Investigated by STM/AFM

Fundamental electronic and magnetic properties of single atoms and molecules depend crucially on their immediate environment. Understanding its exact influence allows for the manipulation and thus tailoring of said properties. In this thesis, we investigate four different nanostructures on a monolayer of MoS2/Au(111) by means of scanning tunnelling microscopy (STM) and atomic force microscopy (AFM). First, single sulfur vacancies in the MoS2 layer were investigated. Here, the missing sulfur atoms are imaged with a three-fold symmetric shape in the STM topographies. Several defect related in-gap states were observed by scanning tunnelling spectroscopy (STS), most prominently a sharp resonance at zero bias. We identified it as a Kondo resonance by temperature and magnetic field dependent measurements. For defects located in regions of the MoS2, where the underlying Au(111) was missing, the Kondo resonance was absent, probably due to a different charge state of the defect. We then investigated the magnetic properties of single iron atoms on the MoS2 monolayer. We found that the exact position of the atoms in the moiré superstructure, which forms due to the lattice missmatch of the MoS2 and the underlying Au(111), has a crucial impact on those properties. Atoms on the moiré minimum exhibit an inelastic excitation, which is a signature of a spin-flip excitation and atoms on the moiré maximum show a Kondo resonance, which is a sign of increased spin screening by the substrate electrons. The transition between those two observed features was continuous along the moiré structure. We explain these changes by a local variation of the density of states along the moiré modulation. An impact of the moiré was also observed on single manganese atoms: they exhibit a Kondo resonance in the weak coupling regime, with the amplitude varying along the moiré. We were able to manipulate single manganese atoms into dimers and found three distinct regimes of interatomic exchange coupling, depending on their atom separation. We focused on the dimers with the closest spacing of one atomic lattice site. They show a direct exchange coupling, which leads to a singlet ground state. The excitation energy from the ground state to the excited triplet state also varies along the moiré structure. In a model calculation we establish that the hybridisation of manganese d-levels with substrate electrons leads to a renormalisation of the singlet-triplet excitation energy. A comparison of experimental values and theoretical prediction suggests that several conduction channels are involved in the renormalisation. Finally, the high-dipole molecule Ethyl-DADQ was investigated. Pre-characterisations on a bare Au(111) substrate show that the molecular dipole is preserved and that the molecules cause a local lowering of the work function of the substrate. The investigations on MoS2 allow for a better energy resolution, which helps to resolve several vibronic sidebands of the positive ion resonance. Their intensities vary depending on the electrostatic environment of the molecule, suggesting a partial damping of some vibrational modes.Wesentliche elektronische und magnetische Eigenschaften von einzelnen Atomen und Molekülen hängen von ihrer unmittelbaren Umgebung ab. Den direkten Einfluss dieser zu verstehen erlaubt die Kontrolle und Manipulation dieser Eigenschaften. In dieser Arbeit untersuchen wir vier verschiedene Nanostrukturen auf einer Monolage MoS2 /Au(111) mit Rastertunnel (RTM)- und Rasterkraftmikroskopie. Als erstes schauen wir auf einzelne Schwefelfehlstellen in der MoS2 Monolage. Wir haben die Fehlstellen als dreizählig symmetrische Form in den RTM Topographien abgebildet. Mehrere Zustände dieser Defekte konnten in der Bandlücke mit Rastertunnelspektroskopie nachgewiesen werden, darunter auch ein Zustand am Ferminiveau. Dieser konnte mit Hilfe von temperatur- und magnetfeldabhängigen Messungen einer Kondo Resonanz zugewiesen werden. In Defekten im MoS2, wo das darunterliegende Au(111) fehlt, war dieser Zustand nicht ausgeprägt, was für einen anderen Ladungszustand des Defektes sprechen kann. Infolge haben wir die magnetischen Eigenschaften von einzelnen Eisenatomen untersucht. Diese Eigenschaften hängen sehr stark von der Position der Atome in der Moiré-Struktur ab, die sich aufgrund eines Unterschiedes in den Gitterkonstanten der MoS2 Schicht und der Au(111) Oberfläche bildet. Atome im Minimum der Moiré-Struktur zeigen inelastische Spin-Flip-Anregungen, und Atome im Maximum der Struktur zeigen eine Kondo Resonanz, die auf eine Abschirmung des Spins durch Substratelektronen hinweist. Der Übergang zwischen diesen beiden Phänomenen erfolgt kontinuierlich über der Moiré-Struktur. Wir erklären den Unterschied mit einer sich über der Moiré-Ordnung ändernden lokalen Zustandsdichte. Die Moiré-Struktur beeinflusst auch die Spektren von einzelnen Manganatomen: diese zeigen eine Kondo Resonanz im schwach gekoppelten Regime, deren Amplitude sich entlang des Moiré-Musters ändert. Wir konnten einzelne Atome zu Dimeren manipulieren und fanden drei verschiedene Kopplungsregime, die sich mit dem Abstand der Atome zueinander verändern. Wir haben uns auf Dimere konzentriert, deren Atome eine atomare Gitterkonstante entfernt waren. Diese sind mittels einer direkten Austauschwechselwirkung gekoppelt und haben einen Singlet Grundzustand. Die Anregungsenergie vom Grundzustand in den Tripletzustand ändert sich je nach der Position in der Moiré-Struktur. In einer störungstheoretischen Rechnung fanden wir, dass die Hybridisierung der Mangan d-Niveaus mit Substratzuständen zu einer Renormalisierung der Anregungsenergie führen kann. Ein Vergleich zwischen den theoretisch erwarteten und experimentellen Werten deutet darauf hin, dass mehrere Elektronenkanäle an der Renormierung beteiligt sind. Zum Schluss haben wir das Ethyl-DADQ Molekül untersucht, welches ein hohes Dipolmoment aufweist. Erste Charakterisierungen auf einer Au(111) Oberfläche zeigen, dass der Dipol erhalten bleibt und die Moleküle die Austrittsarbeit des Substrates lokal absenken. Die Messungen auf dem MoS2 ermöglichten es vibronische Anregungen der positiven Ionenresonanz aufzulösen. Die Intensität derer ist sehr sensitiv auf die unmittelbare elektrostatische Umgebung der Moleküle, was auf eine teilweise Dämpfung einzelner Vibrationen hindeutet

