Crosslinked polyethylene (XLPE) is a key material for power cable insulation due to its superior electrical properties. It is co-extruded with a semiconducting “semicon” layer, which is significantly more conductive than XLPE due to the incorporation of carbon black. Understanding the electrical properties of the XLPE/semicon bilayer and the interface between them is critical due to their common use. Two techniques were used to study electrical properties of XLPE and XLPE/semicon bilayers. One was current-voltage measurements, which analyzed resistivity as a function of time. The other was high-voltage polarization, which analyzed polarizability and dielectric loss as a function of electrical field. Thin films of PE and semicon were made via melt pressing. Dicumyl peroxide was infused to the beads prior to melt pressing such that XLPE was formed. All samples were degassed to remove DCP byproducts. Semicon/polyethylene bilayers were made by pressing the two layers together. LDPE and LDPE/semicon were also studied. Bulk brass electrodes were used. Current-voltage measurements showed that adding the semicon layer increased conductivity by an order of magnitude. Polarization measurements revealed that significant enhancement in the dielectric loss occurred at electric fields of 15 kV/mm and above. Polyethylene by itself and semicon bilayer samples had distinct electrical properties, and thus a proper understanding of the performance of XLPE in power cables required analyzing both. Further work is suggested that focuses on correlating changes in measured conductivity to the nature of the material interface (e.g., via enhanced charge injection and/or introduction of charge carriers).

The transient current in low-density polyethylene (LDPE) is studied, particularly in the presence of the small organic molecule acetophenone (ACP). Crosslinked LDPE is used extensively in high-voltage power transmission, and acetophenone is a common byproduct of the crosslinking chemistry. Time-dependent current measurements of LDPE with and without ACP soaked into the polymer as well as at one or both electrodes are performed by applying step voltages. The results demonstrate that the presence of ACP causes a deviation in the predicted power-law current decay, suggesting that electron and hole injection at the anode and cathode, respectively, are affected by the presence of this small organic molecule. ACP contributes both to the ionic conduction and charge hopping mechanism. The charge mobility depends on the applied electric field and the sample thickness. The results suggests that the dispersive charge transport phenomenon influences the measured current. This study shows how such a molecule may alter charge transport in polyethylene.

Thermally activated direct current (DC) electrical conductivity in low-density polyethylene (LDPE) is known to be subject to the compensation law. Accordingly, the preexponential factor follows a specific relation with activation energy, reducing overall changes in conductivity. This relationship is governed by the Meyer-Neldel temperature. However, there is no published evidence for a corresponding isokinetic point, a temperature where the conductivity of all LDPE samples is the same. Here, it is determined that the compensation law applies to both DC and alternating current (AC) conduction for LDPE and for crosslinked polyethylene (XLPE) without an observed isokinetic point. The potential origins of compensation in polyethylene are discussed as well as reasons for similarity between LDPE and XLPE. It is observed that prolonged water exposure removed the compensation behavior. Meanwhile, preheating samples in the oven prior to measurements modifies the compensation behavior and reduced the spread around the isokinetic point. It is thus deduced that an isokinetic point can be observed in polyethylene but is obscured by contributions from water and other impurities.

Crosslinked polyethylene (XLPE) is a key material used for power cable insulation due to its electrical properties and structure. Here, it was shown that the technique of broadband dielectric spectroscopy can be used to analyze both by extracting the temperature coefficient of capacitance (TCC), dielectric loss, and AC conductivity. TCC for low-density polyethylene (LDPE) can be directly compared to its linear thermal expansion coefficient and used as a tool to compare different types of polyethylene. Degassing, a thermal treatment to remove volatile species and increase crystallinity, can be used to control TCC magnitude. In general, changes in the TCC magnitude are reflective of changes in the crystallinity and byproduct concentrations. Degassing also reduced the dielectric loss for both due to morphological changes and byproduct removal. However, it only reduces conductivity at elevated temperatures such as 90 °C for XLPE. Other processing parameters, as well as excessive byproduct concentrations, were also seen to influence TCC, dielectric loss, and conductivity.

Atomically thin tungsten diselenide (WSe2) is a promising 2D semiconductor for nanoelectronics and optoelectronics. Using UV ozone and low-power O(2)plasma treatments, it is demonstrated that the formation of WSe2(1-x)O2x(WSeyOx) leads to hysteretic behavior in vertical transport measurements and also enables to an improvement in the p-type transfer characteristics in lateral transport measurements. The amount of oxidation correlates well with the resistive switch behavior in oxidized WSe2/graphene, and WSe(y)O(x)formation under the electrical contact of the horizontal devices leads to increased p-branch on/off by 100x. In addition to its effect for residue removal, oxidation on field effect transistor channel also helps mitigate n-type dominated transfer characteristics of WSe(2)commonly seen on sapphire. It is demonstrated that light oxidation of WSe(2)is a multifunctional post-growth treatment that enables vertical resistive switch junctions, contact improvement, and continuous tuning of transistor transport properties.

