High Contact Research Articles

Role of copper and zinc additives in the stiction phenomenon of automotive braking systems

AbstractThe braking system of a motor vehicle is a multi‐material system, subjected to various aggressive conditions. Corrosion of the brake disc during stationary periods can determine the onset of a high adhesion force (stiction) capable of compromising the reliability of the braking system during vehicle motion. The purpose of this work is to study the effect of the introduction of Cu and Zn in the friction material composition. This effect was investigated through electrochemical measurements (electrochemical impedance spectroscopy, potentiodynamic polarization, and stiction tests), conducted using an electrochemical cell simulating the parking brake, complemented by the examination of the brake disc and pad surfaces and water absorption tests. The results suggest that porous components, like vermiculite, in the composite friction material led to high contact force. Moreover, 10 wt% of Cu in the friction material does not significantly affect its stiction behavior in our testing configuration. In contrast, 10 wt% Zn in the friction material significantly reduces the stiction propensity by acting with a complex synergistic mechanism combining physical and chemical shielding effects.

Wetting, droplet evaporation and corrosion behavior of various composite and textured materials

Experimental studies were conducted on the evaporation rate of a droplet located on the surfaces of various composite and textured materials with different wettability at varying surface temperatures. The maximum droplet evaporation rate was recorded on a textured Cu–SiC composite material with superhydrophilic properties. The minimum droplet evaporation rate corresponded to a superhydrophobic AlMg3 substrate obtained using laser texturing with subsequent hydrophobization procedure. An increase in surface temperature led to a significant deterioration of hydrophobicity for a superhydrophobic substrate and a deterioration of hydrophilicity for a superhydrophilic substrate. As a result, with increasing temperature, the influence of the droplet geometry determined by surface wettability on the droplet evaporation rate for these substrates sharply decreases. Advancing and receding dynamic contact angles, as well as contact angle hysteresis were obtained on all studied substrates. It is generally accepted that a hydrophobic surface exhibits less contact angle hysteresis than a hydrophilic one. However, Cu-SiС composite substrate with a textured hydrophobic surface exhibited the opposite behavior. The contact angle hysteresis on the hydrophobic textured surface was found to be four times higher than that on the hydrophilic polished one. A mechanism was proposed that explains the high contact angle hysteresis and four hysteresis time modes. The minimum hysteresis value corresponded to the superhydrophobic AlMg3 substrate. Anti-corrosion properties were studied for all substrates under consideration. The minimum corrosion current corresponded to a copper substrate with a graphene coating, as well as a superhydrophobic AlMg3 substrate. For a given substrate, there are two corrosion modes with a three-fold difference in the corrosion current. In addition, the wettability behavior of different surfaces was examined using molecular dynamics simulations. The simulation results were found to be consistent with the experimental data.

Direct Observation of Semimetal Contact Induced Charge Doping and Strain Effect in CVD‐Grown Monolayer MoS2 Transistors

AbstractTwo‐dimensional Materials (2DMs) offer significant promise for advancing device miniaturization and extending Moore's law. Despite the challenges posed by high contact resistance in transistors, recent discoveries highlight semimetals as an effective approach for achieving ohmic contact with near‐quantum‐limit contact resistance. The energy band hybridization between semimetal and MoS2 is found to create degenerate states and heavily doped contact, which is proposed as the underlying mechanism responsible for reducing contact resistance. However, a quantitative and comprehensive characterization of the semimetal‐MoS2 interface is lacking, leaving the physical interactions elusive. This study reveals that semimetals induce n‐type doping and tensile strain in monolayer MoS2 grown using CVD, which serve as the contact resistance and mobility boosters. Among the semimetals investigated, including Bismuth (Bi), Antimony (Sb), and their alloy, Bi results in the highest electron doping of 2 × 1013 cm−2 and a 0.5% tensile strain, leading to reduced contact resistance and enhanced mobility. First‐principles calculations and spectroscopy measurements unveil the impact of electron doping and strain in MoS2, and the thermal effects are subsequently explored. This research underscores the potential of semimetals in boosting device performance and lays the foundation for reducing contact resistance in transistors made from 2D materials.

