Visualizing electrostatic gating effects in two-dimensional heterostructures

The ability to directly observe electronic band structure in modern nanoscale field-effect devices could transform understanding of their physics and function. One could, for example, visualize local changes in the electrical and chemical potentials as a gate voltage is applied. One could also study intriguing physical phenomena such as electrically induced topological transitions and many-body spectral reconstructions. Here we show that submicron angle-resolved photoemission (micro-ARPES) applied to two-dimensional (2D) van der Waals heterostructures affords this ability. In graphene devices, we observe a shift of the chemical potential by 0.6 eV across the Dirac point as a gate voltage is applied. In several 2D semiconductors we see the conduction band edge appear as electrons accumulate, establishing its energy and momentum, and observe significant band-gap renormalization at low densities. We also show that micro-ARPES and optical spectroscopy can be applied to a single device, allowing rigorous study of the relationship between gate-controlled electronic and excitonic properties.Comment: Original manuscript with 9 pages with 4 figures in main text, 5 pages with 4 figures in supplement. Substantially edited manuscript accepted at Natur

Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures

Combining monolayers of different two-dimensional semiconductors into heterostructures creates new phenomena and device possibilities. Understanding and exploiting these phenomena hinge on knowing the electronic structure and the properties of interlayer excitations. We determine the key unknown parameters in MoSe2/WSe2 heterobilayers by using rational device design and submicrometer angle-resolved photoemission spectroscopy (μ-ARPES) in combination with photoluminescence. We find that the bands in the K-point valleys are weakly hybridized, with a valence band offset of 300 meV, implying type II band alignment. We deduce that the binding energy of interlayer excitons is more than 200 meV, an order of magnitude higher than that in analogous GaAs structures. Hybridization strongly modifies the bands at Γ, but the valence band edge remains at the K points. We also find that the spectrum of a rotationally aligned heterobilayer reflects a mixture of commensurate and incommensurate domains. These results directly answer many outstanding questions about the electronic nature of MoSe2/WSe2 heterobilayers and demonstrate a practical approach for high spectral resolution in ARPES of device-scale structures

Visualizing electrostatic gating effects in two-dimensional heterostructures

The ability to directly monitor the states of electrons in modern field-effect devices-for example, imaging local changes in the electrical potential, Fermi level and band structure as a gate voltage is applied-could transform our understanding of the physics and function of a device. Here we show that micrometre-scale, angle-resolved photoemission spectroscopy (microARPES) applied to two-dimensional van der Waals heterostructures affords this ability. In two-terminal graphene devices, we observe a shift of the Fermi level across the Dirac point, with no detectable change in the dispersion, as a gate voltage is applied. In two-dimensional semiconductor devices, we see the conduction-band edge appear as electrons accumulate, thereby firmly establishing the energy and momentum of the edge. In the case of monolayer tungsten diselenide, we observe that the bandgap is renormalized downwards by several hundreds of millielectronvolts-approaching the exciton energy-as the electrostatic doping increases. Both optical spectroscopy and microARPES can be carried out on a single device, allowing definitive studies of the relationship between gate-controlled electronic and optical properties. The technique provides a powerful way to study not only fundamental semiconductor physics, but also intriguing phenomena such as topological transitions and many-body spectral reconstructions under electrical control

Second asymptomatic carotid surgery trial (ACST-2): a randomised comparison of carotid artery stenting versus carotid endarterectomy

