When particles become smaller than 100 nm, they exhibit properties that are not observed for molecules or their bulk counterparts.[1] Such particles are building blocks for nanotechnology-derived applications such as single-electron devices, ultradense recording media, bioelectronic devices and sensors, bioimaging, optoelectronic devices, catalysis, and chemical sensors, as well as energy conversion and storage. [1,2] The obvious approach to prepare small particles is a top-down approach, in which bulk solid is reduced to small particles by mechanical forces. However, this approach only gives particles on the order of micrometers in size, and nanoparticles are not obtained unless very high energy is applied by a special device such as a high-energy ball mill. [3,4] Thus, nanoparticles are generally produced by bottom-up approaches, in which molecules are allowed to assemble into nanoparticles in solution or the gas phase through chemical reactions. [1,2] We have found that in the case of fullerene C 60 , nanoparticles including those as small as 20 nm are readily produced by hand-grinding the bulk solid in an agate mortar. In this communication, top-down preparation of C 60 nanoparticles and their structure and properties are reported. Figure 1 shows scanning electron microscopy (SEM) images of C 60 before and after hand-grinding. As-received C 60 particles have a faceted morphology and are approximately 100 lm in size (Fig. 1a). Hand-grinding reduced the particle size, as expected (Fig. 1c). Surprisingly, close examination revealed the presence of a significant amount of particles smaller than 100 nm in an agglomerated form (Fig. 1d). Examination by high-resolution transmission electron microscopy (HRTEM) (Figs. 1e,f) revealed nanoparticles, including ones as small as 20 nm (Fig. 1f) with distinct fringes. Lattice spacings calculated from Fourier-transform images agree with those of bulk crystals of C 60 , [5] indicating that these particles are pristine crystals of C 60 . Powder X-ray diffractograms of as-received and hand-ground C 60 also indicate that the crystalline structure remains unchanged after hand-grinding (Fig. 2). The results demonstrate the unusual property of solid C 60 to readily form nanoparticles; top-down preparation of nanoparticles is usually associated with changes in the crystalline structure, including amorphization, because of the high energy applied to the sample. [3] The mechanism resulting in the generation of the C 60 nanoparticles is not clear at present, but the unique properties of the C 60 crystals, such as fast isotropic rotation of the molecule [6] and low cohesive energy (1.6 eV), [7] likely play an important role.A highly turbid dispersion was formed as soon as handground C 60 (7 mg) was mixed with 5 mL of water containing COMMUNICATIONS

Nanoparticles of fullerene C 60 , including those as small as 20 nm, were obtained by simple hand-grinding of bulk solids with an agate mortar and pestle. Crystalline structure, size distribution, and surface characteristics of the hand-ground C 60 nanoparticles were studied. In addition, the C 60 nanoparticles having different sizes were prepared successfully by fractionating the as-prepared nanoparticles by filtration or centrifugation, and size-dependent optical properties were determined for the C 60 nanoparticle. A linear relationship was found between the position of the peak at around 350 nm and the diameter of the C 60 nanoparticles.

No abstract

Inkjet printing is of growing interest due to the attractive technologies for surface patterning. During the printing process, the solutes are transported to the droplet periphery and form a ring-like deposit, which disturbs the fabrication of high-resolution patterns. Thus, controlling the uniformity of particle coating is crucial in the advanced and extensive applications. Here, we find that sweet coffee drops above a threshold sugar concentration leave uniform rather than the ring-like pattern. The evaporative deposit changes from a ring-like pattern to a uniform pattern with an increase in sugar concentration. We moreover observe the particle movements near the contact line during the evaporation, suggesting that the sugar is precipitated from the droplet edge because of the highest evaporation and it causes the depinning of the contact line. By analyzing the following dynamics of the depinning contact line and flow fields and observing the internal structure of the deposit with a FIB-SEM system, we conclude that the depinned contact line recedes due to the solidification of sugar solution without any slip motion while suppressing the capillary flow and homogeneously fixing suspended particles, leading to the uniform coating. Our findings show that suppressing the coffee-ring effect by adding sugar is a cost-effective, easy and nontoxic strategy for improving the pattern resolution.