Diamond-like Crystals Research Articles

Formation of two-dimensional diamond-like colloidal crystals using layer-by-layer electrostatic self-assembly.

We report here that a two-dimensional (2D) diamond-like structure of micron-sized colloidal particles can be obtained by layer-by-layer self-assembly. Positively and negatively charged silica particles, 1 μm in diameter, were used in the experiments. On a positively charged, flat glass substrate, the first layer of negatively charged particles was prepared to form a non-close-packed 2D crystal. Then the second and third layers were fabricated using electrostatic adsorption. The positions of adsorbed particles were controllable by tuning the zeta-potential of the particles and the salt concentration of the medium. The FDTD calculations show that the 2D diamond structures of particles with higher refractive index (titania) have an absorption band in the wavelength range corresponding to the photonic band gap of the 3D bulk crystal. We expect these findings to be useful for the fabrication of novel photonic materials.

Preparation of MIL-88A micro/nanocrystals with different morphologies in different solvents for efficient removal of Congo red from water: Synthesis, characterization, and adsorption mechanisms

In this report, the morphology, size, and surface charge of MIL-88A can be tuned by adjusting the DMF-H2O mixed solvent system in the reaction system. The solvothermal method successfully prepared rod-like, spindle-like, and diamond-like crystals. Surprisingly, these crystals formed in different solvents showed considerable differences in yield and adsorption performance of anionic dyes. The yield of MIL-88A-1 synthesized in H2O/DMF biphasic solvent is the most impressive, about 3.7 times that of MIL-88A-2 synthesized in H2O as the solvent and about 7.5 times that of MIL-88A-3 synthesized in DMF as solvent. MIL-88A has a high pore volume, high BET surface area, and many open metal sites, among which MIL-88A-1 has the best structural performance and adsorption performance. Its maximum adsorption capacity is 555.5 mg∙g−1. The materials were characterized by SEM, FTIR, XRD, TGA, BET, and Zeta. Subsequently, the effects of contact time, PH value, concentration, temperature, adsorbent dosage, and other factors on the adsorption performance were systematically discussed. The adsorption removal rate of CR by MIL-88A-1 can reach 92% within 60 min. The research results show that the adsorption process fits the Langmuir isotherm and pseudo-second-order models to a high degree, and the adsorption process of the whole system can be attributed to the chemisorption of a monolayer on a uniform surface. The adsorption mechanism of MLL-88A is mainly the synergistic effect between electrostatic interaction, hydrogen bonding, and the physicochemical properties (specific surface area, pore volume, and pore size) of the adsorbent.

One-step electrochemical synthesis of γ-Fe2O3@MIL-88a magnetic composite for heterogeneous Fenton-like catalysis

We report a new one-step room-temperature electrochemical synthesis of γ-Fe2O3@MIL-88a magnetic composite. Anode from metallic iron was used as Fe-source. We did not use any toxic or hazardous solvents. A careful, comprehensive characterization of the obtained material was applied, including a synchrotron experiment. The γ-Fe2O3@MIL-88a composite comprised diamond-like MIL-88a crystals of 100–300 nm covered with γ-Fe2O3 nanoparticles. This component provided a magnetic response to the synthesized material. Moreover, γ-Fe2O3 nanoparticles boosted semiconductor MOF crystals. As a result, the γ-Fe2O3@MIL-88a composite demonstrated superior photocatalytic performance toward methylene blue degradation. MIL-88a crystals acted as photo-Fenton catalysts activating H2O2 decomposition with the production of active •OH radicals. Easy magnetic separation and visible-light activated photocatalytic properties make γ-Fe2O3@MIL-88a composite a promising system for removing organic dyes from contaminated water according to the photo-Fenton process.

Liquid Diffused Separation Induced Crystallization to efficiently grow centimeter-sized diamond-like Cs4PbBr6 crystals for light-emitting applications

Large-size single crystal (SCs) is an excellent platform for studying the optoelectronic properties of materials. However, growing high-quality crystals has always been a challenge. Here we develop a liquid-induced diffusion (LDSC) method for high-efficiency and low-cost growth of centimeter-sized Cs4PbBr6 crystals. All-sized crystals with a special diamond-like appearance exhibit strong green photoluminescence (PL) and good stability. In addition, X-ray diffraction (XRD) reveals that the diamond-like Cs4PbBr6 crystal exhibits a different crystal surface orientation from the rhombic SCs. More importantly, different from the CsPbBr3 impurity-induced photoluminescence mechanism, the strong green PL of the as-prepared diamond-like Cs4PbBr6 crystal originates from its defect state: Br vacancies (VBr). Furthermore, high-efficiency white light-emitting diodes (WLED) devices are prepared by using high-luminous intensity Cs4PbBr6 crystals as green light emitters. The optimized devices generate high-quality white light with luminous efficiency of ∼54 lm W−1, which is much better than that of conventional perovskite nanocrystals-based LED devices. Our work demonstrates that the Cs4PbBr6 crystal devices possess higher luminous efficiency, better stability and great application potential in display backlighting.