Large area Terahertz digitated photoconductive antennas based on a single high resistivity metal and nanoplasmonic electrode

Optical excited photoconductive antennas are a central technology for the Terahertz (THz) domain, crucial for both emitting and detecting THz radiation. This work proposes and experimentally realises a new approach in digitated photoconductive antennas (d-PCAs) based on a single digitated high resistivity metal contact with integrated resistances as voltage dividers. This permits a uniform applied electric field over a large surface area and a single step device processing procedure, simplifying the device realisation. This concept is further combined with digitated plasmonic nano-antennas that permits to enhance the light-matter interaction. Through femtosecond optical excitation of such structures, THz pulses can be generated efficiently through this device. Further, for the plasmonic d-PCA, the detected THz electric field of the device shows the effect of polarisation of the incident IR beam, highlighting the role of the nanostructured digitated contacts. This work is supported by electromagnetic simulations showing the optical and THz response of this new type of photoconductive antenna with integrated resistances.

Study on schottky barrier of Cu/Graphene/4H-SiC interface based on first principles

High stability 4H-SiC ohmic contact is currently a key technical challenge that silicon carbide devices urgently need to overcome. In the paper, the interfacial structures, atomic interactions and Schottky barrier height (SBH) of Cu/Graphene/4H-SiC were studied using the first-principles method. According to research, the SBH for Cu/G/4H-SiC is lower than the SBH for Cu/4H-SiC. The reasons for this phenomenon mainly include the following: 1. The graphene C atoms saturate the dangling bonds on the 4H-SiC surface and the influence of the metal-induced-gap-states (MIGS) at the interface is decreased. 2. A new phase is formed by inserting graphene between the Cu and 4H-SiC have low work functions. 3. An interfacial-electric-dipole layer (IEDL) formed at the interface of 4H-SiC and graphene may also reduce the SBH. These results make them to be promising candidates for future radiation resistant electronics.

Durable superhydrophobic coating based on halloysite nanotubes for versatile oil/water separation and reusable water collection

Fog water collection gains increasing attention for harvesting atmospheric water to solve the water resource crisis in arid or semi-arid areas. In this work, a durable superhydrophobic coating based on halloysite nanotubes (HNT) for water collection is fabricated by introducing 1H,1H,2H,2H-perfluorodecyl trimethoxysilane (PFTS) modified HNT into a hydrophobic polydimethylsiloxane (PDMS) coating to construct a rough and superhydrophobic surface. The dip-coating method is employed to apply the coatings onto various substrates. The surface wettability, water collection rate, mechanical stability, and durability, oil/water separation efficiency and flux, and oil absorption capacity are investigated in detail. When the content of fluorinated modified HNT (F-HNT) is 15 %, superhydrophobic F-HNT@PDMS coated fabrics with a high water contact angle (157.3°) as well as a low sliding angle (3.7°) are obtained, and the treated fabrics show excellent self-cleaning ability. After 100 mechanical wear cycles, the coated fabrics remain superhydrophobicity, and the oil/water separation efficiency is maintained above 99.5 %. Furthermore, different substrates dip-coated with F-HNT@PDMS exhibit high-efficiency water collection rates of 952.25–1058.5 mg∙cm−2∙h−1. Therefore, this work provides a feasible strategy for preparing a durable superhydrophobic coating with a high-efficiency water collection rate and is expected to be applied in fog water harvesting in scarce areas.

