@article{lucovsky_miotti_bastos_2012, title={Many-Electron Multiplet Theory Applied to O-Vacancies in (i) Nanocrystalline HfO2 and (ii) Non-crystalline SiO2 and Si Oxynitride Alloys}, volume={23}, ISBN={["978-94-007-2383-2"]}, ISSN={["1567-7354"]}, DOI={10.1007/978-94-007-2384-9_10}, abstractNote={Performance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nanocrystalline transition metal oxides such as HfO2, and the non-crystalline oxides including SiO2, and Si3N4 and Si oxynitride alloys. Multiplet theory provides the theoretical foundation for an equivalentd 2 model for O-vacancy transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have relied on Tanabe-Sugano energy level diagrams for identifying the symmetries and multiplicities of transition energies for an equivalent d2 ground state occupancy. The equivalent d2 model has been applied to nanocrystalline thin films of ZrO2,HfO2,TiO2 and Lu2O3 and provides excellent agreement with X-ray absorption spectroscopy data. The model has also been applied to SiO2 and other Si based dielectrics where very good agreement with multiplet theory has also been demonstrated. The spectra indicate both triplet and singlet final states indicating that the two electrons in the vacancy sites have singlet and triplet ground states that are within a few tenths of an eV of each other. For the transition metal oxides, this is explained by relatively small distortions in the vacancy geometry in which the separation between the respective transition metal atoms is 1.6 times the bond-length in an ideal tetrahedral geometry, or the same factor for two fold coordination in O-atom bonding sites in SiO2 andGeO2. These distortions minimize the exchange energy in triplet spin states, and reduce the radial wave function overlap in singlet spin states.}, journal={VIBRONIC INTERACTIONS AND THE JAHN-TELLER EFFECT: THEORY AND APPLICATIONS}, author={Lucovsky, Gerry and Miotti, Leonardo and Bastos, Karen Paz}, year={2012}, pages={193–211} }
 @article{lucovsky_miotti_bastos_2012, title={O-Vacancies in (i) Nano-Crystalline HfO2 and (i) Non-Crystalline SiO2 and Si3N4 Studied by X-ray Absorption Spectroscopy}, volume={12}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2012.4912}, abstractNote={Performance and reliability in semiconductor devices are limited by electronically active defects, primarily O-atom and N-atom vacancies. Synchrotron X-ray spectroscopy results, interpreted in the context of two-electron multiplet theories, have been used to analyze conduction band edge, and O-vacancy defect states in nano-crystalline transition metal oxides, e.g., HfO2, and the noncrystalline dielectrics, SiO2, Si3N4 and Si-oxynitride alloys. Two-electron multiplet theory been used to develop a high-spin state equivalent d2 model for O-vacancy allowed transitions and negative ion states as detected by X-ray absorption spectroscopy in the O K pre-edge regime. Comparisons between theory and experiment have used Tanabe-Sugano energy level diagrams for determining the symmetries and relative energies of intra-d-state transitions for an equivalent d2 ground state occupancy. Trap-assisted-tunneling, Poole-Frenkel hopping transport, and the negative bias temperature instability have been explained in terms of injection and/or trapping into O-atom and N-atom vacancy sites, and applied to gate dielectric, and metal-insulator-metal structures.}, number={6}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Lucovsky, Gerald and Miotti, Leonardo and Bastos, Karen Paz}, year={2012}, month={Jun}, pages={4811–4819} }
 @article{lucovsky_miotti_bastos_adamo_schlom_2012, title={Spectroscopic Detection of Hopping Induced Mixed Valence for Ti and Sc in GdSc1-xTixO3 for x > 0.165}, volume={12}, ISSN={["1533-4899"]}, DOI={10.1166/jnn.2012.4911}, abstractNote={Only two of the first row transition metals have elemental oxides that are either ferro- or ferri-magnetic. These are CrO2 and Fe3O4. The electron spin alignment that promotes the ferro(i)magnetism is associated with a double exchange mechanism that requires mixed valence as well as metallic conductivity. This paper describes a novel way to realize these two necessary, but not sufficient conditions for double exchange magnetism. These are mixed valence and a hopping conductivity that promotes at least intra-plane electron spin alignment in a complex oxide perovskite host, A(B,C)O3. A is an ordinary metal, or a rare earth atom, B is a d0 transition metal, and C is a d(n) transition metal in which n > or = 1, as for example in GdSc1-xTi(x)O3. This article combines X-ray absorption spectroscopy, multiplet theory, charge transfer multiplet theory and degeneracy removal by Jahn-Teller effect mechanisms to demonstrate mixed valence for both Sc and Ti above a percolation threshold, x > 0.16, in which hopping transport gives rise to a metal to insulator transition.}, number={6}, journal={JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY}, author={Lucovsky, Gerald and Miotti, Leonardo and Bastos, Karen Paz and Adamo, Carolina and Schlom, Darrell G.}, year={2012}, month={Jun}, pages={4749–4756} }
