He Ma

Fast Adaptive Thermal Camouflage Based on Flexible VO2/Graphene/CNT Thin Films

Adaptive camouflage in thermal imaging, a form of cloaking technology capable of blending naturally into the surrounding environment, has been a great challenge in the past decades. Emissivity engineering for thermal camouflage is regarded as a more promising way compared to merely temperature controlling that has to dissipate a large amount of excessive heat. However, practical devices with an active modulation of emissivity have yet to be well explored. In this letter we demonstrate an active cloaking device capable of efficient thermal radiance control, which consists of a vanadium dioxide (VO2) layer, with a negative differential thermal emissivity, coated on a graphene/carbon nanotube (CNT) thin film. A slight joule heating drastically changes the emissivity of the device, achieving rapid switchable thermal camouflage with a low power consumption and excellent reliability. It is believed that this device will find wide applications not only in artificial systems for infrared camouflage or cloaking but also in energy-saving smart windows and thermo-optical modulators.

Cross-stacked superaligned carbon nanotube electrodes for efficient hole conductor-free perovskite solar cells

Cross-stacked superaligned carbon nanotube (CSCNT) sheets drawn from CNT arrays with excellent conductivity, porosity and flexibility are used as low-cost back contacts for hole conductor-free mesoscopic CH3NH3PbI3/TiO2 heterojunction perovskite solar cells (PSCs). PSCs integrated with CSCNTs achieve a power conversion efficiency of up to 8.65% and over 10.54% by further doping the CSCNTs with iodine. Moreover, PSCs encapsulated with a layer of polymer poly(methylmethacrylate) exhibit outstanding stability in the dark and under illumination. This work represents a significant step toward the commercialization of the low-cost, stable and high-efficiency hole conductor-free PSCs.

Combined effect and its mechanism of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr master alloy on microstructures of Al–Si–Cu alloy

Abstract The combined effect of Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr on Al–Si–Cu alloy has been investigated. Equiaxed dendritic grain of 100–120 μm was obtained with holding time of at least 240 min through addition of more than 0.020% Ti and 0.026% B, though the laminar morphology of eutectic Si kept unaltered. Eutectic Si was completely modified for more than 240 min through addition of Al–10wt.%Sr which also had some benefit on the refinement of primary α-Al. The combined addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr led to shorter working time of modification and slightly coarser grain size. The above results are mainly due to the formation of SrB6 through the reaction between Al–10wt.%Sr and Al–3wt.%Ti–4wt.%B. It was found that satisfactory grain refinement and modification could be attained by suitable addition of both Al–3wt.%Ti–4wt.%B and Al–10wt.%Sr in spite of the formation of SrB6.

Flexible, All-Inorganic Actuators Based on Vanadium Dioxide and Carbon Nanotube Bimorphs

Flexible actuators responsive to multiple stimuli are much desired in wearable electronics. However, general designs containing organic materials are usually subject to slow response and limited lifetime, or high triggering threshold. In this study, we develop flexible, all-inorganic actuators based on bimorph structures composed of vanadium dioxide (VO2) and carbon nanotube (CNT) thin films. The drastic, reversible phase transition of VO2 drives the actuators to deliver giant amplitude, fast response up to ∼100 Hz, and long lifetime more than 1 000 000 actuation cycles. The excellent electrical conductivity and light absorption of CNT thin films enable the actuators to be highly responsive to multiple stimuli including light, electric, and heat. The power consumption of the actuators can be much reduced by doping VO2 to lower its phase transition temperature. These flexible bimorph actuators find applications in biomimetic inspect wings, millimeter-scale fingers, and physiological-temperature driven switches.

SWCNT‐MoS2‐SWCNT Vertical Point Heterostructures

A vertical point heterostructure (VPH) is constructed by sandwiching a two-dimensional (2D) MoS2 flake with two cross-stacked metallic single-walled carbon nanotubes. It can be used as a field-effect transistor with high on/off ratio and a light detector with high spatial resolution. Moreover, the hybrid 1D-2D-1D VPHs open up new possibilities for nanoelectronics and nano-optoelectronics.

A Lithography‐Free and Field‐Programmable Photonic Metacanvas

The unique correspondence between mathematical operators and photonic elements in wave optics enables quantitative analysis of light manipulation with individual optical devices. Phase-transition materials are able to provide real-time reconfigurability of these devices, which would create new optical functionalities via (re)compilation of photonic operators, as those achieved in other fields such as field-programmable gate arrays (FPGA). Here, by exploiting the hysteretic phase transition of vanadium dioxide, an all-solid, rewritable metacanvas on which nearly arbitrary photonic devices can be rapidly and repeatedly written and erased is presented. The writing is performed with a low-power laser and the entire process stays below 90 °C. Using the metacanvas, dynamic manipulation of optical waves is demonstrated for light propagation, polarization, and reconstruction. The metacanvas supports physical (re)compilation of photonic operators akin to that of FPGA, opening up possibilities where photonic elements can be field programmed to deliver complex, system-level functionalities.

Freestanding macroscopic metal-oxide nanotube films derived from carbon nanotube film templates

Aligned carbon nanotube films coated with amorphous carbon were developed into novel templates by atomic layer deposition. Freestanding macroscopic metal-oxide nanotube films were then successfully synthesized by using these templates. The reactive amorphous carbon layer greatly improved the nuclei density, which ensured the high quality of the films and allowed for precise control of the wall thickness of the nanotubes. Using template-synthesized alumina nanotube films, we demonstrate a humidity sensor with a high response speed, a transmission electron microscopy (TEM) grid, and a catalyst support. The cross-stacked assembly, ultrathin thickness, chemical inertness, and high thermal stability of the alumina nanotube films contributed to the excellent performance of these devices. In addition, it is expected that the metal-oxide nanotube films would have significant potential owing to their material richness, macroscopic appearance, flexibility, compatibility with the semiconducting technologies, and the feasibility of mass production.