B. Stritzker

Nonreciprocal plasmonics enables giant enhancement of thin-film Faraday rotation

Light propagation is usually reciprocal. However, a static magnetic field along the propagation direction can break the time-reversal symmetry in the presence of magneto-optical materials. The Faraday effect in magneto-optical materials rotates the polarization plane of light, and when light travels backward the polarization is further rotated. This is applied in optical isolators, which are of crucial importance in optical systems. Faraday isolators are typically bulky due to the weak Faraday effect of available magneto-optical materials. The growing research endeavour in integrated optics demands thin-film Faraday rotators and enhancement of the Faraday effect. Here, we report significant enhancement of Faraday rotation by hybridizing plasmonics with magneto-optics. By fabricating plasmonic nanostructures on laser-deposited magneto-optical thin films, Faraday rotation is enhanced by one order of magnitude in our experiment, while high transparency is maintained. We elucidate the enhanced Faraday effect by the interplay between plasmons and different photonic waveguide modes in our system.

Diamond/Ir/SrTiO3: A material combination for improved heteroepitaxial diamond films

Heteroepitaxial diamond films with highly improved alignment have been realized by using the layer sequence diamond/Ir/SrTiO3(001). In a first step, epitaxial iridium films with a misorientation <0.2° have been deposited on polished SrTiO3(001) surfaces by electron-beam evaporation. Using the bias-enhanced nucleation procedure in microwave plasma chemical vapor deposition, epitaxial diamond grains with a density of 109 cm−2 could be nucleated on these substrates. The orientation relationship for this layer system is diamond(001)[100]∥Ir(001)[100]∥SrTiO3(001)[100]. The polar and azimuthal spread for the crystal orientation of a 600 nm thick diamond film is about 1° in each case. For an 8 μm thick diamond film a significantly improved alignment of 0.34° (polar) and 0.65° (azimuthal) has been measured. The latter values, which to the best of our knowledge are superior to those of all former reports about epitaxial diamond films on alternative substrates, indicate the high potential of the substrate Ir/SrTiO3...

Diamond nucleation on iridium buffer layers and subsequent textured growth: A route for the realization of single-crystal diamond films

It is shown that diamond nucleation on iridium buffer layers followed by an appropriate textured-growth step offers a viable way to realize single-crystal diamond films. Bias-enhanced nucleation on iridium layers results in heteroepitaxial diamond films with highly improved alignment. By a subsequent textured-growth step, the mosaicity can be further reduced for tilt as well as for twist in sharp contrast to former experiments using silicon substrates. Minimum values of 0.17° and 0.38° have been measured for tilt and twist, respectively. Plan view transmission electron microscopy of these films shows that, for low thicknesses (0.6 μm and 8 μm), the films are polycrystalline, consisting of a closed network of grain boundaries. In contrast, at the highest thickness (34 μm) most of the remaining structural defects are concentrated in bands of limited extension. The absence of an interconnected network of grain boundaries shows that the latter films are no longer polycrystalline.

Diamond field effect transistors—concepts and challenges

Abstract Field effect transistors (FETs) in diamond should outperform FET structures on other wide bandgap materials like SiC and GaN in high power/high temperature applications due to the ideal diamond materials properties. However, the technology of these structures proved difficult leaving two device concepts to investigate: (1) the boron δ-doped p-channel FET and (2) the hydrogen induced p-type surface-channel-FET. The δ-channel-FET approach follows a traditional design path of power FET structures. Here, simulation results have enabled the extrapolation of a maximum RF output power to 27 W/mm, a value which is indeed higher than for any FET based on III-Nitrides or SiC. However, due to the narrow technological parameter window, fabricated δ-channel-FETs are still well behind expectations. In contrast, concerning the surface-channel-FET the physical/chemical nature of its channel remains still under discussion. Nevertheless, results obtained with this FET concept yielded a VDmax>200 V (LG=1 μm) and a IDmax>360 mA/mm a fT=11.5 GHz and fmaxU>40 GHz (LG=0.2 μm) and a recently obtained RF power measurement at 1 GHz. Furthermore, the 1 GHz power measurement result has been obtained on a diamond quasi-substrate grown on a Ir/SrTiO3 substrate. This result may therefore open up the perspective for wafer scale diamond electronics.

A route to diamond wafers by epitaxial deposition on silicon via iridium/yttria-stabilized zirconia buffer layers

A multilayer structure is presented which allows the deposition of high-quality heteroepitaxial diamond films on silicon. After pulsed-laser deposition of a thin yttria-stabilized zirconia (YSZ) layer on silicon, iridium was deposited by e-beam evaporation. Subsequently, diamond nucleation and growth was performed in a chemical vapor deposition setup. The epitaxial orientation relationship measured by x-ray diffraction is diamond(001)[110]∥Ir(001)[110]∥YSZ(001) [110]∥Si(001)[110]. The mosaicity of the diamond films is about an order of magnitude lower than for deposition directly on silicon without buffer layers and nearly reaches the values reported for single-crystal diamond on Ir/SrTiO3. In the effort towards single-crystal diamond wafers, the present solution offers advantages over alternative growth substrates like large-area oxide single crystals due to the low thermal expansion mismatch.