 @article{lucovsky_miotti_bastos_2012, title={Spectroscopic Detection of Hopping Induced Mixed Valence of Ti and Sc in GdSc1-xTixO3 for x Greater than Percolation Threshold of 0.16}, volume={23}, ISSN={["1567-7354"]}, DOI={10.1007/978-94-007-2384-9_20}, abstractNote={Only two of the first row transition metal binary oxides are either ferro- or ferri-magnetic. These are CrO2 and Fe3O4. The electron spin alignment promoting electron spin alignment is associated with a double exchange mechanism requiring mixed valence as well as metallic conductivity. This chapter describes a novel way to realize these two necessary, but not sufficient conditions for double exchange magnetism. These are mixed valence and a hopping conductivity that can promote intra-plane electron spin alignment in a complex oxide host perovskite, $${\mathrm{GeSc}}_{1-\mathrm{x}}{\mathrm{Ti}}_{\mathrm{x}}{\mathrm{O}}_{3}$$ . This in-plane spin-correlation does necessarily produce for producing spin alignment between alternating (Sc,Ti)O2 atomic planes, especially in distorted perovskite structures. Intra-plane alignment is obtained when the A-atom of a trivalent atom AB(D)O3 peroskite, in this example Gd, is an ordinary metal or a rare earth atom, the B-atom, in this example Sc, is a d0 transition metal, and the dopant atom, D, in this example, Ti3 + in d1 state, is a dn transition with n ≥ 1, as in $${\mathrm{GdSc}}_{1-\mathrm{x}}{\mathrm{Ti}}_{\mathrm{x}}{\mathrm{O}}_{3}$$ . This article combines X-ray absorption spectroscopy, multiplet theory, and degeneracy removal by a Jahn-Teller effect mechanisms to demonstrate intra-layer mixed valence for Sc and Ti above a percolation threshold x ∼ 0.16 at which hopping transport is associated with a metal to insulator transition. This has been observed in epitaxial films, and not in nano-grain nanocrystalline, where the number of Sc atoms in a grain with 2–5nm dimensions is orders of magnitude too small for observation of an a hopping conductivity that requires a percolation mechanism.}, journal={VIBRONIC INTERACTIONS AND THE JAHN-TELLER EFFECT: THEORY AND APPLICATIONS}, author={Lucovsky, Gerry and Miotti, Leonardo and Bastos, Karen Paz}, year={2012}, pages={361–376} }
 @article{soares_krug_miotti_bastos_lucovsky_baumvol_radtke_2011, title={Intermixing between HfO2 and GeO2 films deposited on Ge(001) and Si(001): Role of the substrate}, volume={98}, ISSN={["0003-6951"]}, DOI={10.1063/1.3574093}, abstractNote={Thermally driven atomic transport in HfO2/GeO2/substrate structures on Ge(001) and Si(001) was investigated in N2 ambient as function of annealing temperature and time. As-deposited stacks showed no detectable intermixing and no instabilities were observed on Si. On Ge, loss of O and Ge was detected in all annealed samples, presumably due to evolution of GeO from the GeO2/Ge interface. In addition, hafnium germanate is formed at 600 °C. Our data indicate that at 500 °C and above HfO2/GeO2 stacks are stable only if isolated from the Ge substrate.}, number={13}, journal={APPLIED PHYSICS LETTERS}, author={Soares, G. V. and Krug, C. and Miotti, L. and Bastos, K. P. and Lucovsky, G. and Baumvol, I. J. R. and Radtke, C.}, year={2011}, month={Mar} }
 @article{lucovsky_miotti_bastos_2011, title={Many-electron multiplet theory applied to o-atom vacancies in high-k dielectrics}, volume={50}, DOI={10.7567/jjap.50.04da15}, abstractNote={Two-electron multiplet theory has been used to develop a high-spin effective d2 model for O-vacancy spin-allowed and spin-forbidden dipole transitions, and for negative ion state traps. The transition and negative ion states have been detected by X-ray absorption spectroscopy in the O K pre-edge regime of transition metal (TM) elemental oxides and complex oxides. Occupied ground and excited states of the model satisfy Hund's rules by (i) including only high-spin state arrangements and (ii) using many electron state term symbols consistent with Russell–Saunders coupling. Qualitative and quantitative agreement between theory and experiment is demonstrated by using Tanabe–Sugano energy level diagrams for (i) identifying the symmetries and spin states, and (ii) determining the relative energies of intra-d-state transitions that are allowed in the presence of an intermediate strength ligand field. This includes removal of the spin degeneracy for the allowed transitions by a cooperative Jahn–Teller effect. The effective d2 model is applied to nanocrystalline thin films of ZrO2, HfO2, TiO2, and Lu2O3 and to illustrate the agreement between the new d2 model and the X-ray absorption spectroscopy data. The new model has also been applied with the same degree of success to complex TM oxides and SiO2.}, number={4}, journal={Japanese Journal of Applied Physics. Part 1, Regular Papers, Short Notes & Review Papers}, author={Lucovsky, G. and Miotti, L. and Bastos, K. P.}, year={2011} }
