Role of hafnium doping concentration on the structural and surface properties of ZnO surfaces

The presented thesis deals with the characterisation of hafnium doped zinc oxides with focus on the application as transparent conducting film (TCF) or electron transport layer (ETL) in heterojunction solar cells. Atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrical and optical methods have been applied to characterise the examined samples with the focus on AFM. Different AFM techniques are presented, conducted on some training samples and finally applied to investigate the evolution of the Hamaker constant in dependence of hafnium doping concentrations in zinc oxide. The thin film samples with a thickness of 75 nm were grown by atomic layer deposition and varying cycle ratios of diethyl-zinc and tetrakisethylmethylaminohafnium were used to control the doping concentrations. It has been shown that the Hamaker constant increases with doping concentration and peaks for a 1:1 cycle ratio and decreases at higher doping concentrations. The same trend has been observed for band gap, carrier concentration and force of adhesion. The reliability of retrieving Hamaker constants via the relatively new method of bimodal imaging method in comparison to using reconstructed force curves is presented. The observed high heterogeneity of the samples is assumed to be caused by polycrystallinity. High-resolution transmission electron microscopy (HRTEM) was able to confirm the polycrystallinity of the samples

Towards an understanding of peptide-inorganic interactions

This study has contributed to the developing understanding of fundamental principles through which interactions at peptide-inorganic interfaces occur. The inorganic materials; crystalline zinc oxide (ZnO) and platinum (Pt) together with specific binding peptides identified using the phage display technique and alanine scanning for mutant sequences selected on the basis of peptide stability calculated in silico were synthesized, extensively characterized and the mechanisms of their interaction and the effects thereof studied. Firstly ZnO growth was monitored during solution synthesis from precursors using two different ZnO methods in the absence and presence of ZnO binding peptides (ZnO-BPs); G-12 (GLHVMHKVAPPR), its mutants (G-12A6, G-12A11, G-12A12) and GT-16 (GLHVMHKVAPPR-GGGC). Secondly, adsorption characteristics and thermodynamics of interaction of ZnO with ZnO-BPs and Pt with platinum binding peptides (Pt-BPs) were studied using biophysical tools; quartz crystal microbalance with dissipation monitoring (QCM-D) and isothermal titration calorimetry (ITC)

Investigations into Protein-Surface Interactions via Atomic Force Microscopy and Surface Plasmon Resonance

Protein surface interactions are important in many diverse applications. In this dissertation nonspecific and specific interactions of two proteins (fibrinogen and F1-ATP synthase) with a variety of surfaces have been investigated via atomic force microscopy and surface plasmon resonance. Chapter one provides background information on protein surfaces interactions. Chapter 2 summarizes the techniques and surfaces utilized in the investigations in the following chapters. Chapter 3 provides background and investigations on nonspecific fibrinogen to surfaces. Fibrinogen is an important plasma protein involved in the blood clotting cascade. To improve design of materials for biodevices and implants, more knowledge about the interactions controlling fibrinogen adsorption is essential. Nonspecific adsorption of fibrinogen was investigated on model surfaces of graphite and mica as well as on self-assembled monolayer (SAM) via atomic force microscopy (AFM) to determine conformation. Complementary studies were performed via surface plasmon resonance (SPR) to investigate the dynamics of this adsorption process on gold, and an amine-, carboxyl-, methyl- and hydroxyl-terminated SAM films. Chapter 4 provides background and investigation into F1-Adenosine triphosphate synthase (ATPase) adsorption to surfaces. ATPase is a tiny molecular motor which synthesizes ATP. This motor is of interest in the fabrication of hybrid nanobiodevices. Incorporation of this protein into devices requires precise control over immobilization properties such as location, concentration, orientation, and function. Orientation of ATPase adsorbed nonspecifically on a mica surface was observed via AFM. Control over placement within the device was investigated via nanopatterning of a 1-dodecene SAM surface. Control over orientation was performed via engineering a landing pad within a resist matrix with AFM. This involved patterning a dithiol into a methyl resist matrix and addition of maleimide-NTA with coordination to nickel ions and histidine tags in the protein. The chemistry of this process was validated with SPR and fluorescence microscopy. Information on the kinetic of ATPase-his binding to the NTA surface was obtained. Hopefully information learned from these investigations enables the development of enhanced biocompatible materials design and control over the fabrication of functional hybrid nanobiodevices

Nanoscale Chemical Interrogation of Surfaces using Tip-Enhanced Near-field Optical Microscopy