Direct preparation of high-Tc-superconducting films by laser ablation

Abstract A new method for direct production of high-T c YBa 2 Cu 3 O 7 films on (001)-SrTiO 3 , (random)-ZrO 2 single crystals and YSZ has been developed. Films were found to be polycrystalline with c-axis preferentially oriented normal to the substrate plane. Complete superconducting transition temperatures as high as 92 K with transition widths of about 1 K have been observed even on YSZ substrates.

Structural characterization of diamond films grown epitaxially on silicon

Abstract Diamond films have been deposited on Si(001) and Si(111) substrates. Using a bias pretreatment process resulted in a high portion of epitaxially aligned diamond nuclei on both substrates. Scanning electron microscopy was used to characterize the films qualitatively. X-ray diffraction texture measurements yielded a preferential orientation of the diamond crystallites, which was diamond(001)[110]∥Si(001)[110] and diamond(111)[110]∥Si(111)[110] for Si(001) and Si(111) respectively. Besides the poles of these epitaxially aligned crystals we observe further maxima in the pole figures which we attribute to twins. The latter was confirmed by direct observation in a scanning electron microscope. Rocking curves show a full width at half-maximum of about 12° for diamond on Si(001) and 8° for diamond on Si(111) which gives the amount of polar misalignment. Azimuthal misalignments as deduced from the pole figures are nearly the same size.

Low 1/ f noise single-layer YBa sub 2 Cu sub 3 O sub x dc SQUID at 77 K

Autonomous single‐layer dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser‐deposited YBa2Cu3Ox films on step edge SrTiO3 and LaAlO3 substrates. For device patterning, a SiOx inhibit technique as well as conventional ethylenediaminetetraacetic wet etch was used. The Josephson junctions are of grain boundary type. Their widths are 5 μm. The SQUID hole is a square of about 5 μm; the SQUID inductance is estimated to be about 20 pH. We obtained a very regular, nonhysteretic flux to voltage modulation over more than 100 flux quanta (Φ0). The maximum voltage signal is of the order of 15 μV peak to peak and the maximum transfer function dV/dΦ at the appropriate flux bias is 50 μV/Φ0 at 77 K. The best value of the equivalent flux noise as measured in the flux locked loop mode is 1.4×10−5 Φ0/Hz1/2 at 1 Hz and 1×10−5 Φ0/Hz1/2 in the white noise region for f≳5 Hz. This results in an energy resolution en,w(f≳5 Hz)=1×10−29 J/Hz in the white noise region and 2×10−29 J/Hz at...

Epitaxial growth of monoclinic and cubic ZrO2 on Si(100) without prior removal of the native SiO2

Abstract High-quality epitaxial thin films of pure and yttria-stabilized ZrO 2 (YSZ) were deposited onto Si(100) by electron beam evaporation at substrate temperatures around 880°C. No specific wafer cleaning was employed to remove the native SiO 2 . X-ray diffraction revealed a monoclinic structure for the pure ZrO 2 , whereas a cubic structure was observed for the YSZ. X-ray pole figure analysis showed that in both cases the in-plane axes of the films were essentially parallel to the Si[010] and [001] directions. Rutherford backscattering and channelling analysis resulted in minimum yield values of 7% and 6% for the pure ZrO 2 and the YSZ films respectively, thus indicating a high degree of crystalline perfection. A 20 A thick amorphous SiO 2 layer was observed at the interface using high resolution transmission electron microscopy. It was probably regrown during film deposition, after the original surface oxide of the wafer had been removed in situ .

Comparison of YBCO-films prepared by laser ablation and sputtering

Two different preparation techniques, i.e. laser ablation and dc-sputtering have been applied for the production of thin films from YBa2Cu3O7 − x. Both techniques do not require postannealing steps, as the condensation of the superconducting film is done onto a hot substrate (600–780 °C) at high oxygen pressures (1–6 mbar). Besides the superconducting properties (Tc(R = 0) ≥ 90 K, jc(77 K) > 4 × 106 A/cm2) also the structural properties are very similar (single crystalline, c-axis oriented) as measured by ion channeling (χmin ≈ 5.5 %), x-ray scattering and TEM. The preparation methods require quite different process times, < 10 min for laser ablation compared to about one hour for sputtering. They yield different SEM-appearances of the surface: the sputtered surface is clean and smooth, but the laser oblated film shows in addition balls of 200 nm dia. The properties of films made by both techniques are compared and discussed in detail. In addition results on various buffer layers between YBCO and Si are presented. The interdiffusion of the various components have been analysed by RBS. Promising results have been obtained for buffer layers from ZrO2, where only little interdiffusion could be observed, resulting in good superconducting YBCO-overlayers.