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Vapor-phase film deposition of metal-organic frameworks (MOFs) would facilitate the integration of these materials into electronic devices. We studied the vapor-phase layer-by-layer deposition of zeolitic imidazolate framework 8 (ZIF-8) by consecutive, self-saturating reactions of diethyl zinc, water, and 2-methylimidazole on a substrate. Two approaches were compared: (1) Direct ZIF-8 "molecular layer deposition" (MLD), which enables a nanometer-resolution thickness control and employs only self-saturating reactions, resulting in smooth films that are crystalline as deposited, and (2) two-step ZIF-8 MLD, in which crystallization occurs during a postdeposition treatment with additional linker vapor. The latter approach resulted in a reduced deposition time and an improved MOF quality, i.e., increased crystallinity and probe molecule uptake, although the smoothness and thickness control were partially lost. Both approaches were developed in a modified atomic layer deposition reactor to ensure cleanroom compatibility.

Magnetic nanowires (NWs) are essential building blocks of spintronics devices as they offer tunable magnetic properties and anisotropy through their geometry. While the synthesis and compositional control of NWs have seen major improvements, considerable challenges remain for the characterization of local magnetic features at the nanoscale. Here, we demonstrate nonperturbative field distribution mapping in ultrascaled magnetic nanowires with diameters down to 6 nm by scanning nitrogen-vacancy magnetometry. This enables localized, minimally invasive magnetic imaging with sensitivity down to 3 μT Hz–1/2. The imaging reveals the presence of weak magnetic inhomogeneities inside in-plane magnetized nanowires that are largely undetectable with standard metrology and can be related to local fluctuations of the NWs’ saturation magnetization. In addition, the strong magnetic field confinement in the nanowires allows for the study of the interaction between the stray magnetic field and the nitrogen-vacancy sensor, thus clarifying the contrasting formation mechanisms for technologically relevant magnetic nanostructures.

Background: An extreme ultraviolet (EUV)-transparent pellicle must be used during lithography to protect the photomask from fall-on particles. A pellicle made of free-standing carbon nanotube (CNT) films stops particles despite the presence of gaps while demonstrating high EUV transmission, mechanical stability, low EUV scattering and reflectivity, and DUV transmission that enables through-pellicle mask inspection. Aim: The CNT EUV pellicle properties can be tailored based on the diversity of CNT structures and tunability of their configuration within the CNT film (density, bundle size, composition, etc.) as shown in this work. A remaining challenge is extending the CNT EUV pellicle lifetime in the scanner environment of EUV-induced hydrogen-based plasma, and the effects on different CNT films are explored here. Approach: Optical and thermal properties of different CNT pellicles with respect to the CNT material type, density, composition, and bundle size were explored. The ability of uncoated CNT EUV pellicles to withstand high EUV powers in the hydrogen-based environment was tested. Transmission, spectroscopic, and chemical mapping of the exposed CNT membranes were performed to explore the material modifications under various exposure conditions. Results: Uncoated CNT pellicles withstand 600-W source power equivalent in the EUV scanner-like gas environment but exhibit structural changes with prolonged exposure. Multiwalled CNT pellicles exhibit less EUV transmission change as compared to single-walled CNT pellicles under the same exposure conditions. The protection of CNT material from structural degradation by means of coating was shown. Conclusions: These investigations add to the understanding of CNT EUV pellicle tunability for optimal performance and lifetime limiters of CNT pellicles under the influence of EUV radiation and plasma. We anticipate the need for coating the CNT pellicle to protect the CNT material against plasma damage for the current scanner conditions. Optimization of both the CNT membrane and its coating is in progress.

Research on carbon nanotube (CNT) films for the EUV pellicle application was initiated at imec in 2015 triggered by the remarkable optical, mechanical, and thermal properties of the CNT material. Today the advancement of the CNT material synthesis together with matured methods to fabricate thin CNT membranes make free-standing CNT films a very promising EUV pellicle candidate for high volume EUV lithography. Balancing the CNT material properties for the optimal pellicle performance in EUV scanners remains the ongoing research focus. Depending on the density and morphology of the CNTs within the film and individual CNT parameters, like number of walls, bundle size, metal catalyst content, purity etc., the optical and thermal properties of the CNT pellicle can be tuned. It is critical for the pellicle to be stable in the EUV lithography scanner environment which includes hydrogen plasma and heat loads associated with high powers beyond 250 W. Different types of CNTs, i.e. single-, double-, multi-walled CNTs and their combinations, are explored as building blocks of an optimized pellicle membrane. Optical properties of different pellicles and their ability to withstand high EUV powers in the hydrogen-based environment were tested. Transmission, spectroscopic and chemical composition mapping of the exposed free-standing CNT films are used to study the material changes that occur in the scanner-like environment. A solution is needed to extend the CNT pellicle lifetime and coating is discussed as a potential approach to protect the CNT material from hydrogen plasma damage.

