Multifunctional fibers enable modulation of cortical and deep brain activity during cognitive behavior in macaques.

Recording and modulating neural activity in vivo enables investigations of the neurophysiology underlying behavior and disease. However, there is a dearth of translational tools for simultaneous recording and localized receptor-specific modulation. We address this limitation by translating multifunctional fiber neurotechnology previously only available for rodent studies to enable cortical and subcortical neural recording and modulation in macaques. We record single-neuron and broader oscillatory activity during intracranial GABA infusions in the premotor cortex and putamen. By applying state-space models to characterize changes in electrophysiology, we uncover that neural activity evoked by a working memory task is reshaped by even a modest local inhibition. The recordings provide detailed insight into the electrophysiological effect of neurotransmitter receptor modulation in both cortical and subcortical structures in an awake macaque. Our results demonstrate a first-time application of multifunctional fibers for causal studies of neuronal activity in behaving nonhuman primates and pave the way for clinical translation of fiber-based neurotechnology.

Magnetically Actuated Fiber-Based Soft Robots.

Broad adoption of magnetic soft robotics is hampered by the sophisticated field paradigms for their manipulation and the complexities in controlling multiple devices. Furthermore, high-throughput fabrication of such devices across spatial scales remains challenging. Here, advances in fiber-based actuators and magnetic elastomer composites are leveraged to create 3D magnetic soft robots controlled by unidirectional fields. Thermally drawn elastomeric fibers are instrumented with a magnetic composite synthesized to withstand strains exceeding 600%. A combination of strain and magnetization engineering in these fibers enables programming of 3D robots capable of crawling or walking in magnetic fields orthogonal to the plane of motion. Magnetic robots act as cargo carriers, and multiple robots can be controlled simultaneously and in opposing directions using a single stationary electromagnet. The scalable approach to fabrication and control of magnetic soft robots invites their future applications in constrained environments where complex fields cannot be readily deployed.

Selectively Micro-Patternable Fibers via In-Fiber Photolithography.

Multimaterial fibers engineered to integrate glasses, metals, semiconductors, and composites found applications in ubiquitous sensing, biomedicine, and robotics. The longitudinal symmetry typical of fibers, however, limits the density of functional interfaces with fiber-based devices. Here, thermal drawing and photolithography are combined to produce a scalable method for deterministically breaking axial symmetry within multimaterial fibers. Our approach harnesses a two-step polymerization in thiol-epoxy and thiol-ene photopolymer networks to create a photoresist compatible with high-throughput thermal drawing in atmospheric conditions. This, in turn, delivers meters of fiber that can be patterned along the length increasing the density of functional points. This approach may advance applications of fiber-based devices in distributed sensors, large area optoelectronic devices, and smart textiles.

Necrotic cell death induces melanotic mass formation in Drosophila.

The immune system protects its host from not only invading parasites and parasitoids, but also altered self tissue, including dying cells. Necrotic cells are strongly immunogenic, but in Drosophila this has not been directly addressed, due partially to the fact that knowledge about necrosis in Drosophila currently lags behind that for other models. Upon the loss of cell matrix attachment, endocycling polyploid tissues of the Drosophila larva undergo autophagy instead of apoptosis; we employed this system as a model to examine cell death modalities and immunity. Here, we report that larval fat body cells depleted of integrin undergo not only autophagy, but also necrotic cell death, and that a blockade of reaper, grim, hid, or the downstream caspases enhances necrosis. These cells elicit melanotic mass formation, an autoimmune-like response. We also show that necrosis is the main cause of melanotic mass formation in these anchorage-depleted polyploid cells.

cdc37 is essential for JNK pathway activation and wound closure in Drosophila.

