622 research outputs found
A method for measuring the Neel relaxation time in a frozen ferrofluid
We report a novel method of determining the average Neel relaxation time and
its temperature dependence by calculating derivatives of the measured time
dependence of temperature for a frozen ferrofluid exposed to an alternating
magnetic field. The ferrofluid, composed of dextran-coated Fe3O4 nanoparticles
(diameter 13.7 nm +/- 4.7 nm), was synthesized via wet chemical precipitation
and characterized by x-ray diffraction and transmission electron microscopy. An
alternating magnetic field of constant amplitude (H0 = 20 kA/m) driven at
frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the
temperature dependent magnetic energy absorption rate in the temperature range
from 160 K to 210 K. We found that the specific absorption rate of the
ferrofluid decreased monotonically with temperature over this range at the
given frequencies. From these measured data, we determined the temperature
dependence of the Neel relaxation time and estimate a room-temperature
magnetocrystalline anisotropy constant of 40 kJ/m3, in agreement with
previously published results
Overspending on Online Game App Purchasing Among University Students in Sarawak, Malaysia
This research has sought to ascertain the pattern in-app purchasing in online games amongst university
students. The sample consisted of 100 university students from all over the area of Kuching, Sarawak. This research
revealed that out of the 100 students chosen, 91 were involved in in-app purchasing while 9 did not share the same passion. There are a wide range of factors as to why students are or are not involved in the habit of in-app purchasing in online games amongst university students. This research also studied on spending pattern of students, source of financial aid and factors contributing to reasons for in-app purchasing. While this study was conducted in Kuching, it has affected people from other regions as well, as there are many students who are not only involved in in-app purchasing, but addicted to it
Approaching Disorder-Tolerant Semiconducting Polymers
Doping has been widely used to control the charge carrier concentration in organic semiconductors. However, in conjugated polymers, n-doping is often limited by the tradeoff between doping efficiency and charge carrier mobilities, since dopants often randomly distribute within polymers, leading to significant structural and energetic disorder. Here, we screen a large number of polymer building block combinations and explore the possibility of designing n-type conjugated polymers with good tolerance to dopant-induced disorder. We show that a carefully designed conjugated polymer with a single dominant planar backbone conformation, high torsional barrier at each dihedral angle, and zigzag backbone curvature is highly dopable and can tolerate dopant-induced disorder. With these features, the designed diketopyrrolopyrrole (DPP)-based polymer can be efficiently n-doped and exhibit high n-type electrical conductivities over 120 S cm−1, much higher than the reference polymers with similar chemical structures. This work provides a polymer design concept for highly dopable and highly conductive polymeric semiconductors
Tuning ultrafast electron thermalization pathways in a van der Waals heterostructure
Ultrafast electron thermalization - the process leading to Auger
recombination, carrier multiplication via impact ionization and hot carrier
luminescence - occurs when optically excited electrons in a material undergo
rapid electron-electron scattering to redistribute excess energy and reach
electronic thermal equilibrium. Due to extremely short time and length scales,
the measurement and manipulation of electron thermalization in nanoscale
devices remains challenging even with the most advanced ultrafast laser
techniques. Here, we overcome this challenge by leveraging the atomic thinness
of two-dimensional van der Waals (vdW) materials in order to introduce a highly
tunable electron transfer pathway that directly competes with electron
thermalization. We realize this scheme in a graphene-boron nitride-graphene
(G-BN-G) vdW heterostructure, through which optically excited carriers are
transported from one graphene layer to the other. By applying an interlayer
bias voltage or varying the excitation photon energy, interlayer carrier
transport can be controlled to occur faster or slower than the intralayer
scattering events, thus effectively tuning the electron thermalization pathways
in graphene. Our findings, which demonstrate a novel means to probe and
directly modulate electron energy transport in nanoscale materials, represent
an important step toward designing and implementing novel optoelectronic and
energy-harvesting devices with tailored microscopic properties.Comment: Accepted to Nature Physic
A Molecular Design Approach Towards Elastic and Multifunctional Polymer Electronics
Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facile patternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C–H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V−1 s−1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics
Giant intrinsic photoresponse in pristine graphene
When the Fermi level matches the Dirac point in graphene, the reduced charge
screening can dramatically enhance electron-electron (e-e) scattering to
produce a strongly interacting Dirac liquid. While the dominance of e-e
scattering already leads to novel behaviors, such as electron hydrodynamic
flow, further exotic phenomena have been predicted to arise specifically from
the unique kinematics of e-e scattering in massless Dirac systems. Here, we use
optoelectronic probes, which are highly sensitive to the kinematics of electron
scattering, to uncover a giant intrinsic photocurrent response in pristine
graphene. This photocurrent emerges exclusively at the charge neutrality point
and vanishes abruptly at non-zero charge densities. Moreover, it is observed at
places with broken reflection symmetry, and it is selectively enhanced at free
graphene edges with sharp bends. Our findings reveal that the photocurrent
relaxation is strongly suppressed by a drastic change of fast photocarrier
kinematics in graphene when its Fermi level matches the Dirac point. The
emergence of robust photocurrents in neutral Dirac materials promises new
energy-harvesting functionalities and highlights intriguing electron dynamics
in the optoelectronic response of Dirac fluids.Comment: Originally submitted versio
Developing a Vehicle Cost Calculator to Promote Electric Vehicle Adoption among TNC Drivers
USDOT Grant 69A3551747114This research developed EV Explorer 2.0, an online vehicle cost calculator (VCC) to meet the requirements of transportation network company (TNC) drivers considering acquiring an electric vehicle (EV). The tool was built to also support the needs of other users considering an EV, including other types of gig economy drivers as well as the general population of non-professional drivers. EV Explorer 2.0 includes several important features and functionalities to support the TNC driver use case that are not found in any other available tool: (1) It allows users to estimate TCO for used vehicles as well as new (others only estimate TCO for new vehicles); (2) Outputs include ridehail-driving income estimates, accounting for EV trip bonuses offered by Uber, net driving costs; (3) Estimates of total cost of driving (TCD) include charging network membership fees and charging session fees (in addition to electricity prices). It also includes key features found in other leading tools, such as presenting and tailoring EV purchase/lease incentive estimates (based on a database we developed), and innovative features to benefit all users, such as animations conveying the social and environmental impacts of vehicle choice. Design features were informed and validated in user testing with TNC drivers who had expressed interest in EV adoption
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