Electronic and magnetic properties of single chalcogen vacancies in MoS2_2/Au(111)

Two-dimensional (2D) transition-metal dichalcogenides (TMDC) are considered highly promising platforms for next-generation optoelectronic devices. Owing to its atomically thin structure, device performance is strongly impacted by a minute amount of defects. Although defects are usually considered to be disturbing, defect engineering has become an important strategy to control and design new properties of 2D materials. Here, we produce single S vacancies in a monolayer of MoS$_2$ on Au(111). Using a combination of scanning tunneling and atomic force microscopy, we show that these defects are negatively charged and give rise to a Kondo resonance, revealing the presence of an unpaired electron spin exchange coupled to the metal substrate. The strength of the exchange coupling depends on the density of states at the Fermi level, which is modulated by the moir\'e structure of the MoS$_2$ lattice and the Au(111) substrate. In the absence of direct hybridization of MoS$_2$ with the metal substrate, the S vacancy remains charge-neutral. Our results suggest that defect engineering may be used to induce and tune magnetic properties of otherwise non-magnetic materials

Tuning a two-impurity Kondo system by a moir\'e superstructure

Two-impurity Kondo models are paradigmatic for correlated spin-fermion systems. Working with Mn atoms on Au(111) covered by a monolayer of MoS$_2$, we tune the inter-adatom exchange via the adatom distance and the adatom-substrate exchange via the location relative to a moir\'e structure of the substrate. Differential-conductance measurements on isolated adatoms exhibit Kondo peaks with heights depending on the adatom location relative to the moir\'e structure. Mn dimers spaced by a few atomic lattice sites exhibit split Kondo resonances. In contrast, adatoms in closely spaced dimers couple antiferromagnetically, resulting in a molecular-singlet ground state. Exciting the singlet-triplet transition by tunneling electrons, we find that the singlet-triplet splitting is surprisingly sensitive to the moir\'e structure. We interpret our results theoretically by relating the variations in the singlet-triplet splitting to the heights of the Kondo peaks of single adatoms, finding evidence for coupling of the adatom spin to multiple conduction electron channels

Resolution of intramolecular dipoles and push-back effect of individual molecules on a metal surface

Molecules consisting of a donor and an acceptor moiety can exhibit large intrinsic dipole moments. Upon deposition on a metal surface, the dipole may be effectively screened and the charge distribution altered due to hybridization with substrate electronic states. Here, we deposit Ethyl-Diaminodicyanoquinone molecules, which exhibit a large dipole moment in gas phase, on a Au(111) surface. Employing a combination of scanning tunneling microscopy and non-contact atomic force microscopy, we find that a significant dipole moment persists in the flat-lying molecules. Density-functional theory calculations reveal that the dipole moment is even increased on the metal substrate as compared to the gas phase. We also show that the local contact potential across the molecular islands is decreased by several tens of meV with respect to the bare metal. We explain this by the induced charge-density redistribution due to the adsorbed molecules, which confine the substrate's wavefunction at the interface. Our local measurements provide direct evidence of this so-called push-back or cushion effect at the scale of individual molecules.Comment: This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Journal of Physical Chemistry

