Periodic fracture behaviour of nanomembranes.

Fracture control in membranes is highly desirable in nano-technology, but is a great challenge because of the 'multi-scale' complexity of fracture initiation and propagation. Here, we devise a method that can controllably direct fractures in stiff nanomembranes, realized by 90° peeling of the nanomembrane overlaid on a soft film, i.e., a stiff/soft bilayer, from a substrate underneath. The peeling allows the stiff membrane to be creased into a soft film periodically in the bending region and fractured along the unique bottom line of the crease, i.e, the fracture route is strictly straight and periodic. The facture period is tunable, because the surface perimeter of the creases is determined by the thickness and modulus of the stiff membranes. This is a new kind of fracture behavior of stiff membranes, which is unique to stiff/soft bilayers but universally exists in such systems, promising a new generation of technology for cutting nanomembranes.

Effectively modulating thermal activated charge transport in organic semiconductors by precise potential barrier engineering.

The temperature dependence of charge transport dramatically affects and even determines the properties and applications of organic semiconductors, but is challenging to effectively modulate. Here, we develop a strategy to circumvent this challenge through precisely tuning the effective height of the potential barrier of the grain boundary (i.e., potential barrier engineering). This strategy shows that the charge transport exhibits strong temperature dependence when effective potential barrier height reaches maximum at a grain size near to twice the Debye length, and that larger or smaller grain sizes both reduce effective potential barrier height, rendering devices relatively thermostable. Significantly, through this strategy a traditional thermo-stable organic semiconductor (dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene, DNTT) achieves a high thermo-sensitivity (relative current change) of 155, which is far larger than what is expected from a standard thermally-activated carrier transport. As demonstrations, we show that thermo-sensitive OFETs perform as highly sensitive temperature sensors.

Ultrahigh-Sensitivity Piezoresistive Pressure Sensors for Detection of Tiny Pressure.

High-sensitivity pressure sensors are crucial for the ultrasensitive touch technology and E-skin, especially at the tiny-pressure range below 100 Pa. However, it is highly challenging to substantially promote sensitivity beyond the current level at several to 200 kPa-1 and to improve the detection limit lower than 0.1 Pa, which is significant for the development of pressure sensors toward ultrasensitive and highly precise detection. Here, we develop an efficient strategy to greatly improve the sensitivity near to 2000 kPa-1 using short-channel coplanar device structure and sharp microstructure, which is systematically proposed for the first time and rationalized by the mathematic calculation and analysis. Significantly, benefiting from the ultrahigh sensitivity, the detection limit is improved to be as small as 0.075 Pa. The sensitivity and detection limit are both superior to the current levels and far surpass the function of human skin. Furthermore, the sensor shows fast response time (50 µs), excellent reproducibility and stability, and low power consumption. Remarkably, the sensor shows excellent detection capacity in the tiny-pressure range, including light-emitting diode switching with a pressure of 7 Pa, ringtone (2-20 Pa) recognition, and ultrasensitive (0.1 Pa) electronic glove. This work represents a performance and strategic progress in the field of pressure sensing.

High-Performance Pressure Sensor for Monitoring Mechanical Vibration and Air Pressure.

To realize the practical applications of flexible pressure sensors, the high performance (sensitivity and response time) as well as more functionalities are highly desired. In this work, we fabricated a piezoresistive pressure sensor based on the micro-structured composites films of multi-walled carbon nanotubes (MWCNTs) and poly (dimethylsiloxane) (PDMS). In addition, we establish efficient strategies to improve key performance of our pressure sensor. Its sensitivity is improved up to 474.13 kPa-1 by minimizing pressure independent resistance of sensor, and response time is shorten as small as 2 µs by enhancing the elastic modulus of polymer elastomer. Benefiting from the high performance, the functionalities of sensors are successfully extended to the accurate detection of high frequency mechanical vibration (~300 Hz) and large range of air pressure (6⁻101 kPa), both of which are not achieved before.

Low Hysteresis Carbon Nanotube Transistors Constructed via a General Dry-Laminating Encapsulation Method on Diverse Surfaces.

