Design of organic π-conjugated semiconducting materials is an exciting avenue of research that has already found promising applications in a wide variety of fields, ranging from stretchable electronics to bioimaging and theranostics. With favorable optoelectronic and thermomechanical properties, these materials and related devices can provide a complementary alternative to commercial silicon-based electronics. One of the most important features of organic semiconductors is their ability to be solution processed, allowing access to a wide variety of printing and solution deposition techniques inaccessible to silicon. However, the solution processability of these materials also poses challenges for the development of multilayer electronics due to potential problems such as swelling, film deformation and interfacial mixing that can occur upon successive solution deposition. Use of orthogonal (noncompatible) solvents and solvent-free deposition methods have been extensively investigated as solutions to this challenge, although the applicability of these approaches is limited by the chemical properties of the materials used. Another approach to address this problem is to focus on the materials rather than deposition methods. Through rational design, functional groups can be used to create triggered solvent resistance through covalent or dynamic intermolecular bonds. Design strategies include the incorporation of photo- and thermally cleavable functional groups in the materials, or the use of chemical additives/reagents to significantly alter the solubility of π-conjugated materials and afford solvent-resistant thin films. This spotlight article presents recent progress toward solvent-resistant organic materials with an emphasis on their use in electronic applications. Recent and key developments will be discussed from a personal perspective, providing an overview of the different approaches used to achieve solvent-resistant semiconducting materials toward the fabrication of advanced, multilayer organic electronics.

The electroless plating of metals and their alloys, oxides, and chalcogenides represents a critically important technology for the automotive, aerospace, machine tools, and, especially, the electronics industries. Since the initial efforts involving the plating of industrially important metals, such as Ni, Co, Cu, Ag, and Au, in the mid-20th century, the process has evolved to encompass a growing number of elements. At the same time, this expansion in the palette of accessible metals has enabled progress in these industries and evoked new nonconventional applications. In this review, we collect and survey available electroless processes in aqueous and organic solvent systems for each element organized according to position in the Periodic Table as a resource for the reader. Examples illustrating progress in the field are presented and are described in sufficient detail to be useful and understandable for both the expert and nonexpert. Given the historical importance of electronics as a driver for development of electroless processes, examples are electronics-related where possible. However, we strive to also include examples of applications in nontraditional fields to provide the reader with a sense of generality available for electroless methods. The review closes with an outlook for the field and a challenge to scientists and engineers to adapt electroless processes for new applications to continue the growth of the field.

Two-dimensional (2D) 2H-MoTe2 is an emerging semiconductor with promising electronic and optoelectronic properties. Meanwhile, the in-plane 2D epitaxy mechanism via the 1T′ to 2H phase transition allows the synthesis of 2H-MoTe2 on arbitrary surfaces. Here, we demonstrate two routes for tier-by-tier growth and one-step growth to synthesize multitier 2H-MoTe2 isolated by atomic layer deposition aluminum oxide (Al2O3). Raman, scanning transmission electron microscopy, and other characterizations show that the periodic 2H-MoTe2/Al2O3 multilayer structure exhibits the characteristics of large-area preparation and high crystallinity. Our direct multitier growth routes move the first step toward realizing 3D-ICs and nonvolatile memories based on semiconducting 2H-MoTe2.

Metal–semiconductor–metal (MSM) photodetectors offer efficient solutions for many applications. Here, we combine surface energy assisted wet transfer of a MoS2 monolayer with patterned interdigitated platinum electrodes. The chemical vapor deposition (CVD)-deposited MoS2 monolayer is analyzed for various performance parameters. The achieved dark current and photocurrent are 5.37 × 10–8 A and on the order of 10–5 A, respectively. The achieved peak responsivity and peak external quantum efficiency are 13.15 mA/W at 480 nm and 21.86% at 4.5 V, respectively. The Ion/Ioff ratio obtained is 256 for 5 V with a rise and fall time of 0.06 and 0.14 ms, respectively.

Potassium poly(heptazine imide) (K-PHI) is a two-dimensional carbon nitride polymer that has recently attracted attention as a visible-light-driven photocatalyst. We developed a solid material that does not require a liquid electrolyte as a composite of K-PHI with an ionic liquid or insulating polymer matrix. The obtained K-PHI composites retained some of the unique optoelectronic properties of K-PHI and were in a semisolid state that could be easily shaped in a warm state. Simple devices using these K-PHI composites exhibited photoconductivity by the ionic conduction of potassium cations activated by white light irradiation.

Vertical light-emitting transistors (VLETs) fabricated by integrating organic vertical transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. However, organic vertical transistors normally have non-ohmic injection and a low-mobility channel, resulting in low VLET performance compared to the pristine OLED. The difficulty of fine patterning the source electrode and organic layer in a stacked VLET geometry has also been a technical issue limiting industrial applications. This paper reports on a simple approach to realize a high-performance, miniaturized VLET by using a highly conductive, well-designed inorganic transistor. Here, we investigate the ZnO transistor configured with an insulator-encapsulated source electrode to confine the current pathway in the VLET, which can be easily fabricated and integrated with various solution-processed or vacuum-sublimed inverted OLEDs (IOLEDs). This ZnO transistor exhibits ohmic contact and a high electron mobility of >10 cm2/(V s) that enables effective electron injection and lateral transport in the VLET, forming a millimeter-scale density gradient (channel depth) for strong surface emission. Furthermore, the high mobility of ZnO facilitates the design of a simple source pattern with a large aperture ratio on the ZnO area to control the current density and distribution and thus the VLET output. From a systematic study of the source design, we show that the ZnO transistor can be optimized to achieve homogeneously high conductivity in the ON state and yield the best VLET performance with maximum emission intensity and efficiency close to those of the IOLED, while the emission can be spatially uniform and precisely defined by the ZnO pattern. Finally, we implement a micropixelated VLET-based active matrix panel to demonstrate the prospect of high-resolution display applications.

