J. G. Lozano

Chemical and structural investigation of the role of both Mn and Mn oxide in the formation of manganese silicate barrier layers on SiO2

In this study, Mn silicate (MnSiO3) barrier layers were formed on thermally grown SiO2 using both metallic Mn and oxidized Mn films, in order to investigate the role of oxygen in determining the extent of the interaction between the deposited Mn and the SiO2 substrate. Using x-ray photoelectron spectroscopy, it has been shown that a metallic Mn film with an approximate thickness of 1 nm cannot be fully converted to Mn silicate following vacuum annealing to 500 °C. Transmission electron microscopy (TEM) analysis suggests the maximum MnSiO3 layer thickness obtainable using metallic Mn is ∼1.7 nm. In contrast, a ∼1 nm partially oxidized Mn film can be fully converted to Mn silicate following thermal annealing to 400 °C, forming a MnSiO3 layer with a measured thickness of 2.6 nm. TEM analysis also clearly shows that MnSiO3 growth results in a corresponding reduction in the SiO2 layer thickness. It has also been shown that a fully oxidized Mn oxide thin film can be converted to Mn silicate, in the absence of m...

The dissociation of the [a + c] dislocation in GaN

In 1952, Cottrell proposed that the Lomer dislocation formed by interaction of two glide dislocations in a fcc crystal could transform into an immobile dislocation by dissociation into partial dislocations bounding a stacking fault, causing a block to further slip, a concept important in work hardening. Evidence for this and many other dissociations has been provided by the diffraction contrast technique and in particular by its ‘weak beam’ variant, which has a resolution limit of about 15 angstroms. Today, with the advent of aberration corrected microscopes it is possible to determine directly the atomic structure of the faults and partial dislocations. In this paper, we describe the results of a study using the High Angle Angular Dark Field technique (HAADF) in an aberration corrected scanning transmission electron microscope (STEM), of the dissociation of the [a + c] dislocations in (0 0 0 1) GaN films grown on sapphire substrates. The dislocations are found to be inclined with respect to the c-axis, but optical sectioning imaging methods allow the structure to be determined and an estimate of the tilt angle to be made. The dislocations are found to be dissociated by climb and glide on the a plane and the STEM results, and structural arguments supported by theoretical calculations suggest that the dissociation reaction is [a + c] = 1/2[a + c] + 1/2[a + c] + fault. The structure of the fault is found to be similar to that identified in 1965 by Drum in AlN but frequently modified by steps due to kinks in the inclined dislocation.

Scanning transmission electron microscopy investigations of self-forming diffusion barrier formation in Cu(Mn) alloys on SiO2

Scanning transmission electron microscopy in high angle annular dark field mode has been used to undertake a characterisation study with sub-nanometric spatial resolution of the barrier formation process for a Cu(Mn) alloy (90%/10%) deposited on SiO2. Electron energy loss spectroscopy (EELS) measurements provide clear evidence for the expulsion of the alloying element to the dielectric interface as a function of thermal annealing where it chemically reacts with the SiO2. Analysis of the Mn L23 intensity ratio in the EELS spectra indicates that the chemical composition in the barrier region which has a measured thickness of 2.6 nm is MnSiO3.

Chemical and structural investigations of the interactions of Cu with MnSiO3 diffusion barrier layers

X-ray photoelectron spectroscopy (XPS) has been used to investigate the thermodynamic stability of Cu layers deposited onto Mn silicate (MnSiO3) barrier layers formed on SiO2 surfaces. Using a fully in situ growth and analysis experimental procedure, it has been shown that ∼1 nm Cu layers do not chemically react with ultra thin (∼2.6 nm) MnSiO3 surfaces following 400 °C annealing, with no evidence for the growth of Cu oxide species, which are known to act as an intermediate step in the Cu diffusion process into silica based dielectrics. The effectiveness of MnSiO3 as a barrier to Cu diffusion following high temperature annealing was also investigated, with electron energy loss spectroscopy suggesting that a ∼2.6 nm MnSiO3 layer prevents Cu diffusion at 400 °C. The chemical composition of a barrier layer formed following the deposition of a partially oxidised Mn (MnOx)/Cu alloy was also investigated using XPS in order to determine if the presence of Cu at the Mn/SiO2 interface during MnSiO3 growth inherent...

