Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.R ecent developments in flexible and stretchable electronics, either through structural consideration or by exploring novel materials 1,2 , have imparted otherwise rigid and brittle electronic devices mechanical compliance and bio-compatibility, paving the way for energy-efficient, lightweight, portable, wearable and even implantable electronics 3 . Examples include stretchable and large area display that can undergo complex deformations 4 , bio-inspired material and structural designs that enable bionic functions 5 , and printable sensory system capable of detecting planar strains, normal pressure, temperature, light, moisture and chemical/biological species 6 . Multifunctional sensors, in particular, with sensing abilities akin to or beyond those of human skin 6-12 , are essential for applications such as interactive electronics 13 , structural health monitoring 14 , smart clothing 15 , robotic systems with advanced sensing capabilities 16 , human motion detection 8 and so on. Among the various types of sensors, strain gauge is one of the most important smart sensors, which have been widely used in the measurements of strain, acceleration and tension, as well as structural health monitoring. Conventional strain gauges, made of metal foils, register resistance changes under tensile strains. Actually, mechanical compliance and large strain range (?5%), obviously not the case of metal foils, are required to meet the demands of wearable electronics 15 , human motion detection 8 and interactive robots 17 . Although mercury-in-rubber strain gauge has been used in the biological measurements for decades 18 , the maximum strain limit and toxicity of mercury still block their practically wide applications. In addition, the combination of conformability and optical transparency will facilitate intelligent electronics and self-powered robot where strain sensors are integrated with optoelectronic devices and direct observation through the devices is ne...

Metal-organic frameworks (MOFs) hold tremendous promise for various academic and industrial applications because of their structural merits (e.g., high surface areas, enormous porosity, and regular order). Recently, processable MOF films have been sought for application in various technologies, from separation to sensor devices. Essentially, MOFs deposited as thin films, with thicknesses ranging from nanometres to micrometres, low roughness and high homogeneity, are important for practical use and application-specific configurations, particularly in sensors and electric devices. Several innovative scientific methods have been developed for preparing MOF thin films. Among these methods, the electrochemical method is advantageous because it requires mild preparation, uses a short growth time, is easy to scale up and allows for controlling the phase/morphology and thickness by altering voltages in of the process of fabricating uniform and dense MOF thin films. This review focuses on recent developments of electrochemical methods for forming metal-organic framework thin films (e.g., preparation, growth mechanisms and characterization techniques) and their corresponding applications in sensing and micro-pattern devices and identifies the challenges that must be overcome.

Integrating metal-organic frameworks (MOFs) in microelectronics has disruptive potential because of the unique properties of these microporous crystalline materials. Nanoscale patterning is a fundamental step in the implementation of MOFs in miniaturised solid-state devices. Conventional MOF patterning methods suffer from a low resolution and poorly defined pattern edges. Here, we demonstrate for the first time resist-free, direct X-ray and e-beam lithography of MOFs. This process avoids etching damage and contamination, and leaves the porosity and crystallinity of the patterned MOFs intact. The resulting highquality patterns have a record sub-50 nm resolution, far beyond the state of the art in MOF patterning and approaching the mesopore regime. The excellent compatibility of X-ray and e-beam lithography with existing microfabrication processes, both in research and production facilities, provides an avenue to explore the integration of MOFs in microelectronics further. This approach is the first example of direct lithography of any type of microporous crystalline network solid, and marks an important milestone in the processing of such materials.

Free-standing, hierarchical reticulate single-walled carbon nanotube (SWCNT) fi lms are embedded in poly(dimethylsiloxane) (PDMS) to fabricate stretchable conductors (SWCNT/PDMS stretchable conductors). The stretchable conductors are highly transparent in visible light region and retain excellent conductance under large tensile strains. Strain tests reveal a unique strainhistory dependence behavior of the resistance, and resistance stabilization is achieved upon repetitive stretching and releasing, implying that the SWCNT/ PDMS stretchable conductors can be programmed to be reversibly stretched to a defi ned strain without resistance changes. A quantitative description of the increase in resistance is determined by adopting the Weibull distribution. Moreover, a light-emitting diode is illuminated using a repetitively stretched SWCNT/PDMS strip as the connecting wire, demonstrating the utility of the stretchable conductors as interconnects for stretchable electronics. Because of the high transparency, high conductivity, and excellent stretchability, in addition to the facile fabrication, the SWCNT/PDMS stretchable conductors might be widely used as interconnects and electrodes for stretchable intelligent and functional devices.