Wound closure in the Drosophila larval epidermis mainly involves nonproliferative, endocyling epithelial cells. Consequently, it is largely mediated by cell growth and migration. We discovered that both cell growth and migration in Drosophila require the cochaperone-encoding gene cdc37. Larvae lacking cdc37 in the epidermis failed to close wounds, and the cells of the epidermis failed to change cell shape and polarize. Likewise, wound-induced cell growth was significantly reduced, and correlated with a reduction in the size of the cell nucleus. The c-Jun N-terminal kinase (JNK) pathway, which is essential for wound closure, was not typically activated in injured cdc37 knockdown larvae. In addition, JNK, Hep, Mkk4, and Tak1 protein levels were reduced, consistent with previous reports showing that Cdc37 is important for the stability of various client kinases. Protein levels of the integrin ß subunit and its wound-induced protein expression were also reduced, reflecting the disruption of JNK activation, which is crucial for expression of integrin ß during wound closure. These results are consistent with a role of Cdc37 in maintaining the stability of the JNK pathway kinases, thus mediating cell growth and migration during Drosophila wound healing.

Photogating in the Graphene-Dye-Graphene Sandwich Heterostructure.

In this work, we developed an atomically thin (∼2.5 nm) heterostructure consisting of a monolayer rhodamine 6G (R6G) film as a photoactive layer that was sandwiched between graphene films functioning as channels (graphene-R6G-graphene, G-R-G). Through a comparison of results of both photocurrent measurements and chemically enhanced Raman scattering (CERS) experiments, we found that our G-R-G heterostructure exhibited ∼7 and ∼30 times better performance than R6G-attached single-graphene (R6G-graphene, R-G) and MoS2 devices, respectively; here, the CERS enhancement factor was highly correlated with the relative photoinduced Dirac voltage change. Furthermore, the photocurrent of the G-R-G device was found to be ∼40 times better than that of the R-G photodetector. The top graphene was highly operative in the monolayer, of which the performance is significantly deteriorated by fluorescence and tailored charge transfer efficiency with the increment of R6G film thickness. Overall, the responsivity of the G-R-G photodetector was ∼40 times higher than that of the R-G photodetector because of the more efficient carrier transfer between the organic dye and graphene induced by weaker π-π interactions between the top and bottom graphene channels in the former device. This atomically thin (∼2.5 nm) and highly photosensitive photodetector can be employed for post-Si-photodiode (PD) image sensors, single-photon detection devices, and optical communications.

Multibit MoS2 Photoelectronic Memory with Ultrahigh Sensitivity.

A novel multibit MoS2 photoelectronic nonvolatile memory device is developed by synergistically combining rational device designs and the efficient transfer of large-area MoS2 flakes. The MoS2 photoelectronic memory exhibits excellent memory characteristics, including a large programming/erasing current ratio that exceeds 107 , multilevel data storage of 3 bits (corresponding to eight levels), performance stability over 200 cycles, and stable data retention over 104 s.

Trap-induced photoresponse of solution-synthesized MoS2.

We investigated, for the first time, the photoresponse characteristics of solution-synthesized MoS2 phototransistors. The photoresponse of the solution-synthesized MoS2 phototransistor was solely determined by the interactions of the photogenerated charge carriers with the surface adsorbates and the interface trap sites. Instead of contributing to the photocurrent, the illumination-generated electron-hole pairs were captured in the trap sites (surface and interface sites) due to the low carrier mobility of the solution-synthesized MoS2. The photogenerated holes discharged ions (oxygen and/or water) adsorbed onto the MoS2 surface and were released as neutral molecules. At the same time, the photogenerated electrons filled the traps present at the interface with the underlying substrate during their transport to the drain electrode. The filled trap sites significantly relieved the band bending near the surface region, which resulted in both a negative shift in the turn-on voltage and an increase in the photocurrent. The time-dependent dynamics of the solution-synthesized MoS2 phototransistors revealed persistent photoconductance due to the trapped electrons at the interface. The photoconductance was recovered by applying a short positive gate pulse. The instantaneous discharge of the trapped electrons dramatically reduced the relaxation time to less than 20 ms. This study provides an important clue to understanding the photoresponses of various optoelectronic devices prepared using solution-synthesized two-dimensional nanomaterials.

MoS2-InGaZnO Heterojunction Phototransistors with Broad Spectral Responsivity.

