Ribbon-shaped Crystals Research Articles

Using a Flexible Fountain Pen to Directly Write Organic Semiconductor Patterns with Crystallization Regulated by the Precursor Film.

Organic semiconductor (OSC) films fabricated by meniscus-guided coating (MGC) methods are suitable for cost-effective and flexible electronics. However, achieving crystalline thin films by MGC methods is still challenging because the nucleation and crystal growth processes are influenced by the intertwined interactions among solvent evaporation, stochastic nucleation, and the fluid flow instabilities. Herein, a novel flexible fountain pen with active ink supply is designed and used to print OSCs. This direct-write method allows the flexible pen tip to contact the substrate, maintaining a robust meniscus by eliminating the gap found in conventional MGCs. An in situ optical microscopy observation system shows that the precursor film plays a critical role on the crystallization and the formation of coffee rings and dendrites. The computational fluid dynamics simulations demonstrate that the microstructure of the pen promotes extensional flows, facilitating mass transport and crystal alignment. Highly-aligned ribbon-shaped crystals of a small organic molecule (TIPS-pentacene), as well as a semiconducting polymer (N2200) with highly-ordered orientations, have been successfully printed by the flexible fountain pen. Organic field-effect transistors based on the flexible pen printed OSCs exhibit high performances and strong anisotropic mobility. In addition, the flexible fountain pen is expandable for printing multiple lines or large-area films.

Robust self-replication of combinatorial information via crystal growth and scission

Understanding how a simple chemical system can accurately replicate combinatorial information, such as a sequence, is an important question for both the study of life in the universe and for the development of evolutionary molecular design techniques. During biological sequence replication, a nucleic acid polymer serves as a template for the enzyme-catalyzed assembly of a complementary sequence. Enzymes then separate the template and complement before the next round of replication. Attempts to understand how replication could occur more simply, such as without enzymes, have largely focused on developing minimal versions of this replication process. Here we describe how a different mechanism, crystal growth and scission, can accurately replicate chemical sequences without enzymes. Crystal growth propagates a sequence of bits while mechanically-induced scission creates new growth fronts. Together, these processes exponentially increase the number of crystal sequences. In the system we describe, sequences are arrangements of DNA tile monomers within ribbon-shaped crystals. 99.98% of bits are copied correctly and 78% of 4-bit sequences are correct after two generations; roughly 40 sequence copies are made per growth front per generation. In principle, this process is accurate enough for 1,000-fold replication of 4-bit sequences with 50% yield, replication of longer sequences, and darwinian evolution. We thus demonstrate that neither enzymes nor covalent bond formation are required for robust chemical sequence replication. The form of the replicated information is also compatible with the replication and evolution of a wide class of materials with precise nanoscale geometry such as plasmonic nanostructures or heterogeneous protein assemblies.

Solution-processable pentacene microcrystal arrays for high performance organic field-effect transistors

The authors report the fabrication of one-dimensional crystal arrays of triisopropylsilylethynyl pentacene (TIPS PEN) via simple drop casting on a tilted substrate. By pinning a solution droplet on the tilted substrate, an array of ribbon-shaped crystals aligned in the tilted direction was formed on the substrate. X-ray diffraction analysis revealed that these crystals were oriented in the crystal growth direction. A thin film transistor based on such an array of TIPS PEN crystals was found to have a high field-effect mobility of 0.3cm2∕Vs, which results from the directed organization of the π-conjugated molecules.

Bio-Mimetic Composites

ABSTRACTThe properties of bone, as a polymer reinforced with nanometer-sized ribbon-shaped crystals of mineral, are compared with the properties of synthetic polymer composites. Bone does show some superiority to existing composites. The improvements can be attributed to the microstructure. Methods for reproducing this structure in a synthetic material are discussed.

Crystallization of encapsulated very thin amorphous Ge layers

The crystallization processes and morphologies of a-Ge have been studied in the kinckness range 1–30 nm. The thin Ge layers were evaporated under ultrahigh vacuum (5 × 10 -9 Torr) onto SiO x substrates and were also covered by a thin SiO x layer. The samples were annealed in forming gas and examined by transmission electron microscopy. The morphological stability of the layers depends on the film thickness and surface and interface diffusion processes during crystal growth resulting in ribbon shaped crystals in the thinnest layers. The single crystalline, ribbon-shaped crystals are 100 nm wide and can grow to the length of several μm. The morphological instability of the very thin amorphous layer close to the crystalline phase is proved by the formation of empty regions along the ribbons and around crystalline nuclei. The temperature of crystallization increases with decreasing film thickness in the thickness range 1–5 nm.

