Transport and recombination through weakly coupled localized spin pairs in semiconductors during coherent spin excitation

Semi-analytical predictions for the transients of spin-dependent transport and recombination rates through localized states in semiconductors during coherent electron spin excitation are made for the case of weakly spin-coupled charge carrier ensembles. The results show that the on-resonant Rabi frequency of electrically or optically detected spin-oscillation doubles abruptly as the strength of the resonant microwave field gamma B_1 exceeds the Larmor frequency separation within the pair of charge carrier states between which the transport or recombination transition takes place. For the case of a Larmor frequency separation of the order of gamma B_1 and arbitrary excitation frequencies, the charge carrier pairs exhibit four different nutation frequencies. From the calculations, a simple set of equations for the prediction of these frequencies is derived

Effect of exchange coupling on coherently controlled spin-dependent transition rates

Journal ArticleThe effect of exchange interactions within spin pairs on spin-dependent transport and recombination rates through localized states in semiconductors during coherent electron-spin resonant excitation is studied theoretically. It is shown that for identical spin systems, significant quantitative differences are to be expected between the results of pulsed electrically/optically detected magnetic resonance (pEDMR/pODMR) experiments, where permutation symmetry is the observable, and the results of pulsed electron-spin resonance (pESR) experiments, with polarization in the x-y plane of the rotating frame as the observable. It is predicted that beat oscillations of the spin nutations and not the nutations themselves dominate the transport or recombination rates when the exchange coupling strength or the field strength of the exciting radiation exceed the difference between the Zeeman energies within the spin pair. Furthermore, while the intensities of the rate oscillations decrease with increasing exchange within the spin pairs, the singlet and triplet signals retain their relative strengths. This means that pEDMR and pODMR experiments allow experimental access to ESR forbidden singlet transitions

Electrical detection of 31P spin quantum states

In recent years, a variety of solid-state qubits has been realized, including quantum dots, superconducting tunnel junctions and point defects. Due to its potential compatibility with existing microelectronics, the proposal by Kane based on phosphorus donors in Si has also been pursued intensively. A key issue of this concept is the readout of the P quantum state. While electrical measurements of magnetic resonance have been performed on single spins, the statistical nature of these experiments based on random telegraph noise measurements has impeded the readout of single spin states. In this letter, we demonstrate the measurement of the spin state of P donor electrons in silicon and the observation of Rabi flops by purely electric means, accomplished by coherent manipulation of spin-dependent charge carrier recombination between the P donor and paramagnetic localized states at the Si/SiO2 interface via pulsed electrically detected magnetic resonance. The electron spin information is shown to be coupled through the hyperfine interaction with the P nucleus, which demonstrates the feasibility of a recombination-based readout of nuclear spins

T1T_1- and T2T_2-spin relaxation time limitations of phosphorous donor electrons near crystalline silicon to silicon dioxide interface defects

A study of donor electron spins and spin--dependent electronic transitions involving phosphorous ($^{31}$P) atoms in proximity of the (111) oriented crystalline silicon (c-Si) to silicon dioxide (SiO$_{2}$) interface is presented for [$^{31}$P] = 10$^{15}$ $\mathrm{cm}^{-3}$ and [$^{31}$P] = 10$^{16}$ $\mathrm{cm}^{-3}$ at about liquid $^4$He temperatures ($T = 5$ $\mathrm{K} - 15$ $\mathrm{K}$). Using pulsed electrically detected magnetic resonance (pEDMR), spin--dependent transitions between the \Phos donor state and two distinguishable interface states are observed, namely (i) \Pb centers which can be identified by their characteristic anisotropy and (ii) a more isotropic center which is attributed to E$^\prime$ defects of the \sio bulk close to the interface. Correlation measurements of the dynamics of spin--dependent recombination confirm that previously proposed transitions between \Phos and the interface defects take place. The influence of these electronic near--interface transitions on the \Phos donor spin coherence time $T_2$ as well as the donor spin--lattice relaxation time $T_1$ is then investigated by comparison of spin Hahn--echo decay measurements obtained from conventional bulk sensitive pulsed electron paramagnetic resonance and surface sensitive pEDMR, as well as surface sensitive electrically detected inversion recovery experiments. The measurements reveal that both $T_2$ and $T_1$ of \Phos donor electrons spins in proximity of energetically lower interface states at $T\leq 13$ K are reduced by several orders of magnitude

In vivo Neutralization of Pro-inflammatory Cytokines During Secondary Streptococcus pneumoniae Infection Post Influenza A Virus Infection

