25 research outputs found
Error Events Due to Island Size Variations in Bit Patterned Media
Control of the variations of island properties is one of the key challenges in fabricating Bit-Patterned Media for future storage systems. The presence on any variation in the size and position of an island has a detrimental effect on the ability to recover recorded data, particularly in the case of variation in island size. By analyzing error events when island size variations are present we have identified that these are more likely to be single-bit in nature. To understand the origins of these error events we have investigated the size and magnetization state of islands in the vicinity where a single-bit error event is encountered. It is shown that these error events occur due to particular combinations of island size and magnetization state for the three islands investigated. In every case the central island, from which the data bit is recovered in error, is small compared to the nominal island size. These results show that size variations must be controlled in the fabrication process in order to maximize the bit-error-rate performance of the read channel
Tuning thermoelectric properties of SbTe-AgSbTe nanocomposite thin film -- synergy of band engineering and heat transport modulation
The present study demonstrates a large enhancement in the Seebeck coefficient
and ultralow thermal conductivity (TE) in SbTe-AgSbTe nanocomposite
thin film. The addition of Ag leads to the in-situ formation of AgSbTe
secondary phase nanoaggregates in the SbTe matrix during the growth
resulting in a large Seebeck coefficient and reduction of the thermal
conductivity. A series of samples with different amounts of minor AgSbTe
phases are prepared to optimize the TE performance of SbTe thin films.
Based on the experimental and theoretical evidence, it is concluded that a
small concentration of Ag promotes the band flattening and induces a sharp
resonate-like state deep inside the valence band of SbTe, concurrently
modifying the density of states (DOS) of the composite sample. In addition, the
electrical potential barrier introduced by the band offset between the host TE
matrix and the secondary phases promotes strong energy-dependent carrier
scattering in the composite sample, which is also responsible for enhanced TE
performance. A contemporary approach based on scanning thermal microscopy is
performed to experimentally obtain thermal conductivity values of both the
in-plane and cross-plane directions, showing a reduced in-plane thermal
conductivity value by ~ 58% upon incorporating the AgSbTe phase in the
SbTe matrix. Benefitting from the synergistic manipulation of
electrical and thermal transport, a large ZT value of 2.2 is achieved at 375 K.
The present study indicates the importance of a combined effect of band
structure modification and energy-dependent charge carrier scattering along
with reduced thermal conductivity for enhancing TE properties
Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics
The celebrated electronic properties of graphene have opened way for
materials just one-atom-thick to be used in the post-silicon electronic era. An
important milestone was the creation of heterostructures based on graphene and
other two-dimensional (2D) crystals, which can be assembled in 3D stacks with
atomic layer precision. These layered structures have already led to a range of
fascinating physical phenomena, and also have been used in demonstrating a
prototype field effect tunnelling transistor - a candidate for post-CMOS
technology. The range of possible materials which could be incorporated into
such stacks is very large. Indeed, there are many other materials where layers
are linked by weak van der Waals forces, which can be exfoliated and combined
together to create novel highly-tailored heterostructures. Here we describe a
new generation of field effect vertical tunnelling transistors where 2D
tungsten disulphide serves as an atomically thin barrier between two layers of
either mechanically exfoliated or CVD-grown graphene. Our devices have
unprecedented current modulation exceeding one million at room temperature and
can also operate on transparent and flexible substrates
Atomically thin boron nitride: a tunnelling barrier for graphene devices
We investigate the electronic properties of heterostructures based on
ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between
two layers of graphene as well as other conducting materials (graphite, gold).
The tunnel conductance depends exponentially on the number of h-BN atomic
layers, down to a monolayer thickness. Exponential behaviour of I-V
characteristics for graphene/BN/graphene and graphite/BN/graphite devices is
determined mainly by the changes in the density of states with bias voltage in
the electrodes. Conductive atomic force microscopy scans across h-BN terraces
of different thickness reveal a high level of uniformity in the tunnel current.
Our results demonstrate that atomically thin h-BN acts as a defect-free
dielectric with a high breakdown field; it offers great potential for
applications in tunnel devices and in field-effect transistors with a high
carrier density in the conducting channel.Comment: 7 pages, 5 figure
The LUX-ZEPLIN (LZ) Experiment
We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850' level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements
The LUX-ZEPLIN (LZ) experiment
We describe the design and assembly of the LUX-ZEPLIN experiment, a direct detection search for cosmic WIMP dark matter particles. The centerpiece of the experiment is a large liquid xenon time projection chamber sensitive to low energy nuclear recoils. Rejection of backgrounds is enhanced by a Xe skin veto detector and by a liquid scintillator Outer Detector loaded with gadolinium for efficient neutron capture and tagging. LZ is located in the Davis Cavern at the 4850’ level of the Sanford Underground Research Facility in Lead, South Dakota, USA. We describe the major subsystems of the experiment and its key design features and requirements
The LUX-ZEPLIN (LZ) radioactivity and cleanliness control programs
LUX-ZEPLIN (LZ) is a second-generation direct dark matter experiment with spin-independent WIMP-nucleon scattering sensitivity above 1.4×10−48cm2 for a WIMP mass of 40GeV/c2 and a 1000days exposure. LZ achieves this sensitivity through a combination of a large 5.6t fiducial volume, active inner and outer veto systems, and radio-pure construction using materials with inherently low radioactivity content. The LZ collaboration performed an extensive radioassay campaign over a period of six years to inform material selection for construction and provide an input to the experimental background model against which any possible signal excess may be evaluated. The campaign and its results are described in this paper. We present assays of dust and radon daughters depositing on the surface of components as well as cleanliness controls necessary to maintain background expectations through detector construction and assembly. Finally, examples from the campaign to highlight fixed contaminant radioassays for the LZ photomultiplier tubes, quality control and quality assurance procedures through fabrication, radon emanation measurements of major sub-systems, and bespoke detector systems to assay scintillator are presented