We introduce an amorphous indium-gallium-zinc-oxide (a-IGZO) heterostructure phototransistor consisting of solution-based synthetic molybdenum disulfide (few-layered MoS2, with a band gap of ∼1.7 eV) and sputter-deposited a-IGZO (with a band gap of ∼3.0 eV) films as a novel sensing element with a broad spectral responsivity. The MoS2 and a-IGZO films serve as a visible light-absorbing layer and a high mobility channel layer, respectively. Spectroscopic measurements reveal that appropriate band alignment at the heterojunction provides effective transfer of the visible light-induced electrons generated in the few-layered MoS2 film to the underlying a-IGZO channel layer with a high carrier mobility. The photoresponse characteristics of the a-IGZO transistor are extended to cover most of the visible range by forming a heterojunction phototransistor that harnesses a visible light responding MoS2 film with a small band gap prepared through a large-area synthetic route. The MoS2-IGZO heterojunction phototransistors exhibit a photoresponsivity of approximately 1.7 A/W at a wavelength of 520 nm (an optical power of 1 µW) with excellent time-dependent photoresponse dynamics.

Reduced Water Vapor Transmission Rate of Graphene Gas Barrier Films for Flexible Organic Field-Effect Transistors.

Preventing reactive gas species such as oxygen or water is important to ensure the stability and durability of organic electronics. Although inorganic materials have been predominantly employed as the protective layers, their poor mechanical property has hindered the practical application to flexible electronics. The densely packed hexagonal lattice of carbon atoms in graphene does not allow the transmission of small gas molecules. In addition, its outstanding mechanical flexibility and optical transmittance are expected to be useful to overcome the current mechanical limit of the inorganic materials. In this paper, we reported the measurement of the water vapor transmission rate (WVTR) through the 6-layer 10 × 10 cm(2) large-area graphene films synthesized by chemical vapor deposition (CVD). The WVTR was measured to be as low as 10(-4) g/m(2)·day initially, and stabilized at ∼0.48 g/m(2)·day, which corresponds to 7 times reduction in WVTR compared to bare polymer substrates. We also showed that the graphene-passivated organic field-effect transistors (OFETs) exhibited excellent environmental stability as well as a prolonged lifetime even after 500 bending cycles with strain of 2.3%. We expect that our results would be a good reference showing the graphene's potential as gas barriers for organic electronics.

On-demand doping of graphene by stamping with a chemically functionalized rubber lens.

A customized graphene doping method was developed involving stamping using a chemically functionalized rubber lens as a novel design strategy for fabricating advanced two-dimensional (2D) materials-based electronic devices. Our stamping strategy enables deterministic control over the doping level and the spatial pattern of the doping on graphene. The dopants introduced onto graphene were locally and continuously controlled by directly stamping dopants using a chemically functionalized hemispherical rubber lens onto the graphene. The rubber lens was functionalized using two different dopants: poly(ethylene imine) to achieve n-type doping and bis(trifluoromethanesulfonyl)amine to achieve p-type doping. The graphene doping was systematically controlled by varying both the contact area (between the rubber lens and the graphene) and the contact time. Graphene doping using a stamp with a chemically functionalized rubber lens was confirmed by both Raman spectroscopy and charge transport measurements. We theoretically modeled the conductance properties of the spatially doped graphene using the effective medium theory and found excellent agreement with the experimental results. Finally, complementary inverters were successfully demonstrated by connecting n-type and p-type graphene transistors fabricated using the stamping doping method. We believe that this versatile doping method for controlling charge transport in graphene will further promote graphene electronic device applications. The doping method introduced in this paper may also be applied to other emergent 2D materials to tightly modulate the electrical properties in advanced electronic devices.

Multifunctional graphene optoelectronic devices capable of detecting and storing photonic signals.

