Epitaxial Nature Research Articles

Growth and physical property of epitaxial Co70Fe30 thin film on Si substrate via TiN buffer

Epitaxial Co70Fe30 films with the bcc structure were grown on a Si(001) substrate with TiN as a buffer by sputtering technique. The x-ray diffraction results confirmed the epitaxial nature of the films and the crystallographic relationship was determined as Co70Fe30(002)⟨110⟩∕∕TiN(002)⟨100⟩∕∕Si(004)⟨100⟩. The surface morphology characterized by atomic force microscopy on our films revealed that smooth surfaces could be obtained at growth temperatures below 350°C. The strain state of 60nm epitaxial Co70Fe30 films was studied as a function of growth temperature. Magnetization hysteresis loops of the films grown at 300°C were measured using superconducting quantum interface device magnetometer.

Homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1−x O alloy thin films by pulsed laser deposition technique

In this work, we describe the homo- and hetero-epitaxial growth of hexagonal and cubic MgxZn1−xO thin films on lattice matched substrates of c-Al2O3, ZnO, MgO and SrTiO3. The crystalline quality, composition and epitaxial nature of the alloy films are obtained by x-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques. The RBS channeling yields are in the range 3–8% for homoepitaxial and hetero-epitaxial thin films. The metal–semiconductor–metal and ultraviolet detectors were fabricated on hexagonal and cubic MgxZn1−xO thin films and the leakage current and UV-visible rejection ratio are correlated with the epitaxial relationship between the film and substrates.

Controlling Magnetism with an Electric Field in Multiferroic Complex Oxide Heterostructures: La0.7Sr0.3MnO3/BiFeO3

This is a copy of the slides presented at the meeting but not formally written up for the volume. Interactions at magnetic interfaces are central to the operation of virtually all magnetic heterostructures. When the interface is between two magnetic materials, the exchange interaction between spins at the interface is often a dominant force, and can dramatically change the magnetic response of the overall heterostructure. In ferromagnet (FM)/antiferromagnet (AFM) heterostructures, this interaction is often referred to as exchange anisotropy or bias and it has been widely used over the past decade in a wide array of applications such as magnetic recording heads, MRAMs, etc. The powerful implications of interactions between an AFM and a FM have been realized in a wide range of thin film heterostructure with both metallic and oxide constituents. There is, however, much less work on oxide-oxide FM/AFM systems. On the other hand, the development and understanding of functional oxide materials, especially multifunctional materials like BiFeO3 (BFO), have piqued the interest of researchers worldwide with the promise of coupling between order parameters such as ferroelectricity and antiferromagnetism. Recent research suggests that there is exchange coupling and anisotropy between the metallic ferromagnet Co0.9Fe0.1 (CoFe) and the multiferroic, antiferromagnet BFO, showing the possibility to create highly desirable multifunctional systems with new possibilities for device design. Such a result provides the driving force to create multifunctional oxide-oxide systems where exchange interactions could be much stronger then in metal/oxide structures due the added epitaxial nature of the interface. In this study, we use La0.7Sr0.3MnO3(LSMO)/BFO thin film heterostructures as a model system to explore the exchange interaction at an oxide interface. The heterostructures are grown on various vicinal cuts of SrTiO3 single crystal substrates using laser MBE. Structural analysis using x-ray diffraction, transmission electron microscopy and Rutherford backscattering spectrometry reveals high quality films with the pristine interfaces required for exchange coupling. First results from photoemission electron microscope (PEEM) studies reveal that the magnetic LSMO domain structure mimics underneath ferroelectric BFO domain structure, i..e, it is strongly pinned by the underlying AFM structure. The coupling behavior is being characterized by magnetic measurements (SQUID, VSM), which shows a strong enhancement in the coercivity of the LSMO layer, suggesting the existence of exchange bias coupling. We are probing the strength of this coupling using a combination of careful laser MBE growth experiments and physical property measurements. In this paper, we will report results of experiments in which the LSMO layer has been grown by laser MBE in the thickness range of 2-50nm on a [001] BFO layer.

