Geometrical Lattice Match Research Articles

Preparation of theophylline inhalable microcomposite particles by wet milling and spray drying: The influence of mannitol as a co-milling agent

Inhalable theophylline particles with various amounts of mannitol were prepared by combining wet milling in isopropanol followed by spray drying. The effect of mannitol as a co-milling agent on the micromeritic properties, solid state and aerosol performance of the engineered particles was investigated. Crystal morphology modelling and geometric lattice matching calculations were employed to gain insight into the intermolecular interactions that may influence the mechanical properties of theophylline and mannitol. The addition of mannitol facilitated the size reduction of the needle-like crystals of theophylline and also their assembly in microcomposites by forming a porous structure of mannitol nanocrystals wherein theophylline particles are embedded. The microcomposites were found to be in the same crystalline state as the starting material(s) ensuring their long-term physical stability upon storage. Incorporation of mannitol resulted in microcomposite particles with smaller size, more spherical shape and increased porosity. The aerosol performance of the microcomposites was markedly enhanced compared to the spray-dried suspension of theophylline wet milled without mannitol. Overall, wet co-milling with mannitol in an organic solvent followed by spray drying may be used as a formulation approach for producing respirable particles of water-soluble drugs or drugs that are prone to crystal transformation in an aqueous environment (i.e. formation of hydrates).

Characterization and interpretation of twin related row-matching orientation relationships between Mg2Sn precipitates and the Mg matrix

Two irrational orientation relationships (ORs) are newly observed between β-Mg2Sn precipitates and the α-Mg matrix in an aged Mg–Sn-based alloy, namely OR9: [011]β-9//[0 1 {\bar 1} 0]α, (100)β-9about −15.6° from (0001)αand OR10: [0 {\bar 1} {\bar 1}]β-10//[0 1{\bar 1} 0]α, (100)β-10about 4.0° from ({\bar 2} 1 1 0)α. The ORs have a common reciprocal row-matching condition, which shows that rows of diffraction spots parallel tog(1 1{\bar 1})β-9[org({\bar 1} {\bar 1}1)β-10] from lattice β match those parallel tog(2 {\bar 1} {\bar 1} 4)αfrom lattice α. A twin relationship exists between OR9-type and OR10-type precipitates, of which the major side facets, parallel to the twinning plane, are invariably normal to the matching rows in reciprocal space. The reciprocal row matching of diffraction spots is proven to correspond to a real row matching of lattice sites in direct space. The real matching rows of lattice sites lie in the major side facets, resulting in periodically distributed good matching lattice bands in the facets,i.e.a singular interfacial structure. This explains why the irrational ORs are preferred. This study demonstrates an explicit association of geometric lattice matching with the ORs and the morphologies of precipitates developed during a phase transformation.

Templated Nucleation of Acetaminophen on Spherical Excipient Agglomerates

We investigated the effect of spherical agglomeration of heterogeneous crystalline substrates on the nucleation of acetaminophen (AAP). Optical and electron microscopy showed that the surface morphologies of single crystal triclinic lactose and D-mannitol differed significantly from their counterparts formed via spherical agglomeration. Spherical agglomerates of lactose were shown to enhance the nucleation rate of acetaminophen (AAP) by a factor of 11 compared to single crystal lactose; however, no such enhancement was observed for D-mannitol. X-ray powder diffraction identified the presence of new crystal faces of lactose present only in the spherical agglomerates However, D-mannitol did not show any significant change in crystal morphology. The new crystal faces of triclinic lactose were analyzed using geometric lattice matching software and molecular dynamics simulations to establish any new and significant epitaxial matches between lactose and AAP. A coincident lattice match and a large favorable energy interaction from hydrogen bonding were observed between the (141¯) and (001) crystal faces of lactose and AAP, respectively. The enhanced nucleation kinetics, X-ray data, and computational studies indicated that the spherical crystallization of lactose exposed the (141¯) face on the surface of the agglomerates, which subsequently enhanced the nucleation rate of AAP through geometric lattice matching and molecular functionality. This study highlights the importance of exploring different heterogeneous substrate morphologies for enhancing nucleation kinetics.