As our ability to engineer, design, and modify nanoscale systems continues to advance, characterization methods must keep pace. Light-matter interactions, in particular optical spectroscopy, provide a wealth of information on the vibrational and electronic structure of matter and can be directly related to physical properties such as phase, chemistry, charge transport, etc. However, the fundamental wave-like nature of light prevents radiation from being focused to arbitrarily small length scales using traditional optics. This is known as the diffraction limit, and is on the order of several hundred nanometers for optical wavelengths (~λ/2). One method of overcoming diffraction is to couple light to nanostructures (e.g., optical antennae) that support resonant oscillations of conduction electrons (plasmons). These charge oscillations generate intense optical fields that are spatially controlled by the antenna size, rather than the radiation wavelength. The set of related techniques utilizing nanoscale optical antennae to interrogate and image surfaces are known as tip-enhanced near-field optical microscopy (TENOM).This work details the design, construction, and experimental validation of a TENOM instrument, and demonstrates specific applications in near-field spectroscopy and super-resolution chemical imaging. A commercial inverted optical microscope was integrated with a custom-built shear-force atomic force microscope (AFM). The inverted microscope geometry enables high excitation and collection efficiency of light from the antenna apex, while the shear-force AFM ensures the antenna is always positioned at the sample surface, allowing analytes to interact with the locally enhanced optical fields. Experimental validation of the completed TENOM instrument was accomplished using both copper (CuPc) and metal-free phthalocyanine (H2Pc) species. Chemical images of patterned CuPc and H2Pc were obtained with lateral spatial resolutions below 50 nm (<λ/10), unambiguously demonstrating the super-resolution capabilities of the instrument. Multimode imaging of H2Pc was performed with simultaneous collection of spatially correlated fluorescence, Raman, and topographic data. The combination of these measurements allowed nanoscale mapping of the H2Pc aggregation state across a wide range of surface coverages, including isolated molecules, molecular dimers, and continuous films.Additionally, finite-difference time-domain (FDTD) optical simulations were used to study the fundamental physics of plasmonic optical antennae relevant for near-field spectroscopy. For TENOM applications, tuning the optical properties of support structures with attached plasmonic nanocavities was shown to be critical for either enhancing or quenching local electric field strengths. Support structures with low extinction coefficients were found to produce the largest field enhancements, with the refractive index of the material being further tuned to optimize antenna performance as a function of the specific geometry considered. A quantitative comparison of several antenna designs was carried out, which has not been possible experimentally due to the low reproducibility of nanostructure fabrication procedures and variability in methods of measuring local optical fields. Two promising architectures were identified that both involve focused ion-beam milling a groove near the antenna apex. Methods of tuning the resonance energy of these structures over the full visible spectrum, using different plasmonic metals (Au/Ag) and by varying the groove positions relative to the apex, were also demonstrated.FDTD simulations were also used to study pairs of plasmonic nanoparticles relevant for surface-enhanced Raman spectroscopy applications. Previous work on this system was shown to significantly overestimate field enhancements due to numerical effects present at nano-gap features. Metal bridging structures were used to halt the field divergence at physically relevant lengths scales, allowing accurate study of experimentally relevant parameters including the fused contact area and presence of a dielectric encapsulation layer. It was found that fused dimer antennae are capable of producing large enhancements at infrared energies, but may be challenging to reproducibly fabricate due to the high sensitivity of the supported plasmon resonances to changes in local morphology.Advancements across multiple scientific and engineering disciplines are helping push the TENOM technique forward. Improvements in high-intensity broadband laser sources will enable flexible measurement of both the electronic and vibrational structure of materials, and general improvements in nano-manufacturing are expected to reduce the time and cost of producing high-enhancement resonant antennae with well-defined plasmonic structure. The future is bright for TENOM to find use as a versatile optical and physical surface characterization technique

Enabling Sum Frequency Spectroscopy and Fluorescence Correlation Spectroscopy of Model Cellular Membranes

The majority of proteins secreted from cells contain a signal peptide sequence that is required for secretion mediated by the endoplasmic reticulum and Golgi apparatus. However, many proteins lack the essential signal peptide sequence, yet still undergo secretion. Such proteins are known to regulate cell proliferation, differentiation, and migration. Fibroblast growth factor 1 (FGF-1) is one protein which undergoes non-classical protein transport. The role of its interactions with the cellular membrane during non-classical protein transport is not fully understood, although FGF-1 has shown preferential destabilizing effects on artificial membranes composed of acidic phospholipids. In the present work, physiologically relevant model membrane systems have been developed and characterized in order to investigate the role of phospholipid:FGF-1 interactions in translocation of the protein across the membrane. In addition, a confocal z-scan fluorescence correlation spectrometer (z-scan FCS) and a sum frequency spectrometer (SFS) have been assembled, and temperature controlled liquid sample holders have been designed and fabricated. Z-scan FCS and SFS have been employed to characterize the model membrane systems and have been shown to be suitable tools for elucidating the role of specific phospholipid:FGF-1 interactions in transmembrane translocation

