654 research outputs found
Intrinsic and Atomic Layer Etching Enhanced Area-Selective Atomic Layer Deposition of Molybdenum Disulfide Thin Films
For continual scaling in microelectronics, new processes for precise high volume fabrication are required. Area-selective atomic layer deposition (ASALD) can provide an avenue for self-aligned material patterning and offers an approach to correct edge placement errors commonly found in top-down patterning processes. Two-dimensional transition metal dichalcogenides also offer great potential in scaled microelectronic devices due to their high mobilities and few-atom thickness. In this work, we report ASALD of MoS2 thin films by deposition with MoF6 and H2S precursor reactants. The inherent selectivity of the MoS2 atomic layer deposition (ALD) process is demonstrated by growth on common dielectric materials in contrast to thermal oxide/ nitride substrates. The selective deposition produced few layer MoS2 films on patterned growth regions as measured by Raman spectroscopy and time-of-flight secondary ion mass spectrometry. We additionally demonstrate that the selectivity can be enhanced by implementing atomic layer etching (ALE) steps at regular intervals during MoS2 growth. This area-selective ALD process provides an approach for integrating 2D films into next-generation devices by leveraging the inherent differences in surface chemistries and providing insight into the effectiveness of a supercycle ALD and ALE process
Thermal Atomic Layer Etching of MoS\u3csub\u3e2\u3c/sub\u3e Using MoF\u3csub\u3e6\u3c/sub\u3e and H\u3csub\u3e2\u3c/sub\u3eO
Two-dimensional (2D) layered materials offer unique properties that make them attractive for continued scaling in electronic and optoelectronic device applications. Successful integration of 2D materials into semiconductor manufacturing requires high-volume and high-precision processes for deposition and etching. Several promising large-scale deposition approaches have been reported for a range of 2D materials, but fewer studies have reported removal processes. Thermal atomic layer etching (ALE) is a scalable processing technique that offers precise control over isotropic material removal. In this work, we report a thermal ALE process for molybdenum disulfide (MoS2). We show that MoF6 can be used as a fluorination source, which, when combined with alternating exposures of H2O, etches both amorphous and crystalline MoS2 films deposited by atomic layer deposition. To characterize the ALE process and understand the etching reaction mechanism, in situ quartz crystal microbalance (QCM), Fourier transform infrared (FTIR), and quadrupole mass spectrometry (QMS) experiments were performed. From temperature-dependent in situ QCM experiments, the mass change per cycle was â5.7 ng/cm2 at 150 °C and reached â270.6 ng/cm2 at 300 °C, nearly 50Ă greater. The temperature dependence followed Arrhenius behavior with an activation energy of 13 ± 1 kcal/mol. At 200 °C, QCM revealed a mass gain following exposure to MoF6 and a net mass loss after exposure to H2O. FTIR revealed the consumption of MoâO species and formation of MoâF and MoFx=O species following exposures of MoF6 and the reverse behavior following H2O exposures. QMS measurements, combined with thermodynamic calculations, supported the removal of Mo and S through the formation of volatile MoF2O2 and H2S byproducts. The proposed etching mechanism involves a two-stage oxidation of Mo through the ALE halfreactions. Etch rates of 0.5 Ă
/cycle for amorphous films and 0.2 Ă
/cycle for annealed films were measured by ex situ ellipsometry, Xray reflectivity, and transmission electron microscopy. Precisely etching amorphous films and subsequently annealing them yielded crystalline, few-layer MoS2 thin films. This thermal MoS2 ALE process provides a new mechanism for fluorination-based ALE and offers a low-temperature approach for integrating amorphous and crystalline 2D MoS2 films into high-volume device manufacturing with tight thermal budgets
Nucleation and Growth of Molybdenum Disulfide Grown by Thermal Atomic Layer Deposition on Metal Oxides
To enable greater control over thermal atomic layer deposition (ALD) of molybdenum disulfide (MoS2), here we report studies of the reactions of molybdenum hexafluoride (MoF6) and hydrogen sulfide (H2S) with metal oxide substrates from nucleation to few-layer films. In situ quartz crystal microbalance experiments performed at 150, 200, and 250â°C revealed temperature-dependent nucleation behavior of the MoF6 precursor, which is attributed to variations in surface hydroxyl concentration with temperature. In situ Fourier transform infrared spectroscopy coupled with ex situ x-ray photoelectron spectroscopy (XPS) indicated the presence of molybdenum oxide and molybdenum oxyfluoride species during nucleation. Density functional theory calculations additionally support the formation of these species as well as predicted metal oxide to fluoride conversion. Residual gas analysis revealed reaction by-products, and the combined experimental and computational results provided insights into proposed nucleation surface reactions. With additional ALD cycles, Fourier transform infrared spectroscopy indicated steady film growth after âŒ13 cycles at 200â°C. XPS revealed that higher deposition temperatures resulted in a higher fraction of MoS2 within the films. Deposition temperature was found to play an important role in film morphology with amorphous films obtained at 200â°C and below, while layered films with vertical platelets were observed at 250â°C. These results provide an improved understanding of MoS2 nucleation, which can guide surface preparation for the deposition of few-layer films and advance MoS2 toward integration into device manufacturing
Test of Factorization Hypothesis from Exclusive Non-leptonic B decays
We investigate the possibility of testing factorization hypothesis in
