Composition-Defined Optical Properties and the Direct-to-Indirect Transition in Core-Shell In1-xGaxP/ZnS Colloidal Quantum Dots.

Semiconductors are commonly divided into materials with direct or indirect band gaps based on the relative positions of the top of the valence band and the bottom of the conduction band in crystal momentum (k) space. It has, however, been debated if k is a useful quantum number to describe the band structure in quantum-confined nanocrystalline systems, which blur the distinction between direct and indirect gap semiconductors. In bulk III-V semiconductor alloys like In1-xGaxP, the band structure can be tuned continuously from the direct- to indirect-gap by changing the value of x. The effect of strong quantum confinement on the direct-to-indirect transition in this system has yet to be established because high-quality colloidal nanocrystal samples have remained inaccessible. Herein, we report one of the first systematic studies of ternary III-V nanocrystals by utilizing an optimized molten-salt In-to-Ga cation exchange protocol to yield bright In1-xGaxP/ZnS core-shell particles with photoluminescence quantum yields exceeding 80%. We performed two-dimensional solid-state NMR studies to assess the alloy homogeneity and the extent of surface oxidation in In1-xGaxP cores. The radiative decay lifetime for In1-xGaxP/ZnS monotonically increases with higher gallium content. Transient absorption studies on In1-xGaxP/ZnS nanocrystals demonstrate signatures of direct- and indirect-like behavior based on the presence or absence, respectively, of excitonic bleach features. Atomistic electronic structure calculations based on the semi-empirical pseudopotential model are used to calculate absorption spectra and radiative lifetimes and evaluate band-edge degeneracy; the resulting calculated electronic properties are consistent with experimental observations. By studying photoluminescence characteristics at elevated temperatures, we demonstrate that a reduced lattice mismatch at the III-V/II-VI core-shell interface can enhance the thermal stability of emission. These insights establish cation exchange in molten inorganic salts as a viable synthetic route to nontoxic, high-quality In1-xGaxP/ZnS QD emitters with desirable optoelectronic properties.

Diffusion-Limited Kinetics of Isovalent Cation Exchange in III-V Nanocrystals Dispersed in Molten Salt Reaction Media.

The goal of this work is to determine the kinetic factors that govern isovalent cation exchange in III-V colloidal quantum dots using molten salts as the solvent and cation source. We focus on the reactions of InP + GaI3→ In1-xGaxP and InAs + GaI3→ In1-xGaxAs to create technologically important ternary III-V phases. We find that the molten salt reaction medium causes the transformation of nearly spherical InP nanocrystals to tetrahedron-shaped In1-xGaxP nanocrystals. Furthermore, we determine that the activation energy for the cation exchange reaction is 0.9 eV for incorporation of Ga into InP and 1.2 eV for incorporation of Ga into InAs, both much lower than the measured values in bulk semiconductors. Next, we use powder XRD simulations to constrain our understanding of the structure of the In1-xGaxP nanocrystals. Together our results reveal several important features of molten salt-mediated cation exchange and provide guidance for future development of these materials.

Self-assembly of nanocrystals into strongly electronically coupled all-inorganic supercrystals.

Colloidal nanocrystals of metals, semiconductors, and other functional materials can self-assemble into long-range ordered crystalline and quasicrystalline phases, but insulating organic surface ligands prevent the development of collective electronic states in ordered nanocrystal assemblies. We reversibly self-assembled colloidal nanocrystals of gold, platinum, nickel, lead sulfide, and lead selenide with conductive inorganic ligands into supercrystals exhibiting optical and electronic properties consistent with strong electronic coupling between the constituent nanocrystals. The phase behavior of charge-stabilized nanocrystals can be rationalized and navigated with phase diagrams computed for particles interacting through short-range attractive potentials. By finely tuning interparticle interactions, the assembly was directed either through one-step nucleation or nonclassical two-step nucleation pathways. In the latter case, the nucleation was preceded by the formation of two metastable colloidal fluids.

