Showing papers on "Grain boundary published in 2011"

Grains and grain boundaries in single-layer graphene atomic patchwork quilts

Abstract: The properties of polycrystalline materials are often dominated by the size of their grains and by the atomic structure of their grain boundaries. These effects should be especially pronounced in two-dimensional materials, where even a line defect can divide and disrupt a crystal. These issues take on practical significance in graphene, which is a hexagonal, two-dimensional crystal of carbon atoms. Single-atom-thick graphene sheets can now be produced by chemical vapour deposition on scales of up to metres, making their polycrystallinity almost unavoidable. Theoretically, graphene grain boundaries are predicted to have distinct electronic, magnetic, chemical and mechanical properties that strongly depend on their atomic arrangement. Yet because of the five-order-of-magnitude size difference between grains and the atoms at grain boundaries, few experiments have fully explored the graphene grain structure. Here we use a combination of old and new transmission electron microscopy techniques to bridge these length scales. Using atomic-resolution imaging, we determine the location and identity of every atom at a grain boundary and find that different grains stitch together predominantly through pentagon-heptagon pairs. Rather than individually imaging the several billion atoms in each grain, we use diffraction-filtered imaging to rapidly map the location, orientation and shape of several hundred grains and boundaries, where only a handful have been previously reported. The resulting images reveal an unexpectedly small and intricate patchwork of grains connected by tilt boundaries. By correlating grain imaging with scanning probe and transport measurements, we show that these grain boundaries severely weaken the mechanical strength of graphene membranes but do not as drastically alter their electrical properties. These techniques open a new window for studies on the structure, properties and control of grains and grain boundaries in graphene and other two-dimensional materials.

Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour deposition

Abstract: Chemical vapour deposition is a promising route for large-scale graphene growth. It is now shown that—through the use of seeds—high-quality, large, single-crystal domains can be grown on a patterned arrangement, and can be used to carefully study the transport across grain boundaries.

Grain Boundary Mapping in Polycrystalline Graphene

Abstract: We report direct mapping of the grains and grain boundaries (GBs) of large-area monolayer polycrystalline graphene sheets, at large (several micrometer) and single-atom length scales. Global grain and GB mapping is performed using electron diffraction in scanning transmission electron microscopy (STEM) or using dark-field imaging in conventional TEM. Additionally, we employ aberration-corrected TEM to extract direct images of the local atomic arrangements of graphene GBs, which reveal the alternating pentagon-heptagon structure along high-angle GBs. Our findings provide a readily adaptable tool for graphene GB studies.

Raman Measurements of Thermal Transport in Suspended Monolayer Graphene of Variable Sizes in Vacuum and Gaseous Environments

Abstract: Using micro-Raman spectroscopy, the thermal conductivity of a graphene monolayer grown by chemical vapor deposition and suspended over holes with different diameters ranging from 2.9 to 9.7 μm was measured in vacuum, thereby eliminating errors caused by heat loss to the surrounding gas. The obtained thermal conductivity values of the suspended graphene range from (2.6 ± 0.9) to (3.1 ± 1.0) × 103 Wm−1K−1 near 350 K without showing the sample size dependence predicted for suspended, clean, and flat graphene crystal. The lack of sample size dependence is attributed to the relatively large measurement uncertainty as well as grain boundaries, wrinkles, defects, or polymeric residue that are possibly present in the measured samples. Moreover, from Raman measurements performed in air and CO2 gas environments near atmospheric pressure, the heat transfer coefficient for air and CO2 was determined and found to be (2.9 +5.1/−2.9) and (1.5 +4.2/−1.5) × 104 Wm−2K−1, respectively, when the graphene temperature was heat...

Effects of Polycrystalline Cu Substrate on Graphene Growth by Chemical Vapor Deposition

Abstract: Chemical vapor deposition of graphene on Cu often employs polycrystalline Cu substrates with diverse facets, grain boundaries (GBs), annealing twins, and rough sites. Using scanning electron microscopy (SEM), electron-backscatter diffraction (EBSD), and Raman spectroscopy on graphene and Cu, we find that Cu substrate crystallography affects graphene growth more than facet roughness. We determine that (111) containing facets produce pristine monolayer graphene with higher growth rate than (100) containing facets, especially Cu(100). The number of graphene defects and nucleation sites appears Cu facet invariant at growth temperatures above 900 °C. Engineering Cu to have (111) surfaces will cause monolayer, uniform graphene growth.