Variations of vibronic states in densely-packed structures of molecules with intramolecular dipoles

Electrostatic potentials strongly affect molecular energy levels and charge states, providing the fascinating opportunity of molecular gating. Their influence on molecular vibrations remains less explored. Here, we investigate Ethyl-Diaminodicyanoquinone molecules on a monolayer of MoS$_2$ on Au(111) using scanning tunneling and atomic force microscopy and spectroscopy. These molecules exhibit a large dipole moment in gas phase, which we find to (partially) persist on the MoS$_2$ monolayer. The self-assembled structures consist of chains, where the dipoles of neighboring molecules are aligned anti-parallel. Thanks to the decoupling efficiency of the molecular states from the metal by the MoS$_2$ interlayer, we resolve vibronic states of the molecules, which vary in intensity depending on the molecular surrounding. We suggest that the vibrations are strongly damped by electrostatic interactions with the environment

ГЕМОТОРАКС: ПУТИ ОПТИМИЗАЦИИ ЛЕЧЕБНОЙ ТАКТИКИ

Today we understand that one of the most actual problem in order to patients with coagulated hemothorax – is to choose correct way of therapy. Till now, we didn’t have clear instructions for using one or another method of therapy. This time we have one of the key indicators – period from beginning of illness – and based on them we can choose those or another way of therapy. Was explored 368 cases with hemothorax. Then we reduced number of cases, which important for analyzing, using the criterion of inclusion and exclusion. Next step was comparison groups and searching for similarities or differences. Than we deleted alternatives which have no links with patient’s groups, by means of analyzing dependence between them. For determining patient’s condition, we describe options, which, more or less, can manipulate on group’s differences. This option divided on two groups: physically sourced and lab sourced. Our list of options include some new criteria beside usual as period from illness beginning or roentgenograms data. This options in combining with math’s modeling methods can help us to create the algorithm for choosing personal method of therapy.Purpose. Assess the possibility of creating an algorithm of tactics of treatment of patients with coagulated hemothorax.Methodology: collection of archival information, development of a database, statistical analysis.Results. As a result, was formed set of physically sourced and lab sourced data, as instrument for separation on groups with clear differences between each other.Practical implications: medicine.На сегодняшний день проблема выбора метода лечения, при свернувшемся гемотораксе, остается, несомненно, актуальной. До сих пор нет четких показаний к применению того или иного метода лечения. В настоящее время основным фактором для применения того или иного метода лечения является критерий времени, прошедшего с момента заболевания. Проанализированы истории болезни 368 пациентов. Используя, критерии включения и исключения редуцировали базу данных. Сравнили группы по наличию или отсутствию различий. С помощью применения анализа зависимостей исключили переменные, которые не имеют связи с группировкой пациентов. Описаны параметры оценки состояния пациента, которые, так или иначе, влияют на групповые различия. Среди этих параметров выявлены как физикальные, так и лабораторные. Список переменных превышает общеизвестные критерий времени от начала болезни и данные рентгенологической картины. Данная совокупность сведений о состоянии пациента может быть использована в методах математического моделирования для формирования набора переменных, характерных для каждой группы и в последующем для создания алгоритма выбора метода лечения пациентов.Цель. Оценить возможность создания алгоритма тактики лечения больных со свернувшимся гемотораксом.Методология: сбор архивной информации, формирование базы данных, статистический анализ.Результаты: сформирован набор физикальных и лабораторных данных, по которым группы достоверно отличаются между собой.Область применения результатов: медицина

Moiré Tuning of Spin Excitations: Individual Fe Atoms on MoS2/Au(111)

Magnetic adatoms on properly designed surfaces constitute exquisite systems for addressing, controlling, and manipulating single quantum spins. Here, we show that monolayers of MoS2 on a Au(111) surface provide a versatile platform for controllably tuning the coupling between adatom spins and substrate electrons. Even for equivalent adsorption sites with respect to the atomic MoS2 lattice, we observe that Fe adatoms exhibit behaviors ranging from pure spin excitations, characteristic of negligible exchange and dominant single-ion anisotropy, to a fully developed Kondo resonance, indicating strong exchange and negligible single-ion anisotropy. This tunability emerges from a moiré structure of MoS2 on Au(111) in conjunction with pronounced many-body renormalizations. We also find striking spectral variations in the immediate vicinity of the Fe atoms, which we explain by quantum interference reflecting the formation of Fe-S hybrid states despite the nominally inert nature of the substrate. Our work establishes monolayer MoS2 as a tuning layer for adjusting the quantum spin properties over an extraordinarily broad parameter range. The considerable variability can be exploited for quantum spin manipulations