First Principle Study on Schottky Barrier at Ni/Graphene/4H-SiC Interface

High stability 4H-SiC ohmic contact is currently a key technical challenge that silicon carbide devices urgently need to overcome. It is important to reduce the Schottky barrier height (SBH) at the Ni/4H-SiC interface to optimize ohmic contact. In this paper, the mechanisms of graphene layer changing Ni/4H-SiC interface Schottky barrier height (SBH) are studied based on the first-principles method within the local density approximation. Theoretical studies have shown that graphene intercalation can reduce the SBH of Ni and 4H-SiC interfaces. The reason of SBH reduction may be that the graphene C atoms saturate the dangling bonds on the 4H-SiC surface and the influence of the metal-induced energy gap state at the interface is reduced. In addition, the new phase formed at the interface of graphene and silicon carbide has a lower work function. Furthermore, an interfacial electric dipole layer may be formed at the 4H-SiC/graphene interface which may also reduce the SBH. These results make them to be promising candidates for future radiation resistant electronics.

Research progress of novel functional materials in extraction of algal toxins

Algal toxins are secondary metabolites produced by harmful algae; these metabolites are characterized with strong toxicity, diverse structure and bioaccumulation. Aquatic organisms that feed on harmful algae can accumulate algal toxins in their bodies, and the consumption of these organisms by humans can cause symptoms of paralysis, diarrhea, and even death. The onset of poisoning can occur within as little as 30 min; in many cases, no suitable antidote for algal toxins is available. Thus, algal toxins present significant threats to human health, the aquaculture industry, and aquatic ecosystems. Because the potential risks of algal toxins are a critical issue, these toxins have become a research hotspot. The water environment and various types of aquatic products should be monitored and analyzed to ensure their safety. However, because of possible matrix effects and the low content of algal toxins in actual samples, an efficient pretreatment method is necessary prior to instrumental analyses. Efficient sample pretreatment techniques can not only reduce or eliminate interferences from the sample matrix during analysis but also enrich the target analytes to meet the detection limit of the analytical instrument, thereby ensuring the sensitivity and accuracy of the detection method. In recent years, sample pretreatment techniques such as solid-phase extraction (SPE), solid-phase microextraction (SPME), magnetic SPE (MSPE), dispersive SPE (DSPE), and pipette tip-based SPE (PT-SPE) have gained wide attention in the field of algal-toxin separation and analysis. The performance of these pretreatment techniques largely depends on the characteristics of the extraction materials. Given the diverse physicochemical properties of algal toxins, including their different molecular sizes, hydrophobicity/hydrophilicity, and charges, the design and preparation of materials suitable for algal-toxin extraction is an essential undertaking. The optimal extraction material should be capable of reversible algal-toxin adsorption and preferably possess a porous structure with a large surface area to allow for high recovery rates and good interfacial contact with the toxins. Additionally, the extraction material should exhibit good chemical stability in the sample solution and elution solvent within the working pH range; otherwise, it may dissolve or lose its functional groups. Many research efforts have sought to develop novel adsorbent materials with these properties in the separation and analysis of algal toxins, focusing on carbon-based materials, metal organic frameworks (MOFs), covalent organic frameworks (COFs), molecularly imprinted polymers (MIPs), and their functionalized counterparts. Carbon-based materials, MOFs, and COFs have advantages such as large surface areas and abundant adsorption sites. These extraction materials are widely used in the separation and analysis of target substances in complex environmental, biological, and food samples owing to their excellent performance and unique microstructure. They are also the main adsorbents used for the extraction of algal toxins. These extraction materials play an essential role in the extraction of algal toxins, but they also present a number of limitations: (1) Carbon-based materials, MOFs, and COFs have relatively poor selective-adsorption ability towards target substances; (2) Most MOFs are unstable in aqueous solutions and challenging to apply during extraction from water-based sample solutions; (3) COFs mainly consist of lightweight elements, rendering them difficult to completely separate from sample solutions using centrifugal force, which limits their application range; (4) Although MIPs have good selectivity, issues such as template-molecule loss, slow mass-transfer rates, and low adsorption capacity must be addressed. Therefore, the design and preparation of novel functionalized extraction materials specifically tailored for algal toxins and studies on new composite extraction materials are highly desirable. This article collects representative literature from domestic and international research on algal-toxin analysis over the past decade, summarizes the relevant findings, categorizes the applications of novel functional materials in algal-toxin-extraction processes, and provides an outlook on their future development prospects.

