Material properties of Ga–Sb binary alloy thin films deposited under ultra-high vacuum conditions were studied for analog phase change memory (PCM) applications. Crystallization of this alloy was shown to occur in the temperature range of 180–264 °C, with activation energy >2.5 eV depending on the composition. X-ray diffraction (XRD) studies showed phase separation upon crystallization into two phases, Ga-doped A7 antimony and cubic zinc-blende GaSb. Synchrotron in situ XRD analysis revealed that crystallization into the A7 phase is accompanied by Ga out-diffusion from the grains. X-ray absorption fine structure studies of the local structure of these alloys demonstrated a bond length decrease with a stable coordination number of 4 upon amorphous-to-crystalline phase transformation. Mushroom cell structures built with Ga–Sb alloys on ø110 nm TiN heater show a phase change material resistance switching behavior with resistance ratio >100 under electrical pulse measurements. TEM and Energy Dispersive Spectroscopy (EDS) studies of the Ga–Sb cells after ∼100 switching cycles revealed that partial SET or intermediate resistance states are attained by the variation of the grain size of the material as well as the Ga content in the A7 phase. A mechanism for a reversible composition control is proposed for analog cell performance. These results indicate that Te-free Ga–Sb binary alloys are potential candidates for analog PCM applications.
more »
« less
A Facile Aqueous Solution Route for the Growth of Chalcogenide Perovskite BaZrS3 Films
The prototypical chalcogenide perovskite, BaZrS3 (BZS), with its direct bandgap of 1.7–1.8 eV, high chemical stability, and strong light–matter interactions, has garnered significant interest over the past few years. So far, attempts to grow BaZrS3 films have been limited mainly to physical vapor deposition techniques. Here, we report the fabrication of BZS thin films via a facile aqueous solution route of polymer-assisted deposition (PAD), where the polymer-chelated cation precursor films were sulfurized in a mixed CS2 and Ar atmosphere. The formation of a single-phase polycrystalline BZS thin film at a processing temperature of 900 °C was confirmed by X-ray diffraction and Raman spectroscopy. The stoichiometry of the films was verified by Rutherford Backscattering spectrometry and energy-dispersive X-ray spectroscopy. The BZS films showed a photoluminescence peak at around 1.8 eV and exhibited a photogenerated current under light illumination at a wavelength of 530 nm. Temperature-dependent resistivity analysis revealed that the conduction of BaZrS3 films under the dark condition could be described by the Efros–Shklovskii variable range hopping model in the temperature range of 60–300 K, with an activation energy of about 44 meV.
more »
« less
- NSF-PAR ID:
- 10418625
- Date Published:
- Journal Name:
- Photonics
- Volume:
- 10
- Issue:
- 4
- ISSN:
- 2304-6732
- Page Range / eLocation ID:
- 366
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Applications in soft, flexible optical, and optoelectronic applications demand polymer thin film coatings that can accommodate substantial physical deformations. The preparation of high refractive index polymers (HRIPs) through the quaternization of poly(4‐vinylpyridine) (P4VP) thin films with (di)halomethanes is presented. P4VP thin films are prepared by initiated chemical vapor deposition (iCVD) and then quaternized through exposure to saturated vapors of iodomethane (CH3I), dibromomethane (CH2Br2), and diiodomethane (CH2I2), resulting in refractive indices (RI) as high as 1.67, 1.71, and 2.07, respectively (at 632.8 nm). Fourier‐transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy (XPS) confirmed the quaternization of pyridine pendant groups on the polymer chain to n‐methylpyridinium with primarily an iodide or bromide counterion, though a minor fraction of polyiodides are also detected. Additionally, these films demonstrate superior thermal stability, retaining their refractive index and thickness after thermal excursions to 200 °C. The halogenated P4VP films exhibit superior mechanical flexibility relative to conventional inorganic coatings (Al2O3and Ta2O5) and do not fracture at uniaxial tensile strains as high as 10%. This new material chemistry and fabrication approach method may enable advanced optical designs and functionality in a wide range of substrates and device architectures.
-
The X-ray-induced spin crossover transition of an Fe (II) molecular thin film in the presence and absence of a magnetic field has been investigated. The thermal activation energy barrier in the soft X-ray activation of the spin crossover transition for [Fe{H2B(pz)2}2(bipy)] molecular thin films is reduced in the presence of an applied magnetic field, as measured through X-ray absorption spectroscopy at various temperatures. The influence of a 1.8 T magnetic field is sufficient to cause deviations from the expected exponential spin state transition behavior which is measured in the field free case. We find that orbital moment diminishes with increasing temperature, relative to the spin moment in the vicinity of room temperature.more » « less
-
more » « less
Abstract Superconducting radio‐frequency (SRF) resonators are critical components for particle accelerator applications, such as free‐electron lasers, and for emerging technologies in quantum computing. Developing advanced materials and their deposition processes to produce RF superconductors that yield nΩ surface resistances is a key metric for the wider adoption of SRF technology. Here, ZrNb(CO) RF superconducting films with high critical temperatures (
T c) achieved for the first time under ambient pressure are reported. The attainment of aT cnear the theoretical limit for this material without applied pressure is promising for its use in practical applications. A range ofT c, likely arising from Zr doping variation, may allow a tunable superconducting coherence length that lowers the sensitivity to material defects when an ultra‐low surface resistance is required. The ZrNb(CO) films are synthesized using a low‐temperature (100 – 200 °C) electrochemical recipe combined with thermal annealing. The phase transformation as a function of annealing temperature and time is optimized by the evaporated Zr‐Nb diffusion couples. Through phase control, one avoids hexagonal Zr phases that are equilibrium‐stable but degradeT c. X‐ray and electron diffraction combined with photoelectron spectroscopy reveal a system containing cubic β‐ZrNb mixed with rocksalt NbC and low‐dielectric‐loss ZrO2. Proof‐of‐concept RF performance of ZrNb(CO) on an SRF sample test system is demonstrated. BCS resistance trends lower than reference Nb, while quench fields occur at approximately 35 mT. The results demonstrate the potential of ZrNb(CO) thin films for particle accelerators and other SRF applications. -
null (Ed.)Motivated by their utility in CdTe-based thin film photovoltaics (PV) devices, an investigation of thin films of the magnesium-zinc oxide (MgxZn1−xO or MZO) alloy system was undertaken applying spectroscopic ellipsometry (SE). Dominant wurtzite phase MZO thin films with Mg contents in the range 0 ≤ x ≤ 0.42 were deposited on room temperature soda lime glass (SLG) substrates by magnetron co-sputtering of MgO and ZnO targets followed by annealing. The complex dielectric functions ε of these films were determined and parameterized over the photon energy range from 0.73 to 6.5 eV using an analytical model consisting of two critical point (CP) oscillators. The CP parameters in this model are expressed as polynomial functions of the best fitting lowest CP energy or bandgap E0 = Eg, which in turn is a quadratic function of x. As functions of x, both the lowest energy CP broadening and the Urbach parameter show minima for x ~ 0.3, which corresponds to a bandgap of 3.65 eV. As a result, it is concluded that for this composition and bandgap, the MZO exhibits either a minimum concentration of defects in the bulk of the crystallites or a maximum in the grain size, an observation consistent with measured X-ray diffraction line broadenings. The parametric expression for ε developed here is expected to be useful in future mapping and through-the-glass SE analyses of partial and complete PV device structures incorporating MZO.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/photonics10040366
