We report on the structural, chemical, and optical properties of titanium sesquioxide Ti2O3 thin films on single-crystal sapphire substrates by pulsed laser deposition. The thin film of Ti2O3 on sapphire exhibits light absorption of around 25%-45% in the wavelength range of 2-10 mu m. Here, we design an infrared photodetector structure based on Ti2O3, enhanced by a resonant metasurface, to improve its light absorption in mid-wave and long-wave infrared windows. We show that light absorption in the mid-wave infrared window (wavelength 3-5 mu m) in the active Ti2O3 layer can be significantly enhanced from 30%-40% to more than 80% utilizing a thin resonant metasurface made of low-loss silicon, facilitating efficient scattering in the active layer. Furthermore, we compare the absorptance of the Ti2O3 layer with that of conventional semiconductors, such as InSb, InAs, and HgCdTe, operating in the infrared range with a wavelength of 2-10 mu m and demonstrate that the absorption in the Ti2O3 film is significantly higher than in these conventional semiconductors due to the narrow-bandgap characteristics of Ti2O3. The proposed designs can be used to tailor the wavelengths of photodetection across the near- and mid-infrared ranges.

A broad perspective of quantum technology state of the art is provided and critical stumbling blocks for quantum technology development are identified. Innovations in demonstrating and understanding electron entanglement phenomena using bulk and low-dimensional materials and structures are summarized. Correlated photon-pair generation via processes such as nonlinear optics is discussed. Application of qubits to current and future high-impact quantum technology development is presented. Approaches for realizing unique qubit features for large-scale encrypted communication, sensing, computing, and other technologies are still evolving; thus, materials innovation is crucially important. A perspective on materials modeling approaches for quantum technology acceleration that incorporate physics-based AI/ML, integrated with quantum metrology is discussed.

We successfully grow corundum structured Ti2O3 films on c-plane sapphire substrates using pulsed laser depo-sition. Temperature dependent resistivity measurements show that a metal to insulator transition (MIT) is suppressed, showing conducting behavior at all temperatures. Samples still show an increase in resistivity as temperature is decreased, a characteristic indicative of a semiconducting phase. Our films exhibit grain size on the order of 30 nm which induce a strain consistent with nanoparticle Ti2O3 showing a (c/a) ratio of 2.7. The imposed strain causes an increase in the c-axis length as the temperature is decreased, and thereby suppresses the transition to an insulating phase. Our optical data agrees with this result, showing the lack of a band gap and the electronic structure consistent with bulk high temperature metallic Ti2O3 with the a1g -e pi g interband transition shifted down to 0.7 eV from its bulk insulating value of-1 eV.

