LaSrCoFeO Offers Alternate Cathode Material to Pt for Micro-Fuel Cells
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vacuum (~10 -6 Torr) with a high power electric field. This caused electrothermal self-heating of the GNR to hundreds of degrees which removed p-doping sources. The researchers, then, functionalized GNRs by introducing electron-rich nitrogen species by e-annealing the GNR devices in a ~1-Torr NH3/Ar environment. The GNR devices functionalized in this way showed Dirac point positions shifted by ~-20 V before and after e-annealing in NH3, that stayed stable and constant in vacuum, signifying n-type electronic dop-
ing without degradation of their carrier mobility. The researchers demonstrated by x-ray photoelectron spectroscopy and nanometer-scale secondary ion mass spectroscopy that the thermal annealing with NH 3 generated carbon-nitrogen species mostly at the edges of the graphene where chemical reactivity is high. Theoretical calculations performed by the researchers showed that GNRs functionalized by oxygen and nitrogen species on their edges were p- and n-doped, respectively, which agreed with the experimental
results the researchers obtained. Using the e-annealing approach in NH3, the researchers fabricated n-type sub-10 nm GNRFETs with Ti contact metals and a 5 nm Pd buffer layer that operated at room temperature with a subthreshold slope similar to that of the as-made p-type GNRFETs. The researchers said that the ability to control graphene chemistry through edge doping at the nanoscale is an important step toward controlled graphene electronics. JOAN J. CARVAJAL
Light-Assisted Writing of Bits Achieved on Low-Doped (Ga,Mn)As Ferromagnetic Semiconductors
recently found just such a mechanism in low-doped (Ga,Mn)As thin films at low temperatures using the photocoercivity effect. By removing the need for heating, this could provide a low power alternative to other energy-assisted recording technologies. The researchers demonstrated lightassisted writing in the May 8 issue of Physical Review Letters (DOI: 10.1103/ PhysRevLett.102.187401; #187401). They used low-temperature molecular beam epitaxy to deposit a 360 nm layer of (Ga1-xMnx)As ferromagnetic semiconductors, with x ≈ 0.005. These samples were measured at 2 K with the magnetooptical Kerr effect at two different laser powers, the “dark” condition at 10 μW and the “light” condition at 1 mW. Finding the coercivity to be 525 Oe and 285 Oe, respectively, the researchers returned to 10 μW and found the coercivity recovered to its original value—showing
that the effect is reversible. They then wrote patterns on the substrate in an intermediate field of 470 Oe, evidencing both the locality of the transition and its potential to write bits. The mechanism the researchers propose for this behavior is the mobility of holes. The magnetic behavior of the (Ga,Mn)As is mediated by the holes, and in low-doped samples, the mobility is low. This means that the holes are not free to relocate to their most favored state when a field is applied, and therefore some extra field is required to move domain walls. In comparison, the photocoercivity effect was not seen in more h
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