Epitaxial Ti2AlN(0 0 0 1) thin film deposition by dual-target reactive magnetron sputtering

Ultrahigh-vacuum dual-target reactive magnetron sputtering, in a mixed Ar/N2 discharge was used to deposit epitaxial single-crystal MAX phase Ti2AlN(0001) thin films, without seed layers, onto Al2O3(0001) substrates kept at 1050°C. By varying the N2 partial pressure a narrow process window was identified for the growth of single-crystal Ti2AlN. The film microstructure was characterized by a combination of X-ray diffraction, spherical aberration (Cs) corrected transmission electron microscopy (TEM), high-resolution image simulation and high-resolution scanning TEM. Nitrogen-depleted deposition conditions resulted in the concurrent formation of N-free Ti–Al intermetallics at the film/substrate interface and a steady-state growth of Ti2AlN together with N-free intermetallic phases. At higher N2 partial pressures the growth assumes a columnar epitaxial nature. 1Å resolution of the lattice enabling location of all elements in the Ti2AlN unit cell is demonstrated.

Effects of swift heavy ion irradiation on La0.5Pr0.2Sr0.3MnO3 epitaxial thin films grown by pulsed laser deposition

We report the observation of room temperature insulator to metal transition and magnetoresistance characteristics of Swift Heavy Ions (SHIs) irradiated La0.5Pr0.2Sr0.3MnO3 (LPSMO) epitaxial thin films grown on single crystal (100) SrTiO3 substrates using Pulsed Laser Deposition. The epitaxial nature and crystallanity of the films was confirmed from the structural and magnetoresistance characteristics. Irradiation with the 200MeV Ag15+ ions at a fluence of about 5×1011ions/cm2 showed suppression in the resistivity by ∼68% and 31% for the films with 50nm and 100nm thickness respectively. The possible reasons for this suppression could be either release of strain in the films in the dead layer at the interface of film-substrate or Swift Heavy Ions induced annealing which in turn affects the Mn–O–Mn bond angle thereby favoring the Zener double exchange. Field Coefficient of Resistance (FCR) values for both films, determined from R-H data and magnetoresistance data, showed a marginal enhancement after irradiation.

Effects of periodicity and oxygen partial pressure on the crystallinity and dielectric property of artificial SrTiO 3/BaTiO 3 superlattices integrated on Si substrates by pulsed laser deposition method

Epitaxial SrTiO 3(STO)/BaTiO 3(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.

Epitaxial growth of zinc oxide thin films on epi-GaN/sapphire (0001) by sol–gel technique

Epitaxial ZnO film has been grown using an epi-GaN buffer layer on sapphire (0001) substrate by sol–gel technique. The 2 θ curve full width at half maximum of the ZnO (0002) peak for the film annealed at optimized temperature of 600 °C, was found to be 0.07° from X-ray diffraction spectrum. The atomic force microscopy revealed smooth hexagonal faceting of the ZnO films. Photoluminescence spectrum at room temperature exhibits a sharp exciton emission with a line width of 120 meV with negligible deep level emission. The observed six fold symmetry in reflection high energy electron diffraction pattern confirms the epitaxial nature of the ZnO film.

A new method for the preparation of Ru quasi single crystal surfaces

A new method for the preparation of Ru quasi single crystal electrode surfaces is described. Using the ‘forced deposition’ method followed by resistive heating in nitrogen, it is demonstrated that well-defined Ru films supported on Pt single crystal electrodes may be synthesised which, for the case of Pt{1 1 1} exhibit voltammetry similar to that reported for bulk single crystal Ru(0 0 0 1) electrodes. Moreover, systematic changes in the voltammetric response of the well-ordered supported Ru film upon varying the substrate surface crystallography from Pt{1 1 1} to Pt{1 0 0} (via a series of Pt n{1 1 1} × {1 0 0} and Pt n{1 0 0} × {1 1 1} stepped surfaces) demonstrate unequivocally the epitaxial nature of the films. For surfaces based on Pt{1 0 0} – (1 × 1) terraces, two sharp, intense peaks just positive of the potential of hydrogen evolution signify the presence of fcc Ru{1 0 0} terrace sites. This is significant because fcc {1 0 0} surface sites are not normally associated with hcp bulk phases. In addition, the voltammetric features usually ascribed to fcc {1 0 0} × {1 1 1} step sites and {1 1 1} terraces are clearly identified for the Ru films. The surfaces prepared by this method have been characterised by cyclic voltammetry (CV) in H 2SO 4. The most interesting facet of this new method is the ease of preparation of fcc Ru{ h k l} surfaces relative to analogues derived from variously prepared single crystals of Ru.

