Modification of Oxide Surfaces with Functional Organic Molecules, Nanoparticles, and Hetero-Oxide Layers

Abstract

The research work described in this thesis is concerned with the modification of oxide surfaces, as reflected by its title. The surfaces and their modification have been studied using a range of experimental surface characterization tools, in particular x-ray photoelectron spectroscopy (XPS), fluorescence microscopy, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy.

A large part of the thesis is related to the modification of oxide or metal surfaces with nanoparticles. In particular, three different immobilization schemes for the coupling of molecularly imprinted polymer (MIP) nanoparticles to silicon oxide (SiO2) and gold surfaces were designed and characterized at every step. The first method reports the immobilization of MIPs using a photo-coupling agent in combination with an aminosilane compound. The second method explores an epoxysilane-based coupling agent to directly anchor the nucleophilic core-shell MIP nanoparticle to the surface. Both methods were proven to be non-destructive towards the specific binding sites of the MIP nanoparticles. The third scheme offers the immobilization of nucleophilic core-shell nanoparticles on model gold surfaces using self-assembled monolayers of 11-mercaptoundecanoic acid activated by carbodiimide/N-hydroxysuccinimide. All three coupling methods are quite versatile and can be used in biosensors to couple functional nano-objects with transducer surfaces. In addition to these investigation directly aimed at the immobilization of nanopartciles, more fundamentally oriented studies were carried out on the modification of the rutile TiO2(110) surface with silane molecules to obtain a detailed understanding of adsorption mechanism and geometry of these silanes.

The deposition of a different type of nanopartciles, block copolymer reverse micelles loaded gold nanoparticles, on a titanium dioxide surface was tested using electrospray deposition. The study demonstrates that electrospray deposition is a viable method for depositing metal single-size metal nanoparticles onto a surface in vacuum, thereby retaining the clean vacuum conditions. Furthermore, it was shown that the removal of the block copolymer shell after deposition can be achieved both by atomic oxygen and an oxygen plasma, with the atomic oxygen being somewhat more efficient. Overall, it was demonstrated that a TiO2 surface decorated with narrow sized gold nanoparticles could be created, a result of importance in the catalysis domain.

The last part of the thesis is concerned with the true in-situ investigation of growth of hetero-oxide layers on oxide surfaces from metal precursors. Tetraethyl orthosilicate (TEOS) was used as precursor for the chemical vapor deposition of silicon oxide on rutile TiO2(110). The growth was monitored in real time using ambient pressure XPS (APXPS), which revealed the dissociative adsorption with the formation of new species in the presence of a TEOS gas phase reservoir. Annealing results in the formation of SiO2 and of a mixed titanium/silicon oxide. Furthermore, tetrakis(dimethylamino)titanium was employed in the atomic layer deposition (ALD) of TiO2 on RuO2. The APXPS results showed evidence was for side reactions beyond the idealized scheme of ALD.

Abstract (Swedish)

Popular Abstract in English

It is hard to imagine present day’s lifestyle without the use of modern technologies as prevalent in sectors including bioscience & technology and the semiconductor & chemical industries. In technological advances of biosensors, catalysis, and microelectronics, the surface modification of materials (which includes modification of the wetting, structural, electrical, mechanical properties etc.,) is required. Generally, the surface of a material is defined as the boundary layer between the solid and a gas, vacuum, or liquid phase and it has physical and chemical properties significantly different from the bulk of the material. At the same time many of the surface properties are decisive for how the material behaves in an application. This makes the surfaces of a material particularly interesting for detailed investigations, including the question of how one can deliberately modify their properties. This thesis mainly explores the modification of oxide surfaces with organic molecules and nanoparticles in view of their manifold applications in biosensors, catalysis, and microelectronics.

Often, in case of biosensors, organic molecules are used to couple functional nano-objects with the surface of transducers – a device, which converts one form of energy (in this case an electrical signal) into a measurable form. Here, different immobilization methods were designed and characterized to anchor molecularly imprinted polymers (MIPs) with model supports, e.g., silicon oxide and gold surfaces. MIPs are artificial template made receptors based on the “key-lock” mechanism, where MIPs act as a lock with the template being their key. In this thesis, the template (key) of choice was propranolol, which.is a drug for reducing hypertension, migraine headaches, and high blood pressure. The methods used to firmly anchor the MIPs were proven to be non-destructive towards the template’s binding sites. The coupling methods used in this thesis are fairly versatile to anchor functional nano-objects and can be considered as an initial step towards the formation of working nanosensors. Further, the detailed investigations of these anchoring organic molecules resulted in understanding how they sit on oxide surfaces with respect to their functional groups.

Catalysis uses external substances to make chemical reactions easier and is a very important process in the chemical industry. The conversion of carbon monoxide (CO – a highly poisonous gas for humankind) to a non-poisonous gas, carbon dioxide (CO2), is one of the crucial issues in the automobile industry. The integration of well-distributed small gold nanoparticles with oxide surfaces results in catalysts materials with a high catalytic activity for the conversion of CO into CO2 at or even below room temperature. However, gold nanoparticles have the major drawback of forming big clusters by combination of nearby nanoparticles at high temperatures, thus killing the catalytic properties. This

problem can be solved by surface modification or by using molecular spacers to prevent particle combination. A method has been designed for surface deposited gold nanoparticles with narrow size distribution and presented in this thesis.

Flexible devices are new amazing tools in the semiconductor technology for electronics and telecommunication industry, which requires the ultimate miniaturization of devices. This miniaturization demands new methods to control the fabrication processes at very small scales on the order of the microlevel. Chemical vapor deposition (CVD) and atomic layer deposition (ALD) are promising microfabrication methods to grow high quality thin films with uniform thickness and surfaces. In recent years, thin films have proven their potential in the fabrication of commercially available flexible displays. Both methods involve a chemical reaction of a volatile precursor (parent unit) of the desired material to be deposited on the surface of a substrate and to react there to form the desired thin film. In ALD in then a second reaction step is required with a second volatile parent unit. As part of this thesis, the mechanism of both thin film deposition methods has been investigated for the growth of silicon oxide on titanium dioxide and titanium dioxide on ruthenium dioxide in real-time. The oxide layers grown during the course of this thesis have potential to serve as insulating layers, dielectrics, in microelectronic devices. The investigations of thin film deposition presented in this thesis may help to understand the surface chemistry of these processes to produce the desirable quality of thin films for industrial uses.

• author: Chaudhary, Shilpi
• supervisor: Joachim Schnadt; Lei Ye
• opponent: Valden, Mika, Optoelectronics Research Centre, Tampere University of Technology, Finland
• organization: Synchrotron Radiation Research
• publishing date: 2015
• type: Thesis
• publication status: published
• subject: Atom and Molecular Physics and Optics
• keywords: Fysicumarkivet A:2015:Chaudhary
• pages: 220 pages
• defense location: Rydberg Lecture Hall at the Department of Physics
• defense date: 2015-06-09 10:15:00
• ISBN: 978-91-7623-330-6
• language: English
• LU publication?: yes
• id: 11e3dff4-b534-42c7-a7d9-7fb6a5bde660 (old id 5385246)
• date added to LUP: 2016-04-04 09:55:20
• date last changed: 2018-11-21 20:55:41