An overt pro-inflammatory immune response is a key factor contributing to lethal pneumococcal infection in an influenza pre-infected host and represents a potential target for therapeutic intervention. However, there is a paucity of knowledge about the level of contribution of individual cytokines. Based on the predictions of our previous mathematical modeling approach, the potential benefit of IFN-γ- and/or IL-6-specific antibody-mediated cytokine neutralization was explored in C57BL/6 mice infected with the influenza A/PR/8/34 strain, which were subsequently infected with the Streptococcus pneumoniae strain TIGR4 on day 7 post influenza. While single IL-6 neutralization had no effect on respiratory bacterial clearance, single IFN-γ neutralization enhanced local bacterial clearance in the lungs. Concomitant neutralization of IFN-γ and IL-6 significantly reduced the degree of pneumonia as well as bacteremia compared to the control group, indicating a positive effect for the host during secondary bacterial infection. The results of our model-driven experimental study reveal that the predicted therapeutic value of IFN-γ and IL-6 neutralization in secondary pneumococcal infection following influenza infection is tightly dependent on the experimental protocol while at the same time paving the way toward the development of effective immune therapies

Is Your Community College Technology Ready? An Assessment Instrument to Promote Technology Adoption

Background: Calls by presidents and legislators to raise the U.S. college graduation rate to 60% by 2025 have required educational institutions to find ways to increase accessibility and quality while simultaneously reducing costs (Bautsch, 2018; Smith, 2017). Private foundations such as the Bill and Melinda Gates Foundation are getting involved to scrutinize and question the value of higher education credentials, especially as costs continue to increase (Seltzer, 2019). At hand is the question of higher educations’ return on investment as student borrowing escalates while affordability, flexibility, and outcome-orientation lags (Kreighbaum, 2019). Thus, technology has become a key factor in addressing these challenges. Furthermore, the changing student demographic indicates community colleges are at the forefront of educational delivery to students with varied cultural, social, and economic backgrounds accompanied by a myriad of expectations surrounding knowledge attainment, relevant skill development, and future employment goals (Boggs & McPhail, 2016; O'Banion, 2019). Unfortunately, many educators assume the technology itself is the critical element in leveraging accessible learning, innovative practice, and overall student success. Colleges rush to purchase and implement technologies aimed at increasing student engagement, retention, and completion, but have ignored the overall impact of the change and the elements of successful innovation (Barrington, 2019; Cator, 2019). Lacking are actions, processes, and tools to determine if the college, students, or employees are ready to adopt the technology, or if the technology is achieving its intended objectives (Chen, 2019). Purpose: This research study explores and develops a community college technology readiness instrument, which community college stakeholders can use to support technology adoption. The study will elaborate on the topic of technology integration at community colleges and specifically focus on technology readiness factors that promote and enable successful technology adoption. Research Design: The methods section outlines the two data collection phases, the Delphi method and the survey questionnaire. Both phases employed in the study are described along with the specific tactics to gather data for analysis. The sample included technology subject matter experts in community colleges across the U.S. The phase one, Delphi method, included between 17-20 respondents, while the phase two, online survey, included 182 respondents. The methods included both qualitative and quantitative approaches, but primarily quantitative in the form of descriptive analyses, factor analyses, and multiple regression. Findings: This study showed what technology readiness characteristics are most important in allowing community colleges to achieve their strategic and student-success initiatives. The findings also pointed out the disconnect between people’s technology expectations and their community college’s ability to provide and deliver what is wanted and needed. Additionally, the paper outlined the constraints and hindrances impacting technology readiness, and the benefits of evaluating a college’s readiness prior to technology integration and adoption. The findings demonstrated the relationship between the factors of technology readiness and adoption and technologists’ self-ratings of their college’s readiness to implement technology. Lastly, this paper identified the significance and implications of this type of study to the community college body of knowledge. Conclusion: The overall conclusion of this study indicated the community college organization is insufficiently preparing its people and systems for technology adoption. The resultant technology readiness and assessment instrument was developed based on the findings of the study and includes the key components for successful technology deployment. Areas such as employee and end user training, executive level support, communication, awareness, sufficient funding, accessibility and access, project management, and ongoing technical support were consistent themes in the data. Respondents indicated a significant gap in the expectations of what a technology should do and the ability of the organization to actually do what is necessary to prepare to adopt the technology. Future research is warranted to test the instrument within community colleges as well as exploration of people versus organizational change management