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Register a new userZnCoO Films by Atomic Layer Deposition - influence of a growth temperature on uniformity of cobalt distribution
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We report on the structural, electrical and magnetic properties of ZnCoO thin films grown by Atomic Layer Deposition (ALD) method using reactive organic precursors of zinc and cobalt. As a zinc precursor we applied either dimethylzinc or diethylzinc and cobalt (II) acetyloacetonate as a cobalt precursor. The use of these precursors allowed us the significant reduction of a growth temperature to 300oC and below, which proved to be very important for the growth of uniform films of ZnCoO. Structural, electrical and magnetic properties of the obtained ZnCoO layers will be discussed based on the results of SIMS, SEM, EDS, XRD, AFM, Hall effect and SQUID investigations.
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In the present study we report on properties of ZnCoO films grown at relatively low temperature by the Atomic Layer Deposition, using two reactive organic zinc precursors (dimethylzinc and diethylzinc). The use of these precursors allowed us the significant reduction of a growth temperature to below 300oC. The influence of growth conditions on the Co distribution in ZnCoO films, their structure and magnetic properties was investigated using Secondary Ion Mass Spectroscopy, Scanning Electron Microscopy, Cathodoluminescence, Energy Dispersive X-ray Spectrometry (EDX), X-ray diffraction and Superconducting Quantum Interference Device magnetometry. We achieved high uniformity of the films grown at 160{deg}C. Such films are paramagnetic. Films grown at 200{deg} and at higher temperature are nonuniform. Formation of foreign phases in such films was detected using high resolution EDX method. These samples are not purely paramagnetic and show weak ferromagnetic response at low temperature.
Despite many efforts the origin of a ferromagnetic (FM) response in ZnMnO and ZnCoO is still not clear. Magnetic investigations of our samples, not discussed here, show that the room temperature FM response is observed only in alloys with a non-uniform Mn or Co distribution. Thus, the control of their distribution is crucial for explanation of contradicted magnetic properties of ZnCoO and ZnMnO reported till now. In the present review we discuss advantages of the Atomic Layer Deposition (ALD) growth method, which enables us to control uniformity of ZnMnO and ZnCoO alloys. Properties of ZnO, ZnMnO and ZnCoO films grown by the ALD are discussed.
Atomic layer deposition was used to synthesize niobium silicide (NbSi) films with a 1:1 stoichiometry, using NbF5 and Si2H6 as precursors. The growth mechanism at 200oC was examined by in-situ quartz crystal microbalance (QCM) and quadrupole mass spectrometer (QMS). This study revealed a self-limiting reaction with a growth rate of 4.5 {AA}/cycle. NbSi was found to grow only on oxide-free films prepared using halogenated precursors. The electronic properties, growth rate, chemical composition, and structure of the films were studied over the deposition temperature range 150-400oC. For all temperatures, the films are found to be stoichiometric NbSi (1:1) with no detectable fluorine impurities, amorphous with a density of 6.65g/cm3, and metallic with a resistivity {rho}=150 {mu}{Omega}.cm at 300K for films thicker than 35 nm. The growth rate was nearly constant for deposition temperatures between 150-275oC, but increases above 300oC suggesting the onset of non-self limiting growth. The electronic properties of the films were measured down to 1.2K and revealed a superconducting transition at Tc=3.1K. To our knowledge, a superconducting niobium silicide film with a 1:1 stoichiometry has never been grown before by any technique.
In this paper, a method is presented to create and characterize mechanically robust, free standing, ultrathin, oxide films with controlled, nanometer-scale thickness using Atomic Layer Deposition (ALD) on graphene. Aluminum oxide films were deposited onto suspended graphene membranes using ALD. Subsequent etching of the graphene left pure aluminum oxide films only a few atoms in thickness. A pressurized blister test was used to determine that these ultrathin films have a Youngs modulus of 154 pm 13 GPa. This Youngs modulus is comparable to much thicker alumina ALD films. This behavior indicates that these ultrathin two-dimensional films have excellent mechanical integrity. The films are also impermeable to standard gases suggesting they are pinhole-free. These continuous ultrathin films are expected to enable new applications in fields such as thin film coatings, membranes and flexible electronics.
The direct liquid injection chemical vapor deposition (DLI-CVD) technique has been used for the growth of cobalt ferrite (CFO) films on (100)-oriented MgAl$_2$O$_4$ (MAO) substrates. Smooth and highly epitaxial cobalt ferrite thin films, with the epitaxial relationship $mathrm{MAO} (100):[001] parallel mathrm{CFO} (100):[001]$, are obtained under optimized deposition conditions. The films exhibit bulk-like structural and magnetic properties with an out-of-plane lattice constant of $8.370;mathrm{AA}$ and a saturation magnetization of $420;mathrm{kA/m}$ at room temperature. The Raman spectra of films on MgAl$_2$O$_4$ support the fact that the Fe$^{3+}$- and the Co$^{2+}$-ions are distributed in an ordered fashion on the B-site of the inverse spinel structure. The DLI-CVD technique has been extended for the growth of smooth and highly oriented cobalt ferrite thin films on a variety of other substrates, including MgO, and piezoelectric lead magnesium niobate-lead titanate and lead zinc niobate-lead titanate substrates.
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