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Characteristics of Ultrathin Ni Films
摘要： 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.
关键词： optical measurements,ultrathin films,transparent conductive films,Ni films
更新于2025-09-23 15:23:52
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Ultrathin films of L1 <sub/>0</sub> -MnAl on GaAs (001): A hard magnetic MnAl layer onto a soft Mn-Ga-As-Al interface
摘要： Ferromagnetic MnAl (L10-MnAl phase) ultrathin films with thickness varying from 1 to 5 nm have been epitaxially grown on a GaAs (001) substrate. A coercivity above 8 kOe has been obtained with no need of a buffer layer by tuning the sample preparation and the growth parameters. Surface and interface analysis carried out by in situ characterization techniques (x-ray photoelectron spectroscopy and low energy electron diffraction), available in the molecular beam epitaxy chamber, has shown the formation of a ferromagnetic interface consisting of Mn-Ga-As-Al, which contribution competes with the MnAl alloyed film. The appearance of this interface provides important information to understand the growth mechanism of MnAl-based films reported in the literature.
关键词： x-ray photoelectron spectroscopy,ferromagnetic,GaAs,molecular beam epitaxy,low energy electron diffraction,ultrathin films,L10-MnAl
更新于2025-09-23 15:21:01
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Production and photovoltaic characterisation of n-Si/p-CZTS heterojunction solar cells based on a CZTS ultrathin active layers
摘要： 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/cm2. Short circuit current density (mA/cm2), 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.
关键词： efficiency,ultrathin films,Solar cell,PLD,CZTS,Si
更新于2025-09-11 14:15:04
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Manipulating the Ferroelectric Domain States and Structural Distortion in Epitaxial BiFeO3 Ultrathin Films via Bi Nonstoichiometry
摘要： Exploring and manipulating the domain configurations in ferroelectric thin films are of critical importance for the design and fabrication of ferroelectric heterostructures with novel functional performance. In this study, BiFeO3 (BFO) ultrathin films with various Bi/Fe ratios from Bi-excess to Bi-deficient have been grown on (La0.7Sr0.3)MnO3 (LSMO) covered SrTiO3 substrates by laser molecular beam epitaxy system. Atomic force microscopy and piezoresponse force microscopy measurements show that both the surface morphology and ferroelectric polarization of the films are relevant to the Bi nonstoichiometry. More significantly, the Bi-excess thin films show upward (from substrate to film surface) uniform ferroelectric polarization, while a Bi-deficient thin film exhibits downward uniform polarization, which means the as-grown polarization of the BFO thin films can be controlled by changing Bi contents. Atomic-scale structural and chemical characterizations and second harmonic generation measurements reveal that two different kinds of structural distortion and interface atomic configuration in the BFO/LSMO heterostructures can be induced by the change of Bi nonstoichiometry, leading to the two opposite as-grown ferroelectric polarizations. It has also been revealed that the band gap of the BFO thin films can be modulated via Bi nonstoichiometry. These results demonstrate that Bi nonstoichiometry plays a key role on the ferroelectric domain states and physical properties of BFO thin films, and also open a new avenue to manipulate the structure and ferroelectric domain states in BFO thin films.
关键词： BiFeO3 ultrathin films,interface atomic configuration,ferroelectric domain states,Bi nonstoichiometry,structural distortion
更新于2025-09-09 09:28:46
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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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Hybridization of an unoccupied molecular orbital with an image potential state at a lead phthalocyanine/graphite interface
摘要： The interaction of a molecular orbital with a surface state is important to understand the spatial distribution of the wave function at the molecule/substrate interface. In this study, we focus on hybridization of an unoccupied state of lead phthalocyanine (PbPc) with the image potential state (IPS) on a graphite surface. The hybridization modifies the energy-momentum dispersions of the IPS on PbPc films as observed by angle-resolved two-photon photoemission. On the PbPc 1 monolayer film, the IPS band forms a band gap and back-folding appears at the first Brillouin zone boundary due to the periodic potential by the adsorbate lattice. The modification of the dispersion is accompanied by the intensity enhancement of the IPS. We attributed the origin of the modified dispersion and intensity enhancement to a hybridization of the IPS with a molecule-derived unoccupied level. From the photon energy-dependent measurement on multilayer films, we have found the diffuse unoccupied molecular level in the vicinity of the IPS. The tail part of the IPS wave function in the substrate is enhanced by the hybridization with the unoccupied state, and thus strengthens the transition from the occupied substrate band to the hybridized IPS.
关键词： organic ultrathin films,image potential states,two-photon photoemission spectroscopy,unoccupied states,hybridization
更新于2025-09-04 15:30:14
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Two distinct surface terminations of SrVO <sub/>3</sub> (001) ultrathin films as an influential factor on metallicity
摘要： Pulsed laser deposition-grown SrVO3 (001) ultrathin films on SrTiO3 (001) substrates were investigated by in situ low-temperature scanning tunneling microscopy and spectroscopy. SrVO3 (001) ultrathin films showed two distinct surface terminations. One termination was a ((√2 × √2)-R45° reconstruction as was previously observed for SrVO3 (001) thick films, while the other was a ((√5 × √5)-R26.6° reconstruction. Scanning tunneling spectroscopy revealed that the ((√2 × √2)-R45° surface shows a metallic electronic structure, whereas the ((√5 × √5)-R26.6° surface exhibits a significantly reduced density of states at the Fermi level. These results suggest that the surface reconstruction may be an important factor to influence metallicity in epitaxial ultrathin films of transition metal oxides.
关键词： ultrathin films,scanning tunneling microscopy,scanning tunneling spectroscopy,SrVO3,metallicity,surface terminations
更新于2025-09-04 15:30:14
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Desenvolvimento de filmes poliméricos ultrafinos e reticulados para aplica??es em sensores
摘要： A new method for producing stable films used in sensors is proposed, based on the layer-by-layer deposition of poly(o-ethoxyaniline) and phenol-formaldehyde (POEA/PF) followed by a thermal treatment to promote film crosslinking. The crosslinking process was characterized by Fourier transform infrared and ultraviolet-visible spectroscopic analyses, atomic force microscopy and desorption studies. Sensor analyses were also carried out in order to evaluate cross-linked sensor signal. Results showed that PF resin served as a curing agent, forming a semi-interpenetrating polymer network therefore producing stable films. Although there was a decrease in the sensitivity of sensors with crosslinking, such films are quite stable and can be potentially used in sensors, especially where higher stability is required.
关键词： ultrathin films,conductive polymers,sensors
更新于2025-09-04 15:30:14