Homodyned and Heterodyned Vibrational Sum Frequency Generation Spectroscopy of Electrochemical Interfaces

Since its development in the 1980s the second-order nonlinear optical technique of vibrational sum frequency generation spectroscopy (SFG) evolved into a versatile tool to detect and characterize molecules at interfaces. To obtain complete information on the molecules’ absolute orientation and to disentangle the interference of a possible non-resonant substrate’s response which distorts the spectral line shape, however, phase-resolved measurements need to be applied. In such heterodyned SFG experiments the signal pulse which is generated by the nonlinear interaction between two incoming short pulses and a sample subsequently interferes with a so called local oscillator (LO) pulse. To yield accurate results, relative phase stability between the signal and LO as well as a precise control of their individual timings must be warranted. The simultaneous fulfillment of this two requirements so far have restricted heterodyned SFG experiments to the study of solid/air and liquid/air interfaces. This thesis presents a way to overcome these limitations by integrating a timing control scheme into a collinear high accuracy phase-resolved SFG spectrometer. The versatility of this approach is tested at the solid/liquid interface and extended to potential dependent measurements since among others understanding of electrochemical processes at the electrode/electrolyte interface will be critical in the development of more efficient batteries and fuel cells to tackle the challenges presented by the climate crisis. The obtained heterodyned SFG spectra allow an insight into the parameters that influence the non-resonant substrate’s response, such as an applied potential bias and the presence of specifically and non-specifically adsorbed ions and molecules. In addition a method is presented how to use phase-resolved SFG spectra to determine the phase of the local field Fresnel factors, which so far had to be modeled. The heterodyned spectra are compared to their homodyned analogs to discuss which new information in fact can be obtained and what limits still need to be overcome.Eine verbreitete Methode zur Charakterisierung von molekularen Prozessen an Grenzflächen ist die Summenfrequenz(SFG)-Schwingungsspektroskopie, die auf einem nichtlinearen optischen Effekt zweiter Ordnung beruht. Die ursprüngliche Methode detektiert die Intensität des SFG Signals. Dabei gehen jedoch Informationen über die absolute Orientierung der Moleküle an der Grenzfläche verloren. Außerdem kann ein nichtresonanter Beitrag des unterliegenden Substrats durch Interferenz die Linienform des Spektrums beeinflussen, was die Interpretation erschwert. Daher wurde unter Zuhilfenahme eines lokalen Oszillator (LO) Pulses die phasenaufgelöste SFG-Spektroskopie entwickelt. Zur Gewährleistung einer akkuraten Phasenauflösung muss eine konstante Phasenbeziehung zwischen Signal und LO vorherrschen. Außerdem verlangt die Methode eine präzise Kontrolle der individuellen Pulszeiten. Die gleichzeitige Einhaltung beider Voraussetzungen ist experimentell aufwendig, was bisher einen Einsatz über die Grenzflächen fest/gasförimg und flüssig/gasförmig hinaus verhinderte. Die vorliegende Arbeit erweitert den Einsatzbereich auch auf die fest/flüssig Grenzfläche und erlaubt damit auch phasenaufgelöste in situ Messungen elektrochemischer Prozesse an der Elektrodenoberfläche. Das Verständnis dieser Prozesse ist ein wichtiger Schritt zur Entwicklung effektiverer Batterien und Elektroden für Brennstoffzellen, wichtige Bestandteile zur Eindämmung des Klimawandels. Zur Realisierung solcher Messungen wird ein Schema zur Pulszeitkontrolle vorgestellt und in ein kollineares hoch präzises phasenaufgelöstes SFG-Spektrometer eingeführt. Die entstandenen phasenaufgelösten SFG-Spektren erlauben einen Einblick in die Abhängigkeit des nichtresonanten SFG Beitrags des Substrat von Faktoren wie einer angelegten elektrischen Spannung und der Anwesenheit gebundener/ungebundener Moleküle /Ionen an der Substratgrenzfläche. Desweiteren wird eine Methode vorgestellt, die es erlaubt die Phase der lokalen Feldfaktoren zu bestimmen, die bisher nur theoretisch berechnet werden konnte. Die phasenaufgelösten SFG-Spektren werden mit herkömmlichen SFG-Spektren verglichen um den zusätzlichen Informationsgewinn herauszuarbeiten, aber auch um noch offene Fragen zu erkennen

Approaching religion through linguistics: methodological thoughts on a linguistic analysis of 'religion' in political communication

The constructions of ‘religion’ in general language are seldom themselves in the focus of empirical research. Aiming to retrieve the inherent knowledge that lies within these constructions, this article suggests a term-based textual analysis to focus on the linguistic use of ‘religion’. This method invites us to question the unity of texts through an analysis of textual semantics. It offers the chance to ask about the formation of the concept. The article initially shows how this approach differs from comparative and policy-oriented studies by differentiating between criticism and critique. It then develops the idea of a term-based textual analysis. Using examples from the policy field of foreign aid, the text illustrates how much inherent knowledge there is in the usage of ‘religion’ in political communication and calls for a general reconsideration of the way ‘religion’ is approached in empirical research

Making Plans for Commercial Aquaculture in the North Central Region

Aquaculture is not a new concept. Japanese, Chinese, Romans, Egyptians, and Mayan Indians farmed fish for food and recreation prior to 2000 BC. Ponds were constructed and fish were raised much in the same manner as fish are raised today. Both freshwater and saltwater fish are currently raised commercially throughout the world. Other related aquatic products raised commercially are shrimp, crayfish, oysters, clams, worms, crickets, frogs, and some plants. Aquaculture is the general term used to describe the propagation and rearing of aquatic animals and plants in controlled or selected environments. Although aquaculture is increasing in popularity in this country, the vast majority of fisheries food products eaten in the United States are imported or are captured wild stocks from natural waters

Shifting gear: new agendas in the sociological study of religion

Editorial for the special issue on the new agendas in the sociological study of religio

Letters between F. W. Garling and William Kerr

Letters concerning a student position at the Utah Agricultural College