Nanoscale spectroscopy and imaging of chemically disordered semiconductor surface

Identifying the local heterogeneity of disordered surfaces accurately is an important step toward rationally designing cost-effective and tailor-made materials. Visualizing chemical species in nanostructures remains a complex task, in part because of the insufficient sensitivity in conventional characterization. Therefore, advanced analytical tools are essential for studying chemical structure and the structure–property relationship.In this dissertation, we report the use of micro-Raman spectroscopy and scanning probe microscopy approaches, tip-enhanced Raman spectroscopy and Kelvin probe force microscopy, to image chemically disordered electronic materials. The semiconductor films investigated in this dissertation include organic small molecules thin films, layered materials, and nanoparticle-based amorphous thin films. Additionaly, theoretical calculations and multivariate statistics methods areused to assist analyze vibrational modes and extract insights into chemical species. We use micro-Raman spectroscopy to assign vibrational modes of small molecule isomers 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT) by comparing to density functional theory calculations. Using the characteristic modes as indicators of the pure isomers, we image their spatial distribution within mixed-isomer films with 200-nm resolution. In this way, we demonstrate the use of micro-Raman spectroscopy for characterizing the spatial heterogeneities and clarify the origin of the reduced charge carrier mobility displayed in mixed-isomer diF-TES ADT thin films.Combining Raman spectroscopy with atomic force microscopy imaging, tip-enhanced Raman spectroscopy enables interrogation of molecular monolayer on graphene, providing chemical specificity combined with nanometer spatial resolution. We implement a multivariate analysis pipeline to allow distillation of complex structural and chemical information, presenting new Raman modes observed at nanoscale resolution. Theoretical theory calculations are also used for vibrational mode assignments of the molecular binding sites on graphene.An electrical mode of atomic force microscopy, Kelvin probe force microscopy, probes a molecular-level picture of disorder in amorphous carbon films. By systematically varying linker properties and surface loadings, the spatially resolved surface spectroscopy imaging indicates that conformational flexibility of the monolayer moieties provides direct information about the underlying disorder of films.The results demonstrate the versatility of combined scanning probe microscopy and optical techniques in characterizing local structural disorder, allowing for the connection of this type of disorder to its macroscopic physical and chemical properties.Doctor of Philosoph

Biosensors

A biosensor is defined as a detecting device that combines a transducer with a biologically sensitive and selective component. When a specific target molecule interacts with the biological component, a signal is produced, at transducer level, proportional to the concentration of the substance. Therefore biosensors can measure compounds present in the environment, chemical processes, food and human body at low cost if compared with traditional analytical techniques. This book covers a wide range of aspects and issues related to biosensor technology, bringing together researchers from 11 different countries. The book consists of 16 chapters written by 53 authors. The first four chapters describe several aspects of nanotechnology applied to biosensors. The subsequent section, including three chapters, is devoted to biosensor applications in the fields of drug discovery, diagnostics and bacteria detection. The principles behind optical biosensors and some of their application are discussed in chapters from 8 to 11. The last five chapters treat of microelectronics, interfacing circuits, signal transmission, biotelemetry and algorithms applied to biosensing

Optics and Fluid Dynamics Department annual progress report for 2001

research within three scientific programmes: (1) laser systems and optical materials, (2) optical diagnostics and information processing and (3) plasma and fluid dynamics. The department has core competences in: optical sensors, optical materials, optical storage, biooptics, numerical modelling and information processing, non-linear dynamics and fusion plasma physics. The research is supported by several EU programmes, including EURATOM, by Danish research councils and by industry. A summary of the activities in 2001 is presented. ISBN 87-550-2993-0 (Internet

Ultrafast spectroscopy of model biological membranes

In this PhD thesis, I have described the novel time-resolved sum-frequency generation (TR-SFG) spectroscopic technique that I developed during the course of my PhD research and used it study the ultrafast vibrational, structural and orientational dynamics of water molecules at model biological membranes - key towards understanding the dynamic hydrogen-bonded structure of water interfacial with model biological membranes. The TR-SFG technique developed, follows a pump-probe experimental scheme whereby an intense IR laser pulse excites molecular vibrations and the Sum Frequency Generation (SFG) pulse is used to probe the dynamics of surface molecules as they relax back to the ground state, as a function of the time delay between the excitation and probe pulses. The rate and mechanism of vibrational relaxation (lifetime dynamics) helps in understanding the effects of local molecular structure and hydrogen bonding around these surface molecules.UBL - phd migration 201