Engineering Long-Lived Blue Photoluminescence from InP Quantum Dots Using Isomers of Naphthoic Acid.

Leveraging triplet excitons in semiconductor quantum dots (QDs) in concert with surface-anchored molecules to produce long-lifetime thermally activated delayed photoluminescence (TADPL) continues to emerge as a promising technology in diverse areas including photochemical catalysis and light generation. All QDs presently used to generate TADPL in QD/molecule constructs contain toxic metals including Cd(II) and Pb(II), ultimately limiting potential real-world applications. Here, we report newly conceived blue-emitting TADPL-producing nanomaterials featuring InP QDs interfaced with 1- and 2-naphthoic acid (1-NA and 2-NA) ligands. These constitutional isomers feature similar triplet energies but disparate triplet lifetimes, translating into InP-based TADPL processes displaying two distinct average lifetime ranges upon cooling from 293 to 193 K. The time constants fall between 4.4 and 59.2 µs in the 2-NA-decorated InP QDs while further expanding between 84.2 and 733.2 µs in the corresponding 1-NA-ligated InP materials, representing a 167-fold time window. The resulting long-lived excited states enabled facile bimolecular triplet sensitization of 1O2 phosphorescence in the near-IR and promoted sensitized triplet-triplet annihilation photochemistry in 2,5-diphenyloxazole. We speculate that the discovery of new nanomaterials exhibiting TADPL lies on the horizon as myriad QDs can be readily derivatized using isomers of numerous classes of surface-anchoring chromophores yielding precisely regulated photophysical properties.

Characterization of physical, functional, and cognitive performance in 15 adults with hypophosphatasia.

OBJECTIVE: Given the small but growing body of literature related to physical functioning and the scarce data related to fine motor and cognitive functioning in adults with hypophosphatasia (HPP), our objective was to characterize physical, functional, and cognitive performance in adults with HPP. A future objective is to utilize this characterization to develop guidelines for evaluation by physical therapists (PT), occupational therapists (OT), and speech-language pathologists (SLP). METHOD: We evaluated physical, functional, and cognitive performance in 15 adults with HPP through standardized assessments of mobility, balance, fine motor control, activities of daily living, cognition, and self-reported measures of health-related quality of life, fatigue, depression, and anxiety. The median age at enrollment was 44 years (range 26-79 years). Among the participants, 11 (73%) were women. Five participants (33%) were on enzyme replacement therapy. RESULTS: Compared with the general population, HPP participants traveled shorter distances on the Six-Minute Walk Test (420 m (m) [SD: 132] vs 620 m [SD: 49], p < 0.00005), had slower gait on the 10-Meter Walk Test [HPP men (3.71 ft/s (f/s) [SD: 0.77] vs 4.70 f/s [SD: 0.14], p < 0.00005) and HPP women (3.39 f/s [SD: 0.67] vs 4.56 f/s [SD: 0.09], p < 0.00005)]. HPP participants had decreased upper extremity (UE) dexterity by Nine Hole Peg Test [right UE in HPP men (22.7 s (s) [SD: 2.3] vs 19.0 s [SD: 3.9], p = 0.03), left UE in HPP men (23.3 s [SD: 0.7] vs 19.8 s [SD: 3.7], p = 0.03), right UE in HPP women (19.8 s [SD: 2.0] vs 17.7 s [SD: 3.2], p = 0.01), and left UE in HPP women (21.1 s [SD: 2.5] vs 18.9 s[SD: 3.4], p = 0.02)], and some had abnormally slow bilateral UE reaction times via Dynavision (0.9 s [0.85,0.96], functional speed <1.15 s). On the Short Form-36 (SF36), HPP patients reported worse energy/fatigue (30.4 [SD 22.7] vs 52.2 [SD: 22.4], p = 0.0001), social functioning (54.5 [SD: 34.2] vs 78.8 [SD: 25.5], p = 0.0002), pain (46.1 [SD: 27.3] vs 70.8 [SD: 25.5], p = 0.0001), general health (36.8 [SD: 24.0] vs 57.0 [SD: 21.1], p = 0.0002), and health change i.e. perception of health improvement (32.1 [SD: 15.3] vs 59.1 [SD: 23.1], p < 0.00005) than the general population. Fatigue Severity Scale scores were well above the median for a healthy population (5.21 [SD: 1.8] vs 2.3 [SD: 1.21], p < 0.00005), indicating significant fatigue. HPP participants had significantly higher DASS scores for depression (8.5 [SD: 6.5] vs 5.0 [SD: 7.5], p = 0.02), anxiety (7.9 [SD: 6.7] vs 3.4 [SD: 5.1], p = 0.00009), and stress (14.7 [SD: 12.4] vs 8.1 [SD: 8.4], p = 0.0003) compared to the general population. CONCLUSION: Objective functional assessments demonstrated defects in physical functioning, including decreased ability to walk distances, slow gait speed, and diminished ability to repeatedly rise from a sitting position. In addition, participants self-reported significant limitations due to physical dysfunction. Decreased upper extremity dexterity may indicate problems with activities of daily living and delayed reaction times can have safety implications. Some patients with HPP have increased difficulties with depression, anxiety, and stress. PT, OT, and SLP specialists can aid in establishing baseline assessment of impairment and objective metrics for assessing efficacy of treatment.

