Effects of periodicity and oxygen partial pressure on the crystallinity and dielectric property of artificial SrTiO3/BaTiO3 superlattices integrated on Si substrates by pulsed laser deposition method

Epitaxial SrTiO₃(STO)/BaTiO₃(BTO) artificial superlattices have been grown on TiN buffered Si (001) substrates by pulsed laser deposition method and the effects of stacking periodicity and processing oxygen partial pressure on their crystallinity and dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of STO/BTO superlattices were investigated using X-ray diffraction and transmission electron microscopy. The TiN buffer layer and superlattice thin films were grown with cube-on-cube epitaxial orientation relationship of [110](001)_films∣∣[110](001)_TiN∣∣[110](001)_Si. The c-axis lattice parameter of the STO/BTO superlattice decreased from 0.412 nm to 0.406 nm with increasing oxygen partial pressure and the dielectric constants, measured at the frequency of 100 kHz at room temperature, of the superlattices with 2 nm/2 nm periodicity increased from 312 at 1 × 10^− 5 Torr to 596 at 1 × 10^− 3 Torr. The dielectric constants of superlattices grown at oxygen partial pressure of 1 × 10^− 3 Torr increased from 264 to 678 with decreasing periodicity of the superlattices from 10 nm/10 nm to 1 nm/1 nm.     

Infrared Reflectivity Spectra of Manganite Thin Films Grown on Different Substrates

We have measured the reflectivity infrared (IR) spectra of R_1−x Ca _x MnO₃ (R = La, Pr) manganite thin films grown on different substrates (SrTiO₃ (STO), LaAlO₃ (LAO) and SrLaGaO₄ (SLGO)) manganites over a wide frequency (50–5000 cm⁻¹) range. In the Far IR (FIR) region the substrates dominate over the manganite spectrum. However, the previously observed infrared active modes or mode pairs could be identified. In the mid-IR (MIR) region, a characteristic insulating gap at ∼700 cm⁻¹ is always present for all thin film studied, which shows substrate and thickness dependence.     

Epitaxial growth of Sr x Ba1−x Nb2 O6 (SBN) thin films on Pt coated MgO substrates: the determining control of platinum crystallographic orientation

The growth of (001) oriented Sr _x Ba_1−x Nb₂ O₆ (SBN:x) thin films on MgO single crystals substrates has focused attention due to its potential application to integrated signal waveguiding and electro-optic processing. This paper addresses the possible insertion of a platinum bottom electrode to implement the electro-optic effect, and examines the influence of Pt orientation on the subsequent growth of SBN thin films deposited by R.F. magnetron sputtering. We have first investigated the optimal sputtering conditions of a (001) Pt oriented growth. Experimental evidence is provided for an orientation switching temperature sensitive to R.F. power but insensitive to deposition rate which suggests that kinetic phenomena are not involved in the orientation development of Pt films. Seeding the MgO substrate with Fe, Cu or Cr inhibits the competitive (111) Pt growth without modifying the optimal temperature for (001) growth. Annealing at a temperature sufficient to crystallise the top SBN film causes a drastic evolution of the initial (111) and (001) Pt volume fractions, making particularly critical the deposition conditions for a final dominant (001) Pt texture on unseeded substrates. The (001) oriented growth of SBN is shown to occur exclusively on (001) Pt crystallites stable against subsequent annealing steps. As a final result, (001) SBN films have been obtained epitaxial on both Pt coated and not coated (001) MgO substrates. They display two in-plane orientations mirror symmetric (±α) to the axis of (001) MgO, with α shifted from 31° to 18° by (001) Pt coating.     

The possibility of improving the structural perfection of the new heterojunctions GaAs-(Ge2)1− x (ZnSe)x, Ge-(Ge2)1−x (ZnSe)x, GaP-(Ge2)1−x (ZnSe)x, and Si-(Ge2)1−x (ZnSe)x

Based on morphological investigations, as well as on a study of the scanning patterns and diffraction spectra of the heterostructures GaAs-(Ge₂)_1−x (ZnSe)_x, Ge-(Ge₂)_1−x (ZnSe)_x, GaP-(Ge₂)_1−x (ZnSe)_x, and Si-(Ge₂)_1−x (ZnSe)_x, it is shown that the crystal perfection of these structures depends on the choice of the conditions of liquid-phase epitaxy. It is shown that mirror-smooth epitaxial layers of (Ge ₂)_1−x (ZnSe)_x with the lowest stress levels can be obtained on GaAs (100) and Ge (111) substrates. Pis’ma Zh. Tekh. Fiz. 24, 12–16 (January 26, 1998)     

