Contact resistance strongly deteriorates the performance of devices based on 2-D materials and their nanostructures, masking their exceptional electronic and transport properties. This work explores ...the dependence of contact resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{C} </tex-math></inline-formula>) of graphene nanoribbon (GNR) devices on contact geometry using atomistic quantum transport simulations. The influence and contributions of edge and top contacts and GNR width scaling on <inline-formula> <tex-math notation="LaTeX">{R}_{C} </tex-math></inline-formula> is studied in detail. Metallization effects on the density of states, transmission, and GNR field-effect transistor (GNR FET) driving current are investigated. We show that wider GNRs (~4 nm) exhibit edge-dominated transport and lower <inline-formula> <tex-math notation="LaTeX">{R}_{C} </tex-math></inline-formula> than the ultranarrow GNRs (~0.4 nm) that exhibit much higher contact resistance which is also dependent on the contact area.
Overhead conductors may undergo fretting fatigue failures at contact interfaces located at or near the suspension clamps. Some recent experimental studies were carried out on individual wires to ...understand the fretting fatigue phenomenon. However, the majority of the available results are for the wire-to-wire contact configuration, while little interest has been brought to the wire-to-clamp contact configuration, which is typically a critical interface for conductor fatigue. A new experimental test bench intended to perform fretting fatigue tests on individual strands of overhead conductors is used to study the wire-to-clamp and the wire-to-wire contact configurations. Variable displacement amplitude (VDA) tests under different normal contact forces were carried out on 1350-H19 aluminium wires for both contact types. The experimental results showed a slight difference between the studied contact configurations in terms of the friction coefficient values and the transition sliding amplitude. To complete this analysis, constant displacement amplitude (CDA) tests were carried out sweeping the displacement range and replacing the tested specimen for each test. The resulting contact marks are observed using an optical microscope and a good correlation is found between both types of tests in terms of friction coefficient and transition sliding amplitude. This study allowed characterizing the sliding conditions of wire-to-clamp contact in the context of fretting fatigue of aluminium conductors and is an important step in the development of a method to evaluate the fatigue life of conductors using fretting fatigue tests of individual wire-to-clamp contacts.
Exploring optical memory functions in nonvolatile organic field-effect transistor (OFET) memories with top-gate/bottom-contact (TG/BC) configurations can offer effective routes for developing ...printable, high-density organic memory circuits capable of multi-level data storage. Here, we use a solution process to fabricate TG/BC OFET devices with organic floating-gate structures and investigate their memory characteristics under light illumination. A solution-processable organic composite of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) and poly(methylmethacrylate) is employed to self-organize organic floating-gate structures on a solution-processed semiconductor layer composed of poly(3-hexylthiophene) (P3HT). The floating-gate OFET devices programmed with blue, green, and red light exhibit large threshold voltage (Vth) shifts of approximately 30 V and stable charge retention characteristics even under light illumination. The devices also exhibit high sensitivity to incident light during programming, and the degree of Vth shift and the on-state current can be tuned using light and programming voltage to facilitate distinct storage and readout of multi-level data.
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•OFET memories with organic floating gates were fabricated by solution processes.•Blending of TIPS-pentacene with PMMA allows self-organizing organic floating gates.•OFET memories programmed with blue, green, and red light exhibit large Vth shifts.•Charge retention characteristics are stable even under light illumination.•OFET memories facilitate multi-level storage for electrical and optical signals.
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The properties of organic/ferromagnetic interfaces and their influences on the device functionalities have attracted people's interests in organic spintronics. Based on density ...functional theory, the spin polarization properties of a thiophene molecule which is adsorbed at Co(001), Fe(100), and Ni(111) surfaces are discussed, where the sulfur atoms in the thiophene molecule is placed directly above the atom of the electrodes. It is found that the same molecule interact with different electrodes induce different spin polarization properties and the biggest spin polarization will be obtained when the thiophene molecule adsorbed at the Fe(100) surface, which means that thiophene/Fe interface has high spin polarized injection efficiency. There is a promising expectation in organic spintronics by using Fe as the ferromagnetic electrode. There are charge transfers between the thiophene molecule and the Fe atoms. The spin polarization of the thiophene molecule is originated from the interfacial orbital hybridizations between the 3d orbital of Fe atoms and the 2p hybridized orbital of carbon atoms and sulfur atom. The spin polarization properties could be tuned by changing the adsorption electrodes, which is favorable for the building of molecular spintronic devices. Spin polarization of the thiophene molecule at three different contact configurations near the Fermi level.
•Thiophene molecule could be spin polarized when adsorbed at Co(001), Fe(100), and Ni(111) surfaces.•The biggest spin polarization will be obtained when the thiophene molecule adsorbed at the Fe(100) surface.•The spin polarization is originated from the interfacial orbital hybridizations between the 3d orbital of ferromagnetic electrodes and the 2p orbital of the thiophene molecule.
First principles calculations are adopted to study the spin polarization properties of thiophene molecule which adsorbed at the Co, Fe, and Ni electrode surfaces. The density of states, spin-polarized density distributions as well as the differential charge density distributions are obtained. It is found that the p orbital of the thiophene molecule will interact with the d orbital of the ferromagnetic electrodes, which will generate new spin coupling states and lead to obvious spin polarization in the thiophene molecule. Different electrodes induce different spin polarization properties, and in which the Fe electrode will bring the biggest spin polarization of the thiophene molecule. People can selectively and efficiently inject spin polarized electrons into molecules by choosing suitable ferromagnetic electrodes in organic spintronic devices.
