Facets-Directed Epitaxially Grown Lead Halide Perovskite-Sulfobromide Nanocrystal Heterostructures and Their Improved Photocatalytic Activity.

Lead halide perovskite nanocrystal heterostructures have been extensively studied in the recent past for improving their photogenerated charge carriers mobility. However, most of such heterostructures are formed with random connections without having strong evidence of epitaxial relation. Perovskite-chalcohalides are the first in this category, where all-inorganic heterostructures are formed with epitaxial growth. Going beyond one facet, herein, different polyhedral nanocrystals of CsPbBr3 are explored for facet-selective secondary epitaxial sulfobromide growths. Following a decoupled synthesis process, the heterojunctions are selectively established along {110} as well as {200} facets of 26-faceted rhombicuboctahedrons, the {110} facets of armed hexapods, and the {002} facets of 12-faceted dodecahedron nanocrystals of orthorhombic CsPbBr3. Lattice matching induced these epitaxial growths, and their heterojunctions have been extensively studied with electron microscopic imaging. Unfortunately, these heterostructures did not retain the intense host emission because of their indirect band structures, but such combinations are found to be ideal for promoting photocatalytic CO2 reduction. The pseudo-Type-II combination helped here in the successful movement of charge carriers and also improved the rate of catalysis. These results suggest that facet-selective all-inorganic perovskite heterostructures can be epitaxially grown and this could help in improving their catalytic activities.

Nucleophile-Controlled Halide Release from the Substitution Reaction of Haloketone for Facet Tuning and Manganese Doping in CsPbCl3 Nanocrystals.

Halide content of the reaction medium not only enhances the brightness of CsPbCl3 nanocrystals but also, control the shape modulations as well as doping Mn(II) in these host nanocrystals. Correlating both the shape effect and doping, herein, an in situ reaction of nucleophile-controlled halide release was explored for monitoring facets modulations and doping in CsPbCl3 nanocrystals. This was performed using alkyl amine as nucleophile which reacted with α-halo ketone, phenacyl chloride, to release chloride ions. Increase in amine concentration which released more Cl ions, reduced the possibility of shape transformation from perfect to truncated cubes during annealing. Similarly, for Mn(II) doping, the dopant photoluminescence intensity remained directly proportional to the amount of introduced amine nucleophiles. Quality of both doped and undoped nanocrystals obtained in this procedure remained unparallel and the method provided a strong correlation of rate of halide release with both facet modulations and doping in these nanocrystals.

Cs-Lattice Extension and Expansion for Inducing Secondary Growth of CsPbBr3 Perovskite Nanocrystals.

The increase of the stability of perovskite nanocrystals with respect to exposure to polar media, layers growth, or shelling with different materials is in demand. While these are widely studied for metal chalcogenide nanocrystals, it has yet to be explored for perovskite nanocrystals. Even growth of a single monolayer on any facet or on the entire surface of these nanocrystals could not be established yet. To address this, herein, a secondary growth approach leading to creation of a secondary lattice with subsequent expansion on preformed CsPbBr3 perovskite nanocrystals is reported. As direct layer growth by adding precursors was not successful, Cs-lattice extension to preformed CsPbBr3 nanocrystals was performed by coupling CsBr to these nanocrystals. Opening both {110}/{002} and {200} facets of parent CsPbBr3 nanocrystals, CsBr was observed to be connected with lattice matching to the {200} facets. Further with Pb(II) incorporation, the Cs-sublattices of CsBr were expanded to CsPbBr3 and led to cube-couple nanocrystals. However, as cubes in these nanostructures were differently oriented, these showed lattice mismatch at their junctions. This lattice mismatch though restricted complete shelling but successfully favored the secondary growth on specific facets of parent CsPbBr3 nanocrystals. Details of this secondary growth via lattice extension and expansion are microscopically analyzed and reported. These results further suggest that lead halide perovskite nanocrystals can be epitaxially grown under proper reaction design and more complex as well as heterostructures of these materials can be fabricated to meet the current demands.

Introducing B-Site Cations by Ion Exchange and Shape Anisotropy in CsPbBr3 Perovskite Nanostructures.

