Phonon transmission at crystalline-amorphous interfaces studied using mode-resolved atomistic Green's functions

The transmission and reflection processes of THz phonons at solid interfaces are of fundamental interest and of importance to thermal conduction in nanocrystalline solids. The processes are challenging to investigate, however, because typical experiments and many computational approaches do not provide transmission coefficients resolved by phonon mode. Here, we examine the modal transmission and reflection processes of THz phonons across an amorphous Si region connected to two crystalline Si leads, a model interface for those that occur in nanocrystalline solids, using mode-resolved atomistic Green's functions. We find that the interface acts as a low-pass filter, reflecting modes of frequency greater than around 3 THz while transmitting those below this frequency, in agreement with a recent experimental report [C. Hua et al., Phys. Rev. B 95, 205423 (2017)]. Further, we find that these low frequency modes travel nearly unimpeded through the interface, maintaining their wave vectors on each side of the interface. Our work shows that even completely disordered regions may not be effective at reflecting THz phonons, with implications for efforts to alter thermal conductivity in nanocrystalline solids

Structural Characteristics of Carbon Nanofibers for On-chip Interconnect Applications

In this letter, we compare the structures of plasma-enhanced chemical vapor deposition of Ni-catalyzed and Pd-catalyzed carbon nanofibers (CNFs) synthesized for on-chip interconnect applications with scanning transmission electron microscopy (STEM). The Ni-catalyzed CNF has a conventional fiberlike structure and many graphitic layers that are almost parallel to the substrate at the CNF base. In contrast, the Pd-catalyzed CNF has a multiwall nanotubelike structure on the sidewall spanning the entire CNF. The microstructure observed in the Pd-catalyzed fibers at the CNF-metal interface has the potential to lower contact resistance significantly, as our electrical measurements using current-sensing atomic force microscopy indicate. A structural model is presented based on STEM image analysis

Thermal transport in nanocrystalline Si and SiGe by ab initio based Monte Carlo simulation

Nanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. By fitting the transmission profile of grain boundaries, we obtain excellent agreement with experimental thermal conductivity of nanocrystalline Si [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine phonon transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials

Phonon transmission at crystalline-amorphous interfaces studied using mode-resolved atomistic Green's functions

The transmission and reflection processes of THz phonons at solid interfaces are of fundamental interest and of importance to thermal conduction in nanocrystalline solids. The processes are challenging to investigate, however, because typical experiments and many computational approaches do not provide transmission coefficients resolved by phonon mode. Here, we examine the modal transmission and reflection processes of THz phonons across an amorphous Si region connected to two crystalline Si leads, a model interface for those that occur in nanocrystalline solids, using mode-resolved atomistic Green's functions. We find that the interface acts as a low-pass filter, reflecting modes of frequency greater than around 3 THz while transmitting those below this frequency, in agreement with a recent experimental report [C. Hua et al., Phys. Rev. B 95, 205423 (2017)]. Further, we find that these low frequency modes travel nearly unimpeded through the interface, maintaining their wave vectors on each side of the interface. Our work shows that even completely disordered regions may not be effective at reflecting THz phonons, with implications for efforts to alter thermal conductivity in nanocrystalline solids

Interface Characteristics of Vertically Aligned Carbon Nanofibers for Interconnect Applications

The authors characterize the detailed interface structure of Ni-catalyzed vertically aligned carbon nanofibers (CNFs) prepared by plasma-enhanced chemical vapor deposition for interconnect applications. Stacked graphitic layers and cup-shape structures of CNFs around the interface region have been observed using high-resolution scanning transmission electron microscopy. The interaction between the Ni catalyst and Ti layer dramatically affects the CNF structure during initial growth. The effect of interface nanostructures on contact resistance is also discussed

Healthâ Related Quality of Life Components in Children With Neonatal Brachial Plexus Palsy: A Qualitative Study

BackgroundCurrently, no published, validated patientâ reported outcome (PRO) measures of healthâ related quality of life (HRQOL) exist for use with neonatal brachial plexus palsy (NBPP). NBPP is a debilitating condition that occurs during the perinatal period, resulting in paralysis/paresis and loss of sensation in the affected arm. Commonly used NBPP measures are not comprehensive and do not fully account for clinically meaningful changes in function or progression of the disorder.ObjectiveTo evaluate important components of HRQOL for children with NBPP and identify where new PRO measures are needed.DesignEleven focus groups comprising children with NBPP (4), family members (6), and professional providers (1) to assess HRQOL.SettingBrachial plexus clinic.ParticipantsChildren with NBPP, their parents, and professional providers.Inclusion CriteriaChildren 7â 17 years old with NBPP; parents/caregivers at least 18 years of age; professionals with â ¥2 years’ experience providing NBPP clinical care; ability to read and speak English fluently.MethodsFocus group sessions were recorded, transcribed verbatim, and deidentified. Qualitative frequency analysis identified different aspects of HRQOL relevant to NBPP. This analysis expands on the groundedâ theory approach to qualitative analysis, including development of a domain framework, open and axial coding, selective coding, and descriptive analysis. The resulting HRQOL domain framework (and frequency analysis) was then compared to the domain framework for existing PRO measures (PROMIS and Neuroâ QoL) to identify components of HRQOL where new PRO measures are needed for NBPP.Main Outcome MeasuresNot applicable.ResultsAlthough many physical, social, and emotional health domains were captured by existing PRO measures, some significant NBPPâ specific topics emerged from qualitative analysisâ functionality, sensory, physical appearance, arm/hand compensation and preference, explaining functionality/appearance to others, and selfâ esteem and body image concerns.ConclusionsDevelopment of sensitive and specific measures capturing arm/hand function and body image would improve the clinical care of patients with NBPP.Level of EvidenceNot applicable.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146831/1/pmr2383.pd

Structure-guided SCHEMA recombination generates diverse chimeric channelrhodopsins

Integral membrane proteins (MPs) are key engineering targets due to their critical roles in regulating cell function. In engineering MPs, it can be extremely challenging to retain membrane localization capability while changing other desired properties. We have used structure-guided SCHEMA recombination to create a large set of functionally diverse chimeras from three sequence-diverse channelrhodopsins (ChRs). We chose 218 ChR chimeras from two SCHEMA libraries and assayed them for expression and plasma membrane localization in human embryonic kidney cells. The majority of the chimeras express, with 89% of the tested chimeras outperforming the lowest-expressing parent; 12% of the tested chimeras express at even higher levels than any of the parents. A significant fraction (23%) also localize to the membrane better than the lowest-performing parent ChR. Most (93%) of these well-localizing chimeras are also functional light-gated channels. Many chimeras have stronger light-activated inward currents than the three parents, and some have unique off-kinetics and spectral properties relative to the parents. An effective method for generating protein sequence and functional diversity, SCHEMA recombination can be used to gain insights into sequence–function relationships in MPs