A scoping review of fall hazards in the homes of older adults and development of a framework for assessment and intervention.

INTRODUCTION: Comprehensive evaluation and intervention provided by occupational therapists is effective in reducing the presence of fall hazards in the homes of older adults. The purpose of this study was to document known environmental hazards and to update a previous content analysis. A secondary goal reviewed a framework for evaluation and practice. METHODS: A comprehensive scoping review of published academic articles was performed from 1996 to 2019 to answer: What environmental hazards have been associated with falls in the homes of community-dwelling older adults? Data was extracted in a standardised critical appraisal worksheet and content analysis was conducted. A review of a conceptual framework for assessment and intervention was conducted by international experts (n = 6) in face-to-face interviews. RESULTS: Fourteen studies met the inclusion criteria for the scoping study. The studies reported 17 in-home environmental hazards: throw rugs/carpets, clutter, cords/wires, poorly placed light switches, items placed too low, items placed too high, no grab bars, toilet seats too low, uneven floor surfaces, slippery/wet surfaces, snowy/icy surfaces, backless/unsupportive shoes, unsteady stairs, inadequate lighting, inadequate heating/cooling, step stools without railings, and pets. CONCLUSION: A comprehensive list of specific fall hazards in and around the homes of older adults and a guiding framework offers occupational therapists an evidence-based foundation for fall prevention efforts.

Quantum dot solids showing state-resolved band-like transport.

Improving charge mobility in quantum dot (QD) films is important for the performance of photodetectors, solar cells and light-emitting diodes. However, these applications also require preservation of well defined QD electronic states and optical transitions. Here, we present HgTe QD films that show high mobility for charges transported through discrete QD states. A hybrid surface passivation process efficiently eliminates surface states, provides tunable air-stable n and p doping and enables hysteresis-free filling of QD states evidenced by strong conductance modulation. QD films dried at room temperature without any post-treatments exhibit mobility up to µ ~ 8 cm2 V-1 s-1 at a low carrier density of less than one electron per QD, band-like behaviour down to 77 K, and similar drift and Hall mobilities at all temperatures. This unprecedented set of electronic properties raises important questions about the delocalization and hopping mechanisms for transport in QD solids, and introduces opportunities for improving QD technologies.

Origin of Broad Emission Spectra in InP Quantum Dots: Contributions from Structural and Electronic Disorder.

