Leila Costelle

Lanthanum titanate and lithium lanthanum titanate thin films grown by atomic layer deposition

Thin films of lanthanum titanate and lithium lanthanum titanate (LLT) have been grown by atomic layer deposition (ALD). Studies on the growth of lanthanum titanates showed that the lanthanum deposition rate is reduced when the titanium oxide and lanthanum oxide processes are combined, leading to higher titanium contents in the films. The precursor systems used for deposition of lanthanum titanates were TiCl4 + water and La(thd)3 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) + ozone. Lithium was introduced into the material in order to deposit LLT by using lithium tert-butoxide (LiOtBu) and water as precursors. The deposited films were analyzed by time-of-flight elastic recoil detection analysis (TOF-ERDA), secondary ion mass spectrometry (SIMS), X-ray fluorescence (XRF), X-ray reflectivity (XRR) and X-ray diffraction (XRD). TOF-ERDA gave the film composition of Li0.32La0.30TiOz at saturation conditions.

MeCp)Ir(CHD) and molecular oxygen as precursors in atomic layer deposition of iridium

Iridium thin films were grown by atomic layer deposition (ALD) between 225 and 350 °C using (MeCp)Ir(CHD) (MeCp = methylcyclopentadienyl, CHD = cyclohexadiene) and molecular oxygen as precursors. (MeCp)Ir(CHD) precursor was synthesized and characterized in-house. Also the crystal structure of (MeCp)Ir(CHD) is reported. All the ALD grown Ir films passed a common tape test indicating a good adhesion on Al2O3 nucleation layer. Quite untypically, surface roughness was the highest on films deposited at 225–250 °C and decreased strongly by increasing deposition temperature. Partial decomposition of the (MeCp)Ir(CHD) precursor resulted in defects on the film surface at 350 °C. Ir thin films with good quality were obtained at the deposition temperatures of 275 and 300 °C. A 50 nm thick film grown at 275 °C had a roughness of 1.2 nm, contained about 3 at% oxygen, 0.6 at% carbon and 1.6 at% hydrogen impurities, while the resistivity was as low as 9 µΩ cm.

Binding of deposited gold clusters to thiol self-assembled monolayers on Au(111) surfaces

We study the mechanisms involved in Au nanocluster deposition on thiol self-assembled monolayer modified Au(111) surfaces. Molecular dynamics simulations reveal a wide range of cluster-surface binding configurations within a very narrow deposition energy range (0.2–0.6 eV/atom for ∼2.5 nm diameter clusters). These go from noncovalent to full contact and include surprising intermediate cases in which the clusters are bound to the underlying Au(111) surface via molecular links and nanowires. Experiments show that, subsequently, the clusters are covered by thiols and slightly flattened.

Biofunctional hybrid materials: bimolecular organosilane monolayers on FeCr alloys

Hybrid organic-inorganic interfaces are the key to functionalization of stainless steel (SS). We present a solution-based deposition method for fabricating uniform bimolecular organosilane monolayers on SS and show that their properties and functionalities can be further developed through site-specific biotinylation. We correlate molecular properties of the interface with its reactivity via surface sensitive synchrotron radiation mediated high-resolution photoelectron spectroscopy (HR-PES) and chemical derivatization (CD), and we demonstrate specific bonding of streptavidin proteins to the hybrid interface. The method facilitates efficient growth of uniform bimolecular organosilane monolayers on SS under ambient conditions without the need to prime the SS surface with vacuum-deposited inorganic buffer layers. The obtained insights into molecular bonding, orientation, and behaviour of surface-confined organofunctional silanes on SS enable a new generic approach to functionalization of SS surfaces with versatile nanomolecular organosilane layers.

Spin-glass magnetism of surface rich Au cluster film

The magnetic response of two-dimensional uncapped Au islands tens of nanometers in size was measured using a superconducting quantum interference device magnetometer. The magnetization vs. field was found to exhibit a clear ferromagnetic-like hysteresis loop and a large positive remanent magnetization was acquired after momentary application of a strong magnetic field. The Au magnetic response is assumed to be due to the surface effects in the nanosized islands and the large fraction of canted surface magnetic moments which interaction and mutual orientation differ from the bulk diamagnetic order.

Mechanical response of nanometer thick self-assembled monolayers on metallic substrates using classical nanoindentation

We report here on the mechanical response of thiolate self-assembled monolayers, a few nanometers thick, on gold and silver substrates, using ultra-low load contact probing (the limit of the nanoindentation method used) with a relatively large spherical diamond tip. Careful analysis of a large number of experimental data points enabled us to differentiate the effects stemming from the substrate, the loading rate, and the orientation and reactivity of the molecules. Three distinct patterns for the responses of the monolayers were observed, giving insight into the mechanical response of thiol modified metal surfaces.