Large scale epitaxial growth and transfer of monolayer MoS has attracted great attention in recent years. Here, we report the wafer-scale epitaxial growth of highly oriented continuous and uniform monolayer MoS films on single-crystalline sapphire wafers by chemical vapor deposition (CVD) method. The epitaxial film is of high quality and stitched by many 0°, 60° domains and 60°-domain boundaries. Moreover, such wafer-scale monolayer MoS films can be transferred and stacked by a simple stamp-transfer process, and the substrate is reusable for subsequent growth. Our progress would facilitate the scalable fabrication of various electronic, valleytronic, and optoelectronic devices for practical applications.

Graphene has a range of unique physical properties and could be of use in the development of a variety of electronic, photonic and photovoltaic devices. For most applications, large-area high-quality graphene films are required and chemical vapour deposition (CVD) synthesis of graphene on copper surfaces has been of particular interest due to its simplicity and cost effectiveness. However, the rates of growth for graphene by CVD on copper are less than 0.4 μm s, and therefore the synthesis of large, single-crystal graphene domains takes at least a few hours. Here, we show that single-crystal graphene can be grown on copper foils with a growth rate of 60 μm s. Our high growth rate is achieved by placing the copper foil above an oxide substrate with a gap of ∼15 μm between them. The oxide substrate provides a continuous supply of oxygen to the surface of the copper catalyst during the CVD growth, which significantly lowers the energy barrier to the decomposition of the carbon feedstock and increases the growth rate. With this approach, we are able to grow single-crystal graphene domains with a lateral size of 0.3 mm in just 5 s.

Atomic polarization in ferroelectric compounds is manipulated to control local electronic structure and influence chemical reactivity. Ferroelectric domains are patterned with electron beams or with probe tips, and electron exchange reactions occur preferentially on positive or negative domains. Using photo reduction from aqueous solution, metal nanoparticles are produced in predefined locations on an oxide substrate. Subsequently, organic molecules are reacted selectively to the particles. The process can be repeated to develop complex structures consisting of nanosized elements of semiconductors, metals, or functional organic molecules.

of the device: the cell is assembled in a way that allows a gradient of the dopant concentration. Consequently, a smooth variation of the helical pitch was obtained inside the same cell. The main aspect of this second method is that a simple translation of the cell with respect to the exciting beam enables the fine-tuning of the laser wavelength. In both methods, a shift of the lasing wavelength by 30±40 nm was obtained. ExperimentalInvestigations on photoexcitation were performed using the third harmonic of a Q-switched Nd:YAG laser (Continuum, Surelite II) as the source. The pulse wavelength, width, and repetition rate were 355 nm, 6 ns, and 5±10 Hz, respectively. The excitation beam energy was strongly attenuated, combining a k/2 waveplate, a polarizer, and several neutral density filters. The laser beam was focused using a cylindrical lens (f = 150 mm) to reduce the spot size on the cell to a few hundred micrometers. The pump beam irradiated the sample at an angle of 45 with respect to the cell normal, the usual experimental geometry for this kind of experiment [8,13]. An optical fiber coupled to the spectrometer (an Avantes Fiberoptics mod. AVS-S2000, with a resolution of 1.5 nm) collected the light emitted from the sample.