Growth and properties of Cu thin film deposited on Si(0 0 1) substrate: A molecular dynamics simulation study

Molecular dynamics simulations are used to study the growth and properties of Cu thin film deposited on Si(001) substrate. In particular, growth mode, crystalline structure and orientation, and surface morphology of Cu thin film are investigated in detail. Our simulation results predict that the growth of Cu thin film on Si substrate is three-dimensional island growth mode. In the growth process, interspecies mixing occurs at the interface between Cu film and Si substrate, and the mixing length increases as the increasing of substrate temperature. Based on the common neighbor analysis of atoms, three crystalline structures in the deposited Cu films are indentified. More important, the formed face-centered cubic (fcc) structure of Cu thin film is (001) oriented with a rotation by 45° along 〈001〉 axis when the substrate temperature is 300K, while the fcc structure of Cu thin film becomes to be (111) oriented when the substrate temperature is 900K. The crystalline orientation of deposited film could be explained based on the surface free energy of different crystalline planes as well as the geometrical lattice match rule. In addition, surface roughness of Cu thin film decreases as the increasing of substrate temperature due to the enhancement of surface diffusion.

Nucleation and Growth of Glycine Crystals with Controllable Sizes and Polymorphs on Langmuir–Blodgett Films

Control of crystal polymorph and size is very important in many application fields. Herein we demonstrate that Langmuir–Blodgett (LB) films of stearic acid (SA) and octadecylamine (ODA) can serve as templates and generate different polymorphs of glycine crystals. In the neutral aqueous solutions, γ-glycine crystallizes on LB films of ODA while the polymorphic outcome becomes the α-form on LB films of SA. These observed results could be explained by the electrostatic interactions and geometric lattice matching at the LB film/crystal interfaces, respectively. By keeping the appropriate supersaturation, we have successfully controlled the number of crystals grown on LB films; for example, in some certain cases, only one piece of crystal was grown on LB films in solution. Therefore, large crystals of centimeter size could be prepared. These experimental results suggest a new approach to produce an organic crystal with bulk scale.

Controlling Molecular Crystal Polymorphism with Self-Assembled Monolayer Templates

The control of crystal polymorphism is a long-standing issue in solid-state chemistry, which has many practical implications for a variety of commercial applications. At least four different crystalline forms of 1,3-bis(m-nitrophenyl) urea (MNPU), a classic molecular crystal system, are known to crystallize from solution in various concomitant combinations. Herein we demonstrate that the introduction of gold-thiol self-assembled monolayers (SAMs) of substituted 4'-X-mercaptobiphenyls (X = H, I, and Br) into the crystallization solution can serve as an effective means to selectively template the nucleation and growth of alpha-, beta-, and gamma-MNPU phases, respectively. Polymorph control in the presence of SAM surfaces persists under a variety of solution conditions and consistently results in crystalline materials with high phase purity. The observed selectivity is rationalized on the basis of long-range two-dimensional geometric lattice matching and local complementary chemical interactions at the SAM/crystal interfaces.

Epitaxial Relationships between Cholesterol Crystals and Mineral Phases: Implication for Human Disease

Human gallstones and atherosclerotic plaques are heterogeneous materials that consist of a variety of components, including crystalline cholesterol and assorted mineral phases. EpiCalc, a modeling algorithm that uses a simple geometric lattice matching protocol, was used as a screening tool to identify those surfaces of calcium carbonate and calcium phosphate that could potentially serve as epitaxial substrates for the nucleation and growth of anhydrous cholesterol (Ch) and cholesterol monohydrate (ChM) crystals. A surprisingly large number of coincident epitaxial relationships were identified, with the best match found between calcite (1014) and ChM (001).

