Surface science

Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including solid–liquid interfaces, solid–gas interfaces, solid–vacuum interfaces, and liquid–gas interfaces. It includes the fields of surface chemistry and surface physics. Some related practical applications are classed as surface engineering. The science encompasses concepts such as heterogeneous catalysis, semiconductor device fabrication, fuel cells, self-assembled monolayers, and adhesives. Surface science is closely related to interface and colloid science. Interfacial chemistry and physics are common subjects for both. The methods are different. In addition, interface and colloid science studies macroscopic phenomena that occur in heterogeneous systems due to peculiarities of interfaces. The field of surface chemistry started with heterogeneous catalysis pioneered by Paul Sabatier on hydrogenation and Fritz Haber on the Haber process. Irving Langmuir was also one of the founders of this field, and the scientific journal on surface science, Langmuir, bears his name. The Langmuir adsorption equation is used to model monolayer adsorption where all surface adsorption sites have the same affinity for the adsorbing species and do not interact with each other. Gerhard Ertl in 1974 described for the first time the adsorption of hydrogen on a palladium surface using a novel technique called LEED. Similar studies with platinum, nickel, and iron followed. Most recent developments in surface sciences include the 2007 Nobel prize of Chemistry winner Gerhard Ertl's advancements in surface chemistry, specifically his investigation of the interaction between carbon monoxide molecules and platinum surfaces. Surface chemistry can be roughly defined as the study of chemical reactions at interfaces. It is closely related to surface engineering, which aims at modifying the chemical composition of a surface by incorporation of selected elements or functional groups that produce various desired effects or improvements in the properties of the surface or interface.

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Micro and Nanofabrication (MEMS)

Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.

Microstructure Fabrication Technologies I

Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.

Micro and Nanofabrication (MEMS)

Learn the fundamentals of microfabrication and nanofabrication by using the most effective techniques in a cleanroom environment.

Acquire an understanding of interfacial phenomena, micro-heterogeneous colloidal solution systems and dynamic electrochemistry.

Ultra-high vacuum

Ultra-high vacuum (UHV) is the vacuum regime characterised by pressures lower than about . UHV conditions are created by pumping the gas out of a UHV chamber. At these low pressures the mean free path of a gas molecule is greater than approximately 40 km, so the gas is in free molecular flow, and gas molecules will collide with the chamber walls many times before colliding with each other. Almost all molecular interactions therefore take place on various surfaces in the chamber. UHV conditions are integral to scientific research.

Surface tension

Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to float on a water surface without becoming even partly submerged. At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). There are two primary mechanisms in play.

Extended X-ray absorption fine structure

Extended X-ray absorption fine structure (EXAFS), along with X-ray absorption near edge structure (XANES), is a subset of X-ray absorption spectroscopy (XAS). Like other absorption spectroscopies, XAS techniques follow Beer's law. The X-ray absorption coefficient of a material as a function of energy is obtained using X-rays of a narrow energy resolution are directed at a sample and the incident and transmitted x-ray intensity is recorded as the incident x-ray energy is incremented.

Chemical substances

A chemical substance is a form of matter having constant chemical composition and characteristic properties. Chemical substances can be simple substances (substances consisting of a single chemical element), chemical compounds, or alloys. Chemical substances that cannot be separated into their simpler constituent elements by physical means are said to be 'pure'; this notion intended to set them apart from mixtures.

Phase transitions

In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of matter: solid, liquid, and gas, and in rare cases, plasma. A phase of a thermodynamic system and the states of matter have uniform physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure.

Topics in nanotechnology

Nanotechnology, often shortened to nanotech, is the use of matter on atomic, molecular, and supramolecular scales for industrial purposes. The earliest, widespread description of nanotechnology referred to the particular technological goal of precisely manipulating atoms and molecules for fabrication of macroscale products, also now referred to as molecular nanotechnology. A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defined nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm).

Transfer of Graphene under Ultra-High Vacuum

Darius Constantin Merk

This thesis reports on a novel method for graphene transfer that is fully UHV compatible, which has remained a challenge for a long time due to the necessity of supporting graphene for transfer and most often requiring supporting layer removal post-transfer. Our graphene transfer method is based on the wafer-bonding approach, where graphene is stamped onto a target surface, from a support to which it is weakly bound. We use a bilayer of graphene supported by a teflon tape for the low adhesion between graphene layers and the flexibility of teflon tape to allow adaptability to the target surface.We demonstrate successful transfer onto Cu(100) and Ir(111) single crystal surfaces as well as on gr/Ir(111), thus forming a (partial) graphene bilayer on Ir(111). For in-situ characterization, we use Auger electron spectroscopy and STM. Auger measurements confirm that we are able to transfer an average 0.8-0.9 ML of carbon, by comparison to CVD grown samples. After transfer onto Ir(111), we show that by annealing to 1000 °C, we are able to observe by STM the characteristic moiré pattern formed by CVD grown graphene on Ir(111). Auger spectra show that the graphene-Iridium interaction undergoes a change from physisorption to chemisorption upon annealing. XAS and Raman spectroscopy demonstrate that the annealing step taken post transfer to observe the moiré by STM is only necessary to induce a change in interaction strength but not to heal graphene defects, to increase its domain size, or to make it flat. After transfer onto Cu(100), Raman spectra show that the transferred graphene is of the same quality as the CVD grown graphene before transfer, without further annealing. Comparison of synchrotron based high resolution XAS spectra of transferred gr/Ir(111) to CVD grown samples confirms that the transferred graphene is flat on top of the Ir(111) crystal surface.This enables sample and device fabrication, usually hampered by impurities, to be carried out in UHV leading to fully reproducible results. Clean twisted bilayer graphene samples can be made and studied in UHV. Further, surface science can be extended to the third dimension, by capping layers and continuing growth, etc., all under clean conditions.