In this study, the byproduct-driven conduction current in LDPE was investigated. We built an experimental fixture to measure bulk conductivity in LDPE soaked with byproducts. Ohmic conduction was observed below 10 kV/mm. At above 10 kV/mm, space charge limited current (SCLC) predicts observed conduction in LDPE soaked with byproducts. It is found that the addition of byproducts introduces charge traps with discrete energy levels which dominate conduction. Degassed samples, on the other hand, show slopes of greater than 2.5 in a current-voltage log-log plot which was attributed to the charge traps with continuous energy levels. By analyzing the thickness dependence of the current, we observed a transition from electrode- to bulk-limited current at above 20 kV/mm for acetophenone- and α-cumyl alcohol-soaked samples. The α-methylstyrene-soaked samples only show electrode-limited current.

Cross-linked polyethylene (XLPE) is notable for its use as power cable insulation. Its longevity is limited by space charge buildup linked to impurities such as the byproducts left behind by the cross-linking agent dicumyl peroxide (DCP). The goal of this work is to determine the impacts of these byproducts on charge trapping and detrapping in XLPE using the thermally stimulated depolarization current technique. XLPE with byproducts has one source of trapped charge, which originates from the byproducts. XLPE that was thermally treated via degassing exhibits two other sources of trapped charge, which are charge injection and dipolar relaxations. Oxidation from degassing was shown to control the trapping from these sources, which is useful knowledge for processing this material prior to its use. Reintroducing acetophenone, one of the major byproducts of DCP, suppresses those two peaks once more, showing that it controls the overall space charge buildup characteristics in XLPE.

The intrinsic diffusion of the acetophenone in low density polyethylene (LDPE) is characterized with infrared mapping and it is found to be nearly Fickean with decaying diffusion coefficient over time. The impact of temperature on the diffusion coefficient is examined and an Arrhenius relationship is derived for the temperature dependence. To study the influence of electric field on the acetophenone diffusion, field-test cells were designed and constructed. The infrared mapping revealed presence of a gradient in the acetophenone concentration. Using the COMSOL simulation, we observed the higher acetophenone concentration near high electric field gradient regions. This is attributed to the dielectrophoresis phenomenon that occurs due to higher permittivity of the acetophenone molecules compared to the surrounding medium. The findings of this study help to understand where the byproducts migrate in high voltage power cables.

Crosslinked polyethylene (XLPE) is a common material for power cable insulation due to its low cost, mechanical stability, and insulating nature. It is made by converting low-density polyethylene (LDPE) to a crosslinked variant using the chemical agent dicumyl peroxide (DCP). However, the crosslinking process leaves behind byproducts that may compromise the utility of the XLPE. For example, they can contribute to space charge buildup and degradation over time. Here, the thermally stimulated depolarization current (TSDC) technique is used to analyze the susceptibility of XLPE to charge buildup and the origins of the stored charge. Comparisons to LDPE are made to determine if DCP byproducts play a role. In general, three peaks are observed in both XLPE and LDPE, with only one being observed above room temperature. That homocharge peak arises from charge injection that occurs during poling, and has greater magnitude in LDPE than in XLPE. It's magnitude in XLPE can be controlled by the applied field, but the same cannot be said for LDPE. For the two other peaks observed, one is potentially attributable to polymer motion or glass transition phenomena, while the origin of the other is currently speculated to be related to moisture content.

Crosslinked polyethylene is a common material for power cable insulation due to its low cost, mechanical stability, and insulating nature. However, the crosslinking process leaves behind byproducts that may compromise its utility. Here, the impact of crosslinking on the capacitance and dielectric loss of polyethylene samples is examined. Crosslinked and noncrosslinked samples exhibit similar dielectric loss values at room temperature. However, crosslinked samples are more insulating at 90 °C. We observe that the amount of peroxide added was not directly related to the electrical properties, but that crosslinking temperature and time are. These results imply that the morphology changes upon crosslinking are as important in controlling the conductivity and loss as any residual byproducts. It is also observed that the degassing at elevated temperatures in vacuum that is normally done to remove byproducts also benefited non-crosslinked films, supporting the argument that morphology changes due to the elevated temperatures used in degassing can cause a reduction of dielectric loss. Analysis of mechanical properties through the use of temperature coefficient of capacitance, used to approximate the linear thermal expansion coefficient, allowed for further analysis of the morphology. Crosslinked films expand more than non-crosslinked films, and their expansion is reduced with degassing. Both ambient and vacuum degassing aid in this, implying that recrystallization and byproduct removal combined lead to reductions in dielectric loss and thermal expansion in crosslinked polyethylene.

