53 research outputs found
An Interview on Leadership with Al Carey, CEO, PepsiCo Beverages
Paul T. Barrett, PhD, CPA, is dean and professor of business for the College of Business and Economics, Longwood University, Farmville, VA 23909.
James C. Haug, DBA, is associate professor of management, Longwood University, College of Business and Economics, Farmville, VA 23909.
John N. Gaskins, PhD, currently serves as associate professor of marketing and retailing, Longwood University, College of Business and Economics, Farmville, VA 23909
Validation of the Wiedemann-Franz Law in solid and molten tungsten above 2000 K through thermal conductivity measurements via steady state temperature differential radiometry
We measure the thermal conductivity of solid and molten tungsten using Steady
State Temperature Differential Radiometry. We demonstrate that the thermal
conductivity can be well described by application of Wiedemann-Franz Law to
electrical resistivity data, thus suggesting the validity of Wiedemann-Franz
Law to capture the electronic thermal conductivity of metals in their molten
phase. We further support this conclusion using ab initio molecular dynamics
simulations with a machine-learned potential. Our results show that at these
high temperatures, the vibrational contribution to thermal conductivity is
negligible compared to the electronic component
Interface Controlled Thermal Resistances of Ultra-Thin Chalcogenide-Based Phase Change Memory Devices
Phase change memory (PCM) is a rapidly growing technology that not only offers advancements in storage-class memories but also enables in-memory data processing to overcome the von Neumann bottleneck. In PCMs, data storage is driven by thermal excitation. However, there is limited research regarding PCM thermal properties at length scales close to the memory cell dimensions. Our work presents a new paradigm to manage thermal transport in memory cells by manipulating the interfacial thermal resistance between the phase change unit and the electrodes without incorporating additional insulating layers. Experimental measurements show a substantial change in interfacial thermal resistance as GST transitions from cubic to hexagonal crystal structure, resulting in a factor of 4 reduction in the effective thermal conductivity. Simulations reveal that interfacial resistance between PCM and its adjacent layer can reduce the reset current for 20 and 120 nm diameter devices by up toâ~â40% andâ~â50%, respectively. These thermal insights present a new opportunity to reduce power and operating currents in PCMs
On the thermal and mechanical properties of MgCoNiCuZnO across the high-entropy to entropy-stabilized transition
As various property studies continue to emerge on high entropy and
entropy-stabilized ceramics, we seek further understanding of property changes
across the phase boundary between \enquote{high-entropy} and
\enquote{entropy-stabilized}. The thermal and mechanical properties of bulk
ceramic entropy stabilized oxide composition
MgCoNiCuZnO are investigated across
this critical transition temperature via the transient plane-source method,
temperature-dependent X-ray diffraction, and nano-indentation. Thermal
conductivity remains constant within uncertainty across the multi-to-single
phase transition at a value of ~2.5 W/mK, while the linear coefficient of
thermal expansion increases nearly 24 % from 10.8 to 14.1 x 10 K.
Mechanical softening is also observed across the transition.Comment: 14 pages, 4 figures, to be published in APL Material
Hybridization from Guest-Host Interactions Reduces the Thermal Conductivity of Metal-Organic Frameworks
We experimentally and theoretically investigate the thermal conductivity and mechanical properties of polycrystalline HKUST-1 metalâorganic frameworks (MOFs) infiltrated with three guest molecules: tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), and (cyclohexane-1,4-diylidene)dimalononitrile (H4-TCNQ). This allows for modification of the interaction strength between the guest and host, presenting an opportunity to study the fundamental atomic scale mechanisms of how guest molecules impact the thermal conductivity of large unit cell porous crystals. The thermal conductivities of the guest@MOF systems decrease significantly, by on average a factor of 4, for all infiltrated samples as compared to the uninfiltrated, pristine HKUST-1. This reduction in thermal conductivity goes in tandem with an increase in density of 38% and corresponding increase in heat capacity of âŒ48%, defying conventional effective medium scaling of thermal properties of porous materials. We explore the origin of this reduction by experimentally investigating the guest moleculesâ effects on the mechanical properties of the MOF and performing atomistic simulations to elucidate the roles of the mass and bonding environments on thermal conductivity. The reduction in thermal conductivity can be ascribed to an increase in vibrational scattering introduced by extrinsic guest-MOF collisions as well as guest molecule-induced modifications to the intrinsic vibrational structure of the MOF in the form of hybridization of low frequency modes that is concomitant with an enhanced population of localized modes. The concentration of localized modes and resulting reduction in thermal conductivity do not seem to be significantly affected by the mass or bonding strength of the guest species
CarbonâEnriched Amorphous Hydrogenated Boron Carbide Films for VeryâLowâk Interlayer Dielectrics
A longstanding challenge in ultralargeâscale integration has been the continued improvement in lowâdielectricâconstant (lowâk) interlayer dielectric materials and other specialized layers in backâendâofâtheâline interconnect fabrication. Modeled after the success of carbonâcontaining organosilicate materials, carbonâenriched amorphous hydrogenated boron carbide (aâBxC:Hy) films are grown by plasmaâenhanced chemical vapor deposition from orthoâcarborane and methane. These films contain more extraicosahedral sp3 hydrocarbon groups than nonenriched aâBxC:Hy films, as revealed by FTIR and NMR spectroscopy, and also exhibit lower dielectric constants than their nonenriched counterparts, notably due to low densities combined with a low distortion and orientation contribution to the total polarizability. Films with dielectric constant as low as 2.5 are reported with excellent electrical stability (leakage current of 10â9 A cmâ2 at 2 MV cmâ1 and breakdown voltage of >6 MV cmâ1), good thermal conductivity of 0.31 ± 0.03 W mâ1 Kâ1, and high projected Youngâs modulus of 12 ± 3 GPa. These properties rival those of leading SiOC:H materials, and position aâBxC:Hy as an important complement to traditional Siâbased materials to meet the complex needs of nextâgeneration interconnect fabrication.Carbonâenriched amorphous hydrogenated boron carbide films are demonstrated with dielectric constant (k) as low as 2.5âattributed to low densities combined with networkârigidifying CH2 bridging groupsâas well as excellent electrical, thermal, and mechanical properties, rivaling those of stateâofâtheâart siliconâbased lowâk dielectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/1/aelm201700116_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/2/aelm201700116.pd
Heat-transport mechanisms in molecular building blocks of inorganic/organic hybrid superlattices
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