wileyonlinelibrary.comfunctionality. Some optimized structures could provide tunable responsiveness and switching properties in response to external stimuli (such as temperature, pressure, electric potential, acoustic waves, and chemical environment), leading to the selectivity and sensitivity to detect such particular analytes. [5][6][7] Generally, in order to employ MOFs for chemical detection (except those based on luminescence quenching), [ 3 ] some external means of signal transduction such as optical, electrical, and mechanical schemes have to be applied. [6][7][8][9][10][11][12] Thus, integrating MOFs as thin fi lms on device surfaces is able to form a physical interface for signal transduction. As the change in oscillating frequency of quartz crystal microbalance (QCM) is directly related to the mass change on the surface, [ 13 ] it has shown its applicability in chemical detection coupling with MOF thin fi lms. [14][15][16][17][18] As a sub-class of MOFs, zeolitic-imidazolate frameworks (ZIFs) constructed by linking metal centers (e.g., Zn, Co, and Cd) with imidazolate ligands show high porosity, structure diversity, tunable surface functionality, structure fl exibility, and especially, good chemical and thermal stability which are essential for realistic applications. [19][20][21][22] These interesting properties make them good candidates as host sensing materials. [23][24][25][26] For example, Lu and Hupp [ 25 ] fabricated ZIF-8 fi lm on Fabry-Pérot device for gases and chemical vapors detection by monitoring the changes of refractive index upon adsorption of guest molecules. The repeated direct growth method they used for ZIF-8 fi lm growth offers several advantages including mild growth condition, rapid growth rate, and good control of thickness. However, the method has not been extended to fabricate other functional ZIF thin fi lms up to date. Integrating a range of different ZIFs into thin fi lm devices on various surfaces remains a challenge with respect to various applications such as membrane based gas/ liquid separation, electronic and opto-electronic devices. [8][9][10][11][12] Furthermore, the sensing performances not only depend on the quality of ZIF thin fi lms but also strongly rely on the properties of host ZIF materials such as limited pore diameter (LPD), surface functionality, and structure fl exibility. Thus, the systematic investigation of the effects of these properties on the performance of ZIF based sensors would promote the further development in sensing applications such as array-based sensing Thin fi lms of sodalite-type zeolitic-imidazolate frameworks (ZIFs, ZIF-7, 8, 9, 67, 90, and ZIF-65-Zn) with different metal centers and functional moieties are fabricated on SiO 2 coated quartz crystal microbalance (QCM) substrates using automatic program controlled repeated direct growth method. The repeated direct growth procedure manipulated here shows great applicability for rapid growth of uniform ZIF thin fi lms with controllable thickness. The fabricated ZIF/QCM devices are used to...

Metal-organic frameworks (MOFs) enable the design of host-guest systems with specific properties.I nt his work, we showh ow the confinement of anthracene in aw ellchosen MOF host leads to reversible yellow-to-purple photoswitching of the fluorescence emission. This behavior has not been observed before for anthracene,e ither in pure form or adsorbed in other porous hosts.The photoresponse of the hostguest system is caused by the photodimerization of anthracene, which is greatly facilitated by the pore geometry,c onnectivity, and volume as well as the structural flexibility of the MOF host. The photoswitching behavior was used to fabricate photopatternable and erasable surfaces that, in combination with data encryption and decryption, hold promise in product authentication and secure communication applications.

Control of localized metal-organic framework (MOF) thin fi lm formation is a challenge. Zeolitic imidazolate frameworks (ZIFs) are an important sub-class of MOFs based on transition metals and imidazolate linkers. Continuous coatings of intergrown ZIF crystals require high rates of heterogeneous nucleation. In this work, substrates coated with zinc oxide layers are used, obtained by atomic layer deposition (ALD) or by magnetron sputtering, to provide the Zn 2+ ions required for nucleation and localized growth of ZIF-8 fi lms ([Zn(mim) 2 ]; Hmim = 2-methylimidazolate). The obtained ZIF-8 fi lms reveal the expected microporosity, as deduced from methanol adsorption studies using an environmentally controlled quartz crystal microbalance (QCM) and comparison with bulk ZIF-8 reference data. The concept is transferable to other MOFs, and is applied to the formation of [Al(OH)(1,4-ndc)] n (ndc = naphtalenedicarboxylate) thin fi lms derived from Al 2 O 3 nanolayers.

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