Combined pulsed laser deposition and non-contact atomic force microscopy system for studies of insulator metal oxide thin films

Reduction of noise induced by power supply lines using phase-locked loop

An experimental implementation for the reduction of power-line noise in delicate signal detection is presented. This implementation improves the signal-to-noise ratio without limiting the bandwidth of the measurement. A sinusoidal wave and its harmonics, both synchronized with the frequency of the power line, are used to cancel out the power supply noise induced in the measurement signal. The wave and the harmonics are generated via a phase-locked loop implementation. Their amplitude and phase are adjusted, and then they are added to the measurement signal using a series of operational amplifiers to compensate for the noise. Although we applied this method to the particular case of scanning tunneling microscopy measurements, considerably improving the image quality, our implementation can be applied to other measurement systems for which noise from the power lines can compromise the signal detection.

Oxidation of Anatase TiO2(001) Surface Using Supersonic Seeded Oxygen Molecular Beam

We investigated the oxidation of oxygen vacancies at the surface of anatase TiO₂(001) using a supersonic seeded molecular beam (SSMB) of oxygen. The oxygen vacancies at the top surface and subsurface could be eliminated by the supply of oxygen using an SSMB. Oxygen vacancies are present on the surface of anatase TiO₂(001) when it is untreated before transfer to a vacuum chamber. These vacancies, which are stable in the as-grown condition, could also be effectively eliminated by using the oxygen SSMB.

Investigation into morphological and electromechanical surface properties of reduced-graphene-oxide-loaded composite fibers for bone tissue engineering applications: A comprehensive nanoscale study using atomic force microscopy approach

We decided to implement an extensive atomic force microscopy study in order to get deeper understanding of surface-related nanoscale properties of 3D printed pristine polycaprolactone and its reduced-graphene-oxide-loaded composites. The study included surface visualization and roughness quantification, elastic modulus and adhesion force assessment with force spectroscopy, along with kelvin probe force microscopy evaluation of local changes of surface potential. Atomic force microscopy examination was followed by scanning electron microscopy visualization and wettability assessment. Moreover, systematic examination of reduced graphene oxide flakes fabricated exclusively for this study was performed, including: scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and combustion elemental analysis. The addition of reduced graphene oxide resulted in thickening of the composite fibers and surface roughness enhancement. In addition, elastic modulus of composite fibers was higher and at the same time adhesion forces between scanning probe and tested surface was lower than for pristine polymeric ones. Lastly, we recorded local (nanoscale) alterations of surface potential of fibers with addition of graphene-derivative. The results clearly suggest graphene derivative's dose-dependent alteration of elastic modulus and adhesion force recorded with atomic force microscope. Moreover, changes of the material's surface properties were followed by changes of its electrical properties.

Atomic-resolution imaging of rutile TiO2(110)-(1 × 2) reconstructed surface by non-contact atomic force microscopy

The structure of the rutile TiO₂(110)-(1 × 2) reconstructed surface is a phase induced by oxygen reduction. There is ongoing debate about the (1 × 2) reconstruction, because it cannot be clarified whether the (1 × 2) structure is formed over a wide area or only locally using macroscopic analysis methods such as diffraction. We used non-contact atomic force microscopy, scanning tunneling microscopy, and low-energy electron diffraction at room temperature to characterize the surface. Ti₂O₃ rows appeared as bright spots in both NC-AFM and STM images observed in the same area. High-resolution NC-AFM images revealed that the rutile TiO₂(110)-(1 × 2) reconstructed surface is composed of two domains with different types of asymmetric rows.

Imaging patterns of anatase TiO2(001) with non-contact atomic force microscopy

Image patterns of anatase TiO₂(001) with non-contact atomic force microscopy (NC-AFM) are presented. A combined system of NC-AFM with pulsed laser deposition, scanning tunneling microscopy (STM), and low energy electron diffraction (LEED) enables us to prepare clean surfaces of anatase TiO₂ thin films and to perform measurements on them without breaking the vacuum or the need of cleaning the surface with sputtering and annealing cycles. Results from STM and LEED show that the anatase TiO₂(001) films display a (1 × 4) surface pattern of row structures. At far distances, in which the frequency shift was relatively small, NC-AFM images show three different patterns (labeled as protrusion, hole, and neutral contrast, respectively) similar to the ones that have been reported before in the studies of the rutile TiO₂ surface. At closer tip-sample distances, a periodic pattern consistent with the TiO₂ lattice constant was observed along the higher-positioned TiO₃ rows. We have also observed that energy dissipation is induced only with platinum tips, and not with other tip apexes.