High intensity ultrasound can be used for the production of novel materials and provides an unusual route to known materials without bulk high temperatures, high pressures, or long reaction times.Several phenomena are responsible for sonochemistry and specifically the production or modification of nanomaterials during ultrasonic irradiation. The most notable effects are consequences of acoustic cavitation (the formation, growth, and implosive collapse of bubbles), and can be categorized as primary sonochemistry (gas-phase chemistry occurring inside collapsing bubbles), secondary sonochemistry (solution-phase chemistry occurring outside the bubbles), and physical modifications (caused by high-speed jets or shock waves derived from bubble collapse). This tutorial review provides examples of how the chemical and physical effects of high intensity ultrasound can be exploited for the preparation or modification of a wide range of nanostructured materials.

Two-dimensional atomic crystals are extensively studied in recent years due to their exciting physics and device applications. However, a molecular counterpart, with scalable processability and competitive device performance, is still challenging. Here, we demonstrate that high-quality few-layer dioctylbenzothienobenzothiophene molecular crystals can be grown on graphene or boron nitride substrate via van der Waals epitaxy, with precisely controlled thickness down to monolayer, large-area single crystal, low process temperature and patterning capability. The crystalline layers are atomically smooth and effectively decoupled from the substrate due to weak van der Waals interactions, affording a pristine interface for high-performance organic transistors. As a result, monolayer dioctylbenzothienobenzothiophene molecular crystal field-effect transistors on boron nitride show record-high carrier mobility up to 10 cm 2 V À 1 s À 1 and aggressively scaled saturation voltage B1 V. Our work unveils an exciting new class of two-dimensional molecular materials for electronic and optoelectronic applications.

Ag nanoclusters consist of several to roughly a hundred atoms and possess sizes comparable to the Fermi wavelength of electrons; they exhibit molecule-like properties, including discrete electronic transitions and strong fluorescence. These nanoclusters are of significant interest because they provide the bridge between atomic and nanoparticle behavior in noble metals. Since the first observations of photoluminescence from Ag nanoclusters, substantial effort has been made to prepare Ag nanoclusters and explore their potential applications. The synthesis of well-defined Ag nanoclusters, however, is difficult due to aggregation of nanoclusters, especially in aqueous solutions. In this Research News article, we highlight some recent progress on solution-based synthesis of water-soluble Ag nanoclusters using radiolytic, chemical reduction and photochemical approaches to prepare fluorescent Ag nanoclusters.

Mimicking human skin's functions to develop electronic skins has inspired tremendous efforts in design and synthesis of novel soft materials with simplified fabrication methods. However, it still remains a great challenge to develop electronically conductive materials that are both stretchable and self‐healable. Here it is demonstrated that a ternary polymer composite comprised of polyaniline, polyacrylic acid, and phytic acid can exhibit high stretchability (≈500%) and excellent self‐healing properties. The polymer composite with optimized composition shows an electrical conductivity of 0.12 S cm−1. On rupture, both electrical and mechanical properties can be restored with ≈99% efficiency in a 24 h period, which is enabled by the dynamic hydrogen bonding and electrostatic interactions. It is further shown that this composite is both strain and pressure sensitive, and therefore can be used for fabricating strain and pressure sensors to detect a variety of mechanical deformations with ultrahigh sensitivity. The sensitivity and sensing range are the highest among all of the reported self‐healable piezoresistive pressure sensors and even surpass most flexible mechanical sensors. Notably, this composite is prepared via a solution casting process, which potentially allows for large‐area, low‐cost fabrication electronic skins.

One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two-dimensionally in the first few molecular layers near the dielectric interface.Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered mono-to tetra-layer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to band-like in subsequent layers.Such abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ~3nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals. 3Organic field-effect transistors (OFETs) offer unique advantages of low cost, lightweight and flexibility and are widely used in electronics and display industry.While the mobility of bulk organic semiconductors has increased dramatically [1][2][3], an outstanding issue is to directly examine the structure-property relationship at the semiconductor-dielectric interface [4], where charge transport actually occurs [5][6][7].Ultrathin organic semiconductors down to few-nanometre thickness are often dominated by traps and disorders and far away from intrinsic transport regime [8][9][10].Another challenge in organic electronics is the development of layer-by-layer epitaxy with the precision similar to molecular beam epitaxy in their inorganic counterparts [11]. These challenges may be alleviated if molecular crystals are processed into large-area, highly crystalline monolayers. Such 2D form factor will also bring about new applications such as nanoporous membranes and insulating dielectrics [12,13].Several recent breakthroughs in various types of 2D organic materials such as polymers [14,15], oligomers [16] and covalent organic frameworks [17] have already shown great promises along this direction. However, one of the most fundamental questions regarding the nature of charge transport at the 2D limit has not been addressed. In this work, we study the benchmark molecule pentacene epitaxially crystallized on BN substrate because of its high mobility and simple structure to model. The highly clean system allows us to provide the first definitive scenario of how molecular packing and charge transport are modulated near the interface, without being dominated by extrinsic factors. Our results suggest the possibility of band-like transport...