Preparation of epitaxial DyFeO3 thin films and magnetodielectric coupling

Multiferroic DyFeO₃ thin films deposited on (001) Nb-doped SrTiO₃ (NSTO) substrates are prepared by pulsed laser deposition. We demonstrate the epitaxial deposition of DyFeO₃ thin films on the substrates with the DyFeO₃(001)//NSTO(001) out-of-plane and DyFeO₃[100]//NSTO[110] in-plane epitaxial relationship. In addition, the weak ferromagnetism and significant magnetodielectric coupling effect at low temperature are revealed. It is indicated that the DyFeO₃ thin films have very different properties from the DyFeO₃ single crystals in term of multiferroicity.     

Ferroelastic interactions in bilayered ferroelectric thin films

We present a theoretical investigation of the elastic interactions in a heteroepitaxial bilayer consisting of a (001) tetragonal PbZr _x Ti_1−x O₃ and (001) rhombohedral PbZr_1−x Ti _x O₃ on a thick (001) passive substrate. Analytical expressions for the elastic interaction energies between the layers and the resultant ferroelastic twin formation have been derived as a function of the lattice misfit strain (between layers and the substrate), composition of the ferroelectric and thickness. It is found that the elastic coupling between the tetragonal and rhombohedral layers leads to the equilibrium domain fraction in the tetragonal layer several time larger than that in single-layer films of similar thickness. Most critically, the model finds a significant change in the ferroelastic domain volume fraction in the presence of an applied electric field and hence enhanced piezoelectric properties compared to single-layered epitaxial PZT thin films.     

Properties of Va metal-B films prepared by r.f.-sputtering

Nb_100−x B _x alloy films were prepared by the r.f.-sputtering method in the chemical composition range of 30 ≦x ≦ 76. Nb_100−x B _x (30 ≦x ≦ 54) films consisted of the amorphous state, and NbB₂ crystal phase was observed on Nb_100−xB_x (67 ≦x ≦ 76) films. A remarkable preferred orientation with the (001) plane of NbB₂ in parallel to the film surface was observed on Nb₃₃B₆₇ film. d.c. electrical conductivity of Nb_100−xB_x (30 ≦x ≦ 76) films decreased with increasing content of boron in the range from 7.3×10³ to 7.6 ×10²Ω⁻¹cm⁻¹. Micro-Vickers hardness of Nb_100−x B _x (30 ≦x ≦ 76) films exhibited the values of 1070 to 2060 kg mm².     

Preparation of epitaxial YBa2Cu3O7−x films by magnetron sputtering

Thin films of highT _c superconductor YBa₂Cu₃O_7−x were obtained by magnetron sputtering. MgO, YSZ, YSH and Al₂O₃ single crystals were used as substrates. Epitaxial films with tetragonal structure havingT _c 55–60 K grow at substrate temperaturesT _s between 930 K and 980 K. Orientation of the films in thisT _s range was (100) and (001) for (100) MgO substrate, (111) and (001) for (1012) Al₂O₃ and (111) YSH and (113) or (103) on (110) YSZ and (111) YSH. Single crystalline films with orthorhombic structure and (001) orientation were grown on all the substrates whenT _s exceeded 980 K. They haveT _c>80 K.     

Epitaxial growth and electrical measurement of single crystalline Pb(Zr0.52Ti0.48)O3 thin film on Si(001) for micro-electromechanical systems

We report in this work the epitaxial growth and the electrical characteristics of single crystalline Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film on SrTiO₃(STO)-buffered Si(001) substrate. The STO buffer layer deposited by molecular beam epitaxy allows a coherent oxide/Si interface leading enhanced PZT crystalline quality. 70 nm-thick PZT (52:48) layer was then grown on STO/Si(001) by sol-gel method. X-ray diffraction demonstrates the single crystalline PZT film on Si substrate in the following epitaxial relationship: [110] PZT (001)//[110] STO (001)//[100] Si (001). The macroscopic electrical measurements show a hysteresis loop with memory window of 2.5 V at ± 7 V sweeping range and current density less than 1 μA/cm² at 750 kV/cm. The artificial domains created by piezoresponse force microscopy with high contrast and non-volatile properties provide further evidence for the excellent piezoelectric properties of the single crystalline PZT thin film.     

Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe₂O₄ films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)₂, Zn(acac)₂ and Fe(acac)₃. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min⁻¹) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni_1−xZn_xFe₂O₄ (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g⁻¹ and the coercive force of 20 to 30 Oe.     