Polycrystalline Silicon for Integrated Circuit Applications

Abstract: 1 Deposition.- 1.1 Introduction..- 1.2 Thermodynamics and kinetics.- 1.3 The deposition process.- 1.4 Gas-phase and surface processes.- 1.4.1 Convection.- 1.4.2 The boundary layer.- 1.4.3 Diffusion through the boundary layer.- 1.4.4 Reaction.- 1.4.5 Steady state.- 1.5 Reactor geometries.- 1.5.1 Low-pressure, hot-wall reactors.- 1.5.2 Atmospheric-pressure, cold-wall reactor.- 1.6 Reaction.- 1.6.1 Decomposition of silane.- 1.6.2 Surface adsorption.- 1.6.3 Deposition rate.- 1.6.4 Rate-limiting step.- 1.7 Deposition of doped films.- 1.7.1 n-type deposited films.- 1.7.2 p-type deposited films.- 1.7.3 Electrostatic model.- 1.8 Step coverage.- 1.9 Enhanced deposition techniques.- 1.10 Summary.- 2 Structure.- 2.1 Nucleation.- 2.1.1 Amorphous surfaces.- 2.1.2 Single-crystal surfaces.- 2.2 Surface diffusion and structure.- 2.2.1 Subsurface rearrangement.- 2.3 Evaluation techniques.- 2.4 Grain structure.- 2.5 Grain orientation.- 2.6 Optical properties.- 2.6.1 Index of refraction.- 2.6.2 Absorption coefficient.- 2.6.3 Ultraviolet surface reflectance.- 2.6.4 Use of optical properties for film evaluation.- 2.7 Etch rate.- 2.8 Stress.- 2.9 Thermal conductivity.- 2.10 Structural stability.- 2.10.1 Recrystallization mechanisms.- 2.10.2 Undoped or lightly doped films.- 2.10.3 Heavily doped films.- 2.10.4 Implant channeling.- 2.10.5 Amorphous films.- 2.11 Epitaxial realignment.- 2.12 Summary.- 3 Dopant Diffusion and Segregation.- 3.1 Introduction.- 3.2 Diffusion mechanism.- 3.2.1 Diffusion along a grain boundary.- 3.2.2 Diffusion in polycrystalline material.- 3.3 Diffusion in polysilicon.- 3.3.1 Arsenic diffusion.- 3.3.2 Phosphorus diffusion.- 3.3.3 Antimony diffusion.- 3.3.4 Boron diffusion.- 3.3.5 Limits of applicability.- 3.4 Diffusion from polysilicon.- 3.5 Interaction with metals.- 3.5.1 Aluminum.- 3.5.2 Other metals and silicides.- 3.6 Dopant segregation at grain boundaries.- 3.6.1 Theory of segregation.- 3.6.2 Experimental data.- 3.7 Summary.- 4 Oxidation.- 4.1 Introduction.- 4.2 Oxide growth on polysilicon.- 4.2.1 Oxidation of undoped films.- 4.2.2 Oxidation of doped films.- 4.2.3 Effect of grain boundaries.- 4.2.4 Effects of device geometry.- 4.2.5 Oxide-thickness evaluation.- 4.3 Conduction through oxide on polysilicon.- 4.3.1 Interface features.- 4.3.2 Deposition conditions.- 4.3.3 Oxidation conditions.- 4.3.4 Dopant concentration and annealing.- 4.3.5 Carrier trapping.- 4.4 Summary.- 5 Electrical Properties.- 5.1 Introduction.- 5.2 Undoped polysilicon.- 5.3 Moderately doped polysilicon.- 5.3.1 Carrier trapping at grain boundaries.- 5.3.2 Carrier transport.- 5.3.3 Trap concentration and energy distribution.- 5.3.4 Thermionic field emission.- 5.3.5 Grain-boundary barriers.- 5.3.6 Limitations of models.- 5.3.7 Segregation and trapping.- 5.3.8 Summary.- 5.4 Grain-boundary modification.- 5.5 Heavily doped polysilicon films.- 5.5.1 Solid solubility.- 5.5.2 Method of doping.- 5.5.3 Stability.- 5.5.4 Mobility.- 5.5.5 Future trends.- 5.6 Minority-carrier properties.- 5.6.1 Lifetime.- 5.6.2 Switching characteristics.- 5.7 Summary.- 6 Applications.- 6.1 Introduction.- 6.2 Silicon-gate technology.- 6.2.1 Threshold voltage.- 6.2.2 Polysilicon interconnections.- 6.2.3 Process compatibility.- 6.2.4 New structures.- 6.2.5 Gettering.- 6.2.6 Gate-oxide reliability.- 6.3 Nonvolatile memories.- 6.4 High-value resistors.- 6.5 Fusible links.- 6.6 Polysilicon contacts.- 6.6.1 Reduction of junction spiking.- 6.6.2 Diffusion from polysilicon.- 6.7 Bipolar integrated circuits.- 6.7.1 Vertical npn bipolar transistors.- 6.7.2 Lateral pnp bipolar transistors.- 6.8 Device isolation.- 6.8.1 Dielectric isolation.- 6.8.2 Epi-poly isolation.- 6.8.3 Trench isolation.- 6.8.4 Summary.- 6.9 Trench capacitors.- 6.10 Polysilicon diodes.- 6.11 Polysilicon transistors.- 6.12 Polysilicon sensors.- 6.13 Summary.

