Kelly M. Whitaker

Charge-controlled magnetism in colloidal doped semiconductor nanocrystals

Electrical control over the magnetic states of doped semiconductor nanostructures could enable new spin-based information processing technologies. To this end, extensive research has recently been devoted to examination of carrier-mediated magnetic ordering effects in substrate-supported quantum dots at cryogenic temperatures, with carriers introduced transiently by photon absorption. The relatively weak interactions found between dopants and charge carriers have suggested that gated magnetism in quantum dots will be limited to cryogenic temperatures. Here, we report the observation of a large, reversible, room-temperature magnetic response to charge state in free-standing colloidal ZnO nanocrystals doped with Mn(2+) ions. Injected electrons activate new ferromagnetic Mn(2+)-Mn(2+) interactions that are strong enough to overcome antiferromagnetic coupling between nearest-neighbour dopants, making the full magnetic moments of all dopants observable. Analysis shows that this large effect occurs in spite of small pairwise electron-Mn(2+) exchange energies, because of competing electron-mediated ferromagnetic interactions involving distant Mn(2+) ions in the same nanocrystal.

Electron Transfer Between Colloidal ZnO Nanocrystals

Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e(-)(CB):ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals. EPR spectra of the reverse reaction, e(-)(CB):ZnO-L + ZnO-S, showed that electrons do not transfer from large to small nanocrystals. Stopped-flow kinetics studies monitoring the change in the UV band-edge absorption showed that reactions of 50 μM nanocrystals were complete within the 5 ms mixing time of the instrument. Similar results were obtained for the reaction of charged nanocrystals with methyl viologen (MV(2+)). These and related results indicate that the electron-transfer reactions of these colloidal nanocrystals are quantitative and very rapid, despite the presence of ~1.5 nm long dodecylamine capping ligands. These soluble ZnO nanocrystals are thus well-defined redox reagents suitable for studies of electron transfer involving semiconductor nanostructures.

Ultrafast spin dynamics in colloidal ZnO quantum dots

We perform time-resolved Faraday rotation measurements on colloidal ZnO quantum dots. A biexponential decay of the dephasing time T2* of the electron spins governed by competing recombination processes is observed.

Spin-on Spintronics : Ultrafast Electron Spin Dynamics in ZnO and Zn1-xCoxO Sol-Gel Films

We use time-resolved Faraday rotation spectroscopy to probe the electron spin dynamics in ZnO and magnetically doped Zn(1-x)Co(x)O sol-gel thin films. In undoped ZnO, we observe an anomalous temperature dependence of the ensemble spin dephasing time T(2), i.e., longer coherence times at higher temperatures, reaching T(2) ∼ 1.2 ns at room temperature. Time-resolved transmission measurements suggest that this effect arises from hole trapping at grain surfaces. Deliberate addition of Co(2+) to ZnO increases the effective electron Landé g factor, providing the first direct determination of the mean-field electron-Co(2+) exchange energy in Zn(1-x)Co(x)O (N(0)α = +0.25 ± 0.02 eV). In Zn(1-x)Co(x)O, T(2) also increases with increasing temperature, allowing spin precession to be observed even at room temperature.

Colloidal ZnO quantum dots in ultraviolet pillar microcavities

Three dimensional light confinement and distinct pillar microcavity modes in the ultraviolet have been observed in pillar resonators with embedded colloidal ZnO quantum dots fabricated by focused ion beam milling. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data.

School mental health promotion and intervention: Experiences from four nations

All around the world, partnerships among schools and other youth-serving systems are promoting more comprehensive school-based mental health services. This article describes the development of international networks for school mental health (SMH) including the International Alliance for Child and Adolescent Mental Health and Schools (INTERCAMHS) and the more recent School Mental Health International Leadership Exchange (SMHILE). In conjunction with World Conferences on Mental Health Promotion, SMHILE has held pre-conference and planning meetings and has identified five critical themes for the advancement of global SMH: 1) Cross-sector collaboration in building systems of care; 2) meaningful youth and family engagement; 3) workforce development and mental health literacy; 4) implementation of evidence-based practices; and 5) ongoing monitoring and quality assurance. In this article we provide general background on SMH in four nations, two showing strong progress (the United States and Canada), one showing moderate progress (Norway), and one beginning the work (Liberia). Following general background for each country, actions in relation to the SMHILE themes are reviewed. The article concludes with plans and ideas for future global collaboration towards advancement of the SMH field.