Electrical hysteresis in carbon nanotube thin-film transistor (CNTTFT) due to surface adsorption of H2O/O2 is a severe obstacle for practical applications. The conventional encapsulation methods based on vacuum-deposited inorganic materials or wet-coated organic materials have some limitations. In this work, we develop a general and highly efficient dry-laminating encapsulation method to reduce the hysteresis of CNTTFTs, which may simultaneously realize the construction and encapsulation of CNTTFT. Furthermore, by virtue of dry procedure and wide compatibility of PMMA, this method is suitable for the construction of CNTTFT on diverse surface including both inorganic and organic dielectric materials. Significantly, the dry-encapsulated CNTTFT exhibits very low or even negligible hysteresis with good repeatability and air stability, which is greatly superior to the nonencapsulated and wet-encapsulated CNTTFT with spin-coated PMMA. The dry-laminating encapsulation strategy, a kind of technological innovation, resolves a significant problem of CNTTFT and therefore will be promising in facile transferring and packaging the CNT films for high-performance optoelectronic devices.

Facile Peeling Method as a Post-Remedy Strategy for Producing an Ultrasmooth Self-Assembled Monolayer for High-Performance Organic Transistors.

The modification of dielectric surface with a self-assembled monolayer (SAM) such as octadecyltrichlorosilane (OTS) is a widely used method to tune the electrical property of diverse electronic devices based on organic semiconductors, graphene, transition metal dichalcogenides (TMDs), and so forth. The surface roughness of self-assembled OTS monolayer is a key factor in determining its effect on device performance, but the preparation of an ultrasmooth OTS monolayer is a technologically challenging task. In this work, an ultrasmooth OTS monolayer is prepared via a facile peeling method, which may serve as a postremedy strategy to remove the protuberant aggregates. Such a method has not been reported before. With organic semiconductors as a testing model, ultrasmooth OTS may significantly improve the charge mobility of organic field-effect transistors (OFETs). P-type dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) OFET with an ultrasmooth OTS monolayer yields good reproducibility and unprecendented maximum mobility of 8.16 cm(2) V(-1) s(-1), which is remarkably superior to that of the OFET with a pristine OTS monolayer. This work develops a simple method to resolve the common and significant problem of the quality of OTS modification, which would be highly promising for electronic applications as well as other fields such as surface and interface engineering.

Controlled Growth of Ultrathin Film of Organic Semiconductors by Balancing the Competitive Processes in Dip-Coating for Organic Transistors.

Ultrathin film with thickness below 15 nm of organic semiconductors provides excellent platform for some fundamental research and practical applications in the field of organic electronics. However, it is quite challenging to develop a general principle for the growth of uniform and continuous ultrathin film over large area. Dip-coating is a useful technique to prepare diverse structures of organic semiconductors, but the assembly of organic semiconductors in dip-coating is quite complicated, and there are no reports about the core rules for the growth of ultrathin film via dip-coating until now. In this work, we develop a general strategy for the growth of ultrathin film of organic semiconductor via dip-coating, which provides a relatively facile model to analyze the growth behavior. The balance between the three direct factors (nucleation rate, assembly rate, and recession rate) is the key to determine the growth of ultrathin film. Under the direction of this rule, ultrathin films of four organic semiconductors are obtained. The field-effect transistors constructed on the ultrathin film show good field-effect property. This work provides a general principle and systematic guideline to prepare ultrathin film of organic semiconductors via dip-coating, which would be highly meaningful for organic electronics as well as for the assembly of other materials via solution processes.

Minimizing electrode edge in organic transistors with ultrathin reduced graphene oxide for improving charge injection efficiency.

Electrode materials and geometry play a crucial role in the charge injection efficiency in organic transistors. Reduced graphene oxide (RGO) electrodes show good compatibility with an organic semiconductor from the standpoint of energy levels and ordered growth of the organic semiconductor, both of which are favourable for charge injection. However, the wide electrode edge (>10 nm) in commonly-used RGO electrodes is generally detrimental to charge injection. In this study, ultrathin (about 3 nm) RGO electrodes are fabricated via a covalency-based assembly strategy, which has advantages such as robustness against solvents, high conductivity, transparency, and easy scaling-up. More remarkably, the ultrathin electrode fabricated in this study has a narrow edge, which may facilitate the diffusion and assembly of organic semiconductors and thus form a uniform semiconductor film across the electrode/channel junction area. As a result, the minimized electrode edge may significantly improve the charge injection in organic transistors compared with thick electrodes.