The Physicochemical Origins of Coincident Epitaxy in Molecular Overlayers: Lattice Modeling vs Potential Energy Calculations

The physicochemical basis for epitaxial stabilization of coincident molecular overlayers is illustrated by comparison of optimum overlayer−substrate configurations calculated with potential energy (PE) methods and a simple geometric lattice misfit modeling algorithm (EpiCalc) that neglects molecular orientations and intermolecular potentials. Using β-bis(ethylenedithio)tetrathiafulvalene triiodide (β-ET2I3), perylenetetracarboxylic diimide (PTCDI), and perylenetetracarboxylic dianhydride (PTCDA) overlayers on a graphite substrate as examples, both methods predict identical optimum azimuthal overlayer orientations for each overlayer that also agree with experimental observations. PE calculations for three hypothetical PTCDA overlayers, with identical lattice parameters but different molecular orientations, predict coincidence at the same azimuthal orientation for all overlayers. Identical results are achieved for PE calculations performed with this lattice when it is occupied by naphthalenetetracarboxylic dianhydride (NTCDA) molecules or argon atoms. These results demonstrate that the epitaxial orientation of coincident overlayers is governed more by geometric lattice matching than specific molecule−substrate interactions and that unambiguous determination of the optimum azimuthal orientation relies on establishing the phase relationship between several overlayer supercells and the substrate. In the case of PE methods, calculations with large overlayer sizes are computationally prohibitive and the energy differences between alternative orientations typically are smaller than the confidence limits of the method. In contrast, the calculation time required by EpiCalc is independent of overlayer size, providing a significant advantage over PE methods with respect to computational speed while enabling unambiguous assignment of the optimum coincident configuration. The reliability of EpiCalc in predicting observed epitaxial overlayer orientations indicates that geometric lattice misfit modeling can be used to screen efficiently for the most favorable epitaxial configuration (overlayer lattice parameters and azimuthal angle), which can then be used in subsequent PE calculations that allow for other degrees of freedom such as molecular orientation.

Polypeptide Interactions at Ice and Biomineral Interfaces Are Defined by Secondary Structure-Dependent Chain Orientations

The stereospecific interaction of polypeptides with biominerals and ice represents a unique phenomenon in nature. Here, using the theoretical geometric lattice matching algorithm, CHASM (abbreviation for chain alignment on the surface of materials), we explore the geometric complementarity of specific Cα polypeptide secondary structures (α-helix, β-sheet, γ-turn) with the [001] planes of the biominerals, aragonite and calcite, and the [001], [100], and [201] faces of hexagonal ice. We find that certain secondary structure−surface pairings exhibit a defined set of orientational minima that agree closely with published results. Moreover, no two secondary structures feature the exact same set of global and local orientational minima for a given surface. This suggests that the molecular complementarity of each secondary structure with a given surface is highly specific and cannot be mimicked by another secondary structure. These results suggest that the site and orientation of polypeptide adsorption onto biominerals or ice may be influenced by secondary structure type.

Triaxially oriented growth of CuO on MgO (001): X-ray diffraction studies of pure CuO films and inclusions in superconducting YBaCuO films prepared by MOCVD

We present results on MOCVD-grown CuO films and superconducting YBa 2Cu 3O 7−δ films containing CuO inclusions. The films discussed in detail were deposited on MgO (001) substrates, at 690 °C, under O 2 partial pressures of 11–17 Torr. Various X-ray diffraction methods were used for film characterization, including ø-scan measurements sensitive to the in-plane orientation of the monoclinic CuO phase. These were augmented by scanning electron microscopy and electron probe microanalysis studies. Our CuO films show extreme orientation of CuO (111)∥MgO(001). They are also characterized by one predominant type of in-plane orientation, CuO [1⦶10]∥MgO [110], and display substrate-induced twinning. We rationalize the preffered azimuthal orientation for CuO films in terms of a simple geometrical lattice match, and compare our results with previous reports on CuO growth on MgO (001). The YBa 2Cu 3O 7−δ films typically show zero d.c. resistance at ∼80 K, are highly oriented with YBa 2Cu 3O 7−δ (001 )∥MgO (001), and also show in-plane alignment consistent with other studies. CuO inclusions with diameters of 0.3–1.5 μm occur at typical densities of ∼4 × 10 7 cm −2, and predominantly nucleated at the substrate surface. We shoe that the CuO inclusions display the same type of triaxial orientation as our pure CuO films by means of ø-scan measurements, and comment on the difficulty in detecting (111)-oriented CuO by the θ−2 θ technique. Finally, we discuss preliminary results confirming that the formation of triaxially oriented CuO is very specific to the MgO (001) surface, and deposition conditions favouring initial growth of CuO rather than Cu 2O.

