Crystal-Amorphous Transformation Via Defect-Templating in Phase-Change Materials

Phase-change materials (PCM) such as GeTe and Ge-Sb-Te alloys are potential candidates for non-volatile memory applications, because they can reversibly and rapidly transform between a crystalline phase and an amorphous phase with medium-range order. Traditionally, crystal-amorphous transformation in these materials has been carried out via melt-quench pathway, where the crystalline phase is heated beyond its melting point by the rising edge of an electric pulse, and the melt phase is quenched by the falling edge into a glassy phase. Formation of an intermediate melt phase in this transformation pathway requires usage of large switching current densities, resulting in energy wastage, and device degradation issues. Furthermore, melt-quench pathway is a brute force strategy of amorphizing PCM, and does not utilize the peculiar structural properties in crystalline phase. It will be beneficial from a device perspective that crystal-amorphous transformation is carried out via subtler solid-state pathways. Single-crystalline nanowire phase-change memory, owing to its lateral geometry and large volumes of active material, offers a platform to construct a crystal-amorphous transformation pathway via gradually increasing disorder in the crystalline phase, and study it. Using in situ transmission electron microscopy on GeTe and Ge2Sb2Te5 systems, we showed that the application of an electric pulse (heat-shock) creates dislocations in the PCM that migrate with the hole-wind force, and interact with the already existing ferroelectric boundaries in case of GeTe, changing their nature. We adapted novel tools such as optical second harmonic generation polarimety to carefully study these defect interactions. These defects accumulate at a region of local inhomogeneity, and upon addition of defects beyond a critical limit to that region via electrical pulsing, an amorphous phase nucleates . We also studied the effect of defect dynamics on carrier transport using temperature dependent transport measurements in GeTe, which transforms from a metal to a weakly localized metal to finally an Andersons insulator, upon defect accumulation, prior to amorphization. Taking lessons from these fundamental studies, we defect-engineered GeTe into insulating crystalline states as the starting crystalline states, and demonstrated orders of magnitude drop in the power densities required for switching, compared with those required for melt-quench pathway

DEVELOPMENT OF ABUSE DETERRENT FORMULATIONS USING HOT MELT EXTRUSION

In recent years prescription drug diversion, misuse, abuse represent a growing problem for the United States. Oral ingestion, snorting, injection are most commonly employed routes of abuse. To circumvent this problem hot melt extrusion (HME) was employed to prepare abuse deterrent formulation (ADF). Abuse Deterrent Immediate Release Egg-Shaped Tablet Using 3D Printing Technology: Quality by Design to Optimize Drug Release and Extraction. In current work, we developed egg-shaped tablet (egglet) using fused deposition modeling (FDM) 3D printing. Drug-loaded polymeric filaments (1.5 mm) were prepared using HME followed by printing into egglets of different sizes and infill densities. Based on printability, crush resistance polyvinyl alcohol (PVA) was used further. Later, egglets were evaluated for abuse deterrence properties based on USFDA guidance. A multifactorial design was used to optimize solvent extraction, drug release. Extreme hardness (\u3e 500 N), large particle size (\u3e 1 mm) on mechanical manipulation established snorting deterring property while \u3c20% drug extraction in 5 min (% Sext) demonstrated deterrence for injection abuse. Quality target product profile D85 \u3c 30 min, % Sext \u3c 20 was achieved with egglets of 6 mm diameter, 45% infill density, 15% w/w drug loading. Development of Multi-dose Oral Abuse Deterrent Formulation of Loperamide Using Hot melt extrusion. Loperamide, an over the counter anti-diarrheal drug, also referred as poor man\u27s methadone . Abusers consume more than 30 tablets to achieve euphoria and to combat opioid withdrawal. But supratherapeutic doses causes respiratory depression, cardiac dysrhythmia, mortality. Aim is designing a tablet which can immediate release loperamide in diarrheic patients (single tablet) while stops release in case of intentional multi-dose ingestion. Loperamide was molecularly dispersed into gastric soluble cationic polymers - Eudragit® EPO, Kollicoat® Smartseal 100P using HME to obtain filament. Filaments were milled and compressed into tablets ((Eudragit® EPO (SJU1) and Kollicoat® Smartseal (SJU2)) with optimized amount of L-arginine. Dissolution in 250 mL of Fasted state simulated gastric fluid (FaSSGF) revealed that single tablet of Imodium® (marketed formulation) and SJU1 showed \u3e85% of release in 15 min. In multi-unit dissolution (15 tablets), Imodium® exhibited \u3e90% release but SJU tablets showed \u3c5% of release thus demonstrating its ability to deter multi-dose oral abuse