A Digital Feedback System to Support Implementation of Measurement-Based Care by School-Based Mental Health Clinicians

Evidence supports the utility of measurement-based care (MBC) to improve youth mental health outcomes, but clinicians rarely engage in MBC practices. Digital measurement feedback systems (MFS) may reflect a feasible strategy to support MBC adoption and sustainment. This pilot study was initiated to evaluate the impact of a MFS and brief consultation supports to facilitate MBC uptake and sustainment among mental health clinicians in the education sector, the most common mental health service delivery setting for youth. Following an initial training in MBC, 14 clinicians were randomized to either a digital MFS and brief consultation supports or control. Baseline ratings of MBC attitudes, skill, and use were collected. In addition, daily assessment ratings tracked 2 core MBC practices (i.e., assessment tool administration, provision of feedback) over a 6-month follow-up period. Clinicians in the MFS condition demonstrated rapid increases in both MBC practices, whereas the control group did not significantly change. For clinicians in the MFS group, consultation effects were significant for feedback and approached significance for administration. Over the follow-up period, average decreases in the current study were moderate with only 1 of the 2 outcome variables (administration) decreasing significantly. Inspection of individual clinician trajectories revealed substantial within-group trend variation. MFS may represent an effective MBC implementation strategy beyond initial training, although individual clinician response is variable. Identifying feasible and impactful implementation strategies is critical given the ability of MBC to support precision health care.

Collaborative care in schools: enhancing integration and impact in youth mental health

Abstract Collaborative care (CC) is an innovative approach to integrated mental health service delivery that focuses on reducing access barriers, improving service quality and lowering health care expenditures. A large body of evidence supports the effectiveness of CC models with adults and, increasingly, for youth. Although existing studies examining these models for youth have focused exclusively on primary care, the education sector is also an appropriate analogue for the accessibility that primary care offers to adults. CC aligns closely with the practical realities of the education sector and may represent a strategy to achieve some of the objectives of increasingly popular multi-tiered systems of supports frameworks. Unfortunately, no resources exist to guide the application of CC models in schools. Based on the existing evidence for CC models, the current paper (1) provides a rationale for the adaptation of CC models to improve mental health service accessibility and effectiveness in the education sector; (2) presents a preliminary CC model for use in schools; and (3) describes avenues for research surrounding school-based CC, including the currently funded Accessible, Collaborative Care for Effective School-based Services project.

Perceptions of Recidivism Among Incarcerated Youth: The Relationship Between Exposure to Childhood Trauma, Mental Health Status, and the Protective Effect of Mental Health Services in Juvenile Justice Settings

Research suggests that youth involved the juvenile justice system have trauma histories that are two times higher than the general youth population. Juvenile justice-involved youth also have high rates of mental health symptoms. Fewer studies have examined how trauma links to mental health symptoms among youth offenders, and even less research focuses on how mental health status and service delivery can impact their perceived likelihood for success. This study examines the effects of mental health screening and service delivery on perceived future criminal justice interactions— arrest and incarceration—among adjudicated youth (n=7,073) housed in correctional facilities. Secondary data were used to examine trauma histories, mental health needs, and mental health screening and service delivery. Significant relationships between traumatic events and mental health problems were found, along with relationships between mental health problems and mental health screening and service delivery. Most interestingly, results pointed to the strong inverse relationship between mental health service delivery and youth’s perceived likelihood for recidivism. These findings show the promise of juvenile justice systems appropriately responding to the mental health concerns of youth.

Evaluation of Second Step on Early Elementary Students' Academic Outcomes: A Randomized Controlled Trial

Research has consistently linked social–emotional learning to important educational and life outcomes. Early elementary represents an opportune developmental period to proactively support children to acquire social–emotional skills that enable academic success. Using data from a large scale randomized controlled trial, the purpose of this study was to investigate the impact of the 4th edition of Second Step on early elementary students’ academic-related outcomes. Participants were Kindergarten to 2nd grade students in 61 schools (310 teachers; 7,419 students) across six school districts in Washington State and Arizona. Multilevel models (Time × Condition) indicated the program had no positive main effect impact on academic outcomes. However, moderator analyses revealed that quality of implementation, specifically a measure of student engagement and dosage, was found to be associated with significant, albeit small, reading and classroom behavior outcomes. Findings from this study provide support for Second Step when implemented in the context of high engagement and higher dosage to have small but potentially meaningful collateral impact on early academic-related outcomes.