We report the potential of low-cost sol–gel-synthesized phase pure BiFeO3 thin films as an active material with Cu as the top contact and fluorine-doped tin oxide (FTO) as the bottom contact, that is, Cu/BiFeO3/FTO-based devices for analogue resistive switching characteristics, suitable for beyond von Neumann computing. The Cu/BiFeO3/FTO device showed robust repeatability of bipolar resistive switching up to 3000 cycles. Moreover, retention measurements suggest that the device is stable for 17,000 s at 0.2 V, and endurance measurements suggest reliability for 5000 cycles at 1 and −1 V. Moreover, the Cu/BiFeO3/FTO device showed synaptic behavior, including short- and long-term plasticity and change in ionic conductance with time-dependent pulses suitable for neural network applications. The pulse paired facilitation (PPF) measurements demonstrated a reduction in the PPF value from 9 to 1% with the increasing pulse width from 10 to 400 ms. The strengthening in signal transmission is shown by increasing the synaptic weight from 20 to 22.5 approximately, with the increasing scan rate from 100 to 400 mV/s. The increase in the scan rate resulted in the synaptic weight saturation, and a change in ionic conductance is observed at 0.7 and 0.2 V with varying pulse widths ∼10, 20, and 50 ms, having a 10 ms pulse interval. The spike time-dependent plasticity measurement is carried out for the symmetric and asymmetric Hebbian rule with 4 s pulse width at 1.2 and −1.2 V pulse amplitude. The device also showed ∼96% recognition characteristics, as estimated from retention loss characteristics. Thus, the present work emphasizes the utility of BiFeO3-based analogue devices for memristive neuromorphic computing devices.

In this study, we demonstrate a quasi van der Waals epitaxy approach to prepare an epitaxial Ru ultrathin film on large-scale, single-crystalline, monolayer graphene. Physical and epitaxial properties of the bulk, near surface, and surface of ultrathin Ru films were comprehensively studied using various structural, morphological, compositional, and electrical characterization techniques. We confirm that Ru can epitaxially grow on single-crystalline, monolayer graphene using magnetron sputtering at an elevated temperature of 600 °C. The epitaxial Ru films with film thickness ranging from 94.2 nm down to 3.9 nm show the (0001) out-of-plane orientation. The epitaxial relationships between Ru and graphene are out-of-plane Ru(0001) || graphene(0001) and in-plane Ru[112̅0] || graphene[112̅0]. All the Ru films show smooth surfaces with a root-mean-square roughness of less than 0.8 nm and have a negligible oxide layer on the surface. The Ru films on graphene demonstrate significantly reduced electrical resistivity compared to their counterparts grown on bare SiO2, which show a polycrystalline nature. For 7.1 to 3.9 nm film thicknesses, the resistivity of Ru on graphene shows a 38 to 45% resistivity decrease from that of the Ru film on bare SiO2 without graphene. Our observations suggest the existence of the above-classical van der Waals interaction between Ru and graphene. On the other hand, graphene is capable of effectively blocking the interdiffusion/interaction between Ru and SiO2 during a 1000 °C annealing process.

Sb2Te3 is a topological insulator (TI) material that can be used in a wide range of applications from energy harvesting to Spin-Orbitronics. In this paper, the structural, electrical, and thermal transport properties of nanocrystalline ion beam sputtered Sb2Te3 thin films were studied. Films with thicknesses between 35 and 300 nm, with nanocrystallites of sizes 10–20 nm, have a high resistivity between 0.072 and 2.03 Ω cm at 300 K, increasing with cooling. The Seebeck coefficient demonstrates the coexistence of n-type and p-type conduction, the latter being more prominent at high temperatures and in thicker films. The morphological and transport properties reveal that the films are constituted by two layers having different majority charge carriers, with the electronic bulk conduction being described by two semiconductor layers conducting in parallel, one p-type at the surface and another n-type, each described by an activation energy-dependent conductivity. Besides these bulk contributions, weak antilocalization (WAL) cusps are observed in the magnetoconductance below 10 K and at low magnetic fields. Analysis of the WAL hints that there is one two-dimensional conduction channel open at low temperatures for the thinner films, whereas for the thicker film, this 2D conduction appears to be masked by the bulk channels. However, a magnetic localization length LΦ between 62 and 90 nm at 2 K is observed for all thin films. This behavior suggests that as the bulk activation energy conductions freeze out at low temperatures, the electrical conduction is carried by the supposed 2D state, which appears to have some of the features of a TI surface state. Through these measurements, we demonstrate that the type of dominant conduction can be controlled by the Sb2Te3 film thickness in these large area sputtered films, while the conduction at low temperatures appears to be dominated by a robust TI state.

We investigate the viability of 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT) as a photosensor and show that there is a direct correlation between the absorption spectrum of the material and the magnitude of the resulting drain current in a field-effect transistor device made from it. We show that the diF-TES ADT device exhibits very high photosensitivity and photoresponsivity for green and blue light. We also propose a hybrid device structure that leverages the high absorptivities of two organic semiconductors to make a sandwich device with high phototransistor metrics across all wavelengths of visible light.