1,320 research outputs found
MOCVD synthesis of compositionally tuned topological insulator nanowires
Device applications involving topological insulators (TIs) will require the
development of scalable methods for fabricating TI samples with sub-micron
dimensions, high quality surfaces, and controlled compositions. Here we use
Bi-, Se-, and Te-bearing metalorganic precursors to synthesize TIs in the form
of nanowires. Single crystal nanowires can be grown with compositions ranging
from Bi2Se3 to Bi2Te3, including the ternary compound Bi2Te2Se. These high
quality nanostructured TI compounds are suitable platforms for on-going
searches for Majorana Fermions
Large anomalous Hall effect in ferromagnetic insulator-topological insulator heterostructures
We demonstrate the van der Waals epitaxy of the topological insulator
compound Bi2Te3 on the ferromagnetic insulator Cr2Ge2Te6. The layers are
oriented with (001) of Bi2Te3 parallel to (001) of Cr2Ge2Te6 and (110) of
Bi2Te3 parallel to (100) of Cr2Ge2Te6. Cross-sectional transmission electron
microscopy indicates the formation of a sharp interface. At low temperatures,
bilayers consisting of Bi2Te3 on Cr2Ge2Te6 exhibit a large anomalous Hall
effect (AHE). Tilted field studies of the AHE indicate that the easy axis lies
along the c-axis of the heterostructure, consistent with magnetization
measurements in bulk Cr2Ge2Te6. The 61 K Curie temperature of Cr2Ge2Te6 and the
use of near-stoichiometric materials may lead to the development of spintronic
devices based on the AHE.Comment: Related papers at http://pettagroup.princeton.ed
Controlled MOCVD growth of Bi2Se3 topological insulator nanoribbons
Topological insulators are a new class of materials that support
topologically protected electronic surface states. Potential applications of
the surface states in low dissipation electronic devices have motivated efforts
to create nanoscale samples with large surface-to-volume ratios and highly
controlled stoichiometry. Se vacancies in Bi2Se3 give rise to bulk conduction,
which masks the transport properties of the surface states. We have therefore
developed a new route for the synthesis of topological insulator nanostructures
using metalorganic chemical vapour deposition (MOCVD). MOCVD allows for control
of the Se/Bi flux ratio during growth. With the aim of rational growth, we vary
the Se/Bi flux ratio, growth time, and substrate temperature, and observe
morphological changes which indicate a growth regime in which nanoribbon
formation is limited by the Bi precursor mass-flow. MOCVD growth of Bi2Se3
nanostructures occurs via a distinct growth mechanism that is nucleated by gold
nanoparticles at the base of the nanowire. By tuning the reaction conditions,
we obtain either single-crystalline ribbons up to 10 microns long or thin
micron-sized platelets.Comment: Related papers at http://pettagroup.princeton.ed
Stem Cells to Regenerate Cardiac Tissue in Heart Failure
Myocardial regeneration is one of the most promising
therapeutic strategies for heart failure patients. Many experimental
studies have demonstrated that different types
of stem cell can differentiate into myocardial cells and tissues
necessary for regeneration of the damaged myocardium,
while studies in experimental animals suggest that
muscle (myoblast), bone marrow (mesenchymal, endothelial
or hematopoietic progenitors) and even heart cells
can help to improve heart contractility in vivo. These findings
have led several groups to undertake studies in patients
with myocardial infarction. However, the use of cellular
therapy in clinical trials is not without controversy,
mainly related with the need for better knowledge before
these therapeutic strategies are used in clinical practice.
Although significant enhancement of our knowledge of
the processes involved is fundamental, we do not consider
it unreasonable to initiate clinical trials in which specific
questions are posed, whose answers will allow us to
make further progress
Utilización de células madre para la regeneración miocárdica en la insuficiencia cardíaca
La terapia celular en la reparación miocárdica se vislumbra
como una de las estrategias terapéuticas con
mayor futuro en el tratamiento de la insuficiencia cardíaca.
Numerosos estudios in vitro recientes apoyan la potencialidad
de distintos tipos de células madre de diferenciarse
hacia los tejidos necesarios para regenerar el
tejido miocárdico dañado, mientras que estudios en animales
de experimentación sugieren que células madre
de músculo (mioblastos), médula ósea (progenitores mesenquimales,
endoteliales o hematopoyéticos) e incluso
del propio corazón pueden contribuir in vivo a mejorar la
contractilidad cardíaca. Estos trabajos han conducido a
que diversos grupos hayan iniciado estudios en pacientes
con infarto de miocardio. Sin embargo, la utilización
de la terapia celular en ensayos clínicos no está desprovista
de controversia, fundamentalmente relacionada con
la necesidad de aumentar nuestro conocimiento antes
de pasar a la aplicación clínica de estas estrategias terapéuticas.
Aunque es fundamental aumentar significativamente
el conocimiento de los procesos, no consideramos
irrazonable iniciar ensayos clínicos en los que se
identifiquen preguntas concretas cuya respuesta nos
permita avanzar en esta dirección
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