The ensemble emission spectra of colloidal InP quantum dots are broader than achievable spectra of cadmium- and lead-based quantum dots, despite similar single-particle line widths and significant efforts invested in the improvement of synthetic protocols. We seek to explain the origin of persistently broad ensemble emission spectra of colloidal InP quantum dots by investigating the nature of the electronic states responsible for luminescence. We identify a correlation between red-shifted emission spectra and anomalous broadening of the excitation spectra of luminescent InP colloids, suggesting a trap-associated emission pathway in highly emissive core-shell quantum dots. Time-resolved pump-probe experiments find that electrons are largely untrapped on photoluminescence relevant time scales pointing to emission from recombination of localized holes with free electrons. Two-dimensional electronic spectroscopy on InP quantum dots reveals multiple emissive states and increased electron-phonon coupling associated with hole localization. These localized hole states near the valence band edge are hypothesized to arise from incomplete surface passivation and structural disorder associated with lattice defects. We confirm the presence and effect of lattice disorder by X-ray absorption spectroscopy and Raman scattering measurements. Participation of localized electronic states that are associated with various classes of lattice defects gives rise to phonon-coupled defect related emission. These findings explain the origins of the persistently broad emission spectra of colloidal InP quantum dots and suggest future strategies to narrow ensemble emission lines comparable to what is observed for cadmium-based materials.

Conduction Band Fine Structure in Colloidal HgTe Quantum Dots.

HgTe colloidal quantum dots (QDs) are of interest because quantum confinement of semimetallic bulk HgTe allows one to synthetically control the bandgap throughout the infrared. Here, we synthesize highly monodisperse HgTe QDs and tune their doping both chemically and electrochemically. The monodispersity of the QDs was evaluated using small-angle X-ray scattering (SAXS) and suggests a diameter distribution of ∼10% across multiple batches of different sizes. Electron-doped HgTe QDs display an intraband absorbance and bleaching of the first two excitonic features. We see splitting of the intraband peaks corresponding to electronic transitions from the occupied 1Se state to a series of nondegenerate 1Pe states. Spectroelectrochemical studies reveal that the degree of splitting and relative intensity of the intraband features remain constant across doping levels up to two electrons per QD. Theoretical modeling suggests that the splitting of the 1Pe level arises from spin-orbit coupling and reduced QD symmetry. The fine structure of the intraband transitions is observed in the ensemble studies due to the size uniformity of the as-synthesized QDs and strong spin-orbit coupling inherent to HgTe.

New Forms of CdSe: Molecular Wires, Gels, and Ordered Mesoporous Assemblies.

This work investigates the structure and properties of soluble chalcogenidocadmates, a molecular form of cadmium chalcogenides with unprecedented one-dimensional bonding motifs. The single crystal X-ray structure reveals that sodium selenocadmate consists of infinite one-dimensional wires of (Cd2Se3)n2n- charge balanced by Na+ and stabilized by coordinating solvent molecules. Exchanging the sodium cation with tetraethylammonium or didodecyldimethylammonium expands the versatility of selenocadmate by improving its solubility in a variety of polar and nonpolar solvents without changing the anion structure and properties. The introduction of a micelle-forming cationic surfactant allows for the templating of selenocadmate, or the analogous telluride species, to create ordered organic-inorganic hybrid CdSe or CdTe mesostructures. Finally, the interaction of selenocadmate "wires" with Cd2+ ions creates an unprecedented gel-like form of stoichiometric CdSe. We also demonstrate that these low-dimensional CdSe species show characteristic semiconductor behavior, and can be used in photodetectors and field-effect transistors.

Someone to talk to: young mothers' experiences of participating in a young parents support programme.

