This paper demonstrates that air‐stable radicals enhance the stability of triboelectric charge on surfaces. While charge on surfaces is often undesirable (e.g., static discharge), improved charge retention can benefit specific applications such as air filtration. Here, it is shown that self‐assembled monolayers (SAMs) containing air‐stable radicals, 2,2,6,6‐tetramethylpiperidin‐1‐yl)oxidanyl (TEMPO), hold the charge longer than those without TEMPO. Charging and retention are monitored by Kelvin Probe Force Microscopy (KPFM) as a function of time. Without the radicals on the surface, charge retention increases with the water contact angle (hydrophobicity), consistent with the understanding that surface water molecules can accelerate charge dissipation. Yet, the most prolonged charge retention is observed in surfaces treated with TEMPO, which are more hydrophilic than untreated control surfaces. The charge retention decreases with reducing radical density by etching the TEMPO‐silane with tetrabutylammonium fluoride (TBAF) or scavenging the radicals with ascorbic acid. These results suggest a pathway toward increasing the lifetime of triboelectric charges, which may enhance air filtration, improve tribocharging for patterning charges on surfaces, or boost triboelectric energy harvesting.
- Award ID(s):
- 1760348
- NSF-PAR ID:
- 10343871
- Date Published:
- Journal Name:
- Micromachines
- Volume:
- 12
- Issue:
- 12
- ISSN:
- 2072-666X
- Page Range / eLocation ID:
- 1460
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
The discovery of oxide electronics is of increasing importance today as one of the most promising new technologies and manufacturing processes for a variety of electronic and optoelectronic applications such as next-generation displays, batteries, solar cells, and photodetectors. The high potential use seen in oxide electronics is due primarily to their high carrier mobilities and their ability to be fabricated at low temperatures. However, since the majority of oxide semiconductors are n-type oxides, current applications are limited to unipolar devices, eventually developing oxide-based bipolar devices such as p-n diodes and complementary metal-oxide semiconductors. We have contributed to wide range of oxide semiconductors and their electronics and optoelectronic device applications. Particularly, we have demonstrated n-type oxide-based thin film transistors (TFT), integrating In2O3-based n-type oxide semiconductors from binary cation materials to ternary cation species including InZnO, InGaZnO (IGZO), and InAlZnO. We have suggested channel/metallization contact strategies to achieve stable TFT performance, identified vacancy-based native defect doping mechanisms, suggested interfacial buffer layers to promote charge injection capability, and established the role of third cation species on the carrier generation and carrier transport. More recently, we have reported facile manufacturing of p-type SnOx through reactive magnetron sputtering from a Sn metal target. The fabricated p-SnOx was found to be devoid of metallic phase of Sn from x-ray photoelectron spectroscopy and demonstrated stable performance in a fully oxide based p-n heterojunction together with n-InGaZnO. The oxide-based p-n junctions exhibited a high rectification ratio greater than 103 at ±3 V, a low saturation current of ~2x10-10, and a small turn-on voltage of -0.5 V. With all the previous achievements and investigations about p-type oxide semiconductors, challenges remain for implementing p-type oxide realization. For the implementation of oxide-based p-n heterojunctions, the performance needs to be further enhanced. The current on/off ration may be limited, in our device structure, due to either high reverse saturation current (or current density) or non-ideal performance. In this study, two rational strategies are suggested to introduce an “intrinsic” layer, which is expected to reduce the reverse saturation current between p-SnOx and n-IGZO and hence increase the on/off ratio. The carrier density of n-IGZO is engineered in-situ during the sputtering process, by which compositionally homogeneous IGZO with significantly reduced carrier density is formed at the interface. Then, higher carrier density IGZO is formed continuously on the lower carrier density IGZO during the sputtering process without any exposure of the sample to the air. Alternatively, heterogeneous oxides of MgO and SiO2 are integrated into between p-SnOx and n-IGZO, by which the defects on the surface can be passivated. The interfacial properties are thoroughly investigated using transmission electron microscopy and atomic force microscopy. The I-V characteristics are compared between the set of devices integrated with two types of “intrinsic” layers. The current research results are expected to contribute to the development of p-type oxides and their industrial application manufacturing process that meets current processing requirements, such as mass production in p-type oxide semiconductors.more » « less
-
more » « less
Abstract The effects of water and temperature on the triboelectrification of granular materials have been reported by numerous authors, but have not been studied robustly in the context of volcanic plumes. Here, we present the results of a set of experiments designed to elucidate how environmental conditions modulate the triboelectric characteristics of volcanic ash in the upper region of the convective column. We find that small amounts of water can reduce the charge collected by submillimeter‐sized ash grains by up to an order of magnitude. Increasing temperature at a constant relative humidity also appears to decrease the amount of charge gained by particles. Analysis of our data shows that if particles undergo low‐energy, low‐frequency collisions in humid environments under minute‐long time scales, charge dissipation dominates over charge accumulation. Thus, our work suggests that triboelectric charging may be an inefficient electrification mechanism outside of the gas‐thrust region where collision energies and rates are high and residence times are low.
-
more » « less
Abstract While many mechanistic studies have focused on the lubricious properties of ionic liquids (ILs) on ideally smooth surfaces, little is known about the mechanisms by which ILs lubricate contacts with nanoscale roughness. Here, substrates with controlled density of nanoparticles are prepared to examine the influence of nanoscale roughness on the lubrication by 1‐hexyl‐3‐methyl imidazolium bis(trifluoromethylsulfonyl)imide. Atomic force microscopy is employed to investigate adhesion, hydrodynamic slip, and friction at the lubricated contact as a function of surface topography for the first time. This study reveals that nanoscale roughness has a significant influence on the slip along the surface and leads to a maximum slip length on the substrates with intermediate nanoparticle density. This coincides with the minimum friction coefficient at sufficiently small contact stresses, likely due to the lower resistance of the IL film to shear. However, at the higher pressures applied with a sharp tip, friction increases with nanoparticle density, indicating that the IL is not able to alleviate the increased dissipation due to roughness. The results of this work point toward a complex influence of the surface topology on friction. This study can help design ILs and nanopatterned substrates for tribological applications and nano‐ and microfluidics.
-
Electret based energy scavenging devices utilize electro-static induction to convert mechanical energy into electrical energy. Uses for these devices include harvesting ambient energy in the environment and acting as sensors for a range of applications. These types of devices have been used in MEMS applications for over a decade. However, recently there is an interest in triboelectric generators/harvesters, i.e., electret based harvesters that utilize triboelectrification as well as electrostatic induction. The literature is filled with a variety of designs for the latter devices, constructed from materials ranging from paper and thin films; rendering the generators lightweight, flexible and inexpensive. However, most of the design of these devices is ad-hoc and not based on exploiting the underlying physics that govern their behavior; the few models that exist neglect the coupled electromechanical behavior of the devices. Motivated by the lack of a comprehensive dynamic model of these devices this manuscript presents a generalized framework based on a Lagrangian formulation to derive electromechanical equation for a lumped parameter dynamic model of an electret-based harvester. The framework is robust, capturing the effects of traditional MEMS devices as well as triboelectric generators. Exploiting numerical simulations the predictions are used to examine the behavior of electret based devices for a variety of loading conditions simulating real-world applications such as power scavengers under simple harmonic forcing and in pedestrian walking.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/mi12121460