Observation and analysis of epitaxial growth of CoSi2 on (100) Si

CoSi2 layers formed by the thermal reaction of vapor-deposited Co films on Si(100) substrates have been studied by transmission electron microscopy, and x-ray diffraction. It is shown that first a layer of CoSi is formed between Co and Si. Only thereafter is the formation of CoSi2 initiated at the Si/CoSi interface. In view of the similarity of the crystal structure and the small lattice mismatch between the Si and the CoSi2, epitaxy of aligned (100) CoSi2 is expected to occur. However, in addition to an aligned (100) orientation, CoSi2 occurs in a number of orientations, including a (110) preferential orientation. Many individual grains are composed of subgrains, slightly rotated with respect to each other and connected by small-angle boundaries. It is shown that the observations can be largely attributed to the geometrical lattice match between CoSi2 and Si. A computer program has been developed that searches systematically for a large number of possible geometrical matches. It allows us to calculate epitaxial relationships between CoSi2 and the Si(100) substrate. The probability of various fits is estimated on the basis of their strain energy and coincidence site density, showing good correspondence with the experimental observations.

Epitaxy of Fe films on spherical Cu and Au substrates

Abstract The morphology and crystallography of thin Fe films deposited on spherical surfaces of Cu and Au have been examined using field-ion microscopy. The Fe films exhibited nearly the Kurdjumov-Sachs orientation relationship to the Cu substrates and nearly the Bain relationship to the Au substrates. Such a difference in the epitaxial growth mode of Fe could be reasonably explained from a minimization criterion of misfit strain energy together with a geometrical lattice match consideration.

Simple criteria for epitaxial relationships between f.c.c. and b.c.c. crystals

Experimental and theoretical studies on epitaxial relationships between f.c.c. and b.c.c. crystals, one as a deposit and the other as a substrate, have been reviewed. Simple criteria, based on geometrical lattice match and misfit strain energy considerations, are proposed to predict and explain favourable epitaxial relationships on various f.c.c.-b.c.c. interface orientations. Excellent applicability of the criteria is demonstrated for various observed eptixial relationships not only on low index substrate planes but also on higher index and curved substrate surfaces.

A search for geometrical lattice matching in semiconductor heteroepitaxy

The optimum geometrical lattice match of Si and Ge with (001), (011) and (111) faces of the commonly used semiconductors has been calculated following the systematic procedure of Zur and McGill [J. Appl. Phys. 55 (1984) 378]. Some of the most promising cases for semiconductor heteroepitaxy have been investigated experimentally using Rutherford backscattering in conjunction with planar channeling and blocking. No differences in orientation (in- or out-of-plane) of epitaxial films and substrates were found.

Nucleation and Growth of Cosi2 on (001) and (111) Si

ABSTRACTNucleation and growth of epitaxial CoSi2 on Si by the thermal reaction of vapour deposited Co on (001) and (111) Si have been studied by transmission electron microscopy (TEM). On (001)-Si the layer consists of CoSi2 grains. Apart from an aligned (a)-orientation, CoSi2 occurs in a number of orientations, including a (110) preferential (b)-orientation. On (111) Si, single-crystalline layers are obtained, predominantly in the B-type orientation, which is rotated through 180° relative to the aligned (111)-orientation (A-type). The interfacial defect structure consists of misfit dislocations of edge-type with Burgers vector b=a/6<112>, running in <110> directions. The observations for both (001) and (111) Si are related to geometrical lattice match between CoSi2 and Si. In addition to the experimental results, a computer program has been made which calculates the matching between various orientations of CoSi2 and Si. The nucleation of B-type CoSi2 for (111) Si and the different oriented grains for (001) Si are discussed in terms of a nucleation mechanism at steps at the interface in combination with a relatively large mismatch.