Thin film quantum materials

Abstract:

Optical lithography has been widely used in mass production of various electronic devices, mainly because of its high throughput capability. However, the resolution in conventional lithography is diffraction limited. Cost issues, on the other hand, make slower but higher resolution methods, like electron beam lithography, unattractive for industrial applications. In order to be able to continue the use of optical lithography, new schemes were developed that enhance the resolution. Phase-shifting masks, for example, alter both the amplitude and the phase of the exposing light and lead to higher resolution. Using the related phase edge method it has been shown that 100 nm features can be produced using 248 nm light. Furthermore, employing an elastomeric phase mask, commercially available photo resist, and incoherent light, down to 90 nm features were demonstrated. Here, we report on the application of a near-field phase shift technique on the fabrication of SAW transducers. This simple and low cost technique is best suited for the fabrication of SAW structures, where the metallization ratio is different from 1:1, like Narrow Gap Floating Electrode Unidirectional Transducers (NG-FEUDTS).

Abstract:

Scanning Acoustic Force Microscopy (SAFM) has been used to study scattering and diffraction phenomena of SAWs (surface acoustic waves) with a spatial resolution on the nanoscale. With other acoustic imaging methods, it has been difficult to achieve both nanometer lateral resolution and sub-Å wave amplitude detection sensitivity at the same time. With SAFM, amplitude distribution and phase velocity of arbitrarily polarized modes are accessible on the nanoscale. We present a model of the SAFM contrast formation and give some examples for simple experimental situations. SAW excitation by a single SAW source and the wavefield distribution within an acoustic charge transport structure are examined.

Abstract:

When Ti is deposited on Si in the 600-700 °C temperature range, the lattice mismatch between the Ti-containing deposit and the Si substrate causes TiSix nanoislands to form. The nanoislands grow when annealed at temperatures above 800 °C. When the nanoislands (either unannealed or annealed) are exposed to a Si-containing precursor gas, the Ti catalyzes the decomposition of the gas, allowing one-dimensional nanowires to grow. If oxide-patterned Si substrates are used, the Ti islands form selectively on the exposed Si and are preferentially positioned near the pattern edges. The subsequently grown Si nanowires are, therefore, positioned with respect to the larger lithographically formed pattern. Exposing the wires to an ion beam after deposition promotes the parallel alignment of nanowires. © 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We present a study of the origin of ultrasound-induced friction reduction in microscopic mechanical contacts. The effect of friction reduction caused by Rayleigh-type surface acoustic waves (SAWs) is demonstrated for propagating and two-dimensional, standing wave fields using lateral force microscopy (LFM). It is shown that with increasing wave amplitude, friction is completely suppressed. To detect and distinguish between the effect of lateral and vertical surface oscillation components on the cantilever movement, we employed multimode scanning acoustic force microscopy (SAFM). We found that the friction reduction effect is only due to the vertical oscillation component. Because this effect does not appear for purely in-plane polarized Love waves, we concluded that the mechanical diode effect is most probably responsible for the SAW-induced lubrication. This explanation is also supported by vertical and longitudinal SAFM measurements, which show that, in areas where friction is completely suppressed, low frequency vertical cantilever oscillations can still be observed, whereas lateral or torsional oscillations are no longer excited.

Abstract:

© 2002 IEEE. Epitaxial MnAs films on GaAs are of interest as ferromagnetic layers suitable for spin injection into semiconductors. Recent studies revealed that the phase transition near room temperature from the paramagnetic orthorhombic β phase above 40°C to the ferromagnetic hexagonal α phase below 40°C is of crucial importance for the structural and magnetic properties of the films. In this paper we report about ordered structures of the coexisting phases as a result of epitaxial strain and demonstrate the strong coupling between the magnetic order and the two-phase system.