Epitaxial growth of cubic MnSb on GaAs AND InGaAs(111)

The cubic polymorph of the binary transition metal pnictide (TMP) MnSb, c-MnSb, has been predicted to be a robust half-metallic ferromagnetic (HMF) material with minority spin gap ≳1 eV. Here, MnSb epilayers are grown by molecular beam epitaxy (MBE) on GaAs and In0.5Ga0.5As(111) substrates and analyzed using synchrotron radiation X-ray diffraction. We find polymorphic growth of MnSb on both substrates, where c-MnSb co-exists with the ordinary niccolite n-MnSb polymorph. The grain size of the c-MnSb is of the order of tens of nanometer on both substrates and its appearance during MBE growth is independent of the very different epitaxial strain from the GaAs (3.1%) and In0.5Ga0.5As (0.31%) substrates

Microwave Properties of Ba-Substituted Pb(Zr0.52_{0.52}Ti0.48_{0.48})O3_3 after Chemical-Mechanical Polishing

We have studied the effect of chemical-mechanical polishing (CMP) on the ferroelectric, piezoelectric, and microwave dielectric properties of Ba-substituted PZT (BPZT), deposited by pulsed laser deposition. CMP allowed for the reduction of the root mean square surface roughness of 600 nm thick BPZT films from 12.1nm to 0.79 nm. Ammonium peroxide (SC-1) cleaning was effective to remove Si CMP residuals. Measurements of the ferroelectric hysteresis after CMP indicated that the ferroelectric properties of BPZT were only weakly affected by CMP, while the piezoelectric d33 coefficient and the microwave permittivity were reduced slightly by 10%. This can be attributed to the formation of a thin dead layer at the BPZT surface. Moreover, the intrinsic dielectric permittivity at microwave frequencies between 1 and 25 GHz was not influenced by CMP, whereas the dead layer series capacitance decreased by 10%. The results indicate that the CMP process can be used to smoothen the BPZT surface without affecting the film properties strongly.Comment: 13 pages of text, 4 tables and 7 figures. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 801055 "Spin Wave Computing for Ultimately-Scaled Hybrid Low-Power Electronics" - CHIRO

An investigation into controlling the growth modes of ferroelectric thin films using pulsed laser deposition and RHEED

Thin film ferroelectricss are widely considered for tunable microwave applications, the reduced small dimensions leading to low tuning voltages. The incipient ferroelectric strontium titanate is an ideal solution for tunable microwave devices, particularly in conjunction with high temperature superconductors. It has no spontaneous polarisation yet possesses a large permittivity at low temperatures that is sensitive to an electric field bias with relatively low loss. For such applications it is essential to use a low loss substrate such as magnesium oxide. In general, thin films have less favourable dielectric properties compared with their bulk counterparts due to differences in microstructure. strontium titanate films on MgO substrate prove difficult to grow due to the high lattice mismatch and issues connected with chemical incompatibility at the film/substrate interface. It has been shown here that it is possible to engineer the growth mode of this system, altering the strain and the defect concentration. These are both known factors influencing the dielectric properties of thin films. Reflection high energy electron diffraction (RHEED) in combination with interval pulsed laser deposition (PLD) has been used to achieve a two dimensional, layer-by-layer growth mode. Crucial to this was the deposition of a unit-cell thick titanium dioxide buffer layer on the surface, the deposition of which was also controlled by RHEED. The growth mode and microstructure of films grown using standard PLD with and without the buffer layer and films grown by interval PLD with and without the buffer layer have been compared by analysis of the RHEED data and transmission electron microscopy. This is the first time layer-by-layer growth has been achieved in this highly-mismatched epitaxial systems. The results point the way towards control of defects in oxide thin films from which microstructure-property relationships may be more clearly determined

Growth of M-type hexaferrite thin films with conical magnetic structure

Thin films of the M-type hexaferrite, BaFe10.2Sc1.8O19, have been grown on Al2O3 (00.1) substrates by pulsed laser deposition. Post-deposition annealing improves the structural quality and produces completely relaxed thin films. The post-annealed films show magnetic behavior corresponding to a conical magnetic structure, which is required to establish the magnetoelectric effect in hexaferrites. The magnetic phase diagram has been obtained from hard magnetization curves. Finite-size effects due to the restricted length scale of the magnetic helix explain differences in magnetic properties between thin films and the bulk