skip to main content

Title: Searching for a route to synthesize in situ epitaxial Pr2Ir2O7 thin films with thermodynamic methods
Abstract

In situ growth of pyrochlore iridate thin films has been a long-standing challenge due to the low reactivity of Ir at low temperatures and the vaporization of volatile gas species such as IrO3(g) and IrO2(g) at high temperatures and highPO2. To address this challenge, we combine thermodynamic analysis of the Pr-Ir-O2system with experimental results from the conventional physical vapor deposition (PVD) technique of co-sputtering. Our results indicate that only high growth temperatures yield films with crystallinity sufficient for utilizing and tailoring the desired topological electronic properties and the in situ synthesis of Pr2Ir2O7thin films is fettered by the inability to grow withPO2on the order of 10 Torr at high temperatures, a limitation inherent to the PVD process. Thus, we suggest techniques capable of supplying high partial pressure of key species during deposition, in particular chemical vapor deposition (CVD), as a route to synthesis of Pr2Ir2O7.

Authors:
; ; ; ; ; ;
Award ID(s):
1825538 1720415
Publication Date:
NSF-PAR ID:
10307550
Journal Name:
npj Computational Materials
Volume:
7
Issue:
1
ISSN:
2057-3960
Publisher:
Nature Publishing Group
Sponsoring Org:
National Science Foundation
More Like this
  1. Herein, we describe an atomic layer deposition (ALD) system that is optimized for the growth of thin films on high-surface-area, porous materials. The system incorporates a moveable dual-zone furnace allowing for rapid transfer of a powder substrate between heating zones whose temperatures are optimized for precursor adsorption and oxidative removal of the precursor ligands. The reactor can both be evacuated, eliminating the need for a carrier gas during precursor exposure, and rotated, to enhance contact between a powder support and the gas phase, both of which help us to minimize mass transfer limitations in the pores during film growth. The capabilities of the ALD system were demonstrated by growing La2O3, Fe2O3, and LaFeO3films on a 120 m2 g−1MgAl2O4powder. Analysis of these films using scanning transmission electron microscopy and temperature-programmed desorption of 2-propanol confirmed the conformal nature of the oxide films.

  2. High crystalline quality thick β-Ga2O3drift layers are essential for multi-kV vertical power devices. Low-pressure chemical vapor deposition (LPCVD) is suitable for achieving high growth rates. This paper presents a systematic study of the Schottky barrier diodes fabricated on four different Si-doped homoepitaxial β-Ga2O3thin films grown on Sn-doped (010) and (001) β-Ga2O3substrates by LPCVD with a fast growth rate varying from 13 to 21  μm/h. A higher temperature growth results in the highest reported growth rate to date. Room temperature current density–voltage data for different Schottky diodes are presented, and diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage are studied. Temperature dependence (25–250 °C) of the ideality factor, barrier height, and specific on-resistance is also analyzed from the J–V–T characteristics of the fabricated Schottky diodes.

  3. Abstract

    Quantum spin systems such as magnetic insulators usually show magnetic order, but such classical states can give way toquantum liquids with exotic entanglementthrough two known mechanisms of frustration: geometric frustration in lattices with triangle motifs, and spin-orbit-coupling frustration in the exactly solvable quantum liquid of Kitaev’s honeycomb lattice. Here we present the experimental observation of a new kind of frustrated quantum liquid arising in an unlikely place: the magnetic insulator Ba4Ir3O10where Ir3O12trimers form an unfrustrated square lattice. The crystal structure shows no apparent spin chains. Experimentally we find a quantum liquid state persisting down to 0.2 K that is stabilized by strong antiferromagnetic interaction with Curie–Weiss temperature ranging from −766 to −169 K due to magnetic anisotropy. The anisotropy-averaged frustration parameter is 2000, seldom seen in iridates. Heat capacity and thermal conductivity are both linear at low temperatures, a familiar feature in metals but here in an insulator pointing to an exotic quantum liquid state; a mere 2% Sr substitution for Ba produces long-range order at 130 K and destroys the linear-T features. Although the Ir4+(5d5) ions in Ba4Ir3O10appear to form Ir3O12trimers of face-sharing IrO6octahedra, we propose that intra-trimer exchange is reduced and the lattice recombines into an array of coupled 1Dmore »chains with additional spins. An extreme limit of decoupled 1D chains can explain most but not all of the striking experimental observations, indicating that the inter-chain coupling plays an important role in the frustration mechanism leading to this quantum liquid.

    « less
  4. Abstract

    We report quantum phenomena in spin-orbit-coupled single crystals that are synthesized using an innovative technology that “field-alters” crystal structures via application of magnetic field during crystal growth. This study addresses a major challenge facing the research community today: A great deal of theoretical work predicting exotic states for strongly spin-orbit-coupled, correlated materials has thus far met very limited experimental confirmation. These conspicuous discrepancies are due in part to the extreme sensitivity of these materials to structural distortions. The results presented here demonstrate that the field-altered materials not only are much less distorted but also exhibit phenomena absent in their non-altered counterparts. The field-altered materials include an array of4dand5dtransition metal oxides, and three representative materials presented here are Ba4Ir3O10, Ca2RuO4, and Sr2IrO4. This study provides an approach for discovery of quantum states and materials otherwise unavailable.

  5. Abstract

    A multistep deposition technique is developed to produce highly oriented diamond films by hot filament chemical vapor deposition (HFCVD) on Si (111) substrates. The orientation is produced by use of a thin, 5–20 nm, Ni interlayer. Annealing studies demonstrate diffusion of Ni into Si to form nickel silicides with crystal structure depending on temperature. The HFCVD diamond film with Ni interlayer results in reduced non-diamond carbon, low surface roughness, high diamond crystal quality, and increased texturing relative to growth on bare silicon wafers. X-ray diffraction results show that the diamond film grown with 10 nm Ni interlayer yielded 92.5% of the diamond grains oriented along the (110) crystal planes with ~ 2.5 µm thickness and large average grain size ~ 1.45 µm based on scanning electron microscopy. Texture is also observed to develop for ~ 300 nm thick diamond films with ~ 89.0% of the grains oriented along the (110) crystal plane direction. These results are significantly better than diamond grown on Si (111) without Ni layer with the same HFCVD conditions. The oriented growth of diamond film on Ni interlayers is explained by a proposed model wherein the nano-diamond seeds becoming oriented relative to the β1-Ni3Si that forms during the diamond nucleation period. The model also explains the silicidation and diamond growthmore »processes.

    Article Highlights

    High quality diamond film with minimum surface roughness and ~93% oriented grains along (110) crystallographic direction is grown on Si substrate using a thin 5 to 20 nm nickel layer.

    A detailed report on the formation of different phases of nickel silicide, its stability with different temperature, and its role for diamond film texturing at HFCVD growth condition is presented.

    A diamond growth model on Si substrate with Ni interlayer to grow high quality-oriented diamond film is established.

    « less