76 research outputs found
Isotropic plasma-thermal atomic layer etching of superconducting TiN films using sequential exposures of molecular oxygen and SFH plasma
Microwave loss in superconducting titanium nitride (TiN) films is attributed
to two-level systems in various interfaces arising in part from oxidation and
microfabrication-induced damage. Atomic layer etching (ALE) is an emerging
subtractive fabrication method which is capable of etching with Angstrom-scale
etch depth control and potentially less damage. However, while ALE processes
for TiN have been reported, they either employ HF vapor, incurring practical
complications; or the etch rate lacks the desired control. Further, the
superconducting characteristics of the etched films have not been
characterized. Here, we report an isotropic plasma-thermal TiN ALE process
consisting of sequential exposures to molecular oxygen and an SF/H
plasma. For certain ratios of SF:H flow rates, we observe selective
etching of TiO over TiN, enabling self-limiting etching within a cycle.
Etch rates were measured to vary from 1.1 \r{A}/cycle at 150 C to 3.2
\r{A}/cycle at 350 C using ex-situ ellipsometry. We demonstrate that
the superconducting critical temperature of the etched film does not decrease
beyond that expected from the decrease in film thickness, highlighting the
low-damage nature of the process. These findings have relevance for
applications of TiN in microwave kinetic inductance detectors and
superconducting qubits.Comment: 17 pages, 7 figure
Demonstration of Universal Parametric Entangling Gates on a Multi-Qubit Lattice
We show that parametric coupling techniques can be used to generate selective
entangling interactions for multi-qubit processors. By inducing coherent
population exchange between adjacent qubits under frequency modulation, we
implement a universal gateset for a linear array of four superconducting
qubits. An average process fidelity of is estimated for
three two-qubit gates via quantum process tomography. We establish the
suitability of these techniques for computation by preparing a four-qubit
maximally entangled state and comparing the estimated state fidelity against
the expected performance of the individual entangling gates. In addition, we
prepare an eight-qubit register in all possible bitstring permutations and
monitor the fidelity of a two-qubit gate across one pair of these qubits.
Across all such permutations, an average fidelity of
is observed. These results thus offer a path to a scalable architecture with
high selectivity and low crosstalk
Configurational Thermodynamics of Alloyed Nanoparticles with Adsorbates
Changes in the chemical configuration of alloyed nanoparticle (NP) catalysts induced by adsorbates under working conditions, such as reversal in core–shell preference, are crucial to understand and design NP functionality. We extend the cluster expansion method to predict the configurational thermodynamics of alloyed NPs with adsorbates based on density functional theory data. Exemplified with PdRh NPs having O-coverage up to a monolayer, we fully detail the core–shell behavior across the entire range of NP composition and O-coverage with quantitative agreement to in situ experimental data. Optimally fitted cluster interactions in the heterogeneous system are the key to enable quantitative Monte Carlo simulations and design
Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO
The shape dependence of the catalytic reduction of nitric oxide by carbon monoxide on rhodium nanopolyhedra and nanocubes was studied from 230 to 270 degrees C. The nanocubes are found to exhibit higher turnover frequency and lower activation energy than the nanopolyhedra. These trends are compared to previous studies on Rh single crystals.Chemistry, PhysicalSCI(E)EI21ARTICLE3-4317-32213
Surface Composition and Catalytic Evolution of Au x Pd1−x (x = 0.25, 0.50 and 0.75) Nanoparticles Under CO/O2 Reaction in Torr Pressure Regime and at 200 °C
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