Lead halide perovskite nanocrystals, whether formed by their own nucleation and growth or by ion diffusion into the lattice of others, are still under investigation. Moreover, beyond isotropic nanocrystals, fabricating anisotropic perovskite nanocrystals by design has remained difficult. Exploring the lattice of orthorhombic-phase Cs2ZnBr4 with the complete replacement of Zn tetrahedra by Pb octahedra, dimension-tunable anisotropic nanocrystals of CsPbBr3 are reported. This B-site ion introduction led to CsPbBr3 nanorods having [100] as major axis, in contrast with all reports on rods/wires where the lengths were along the [001] direction. This was possible by using derivatives of α-bromo ketones, which helped in tuning the shape of Cs2ZnBr4 and also the facets of transformed CsPbBr3. While similar experiments are extended to orthorhombic Cs2HgBr4, standard nanorods with [001] as the major axis were observed. From these results, it is further concluded that anisotropic perovskite nanocrystals might not follow any specific rules for directional growth and instead might depend on the structure of the parent lattice.

Suicidality among gender minorities in Karnataka, South India.

BACKGROUND: It is argued that Indian gender minorities displayed differential mental health problems and suicide attempts. Hence, the study was intended to understand the prevalence of anxiety, depression and suicidality among this group, specifically those living in a metropolitan city in South India. METHODS: The data was generated from a cross-sectional study that employed a structured questionnaire to collect information about experiences of anxiety, depression and suicidal behavior among gender-diverse individuals in Bangalore, the capital city of Karnataka state. The study used stratified simple random sampling of eligible individuals who were 18 years of age and older and who were enrolled in an HIV prevention program implemented for gender-diverse individuals run by the Karnataka Health Promotion Trust and the University of Manitoba at the time of the study (2012). Bivariate and multivariate analyses were used to assess the relative contribution of various factors that affect suicide ideation or actual attempts among the gender diverse participants. RESULTS: Results showed that 62% whose main source of income was Basti (socially sanctioned practice of begging), 52% of Hijras, 56% who lived with their Gurus, 58% who were not happy with their physical appearance, 55% who consumed alcohol daily, and 63% who experienced high depression had ever thought of or attempted suicide in the month prior to the survey. However, multivariate analysis showed that respondents who were not happy with their physical appearance and thought of changing it had significantly higher odds (AOR = 2.861; CI 1.468,5.576; p = 0.002) of either having thoughts that it was better being dead or wished they died. Similarly, those who experienced high depression, their odds of either having had thoughts of or having attempted suicide increased by three times (AOR = 3.997; CI 1.976, 8.071; p < 0.000). CONCLUSIONS: It is observed that a high percentage of gender minorities had attempted suicide or thought of suicide during the month preceding the data collection. The findings bring new insights on the proximate determinant of physical appearance on the suicidality of gender minorities assigned male at birth and appropriate to account for this while addressing the mental health issues.

Facets and Defects in Perovskite Nanocrystals for Photocatalytic CO2 Reduction.

Light-emitting lead halide perovskite nanocrystals are typically obtained in a six-faceted cube shape. However, for applications such as catalysis, more active facets for the adsorption/desorption of reactants/products and the suppression of carrier recombination are essentially required. To meet these challenges, herein CsPbBr3 perovskite nanocrystals in cube and faceted noncube shapes were explored for photocatalytic reductions of CO2. Importantly, halide-deficient dim multifaceted noncube emitters having less than 1% photoluminescence quantum yields showed superior catalytic activity compared to that of bright halide-rich cube nanocrystals. Beyond these, hexapod-shaped nanocrystals were also explored, and these remained in an intermediate state. With the support of density functional theory, the adsorption and desorption probabilities of reactants/products on different facets were also calculated and correlated with experimental findings. These results indicated that facets and defects of perovskite nanocrystals are equally important for carrying out catalytic reactions.

Facets Directed Connecting Perovskite Nanocrystals.

Connecting nanocrystals with removal of interface ligand barriers is one of the key steps for efficient carrier transportation in optoelectronic device fabrication. Typically, ion migration for crystal deformation or connection with other nanocrystals needs a solvent as medium. However, on the contrary, this has been observed for CsPbBr3 perovskite nanocrystals in film where nanocrystals were swollen to get wider and fused with adjacent nanocrystals in self-assembly on film during solvent evaporation. Depending on precursor composition and exposed facets, again these connections could be programmed for tuning their connecting directions leading to different shapes. Aging further on solid substrate, these were also turned to continuous film of nanostructures eliminating all interparticle gaps on the film. This transformation could be ceased at any point of time, simply by heating or adding sufficient ligands. Analysis suggested that these unique and controlled connections were only observed with polyhedron shaped nanostructures with certain compositions and not with traditionally cubes. Details of this solid-surface transformation during solvent evaporation were analyzed, and an interparticle material transfer type mechanism was proposed. As these observations were not seen in chalcogenide and oxide nanocrystals and exclusively observed in perovskite nanocrystals, this would add new fundamentals to the insights of crystal growths of nanocrystals and would also help in obtaining films of connecting nanocrystals.

