Low Electrical Threshold Research Articles

CVD Encapsulation of Laser-Graphitized Electrodes in Diamond Electro-Optical Devices

Conductive graphitized grooves on the dielectric surface of diamond have been created by KrF excimer laser radiation. The advantages of such a circuit board in high-field applications is rather limited because the crystal surface has a relatively low electrical breakdown threshold. To increase the electrical strength, a method of encapsulating surface conductive graphitized structures by chemical vapor deposition of an epitaxial diamond layer has been proposed and realized. The quality of the growth diamond is proved by Raman spectroscopy. A comparative study of the electrical resistivity of graphitized wires and the breakdown fields between them before and after diamond growth was carried out. The proposed technique is crucial for diamond-based high-field electro-optical devices, such as THz photoconductive emitters.

Accurate damage localization and enhanced mechanical performance of self‐sensing epoxy nanocomposites using graphene platelets

AbstractRecently, there has been growing interest in the use of composites structure with self‐sensing functionalities in the aerospace, automotive, and renewable energy industries. However, the integration of sensors such as Fiber Bragg Grating or piezoelectric ceramic transducers into the composite structure can significantly reduce the structure's inherent strength. To address this issue, we present a novel approach for developing self‐sensing composites by incorporating graphene platelets (GnPs) as an electric filler into an epoxy matrix. Our method involves the uniform dispersion of GnPs in epoxy, with some GnPs connected to each other to achieve a low electrical threshold of 0.61 vol% in the resulting nanocomposites. The resulting composite film exhibits high sensitivity to tensile strains ranging from 0% to 1.8%, with gauge factors (GFs) ranging from 19 to 172. This variation in GF is due to the calibration process, which relies on the relationship between input and output data and does not require a constant factor. In addition to its high sensitivity to tensile strains, the composite film also demonstrates excellent self‐sensing performance for bending deformation. Moreover, the composite film effectively responds to impact damage evolution, making it a promising candidate for practical applications. This work represents an advancement in the development of self‐sensing nanocomposites using two‐dimensional materials, offering exceptional sensitivity and adaptability for potential future use.

Different electrode anodes used in OLED devices Diferentes eletrodos anodos usados em dispositivos OLEDs

Transparent conductive oxides (TCOs) known as indium tin oxide (ITO) and fluorine tin oxide (FTO) deposited on glass were compared by different techniques and also as anodes in organic light-emitting diode (OLED) devices with same structure. ITO produced at laboratory was compared with the commercial one manufactured by different companies: Diamond Coatings, Displaytech and Sigma-Aldrich, and FTO produced at laboratory was compared with the commercial one manufactured by Flexitec Company. FTO thin films produced at laboratory presented the lowest performance measured by Hall effect technique and also by I-V curve of OLED device with low electrical current and high threshold voltage. ITO thin films produced at laboratory presented elevated sheet resistance in comparison with commercial ITOs (approximately one order of magnitude greater), that can be related by a high number of defects as discontinuity of the chemical lattice or low crystalline structure. In the assembly of OLED devices with ITO and FTO produced at laboratory, neither presented luminances. ITO manufactured by Sigma-Aldrich company presented better electrical and optical characteristics, as low electrical resistivity, good wettability, favorable transmittance, perfect physicalchemical stability and lowest threshold voltage (from 3 to 4.5 V) for OLED devices.

Different electrode anodes used in OLED devices Diferentes eletrodos anodos usados em dispositivos OLEDs

Transparent conductive oxides (TCOs) known as indium tin oxide (ITO) and fluorine tin oxide (FTO) deposited on glass were compared by different techniques and also as anodes in organic light-emitting diode (OLED) devices with same structure. ITO produced at laboratory was compared with the commercial one manufactured by different companies: Diamond Coatings, Displaytech and Sigma-Aldrich, and FTO produced at laboratory was compared with the commercial one manufactured by Flexitec Company. FTO thin films produced at laboratory presented the lowest performance measured by Hall effect technique and also by I-V curve of OLED device with low electrical current and high threshold voltage. ITO thin films produced at laboratory presented elevated sheet resistance in comparison with commercial ITOs (approximately one order of magnitude greater), that can be related by a high number of defects as discontinuity of the chemical lattice or low crystalline structure. In the assembly of OLED devices with ITO and FTO produced at laboratory, neither presented luminances. ITO manufactured by Sigma-Aldrich company presented better electrical and optical characteristics, as low electrical resistivity, good wettability, favorable transmittance, perfect physicalchemical stability and lowest threshold voltage (from 3 to 4.5 V) for OLED devices.