Volatile memristor devices are used in neuromorphic computing systems because they mimic the spike action of neurons in the brain [1].A physical artificial neural network can be constructed using threshold (i.e., rapid) switching phase change materials such as TiO 2 or NbO 2 to meet the non-linear and "short term memory" requirements for a reservoir computing architecture.In the case of NbO 2 , an induced current applied to the device causes localized Joule heating to enable a reversible insulator-to-metal phase transition between the rutile (R-NbO 2 ; E g = 1 eV) and tetragonal (T-NbO 2 ) crystal structures [2].This phase transition has been shown to be consistent with a Peierls transition model, in which conducting chains of Nb dimers are formed through a small reorganization of NbO 6 octahedra.Practical NbO 2 memristor devices can be constructed using atomic layer deposition (ALD) growth, followed by annealing to generate a final, transitionable, thin film [3].Since Nb-oxide has multiple metastable phases, several Nb 2 O 5 and NbO 2 phase transitions were observed during annealing to form a contiguous NbO 2 thin film [4].Introducing hydrogen plasma exposure in the ALD chamber between successive deposition layers can lead to intermediate NbO x compositions with unique memristor capability.Here we used correlated transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and atom-probe tomography (APT) on a set of ALD-deposited Nb-oxide thin films annealed to 800 °C and 1000 °C (for 20 min each), along with an unheated control sample.Cross-sections of each sample were prepared by FIB liftout methods with a ThermoFisher Helios G3 DualBeam FIB-SEM.The distribution of Nb-oxide phases within the thin films were measured by electron energy-loss spectroscopy (EELS) with an aberration Nion UltraSTEM 200-X, using a Gatan Enfinium EELS spectrometer modified with a Quantun Detectors MerlinEELS direct electron detector.EELS spectrum images were acquired at the Nb N-edge and plasmon (∼20 eV), O K-edge (∼532 eV), Nb L-edge (∼2370 eV).Fine-structure at these EELS edges provides sensitive information about Nb cation coordination and NbO 6 octahedra edge-vs.-cornersharing.Reference EELS spectra exist for the stable rutile R-NbO 2 and monoclinic H-Nb 2 O 5 phases [5], but none of the other metastable phases identified by Twigg et al. [4] in similar ALD-deposited thin films (e.g., T-NbO 2 , T-Nb 2 O 5 , and B-Nb 2 O 5 ).Distinct phases in spectrum images were identified using PCA and cluster analysis with HyperSpy 1.7. 3 [6] Characterization of the unheated sample reveals that three compositions of NbO x were deposited in a multilayer film by plasma-assisted ALD (Figure 1).The first layer (30 nm) at the bottom of the stack is crystalline and shows O-K and Nb-N spectra that match R-NbO 2 .Above this layer is 30 nm of amorphous film, where the O-K spectra of top 15 nm is consistent with the predominantly corner-sharing NbO 6 octahedra of Nb 2 O 5 phases.The O-K spectrum of the middle 15 nm layer does not match either of the two reference spectra, and the broad peak at 540 eV indicates that complex O coordination is present.The fully annealed sample retains the multilayer structure of the initial ALD thin film.Octahedra edge-vs.-cornersharing does not change after annealing, as O K-edge spectra for each layer does not change from the initial thin film.However, the peak distance between Nb L 2 and L 3 peaks does increase by 0.5 eV from crystallization of Nb 2 O 5 .These data indicate that alternate NbO x compositions can be stabilized for memristor devices by H plasma-assisted ALD growth.However, vesicle growth along interlayer boundaries observed by TEM may cause difficulties in memristor switching due to blocking the formation of contiguous phase transformation channels through the device [7].

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Chemiresistive graphene sensors are promising for chemical sensing applications due to their simple device structure, high sensitivity, potential for miniaturization, low-cost, and fast response. In this work, we investigate the effect of (1) ZnO nanoparticle functionalization and (2) engineered defects onto graphene sensing channel on device resistance and low frequency electrical noise. The engineered defects of interest include 2D patterns of squares, stars, and circles and 1D patterns of slots parallel and transverse to the applied electric potential. The goal of this work is to determine which devices are best suited for chemical sensing applications. We find that, relative to pristine graphene devices, nanoparticle functionalization leads to reduced contact resistance but increased sheet resistance. In addition, functionalization lowers 1/f current noise on all but the uniform mesa device and the two devices with graphene strips parallel to carrier transport. The strongest correlations between noise and engineering defects, where normalized noise amplitude as a function of frequency f is described by a model of AN/fγ, are that γ increases with graphene area and contact area but decreases with device total perimeter, including internal features. We did not find evidence of a correlation between the scalar amplitude, AN, and the device channel geometries. In general, for a given device area, the least noise was observed on the least-etched device. These results will lead to an understanding of what features are needed to obtain the optimal device resistance and how to reduce the 1/f noise which will lead to improved sensor performance.

Graphene, the first isolated two-dimensional material, has captivated researchers for the last decade due to its unique structure that leads to novel electronic, chemical, mechanical, and thermal properties. The most intriguing properties are the large electronic mobilities that are achievable for low carrier concentrations and the large tunability of graphene's electrical properties via electrostatic gating, in which the Fermi energy is shifted relative to the charge neutrality, or Dirac, point and the high electronic mobilities obtained when the Fermi energy is close to that point. In this report, we show that both covalent and non-covalent functionalization of graphene leads to adsorbate-induced doping. This results in a three-fold increase in the graphene systems' mobilities and the observation of quantum transport phenomena (Hall effect plateaus, Shubnikov-de Haas oscillations, and Berry's phase) which were not observed in the unfunctionalized graphene. This ability to control the electronic properties without electrostatic gating is critical for chemical and biological sensing, optical, and electronic applications, which require both low carrier concentrations and the attachment of nanocrystals, biomolecules, increased adhesion and wettability of graphene layers, and enable strong cohesion between graphene layers in stacked graphene structures.