Magnetic Domain Wall Based Synaptic and Activation Function Generator for Neuromorphic Accelerators.

Magnetic domain walls are information tokens in both logic and memory devices and hold particular interest in applications such as neuromorphic accelerators that combine logic in memory. Here, we show that devices based on the electrical manipulation of magnetic domain walls are capable of implementing linear, as well as programmable nonlinear, functions. Unlike other approaches, domain-wall-based devices are ideal for application to both synaptic weight generators and thresholding in deep neural networks. Prototype micrometer-size devices operate with 8 ns current pulses and the energy consumption required for weight modulation is ≤16 pJ. Both speed and energy consumption compare favorably to other synaptic nonvolatile devices, with the expected energy dissipation for scaled 20 nm devices close to that of biological neurons.

Doping Iron in CsPbBr3 Perovskite Nanocrystals for Efficient and Product Selective CO2 Reduction.

Lead halide perovskite nanocrystals have recently emerged as an efficient optical material for light harvesting. While these have been extensively studied for obtaining bright emissions, their use as catalysts for enhancing the rate of chemical reactions has been explored little. Considering their importance in catalysis, herein, Fe(II)-doped CsPbBr3 perovskite nanocrystals have been explored for photocatalytic reduction of CO2. In comparison to undoped CsPbBr3, doped nanocrystals showed enhanced catalytic activity and also predominantly led to evolution of CH4 instead of CO. The observation of a reverse trend of predominated CH4 evolution in doped nanocrystals rather than CO observed for undoped nanocrystals was correlated to the adsorption/desorption energy of respective products established theoretically earlier. This selective evolution of major products on doping remained unique and also a step forward for understanding more regarding light to chemical energy conversions using perovskite nanocrystals.

Violence and Mental Health Among Gender-Diverse Individuals Enrolled in a Human Immunodeficiency Virus Program in Karnataka, South India.

Purpose: Gender-diverse individuals in India face considerable discrimination, stigma, and violence. There is a dearth of published literature describing experiences of violence among this population and potential links to mental health. Methods: A questionnaire was administered to 282 study participants, 18 years of age and older, who self-identified as hijra, kothi, double decker, or bisexual and were actively enrolled in a local HIV prevention program in Bangalore, India in 2012. Responses were used to calculate a composite depression/anxiety score. Associations between sociodemographic characteristics and experiences of physical and sexual violence in the previous six months were tested and differences in depression/anxiety score based on experiences of violence were explored. Results: Recent physical violence was common among study participants and was reported among 46% of nirvan (emasculated) hijras (transgender), 42% of akwa (not emasculated) hijras, and 25% of kothis (feminine acting males). Rape in the previous year was particularly common among akwa hijras (39%). Factors associated with being raped included younger age, less education, and employment in basti (blessings), sex work, chela (disciple of hijra guru), or at a community-based organization. Kothis had the highest depression/anxiety score. No significant difference in depression/anxiety score based on recent history of physical violence or rape was found. Conclusions: Physical violence and poor mental health are common among gender-diverse individuals in Bangalore, Karnataka. There is a need for services that cater to the unique mental health needs of gender-diverse individuals in India, following rights-based approaches that address the underlying roots of oppression they encounter.

Coupled Halide-deficient and Halide-rich Reaction System for Doping in Perovskite Armed Nanostructures.

Insights of Mn(II) doping in CsPbCl3-armed hexapod nanostructures is reported. These complex structures were typically formed in halide concentration tuned modulated reactions. Cores were first formed under halide deficient condition and with enriching halides; these were transformed to armed structures. Doping of Mn(II) was observed facilitated during the arm growth in the second stage of the reaction. These observations were supported with decoupled reactions with minimized and maximized halide concentrations carried out in separate reactions. However, less interference for the exciton to dopant energy transfer was noticed for the defect states created in halide-deficient medium, and the intensity of the dopant emission remained proportional to the amount of dopant inserted in the nanocrystals. Being this is an in situ observation in the coupled reactions of both poor and rich halide reaction systems, the finding would strengthen the understanding of doping in perovskite host nanocrystals.

Arm Growth and Facet Modulation in Perovskite Nanocrystals.