Fabrication of Superhydrophobic Coating by Spraying PDMS-SiO2 Suspension for Self-Cleaning Application

Superhydrophobic surfaces that mimic lotus leaf surfaces have been widely studied due to their unique self-cleaning ability. Herein, we have fabricated a self-cleaning superhydrophobic coating on a glass substrate using the facile sol-gel spray coating method. The silica particles were synthesized via the sol-gel method in acidic conditions. A self-cleaning superhydrophobic coating was achieved by spraying a suspension of synthesized SiO2 particles and PDMS on a glass substrate at room temperature. The incorporation of SiO2 particles in the PDMS matrix resulted in the formation of a rough structure on the glass surface. This surface exhibited excellent superhydrophobic properties with a high water contact angle (WCA) of 154° and a low sliding angle (SA) of 4°. In addition, the prepared samples showed strong mechanical resistance against various tests such as multiple adhesive tape peeling, sandpaper abrasion, and pencil hardness. As a result, the developed superhydrophobic coating holds great potential for self-cleaning applications on a larger scale.

Enhancing amorphous carbon wear resistance at high contact stresses through Ag incorporation

High load capacity is desirable in various industrial applications, such as gudgeon pins, cam followers, gears and bearings. Amorphous carbon (a-C) coatings, known for their minimal friction and low wear rates, have found extensive application in automotive components. However, the a-C films often fail at high contact stress (>2 GPa). Extensive efforts have been devoted for the application of a-C under high contact stress, and a few groups can prevent the sudden failure of a-C in high load condition up to now. Nevertheless, the wear rate is still high, which is in the range of ∼10−7 mm3/Nm, at least ten times greater than that of films under low stresses (<2 GPa). To tackle this issue, Ag-C supra-nano-dual-phase composite (SNDP) was fabricated using magnetron sputtering (‘supra-nano-dual-phase’ means the diameter of each phase is smaller than 10 nm). Various methods were employed to examine the structural features, mechanical attributes, and tribological performance of Ag-C SNDP. The research revealed that Ag nanocrystals, ranging in size from 2 to 4 nm, were uniformly incorporated within the amorphous carbon matrix. The Ag-C SNDP film with 4.0 at.% Ag shows an order of magnitude lower than amorphous carbon (a-C) at wear rate. It also pushes the load-bearing capacity as high as 4.0 GPa, which has rarely been reported before. The superior tribological behavior of Ag-C SNDP composite can be explained in three factors: (1) the ‘supra-nanometer-sized dual-phase’ structure provides adequate strength; (2) the surface graphitization within several nanometers from the surface enables low friction coefficient and prevents sudden failure; (3) incorporating Ag into the films resulted in a reduction in residual stress and an increase in film toughness.

Mechanism of Fermi Level Pinning for Metal Contacts on Molybdenum Dichalcogenide.

The high contact resistance of transition metal dichalcogenide (TMD)-based devices is receiving considerable attention due to its limitation on electronic performance. The mechanism of Fermi level (EF) pinning, which causes the high contact resistance, is not thoroughly understood to date. In this study, the metal (Ni and Ag)/Mo-TMD surfaces and interfaces are characterized by X-ray photoelectron spectroscopy, atomic force microscopy, scanning tunneling microscopy and spectroscopy, and density functional theory systematically. Ni and Ag form covalent and van der Waals (vdW) interfaces on Mo-TMDs, respectively. Imperfections are detected on Mo-TMDs, which lead to electronic and spatial variations. Gap states appear after the adsorption of single and two metal atoms on Mo-TMDs. The combination of the interface reaction type (covalent or vdW), the imperfection variability of the TMD materials, and the gap states induced by contact metals with different weights are concluded to be the origins of EF pinning.