Nerve growth factor locally sensitizes nociceptors in human skin.

Nerve growth factor (NGF) injected into the human skin causes local hyperalgesia to mechanical and electrical stimuli lasting for weeks. Pig data suggested axonal sensitization of C-nociceptors as a contributing mechanism. Here, we recorded single C-nociceptors in 11 human subjects 3 weeks after intracutaneous injection of 1 μg NGF into the foot dorsum. For each identified unit, the receptive field was mapped and, whenever possible, we recorded 2 terminal branches of the same unit, 1 from the hyperalgesic NGF-site ("inside") and the other from the nonsensitized skin ("outside"). In the saline-treated control feet, mechano-insensitive nociceptors (CMi) were more abundant than at the NGF sites (36% vs 19%). Units with axonal properties of CMi fibres but displaying positive mechanical responses ("CMi-like") dominated at the NGF site (27% vs 6%). Moreover, axonal branches innervating the hyperalgesic skin displayed significantly lower electrical thresholds and less activity-dependent conduction velocity slowing when compared with "outside" or control skin. The "inside" branches also showed long-lasting after-discharges and less adaptation to repeated mechanical stimuli. NGF-induced long-term nociceptor hyperexcitability was maximum at the terminal branches directly treated with NGF. The sensitization included sensory and axonal components affecting both activation thresholds and supra-threshold responses. Our data suggest that a combination of sensory sensitization and axonal hyperexcitability is underlying the localized hyperalgesia by facilitating action potential generation and conduction. Axonal changes were also found in the asymptomatic skin surrounding the NGF-treatment sites, thereby possibly reflecting "nociceptive priming."

Terahertz quantum cascade lasers with thin resonant-phonon depopulation active regions and surface-plasmon waveguides

We report three-well, resonant-phonon depopulation terahertz quantum cascade lasers with semi-insulating surface-plasmon waveguides and reduced active region (AR) thicknesses. Devices with thicknesses of 10, 7.5, 6, and 5 μm are compared in terms of threshold current density, maximum operating temperature, output power, and AR temperature. Thinner ARs are technologically less demanding for epitaxial growth and result in reduced electrical heating of devices. However, it is found that 7.5-μm-thick devices give the lowest electrical power densities at threshold, as they represent the optimal trade-off between low electrical resistance and low threshold gain.

Low electrical conductivity threshold and crystalline morphology of single-walled carbon nanotubes – high density polyethylene nanocomposites characterized by SEM, Raman spectroscopy and AFM

The electrical conductivities ( σ) of nanocomposites of single-walled carbon nanotubes (SWCNTs) and high density polyethylene (HDPE) have been studied for a large number of nanocomposites prepared in a SWCNT concentration range between 0.02 and 8 wt%. The values of σ obey a percolation power law with an SWCNT concentration threshold, p c = 0.13 wt%, the lowest yet obtained for any kind of carbon–polyethylene nanocomposites. Improved electrical conductivities attest to an effective dispersion of SWCNT in the polyethylene matrix, enabled by the fast quenching crystallization process used in the preparation of these nanocomposites. Characterization by scanning electron microscopy (SEM) and Raman spectroscopy consistently points to a uniform dispersion of separate small SWCNT bundles at concentrations near p c and increased nanotube clustering at higher concentrations. Near p c, high activation energies and geometries of long isolated rods suggest that electron transport occurs by activated electron hopping between nanotubes that are close to each other but still geometrically separate. The degree of SWCNT clustering given by Raman spectroscopy and the barrier energy for electrical conductivity are highly correlated. The nanotubes act as nucleants in the crystallization of the polyethylene matrix, and change the type of supermolecular aggregates from spherulites to axialitic-like objects. The size of crystal aggregates decreases with SWCNT loading, however, in reference to the unfilled polyethylene, the three-dimensional growth geometry extracted from the Avrami exponents remains unchanged up to 2 wt%. Consistency between SEM, Raman and electrical transport behavior suggests that the electrical conductivity is dominated by dispersion and the geometry of the SWCNT in the nanocomposites and not by changes or lack thereof in the HDPE semicrystalline structure.