Instability and risk of fall during standing and walking are common challenges for biped robots. While existing criteria from state-space dynamical systems approach or ground reference points are ...useful in some applications, complete system models and constraints have not been taken into account for prediction and indication of fall for general legged robots. In this study, a general numerical framework that estimates the balanced and falling states of legged systems is introduced. The overall approach is based on the integration of joint-space and Cartesian-space dynamics of a legged system model. The full-body constrained joint-space dynamics includes the contact forces and moments term due to current foot (or feet) support and another term due to altered contact configuration. According to the refined notions of balanced, falling, and fallen, the system parameters, physical constraints, and initial/final/boundary conditions for balancing are incorporated into constrained nonlinear optimization problems to solve for the velocity extrema (representing the maximum perturbation allowed to maintain balance without changing contacts) in the Cartesian space at each center-of-mass (COM) position within its workspace. The iterative algorithm constructs the stability boundary as a COM state-space partition between balanced and falling states. Inclusion in the resulting six-dimensional manifold is a necessary condition for a state of the given system to be balanced under the given contact configuration, while exclusion is a sufficient condition for falling. The framework is used to analyze the balance stability of example systems with various degrees of complexities. The manifold for a 1-degree-of-freedom (DOF) legged system is consistent with the experimental and simulation results in the existing studies for specific controller designs. The results for a 2-DOF system demonstrate the dependency of the COM state-space partition upon joint-space configuration (elbow-up vs. elbow-down). For both 1- and 2-DOF systems, the results are validated in simulation environments. Finally, the manifold for a biped walking robot is constructed and illustrated against its single-support walking trajectories. The manifold identified by the proposed framework for any given legged system can be evaluated beforehand as a system property and serves as a map for either a specified state or a specific controller’s performance.
In this paper, the contact configuration of single molecular junction is controlled through side group, which is explored by electrochemical jump-to-contact STM break junction. The conductance values ...of 2-methoxy-1,3-benzenedicarboxylic acid (2-M-1,3-BDC) is around 10
–3.65
G
0
, which is different from that of 5-methoxy-1,3-benzenedicarboxylic acid (5-M-1,3-BDC) with 10
–3.20
G
0
. Interestingly, the conductance value of 2-M-1,3-BDC is the same as that of 1,3-benzenedicarboxaldehyde (1,3-BDCA), while single molecular junctions of 5-M-1,3-BDC and 1,3-benzenedicarboxylic acid (1,3-BDC) give out similar conductance value. Since 1,3-BDCA binds to the Cu electrode through one oxygen atom, the dominated contact configuration for 1,3-BDC is through two oxygen atoms. The different conductance values between 2-M-1,3-BDC and 5-M-1,3-BDC can be attributed to the different contact configurations caused by the position of the side group. The current work provides a feasible way to control the contact configuration between the anchoring group and the electrode, which may be useful in designing future molecular electronics.
The goal of this study was to compare the motor response to sacral neuromodulation (SNM) with different pairs of stimulating electrodes in anesthetized and awake sheep.
Similar to SNM clinical use in ...humans, the InterStim
quadripolar tined lead was implanted adjacent to the S3 nerve root in sheep and bipolar stimulation was configured with one electrode negative and one electrode positive on the four contacts (0 most distal to device, 1, 2, and 3 most proximal).
Electrode 3-cathode and electrode 0-anode (3-/0+) stimulation had the lowest visual response threshold (0.46 ± 0.14V, anesthetized, 0.56 ± 0.21V, conscious), representing the most sensitive stimulation. Stimulation on electrode 0 (0-/1+) had the highest response threshold among tested electrodes (2.70 ± 0.23V, anesthetized, 3.38 ± 0.96V, conscious). The order according to response threshold from low to high was 3 < 2 < 1 < 0. The triggered response by 3-/0+ stimulation solely occurred in the perineum, tail, or bellows. In contrast, the 0-/1+ stimulation frequently evoked response in gluteal and thigh regions. The electromyographic activities from the anus were sensitive to low intensities of stimulation on electrode 3 (e.g., 3-/0+, 3-/2+).
Objective motor responses to SNM as a functional indicator for optimal lead placement may be used to demonstrate that the contact which is most proximal to the foramen (electrode 3) is an optimal electrode to trigger an "on-target" response to lower intensity stimulation. Data from this preclinical work suggest that there are several principles that may be referenced to simplify and expedite the programming process in clinical practice.
Abstract
BACKGROUND:
In spinal cord stimulation for the management of chronic, intractable pain, a satisfactory analgesic effect can be obtained only when the stimulation-induced paresthesias cover ...all painful body areas completely or partially.
OBJECTIVE:
To investigate the effect of stimulus pulse width (PW) and contact configuration (CC) on the area of paresthesia (PA), perception threshold (VPT), discomfort threshold (VDT), and usage range (UR) in spinal cord stimulation.
METHODS:
Chronic pain patients were tested during a follow-up visit. They were stimulated monopolarly and with the CC giving each patient the best analgesia. VPT, VDT, and UR were determined for PWs of 90, 210, and 450 microseconds. The paresthesia contours at VDT were drawn on a body map and digitized; PA was calculated; and its anatomic composition was described. The effects of PW and CC on PA, VPT, VDT, and UR were tested statistically.
RESULTS:
Twenty-four of 31 tests with low thoracic stimulation and 8 of 9 tests with cervical stimulation gave a significant extension of PA at increasing PW. In 14 of 18 tests (low thoracic), a caudal extension was obtained (primarily in L5-S2). In cervical stimulation the extension was predominantly caudal as well. In contrast to VPT and VDT, UR is not significantly different when stimulating with any CC.
CONCLUSION:
PA extends caudally with increasing PW. The mechanism includes that the larger and smaller dorsal column fibers have a different mediolateral distribution and that smaller dorsal column fibers have a smaller UR and can be activated only when PW is sufficiently large. A similar effect of CC on PA is unlikely as long as electrodes with a large intercontact distance are applied.
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