Single layers of tungsten diselenide (WSe2) can be used to construct ultra-thin, high-performance electronics. Additionally, there has been considerable progress in controlled and direct growth of single layers on various substrates. Based on these results, high-quality WSe2-based devices that approach the limit of physical thickness are now possible. Such devices could be useful for space applications, but understanding how high-energy radiation impacts the properties of WSe2 and the WSe2/substrate interface has been lacking. In this work, we compare the stability against high energy proton radiation of WSe2 and silicon carbide (SiC) heterostructures generated by mechanical exfoliation of WSe2 flakes and by direct growth of WSe2 via metal-organic chemical vapor deposition (MOCVD). These two techniques produce WSe2/SiC heterostructures with distinct differences due to interface states generated during the MOCVD growth process. This difference carries over to differences in band alignment from interface states and the ultra-thin nature of the MOCVD-grown material. Both heterostructures are not susceptible to proton-induced charging up to a dose of 1016 protons/cm2, as measured via shifts in the binding energy of core shell electrons and a decrease in the valence band offset. Furthermore, the MOCVD-grown material is less affected by the proton exposure due to its ultra-thin nature and a greater interaction with the substrate. These combined effects show that the directly grown material is suitable for multi-year use in space, provided that high quality devices can be fabricated from it.

Semiconducting two-dimensional materials (2DMs) such as molybdenum disulfide and tungsten diselenide have attracted significant attention due to their unique electronic properties. Understanding their nanoscale radiation tolerance is needed for developing radiation-hardened nanoelectronics. Here, we report that the XPS environment of soft X-ray (E = 1.486 keV) exposure in a vacuum combined with a low energy electron flood gun leads to charge accumulation in the 2D layers over time, with little impact on layer chemistry. Additionally, the charging that induced the 2DM/substrate heterostructure depends more on the growth technique, the size of as-grown domains, and the surface coverage of the 2DM than the conductivity of the substrate. Charging is minimized for the combination of a continuous 2DM film and strong coupling between the 2DM and the substrate.

The remarkable electronic properties of layered semiconducting transition metal dichalcogenides (TMDs) make them promising candidates for next-generation ultrathin, low-power, high-speed electronics. It has been suggested that electronics based upon ultra-thin TMDs may be appropriate for use in high radiation environments such as space. Here, we present the effects of irradiation by protons, iron, and silver ions at MeV-level energies on a WSe2/6H-SiC vertical heterostructure studied using XPS and UV-Vis-NIR spectroscopy. It was found that with 2 MeV protons, a fluence of 1016 protons/cm2 was necessary to induce a significant charge transfer from SiC to WSe2, where a reduction of valence band offset was observed. Simultaneously, a new absorption edge appeared at 1.1 eV below the conduction band of SiC. The irradiation with heavy ions at 1016 ions/cm2 converts WSe2 into a mixture of WOx and Se-deficient WSe2. The valence band is also heavily altered due to oxidation and amorphization. However, these doses are in excess of the doses needed to damage TMD-based electronics due to defects generated in common dielectric and substrate materials. As such, the radiation stability of WSe2-based electronics is not expected to be limited by the radiation hardness of WSe2, but rather by the dielectric and substrate.