Neurotrophin‐eluting hydrogel coatings for neural stimulating electrodes

Improved sensory and motor prostheses for the central nervous system will require large numbers of electrodes with low electrical thresholds for neural excitation. With the eventual goal of reducing stimulation thresholds, we have investigated the use of biodegradable, neurotrophin-eluting hydrogels (i.e., poly(ethylene glycol)-poly(lactic acid), PEGPLA) as a means of attracting neurites to the surface of stimulating electrodes. PEGPLA hydrogels with release rates ranging from 1.5 to 3 weeks were synthesized. These hydrogels were applied to multielectrode arrays with sputtered iridium oxide charge-injection sites. The coatings had little impact on the iridium oxide electrochemical properties, including charge storage capacity, impedance, and voltage transients during current pulsing. Additionally, we quantitatively examined the ability of neurotrophin-eluting, PEGPLA hydrogels to promote neurite extension in vitro using a PC12 cell culture model. Hydrogels released neurotrophin (nerve growth factor, NGF) for at least 1 week, with neurite extension near that of an NGF positive control and much higher than extension seen from sham, bovine serum albumin-releasing boluses, and a negative control. These results show that neurotrophin-eluting hydrogels can be applied to multielectrode arrays, and suggest a method to improve neuron-electrode proximity, which could result in lowered electrical stimulation thresholds. Reduced thresholds support the creation of smaller electrode structures and high density electrode prostheses, greatly enhancing prosthesis control and function.

Restoring balance to the reflex actions of the muscle spindle: the secondary endings also matter

Restoring balance to the reflex actions of the muscle spindle: the secondary endings also matter

Electrically evoked itch in humans

We compared itch sensations and axon reflex flare induced by transcutaneous electrical (0.08–8 ms, 2–200 Hz) and chemical (histamine iontophoresis; 100 μC) stimulation. Stimuli were applied to non-lesional volar wrist skin in 20 healthy human subjects and 10 patients with atopic dermatitis. Intensity of evoked itch and pain sensations were rated on a numerical rating scale (NRS) of 0 (no sensation) to 10 (the maximum sensation imaginable). The axon reflex erythema was measured by laser Doppler imager and areas of alloknesis (itch evoked by light brushing) and hyperknesis (itch evoked by pricking) were assessed psychophysically. Electrical stimulation was most effective for stimulus durations ≥2 ms and frequencies ≥50 Hz. It evoked pure itch as threshold sensation in 80% of the subjects that was perceived with a delay of approximately 1 s. Itch intensities of up to 7/10 were not accompanied by an axon reflex flare. In contrast, histamine provoked a massive increase of axon reflex erythema and maximum itch ratings of 3.1±0.2. The extention of alloknesis areas (2.3±0.5 cm) evoked by electrical stimulation clearly exceeded those induced by histamine (0.7±0.3 cm). Healthy subjects and patients with atopic dermatitis did not differ significantly in their response to either stimulation. We conclude that C-fiber activation underlies the electrically evoked itch sensation. The low electrical thresholds and the absence of an axon reflex flare suggest that these fibers are not identical with the previously described mechano-insensitive histamine responsive C fibers, but represent a separate peripheral neuronal system for the induction of itch.

Low carbon black filled polyurethane composite as candidate for wide spectrum gas-sensing element

To reduce the amount of carbon black and to broaden the applicability of conductive polymer composites serving as gas sensors, polyurethane-based composite was prepared by latex blending. The composite has very low electrical threshold and hence provides improved processability. In the environment of organic solvent vapors, the composite with 3.5 wt.% of carbon black exhibits significant increase of its electrical resistance regardless of the solvents' polarities and the maximum variation in resistance decreases linearly with decreasing vapor concentration. Besides, the slopes of the linear dependences change with the solvent species, which might allow quantifying vapor concentration and species. The measurable vapor concentrations of the composite are lower than or equal to the Chinese standard of exposure limits. Besides, the composite also shows high reproducibility as evidenced by over 5000 times of repeated sensing tests. It is believed that the composite can be used in gas sensor arrays with much smaller sizes and wide sensitivity.