PDMS/functionalized h-BN/liquid metal flexible composite with dual-network structure for achieving superior thermal conductivity and low thermal resistance via interfacial grafting

Thermal interface materials (TIMs) play a crucial role in addressing the heat dissipation challenges associated with high-power electrical equipment. Apart from possessing excellent thermal conductivity, and they must also exhibit low contact thermal resistance to facilitate efficient heat transfer at the interface. In this study, a novel composite with a dual-network structure was prepared by interfacial grafting to achieve superior thermal conductivity. The composite comprises polydimethylsiloxane (PDMS), functionalized boron nitride (f-BN), and liquid metal (LM). This dual network structure effectively enhances phonon transportation and significantly improves the thermal transport performance of the composite. The thermal conductivity of the obtained composite can achieve 4.4 W/m·K, accompanied by a low contact thermal resistance of 0.32 °C·cm2/W. Furthermore, the dual network structure ensures the flexibility of the composite, as evidenced by the maximum elongation reaching 267.43% at a tensile strength of 0.35 MPa. This exceptional mechanical performance is expected to alleviate stress concentration issues arising from thermal expansion mismatch, thereby enhancing the practical applicability of the prepared TIMs. Overall, this study introduces a novel approach for fabricating flexible composites with high thermal conductivity and low contact thermal resistance, offering new insights into the preparation of TIMs.

Enhancing mechanical performance and high-temperature lubrication enabled by MoS2/WB2 nanolayered films

Molybdenum disulfide (MoS2) films are widespread application in aerospace, nuclear, mechanical, and electronic fields owing to their unique structural characteristics and inherent interlayer slip. However, their utility is hindered by environmental susceptibility, particularly oxidation at elevated temperatures and in humid environments, limiting their effectiveness. Herein, we report a nanocomposite integrating MoS2 with WB2 by periodic alternating arrangement, synthesized using magnetron sputtering technology. This nanolayered architecture effectively harnesses the synergistic properties of both materials, imparting exceptional mechanical properties, superior environmental adaptability and efficient high-temperature lubrication. Methodical experiments and atomistic simulations reveal the incorporation of WB2 promotes preferential growth of MoS2 along the (002) plane, yielding an impressive hardness-to-elastic modulus ratio of approximately 0.1. The resultant film demonstrates notable achievements: a minimal friction coefficient of 0.056 and a specific wear rate of 1.88 × 10−7 mm3 N−1 m−1 in humid air. These findings are primarily stem from the interaction between MoS2 nanosheets and metal-oxide nanoparticles at the sliding interface. Remarkably, even at 400 °C, the engineered MoS2/WB2 nanocomposite achieves low friction and wear under high contact stress, outperforming conventional MoS2-based materials. This innovative design, complemented by insights into the high-temperature friction mechanism, holds promise for advancing the development of robust and high-temperature-resistant lubricants.

A Latent Profile Analysis of Social Support, Online Contacts, and Preference for Online Communication Among Same- and Both-Sex Attracted and Other-Sex Attracted Adolescents

ABSTRACT This study aimed to assess differences between other-sex attracted and same- and both-sex attracted adolescents in profiles of peer and family social support, online contacts, and preferences for online communication. Data stem from the 2017 Dutch “Health and Behavior in School-Aged Children” (HBSC) survey (N = 6,823; 4.0% same- and both-sex attracted; M age=14.73, SD = 1.59, range = 12–18). We conducted latent profile analyses to estimate profiles in peer and family social support, online contacts, and preferences for online communication. Then we assessed the association between sexual attraction and profile membership. A five-profile solution fitted the data best. Profiles were characterized as high support, online contact, and average online communication preference (35.6%); high support, low online contact, and weak online communication preference (42.9%); average support, high online contact, and strong online communication preference (9.9%); low support, low online contact, and average online communication preference (6.9%); and low support, average online contact, and average online communication preference (5.0%). Same- and both-sex attracted adolescents had higher odds than other-sex attracted adolescents of being in the latter three profiles than in the first profile. Thus, same- and both-sex attracted adolescents were more likely to report average to low rates of peer and family social support, high to low frequency of online contact, and an average to strong preference for online communication than other-sex attracted adolescents. The average to low levels of support especially influenced these sexual orientation-based differences in profile membership.