Highly emissive isotropic CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals are typically observed in a six-faceted cube shape. When a unique approach is adopted and the reaction medium is enriched with halides, arm growth on all six facets was carried out and reported. Analysis suggested that these armed nanostructures were obtained from intermediate polyhedron shaped structures having 26 facets, and these were formed under halide-deficient conditions. Surface energy calculations further supported the possible existence of all facets for both of these structures under different halide composition environments. The entire study was first explored for CsPbBr3 and then extended to CsPbCl3; however, for CsPbI3 nanocrystals, Sr(II) dopant was used for obtaining stable emission. Arm lengths could also be tuned with a function of reaction temperature for CsPbBr3. Formation of stable facets in polyhedron shaped nanostructures and their transformation to respective hexapods under halide-deficient and halide-rich conditions add new fundamental concepts for these nanostructures and their shape evolutions.

Following the divine: an ethnographic study of structural violence among transgender jogappas in South India.

Newly proposed legislation that aims to protect the well-being of transgender people in India offers hope of greater recognition of human rights and improved access to entitlements for these marginalised groups. However, social welfare and health institutions have a long way to go in translating proposed legislation into policies that can concretely address the social suffering of transgender people. Drawing on ethnographic field research in northern Karnataka among a highly understudied transgender group known as the jogappas, we describe the effects of overlapping forms of structural violence surrounding education, subsistence, family life and attempts to access social and health services. Findings reveal how social inequities are implicated in the emergence of transgender subjectivities along the road to becoming a jogappa. Our findings alert policy makers to the diverse needs of transgender people in India, which continually evolve while rooted in moral histories of religiosity.

Blue-Emitting CsPbCl3 Nanocrystals: Impact of Surface Passivation for Unprecedented Enhancement and Loss of Optical Emission.

High-energy-emitting CsPbCl3 nanocrystals have shown significant loss and enhancement of their emission intensity (∼40-50 folds) during purification and surface treatments, respectively. This confirms that the surfaces of these nanocrystals are very sensitive. In this Letter, physical insights of the interface bindings on the surface of these blue-emitting CsPbCl3 nanocrystals with different passivating agents and their consequential impact on purification are investigated. Using various metal chlorides irrespective of the charge and size of the metal ions, metal acetates, and nonmetal chloride, the predominant influence of chloride ions in helping retrieve/intensify the blue emission is established. The purification processes are observed to be very delicate, and successive purifications with introduction of polar nonsolvents led to the transformation of an emitting cubic CsPbCl3 phase to nonemitting tetragonal CsPb2Cl5 phase nanocrystals irreversibly. The impact of various salt additions only temporarily helped in enhancing the emission, but the phase change remained inevitable upon successive purification. However, as a remedy, by in situ use of alkylammonium chloride salt in high-temperature reactions, the surface binding was improved, and significant emission as well as the phase could be retained with successive purifications.

Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention.

Annealing perovskite nanocrystals at high reaction temperature changes their crystal phase, shape, and optical properties. Carrying out reactions between 180 and 250 °C, the impact of thermal annealing for CsPbCl3 and CsPbBr3 nanocrystals in a reaction flask was investigated here. At higher temperature, a phase change was observed instantly, which could not be trapped even with ice-bath cooling. Interestingly, using a calculated amount of preformed alkylammonium halides as dual passivating agents, the nanocrystals of both CsPbCl3 and CsPbBr3 could even be stabilized for hours of annealing at 250 °C. CsPbCl3, which was reported to be a poor emissive nanocrystal in comparison to CsPbBr3, could sustain even more than 5 h of annealing at 250 °C and recorded ∼51% absolutely quantum yield. Details of the interface chemistry and the role of the used dual passivating agent for providing thermal stability are studied and reported in this Letter.

Phase-Stable CsPbI3 Nanocrystals: The Reaction Temperature Matters.

High temperature colloidal synthesis for obtaining thermal, colloidal and phase-stable CsPbI3 nanocrystals with near-unity quantum yield is reported. While standard perovskite synthesis reactions were carried out at 160 °C (below 200 °C), increase of another ≈100 °C enabled the alkylammonium ions to passivate the surface firmly and prevented the nanocrystals from phase transformation. This did not require any inert atmosphere storage, use of heteroatoms, specially designed ligands, or the ice cooling protocol. Either at high temperature in reaction flask or in the crude mixture or purified dispersed solution; these nanocrystals were observed stable and retained the original emission. Different spectroscopic analyses were carried out and details of the surface binding of alkyl ammonium ligands in place of surface Cs in the crystal lattice were investigated. As CsPbI3 is one of the most demanding optical materials, bringing stability by proper surface functionalization without use of secondary additives would indeed help in wide spreading of their applications.