The advantages of graphene photodetectors were utilized to design a new multifunctional graphene optoelectronic device. Organic semiconductors, gold nanoparticles (AuNPs), and graphene were combined to fabricate a photodetecting device with a nonvolatile memory function for storing photonic signals. A pentacene organic semiconductor acted as a light absorption layer in the device and provided a high hole photocurrent to the graphene channel. The AuNPs, positioned between the tunneling and blocking dielectric layers, acted as both a charge trap layer and a plasmonic light scatterer, which enable storing of the information about the incident light. The proposed pentacene-graphene-AuNP hybrid photodetector not only performed well as a photodetector in the visible light range, it also was able to store the photonic signal in the form of persistent current. The good photodetection performance resulted from the plasmonics-enabled enhancement of the optical absorption and from the photogating mechanisms in the pentacene. The device provided a photoresponse that depended on the wavelength of incident light; therefore, the signal information (both the wavelength and intensity) of the incident light was effectively committed to memory. The simple process of applying a negative pulse gate voltage could then erase the programmed information. The proposed photodetector with the capacity to store a photonic signal in memory represents a significant step toward the use of graphene in optoelectronic devices.

Achieving type I, II, and III heterojunctions using functionalized MXene.

In the present work, type I, II, and III heterostructures are constructed with the same base material using three representative functionalized monolayer scandium carbides (Sc2CF2, Sc2C(OH)2, and Sc2CO2) by first-principles calculations based on density functional theory. In contrast to general bilayer heterosystems composed of two-dimensional semiconductors, type I and III heterojunctions are obtained in one Sc2CF2/Sc2CO2 system and the remains of the functionalized Sc2C heterostructures, respectively. It is noteworthy that the same monolayer Sc2CF2 and Sc2CO2 constituents lead to dissimilar heterostructure types in the two Sc2CF2/Sc2CO2 systems by modifying the stacking interface. In addition, in the two Sc2CF2/Sc2CO2 systems, remarkable changes in the heterojunction type are induced by a strain, and two distinct type-II heterostructures are generated where one layer with the conduction band minimum state and the other layer including the valence band maximum level are different. The present work suggests an attractive direction to obtain all heterostructure types with the same base material for novel nanodevices in various fields such as photonics, electronics, and optoelectronics using only the two monolayer components Sc2CF2 and Sc2CO2.

Wide-range controllable n-doping of molybdenum disulfide (MoS2) through thermal and optical activation.

Despite growing interest in doping two-dimensional (2D) transition metal dichalcogenides (TMDs) for future layered semiconductor devices, controllability is currently limited to only heavy doping (degenerate regime). This causes 2D materials to act as metallic layers, and an ion implantation technique with precise doping controllability is not available for these materials (e.g., MoS2, MoSe2, WS2, WSe2, graphene). Since adjustment of the electrical and optical properties of 2D materials is possible within a light (nondegenerate) doping regime, a wide-range doping capability including nondegenerate and degenerate regimes is a critical aspect of the design and fabrication of 2D TMD-based electronic and optoelectronic devices. Here, we demonstrate a wide-range controllable n-doping method on a 2D TMD material (exfoliated trilayer and bulk MoS2) with the assistance of a phosphorus silicate glass (PSG) insulating layer, which has the broadest doping range among the results reported to date (between 3.6 × 10(10) and 8.3 × 10(12) cm(-2)) and is also applicable to other 2D semiconductors. This is achieved through (1) a three-step process consisting of, first, dopant out-diffusion between 700 and 900 °C, second, thermal activation at 500 °C, and, third, optical activation above 5 µW steps and (2) weight percentage adjustment of P atoms in PSG (2 and 5 wt %). We anticipate our widely controllable n-doping method to be a starting point for the successful integration of future layered semiconductor devices.

High-performance perovskite-graphene hybrid photodetector.

A high-performance novel photodetector is demonstrated, which consists of graphene and CH3 NH3 PbI3 perovskite layers. The resulting hybrid photodetector exhibits a dramatically enhanced photo responsivity (180 A/W) and effective quantum efficiency (5× 10(4) %) over a broad bandwidth within the UV and visible ranges.

Achieving a direct band gap in oxygen functionalized-monolayer scandium carbide by applying an electric field.

