Bradac, Carlo

With wide applications ranging from quantum communication and metrology to biomedicine, single photon sources in solid-state hosts have become a major area of study. Here, we focus on three applications: nanothermometry, optically detected magnetic resonance (ODMR), and second order autocorrelation. We present novel statistical and machine learning (ML) approaches to extract information from experimental and simulated data and benchmark these methods against traditional inference-based statistical approaches. We found that compared to traditional inference-based methods ML algorithms can: i) predict temperatures at the nanoscale with greater accuracy and with less calibration points than traditional fitting methods; ii) identify the resonance peaks in ODMR spectra with factors ~1.3x and ~4.7x better accuracy and resolution and achieved equal or better performance with ~5x less data; and iii) have the potential to parse second order autocorrelation data more efficiently. ML algorithms are thus powerful tools for quantum sensing techniques.

Author Keywords: colour centers, machine learning, nanosensing, nanothermometry, optically detected magnetic resonance, second order autocorrelation

Petroleum coke (petcoke) is a waste by-product of the upgrading process in the oil refining industry. It has limited utility in other areas of application.1 High carbon content (over 85 wt.%), low ash content, and softness make petcoke a potentially valuable precursor for graphitization, where amorphous carbon can be transformed into graphitic carbon. The synthetic production of graphite is gaining more interest due to the increasing demand for battery materials.2,3 Without metal moderators, achieving graphitization requires significantly high temperatures (> 2500 °C). Magnesium (Mg) has been identified as a promising reactant because of its efficacy in promoting graphitization and its relatively simple removal from the final product.3–5 The optimized conditions of magnesium-assisted graphitization showed an electrical conductivity of (3552.0 ± 78.5) S/m at 10 mA. Furthermore, bimetallic metal mediators can exhibit improved catalytic activity in graphitization due to the synergistic effect.3,6,7 Raney nickel alloy (Ni-Al alloy) contains 50 wt.% nickel and 50 wt.% aluminum. Individually, nickel and aluminum have shown efficacy in graphitization.8 However, no research has been conducted on the efficacy of Raney nickel alloy as a metal mediator in petcoke graphitization. We present our work on the graphitization of petcoke and its derived activated carbon using magnesium and Ni-Al alloy at 1000 °C and 1500 °C, respectively. This study assesses the effects of heating time, temperature, and precursor particle size on the degree of graphitization. Additionally, magnesium was completely removed after the graphitization process, and the residual Raney nickel alloy percentage was minimal.

Author Keywords: activated carbon, magnesium, Petroleum coke, Raney nickel alloy, synthetic graphitization

In electron-doped ferroelectrics, the free electrons can become concentrated along the domain walls which act like a conducting surface. We consider the impact of free electrons occupying the t2g orbitals on the domain walls of an electron-doped perovskite ferroelectric. We build an analytical model based on Landau-Ginzburg-Devonshire theory, and a trio of tight-binding Hamiltonians for free electrons. We self-consistently solve for the polarization, potential, and electron density using a finite-difference approximation. We find that the ferroelectric is effectively charge neutral. The free electrons are attracted to the positively-charged domain wall, leaving it with a small residual charge. As the electron density increases, the domain walls tilt to form zig-zag domain walls. Orbital selectivity of the t2g orbitals depends on the relative orientations of the orbital plane and the domain wall. This property influences the rate at which the domain wall tilts as a function of the electron density.

Author Keywords: Charged Domain Wall, Domain Wall, Ferroelectric, Landau-Ginzburg, Perovskite, Strontium Titanate

The generation of polymer brushes by surface-initiated polymerization techniques has become a powerful tool for the creation of hybrid materials. Governed by the type and amount of polymer used in the modification, the chemical and physical properties of a surface can be tailored by polymer grafting. In this study, a commonly used polymer flocculant, polyacrylamide (PAM), was grafted onto the surface of activated carbon (AC). This hybrid material was designed with the intent of combining the functionalities of both the activated carbon and the polymer flocculant, potentially acting in a synergistic manner. The PAM grafted AC (AC-PAM) was examined as a flocculant in the treatment of mature fine tailings (MFT). AC-PAM was synthesized by surface-initiated activators generated by electron transfer atom transfer radical polymerization (SI-AGET ATRP). This was accomplished by pre-functionalizing the surface of activated carbon by oxidation, followed by the attachment of an ATRP initiator. From this surface, SI-AGET ATRP of acrylamide monomers was performed. The resulting AC-PAM was characterized by FTIR, XPS, TGA, SEC, and BET analysis. Characterization results indicated the successful grafting of polyacrylamide from the surface of activated carbon. The AC-PAM was measured to contain approximately 10.6% PAM by weight, and the average-number molecular weight of the grafted polymer was 176,100 g/mol. The flocculation performance of AC-PAM and PAM were compared by performing settling tests with 5 wt% MFT. The optimal polymer dosage for PAM was found to be 10,000 ppm, producing an initial settling rate of 3.51 m/hr and a supernatant turbidity of 430 NTU. Comparatively, the optimal dosage for AC-PAM was found to be 20,000 ppm, producing a supernatant turbidity of 114 NTU and a fast initial settling rate of 27.54 m/hr. The improved flocculation performance is hypothesized to occur due to the effective increase in the molecular weight of PAM when grafted from the surface of activated carbon. In all, our work demonstrates the successful grafting of PAM from AC, as well as potential wastewater treatment applications for these types of hybrid materials.

Author Keywords: Activated carbon, Atom transfer radical polymerization, Flocculation, Grafting, Polyacrylamide, Surface-initiated polymerization

In electron-doped ferroelectrics, the free electrons can become concentrated along the domain walls which act like a conducting surface. We consider the impact of free electrons occupying the t2g orbitals on the domain walls of an electron-doped perovskite ferroelectric. We build an analytical model based on Landau-Ginzburg-Devonshire theory, and a trio of tight-binding Hamiltonians for free electrons. We self-consistently solve for the polarization, potential, and electron density using a finite-difference approximation. We find that the ferroelectric is effectively charge neutral. The free electrons are attracted to the positively-charged domain wall, leaving it with a small residual charge. As the electron density increases, the domain walls tilt to form zig-zag domain walls. Orbital selectivity of the t2g orbitals depends on the relative orientations of the orbital plane and the domain wall. This property influences the rate at which the domain wall tilts as a function of the electron density.

Author Keywords: Charged Domain Wall, Domain Wall, Ferroelectric, Landau-Ginzburg, Perovskite, Strontium Titanate