Chemically and electrically induced sweating and flare reaction

Both thin afferent (nociceptors) and efferent (sympathetic sudomotor) nerve fibers can be activated electrically and chemically, resulting in neurogenic erythema and sweating. These reactions have been used before to assess the impairment of sympathetic and nociceptor fibers in humans. In this study, electrically induced sweating and erythema were assessed simultaneously in the foot dorsum and thigh, and were compared to chemically induced activation. Reproducible intensity–response relations (stimulation intensities 0–30 mA, 1 Hz) were obtained from 32 subjects. The steepest increase of the sweat response was induced at lower intensities as compared to that of the erythema (18.3 mA vs. 25.7 mA, p<0.01) and reached a plateau for intensities above 25 mA, suggesting lower electrical thresholds for sudomotor fibers. Maximum flare areas induced electrically with 30 mA were smaller than those evoked chemically (flare size: 4.5 cm 2 vs. 10.6 cm 2). In contrast, the electrically evoked sweating rate was higher than that evoked chemically (acetylcholine, or ACh; sweating rate 0.31 vs. 0.21 μl/cm 2/min, p<0.01), which might be attributed to an increased effectiveness of synchronized discharge in sympathetic fibers upon electrical stimulation.

Innervation territories of mechano-insensitive C nociceptors in human skin.

Microneurographic recordings were obtained in the peroneal nerve from 20 mechano-insensitive units (CMi) and six mechano-heat responsive C units (CMH) in healthy human subjects. Their innervation territories in the skin of the leg or foot were assessed by transcutaneous electrical stimulation with a pointed probe at intensities of 10 to 100 mA (0.2 ms) and, when applicable, by mechanical von Frey hair stimulation. Electro-receptive fields (eRFs) of CMH units had a median area of 1.95 cm(2) when mapped with 10 mA that coincided approximately with mechano-receptive fields (mRFs) as mapped with a 750-mN von Frey hair. Fifty-milliampere stimuli increased the eRFs to 3.08 cm(2) in a concentric manner. This was probably due to current spread since these units are known to have low electrical thresholds. Further increase of the stimulus strength to 70 or 100 mA increased the eRFs only marginally. Mechano-insensitive units had much smaller eRFs (median: 0.35 cm(2)) than CMH units when mapped with the same pointed probe at 10 mA (n = 13). The receptive territories consisted of one distinct spot or of several spots separated by distances of more than 1 cm. However, when mapping stimuli of 50 mA were applied, eRFs became continuous and grew to a median area of 5.34 cm(2), i.e., larger than those of CMHs. The borders of eRFs of CMi units were significantly more irregular compared with CMH units. A further increase of the stimulus intensity to a maximum of 100 mA only marginally enlarged the eRFs. The CMi units could be activated by heat or chemical substances applied inside the 50-mA eRF, indicating that receptive nerve endings were mapped. Responsiveness to these stimuli was inhomogeneous within the eRFs. It was concluded that innervation territories of CMi units in human skin exceed those of CMH units in size by a factor of approximately 3. The widely branched terminals underlying the large fields are consistent with a role of this nociceptor class in axon reflex flare and preclude a role in exact spatial discrimination of noxious stimuli.

Perimodiolar Electrodes in Cochlear Implant Surgery

Perimodiolar-positioned cochlear implant electrodes have been developed in order to bring the electrode contacts as close as possible to the spiral ganglion cells, which are the target of electrostimulation. This results in lower electrical thresholds, higher dynamic ranges and less channel interaction when compared with normal implant electrodes which are usually located peripherally within the scala tympani. In this study we evaluated 4 different types of perimodiolar electrode: the Clarion Preformed electrode, the Clarion Preformed electrode with positioner, the Nucleus Contour electrode and the Med-El Perimodiolar Combi 40 electrode. These devices require different approaches to achieve a perimodiolar electrode position. The electrodes were inserted in fresh human temporal bones. After processing these bones with the electrodes in situ by employing a sawing, grinding and polishing technique, the inner ear structures as well as the electrode positions could be evaluated in detail. All electrode types studied had a more or less perimodiolar position; however, each type produced a certain amount of trauma to cochlear structures which is discussed in relation to mechanical properties. Further human temporal bone studies with improved perimodiolar cochlear implant electrodes are necessary in order to find an optimized type of electrode.

