Stability of the Interface Between LIPON and LCO During TEM Sample Preparation by FIB.

An amorphous interphase between lithium phosphorus oxynitride (LIPON) solid electrolyte and lithium cobalt oxide (LCO) has been reported recently in several electron microscopy studies of Li ion thin-film micro-batteries (TFMB), along with its implications to battery operation. However, the origin of the observed interphase at the as-made LIPON/LCO interface remained obscure. In this work, this interface has been characterized comprehensively by scanning electron microscope (SEM) imaging at all steps of the in situ focused ion beam (FIB) lift-out procedure for transmission electron microscopy (TEM) sample preparation. It was found that the interphase is formed during TEM lamella preparation when the portion of LIPON layer contained within the lamella is physically disconnected from the rest of the LIPON layer by FIB. Therefore, it was demonstrated that a disordered interphase can form in LCO at its interface with LIPON during TEM sample preparation by the FIB lift-out procedure and that subtle nature of the interphase formation makes it likely to go unnoticed during the preparation. This interphase was not produced even after galvanostatic charging of a battery with a Li metal anode but inevitably appeared after the FIB lift-out of that sample.

Nucleation and early stage crystallization in barium disilicate glass.

Barium disilicate is one of the glass-ceramic systems where internal nucleation and crystallization can occur from quenched glass upon heat treatment without requiring nucleating agents. The structural origin of the nano-clusters formed during low temperature heat treatment is of great interest in gaining a fundamental understanding of nucleation kinetics in silicate glasses. Here, we present experimental investigations on the low temperature heat treatment of barium disilicate (BaO·2SiO2) glass. Several experimental techniques were used to characterize the structural nature of barium disilicate glasses that were heat treated between the glass transition temperature, Tg, and the peak temperature of crystal growth, Tcr. The data show that small amounts of crystallites including BaSi2O5 as well as other higher Ba/Si ratio phases are formed. Moreover, unlike that reported for lower BaO content (BaO<33mol%) barium silicate glass or the analogous Li2O-SiO2 glasses, no clear evidence is observed for liquid/liquid phase separation in barium disilicate glass.

Interferometric Diffraction from Amorphous Double Films.

We explore the interference fringes that arise in diffraction patterns from double-layer amorphous samples where there is a substantial separation, up to about a micron, between two overlapping thin films. This interferometric diffraction geometry, where both waves have interacted with the specimen, reveals phase gradients within microdiffraction patterns. The rapid fading of the observed fringes as the magnitude of the diffraction vector increases confirms that displacement decoherence is strong in high-energy electron scattering from amorphous samples. The fading of fringes with increasing layer separation indicates an effective illumination coherence length of about 225 nm, which is consistent with the value of 270 nm expected for the heated Schottky field emitter source. A small reduction in measured coherence length is expected because of the additional energy spread induced in the beam after it passes through the first layer.

Speckle Suppression by Decoherence in Fluctuation Electron Microscopy.

We compare experimental fluctuation electron microscopy (FEM) speckle data with electron diffraction simulations for thin amorphous carbon and silicon samples. We find that the experimental speckle intensity variance is generally more than an order of magnitude lower than kinematical scattering theory predicts for spatially coherent illumination. We hypothesize that decoherence, which randomizes the phase relationship between scattered waves, is responsible for the anomaly. Specifically, displacement decoherence can contribute strongly to speckle suppression, particularly at higher beam energies. Displacement decoherence arises when the local structure is rearranged significantly by interactions with the beam during the exposure. Such motions cause diffraction speckle to twinkle, some of it at observable time scales. We also find that the continuous random network model of amorphous silicon can explain the experimental variance data if displacement decoherence and multiple scattering is included in the modeling. This may resolve the longstanding discrepancy between X-ray and electron diffraction studies of radial distribution functions, and conclusions reached from previous FEM studies. Decoherence likely affects all quantitative electron imaging and diffraction studies. It likely contributes to the so-called Stobbs factor, where high-resolution atomic-column image intensities are anomalously lower than predicted by a similar factor to that observed here.

Phase separation in mullite-composition glass.

Aluminosilicates (AS) are ubiquitous in ceramics, geology, and planetary science, and their glassy forms underpin vital technologies used in displays, waveguides, and lasers. In spite of this, the nonequilibrium behavior of the prototypical AS compound, mullite (40SiO2-60Al2O3, or AS60), is not well understood. By deeply supercooling mullite-composition liquid via aerodynamic levitation, we observe metastable liquid-liquid unmixing that yields a transparent two-phase glass, comprising a nanoscale mixture of AS7 and AS62. Extrapolations from X-ray scattering measurements show the AS7 phase is similar to vitreous SiO2 with a few Al species substituted for Si. The AS62 phase is built from a highly polymerized network of 4-, 5-, and 6-coordinated AlOx polyhedra. Polymerization of the AS62 network and the composite morphology provide essential mechanisms for toughening the glass.

Ultrathin Metals on a Transparent Seed and Application to Infrared Reflectors.

Ultrathin metal films (UTMFs) are widely used in optoelectronic applications, from transparent conductors to photovoltaic cells, low emissivity windows, and plasmonic metasurfaces. During the initial deposition phase, many metals tend to form islands on the receiving substrate rather than a physically connected (percolated) network, which eventually evolves into continuous films as the thickness increases. For example, in the case of Ag and Au on dielectric surfaces, percolation begins when the thickness of the metal film is at least about 5 nm. It is known that the type of growth can be changed when a proper seed layer is used. Here, we show that a CuO layer directly deposited on a substrate can dramatically influence surface wetting and promote early percolation of polycrystalline Ag and Au UTMFs. We demonstrate that the proposed seed is effective even when its thickness is sub-nanometric, in this way maintaining the full transparency of the receiving substrate. The Ag and Au films seeded with CuO showed a percolation thickness close to 1 nm and were morphologically and optically characterized from an ultraviolet (λ = 300 nm) to a midinfrared (λ = 15 µm) wavelength. Infrared reflectors, a mirror and a resonant plasmonic structure, were also demonstrated and uniquely tuned by electrical gating, this being possible owing to the small thickness of the constituting Au UTMF.

Nucleation pathways in barium silicate glasses.

Nucleation is generally viewed as a structural fluctuation that passes a critical size to eventually become a stable emerging new phase. However, this concept leaves out many details, such as changes in cluster composition and competing pathways to the new phase. In this work, both experimental and computer modeling studies are used to understand the cluster composition and pathways. Monte Carlo and molecular dynamics approaches are used to analyze the thermodynamic and kinetic contributions to the nucleation landscape in barium silicate glasses. Experimental techniques examine the resulting polycrystals that form. Both the modeling and experimental data indicate that a silica rich core plays a dominant role in the nucleation process.

Fluctuation electron microscopy study of crystal nucleation in TiO2-SiO2 glass with heat treatment.

We have used fluctuation electron microscopy (FEM) to investigate the nucleation stage of TiO2 crystal formation in binary TiO2-SiO2 glasses with heat treatment. It was found that spatial fluctuations of electron scattering in the glass with 13 wt% TiO2 increases with heat treatment above 800 °C but before any crystals precipitate, i.e. before crystals are detectable by electron diffraction. We have attributed this to TiO2 clustering and increasing medium-range order due to gradual ordering of TiO2 phase. Moreover, we have found that FEM is sensitive to structural changes at temperatures as low as 400 °C but the nature of the changes yet to be determined. This demonstrates that FEM can be sensitive to structural changes in oxide glasses occurring during thermal treatment but preceding detection of the first crystals.