Dutiful daughters: HIV/AIDS, moral pragmatics, female citizenship and structural violence among Devadasis in northern Karnataka, India.

Decades of research have documented how sex workers worldwide, particularly female sex workers (FSWs), shoulder a disproportionate burden of the HIV epidemic. In India, although a substantial progress has been made in controlling the epidemic, its prevalence among FSWs and the Devadasis (also called traditional sex workers) in northern Karnataka is still significantly high. On the other hand, much of the HIV prevention research has focused on their mapping and size estimation, typologies, bio-behavioural surveillance, condom use and other prevention technologies. In this article, drawing on critical theoretical perspectives, secondary historical sources and in-depth interviews, we unravel wider social, cultural and political economic complexities surrounding the lives of Devadasis, and specifically illuminate the moral pragmatics that shed light on their entry into sex trade and vulnerability to HIV. Findings from this research are extremely important since while much is known about Devadasis in social sciences and humanities, relatively little is known about the complexities of their lives within public health discourses related to HIV. Our work has direct implications for ongoing HIV prevention and health promotion efforts in the region and beyond.

The Spatial Resolution Limit for an Individual Domain Wall in Magnetic Nanowires.

Magnetic nanowires are the foundation of several promising nonvolatile computing devices, most notably magnetic racetrack memory and domain wall logic. Here, we determine the analog information capacity in these technologies, analyzing a magnetic nanowire containing a single domain wall. Although wires can be deliberately patterned with notches to define discrete positions for domain walls, the line edge roughness of the wire can also trap domain walls at dimensions below the resolution of the fabrication process, determining the fundamental resolution limit for the placement of a domain wall. Using a fractal model for the edge roughness, we show theoretically and experimentally that the analog information capacity for wires is limited by the self-affine statistics of the wire edge roughness, a relevant result for domain wall devices scaled to regimes where edge roughness dominates the energy landscape in which the walls move.

Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals.

Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots. The fast formation of perovskites makes the dopant insertions more competitive and challenging. Introducing alkylamine hydrochloride (RNH3 Cl) as a promoting reagent, precise controlled doping of MnII in CsPbCl3 perovskite nanocrystals is reported. Simply, by changing the amount of RNH3 Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d-d emission intensities are tailored. Investigations suggested that RNH3 Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles. This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions. Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared.

Contextualizing willingness to participate: recommendations for engagement, recruitment & enrolment of Kenyan MSM in future HIV prevention trials.

BACKGROUND: The HIV epidemic among men who have sex with men (MSM) continues to expand globally. The addition of an efficacious, prophylactic vaccine to combination prevention offers immense hope, particularly in low- and middle- income countries which bear the greatest global impact. However, in these settings, there is a paucity of vaccine preparedness studies that specifically pertain to MSM. Our study is the first vaccine preparedness study among MSM and female sex workers (FSWs) in Kenya. In this paper, we explore willingness of Kenyan MSM to participate in HIV vaccine efficacy trials. In addition to individual and socio-cultural motivators and barriers that influence willingness to participate (WTP), we explore the associations or linkages that participants draw between their experiences with or knowledge of medical research both generally and within the context of HIV/AIDS, their perceptions of a future HIV vaccine and their willingness to participate in HIV vaccine trials. METHODS: Using a social network-based approach, we employed snowball sampling to recruit MSM into the study from Kisumu, Mombasa, and Nairobi. A field team consisting of seven community researchers conducted in-depth interviews with a total of 70 study participants. A coding scheme for transcribed and translated data was developed and the data was then analysed thematically. RESULTS: Most participants felt that an HIV vaccine would bring a number of benefits to self, as well as to MSM communities, including quelling personal fears related to HIV acquisition and reducing/eliminating stigma and discrimination shouldered by their community. Willingness to participate in HIV vaccine efficacy trials was highly motivated by various forms of altruism. Specific researcher responsibilities centred on safe-guarding the rights and well-being of participants were also found to govern WTP, as were reflections on the acceptability of a future preventive HIV vaccine. CONCLUSION: Strategies for engagement of communities and recruitment of trial volunteers for HIV vaccine efficacy trials should not only be grounded in and informed by investigations into individual and socio-cultural factors that impact WTP, but also by explorations of participants' existing experiences with or knowledge of medical research as well as attitudes and acceptance towards a future HIV vaccine.