Hexagonal La2O3 Research Articles

Chemical and structural properties of atomic layer deposited La2O3 films capped with a thin Al2O3 layer

X-ray diffraction and infrared spectroscopy measurements are conducted in order to assess the crystallographic structure and chemical purity of lanthanum oxide (La2O3) films grown by atomic layer deposition (ALD) on Si substrates. In situ capping with thin aluminum oxide (Al2O3) layer is proved to be beneficial in preventing the formation of lanthanum hydroxide phases. The effect of two process parameters, namely, La2O3 film growth temperature (260–500°C range) and postdeposition annealing temperature (600–1100°C range), on the chemical and structural evolutions of Al2O3∕La2O3∕Si stacks is discussed. This study enables the identification of the optimum ALD growth recipe yielding the highest hexagonal La2O3 phase content, which might be suitable for integration into innovative metal oxide semiconductor devices.

ALD-Grown Rare Earth Oxides for Advanced Gate Stacks

Atomic Layer Deposition (ALD) has gained increasing attention for the sub-nm growth of high permittivity (k) rare earth oxide films. State of the art device operation heavily depends on the oxide/semiconductor interface properties. In this work, we address mainly through HRTEM-EELS experiments interface issues for ALD-grown Lu2O3/Si and La2O3/Si interfaces. Complementary results from GIXRD and electrical measurements on selective samples are presented. We show that, after exposure to air, Lu2O3 films capped with an Al2O3 layer are essentially free of interfacial layer formation, even if the starting Si surface is chemically oxidized. We also demonstrate that the La2O3 film reactivity with Si can be controlled up to a certain extent by appropriately choosing the ALD precursor combination. In particular, the La(Cp)3+O3 scheme favours over the La(Cp3)+H2O one in terms of a (i) smaller low-k interfacial layer thickness and interface trap density and (ii) stabilization of the high-k hexagonal La2O3 phase.

Vibrational and electrical properties of hexagonal La2O3 films

La 2 O 3 films are obtained by annealing in vacuum La(OH)3 layers produced upon air exposure of La2O3 layers grown using atomic layer deposition. Sample thickness determines whether hexagonal or cubic La2O3 form. The observed infrared active phonon mode with minimum frequency for hexagonal La2O3 films is located at 198cm−1, in good agreement with the first principles calculations, and at a lower frequency than the corresponding mode for cubic La2O3 is at 235cm−1. Accordingly, electrical measurements reveal a dielectric constant around 27 for hexagonal La2O3 films, significantly higher than the one around 17 derived for cubic La2O3 layers.

Synthesis and X-ray Structure of the Novel Polymeric Lanthanum(III) 2,2'-Oxydiacetate [La(2)(C(4)H(4)O(5))(3)(H(2)O)(3).5H(2)O](n)().

The synthesis and X-ray structure of the novel polymeric lanthanum(III) oxydiacetate complex [La2(C4H4O5)3(H2O)3·5H2O]n (1) is reported. One metal ion is coordinated to three tridentate oxydiacetate ligands, the other, to six outer carboxylate oxygens and three oxygens from metal-bound water molecules. The crystal structure of 1 shows it to be a three-dimensional polymer where the lanthanum centers are bridged by the carboxylate groups of the oxydiacetate ligands. Upon thermolysis 1 is converted into hexagonal La2O3.

17O Solid-state NMR examination of La2O3 formation

Solid-state 17O magic-angle spinning (MAS) NMR spectroscopy has been used to study the formation of hexagonal La2O3 from both dehydroxylation of La(OH)3 and a sol–gel route starting from lanthanum isopropoxide. Both routes proceed via the formation of the oxyhydroxide [LaO(OH)] which is not commonly observed for other simple oxides. 17O NMR spectroscopy is very sensitive to structural change even in amorphous samples and the resonances of specific phases are assigned elucidating the chemical shift ranges of the local oxygen coordinations in these materials. The quadrupolar coupling constant for the OLa4 site in La2O3 is determined by the application of satellite transition NMR spectroscopy.

TEM studies of cross sections of oxidized Fe-25Cr-6Al-La alloy

The oxidation behavior of the alloy Fe−25%Cr−6%Al-RE (rich in lanthanum) was investigated by means of TEM analysis. The results show that after 2 hr oxidation of the alloy, in pure oxygen at 1200° C, La precipitated in the oxide scale at the top of α-Al2O3 grains and at the grain-boundary regions in the form of tiny particles of hexagonal La2O3. These tiny particles prevented aluminum from diffusing toward the surface and suppressed lateral growth of the oxide scale. The rare-earth constituents accelerated the internal oxidation of the alloy during thermal cycling between 1200° C and room temperature. They appeared as particles of aluminum oxide and lanthanum oxide. Particles of cubic La2O3 precipitated in the alloy matrix near the oxide scale-metal interface in a direction parallel to grain boundaries.

Electric field gradients of111Cd in the hexagonal (A-phase) La2O3 and Nd2O3 sesquioxides

Perturbed angular correlation measurements of111In in hexagonal La2O3 and Nd2O3 yield well defined symmetric electric field gradients with coupling constantv Q =280 MHz (extrapolated) in La2O3 andv Q =269 MHz for Nd2O3 at room temperature. The coupling constant in La2O3 linearly decreases with temperature. The spectra of La2O3, strongly damped at RT, rise to full amplitude at 870 K indicating dynamical interactions.

Structural and magnetic studies of hexagonal β-242Pu2O3

Neutron diffraction and magnetic susceptibility measurements have been used to characterize the structural and magnetic properties of β-Pu2O3 with the hexagonal La2O3 structure. High-resolution neutron powder patterns combined with profile analysis have given the cell constants, atomic positional parameters, and the stoichiometry with high precision. The latter is in agreement with the value determined from thermodynamic methods. The antiferromagnetic structure in the temperature range 4 K<T<TN∼19 K consists of Pu moments in the basal plane, but they vary along the c direction in a pseudospiral way. Two components are required to describe this modulation. The value of the maximum Pu moment at 10 K is ∼0.85 μB, each component having an amplitude of ∼0.6 μB/Pu. At 4 K a spin rotation takes place so that μ∥c. Susceptibility measurements reflect the existence of TN but show very little response near the spin rotation temperature.