Thermal Conductivity of Nanocrystalline Silicon: Importance of Grain Size and Frequency-Dependent Mean Free Paths

Abstract: The thermal conductivity reduction due to grain boundary scattering is widely interpreted using a scattering length assumed equal to the grain size and independent of the phonon frequency (gray). T...

Influence of Copper Morphology in Forming Nucleation Seeds for Graphene Growth

Abstract: We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts.

Grain boundary energy anisotropy: a review

Abstract: This paper reviews findings on the anisotropy of the grain boundary energies. After introducing the basic concepts, there is a discussion of fundamental models used to understand and predict grain boundary energy anisotropy. Experimental methods for measuring the grain boundary energy anisotropy, all of which involve application of the Herring equation, are then briefly described. The next section reviews and compares the results of measurements and model calculations with the goal of identifying generally applicable characteristics. This is followed by a brief discussion of the role of grain boundary energies in nucleating discontinuous transitions in grain boundary structure and chemistry, known as complexion transitions. The review ends with some questions to be addressed by future research and a summary of what is known about grain boundary energy anisotropy.

Grain boundary engineering: historical perspective and future prospects

Abstract: A brief introduction of the historical background of grain boundary engineering for structural and functional polycrystalline materials is presented herewith. It has been emphasized that the accumulation of fundamental knowledge about the structure and properties of grain boundaries and interfaces has been extensively done by many researchers during the past one century. A new approach in terms of the concept of grain boundary and interface engineering is discussed for the design and development of high performance materials with desirable bulk properties. Recent advancements based on these concepts clearly demonstrate the high potential and general applicability of grain boundary engineering for various kinds of structural and functional materials. Future prospects of the grain boundary and interface engineering have been outlined, hoping that a new dimension will emerge pertaining to the discovery of new materials and the generation of a new property originating from the presence of grain boundaries and interfaces in advanced polycrystalline materials.

Softened elastic response and unzipping in chemical vapor deposition graphene membranes.

Abstract: We use atomic force microscopy to image grain boundaries and ripples in graphene membranes obtained by chemical vapor deposition. Nanoindentation measurements reveal that out-of-plane ripples effectively soften graphene’s in-plane stiffness. Furthermore, grain boundaries significantly decrease the breaking strength of these membranes. Molecular dynamics simulations reveal that grain boundaries are especially weakening when subnanometer voids are present in the lattice. Finally, we demonstrate that two graphene membranes brought together form membranes with higher resistance to breaking.

Thermal transport across twin grain boundaries in polycrystalline graphene from nonequilibrium molecular dynamics simulations.