Si기판 위에 Ba0.5Sr0.5TiO3산화물 에피 박막의 집적화 및 박막의 유전 특성에 관한 연구

Epitaxial Ba 0.5 Sr 0.5 TiO₃ (BSTO) thin films have been grown on TiN buffered Si (001) substrates by Pulsed Laser Deposition (PLD) method and the effects of substrate temperature and oxygen partial pressure during the deposition on their dielectric properties and crystallinity were investigated. The crystal orientation, epitaxy nature, and microstructure of oxide thin films were investigated using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Thin films were prepared with laser fluence of 4.2 J/㎠ and 3 J/㎠, repetition rate of 8 Hz and 10 Hz, substrate temperatures of 700℃ and ranging from 350℃ to 700℃ for TiN and oxide, respectively. BSTO thin-films were grown on TiN-buffered Si substrates at various oxygen partial pressure ranging from 1×10 ?4 torr to 1×10 ?5 torr. The TiN buffer layer and BSTO thin films were grown with cube-on-cube epitaxial orientation relationship of [110](001) BSTO ∥[110](001) TiN ∥[110](001) Si . The crystallinity of BSTO thin films was improved with increasing substrate temperature. C-axis lattice parameters of BSTO thin films, calculated from XRD θ-2θ scans, decreased from 0.408 nm to 0.404 nm and the dielectric constants of BSTO epitaxial thin films increased from 440 to 938 with increasing processing oxygen partial pressure.

Structural and electrical characterizations of the pulsed-laser-deposition-grown Sc2O3∕GaN heterostructure

Single-crystalline Sc2O3 was grown on GaN/sapphire template using pulsed laser deposition and the interface characteristics of the Sc2O3∕GaN heterostructure were investigated. An epitaxial relationship of [112]Sc2O3‖[213¯0]GaN and (222)Sc2O3‖(0002)GaN was revealed by x-ray diffraction and cross-sectional transmission electron microscopy. A valence band offset of 0.84eV was obtained by x-ray photoelectron spectroscopy, indicating a conduction band offset of 2.04eV across the Sc2O3∕GaN heterointerface. In addition, a low interface state density of 4×1011eV−1cm−2 was estimated from capacitance-voltage measurements. The epitaxial nature with good interface characteristics has rendered a substantially low leakage current of 1μA∕cm2 at a reverse gate bias of 30V in the Sc2O3∕GaN metal-oxide-semiconductor structures.

Epitaxial growth and ferroelectric properties of Pb(Zr 0.52Ti 0.48)O 3/SrRuO 3 heterostructures on exact SrTiO 3(0 0 1) substrates

High quality Pb(Zr 0.52Ti 0.48)O 3/SrRuO 3 (PZT/SRO) perovskite oxide heterostructures have been grown on polished as-received (0 0 1) SrTiO 3 substrates without any further treatment by pulsed laser deposition. X-ray diffraction θ–2 θ and ω scans showed that the heterostructures had good (0 0 l) out-of-plane orientation and crystalline quality with the full-width at half-maximum values of rocking curves of only 0.04° and 0.2° for the SRO and PZT films, respectively. Transmission electron microscopy observation confirmed the epitaxial nature of the heterostructures. The SRO films showed a periodic step-terrace topography structure with an atomically flat surface, indicating step-flow growth mode, while the PZT films grew by island growth mechanism. The polarization-electric field hysteresis measurement showed that the remnant polarization P r and the coercive field E c at 5 V were 42 μC/cm 2 and 135 kV/cm, respectively.

