15 research outputs found
Spatially Resolving Spin-split Edge States of Chiral Graphene Nanoribbons
A central question in the field of graphene-related research is how graphene
behaves when it is patterned at the nanometer scale with different edge
geometries. Perhaps the most fundamental shape relevant to this question is the
graphene nanoribbon (GNR), a narrow strip of graphene that can have different
chirality depending on the angle at which it is cut. Such GNRs have been
predicted to exhibit a wide range of behaviour (depending on their chirality
and width) that includes tunable energy gaps and the presence of unique
one-dimensional (1D) edge states with unusual magnetic structure. Most GNRs
explored experimentally up to now have been characterized via electrical
conductivity, leaving the critical relationship between electronic structure
and local atomic geometry unclear (especially at edges). Here we present a
sub-nm-resolved scanning tunnelling microscopy (STM) and spectroscopy (STS)
study of GNRs that allows us to examine how GNR electronic structure depends on
the chirality of atomically well-defined GNR edges. The GNRs used here were
chemically synthesized via carbon nanotube (CNT) unzipping methods that allow
flexible variation of GNR width, length, chirality, and substrate. Our STS
measurements reveal the presence of 1D GNR edge states whose spatial
characteristics closely match theoretical expectations for GNR's of similar
width and chirality. We observe width-dependent splitting in the GNR edge state
energy bands, providing compelling evidence of their magnetic nature. These
results confirm the novel electronic behaviour predicted for GNRs with
atomically clean edges, and thus open the door to a whole new area of
applications exploiting the unique magnetoelectronic properties of chiral GNRs
Effect of microenvironment pH of swellable and erodable buffered matrices on the release characteristics of diclofenac sodium
The aim of this work is to design pH-dependent swellable and erodable-buffered matrices and to study the effect of the microenvironment pH on the release pattern of diclofenac sodium. Buffered matrix tablets containing diclofenac sodium, physically mixed with hydrophilic polymer (hydroxypropyl methylcellulose [HPMC]) and pH-dependent solubility polymer (Eudragit L100-55) were prepared with different microenvironment pHs. The release of diclofenac sodium from the buffer matrices was studied in phosphate buffer solutions of pH 5.9 and 7.4. The swelling and erosion matrices containing only HPMC and Eudragit L100-55 were studied in phosphate buffer solution of pH similar to the microenvironment pHs of the matrices. Drug release from matrices was found to be linear as a function of time. Amount of drug released was found to be higher in the medium of pH 7.4 than that of pH 5.9. The rate of drug release increased with the increase of the microenvironment pH of the matrices as determined from the slope. The pattern of drug release did not change with the change of microenvironment pH. The swelling and erosion occurred simultaneously from matrices made up of HPMC and Eudragit L100-55. Both extent of swelling and erosion increased with increase of the medium pH. It was concluded from this study that changing the pH within the matrix influenced the rate of release of the drug without affecting the release pattern