non-leptonic exclusive decays of B-meson. In particular, we considered the non
factorizable \bar{B^0} -> D^{(*)+} D_s^{(*)-} modes and \bar{B^0} -> D^{(*)+}
(\pi^-, \rho^-) known as well-factorizable modes. By taking the ratios
BR(\bar{B^0}-> D^{(*)+}D_s^{(*)-})/BR(\bar{B^0}-> D^{(*)+}(\pi^-,\rho^-)), we
found that under the present theoretical and experimental uncertainties there's
no evidence for the breakdown of factorization description to heavy-heavy
decays of the B meson.Comment: 11 pages; submitted to PR
Study of the decay
The decay is studied
in proton-proton collisions at a center-of-mass energy of TeV
using data corresponding to an integrated luminosity of 5
collected by the LHCb experiment. In the system, the
state observed at the BaBar and Belle experiments is
resolved into two narrower states, and ,
whose masses and widths are measured to be where the first uncertainties are statistical and the second
systematic. The results are consistent with a previous LHCb measurement using a
prompt sample. Evidence of a new
state is found with a local significance of , whose mass and width
are measured to be and , respectively. In addition, evidence of a new decay mode
is found with a significance of
. The relative branching fraction of with respect to the
decay is measured to be , where the first
uncertainty is statistical, the second systematic and the third originates from
the branching fractions of charm hadron decays.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-028.html (LHCb
public pages
Measurement of the ratios of branching fractions and
The ratios of branching fractions
and are measured, assuming isospin symmetry, using a
sample of proton-proton collision data corresponding to 3.0 fb of
integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The
tau lepton is identified in the decay mode
. The measured values are
and
, where the first uncertainty is
statistical and the second is systematic. The correlation between these
measurements is . Results are consistent with the current average
of these quantities and are at a combined 1.9 standard deviations from the
predictions based on lepton flavor universality in the Standard Model.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-039.html (LHCb
public pages
Multidifferential study of identified charged hadron distributions in -tagged jets in proton-proton collisions at 13 TeV
Jet fragmentation functions are measured for the first time in proton-proton
collisions for charged pions, kaons, and protons within jets recoiling against
a boson. The charged-hadron distributions are studied longitudinally and
transversely to the jet direction for jets with transverse momentum 20 GeV and in the pseudorapidity range . The
data sample was collected with the LHCb experiment at a center-of-mass energy
of 13 TeV, corresponding to an integrated luminosity of 1.64 fb. Triple
differential distributions as a function of the hadron longitudinal momentum
fraction, hadron transverse momentum, and jet transverse momentum are also
measured for the first time. This helps constrain transverse-momentum-dependent
fragmentation functions. Differences in the shapes and magnitudes of the
measured distributions for the different hadron species provide insights into
the hadronization process for jets predominantly initiated by light quarks.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2022-013.html (LHCb
public pages
Motor primitives in space and time via targeted gain modulation in cortical networks
Motor cortex (M1) exhibits a rich repertoire of activities to support the generation of complex movements. Recent network models capture many qualitative aspects of M1 dynamics, but they can generate only a few distinct movements (all of the same duration). We demonstrate that simple modulation of neuronal inputâoutput gains in recurrent neuronal network models with fixed connectivity can dramatically reorganize neuronal activity and consequently downstream muscle outputs. We show that a relatively small number of modulatory control units provide sufficient flexibility to adjust high-dimensional network activity using a simple reward-based learning rule. Furthermore, novel movements can be assembled from previously-learned primitives and we can separately change movement speed while preserving movement shape. Our results provide a new perspective on the role of modulatory systems in controlling recurrent cortical activity.Our work was supported by grants from the Wellcome Trust (TPV and JPS WT100000, 246 GH 202111/Z/16/Z) and the Engineering and Physical Sciences Research Council (JPS)
Characterisation of in-hospital complications associated with COVID-19 using the ISARIC WHO Clinical Characterisation Protocol UK: a prospective, multicentre cohort study
Background:
COVID-19 is a multisystem disease and patients who survive might have in-hospital complications. These complications are likely to have important short-term and long-term consequences for patients, health-care utilisation, health-care system preparedness, and society amidst the ongoing COVID-19 pandemic. Our aim was to characterise the extent and effect of COVID-19 complications, particularly in those who survive, using the International Severe Acute Respiratory and Emerging Infections Consortium WHO Clinical Characterisation Protocol UK.
Methods:
We did a prospective, multicentre cohort study in 302 UK health-care facilities. Adult patients aged 19 years or older, with confirmed or highly suspected SARS-CoV-2 infection leading to COVID-19 were included in the study. The primary outcome of this study was the incidence of in-hospital complications, defined as organ-specific diagnoses occurring alone or in addition to any hallmarks of COVID-19 illness. We used multilevel logistic regression and survival models to explore associations between these outcomes and in-hospital complications, age, and pre-existing comorbidities.