Biomechanical response in the ankle to stimulation of lumbosacral nerve roots with spiral cuff multielectrode--preliminary study.

Biomechanical response in the ankle to tetanic stimulation of the lumbosacral root was investigated to assess the potential for lower limb functional neurostimulation. Myotomal response in the leg was measured as the three-dimensional isometric torque in the ankle after extradural tetanic stimulation of the L3-S1 roots exposed surgically for herniated disc removal in five patients. The cuff multielectrode was employed to investigate functional topography of the roots by monopolar, bipolar, and tripolar electrode configurations. Four response patterns in the direction of three-dimensional torque vectors were observed. The L-5 and S-1 roots had the same response pattern, but S-1 roots produced stronger torques. Dorsiflexion torque was not obtained by stimulation of L-5 roots despite coactivation of the tibial anterior and peroneal muscles. Dorsiflexion torques were produced only by stimulating the L-4 roots. More selective bipolar and tripolar stimulations recruited force at higher thresholds and less gain. Additionally, some muscles were not activated by tripolar stimulation of the same root. In one L-4 root, the torque at lower electrical threshold was replaced by inverse torque at higher threshold, providing indirect evidence that different muscles may have motoneuron populations that differ in diameter or location within the root. Although dorsiflexion and plantarflexion torques are functional per se, they are accompanied by foot inversion and leg rotation torques (as well as proximal muscle contractions). Further experimental investigations on direct extradural stimulation of lumbosacral roots, either single or in combination, are recommended to explore the potential of lumbosacral nerve root stimulation for restoration of leg function.

The Hoffmann reflex of human plantar foot muscles

Electrical stimulation of the tibial nerve in the popliteal fossa evoked an M wave (10.9 ms) and a late reflex response (38.1 ms) in the plantar foot muscles of all 10 volunteers. The late response had a somewhat lower electrical threshold than the corresponding M wave (8.5 versus 9 mA), and reached a maximum of amplitude when the stimulus intensity was increased, but was strongly suppressed by further increased intensity. A more distal stimulation of the tibial nerve at the ankle shortened the onset latency of the M wave and lengthened that of the late response. The reflex was facilitated by activation of synergists and inhibited by activation of antagonists. We showed that the late response was contaminated neither by volume conducted activity from the soleus muscle, as shown by intramuscular recordings from the abductor hallucis muscle, nor by a F wave, as shown by double stimulation. In summary, we conclude that this late response in human plantar foot muscles corresponded to an H reflex, which may be used to assess alterations of distal motoneuronal excitability. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:732–738, 1998.

The Hoffmann reflex of human plantar foot muscles.

Electrical stimulation of the tibial nerve in the popliteal fossa evoked an M wave (10.9 ms) and a late reflex response (38.1 ms) in the plantar foot muscles of all 10 volunteers. The late response had a somewhat lower electrical threshold than the corresponding M wave (8.5 versus 9 mA), and reached a maximum of amplitude when the stimulus intensity was increased, but was strongly suppressed by further increased intensity. A more distal stimulation of the tibial nerve at the ankle shortened the onset latency of the M wave and lengthened that of the late response. The reflex was facilitated by activation of synergists and inhibited by activation of antagonists. We showed that the late response was contaminated neither by volume conducted activity from the soleus muscle, as shown by intramuscular recordings from the abductor hallucis muscle, nor by a F wave, as shown by double stimulation. In summary, we conclude that this late response in human plantar foot muscles corresponded to an H reflex, which may be used to assess alterations of distal motoneuronal excitability.

Effects of stimulation of hindlimb flexor group II afferents during fictive locomotion in the cat.