Ferromagnetism in Rutile Structure Cr Doped VO<Subscript>2</Subscript> Thin Films Prepared by Reactive-Bias Target Ion Beam Deposition

First generation spintronics has entered the mainstream of information technology through its utilization of the magnetic tunnel junction in applicable devices such as read head sensors for hard disk drives and magnetic random access memory. The future of spintronic devices requires next generation spintronic materials (Wolf et al. in IBM J. Res. Dev. 9:101, [2006]). Here we report on the structural, transport, and magnetic characteristics of V_1−x Cr _x O₂ (0.1≤x≤0.2) thin films deposited on (001) Al₂O₃ substrates. We show that the metal-insulator transition of VO₂ is suppressed and the rutile structure is stable down to 100 K. The films are remarkably smooth having a root-mean squared surface roughness of 0.3 nm. Films are conductive at room temperature and appear to follow a variable-range-hopping conduction mechanism below that. Ferromagnetism is observed at room temperature and is dependent on Cr concentration. The combination of these characteristics makes V_1−x Cr _x O₂ a viable candidate material for next generation spintronic multilayer devices.     

Magnetic and structural properties of Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript> on MgO(110) substrates

Fe _x Pt_100−x (70.1 ≤ x ≤ 83.4) thin films with ordered Fe₃Pt phase were grown successfully onto MgO(110) substrates by electron beam evaporation. The unit cell of ordered Fe₃Pt phase is elongated along c-axis direction and the thin films become more chemically ordered with decreasing Fe content. The magnetization of thin films shows a decrease when Fe content is around 79 at.%. The relationship between magnetic anisotropy and structural parameters suggests that the change of magnetic anisotropy in ordered Fe₃Pt thin films with different compositions most likely stems from the magnetocrystalline origin.     

Microstructure and secondary phases in epitaxial LaBaCo_2O_(5.5 + δ) thin films

Aberration-corrected scanning transmission electron microscopy was employed to investigate the microstructures and secondary phases in LaBaCo_2O_(5.5 + δ)(LBCO) thin films grown on SrTiO_3(STO) substrates. The as-grown films showed an epitaxial growth on the substrates with atomically sharp interfaces and orientation relationships of [100]_(LBCO)//[100]_(STO)and(001)_(LBCO)//(001)_(STO). Secondary phases were observed in the films, which strongly depended on the sample fabrication conditions. In the film prepared at a temperature of 90℃, nano-scale CoO pillars nucleated on the substrate, and grew along the [001]direction of the film. In the film grown at a temperature of 1000℃, isolated nano-scale Co_3O_4 particles appeared, which promoted the growth of {111} twinning structures in the film. The orientation relationships and the interfaces between the secondary phases and the films were illustrated, and the growth mechanism of the film was discussed.     

Fabrication of epitaxial conductive LaNiO3 films on different substrates by pulsed laser ablation

LaNiO₃ (LNO) thin films were deposited on (1 0 0) MgO, SrTiO₃ (STO) and LaAlO₃ (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the (l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La₂NiO₄ phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.     

Room-Temperature Photomagnetic Effect of Fe<Subscript>3</Subscript>Ga<Subscript>4</Subscript> Grown on GaAs Substrates

Ga–As–Fe composite films prepared by molecular beam epitaxy at 600°C on GaAs(100) substrates with the stacking sequence of [100-nm GaAs/50-nm Fe₃Ga_{2− x} As _x /100-nm GaAs] exhibit the distinct photo-enhanced magnetization at room temperature. Transmission electron microscopy reveals the formation of metamagnetic Fe₃Ga₄ grains on the sample surface. Illumination power dependence of the enhanced magnetization has been carefully compared with the antiferromagnetic-type magnetization–temperature (M–T) curve (Neel temperature of T _N = 340–390 K), from which we have discussed the existence of photon-mode photo-enhanced magnetization of some sort in addition with the enhancement due to the light-induced heating.     

Epitaxial growth of SrTiO3 films with different orientations on TiN buffered Si(001) by pulsed laser deposition

Epitaxial SrTiO₃ (STO) films have been grown on TiN buffered Si(001) by pulsed laser deposition. The TiN layer was in situ deposited at 540, 640 or 720°C whereas the STO film was grown at a fixed temperature of 640°C. We have studied the effect of the growth temperature of TiN on the epitaxial relationship of STO/TiN heterostructures. It is found that for TiN grown at 540 or 640°C the epitaxial relationship is 001STO 001TiN, and for TiN grown at 720°C it changes to (101)STO (001)TiN and [ 01]STO [1 0]TiN (or [ 01]STO [110]TiN). This change of relationship is accompanied by a sharp reduction in the out-of-plane lattice constant of the TiN layer. Fourier transform infrared spectra show that the longitudinal optic modes are active for all the STO films, but the absorption peak associated with the transverse optic mode is observed only in the (101) oriented STO films.     