Findings:
Between Jan 17 and Aug 4, 2020, 80â388 patients were included in the study. Of the patients admitted to hospital for management of COVID-19, 49·7% (36â367 of 73â197) had at least one complication. The mean age of our cohort was 71·1 years (SD 18·7), with 56·0% (41â025 of 73â197) being male and 81·0% (59â289 of 73â197) having at least one comorbidity. Males and those aged older than 60 years were most likely to have a complication (aged â„60 years: 54·5% [16â579 of 30â416] in males and 48·2% [11â707 of 24â288] in females; aged <60 years: 48·8% [5179 of 10â609] in males and 36·6% [2814 of 7689] in females). Renal (24·3%, 17â752 of 73â197), complex respiratory (18·4%, 13â486 of 73â197), and systemic (16·3%, 11â895 of 73â197) complications were the most frequent. Cardiovascular (12·3%, 8973 of 73â197), neurological (4·3%, 3115 of 73â197), and gastrointestinal or liver (0·8%, 7901 of 73â197) complications were also reported.
Interpretation:
Complications and worse functional outcomes in patients admitted to hospital with COVID-19 are high, even in young, previously healthy individuals. Acute complications are associated with reduced ability to self-care at discharge, with neurological complications being associated with the worst functional outcomes. COVID-19 complications are likely to cause a substantial strain on health and social care in the coming years. These data will help in the design and provision of services aimed at the post-hospitalisation care of patients with COVID-19.
Funding:
National Institute for Health Research and the UK Medical Research Council
Atomic Layer Processing of Molybdenum Disulfide Thin Films
As feature sizes in semiconductor devices continue to shrink, it is of upmost importance to synthesize materials that can accommodate the drastic degree of scaling. One such material receiving great attention is molybdenum disulfide (MoS2), which is a semiconducting two-dimensional (2D) material in its most favorable few-layer form. The distinctive electrical properties make few to single-layer MoS2 a potential candidate to replace silicon in many microelectronic devices. MoS2 research is commonly conducted on mechanically exfoliated films due to the high quality, low defect layers that can be prepared. However, exfoliation is not a scalable method due to the lack of dimensional control and poor layer reproducibility. Currently, there is a lack of suitable methods for integrating MoS2 films into manufacturing. Thus, there is a need for scalable industry-compatible processing methods to enable integration of MoS2 in modern electronics manufacturing.
One processing technique that can be used for MoS2 integration is atomic layer deposition (ALD). This technique is suitable because of its self-limiting, vapor-phase surface reactions used for thin film deposition. This process offers low temperature deposition of thin and conformal films with angstrom level control. This method is commonly used in high volume manufacturing, making it a clear choice as the processing technique that can be used for MoS2 integration. One drawback, however, is the lack of in-depth knowledge of ALD MoS2 thin films. By investigating the nucleation and growth of MoS2 films, key insights can be established to allow for greater control over the deposition process and resulting material quality. This understanding of the ALD nucleation process can also help identify new processing methods, such as area-selective ALD (ASALD). ASALD can further support the efforts towards MoS2 integration. This process can help solve the issue of placement errors found in standard lithography patterning. It can additionally provide another tool for creating complex device structures. Lastly, other processing techniques such as atomic layer etching (ALE) are also critical in manufacturing. Similar to ALD, ALE is the complementary vapor phase technique for layer-by-layer etching of uniform thin films. Combined, ALD and ALE provide scalable approaches for precise atomic layer processing and advanced manufacturing. To realize these useful processing methods, efforts need to be made to better understand the film substrate interactions and subsequent film growth or removal.
In this work, we present the study of the early stages of growth and nucleation of MoS2 films on common metal oxide surfaces used in semiconductor manufacturing. We show the temperature dependence of nucleation over the range of 150-250 °C. This work identifies that hydroxyl concentrations on metal oxide surfaces are directly related to the disassociation of MoF6 precursor on the substrate surface. This precursor disassociation leads to metal fluoride bonding, revealing the interface layer formation between deposited MoS2 films and the substrate. Film morphology was additionally studied, revealing the critical role that temperature has on growth mechanisms during MoS2 ALD. At increased growth temperatures, MoS2 films exhibited higher degrees of MoS2 bonding and crystalline grains oriented perpendicular to the growth surface. This study of the nucleation and growth process provides a greater understanding of 2D film-substrate interactions and offers more control over processing. Additionally, this work explores ASALD of MoS2 films on common semiconductor surfaces by exploiting inherent differences in surface chemistry between substrate materials. Selective ALD was established between various materials including alumina and thermal oxide substrates. To our knowledge, this is the first ASALD process for a 2D material that achieves selectivity without the use of inhibitors. Lastly, we established a new thermal ALE process for the removal of MoS2 films. This work identifies the removal of the MoS2 films by means of fluorination and oxidation to create volatile moly-oxyfluoride byproducts. This method was shown to etch both amorphous and crystalline ALD films, where the etch rates were highly dependent on crystallinity and temperature.
This work provides insights and processing required for MoS2 integration into nanoscale electronics, as well as many other applications. By the study of both the deposition and etching of MoS2 films, we provide a greater depth of knowledge that will be required for MoS2 integration into nanoscale manufacturing
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