AIMS: To identify young parents' perceptions and experiences of a parenting support programme, run by a non-government organisation, which provided both community group-based, and one-on-one home visiting, support. STUDY DESIGN: A qualitative descriptive study was conducted in one of the most socio-economically disadvantaged areas of Sydney, NSW; this is also an area with one of the highest percentage of births among young parents. Young parents were eligible to participate whether they attended one of the parenting groups and/or received professional home visiting through the young parents programme. Eighteen young women were interviewed, and a further ten participated in a focus group. Thematic analysis of the focus groups and interviews was undertaken. FINDINGS: Four themes were identified in the analysis: 'someone I know and trust', 'we just talk about anything and everything', 'doing the personal' and 'getting out and relaxing'. These themes were linked through the common thread of relationships; the relationships between themselves and other young mothers, and with the workers on the programme. The characteristics of the person with whom they had a relationship, the type of relationship, the content of their interactions and the benefits of these relationships were all important. CONCLUSIONS: This study is limited by the small sample size and the 'low risk' status of the young parents who engaged in the programme. This study demonstrated not only the importance for young parents of all forms of interaction, whether it is one-on-one, in a group or social networking; but most importantly, the benefits of having someone to talk to.

What works to engage young parents into services? Findings from an appreciative inquiry workshop.

AIM: Lack of engagement in parenting support programs by young parents has been identified previously in the literature. This paper reports an innovative strategy utilizing appreciative inquiry (AI) to involve service providers and young parents in identifying strategies to engage young parents in services and programs. METHODS: A one-day workshop was held involving service/program staff and young mothers in three phases of AI: discovery, dreaming, and delivery. A variety of activities were used to gather data from participants: Small group discussion, creative 'art work' development, and notes. RESULTS: Results identified strategies that would promote and sustain young parents' engagement in services/programs, such as supportive non-judgmental attitude of staff, having a 'one stop shop' for services, and meeting childcare and educational needs of parents. CONCLUSION: Through AI, factors were identified that promote and sustain engagement of young parents into parenting support programs, and the need to engage fathers was also recognized.

Connecting, learning, leaving: supporting young parents in the community.

Providing support and parenting education through home visiting is a key early intervention strategy with young parents. Less is known about what home visitors do that makes a difference. The purpose of this paper is to describe the role and experiences of professional staff working with young parents participating in a multicomponent parent support programme (home visiting and supported parenting groups) provided by a non-government organisation in a socially disadvantaged area of Sydney, Australia. This was a qualitative descriptive study. Data were collected through three focus groups conducted with the same six staff over an 18-month period. Participant descriptions of their role and experiences working with young mothers were analysed thematically. Additional data from 20 anonymised client records were analysed through content analysis. Analysis of the focus group data revealed two themes, 'Connecting' and 'Facilitating Learning'. The theme 'Connecting' reflected the development of a relationship with the young mother commencing with 'how do we engage them?', 'building trust' through to formation of a relationship described as 'they know we're not friends, they know we're workers'. The second theme, 'Facilitating Learning' was informed by the analysis of both group and client record data and comprised a number of themes around what and how mothers learnt, through to 'ending the relationship' as the mothers left the programme. The quality of a mothers' learning was dependent on the quality of the connection between herself and the staff, similarly their capacity and, or confidence to leave the programme was dependent on the relationship, 'connecting' and the learning undertaken. Role modelling through interactions with children as well as with each other was seen as the most effective way to facilitate social and parenting skill development, while formal education sessions were evaluated by the workers to be less successful than informal ones.

Attitudes toward the diagnosis and disclosure of dementia among family caregivers and primary care physicians.

PURPOSE: This study examined attitudes of caregivers and physicians toward assessing and diagnosing dementia, with an emphasis on how a diagnosis is disclosed. DESIGN AND METHODS: Seventeen focus group interviews were conducted with caregivers or physicians from three sites; 52 caregivers participated in nine interviews (three each at the three sites), and 39 physicians participated in eight interviews (three each at two sites; two at one site). Structured interview protocols were used to assess diagnostic disclosure, first reactions, and suggestions for improving the diagnostic process. RESULTS: Caregivers recounted a highly negative emotional response to the disclosure, whereas many physicians reported that families handled the information well. Caregivers expressed a range of preferences for how the diagnosis should have been disclosed, from a direct approach to having the physician ease them into the results. IMPLICATIONS: Whenever possible, physicians should consult with the patient and family at the outset of the diagnostic process to better understand their preferences for diagnostic disclosure. Addressing diagnostic disclosure as part of physician education programs on dementia is recommended.