EPFL2022

Electric metal contacts to monolayer blue phosphorus: electronic and chemical properties

Xiao Zhou, Cheng Chen, Pengfei Ou

The contact nature when monolayer blue phosphorus (blueP) interfaces with three transition metal electrodes (i. e., Pd, Ir, and Pt) was unraveled by the ab initio density functional theory calculations. Specifically, n-type Schottky contact is observed for Ir(111)-blueP, in contrast, p-type Schottky contacts are formed for Pd(111)- and Pt(111)-blueP. The Fermi level is pinned partially at metal-blueP interfaces due to two interfacial behaviors: one being the modification of metal work function caused by interface dipole formation ascribed to a redistribution of charges, and the other being the production of gap states that are dominated by P p-orbitals since the intralayer P-P bonds are weakened by the interfacial metal-P interactions. The incorporation of metal substrates would also significantly alter the chemical properties of the adsorbed monolayer blueP. The binding strength of hydrogen can be enhanced by as much as 0.9 eV, which resulted from two parts: one is the charge transfer from metal substrate to monolayer blueP rendering a stronger H-P coupling; the other is a strong interfacial interaction after the hydrogen adsorption. The free energy change of H adsorption onto Ir(111)-blueP is as low as 0.16 eV which is comparable to the most efficient catalyst of Pt. These findings would provide theoretical guidance for the future design of electronic devices based on blueP and exploration of its potential in novel catalysts for hydrogen evolution reaction.

ELSEVIER2022

Characterization and prediction of peptide structures on inorganic surfaces

Dmitrii Maksimov

Interfaces between peptides and metallic surfaces are the subject of great interest for possible use in technological and medicinal applications, mainly since organic systems present an extensive range of functionalities, are abundant, cheap, and exhibit low toxicity. Exemplary applications are biosensors that may be sensitive to specific metabolites or harmful compounds. However, these hybrid interfaces pose a challenge to computational modelling, particularly regarding predicting the most relevant configurations at the surface, which determines the electronic properties of the system as a whole. From a theoretical point of view, predicting the most stable interface configuration requires searching through the enormous structure space of flexible biomolecules with respect to the surface for different configurations and performing computational calculations of their properties. However, it is impossible to investigate those parts separately due to complex interactions during adsorption. In order to capture these complex interactions, one has to employ accurate theoretical methods, which are very computationally expensive. In this thesis, we provide a comprehensive description of the complex nature of the interaction of selected amino acids with metallic surfaces using state-of-the-art dimensionality reduction techniques and accurate ab initio theoretical methods and creation of tools tailored for the high-throughput investigations of interface systems. The theoretical methods used in the thesis are described in the first part of the thesis. The second section looks into the conformational space changes of Arginine (Arg) and its protonated counterpart after adsorption on three noble metallic surfaces. Arg is an excellent testbed because it is tiny enough to be treated using density functional theory, which is considered the best compromise between accuracy and computational efficiency. At the same time, Arg is complex enough due to a highly flexible side-chain that allows for hundreds of different configurations in the gas phase alone. The examination of adsorption behavior requires creating a database by performing a large number of geometry optimizations of various conformations and orientations. The investigation of that database includes creating a low-dimensional representation of the conformational spaces using recent dimensionality reduction techniques, followed by examining various bonding and charge transfer patterns and how they affect the available conformational spaces.The third section of the thesis is concerned with developing tools for the automated structure search of interface systems and the modelling of self-assembly patterns formed after adsorption. Different geometry optimization algorithms and a flexible method of preconditioning the quasi-Newton optimization algorithms are implemented in the GenSec package that was developed. Together, these enable a more straightforward interface with a wide range of quantum chemistry packages for sampling the conformational spaces of flexible molecules in 1D (ions), 2D (surfaces), and 3D (cavities and molecules) systems. Structure search of the conformational space of a flexible molecule using GenSec provided satisfactory results for di-L-alanine adsorbed on Cu(110) surface.

EPFL2022

Explores capillarity, wetting, and surface tension, discussing contact angles, hysteresis, and wetting states.

Explores chemisorption, catalysis, and adsorption on solid surfaces, including energy differences and bond formation.

Covers the fundamentals of surface tension, adhesion forces, and laser manufacturing technologies.