Thermal and Thermoelectric Properties of Molecular Junctions

Molecular junctions (MJs) represent an ideal platform for studying charge and energy transport at the atomic and molecular scale and are of fundamental interest for the development of molecular‐scale electronics. While tremendous efforts have been devoted to probing charge transport in MJs during the past two decades, only recently advances in experimental techniques and computational tools have made it possible to precisely characterize how heat is transported, dissipated, and converted in MJs. This progress is central to the design of thermally robust molecular circuits and high‐efficiency energy conversion devices. In addition, thermal and thermoelectric studies on MJs offer unique opportunities to test the validity of classical physical laws at the nanoscale. A brief survey of recent progress and emerging experimental approaches in probing thermal and thermoelectric transport in MJs is provided, including thermal conduction, heat dissipation, and thermoelectric effects, from both a theoretical and experimental perspective. Future directions and outstanding challenges in the field are also discussed.Probing thermal and thermoelectric properties of molecular junctions is key to the development of robust molecular‐scale circuits and high‐efficiency energy conversion devices. Recent theoretical and experimental efforts towards understanding thermal and thermoelectric transport in molecular junctions are presented. Strategies to manipulate thermal conduction, heat dissipation, and thermopower of molecular junctions are introduced. Future directions and outstanding challenges are also discussed.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154389/1/adfm201904534_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154389/2/adfm201904534.pd

Saccadic suppression in schizophrenia

About 40% of schizophrenia patients report discrete visual disturbances which could occur if saccadic suppression, the decrease of visual sensitivity around saccade onset, is impaired. Two mechanisms contribute to saccadic suppression: eeference copy processing and backwards masking. Both are reportedly altered in schizophrenia. However, saccadic suppression has not been investigated in schizophrenia. 17 schizophrenia patients and 18 healthy controls performed a saccadic suppression task using a Gabor stimulus with individually adjusted contrast, which was presented within an interval 300 ms around saccade onset. Visual disturbance scores were higher in patients than controls, but saccadic suppression strength and time course were similar in both groups with lower saccadic suppression rates being similarly related to smaller saccade amplitudes. Saccade amplitudes in the saccadic suppression task were reduced in patients, in contrast to unaltered amplitudes during a saccade control task. Notably, smaller saccade amplitudes were related to higher visual disturbances scores in patients. Saccadic suppression performance was unrelated to symptom expression and antipsychotic medication. Unaltered saccadic suppression in patients suggests sufficiently intact eeference copy processing and backward masking as required for this task. Instead, visual disturbances in patients may be related to restricted saccadic amplitudes arising from cognitive load while completing a task

Room temperature picowatt-resolution calorimetry

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98693/1/ApplPhysLett_99_043106.pd

Electrical conductance and thermopower of β-substituted porphyrin molecular junctions ─ synthesis and transport

Molecular junctions offer significant potential for enhancing thermoelectric power generation. Quantum interference effects and associated sharp features in electron transmission are expected to enable the tuning and enhancement of thermoelectric properties in molecular junctions. To systematically explore the effect of quantum interferences, we designed and synthesized two new classes of porphyrins, P1 and P2, with two methylthio anchoring groups in the 2,13- and 2,12-positions, respectively, and their Zn complexes, Zn–P1 and Zn–P2. Past theory suggests that P1 and Zn–P1 feature destructive quantum interference in single-molecule junctions with gold electrodes and may thus show high thermopower, while P2 and Zn–P2 do not. Our detailed experimental single-molecule break-junction studies of conductance and thermopower, the latter being the first ever performed on porphyrin molecular junctions, revealed that the electrical conductance of the P1 and Zn–P1 junctions is relatively close, and the same holds for P2 and Zn–P2, while there is a 6 times reduction in the electrical conductance between P1 and P2 type junctions. Further, we observed that the thermopower of P1 junctions is slightly larger than for P2 junctions, while Zn–P1 junctions show the largest thermopower and Zn–P2 junctions show the lowest. We relate the experimental results to quantum transport theory using first-principles approaches. While the conductance of P1 and Zn–P1 junctions is robustly predicted to be larger than those of P2 and Zn–P2, computed thermopowers depend sensitively on the level of theory and the single-molecule junction geometry. However, the predicted large difference in conductance and thermopower values between Zn–P1 and Zn–P2 derivatives, suggested in previous model calculations, is not supported by our experimental and theoretical findings