Effective resuscitation by nurses: perceived barriers and needs.

Nurses work in a variety of clinical settings. Some of these areas involve care of patients with acute illnesses while others do not. No matter in which setting a nurse works, the possibility exists that he or she will participate in the resuscitation of a patient. When patients face a life-threatening event such as cardiopulmonary arrest, they rely on the competence and skills of healthcare professionals. Because nurses are often the healthcare providers closest to the bedside and the first to respond to patients' needs, their knowledge and skills need to be optimal and their performance proficient.

Reproductive health in school-based health centers: findings from the 1998-99 census of school-based health centers.

PURPOSE: To describe the state of reproductive health services, including access to contraception and health center policies, among school-based health centers (SBHCs) serving adolescents in the United States METHODS: We examined questionnaire data on provision of reproductive health services from the 1998-99 Census of School-Based Health Centers (response rate 70%). We examined 551 SBHCs in schools with high or middle school grades. We used logistic regression to define factors independently associated with services and policies. RESULTS: Most SBHCs (76%) were open full-time; over one-half (51%) of centers had opened in the past 4 years. Services provided, either on-site or by referral, included gynecological examinations (95%), pregnancy testing (96%), sexually transmitted disease (STD) diagnosis and treatment (95%), Human Immunodeficiency Virus (HIV) counseling (94%), HIV testing (93%), oral contraceptive pills (89%), condoms (88%), Depo-Provera (88%), Norplant (78%), and emergency contraception (77%). Counseling, screening, pregnancy testing, and STD/HIV services were often provided on-site (range 55%-82%); contraception was often provided only by referral (on-site availability = 3%-28%). SBHCs with more provider staffing were more likely to provide services on-site; rural SBHCs and those serving younger grades were less likely to provide these services on-site. Over three-quarters (76%) of SBHCs reported prohibitions about providing contraceptive services on-site; the sources of these prohibitions included school district policy (74%), school policy (30%), state law (13%), and health center policy (12%). While SBHCs generally required parental permission for general health services, many allowed adolescents to access care independently for certain services including STD care (48%) and family planning (40%). Older SBHCs were more likely to allow independent access. CONCLUSIONS: SBHCs provide a broad range of reproductive health services directly or via referral; however, they often face institutional and logistical barriers to providing recommended reproductive health care.

Developing a culturally appropriate video to promote dual-method use by urban teens: rationale and methodology.

This article describes the development and production of a video targeted to urban adolescent women who use hormonal contraception. Research has shown that this population is at high risk for nonuse of condoms. Extensive preliminary qualitative and quantitative studies were done to understand the situations in which young women do and do not ask their partners to use a condom. Combining constructs from the health belief model, social cognitive learning theory and the theory of reasoned action with insights gleaned from the preliminary studies, the researchers developed a video that features two young HIV-positive women and two young HIV-negative men. Focus groups with young women helped the researchers edit the video to its current length of 21 minutes. Responses from the focus groups suggest that the video has a strong impact on young women. The video is currently part of a randomized controlled trial of two HIV prevention interventions.

The development of an Alzheimer's disease channel for the Michigan Interactive Health Kiosk Project.

The overall objective of this article is to describe the development and implementation of an Alzheimer's disease (AD) module for the Michigan Interactive Health Kiosk Project. This project provides access to health information via 100 kiosks located in public places throughout the state (e.g., churches, senior centers, schools, shopping malls, grocery stores, hospitals) using interactive multimedia software. Because the kiosk screen was designed to resemble a television set, program modules are referred to as "channels." The AD channel is designed to increase knowledge and awareness of the disease among the general public. After an overview of the overall project, the steps involved in developing the AD channel and strategies designed to monitor its use are described, including touch-screen usage data and an on-line user survey. Finally, marketing and promotion of the channel and the implications of this initiative for disseminating information about AD are discussed.