Abstract: We have studied the thermal conductance of tilt grain boundaries in graphene using nonequilibrium molecular dynamics simulations. When a constant heat flux is allowed to flow, we observe sharp jumps in temperature at the boundaries, characteristic of interfaces between materials of differing thermal properties. On the basis of the magnitude of these jumps, we have computed the boundary conductance of twin grain boundaries as a function of their misorientation angles. We find the boundary conductance to be in the range 1.5 × 1010 to 4.5 × 1010 W/(m2 K), which is significantly higher than that of any other thermoelectric interfaces reported in the literature. Using the computed values of boundary conductances, we have identified a critical grain size of 0.1 μm below which the contribution of the tilt boundaries to the conductivity becomes comparable to that of the contribution from the grains themselves. Experiments to test the predictions of our simulations are proposed.

Enhancement in Thermoelectric Figure‐Of‐Merit of an N‐Type Half‐Heusler Compound by the Nanocomposite Approach

Abstract: An enhancement in the dimensionless thermoelectric fi gure-of-merit ( ZT ) of an n-type half-Heusler material is reported using a nanocomposite approach. A peak ZT value of 1.0 was achieved at 600 ° C‐700 ° C, which is about 25% higher than the previously reported highest value. The samples were made by ball-milling ingots of composition Hf 0.75 Zr 0.25 NiSn 0.99 Sb 0.01 into nanopowders and hot-pressing the powders into dense bulk samples. The ingots were formed by arc-melting the elements. The ZT enhancement mainly comes from reduction of thermal conductivity due to increased phonon scattering at grain boundaries and crystal defects, and optimization of antimony doping.

Effect of microstructure on the nucleation of deformation twins in polycrystalline high-purity magnesium: A multi-scale modeling study

Abstract: A multi-scale, theoretical study of twin nucleation from grain boundaries in polycrystalline hexagonal close packed (hcp) metals is presented. A key element in the model is a probability theory for the nucleation of deformation twins based on the idea that twins originate from a statistical distribution of defects in the grain boundaries and are activated by local stresses at the grain boundaries. In this work, this theory is integrated into a crystal plasticity constitutive model in order to study the influence of these statistical effects on the microstructural evolution of the polycrystal, such as texture and twin volume fraction. Recently, a statistical analysis of exceptionally large data sets of {1012} deformation twins was conducted for high-purity Mg ( Beyerlein et al., 2010a ). To demonstrate the significantly enhanced accuracy of the present model over those employing more conventional, deterministic approaches to twin activation, the model is applied to the case of {1012} twinning in Mg to quantitatively interpret the many statistical features reported for these twins (e.g., variant selection, thickness, numbers per grain) and their relationship to crystallographic grain orientation, grain size, and grain boundary misorientation angle. Notably the model explains the weak relationship observed between crystal orientation and twin variant selection and the strong correlation found between grain size and the number of twins formed per grain. The predictions suggest that stress fluctuations generated at grain boundaries are responsible for experimentally observed dispersions in twin variant selection.

Advantageous grain boundaries in iron pnictide superconductors

Abstract: High critical temperature superconductors have zero power consumption and could be used to produce ideal electric power lines. The principal obstacle in fabricating superconducting wires and tapes is grain boundaries-the misalignment of crystalline orientations at grain boundaries, which is unavoidable for polycrystals, largely deteriorates critical current density. Here we report that high critical temperature iron pnictide superconductors have advantages over cuprates with respect to these grain boundary issues. The transport properties through well-defined bicrystal grain boundary junctions with various misorientation angles (θ(GB)) were systematically investigated for cobalt-doped BaFe(2)As(2) (BaFe(2)As(2):Co) epitaxial films fabricated on bicrystal substrates. The critical current density through bicrystal grain boundary (J(c)(BGB)) remained high (>1 MA cm(-2)) and nearly constant up to a critical angle θ(c) of ∼9°, which is substantially larger than the θ(c) of ∼5° for YBa(2)Cu(3)O(7-δ). Even at θ(GB)>θ(c), the decay of J(c)(BGB) was much slower than that of YBa(2)Cu(3)O(7-δ).