In the present paper, the band gap characteristics of oxygen functionalized-monolayer scandium carbide (monolayer Sc2CO2) under a perpendicular external electric field (E-field) were studied using DFT calculations for the potential application of MXene in optoelectronic and optical nanodevices. In contrast to general pristine single-layer materials under an external E-field, monolayer Sc2CO2 undergoes an indirect to direct band gap transition under a positive E-field, and the band gap value changes sharply after the band gap transition. Remarkable variations of the band gap properties are induced by the distinct sensitivity between the Γ and K points in the lowest conduction band to the perpendicular E-field, and different types of orbital lead to the dissimilar response of each point. The present work clearly suggests an effective direction to obtain attractive band gap properties in monolayer MXene using an external E-field for next generation optoelectronic and optical devices.

Electronic properties of transition-metal-decorated silicene.

The electronic properties of 3d transition metal (TM)-decorated silicene were investigated by using density functional calculations in an attempt to replace graphene in electronic applications, owing to its better compatibility with Si-based technology. Among the ten types of TM-doped silicene (TM-silicene) studied, Ti-, Ni-, and Zn-doped silicene became semiconductors, whereas Co and Cu doping changed the substrate to a half-metallic material. Interestingly, in cases of Ti- and Cu-doped silicene, the measured band gaps turned out to be significantly larger than the previously reported band gap in silicene. The observed band-gap openings at the Fermi level were induced by breaking the sublattice symmetry caused by two structural changes, that is, the Jahn-Teller distortion and protrusion of the TM atom. The present calculation of the band gap in TM-silicene suggests useful guidance for future experiments to fabricate various silicene-based applications such as a field-effect transistor, single-spin electron source, and nonvolatile magnetic random-access memory.

Tunable indirect to direct band gap transition of monolayer Sc2CO2 by the strain effect.

MXene has not yet been investigated in optical applications because it is a newly suggested two-dimensional material. In the present work, the first investigation of the prospects of MXene as a novel optical nanodevice was done by applying strain to monolayer Sc2CO2 using first-principles density-functional theory. This single-layer material experiences an indirect to direct band gap transition with variation of the band gap size at a relatively small critical strain of about 2%. The present work emphasizes that monolayer MXene can become a promising material for an optical nanodevice by modulating the band gap properties using strain engineering.

Dye-sensitized MoS2 photodetector with enhanced spectral photoresponse.

We fabricated dye-sensitized MoS2 photodetectors that utilized a single-layer MoS2 treated with rhodamine 6G (R6G) organic dye molecules (with an optical band gap of 2.38 eV or 521 nm). The proposed photodetector showed an enhanced performance with a broad spectral photoresponse and a high photoresponsivity compared with the properties of the pristine MoS2 photodetectors. The R6G dye molecules deposited onto the MoS2 layer increased the photocurrent by an order of magnitude due to charge transfer of the photoexcited electrons from the R6G molecules to the MoS2 layer. Importantly, the photodetection response extended to the infrared (λ < 980 nm, which corresponded to about half the energy band gap of MoS2), thereby distinguishing the device performance from that of a pristine MoS2 device, in which detection was only possible at wavelengths shorter than the band gap of MoS2, i.e., λ < 681 nm. The resulting device exhibited a maximum photoresponsivity of 1.17 AW(­1), a photodetectivity of 1.5 × 10(7) Jones, and a total effective quantum efficiency (EQE) of 280% at 520 nm. The device design described here presents a significant step toward high-performance 2D nanomaterial-based photodetector.

Synthesis of wafer-scale uniform molybdenum disulfide films with control over the layer number using a gas phase sulfur precursor.

We describe a method for synthesizing large-area and uniform molybdenum disulfide films, with control over the layer number, on insulating substrates using a gas phase sulfuric precursor (H2S) and a molybdenum metal source. The metal layer thickness was varied to effectively control the number of layers (2 to 12) present in the synthesized film. The films were grown on wafer-scale Si/SiO2 or quartz substrates and displayed excellent uniformity and a high crystallinity over the entire area. Thin film transistors were prepared using these materials, and the performances of the devices were tested. The devices displayed an on/off current ratio of 10(5), a mobility of 0.12 cm(2) V(-1) s(-1) (mean mobility value of 0.07 cm(2) V(-1) s(-1)), and reliable operation.