The progress in quantum technology relies on high performing qubits with minimal losses in superconducting and dielectric properties, as well as in their interfaces. Understanding what causes the loss of performance is of paramount importance. In this work, we focus on the development of chemical molecules that possess molecular rotors (CF, OH-functional groups) in their structures that move at a particular microwave frequency. Tracking of these frequencies provides unprecedented insight into the loss mechanisms in lossy dielectric systems. The goal of this work is to develop deposition methods of self-assembled molecules onto hydrogen terminated Si surfaces using strong Si-C bonds for molecular attachment rather than the typical Si-O. In the first part of the report we discuss the synthesis and the deposition of w-F alkyne monolayers containing ten (C 10 ) and eighteen (C 18 ) carbon chains in their structure onto Si surfaces. We found that deposition of these molecules following established literature protocols did not produce uniform closely packed monolayers. Thus, we developed new deposition protocols and established critical parameters that needed attention for further process optimization. The second part of the report is devoted to the deposition of 4-(vinyl)phenol (VP), 3-(ethenyl)phenol (EP), and 4-(vinylphenol)methanol (VPM) onto Si surfaces. The most successful deposition was achieved with EP molecules which produced multilayer films with hydrophobic nature, followed by VP, and finally, VPM films. Further experiments with increased deposition temperature and catalyst are needed to optimize the developed protocols

Superconducting microwave resonators are important components of superconducting quantum information and astronomy detector systems. In this paper, we show how to modify the microwave resonator performance after fabrication through surface engineering. In particular, we focus on titanium nitride (TiN)/silicon (Si) resonators because they have shown potential for achieving high-quality factors (Q(i)s). Depending on the type of surface treatment, chemical-or plasma-based, we found Q(i)s that vary by approximately a factor of 18. We used inductively coupled plasma (ICP) combined with reactive ion etching (RIE) for the plasma surface treatment. We found that the microwave resonator performance depends on the type of plasma environment, such as single gas (oxygen) or gas mixtures [argon/hydrogen (Ar/H-2), argon/octafluorocyclobutane (Ar/C4F8), and argon/sulfur hexafluoride (Ar/SF6)], and the plasma processing conditions, such as treatment time, ICP power, and RIE power. Of the plasma surface treatments, the Ar/SF6 environments with no or low ICP power showed the highest potential to improve Q(i). The processing conditions determined the chemistry and roughness of the Si and TiN surfaces, TiN film thickness, and the overall TiN/Si resonator structure (edge and sidewall). Our results can be used as a guideline for optimizing the microwave resonator performance using surface treatments.

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma, where unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (~keV) electron beam. The resulting plasmas are characterized by large electron densities (1010–1011cm−3) and low electron temperatures (0.3–1.0eV). Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies of only a few eV, a feature that can be attractive to processing applications that require low damage and atomic layer precision. This work describes the salient features of these plasmas produced in mixtures of argon and sulfur hexafluoride (SF6) and their use in silicon nitride etching, with particular attention paid to developing processing parameters relevant to atomic layer processing.

Charged tunneling defects at the vacuum-dielectric interfaces are known to be deleterious to quantum bits in superconducting quantum computing. In this work, we explored both chemical and plasma based functionalization strategies to substitute siloxane functional groups with Si-H and Si-F on the silicone surface. The chemical used was hydrofluoric acid, which had two effects - removing all residual hydrocarbons left from the surfaces and the aluminium passivation layer deposited on top of the TiN. The plasma functionalization was performed in Ar/SF 6 , Ar/H 2 , Ar/C 4 F 8 and O 2 environments. Best results were obtained after combining the chemical and plasma treatment in Ar/SF 6 . Q-factors of 800k were measured for devices produced with 25 nm TiN thick films with 12 μm spacing and 3 μm line width. We correlate the change in Q factors with chemical, structural and morphological modifications of the TiN and Si surfaces.