Fabrication of CP-Ti structure with controllable wettability using powder bed fusion and eco-friendly post-process

Hydrophobic surfaces have a wide range of applications, such as water harvesting, self-cleaning, and anti-biofouling. However, traditional methods of achieving hydrophobicity often involve the use of toxic materials such as fluoropolymers. This study aims to create controllable wettability surfaces with a three-dimensional geometry using a laser base powder bed fusion (PBF) process with commercially pure titanium (CP-Ti) and silicone oil as non-toxic materials. The optimal PBF process parameters for fabricating micropillar structures, which are critical for obtaining the surface roughness necessary for achieving hydrophobic properties, were investigated experimentally. After fabricating the micropillar structures using PBF, their surface energy was reduced by treatment with silicone oil. Silicone oil provides a low-surface-energy coating that contributes to the water-repellent nature of hydrophobic surfaces. The wettability of the treated CP-Ti surfaces was evaluated based on the diameter of the pillars and the space between them. The structure with the optimal diameter and spacing of micropillars exhibited a high contact angle (156.15°). A pronounced petal effect (sliding angle of 25.9°) was achieved because of the morphology of the pillars, indicating the controllability of wetting. The micropillar diameter, spacing, and silicone oil played crucial roles in determining the water contact and sliding angle, which are key metrics for surface wettability.

Strong contact resistance effects on vertical carrier density profile and surface trap density in WSe2 multilayers

Conducting channel migration depending on the thickness of 2D multilayers has been demonstrated theoretically and experimentally by ascribing it to the high interlayer barrier and thickness-dependent carrier mobility via an electrostatic gate and drain bias. However, the unique charge carrier transport feature is significantly suppressed when a high contact resistance is exhibited at the metal-to-2D semiconducting multilayers, in addition to the inherent tunneling barrier between neighboring layers. Herein, we report strong channel access contact resistance effects on the vertical carrier density profile and surface trap density along the thickness of WSe2 multilayer transistors. For the constructed top-contact electrodes demonstrating pseudo-ohmic behavior, we observed clear double humps in the second derivative of the transconductance (dgm) curves, implying conducting channel migration along the c-axis of the WSe2 multilayers, regardless of the drain bias (VD) conditions. Meanwhile, at the bottom-contact electrodes, demonstrating a relatively high contact resistance effect, the second hump of dgm exclusively appears at high VD regimes (3.0 V ≤ VD), signaling the restricted channel migration caused by poor contact quality, even in identical WSe2 multilayers. We further confirmed this distinct feature in dgm curves by connecting the top and bottom electrodes to support our observations. Furthermore, low-frequency noise measurements were performed to determine the surface trap density of the supporting dielectrics and the relevant carrier scattering mechanism. Our study provides valuable insight into the effects of contact resistance on carrier transport and the scattering mechanism in WSe2 multilayer transistors, shedding light on the optimization of device performance and contact quality.

Engineering binary-network structured montmorillonite/silica composite aerogels with improved mechanical strength as water-resistant thermal insulators

Developing clay-based aerogel composites with integrated high strength, low thermal conductivity, and hydrophobicity remains a great challenge. Here, binary-network structured montmorillonite/silica composite aerogels (CSACs) with improved mechanical strength were engineered via the in-situ growth of silica networks in the montmorillonite aerogel scaffolds. Tunable density (0.065–0.149 cm3/g) and porosity (92.3–96.2%) can be achieved by different silica sol volumes (silica network content). The filled silica networks endow aerogels with a complete transition from hydrophilicity to hydrophobicity, showing high water contact angles of >130° and extremely low water absorption of 9.9%. CSACs show enhanced stress transfer and load-bearing capacity, with 2.6 and 4.4 times increased compressive modulus and strength compared to pure montmorillonite aerogel scaffolds. Moreover, a noteworthy reduction in thermal conductivity (0.041 to 0.034 W/(m∙K)), the decreased maximum thermal decomposition rates (dw/dt), increased temperature at the maximum decomposition rates (Tmax), and residues confirm the improved thermal insulation and thermal stability of CSACs, respectively. This research provides new insights into the design of efficient thermal insulation materials for diverse energy-saving scenarios that require excellent combined properties.