Magnetic properties of Fe films and Fe∕Si∕Fe trilayers grown on GaAs(001) and MgO(001) by ion-beam sputter epitaxy

We grow monocrystalline Fe(001) films and Fe∕Si∕Fe(001) trilayers by ion-beam sputter epitaxy on GaAs(001) and MgO(001) substrates. Ion-beam sputtering parameters such as substrate presputtering time, substrate temperature, beam voltage, and target angle are optimized for 10-nm-thick Fe(001) films with respect to epitaxial growth and magnetic properties. In situ low-energy electron diffraction patterns confirm the epitaxial and monocrystalline nature of the sputtered films, surprisingly even on untreated and thus oxidized substrates. The magneto-optical Kerr effect and ferromagnetic resonance are employed to investigate the magnetic properties, and the structural properties are characterized by atomic force microscopy and x-ray reflectivity measurements. Using the optimized set of parameters that yields the best magnetic properties for single Fe films on GaAs, we deposit epitaxial Fe∕Si∕Fe(001) structures and observe antiferromagnetic interlayer exchange coupling for epitaxially sputtered Fe∕Si∕Fe(001) trilayers on GaAs(001). The total coupling strength reaches values of up to 2mJ∕m2 at a Si thickness of 15Å.

Epitaxial ZnO/Pt layered structures and ZnO-Pt nanodot composites on sapphire (0001)

We report the epitaxial growth and properties of ZnO-Pt layered structures and ZnO-Pt nanodot composites on sapphire (0001) substrates fabricated by using the pulsed laser deposition (PLD) technique. Heteroepitaxial growth of these structures was accomplished by using domain-matching epitaxy. The heterostructures were characterized using x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), optical transmittance, photoluminescence, and electrical resistivity measurements. XRD and HRTEM experiments revealed the epitaxial nature of these structures, with orientation relationship between ZnO and Pt, as [0001]ZnO∥[111]Pt and [\(\bar 2\)110]ZnO∥[011]Pt, which is equivalent to no rotation between ZnO and Pt. For Pt epitaxy on (0001) sapphire, the epitaxial relationship was determined to be [001]Pt∥[0001]Sap and [110]Pt∥[01\(\bar 1\)0]Sap, which is equivalent to a 30° rotation in the basal plane. Electrical and optical measurements showed that these heterostructures exhibit very high electrical conductivity and at the same time possess interesting optical transmittance spectra and exhibit room temperature photoluminescence characteristics.

Growth of highly conducting epitaxial ZnO–Pt–ZnO heterostructure on α-Al 2O 3 (0 0 0 1)

Here we report the growth of epitaxial ZnO–Pt–ZnO trilayer structures on sapphire (0 0 0 1) substrate by using pulsed laser deposition technique. These structures were characterized using X-ray diffraction, conventional and high-resolution transmission electron microscopy, STEM (scanning Transmission Electron microscopy-Atomic number) Z-contrast, optical transmittance and electrical resistivity measurements. X-ray diffraction and TEM experiments revealed the epitaxial nature of these structures, the orientation relationship being: 〈1 1 1〉 pt||〈0 0 0 1〉 ZnO||〈0 0 0 1〉〈0 0 0 1〉 sapphire (out of plane) and 〈1 1 0〉 pt||〈2 1¯ 1¯ 0〉 ZnO||〈0 1 1¯ 0〉 sapphire (in Plane) for the trilayer structure. Electrical and optical measurements showed that these heterostructures exhibit quite good electrical conductivity and at the same time possess moderate optical transmittance.

Self-assembled nanocrystalline epitaxial manganite films on SrTiO3∕Si heterostructures

We report the growth and magnetic characterizations of La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on SrTiO3-buffered Si (100) and Si (111) substrates by pulsed-laser deposition. The structural studies show the epitaxial nature of the films. The microscopic studies show that the films consist of nanocrystalline particles. All films display sharp magnetic and electrical transitions associated with the colossal magnetoresistance behavior at and above room temperature, illustrating the superior quality of the films.