Background: Among asymptomatic patients with severe carotid artery stenosis but no recent stroke or transient cerebral ischaemia, either carotid artery stenting (CAS) or carotid endarterectomy (CEA) can restore patency and reduce long-term stroke risks. However, from recent national registry data, each option causes about 1% procedural risk of disabling stroke or death. Comparison of their long-term protective effects requires large-scale randomised evidence. Methods: ACST-2 is an international multicentre randomised trial of CAS versus CEA among asymptomatic patients with severe stenosis thought to require intervention, interpreted with all other relevant trials. Patients were eligible if they had severe unilateral or bilateral carotid artery stenosis and both doctor and patient agreed that a carotid procedure should be undertaken, but they were substantially uncertain which one to choose. Patients were randomly allocated to CAS or CEA and followed up at 1 month and then annually, for a mean 5 years. Procedural events were those within 30 days of the intervention. Intention-to-treat analyses are provided. Analyses including procedural hazards use tabular methods. Analyses and meta-analyses of non-procedural strokes use Kaplan-Meier and log-rank methods. The trial is registered with the ISRCTN registry, ISRCTN21144362. Findings: Between Jan 15, 2008, and Dec 31, 2020, 3625 patients in 130 centres were randomly allocated, 1811 to CAS and 1814 to CEA, with good compliance, good medical therapy and a mean 5 years of follow-up. Overall, 1% had disabling stroke or death procedurally (15 allocated to CAS and 18 to CEA) and 2% had non-disabling procedural stroke (48 allocated to CAS and 29 to CEA). Kaplan-Meier estimates of 5-year non-procedural stroke were 2·5% in each group for fatal or disabling stroke, and 5·3% with CAS versus 4·5% with CEA for any stroke (rate ratio [RR] 1·16, 95% CI 0·86–1·57; p=0·33). Combining RRs for any non-procedural stroke in all CAS versus CEA trials, the RR was similar in symptomatic and asymptomatic patients (overall RR 1·11, 95% CI 0·91–1·32; p=0·21). Interpretation: Serious complications are similarly uncommon after competent CAS and CEA, and the long-term effects of these two carotid artery procedures on fatal or disabling stroke are comparable. Funding: UK Medical Research Council and Health Technology Assessment Programme

Основні положення настанов по веденню хворих з алергією до коров'ячого молока. Частина V. Лікування алергії до коров'ячого молока

The article presents the sections 15, 16, 17, 18, 19 f the World Allergy Organization guidelines DRACMA (Diagnosis and Rationale for Action against Cow's Milk Allergy), which was the prototype for the creation of national guidelines for the management of patients with the cow milk allergy. These sections cover the issues concerning the main characteristics of the milk of different animals, which is used to replace cow's milk (section 15); ensuring nutritional value in the treatment of CMA (section 16); the choice of theratment formula in different clinical situations (section 17); GRADE&recommendations for CMA immunotherapy (section 18) and guidelines for research and implementation of DRACMA (section 19). Guidelines developed by the panel on the initiative of Ukrainian Allergy Organization, Ukrainian Organization of children gastroenterologists and nutritionists, Ukrainian Organization of immunologists, allergists and imunoreabilitologists and supported by the Ministry of Health of Ukraine. Key words: allergy, cow's milk, proteins, treatment.В статье представлены разделы 15, 16, 17, 18 и 19 руководства Всемирной организации аллергологов DRACMA (Diagnosis and Rationale for Action against Cow's Milk Allergy), ставшего прототипом для создания отечественного Руководства по ведению больных с аллергией к коровьему молоку. В этих разделах рассматриваются основные характеристики молока разных животных, которое используют для замены коровьего молока (глава 15); обеспечение пищевой ценности при лечении АКМ (глава 16); выбор лечебной смеси в различных клинических ситуациях (глава 17); Grade-рекомендации касательно иммунотерапии АКМ (глава 18) и рекомендации для исследований и внедрений DRACMA (глава 19). Рекомендации разработаны рабочей группой по инициативе Ассоциации аллергологов, Ассоциации детских гастроэнтерологов и нутрициологов, Ассоциации иммунологов, аллергологов и иммунореабилитологов Украины и при поддержке МЗ Украины. Ключевые слова: аллергия, коровье молоко, лечение.У статі наведено розділи 15, 16, 17, 18 та 19 керівництва Всесвітньої організації алергологів DRACMA (Diagnosis and Rationale for Action against Cow's Milk Allergy), що стало прототипом для створення вітчизняних Настанов по веденню хворих з алергією до коров'ячого молока (АКМ). У цих розділах розглядаються основні характеристики молока від різних тварин, яке використовують для заміни коров'ячого молока (розділ 15); забезпечення харчової цінності при лікуванні АКМ (розділ 16); вибору лікувальної суміші при різних клінічних ситуаціях (розділ 17); Grade-рекомендації стосовно імунотерапії АКМ (роздiл 18) та рекомендації для дослідження та впровадження DRACMA (розділ 19). Настанови розроблені робочою групою за ініціативи Асоціації алергологів, Асоціації дитячих гастроентерологів та нутриціологів, Асоціації імунологів, алергологів та імунореабілітологів України та за підтримки МОЗ України. Ключові слова: алергія, коров'яче молоко, лікування