We report a low-temperature colloidal synthesis of single-layer, five-atom-thick, β-In2Se3 nanosheets with lateral sizes tunable from ∼300 to ∼900 nm, using short aminonitriles (dicyandiamide or cyanamide) as shape controlling agents. The phase and the monolayer nature of the nanosheets were ascertained by analyzing the intensity ratio between two diffraction peaks from two-dimensional slabs of the various phases, determined by diffraction simulations. These findings were further backed-up by comparing and fitting the experimental X-ray diffraction pattern with Debye formula simulated patterns and with side-view high-resolution transmission electron microscopy imaging and simulation. The β-In2Se3 nanosheets were found to be indirect band gap semiconductors (Eg = 1.55 eV), and single nanosheet photodetectors demonstrated high photoresponsivity and fast response times.

CsPbBr3 nanocrystals passivated with short molecular ligands and deposited on a substrate were annealed from room temperature to 400 °C in inert atmosphere. Chemical, structural, and morphological transformations were monitored in situ and ex situ by different techniques, while optoelectronic properties of the film were also assessed. Annealing at 100 °C resulted in a 1 order of magnitude increase in photocurrent and photoresponse as a result of partial sintering of the NCs and residual solvent evaporation. Beyond 150 °C the original orthorhombic NCs were partially transformed into tetragonal CsPb2Br5 crystals, due to the desorption of weakly bound propionic acid ligands. The photocurrent increased moderately until 300 °C although the photoresponse became slower as a result of the formation of surface trap states. Eventually, annealing beyond 350 °C removed the strongly bound butylamine ligands and reversed the transition to the original orthorhombic phase, with a loss of photocurrent due to the numerous defects induced by the stripping of the passivating butylamine.

Two-dimensional, solution-processable semiconductor materials are anticipated to be used in low-cost electronic applications, such as transistors and solar cells. Here, lead sulfide nanosheets with a lateral size of several micrometers are synthesized and it is shown how their height can be tuned by the variation of the ligand concentrations. As a consequence of the adjustability of the nanosheets' height between 4 to more than 20 nm charge carriers are in confinement, which has a decisive impact on their electronic properties. This is demonstrated by their use as conduction channel in a field-effect transistor. The experiments show that the performance in terms of current, On/Off ratio, and sub-threshold swing is tunable over a large range.

Two-dimensional materials are considered for future quantum devices and are usually produced by extensive methods like molecular beam epitaxy. We report on the fabrication of field-effect transistors using individual ultra-thin lead sulfide nanostructures with lateral dimensions in the micrometer range and a height of a few nanometers as conductive channel produced by a comparatively fast, inexpensive, and scalable colloidal chemistry approach. Contacted with gold electrodes, such devices exhibit p-type behavior and temperature-dependent photoconductivity. Trap states play a crucial role in the conduction mechanism. The performance of the transistors is among the ones of the best devices based on colloidal nanostructures.Inexpensive electronic applications require semiconductor materials which can be easily processed, e.g. by spin-coating or dip-coating [1]. Thus, researchers are looking for materials that are solution processable while exhibiting reasonable electronic properties. Colloidal semiconductor nanoparticles are among the candidates to be integrated into low-cost electronic devices [2]. They are suspended in liquid media, mass-producible, and tunable in their optical and electrical properties due to quantum confinement effects [3]. Colloidal nanomaterials are promising due to the simplicity and thus the inexpensiveness of their production and subsequent processing. One hurtle which needs to be overcome is the presence of tunnel barriers in the nanoparticle films which lead to high resistances. This effect is the consequence of long isolating organic ligands capping the nanoparticles surface. These ligands can be either replaced by shorter ones including halides [4], or removed by physicochemical processes [5]. These post-treatments deteriorate the nanoparticle surface but reduce the resistive power losses. A different approach to reduce the tunnel barriers consists in the use of inorganic capping "ligands" such as In 2 Se 2− on CdSe nanoparticles [6]. Such films find applications e.g. as field-effect transistors [7], thermoelectrics [8], and photoconductors [9].Yet another approach is to avoid tunnel barrier from the beginning on and to synthesize continuous twodimensional materials in solution. Indeed, some progress has been made in controlling the lateral dimensions [10] and thickness [11] of nanostructures through varying parameters like the nature of the ligands which are used to bind to specific facets of the nanocrystals and inhibit an isotropic growth [12]. Recently, we demonstrated that two-dimensional PbS nanosheets can be produced in solution by colloidal chemistry [13]. We showed that lead sulfide nanosheets form due to two-dimensional oriented attachment of small zero-dimensional colloidal nanocrystals. The nanosheets have a height of a few nanometers and exhibit lateral dimensions in the order of a micron. Nevertheless, the control of anisotropic growth in nanocrystal syntheses is still a great challenge. The PbS nanosheets used in the here presented study were synthesized based on the rec...

Laser-Induced Localized Growth of Methylammonium Lead Halide Perovskite Nano-and Microcrystals on SubstratesStable MAPbBr 3 crystals with different sizes are successfully localized on a flat substrate via laser-induced heating of the liquid precursors. By adjusting the infrared laser parameters, luminescent arrays and photoconductive wires are grown on-site. This technique can be used to guide the writing of other patterns for specific functionalities.