 @article{lucovsky_miotti_bastos_2011, title={O-vacancies in (i) nanocrystalline HfO2 and (i) noncrystalline SiO2 and Si3N4 studied by x-ray absorption spectroscopy}, volume={29}, ISSN={["2166-2746"]}, DOI={10.1116/1.3533758}, abstractNote={Performance and reliability of semiconductor-oxide-metal devices with high-κ gate dielectrics are limited by electronically active O-atom vacancy defects. Synchrotron x-ray spectroscopy defect features have been interpreted using two-electron multiplet theory. This approach quantifies conduction band edge and pre-edge features assigned to intrinsic bonding effects. Theoretical studies based on density functional theory have identified these defects as neutral and negatively-charged O-atom vacancies in transition metal (TM) oxides including HfO2 and ZrO2. However, agreement between calculated electronic states and experiment has been less than satisfactory. In this paper the O-vacancy electronic structure is addressed using a theoretical approach extended from multiplet theory traditionally applied to occupied intrinsic, and alloy and impurity atom d states in TM oxides. An equivalent d2 model based occupation of two d orbitals of the TM atoms that border the neutral vacancy site has been used to determine...}, number={1}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Lucovsky, Gerald and Miotti, Leonardo and Bastos, Karen Paz}, year={2011}, month={Jan} }
 @article{miotti_bastos_lucovsky_radtke_nordlund_2010, title={Ge doped HfO2 thin films investigated by x-ray absorption spectroscopy}, volume={28}, ISSN={["0734-2101"]}, DOI={10.1116/1.3430562}, abstractNote={The stability of the tetragonal phase of Ge doped HfO2 thin films on Si(100) was investigated. Hf(Ge)O2 films with Ge atomic concentrations varying from 0% to 15% were deposited by remote plasma chemical vapor deposition. The atomic structure on the oxide after rapid thermal annealing was investigated by x-ray absorption spectroscopy of the O and Ge K edges and by Rutherford backscattering spectrometry. The authors found that Ge concentrations as low as 5 at. % effectively stabilize the tetragonal phase of 5 nm thick Hf(Ge)O2 on Si and that higher concentrations are not stable to rapid thermal annealing at temperatures above 750 °C.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Miotti, Leonardo and Bastos, Karen P. and Lucovsky, Gerald and Radtke, Claudio and Nordlund, Dennis}, year={2010}, pages={693–696} }
 @article{bastos_miotti_lucovsky_chung_nordlund_2010, title={Monoclinic textured HfO2 films on GeOxNy/Ge(100) stacks using interface reconstruction by controlled thermal processing}, volume={28}, ISSN={["0734-2101"]}, DOI={10.1116/1.3430563}, abstractNote={The authors used x-ray absorption spectroscopy of the O K edge to investigate the nanocrystalline structure of thin HfO2 films deposited by remote plasma enhanced chemical vapor deposition on Ge(100). Postdeposition thermal process induced the interfacial reconstruction and the crystallization of the HfO2 in the monoclinic structure driven by the Ge(100) substrate. The substrate templating of the HfO2 crystallization is an evidence that the processing used here removes the undesired the interfacial layer and has the potential to yield interfaces with low density of defects.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Bastos, Karen Paz and Miotti, Leonardo and Lucovsky, Gerald and Chung, Kwun-Bum and Nordlund, Dennis}, year={2010}, pages={662–664} }
 @article{lucovsky_chung_miotti_bastos_amado_schlom_2009, title={Comparisons between intrinsic bonding defects in d(0) transition metal oxide such as HfO2, and impurity atom defects in d(0) complex oxides such as GdScO3}, volume={53}, ISSN={["1879-2405"]}, DOI={10.1016/j.sse.2009.10.012}, abstractNote={This article addresses O-atom vacancy defects in the d0 transition metal (TM) oxides HfO2 and TiO2, and Ti substitutions for Sc in the d0 complex oxide GdScO3. In each instance this results in occupied TM atoms with d1 state representations. These are important for different aspects of the ultimate scaling limits for performance and functionality in nano-scale Si devices. The occupancy of d1 states is cast in terms of many-electron theory in order to determine the effects of correlation on device performance and functionality. The first section of this article identifies equivalent d-state representations using on an ionic model for the effective valence states of Ti and Hf atoms bordering on O-atom vacancy defects. Removal of an O atom to create a neutral vacancy; this is equivalent to the bonding of two electrons to each vacancy site. This give rise to two coupled d1 states for a mono-vacancy defect. Transitions from these occupied states generate spectroscopic features in the (i) pre-edge shake-up, and (ii) virtual bound state (VBS) shake-off energy regimes in O K edge XAS spectra. The number of states confirm that these are mono-vacancy defects. The second section addresses incorporation of Ti tetravalent impurities into trivalent GdScO3, forcing Ti into a Ti3+ state and generating a d1 electronic structure. Vacancy defect concentrations in HfO2 are generally <1019 cm−3. However, the Ti solubility in GdScO3 is higher, and relative concentrations in excess of 16–17% lead to an insulator to metal transition with a ferri-magnetic electronic structure.}, number={12}, journal={SOLID-STATE ELECTRONICS}, author={Lucovsky, Gerald and Chung, Kwun-Bum and Miotti, Leonardi and Bastos, Karen Pas and Amado, Carolina and Schlom, Darrell}, year={2009}, month={Dec}, pages={1273–1279} }