Icephobic Gradient Polymer Coatings Deposited via iCVD: A Novel Approach for Icing Control and Mitigation.

Materials against ice formation and accretion are highly desirable for different industrial applications and daily activities affected by icing. Although several concepts have been proposed, no material has so far shown wide-ranging icephobic features, enabling durability and manufacturing on large scales. Herein, we present gradient polymers made of 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4D4) and 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) deposited in one step via initiated chemical vapor deposition (iCVD) as an effective coating to mitigate ice accretion and reduce ice adhesion. The gradient structures easily overcome adhesion, stability, and durability issues of traditional fluorinated coatings. The coatings show promising icephobic performance by reducing ice adhesion, depressing the freezing point, delaying drop freezing, and inhibiting ice nucleation and frost propagation. Icephobicity correlates with surface energy discontinuities at the surface plane resulting from the random orientation of the fluorinated groups of PFDA, as confirmed by grazing-incidence X-ray diffraction measurements. The icephobicity could be further improved by tuning the surface crystallinity rather than surface wetting, as samples with random crystal orientation show the lowest ice adhesion despite high contact angle hysteresis. The iCVD-manufactured coatings show promising results, indicating the potential for ice control on larger scales and various applications.

Remarkable reduction in thermal contact resistance between target and heat exchanger using TIMs in isotope neutron source accelerator

The high thermal contact resistance (TCR) between the target and the heat exchanger in the Isotope Neutron Source Accelerator will cause the high-energy charged particle beam to stay in the target, resulting in a remarkable increase of temperature which affects the production of stable isotopes. At present, the usage of thermal interface materials (TIMs) can fill the gap at the contact surface and thus reduces the TCR. In this paper, aiming at the actual working condition of neutron source, the steady-state TCR measurement experiment is designed under vacuum and high temperature environment. The TCR at the contact surface was reduced after adding graphite films, thermal greases, liquid metals and preloads. The improvement of TCR of the contact surface between palladium (Pd), copper (Cu) and graphite (Gr) were measured respectively. The results show that the TCR between palladium and graphite is reduced by 95 % by adding liquid metal (Gallium alloy). The TCR between copper and graphite was reduced by 91 % by brazing method. Compared with other TIMs, graphite film has the advantages of high thermal conductivity, high temperature resistance and no fluidity. Adding 0.08 mm thick graphite film between Pd/Gr and Cu/Gr contact surface can reduce the TCR by 50 % and 70 %, respectively. The improvement effect between the two contact surfaces was not obvious when 15.9–318.3 kPa preload was applied.

Evaluating mobility extraction reliability in non-ideal organic transistors utilizing weak epitaxy-grown pentacene films

Organic thin-film transistors (OTFTs) have exhibited enhanced carrier mobilities, albeit often accompanied by non-ideal electrical characteristics, posing challenges in accurately assessing device performance. Therefore, it is critical to understand the reliability of mobility values derived from these non-ideal current–voltage curves. In this study, high-quality pentacene films and their OTFTs were fabricated by using organic weak-epitaxy growth technology. We focused on investigating the relationship between effective mobilities and contact resistance by varying the interlayer thicknesses of MoO3 while maintaining the optimized semiconductor layer unchanged. An inverse correlation between the reliability factors and claimed mobilities is identified. For OTFTs with moderate contact resistance, the effective mobility exhibited minimal variation, remaining within a narrow 10% margin, accompanied high reliability factor. These results indicated the reliability of mobility extraction. Notably, the optimal thickness of MoO3 ranged between 2.0–3.0 nm. In contrast, a thicker MoO3 layer significantly decreased the reliability factor due to a high contact resistance, thereby rendering the effective mobility unreliable. Our works underscore the robustness of the estimation method for OTFTs featuring moderate contact resistance, providing guidance for the evaluation of material and device performance.