Oxygen redox chemistry without excess alkali-metal ions in Na2/3[Mg0.28Mn0.72]O2

The search for improved energy-storage materials has revealed Li- and Na-rich intercalation compounds as promising high-capacity cathodes. They exhibit capacities in excess of what would be expected from alkali-ion removal/reinsertion and charge compensation by transition-metal (TM) ions. The additional capacity is provided through charge compensation by oxygen redox chemistry and some oxygen loss. It has been reported previously that oxygen redox occurs in O 2p orbitals that interact with alkali ions in the TM and alkali-ion layers (that is, oxygen redox occurs in compounds containing Li+-O(2p)-Li+ interactions). Na2/3[Mg0.28Mn0.72]O2 exhibits an excess capacity and here we show that this is caused by oxygen redox, even though Mg2+ resides in the TM layers rather than alkali-metal (AM) ions, which demonstrates that excess AM ions are not required to activate oxygen redox. We also show that, unlike the alkali-rich compounds, Na2/3[Mg0.28Mn0.72]O2 does not lose oxygen. The extraction of alkali ions from the alkali and TM layers in the alkali-rich compounds results in severely underbonded oxygen, which promotes oxygen loss, whereas Mg2+ remains in Na2/3[Mg0.28Mn0.72]O2, which stabilizes oxygen.

Chemical and structural investigations of the incorporation of metal manganese into ruthenium thin films for use as copper diffusion barrier layers

The incorporation of manganese into a 3 nm ruthenium thin-film is presented as a potential mechanism to improve its performance as a copper diffusion barrier. Manganese (∼1 nm) was deposited on an atomic layer deposited Ru film, and the Mn/Ru/SiO2 structure was subsequently thermally annealed. X-ray photoelectron spectroscopy studies reveal the chemical interaction of Mn with the SiO2 substrate to form manganese-silicate (MnSiO3), implying the migration of the metal through the Ru film. Electron energy loss spectroscopy line profile measurements of the intensity of the Mn signal across the Ru film confirm the presence of Mn at the Ru/SiO2 interface.

Degradation Mechanisms at the Li10GeP2S12/LiCoO2 Cathode Interface in an All-Solid-State Lithium-Ion Battery

All-solid-state batteries (ASSBs) show great potential for providing high power and energy densities with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high-performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode/electrolyte interfaces is pivotal. While the lithium metal/solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO2 cathode and the Li10GeP2S12 solid electrolyte interface. Indium and Li4Ti5O12 are used as anode materials to avoid the instability problems associated with Li-metal anodes. Capacity fading and increased impedances are observed during long-term cycling. Postmortem analysis with scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy show that electrochemically driven mechanical failure and degradation at the cathode/solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode/SE interfaces are crucial for achieving reliable SSB performance.

Observation of depth-dependent atomic displacements related to dislocations in GaN by optical sectioning in the STEM

We demonstrate that it is possible to observe depth-dependent atomic displacements in a GaN crystal due to the sufficiently small depth of field achievable in the aberration-corrected scanning transmission electron microscope. The depth-dependent displacements associated with the Eshelby twist of screw dislocations in GaN viewed end on are directly imaged, and makes possible the determination of the sign of the Burgers vector of the dislocation. The experimental results are in good agreement with theoretical images.

(S)TEM analysis of the interdiffusion and barrier layer formation in Mn/Cu heterostructures on SiO2 for interconnect technologies

Mn/Cu heterostructures thermally evaporated onto SiO2 and subsequently annealed were investigated by transmission electron microscopy (TEM) related techniques in order to study the diffusion interactions which lead to barrier layer formation. Electron energy loss spectroscopy provide evidence for the interdiffusion between the Mn and Cu layers following a 450 °C anneal, where the Mn diffuses towards the surface of the structure, while Cu diffuses towards the Mn/SiO2, surrounding metallic Mn clusters but not propagating into the dielectric. The chemical composition of the 2-3 nm interfacial layer is primarily a mixture of +2 and +3 Mn valencies, in good agreement with previously reported results.

The addition of aluminium and manganese to ruthenium liner layers for use as a copper diffusion barrier

The chemical interaction of Al and Mn deposited on Ru thin films for use as copper diffusion barrier layers are assessed in-situ using x-ray photoelectron spectroscopy (XPS). Thin (~1-2 nm) Al and Mn films were separately deposited on 3 nm Ru liner layers on SiO₂, and both Al/Ru/SiO₂ and Mn/Ru/SiO₂ structures were subsequently thermally annealed. Results indicate the diffusion of both metals through the Ru thin films and the subsequent chemical interaction with the underlying SiO₂ substrate to form Al₂O₃ and MnSiO₃. In both cases, the reduction of SiO₂ leads to the release of Si from the dielectric and the upward diffusion of Si into the Ru liner layers.