Under the microscope: Single molecule symposium at the University of Michigan, 2006

In recent years, a revolution has occurred in the basic sciences, which exploits novel single molecule detection and manipulation tools to track and analyze biopolymers in unprecedented detail. A recent Gordon Research Conference style meeting, hosted by the University of Michigan, highlighted current status and future perspectives of this rising field as researchers begin to integrate it with mainstream biology and nanotechnology. © 2006 Wiley Periodicals, Inc. Biopolymers 85:106–114, 2007Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/55865/1/20621_ftp.pd

How substituents tune quantum interference in meta-OPE3 molecular junctions to control thermoelectric transport

Quantum interference (QI) can strongly affect electric and thermoelectric properties of molecular junctions (MJs). So far, however, a limited number of experimental studies have explored the influence of QI on thermoelectric transport in MJs. To address this open point, we synthesized derivatives of meta-OPE3 with an electron-withdrawing nitro (–NO2) substituent or an electron-donating N,N-dimethyl amine (–NMe2) substituent, attached at two different positions of the central phenylene ring, and systematically studied the electrical conductance and thermopower of the corresponding gold–molecule–gold junctions. We show that (i) the electrical conductance of MJs depends weakly on the polarity of the substituents but strongly on the substitution position and (ii) MJs with the N,N-dimethyl amine group feature a higher thermopower than MJs with the nitro group. We also present calculations based on first principles, which explain these trends and show that the transport properties are highly sensitive to microscopic details in junctions, exhibiting destructive QI features

Kinesin's backsteps under mechanical load

Kinesins move processively toward the plus end of microtubules by hydrolyzing ATP for each step. From an enzymatic perspective, the mechanism of mechanical motion coupled to the nucleotide chemistry is often well explained using a single-loop cyclic reaction. However, several difficulties arise in interpreting kinesin's backstepping within this framework, especially when external forces oppose the motion of kinesin. We review evidence, such as an ATP-independent stall force and a slower cycle time for backsteps, that has emerged to challenge the idea that kinesin backstepping is due to ATP synthesis, i.e., the reverse cycle of kinesin's forward-stepping chemomechanics. Supplementing the conventional single-loop chemomechanics with routes for ATP-hydrolyzing backward steps and nucleotide-free steps, especially under load, gives a better physical interpretation of the experimental data on backsteps.Comment: 5 figures and 2 table

Complex Feeding Tracks of the Sessile Herbivorous Insect Ophiomyia maura as a Function of the Defense against Insect Parasitoids

Because insect herbivores generally suffer from high mortality due to their natural enemies, reducing the risk of being located by natural enemies is of critical importance for them, forcing them to develop a variety of defensive measures. Larvae of leaf-mining insects lead a sedentary life inside a leaf and make conspicuous feeding tracks called mines, exposing themselves to the potential risk of parasitism. We investigated the defense strategy of the linear leafminer Ophiomyia maura Meigen (Diptera: Agromyzidae), by focusing on its mining patterns. We examined whether the leafminer could reduce the risk of being parasitized (1) by making cross structures in the inner area of a leaf to deter parasitoids from tracking the mines due to complex pathways, and (2) by mining along the edge of a leaf to hinder visually searching parasitoids from finding mined leaves due to effective background matching of the mined leaves among intact leaves. We quantified fractal dimension as mine complexity and area of mine in the inner area of the leaf as interior mine density for each sample mine, and analyzed whether these mine traits affected the susceptibility of O. maura to parasitism. Our results have shown that an increase in mine complexity with the development of occupying larvae decreases the probability of being parasitized, while interior mine density has no influence on parasitism. These results suggest that the larval development increases the host defense ability through increasing mine complexity. Thus the feeding pattern of these sessile insects has a defensive function by reducing the risk of parasitism