Fabrication of indium arsenic-antimony-bismuthide multilayer heterostructures by “capillary” liquid-phase epitaxy

Low-temperature “capillary” liquid-phase epitaxy is used to grow InAs_{1−x− y} Sb_xBi_y/InSb_1−y Bi_y multilayer epitaxial heterostructures on InSb(111)A substrates. The heterostructures contained up to sixty epitaxial layers of thickness between 0.05 and 0.15 μm, which was controlled by the epitaxial growth conditions. The heterostructures were investigated by scanning electron microscopy and secondary-ion mass spectrometry, and results are presented. Pis’ma Zh. Tekh. Fiz. 23, 51–55 (April 12, 1997)     

A Chemical Route to Monolithic Integration of Crystalline Oxides on Semiconductors

This work demonstrates the growth of crystalline SrTiO₃ (STO) directly on germanium via a chemical method. After thermal deoxidation, the Ge substrate is transferred in vacuo to the deposition chamber where a thin film of STO (2 nm) is deposited by atomic layer deposition (ALD) at 225 °C. Following post‐deposition annealing at 650 °C for 5 min, the STO film becomes crystalline with epitaxial registry to the underlying Ge (001) substrate. Thicker STO films (up to 15 nm) are then grown on the crystalline STO seed layer. The crystalline structure and orientation are confirmed via reflection high‐energy electron diffraction, X‐ray diffraction, and transmission electron microscopy. Electrical measurements of a 15‐nm thick epitaxial STO film on Ge show a large dielectric constant (k ≈ 90), but relatively high leakage current of ≈10 A/cm² for an applied field of 0.7 MV/cm. To suppress the leakage current, an aluminum precursor is cycled during ALD growth to grow crystalline Al‐doped STO (SrTi_1‐x­Al_xO_3‐δ) films. With sufficient Al doping (≈13%), the leakage current decreases by two orders of magnitude for an 8‐nm thick film. The current work demonstrates the potential of ALD‐grown crystalline oxides to be explored for advanced electronic applications, including high‐mobility Ge‐based transistors.     

Synthesis and temperature dependent photoluminescence of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O films grown by ultrasonic spray pyrolysis

Zn_1−x Mg _x O films were deposited on single crystal Si (100) substrates using ultrasonic spray pyrolysis under ambient atmosphere. A strong ultraviolet near-band-edge (NBE) emission was observed in the room temperature photoluminescence (PL) measurement for all the as-grown Zn_1−x Mg _x O films, while the deep-level emission was almost undetectable, suggesting that the obtained Zn_1−x Mg _x O-based films are well close to stoichiometry and of optically high quality. A distinct blue-shift of NBE emission peak from 386 nm to 358 nm was observed as the Mg concentration increases from 0% to 25 %. The photoluminescence spectra as a function of temperature were also investigated to examine the emission mechanism of Zn_1−x Mg _x O films.     

Growth and fatigue properties of pulsed laser deposited Pb1 − x La x (Zr y Ti z )O3 thin films with [0 0 /] preferred orientation

Growth of [0 0 /] preferentially oriented Pb_{1 - x} La _x (Zr _y Ti _z ) O₃ (PLZT) thin films was carried out by using targets of either tetragonal or rhombohedral structure. The tetragonal films grew in a similar manner to the rhombohedral films. Both the substrate temperature (500 or 550 C) and oxygen pressure (0.1 mbar, 10 Pa) required stringent control in order to deposit [0 0 /]-textured PLZT thin films. The ferroelectric and fatigue properties were examined.The films deposited on YBa₂Cu₃O_{7 - x} and CeO₂ coated silicon (YBCO/CeO₂/Si) substrates possessed substantially lower remanent polarization than those grown on YBCO coated SrTiO₃ (YBCO/STO) substrates; this is ascribed to inferior crystallinity of the PLZT/YBCO/CeO₂/Si films. The remanent polarization of tetragonal PLZT films was degraded insignificantly up to 10⁸ polarization switching cycles, whereas that of rhombohedral PLZT films was already reduced to 80% of the initial value after 10⁸ cycles. Low endurance of rhombohedral films was ascribed to the periodic stress induced when the inclined spontaneous polarization vector (P = [111]) switched. On the other hand, high endurance of tetragonal films was explained by the fact that the spontaneous polarization vector (P = [001]) lies along the film's normal such that switch cycles cause no lateral stress.