Enhanced piezoelectric properties of (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 lead-free ceramics by optimizing calcination and sintering temperature

Abstract: Lead-free (Ba0.85Ca0.15)(Ti0.9Zr0.1)O3 (BCTZ) piezoelectric ceramics were prepared by conventional oxide-mixed method at various calcination and sintering temperatures. Both calcination and sintering temperatures have a significant effect on the density and grain size, which are closely related with piezoelectric and other properties of ceramics. The calcination temperature has a great influence on the grain boundary, which also plays an important role in piezoelectric properties. With increased calcination and sintering temperature, the ferroelectric and piezoelectric properties have enhanced significantly. The BCTZ ceramics calcined at 1300 °C and sintered at 1540 °C exhibit optimal electrical properties: d33 = 650 pC/N, d31 = 74 pC/N, kp = 0.53, kt = 0.38, k31 = 0.309, s 11 E = 14.0 × 10 − 12 m 2 /N , ɛr = 4500, Pr = 11.69 μC/cm2, which is a promising lead-free piezoelectric candidate.

Amorphous Carbon Coated High Grain Boundary Density Dual Phase Li4Ti5O12‐TiO2: A Nanocomposite Anode Material for Li‐Ion Batteries

Abstract: This work introduces an effective, inexpensive, and large-scale production approach to the synthesis of a carbon coated, high grain boundary density, dual phase Li4Ti5O12-TiO2 nanocomposite anode material for use in rechargeable lithium-ion batteries. The microstructure and morphology of the Li4Ti5O12-TiO2-C product were characterized systematically. The Li4Ti5O12-TiO2-C nanocomposite electrode yielded good electrochemical performance in terms of high capacity (166 mAh g−1 at a current density of 0.5 C), good cycling stability, and excellent rate capability (110 mAh g−1 at a current density of 10 C up to 100 cycles). The likely contributing factors to the excellent electrochemical performance of the Li4Ti5O12-TiO2-C nanocomposite could be related to the improved morphology, including the presence of high grain boundary density among the nanoparticles, carbon layering on each nanocrystal, and grain boundary interface areas embedded in a carbon matrix, where electronic transport properties were tuned by interfacial design and by varying the spacing of interfaces down to the nanoscale regime, in which the grain boundary interface embedded carbon matrix can store electrolyte and allows more channels for the Li+ ion insertion/extraction reaction. This research suggests that carbon-coated dual phase Li4Ti5O12-TiO2 nanocomposites could be suitable for use as a high rate performance anode material for lithium-ion batteries.

Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics

Abstract: Microwaves and spark plasma sintering (SPS) enhance sinterability. Simple electrical fields, applied by means of a pair of electrodes to bare specimens, have been shown to accelerate the rate of superplastic deformation, reduce the time and temperature for sintering, and to retard the rate of grain growth. By inference, the influence of electrical and electromagnetic fields on grain boundary energetics and kinetics is unmistakable. Often, in ceramics, grain boundaries are themselves endowed with space charge that can couple with externally applied fields. The frequency dependence of this coupling ranging from zero frequency to microwave frequencies is discussed. The classical approach for modeling grain growth, creep, and sintering, considers chemical diffusion (self-diffusion) under a thermodynamic driving force, underpinned by a physical mechanism that visualizes the flow of mass transport in a way that reproduces the phenomenological observations. In all instances, the final analytical result can be separated into a product of three functions: one of the grain size, the second related to the thermodynamic driving force, and the third to the kinetics of mass transport. The influence of an electrical field on each of these functions is addressed.The fundamental mechanisms of these electrical interactions are discussed in the following ways: (i) dielectric loss and Joule heating in the crystal and at the grain boundary, (ii) the coupling between mechanical stress and the electrochemical potential of charged species, (iii) the interaction between applied electrical fields and the intrinsic fields that exist within the space charge layers, (iv) and the possibility of nucleating defect avalanches under electrical fields. We limit ourselves to ceramics that have at least some degree of ionic character. In these experiments the electrical fields range from several volts to several hundred volts per centimeter, and the power dissipation from Joule heating is of the order of several watts per cubic centimeter of the specimen. Metals, where very high current densities are obtained at relatively low applied electric fields, leading to phenomenon such as electromigration, are not considered.

