub> /H <sub/>2</sub> on sp <sup>2</sup> fraction of amorphous carbon films and dissociated methyl density during radical-injection plasma-enhanced chemical vapor deposition
摘要： Quadruple mass spectrometric measurements of CH3 density during radical-injection plasma-enhanced chemical vapor deposition to consider the sp2 fraction of amorphous carbon (a-C) films were performed. The sp2 fraction of the a-C films reached a minimum of 46%, where the CH3 density was maximum for a residence time of 6 ms. The sp2 fraction of the a-C films was tailored with the gaseous phase CH3 density during the deposition. This knowledge is useful for understanding the formation mechanism of bonding structures in the a-C films, which enables the precise control of their electronic properties.
关键词： CH3 density,sp2 fraction,radical-injection plasma-enhanced chemical vapor deposition,amorphous carbon films,gas residence time
更新于2025-09-04 15:30:14