physica status solidi (a)Volume 213, Issue 12 p. 3268-3268 Back CoverFree Access Radiation effects on two-dimensional materials (Phys. Status Solidi A 12∕2016) R. C. Walker II, R. C. Walker II Department of Materials Science, Penn State, University Park, PA, 16802 USA Center for Two-Dimensional Layered Materials, Penn State, University Park, PA, 16802 USASearch for more papers by this authorT. Shi, T. Shi Department of Mechanical and Nuclear Engineering, Penn State, University Park, PA, 16802 USA Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109 USASearch for more papers by this authorE. C. Silva, E. C. Silva GlobalFoundries, Malta, NY, 12020 USASearch for more papers by this authorI. Jovanovic, I. Jovanovic Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109 USASearch for more papers by this authorJ. A. Robinson, Corresponding Author J. A. Robinson jrobinson@psu.edu Department of Materials Science, Penn State, University Park, PA, 16802 USA Center for Two-Dimensional Layered Materials, Penn State, University Park, PA, 16802 USASearch for more papers by this author R. C. Walker II, R. C. Walker II Department of Materials Science, Penn State, University Park, PA, 16802 USA Center for Two-Dimensional Layered Materials, Penn State, University Park, PA, 16802 USASearch for more papers by this authorT. Shi, T. Shi Department of Mechanical and Nuclear Engineering, Penn State, University Park, PA, 16802 USA Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109 USASearch for more papers by this authorE. C. Silva, E. C. Silva GlobalFoundries, Malta, NY, 12020 USASearch for more papers by this authorI. Jovanovic, I. Jovanovic Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, 48109 USASearch for more papers by this authorJ. A. Robinson, Corresponding Author J. A. Robinson jrobinson@psu.edu Department of Materials Science, Penn State, University Park, PA, 16802 USA Center for Two-Dimensional Layered Materials, Penn State, University Park, PA, 16802 USASearch for more papers by this author First published: 05 December 2016 https://doi.org/10.1002/pssa.201670681Citations: 5AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Two-dimensional materials (2DMs) such as graphene, layered transition metal dichalcogenides, and hexagonal boron nitride have seen renewed research interest over the past decade in the search of novel nano-scale physics and devices. These materials have been shown to be highly sensitive to their surroundings, which has revealed the importance of interface states for growth processes and device operation. This has also allowed for the development of gas and biomolecule sensors based on charge transfer to the 2DMs. In the Feature Article by R. C. Walker et al. (pp. 3065–3077), the focus is on the sensitivity of 2DMs to electromagnetic radiation and charged particle interactions. Such interactions are key in developing 2DMs for applications as light sensors, radiation detectors, and radiation-hardened space electronics. Many years of developing opto-electronics based on 2DMs have shown that they are suitable for visible and ultraviolet light detection, but more development must be done for infrared and terahertz wave detection. This review also discusses initial work in determining damage mechanisms in 2DMs due to X-rays, gamma rays, electron beams, protons and heavy ions, and proposes future research directions. Citing Literature Volume213, Issue12December 2016Pages 3268-3268 RelatedInformation

The effects of electromagnetic and particle irradiation on two‐dimensional materials (2DMs) are discussed in this review. Radiation creates defects that impact the structure and electronic performance of materials. Determining the impact of these defects is important for developing 2DM‐based devices for use in high‐radiation environments, such as space or nuclear reactors. As such, most experimental studies have been focused on determining total ionizing dose damage to 2DMs and devices. Total dose experiments using X‐rays, gamma rays, electrons, protons, and heavy ions are summarized in this review. We briefly discuss the possibility of investigating single event effects in 2DMs based on initial ion beam irradiation experiments and the development of 2DM‐based integrated circuits. Additionally, beneficial uses of irradiation such as ion implantation to dope materials or electron‐beam and helium‐beam etching to shape materials have begun to be used on 2DMs and are reviewed as well. For non‐ionizing radiation, such as low‐energy photons, we review the literature on 2DM‐based photo‐detection from terahertz to UV. The majority of photo‐detecting devices operate in the visible and UV range, and for this reason they are the focus of this review. However, we review the progress in developing 2DMs for detecting infrared and terahertz radiation.

The effects of different processing steps and processing conditions for the fabrication of Y2O3 and Lu2O3 ceramics were investigated, particularly the effects of calcination, and sintering temperature on the content of open‐volume and electronic defects. Ceramic bodies were prepared from calcined powders by sintering from 1400°C to 1700°C for 20 h. Density was determined by the Archimedes method and showed pellets reached about 99% of Y2O3 density for temperatures ≥1450°C, and reached 98% for sintering at 1700°C for Lu2O3. The content of open‐volume defects was followed by positron annihilation lifetime (PAL) measurements. For both materials, two lifetimes were obtained. The faster lifetime, 211 ps for Y2O3 and 204 ps for Lu2O3, was assigned to bulk annihilation with possible contribution of grain boundaries. The longer lifetime was assigned to positronium annihilation in open‐volume defects with radii of 2–4 Å. Doppler broadening analysis revealed the same type of defect in Lu2O3 ceramics for all sintering temperatures. PAL analysis results showed that densification was achieved through the elimination and agglomeration of open‐volume defects. Thermoluminescence (TL) measurements of Y2O3 showed that sintering is beneficial in eliminating traps and/or recombination centers, and that higher sintering temperatures increase TL signal.