The Role of a Bilayer Interfacial Phase on Liquid Metal Embrittlement

Abstract: Intrinsically ductile metals are prone to catastrophic failure when exposed to certain liquid metals, but the atomic-level mechanism for this effect is not fully understood. We characterized a model system, a nickel sample infused with bismuth atoms, by using aberration-corrected scanning transmission electron microscopy and observed a bilayer interfacial phase that is the underlying cause of embrittlement. This finding provides a new perspective for understanding the atomic-scale embrittlement mechanism and for developing strategies to control the practically important liquid metal embrittlement and the more general grain boundary embrittlement phenomena in alloys. This study further demonstrates that adsorption can induce a coupled grain boundary structural and chemical phase transition that causes drastic changes in properties.

Direct observation of nanometer-scale amorphous layers and oxide crystallites at grain boundaries in polycrystalline Sr1-xKxFe2As2 superconductors

Abstract: We report here an atomic resolution study of the structure and composition of the grain boundaries in polycrystalline Sr0.6K0.4Fe2As2 superconductor. A large fraction of grain boundaries contain amorphous layers larger than the coherence length, while some others contain nanometer-scale particles sandwiched in between amorphous layers. We also find that there is significant oxygen enrichment at the grain boundaries. Such results explain the relatively low transport critical current density (Jc) of polycrystalline samples with respect to that of bicrystal films.

Grain boundary sliding in San Carlos olivine: Flow law parameters and crystallographic‐preferred orientation

Abstract: [1] We performed triaxial compressive creep experiments on aggregates of San Carlos olivine to develop a flow law and to examine microstructural development in the dislocation-accommodated grain boundary sliding regime (GBS). Each experiment included load and temperature steps to determine both the stress exponent and the activation energy. Grain boundary maps, created with electron backscatter diffraction data, were used to quantify grain size distributions for each sample. Inversion of the resulting data produced the following flow law for GBS: GBS = 104.8 ± 0.8 (σ2.9 ± 0.3/d0.7 ± 0.1) exp[(−445 ± 20 kJ mol−1)/RT], with σ, d, and GBS in units of MPa, μm, and s−1, respectively. Although relatively weak, crystallographic-preferred orientations (CPOs) have [010] maxima parallel to the compression direction along with [100] and [001] girdles perpendicular to the compression direction. CPOs and subgrain boundary misorientation axes suggest that the (010)[100] slip system contributes significantly to deformation. We propose that these experimental results are best modeled by a deformation mechanism in which strain is accomplished primarily through grain boundary sliding accommodated by the motion of dislocations. Extrapolation of our flow laws to mantle conditions suggests that GBS is likely to be the dominant deformation mechanism in both lithospheric shear zones and asthenospheric flow, and therefore strong upper mantle seismic anisotropy can not be attributed solely to the dominance of dislocation creep.

Atom-resolved imaging of ordered defect superstructures at individual grain boundaries

Abstract: The ability to resolve spatially and identify chemically atoms in defects would greatly advance our understanding of the correlation between structure and property in materials. This is particularly important in polycrystalline materials, in which the grain boundaries have profound implications for the properties and applications of the final material. However, such atomic resolution is still extremely difficult to achieve, partly because grain boundaries are effective sinks for atomic defects and impurities, which may drive structural transformation of grain boundaries and consequently modify material properties. Regardless of the origin of these sinks, the interplay between defects and grain boundaries complicates our efforts to pinpoint the exact sites and chemistries of the entities present in the defective regions, thereby limiting our understanding of how specific defects mediate property changes. Here we show that the combination of advanced electron microscopy, spectroscopy and first-principles calculations can provide three-dimensional images of complex, multicomponent grain boundaries with both atomic resolution and chemical sensitivity. The high resolution of these techniques allows us to demonstrate that even for magnesium oxide, which has a simple rock-salt structure, grain boundaries can accommodate complex ordered defect superstructures that induce significant electron trapping in the bandgap of the oxide. These results offer insights into interactions between defects and grain boundaries in ceramics and demonstrate that atomic-scale analysis of complex multicomponent structures in materials is now becoming possible.