Giant electrostriction in bulk RE (III) substituted CeO2: effect of RE 3+ and its concentration

Recent discovery of giant electrostriction in rare earth (RE (III)) substituted ceria (CeO2) thin films driven by electroactive defect complexes and their coordinated elastic response, expands the material spectrum for electrostrain applications beyond the conventional piezoelectric materials. Especially Gd substituted CeO2, with Gd concentration >10% seems to be an ideal material to obtain such large electrostrain response. However, there are not many experimental studies that systematically investigate the effect of RE (III) ion-defect interaction and RE concentration on electrostriction. Here we perform structure-property correlation studies in bulk ceramics of RE3+ substituted ceria doped with RE=Y, La and Gd at various concentrations upto a maximum of 20%, to understand the features responsible for giant electrostriction. Our results show that Y substituted ceria, with atleast 20% Y substitution, is clearly both a giant M and a Q electrostrictor at low frequencies (<20 Hz), and this correlates with the unique attractive defect-dopant interaction of Y with oxygen vacancies. La has a repulsive interaction with oxygen vacancies, and La doped ceria at all the studied compositions (upto 20%) does not show giant electrostiction. Gd has a neutral interaction, and only 20% Gd doped ceria at best falls at the border of classification between giant and non-giant electrostrictors at frequencies <0.05 Hz. Our work takes a step back from thin-films and assesses the fundamental defect features required in the design of giant electrostrictors.Comment: 11 pages, 8 figure

Structure and magnetic properties of epitaxial CaFe2O4 thin films

CaFe2O4 is a highly anisotropic antiferromagnet reported to display two spin arrangements with up-up-down-down (phase A) and up-down-up-down (phase B) configurations. The relative stability of these phases is ruled by the competing ferromagnetic and antiferromagnetic interactions between Fe3+ spins arranged in two different environments, but a complete understanding of the magnetic structure of this material does not exist yet. In this study we investigate epitaxial CaFe2O4 thin films grown on TiO2 (110) substrates by means of Pulsed Laser Deposition (PLD). Structural characterization reveals the coexistence of two out-of-plane crystal orientations and the formation of three in-plane oriented domains. The magnetic properties of the films, investigated macroscopically as well as locally, including highly sensitive Mossbauer spectroscopy, reveal the presence of just one order parameter showing long-range ordering below T = 185 K and the critical nature of the transition. In addition, a non-zero in-plane magnetization is found, consistent with the presence of uncompensated spins at phase or domain boundaries, as proposed for bulk samples.Comment: Changes are made to take into account the newly published paper by Songvilay et al. (PRB 101,014407) Changes are in last sentence of the abstract, 5th paragraph of the discussion section and conclusions paragrap

Robust atmospherically stable hybrid SrVO3/Graphene//SrTiO3 template for fast and facile large-area transfer of complex oxides onto Si