Barium titanate (BaTiO3 or BTO) is a perovskite structure material with interesting intrinsic properties, such as spontaneous ferroelectricity or electro-optical behavior, which strongly depend on thin film crystallinity. For such functional oxide systems, the pulsed-laser deposition (PLD) approach is one promising growth technique due to its precise stoichiometry control of the metals composing the perovskite crystal and higher oxygen environment compared to the classically used molecular beam epitaxy (MBE) approach. In this article, we demonstrate a BTO epitaxial layer by PLD onto an Si(001) substrate thanks to a thin pseudomorphic SrTiO3 buffer layer grown by MBE. In our study, the various investigated PLD parameters show strong impacts on the BTO polarization orientation. Hence, adjusting the growth conditions allows control of the polarization orientation, which is crucial for both electronic and optical applications. In addition, lattice parameter changes of BTO layers are investigated using x-ray diffraction and cross-sectional transmission electron microscopy, which evidenced a correlation between mismatch relaxation and oxygen growth pressure. Finally, with the analysis of BTO C– V curves, the polarization direction transition is demonstrated electrically. ispartof: Journal Of Applied Physics vol:128 issue:10 pages:104104-104104 status: published

International audience; We present a study of blue III-nitride light-emitting diodes (LEDs) with multiple quantum well (MQW) and quantum dot (QD) active regions (ARs), comparing experimental and theoretical results. The LED samples were grown by metalorganic vapor phase epitaxy, utilizing growth interruption in the hydrogen/nitrogen atmosphere and variable reactor pressure to control the AR microstructure. Realistic configuration of the QD AR implied in simulations was directly extracted from HRTEM characterization of the grown QD-based structures. Multi-scale 2D simulations of the carrier transport inside the multiple QD AR have revealed a non-trivial pathway for carrier injection into the dots. Electrons and holes are found to penetrate deep into the multi-layer AR through the gaps between individual QDs and get into the dots via their side edges rather than via top and bottom interfaces. This enables a more homogeneous carrier distribution among the dots situated in different layers than among the laterally uniform quantum well (QWs) in the MQW AR. As a result, a lower turn-on voltage is predicted for QD-based LEDs, as compared to MQW ones. Simulations did not show any remarkable difference in the efficiencies of the MQW and QD-based LEDs, if the same recombination coefficients are utilized, i.e. a similar crystal quality of both types of LED structures is assumed. Measurements of the current–voltage characteristics of LEDs with both kinds of the AR have shown their close similarity, in contrast to theoretical predictions. This implies the conventional assumption of laterally uniform QWs not to be likely an adequate approximation for the carrier transport in MQW LED structures. Optical characterization of MQW and QD-based LEDs has demonstrated that the later ones exhibit a higher efficiency, which could be attributed to better crystal quality of the grown QD-based structures. The difference in the crystal quality explains the recently observed correlation between the growth pressure of LED structures and their efficiency and should be taken into account while further comparing performances of MQW and QD-based LEDs. In contrast to experimental results, our simulations did not reveal any advantages of using QD-based ARs over the MQW ones, if the same recombination constants are assumed for both cases. This fact demonstrates importance of accounting for growth-dependent factors, like crystal quality, which may limit the device performance. Nevertheless, a more uniform carrier injection into multi-layer QD ARs predicted by modeling may serve as the basis for further improvement of LED efficiency by lowering carrier density in individual QDs and, hence, suppressing the Auger recombination losses.

Stranski-Krastanow (S-K) grown self-assembled quantum dots (QDs) are considered as an efficient active layer for many optoelectronic applications, such as semiconductor laser, photodetector, due to the possibility to confine carriers in three dimensions. Towards the device application, the subsequent growth of an encapsulation layer is a key step to obtain the desired QDs-based heterostructures. In this work, we have studied step-by-step the encapsulation process of S-K grown InAs QDs/InP(0 0 1) by InAlGaAs (lattice matched to InP) in MOVPE. A detailed investigation with Electron Channeling Contrast Imaging (ECCI) and cross-sectional Transmission Electron Microscopy (TEM), indicated that after the InAlGaAs capping the partially relaxed, dome shaped InAs QDs are transformed into fully biaxially strained, truncated pyramids however without introducing any defects in the heterostructure. The study also presents the important role of the capping layer thickness on the QDs photoluminescence efficiency. The gradual change of the surface morphology during the encapsulation process, has been investigated step-by-step in-depth by atomic force microscopy. The morphological changes can be explained by a capping model based on the localized growth rates. We show that two growth steps of Non-uniform capping, where growth rates are different from each other, result in the successful planarization of the InAlGaAs capping without forming any defect.

In this work, the epitaxy of SrTiO3 and BaTiO3 perovskites on the (001)-oriented silicon substrate by molecular beam epitaxy is investigated. The heterostructures are studied by means of various structural and electrical characterization techniques. In this study especially, the authors reveal experimentally by nanobeam electron diffraction analysis the critical thickness prior relaxation of BaTiO3 grown on an SrTiO3/Si pseudosubstrate. They also propose to use a strain mediated superlattice composed of stacked [BaTiO3/SrTiO3] bilayers to prevent misfit dislocation formation. Using this approach, they could demonstrate high quality and dislocation free BaTiO3 ferroelectric layers integrated on silicon as confirmed by piezo-force microscopy techniques.In this work, the epitaxy of SrTiO3 and BaTiO3 perovskites on the (001)-oriented silicon substrate by molecular beam epitaxy is investigated. The heterostructures are studied by means of various structural and electrical characterization techniques. In this study especially, the authors reveal experimentally by nanobeam electron diffraction analysis the critical thickness prior relaxation of BaTiO3 grown on an SrTiO3/Si pseudosubstrate. They also propose to use a strain mediated superlattice composed of stacked [BaTiO3/SrTiO3] bilayers to prevent misfit dislocation formation. Using this approach, they could demonstrate high quality and dislocation free BaTiO3 ferroelectric layers integrated on silicon as confirmed by piezo-force microscopy techniques.