Integration of artificial SrTiO 3/BaTiO 3 superlattices on Si substrates using a TiN buffer layer by pulsed laser deposition method

Epitaxial SrTiO 3(STO)/BaTiO 3(BTO) artificial superlattices, STO, BTO, and (Ba 0.5,Sr 0.5)TiO 3 (BSTO) thin films have been grown on TiN-buffered Si (0 0 1) substrates by pulsed laser deposition method and their dielectric properties were studied. The crystal orientation, epitaxy nature, and microstructure of epitaxial oxide thin films were investigated using X-ray diffraction and transmission electron microscopy. Thin films were prepared with laser fluence of 3 and 2 J/cm 2, repetition rate of 8 and 10 Hz, substrate temperature of 700 and 650 °C for TiN and oxide, respectively. The TiN buffer layer and oxide thin films were grown with cube-on-cube epitaxial orientation relationship of [1 1 0](0 0 1) films∥[1 1 0](0 0 1) TiN∥[1 1 0](0 0 1) Si. The dielectric constants of BTO, STO, BSTO, and STO/BTO superlattice epitaxial thin films with 1 nm/1 nm periodicity were shown to be as high as 300, 410, 520, and 680 at the frequency of 100 kHz, respectively.

Oxygen exchange kinetics of epitaxial PrBaCo2O5+δ thin films

The oxygen exchange kinetics of thin films of the oxygen-deficient double perovskite PrBaCo2O5+δ (PBCO) have been determined by electrical conductivity relaxation (ECR) and by oxygen-isotope exchange and depth profiling (IEDP). Microstructural studies indicate that the PBCO films, prepared by pulsed laser deposition, have excellent single-crystal quality and epitaxial nature. The ECR and IEDP measurements reveal that the PBCO films have high electronic conductivity and rapid surface exchange kinetics, although the ECR data indicate the presence of two distinct kinetic pathways. The rapid surface kinetics compared with those of other perovskites suggest the application of PBCO as a cathode material in intermediate-temperature solid oxide fuel cells.

Epitaxial Silicon Thin Films by Low Temperature Aluminum Induced Crystallization of Amorphous Silicon

AbstractEpitaxial silicon thin film growth has been achieved on crystalline silicon substrates using aluminum induced crystallization of amorphous silicon. The phenomenon of layer inversion has been utilized in this process. Silicon wafers <100> were used as the starting crystalline structure for the grown films. After the wafer is cleaned a thin layer of aluminum (300 nm) was deposited by sputtering. This deposition was followed by 300 nm film of amorphous silicon deposited using plasma enhanced chemical vapor deposition method. After annealing the samples for 40 minutes at 525 °C, a continuous film of silicon was formed on the silicon substrate. X-ray diffraction spectrum indicated that this film has the same orientation as that of the substrate. Scanning electron microscopy cross section images showed indistinguishable interface between the substrate and the crystallized film. Cross sectional transmission electron microscopy studies of the crystallized structure showed epitaxial nature of the films.

Pulsed laser deposition of epitaxial Al-doped ZnO film on sapphire with GaN buffer layer

Al-doped ZnO (ZnO:Al) films with thickness in the range of 0.5–0.9 μm were grown epitaxially on epi-GaN/sapphire (0001) by pulsed laser deposition (PLD; XeCl, λ=308 nm). The growth parameters such as substrate temperature, oxygen pressure and pulse repetition rate were established in a sequential manner to obtain highly epitaxial ZnO:Al film. The best films were obtained at substrate temperature of 400 °C, oxygen pressure of 1 mTorr and pulse repetition rate of 5 Hz. Reflection high-energy electron diffraction (RHEED) and low temperature photoluminescence (PL) studies confirm the high quality epitaxial nature of the film with near match and stacking order between ZnO and GaN.

State of the art on epitaxial GaAs detectors

We first briefly review the performances for X-ray detection which are obtained using thin epitaxial GaAs layers. We then show that good detectors can be realized on thick and large area epitaxial GaAs layers which are now available, making them suitable for X-ray imaging. We finally discuss the main limitation imposed by the epitaxial nature of this new material and ways to overcome it.