Heterogenous integration of complex epitaxial oxides onto Si and other target substrates is recently gaining traction. One of the popular methods involves growing a water-soluble and highly reactive sacrificial buffer layer, such as Sr3Al2O6 (SAO) at the interface, and a functional oxide on top of this. To improve the versatility of layer transfer techniques, it is desired to utilize stable (less reactive) sacrificial layers, without compromising on the transfer rates. In this study, we utilized a combination of chemical vapor deposited (CVD) graphene as a 2D material at the interface and pulsed laser deposited (PLD) water-soluble SrVO3 (SVO) as a sacrificial buffer layer. We show that the graphene layer enhances the dissolution rate of SVO over ten times without compromising its atmospheric stability. We demonstrate the versatility of our hybrid template by growing ferroelectric BaTiO3 (BTO) via PLD and Pb(Zr, Ti)O3 (PZT) via Chemical Solution Deposition (CSD) technique and transferring them onto the target substrates and establishing their ferroelectric properties. Our hybrid templates allow for the realization of the potential of complex oxides in a plethora of device applications for MEMS, electro-optics, and flexible electronics.Comment: 35 pages, 23 figure

Direct Epitaxial Growth of Polar (1-x)HfO2-(x)ZrO2 Ultrathin Films. on Silicon

Ultra-thin Hf1-xZrxO2 films have attracted tremendous interest owing to their Si-compatible ferroelectricity arising from polar polymorphs. While these phases have been grown on Si as polycrystalline films, epitaxial growth was only achieved on non-Si substrates. Here we report direct epitaxy of polar phases on Si using pulsed laser deposition enabled via in situ scavenging of the native a-SiOx under ballistic conditions. On Si (111), polar rhombohedral (r)-phase and bulk monoclinic (m-) phase coexist, with the volume of the former increasing with increasing Zr concentration. R-phase is stabilized in the regions with a direct connection between the substrate and the film through the compressive strain provided by an interfacial crystalline c-SiO2 layer., The film relaxes to a bulk m-phase in regions where a-SiOx regrows. On Si (100), we observe polar orthorhombic o-phase coexisting with m-phase, stabilized by inhomogeneous strains at the intersection of monoclinic domains. This work provides fundamental insight into the conditions that lead to the preferential stabilization of r-, o- and m-phases.Comment: 18 pages of manuscript, 7 figure

Crystallization of GeO2 thin films into α-quartz: From spherulites to single crystals

Piezoelectric quartz (SiO2) crystals are widely used in industry as oscillators. As a natural mineral, quartz and its relevant silicates are also of interest in geoscience and mineralogy. However, the nucleation and growth of quartz crystals are difficult to control and not fully understood. Here we report successful solid-state crystallization of thin film of amorphous GeO2 into quartz on various substrates, including Al2O3, MgAl2O4, MgO, LaAlO3 and SrTiO3. At relatively low annealing temperatures, the crystallization process is spherulitic: with fibers growing radially from the nucleation centers and the crystal lattice rotating along the growth direction with a linear dependence between the rotation angle and the distance to the core. For increasingly higher annealing temperatures, quartz crystals begin to form. The edges of the sample play an important role in facilitating nucleation followed by growth sweeping inward until the whole film is crystallized. Control of the growth allows single crystalline quartz to be synthesized, with crystal sizes of hundreds of microns achieved on sapphire substrates, which is promising for further piezoelectric applications. Our study reveals the complexity of the nucleation and growth process of quartz and provides insight for further studies

Guidelines for the stabilization of a polar rhombohedral phase in epitaxial Hf0.5Zr0.5O2 thin films

The unconventional Si-compatible ferroelectricity in hafnia-based systems, which becomes robust only at nanoscopic sizes, has attracted a lot of interest. While a metastable polar orthorhombic (o-) phase (Pca21) is widely regarded as the responsible phase for ferroelectricity, a higher energy polar rhombohedral (r-) phase is recently reported on epitaxial HfZrO4 (HZO) films grown on (001) SrTiO3 (R3m or R3), (0001) GaN (R3), and Si (111). Armed with results on these systems, here we report a systematic study leading towards identifying comprehensive global trends for stabilizing r-phase polymorphs in epitaxially grown HZO thin films (6 nm) on various substrates (perovskites, hexagonal and Si).Comment: Final version as it appears in the 50th Anniversary issue of Ferroelectric