Anisotropy of thermoelastic stresses in shaped sapphire single crystals

The present paper considers the influence of the anisotropy of thermal and elastic properties of crystals on thermoelastic stresses in shaped corundum single crystals grown by the Stepanov technique. On the basis of the general principle of symmetry the forms of stress tensors are determined depending on the orientation for single crystals of different shapes. The applicability of approximate formulae for calculating the thermoelastic stresses in transparent crystals is discussed and the results of the numerical calculations are given. Factors introducing anisotropy of thermoelastic properties for rod- and ribbon-shaped crystals are introduced to obtain the quantitative characteristics of the influence of anisotropy. The values of these factors are determined from the single crystal properties and depend only on its orientation. The orientations providing minimum stress values during crystal growth under temperature conditions realized in practice, are indicated for sapphire single crystals.

Growth of polysilicon sheets by the RAD process

The ribbon against drop (RAD) process designed for the deposition of thin silicon sheets on ribbon-like carbon substrates is described. Aspects relating to the growth of the layers and the equipment are presented. The crystallographic and electrical characteristics of the sheets are discussed and shown to be similar to those reported for unsupported ribbon-shaped crystals. The minimal silicon consumption and the promising performance of the solar cells fabricated from this material support the interest of the RAD process for producing low-cost solar cells.

The growth of EFG silicon ribbons

The technology associated with the Edge-Defined, Film-Fed Growth (EFG) process of producing ribbon-shaped crystals of silicon is discussed. Aspects relating to the growth of crystals, equipment and theoretical considerations are presented. The crystallographic and electrical characteristics of these crystal are discussed in terms of their impact on the performance characteristics of solar cells. Solar cell data are presented demonstrating the capability of these crystals of furnishing cells with conversion efficiencies in excess of 10%.

Maximum growth rates for melt-grown ribbon-shaped crystals

From heat-balance considerations at the growing interface and an assumption of predominantly radiative heat loss from the surface, an expression for the maximum growth rate of melt-grown ribbon-shaped crystals has been derived. For a given material and a large width-to-thickness ratio W/t, the maximum growth rate varies as t−1/2 and is independent of W. A comparison of the maximum cylindrical and ribbon growth rates is made for the silicon system. Some representative values at 7.5 cm diameter or width are 45 cm/h or 2000 cm3/h, for a cylindrical Czochralski-grown crystal and 625 cm/h or 95 cm3/h for a 0.02-cm-thick ribbon.

Growth of ribbon-shaped crystals of gadolinium gallium garnet for bubble memory substrates

In preliminary work to adapt the edge-defined, film-fed growth (EFG) process to GGG, a number of 1 cm wide × 0.5 mm thick ribbon crystals were obtained. Most of the crystals contained longitudinal thermal stress patterns and associated dislocation arrays. Also evident were occasional arrays of microvoids just under the external surface. In one case where the thermal stresses were avoided, the crystal quality appeared to be sufficient for use in magnetic bubble devices. Off-stoichiometric inclusions on the gallia-rich side were eutectic structures of gallia and garnet and on the gadolinia-rich side were an unidentified gadolinium-rich compound. Lattice parameter measurements of the EFG crystals show that the effective distribution coefficients are much higher than those for the Czochralski growth method.

The Growth of Copper Selenide Crystals Produced by Solid-State Reaction

Electron microscopic observation was carried out to investigate the growth of crystals produced by the reaction of vacuum-deposited selenium films with copper metal. Cuprous and cupric selenide crystals were found to grow in ribbon or fan shapes within the selenium films. The ribbon-shaped crystals were composed of many narrow crystals whose lattices were twisted with each other. The fan-shaped crystals grew radially from the tips of ribbon-shaped crystals. The growth of these crystals is explained by assuming that it is controlled by self-diffusion of copper atoms in the growing crystals.