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...

Insights to the mechanism of CdSe nanoparticle attachment to carbon nanotubes following the hot injection method are discussed. It was observed that the presence of water improves the nanotube coverage while Cl containing media are responsible for the shape transformation of the nanoparticles and further attachment to the carbon lattice. The experiments also show that the mechanism taking place involves the right balance of several factors, namely, low passivated nanoparticle surface, particles with well-defined crystallographic facets, and interaction with an organics-free sp 2 carbon lattice. Furthermore, this procedure can be extended to cover graphene by quantum dots.The extraordinary properties of nanosized materials have boosted intensive work in the development of several synthetic methodologies in the last decades. The so called hot injection method [1] is, among them, a versatile and relatively cheap means that nowadays provides a high degree of perfection, reproducibility and control of semiconductor [2,3], and magnetic [1, 4] nanocrystals. This colloidal synthetic route is based on the reaction of highly reactive species in media where surfactants play an essential role in the final shape, size, and stability of the desired nanomaterial. However, small variations in monomer concentrations, temperatures, time, or presence of impurities may drive the reaction into different regimes. As a consequence, diverse sizes, shapes, and compositions of nanoparticles can be obtained. A. J. Houtepen et al. [5] describes the role of acetate in the synthesis of PbSe nanoparticles. Traces of acetate can be responsible for a great variety of nanoparticles shapes. It is also known that small traces of phosphonic acids can influence decisively the mechanism, the yield, and the shape of the nanoparticles [6,7,8]. Recently, the hot injection method was also followed to produce composites of CdSe semiconductor nanoparticles and carbon nanotubes (CdSe-CNTs) [9,10,11]. It was observed that in the presence of CNTs, CdSe nanorods evolved into pyramidal-like nanoparticles that connected to CNTs by the wurtzite (001) facets [9,10,11,12]. Furthermore, rods and pyramidal-like nanoparticles showed different interaction with CNTs, the latter showing a clear tendency to attach to the carbon lattice. Unlike heterogeneous growth on a seed surface, the reaction of CdSe nanorods in the presence of carbon nanotubes proceeds independently of the carbon lattice during their nucleation and growth. The proposed mechanism so far [9] suggested that the shape transformation of the nanoparticles as a result of nanotube-nanoparticle interaction and a decisive role of octadecylphosphonic acid (ODPA). ODPA is used as complexing agent of the cadmium source and acts as capping ligand of the nanoparticles at Cd sites [13].In this letter, we address the influence of the CNTs dis- * Electronic address: hernande@chemie.uni-hamburg.de persant (solvent) and water on the shape of the nanoparticles and the requirements for further attachment to the carbon latt...

We report the growth of an unstable shell-like gold structure around dihexagonal pyramidal CdSe nanocrystals in organic solution and the structural transformation to spherical domains by two means: i) electron beam irradiation (in situ) and (ii) addition of a strong reducing agent during synthesis. By varying the conditions of gold deposition, such as ligands present or the geometry of the CdSe nanocrystals, we were able to tune the gold domain size between 1.4 nm to 3.9 nm and gain important information on the role of surface chemistry in hetero nanoparticle synthesis and seed reactivity, both of which are crucial points regarding the chemical design of new materials for photocatalysis and optoelectronic applications.Recent developments in materials physics and chemistry allow the synthesis of colloidal nanocrystals (NCs) with unique optical and electrical properties [1,2]. However, it remains a grand challenge to prepare multicomponent or hybrid structures in which two or more NC domains of different materials with individually tailored properties and controlled composition are integrated into one nanostructure in core-shell or oligomertype configurations. These new hybrid NCs (HNCs) with a higher level of structural complexity are expected to exhibit modified physicochemical properties [3, 4] and provide systems which allow site-specific functionalization with biomolecules [5,6] and their use in photocatalysis and optoelectronic applications. The most common strategy for the synthesis of these HNCs is the seedmediated method in which one material is used as seed particle and a different material is grown around (coreshell HNCs [7,8]) or forming domains on their surface (oligomer-like HNCs). Examples of the latter case are metal-semiconductor heterodimers made of spherical domains [9][10][11][12], dumbbell-like [13,14], peanut-like [15] and matchstick-shaped [13,16,17] structures. Several reviews on heterostructured nanocrystals summarize the progress and the perspectives on this emerging field [3,4]. Additionally, these systems are unique platforms to study nucleation, growth, dissolution and reshaping of HNCs. In this context, Banin's group reported how dumbbelllike structures, formed by preferential nucleation of gold on crystal facets with high reactivity, evolved into a hetero structure with only one end covered due to a ripening process [13,17] while a recent publication of Manna and coworkers investigated the structural and morphological evolution of as-synthesized CdSe-Au HNCs subjected to thermal annealing [18]. The reactivities of crystal facets are closely associated to particle geometry and the degree of surface passivation. Thus, the use of NCs with * Electronic address: klinke@chemie.uni-hamburg.de a different topology as substrates for the Au growth can provide new insights not only into the formation of hybrid structures but also to the role of the NCs ligand density on the final hybrid structure.

We synthesized monodisperse cobalt-platinum nanoparticles Co(0.14-0.22)Pt(0.86-0.78) of 9 nm in diameter by colloidal chemistry methods and deposited them by the Langmuir-Blodgett technique as highly ordered monolayers onto substrates with e-beam defined gold electrodes. Upon annealing we observe an increase of conductivity over more than 4 orders of magnitude. A first attempt of explanation of this unanticipated effect, a nanoparticle displacement, could not be confirmed for annealing temperatures below 400 °C. A second approach, a carbonization of the ligands, however, could be confirmed by Raman spectroscopy. The simple thermal treatment allows tuning essential properties of electronic devices based on nanoparticles by the manipulation of the interparticle coupling, namely the electrical conductivity, the Coulomb blockade characteristic, and the activation energy of the system.

We demonstrate that by means of a local top-gate current oscillations can be observed in extended, monolayered films assembled from monodisperse metal nanocrystals -realizing transistor function. The oscillations in this metal-based system are due to the occurrence of a Coulomb energy gap in the nanocrystals which is tunable via the nanocrystal size. The nanocrystal assembly by the Langmuir-Blodgett method yields homogeneous monolayered films over vast areas. The dielectric oxide layer protects the metal nanocrystal field-effect transistors from oxidation and leads to stable function for months. The transistor function can be reached due to the high monodispersity of the nanocrystals and the high super-crystallinity of the assembled films. Due to the fact that the film consists of only one monolayer of nanocrystals and all nanocrystals are simultaneously in the state of Coulomb blockade the energy levels can be influenced efficiently (limited screening).