1. This study examines the effects of electrical stimulation of hindlimb flexor nerves on the fictive locomotion pattern. Locomotion was initiated by stimulation of the mesencephalic locomotor region in the decerebrate paralysed cat and monitored by recording the electroneurogram from selected hindlimb flexor and extensor muscle nerves. Flexor nerves were stimulated using short trains (20-50 stimuli at 100 Hz) during either the flexor or the extensor phase of the fictive locomotor cycle. 2. Stimulation of tibialis anterior (TA), posterior biceps and semitendinosus (PBSt) or sartorius (Sart) nerves at 5 times threshold (T) during the flexor phase of the fictive locomotor cycle terminated on-going activity in flexor nerves and initiated activity in extensors. Thus, flexor nerve stimulation during flexion shortened the locomotor cycle by resetting to extension. The failure of lower intensity (2T) stimulation of PBSt or Sart nerves to reset the step cycle to extension suggests that group II afferents are responsible for these actions. Resetting evoked by 2T stimulation of the TA nerve may be due to a high proportion of group II afferents with low electrical threshold. 3. During extension, stimulation of TA and PBSt nerves at 5T did not perturb the locomotor rhythm whereas Sart stimulation prolonged the locomotor cycle. 4. Stimulation of cutaneous or knee joint afferents failed to produce effects similar to those evoked by stimulation of flexor muscle nerves at group II strength. These findings are at odds with those obtained elsewhere in the acute spinal, DOPA fictive locomotion preparation. The possibility that group II resetting during fictive locomotion is not mediated by flexion reflex pathways but by previously unknown pathways released in the present preparation is discussed. 5. Since many of the flexor afferents recruited by 5T electrical stimulation are the length-sensitive group II fibres, spindle secondaries may act to regulate the duration and onset of flexor and extensor activity during real locomotion. The resetting from flexion to extension also suggests that unexpected or enhanced activity of flexor secondaries during swing would promote a switch of the step cycle to stance.

X- and Y-mediated current sources in areas 17 and 18 of cat visual cortex

X- and Y-mediated input to areas 17 and 18 of the cat visual cortex was studied using current-source-density analysis of field potentials evoked by stimulation of the optic nerves. A cuff-shaped electrode was used for stimulation so that Y axons, by virtue of their larger diameters, would have lower electrical thresholds than X axons. The effect in each cortical area of activating Y axons alone could therefore be determined by low-amplitude stimulation of the optic nerves. Current-source densities were calculated by two separate methods. (1) In five experiments, field potentials were measured sequentially at different cortical depths with a single tungsten electrode. Current densities were then calculated by computer. (2) In two experiments, current densities were derived in real time from field potentials recorded simultaneously from three sites with a multi-electrode probe. The calculation was performed by an analog circuit specially designed for this purpose. This method has several advantages over the standard, single-electrode method. At stimulus strengths sufficient to activate the majority of Y axons in the optic nerves, but subthreshold to most X axons, the field potentials evoked in area 17 changed little from layer to layer. When the current-source-density analysis was applied to these potentials, no significant sources or sinks were detectable. Only when the stimulus strength was raised to the point that both X and Y axons were activated by the stimulus were any current sources or sinks detected in area 17. The currents were similar in time course and laminar pattern to those recorded after stimulation of the optic chiasm. In area 18, large sources and sinks were evoked by stimulation of Y axons alone. These currents changed little when the stimulus strength was increased to activate X axons as well. Area 18, therefore, in contrast to area 17, seems to be dominated by Y input and receives little X input. These results support the conclusions of the accompanying paper in which synaptic potentials were recorded intracellularly from cortical neutrons. The intracellular experiments failed to show substantial Y input to area 17. The projections of X and Y axons may therefore be much more highly segregated into areas 17 and 18 than previously thought. Alternatively, the nature of the Y input to area 17 may be very different from that to area 18 in that it cannot be easily detected with intracellular or current-source-density techniques.

The dorsal column projection of muscle afferent fibres from the cat hindlimb.

1. The extent of the projection of hindlimb muscle afferent fibres ascending the dorsal columns has been studied in barbiturate-anaesthetized cats. This has been investigated using electrical stimulation of the dorsal columns at different spinal levels while recording from (i) peripheral muscle nerves, and (ii) single muscle afferent fibres within the dorsal columns. These two approaches have produced complementary results. 2. The conduction velocity of both group I and group II afferent fibres decreased progressively after entering the dorsal columns. 3. The majority of group I and group II fibres project at least as far as L2 but leave the dorsal columns at or before the lower thoracic segments. 4. By taking advantage of the lower electrical threshold of Ia compared to Ib fibres in the hamstring nerves, it could be shown that both Ia and Ib fibres leave the dorsal columns at similar locations. 5. A small number of afferent fibres were found to project to C1. On the basis of previous work it is likely that such fibres originate from Pacinian or paciniform corpuscles.