Exploring diamondlike lattice thermal conductivity crystals via feature-based transfer learning

Ultrahigh lattice thermal conductivity materials hold great importance since they play a critical role in the thermal management of electronic and optical devices. Models using machine learning can search for materials with outstanding higher-order properties like thermal conductivity. However, the lack of sufficient data to train a model is a serious hurdle. Herein we show that big data can complement small data for accurate predictions when lower-order feature properties available in big data are selected properly and applied to transfer learning. The connection between the crystal information and thermal conductivity is directly built with a neural network by transferring descriptors acquired through a pretrained model for the feature property. Successful transfer learning shows the ability of extrapolative prediction and reveals descriptors for lattice anharmonicity. The resulting model is employed to screen over $60\phantom{\rule{0.16em}{0ex}}000$ compounds to identify novel crystals that can serve as alternatives to diamond. Even though most materials in the top list are superhard materials, we reveal that superhard property does not necessarily lead to high lattice thermal conductivity. Large hardness means high elastic constants and group velocity of phonons in the linear dispersion regime, but the lattice thermal conductivity is determined also by other important factors such as the phonon relaxation time. What is more, the average or maximum dipole polarizability and the van der Waals radius are revealed to be the leading descriptors among those that can also be qualitatively related to anharmonicity.

Colloidal route yields diamond-like crystals

Thirty years ago, theoreticians predicted that ordered materials with a diamond-like structure would be able to control the flow of light in much the same way that semiconductors control the flow o...

Electronic Structure of CO2 and CS2 Crystals

Density functional theory methods are used to study diamond-like crystals CO2 and CS2 with defect chalcopyrite structure (β-SiO2). Equilibrium crystal lattice parameters are determined, energy band spectra are calculated for these crystals and for their cation (C) and anion (O, S) sublattices. The formation of chemical bonding in the crystals is studied by analysing total and partial densities of states and distribution maps of differential and deformation charge densities of valence electrons.

Light Dispersion in Diamond-like Crystals

Dispersion of light in diamond-like crystals is investigated. Dispersion laws of exciton polaritons in this structures, which (apart from the diamond itself) include silicon and germanium is obtained within the quasi-molecular model of valent crystals. Dispersion curves point to the fact that in the vicinity of exciton resonance under small damping one must account for the exciton-photon interaction. The calculation shows that in a certain frequency range the existence of an additional light wave is possible. The dispersion laws of exciton polaritons in a diamond-like structure in the vicinity of frequency of the lowest dipole transition of a crystalline quasi-molecule (a σ-bond) are obtained.

Finite element modeling of nanoindentation and scratching of Si, SiC, Ge crystals with anisotropic plasticity

Parameters of Hill’s anisotropic elastoplasticity for diamond and Si, SiC, Ge semiconductors have been estimated from nonlinear stress-strain curves obtained by computational quantum chemistry. Using these parameters, finite element modeling of nanoindentation with Berkovich pyramid and frictionless scratching with spherical tip have been carried out. It has been shown, that the plastic anisotropy leads to the hardness anisotropy commonly observed by experimental indentation of (111), (011) and (001) crystallographic surfaces of the diamond-like crystals. The creep flow has been regarded in a quasi-static approach. Propagation of a median crack has been accounted by cohesive zone model.

Gas jet deposition of diamond structures by thermal activation on an expanded surface

We present new approaches to gas phase deposition of diamond and diamond-like structures, films, and crystals. They are based on the activation of initial gases on hot expanded surfaces due to multiple collisions of molecules. The possibility of realizing the diamond synthesis at a very wide range of regime parameters is a distinctive feature of the method. The success of the research is due to the computer modeling of gas dynamic processes which allows us to predict and analyze the results of experiments. We dealt with a mixture of hydrogen and methane. Some results were obtained by using a separate or joint delivery of components to activating surfaces. The vitality of this new method is proved. The development and optimization of the method led to the creation of an energy saving system.

The Even-Odd and the Isoelectronicity Rules Applied to Single Covalent Bonds in Ionic, Double-Face-Centered Cubic and Diamond-Like Crystals

Although atom configuration in crystals is precisely known thanks to imaging techniques, there is no experimental way to know the exact location of bonds or charges. Many different representations have been proposed, yet no theory to unify conceptions. The present paper describes methods to derive bonds and charge location in double-face-centered cubic crystals with 4 and 6 atoms per unit cell using two novel rules introduced in earlier works: the even-odd and the isoelectronicity rules. Both of these rules were previously applied to ions, molecules and some solids, and the even-odd rule was also tested on two covalent crystal structures: centered-cubic and single-face-centered cubic crystals. In the present study, the diamond-like structure was subjected to the isoelectronicity rule in order to derive Zinc-blende structures. Rock-salt-like crystals were derived from each other using both rules. These structures represent together more than 230 different crystals. Findings for these structures are threefold: both rules describe a very sure method to obtain valid single covalent-bonded structures; single covalent structures can be used in every case instead of the classical ionic model; covalent bonds and charges positions do not have any relation with the valence number given in the periodic table.

Basic Things are Simple

During a primordial ice age, ice crystallized in pools of liquid nitrogen on its poles, forming diamond-like crystals creating order from chaos. Models made from matchsticks and Plastacine™ or criss-crossed strips of cardboard stapled together are surprisingly strong (Figures 1 and 2). Random temperature fluctuations drove a ferroelectric phase transition at 72 degrees Kelvin, accommodating water molecules’ irregular tetrahedral shape and releasing latent energy as infrared laser light, ice light with wavelength λ ~ 4 μ. When such light was tried for de-icing aircraft wings, it was reflected. Likewise, it would have been reflected by surface ice and ice in clouds, just as Marconi’s first trans-Atlantic radio signals were. Lightning created nucleotides in the warm tropical waters Charles Darwin described, they absorbed ice light which photophosphorylated them. Reflection polarized the light, so only left or right-handed, chiral nucleotides were chosen (remember the thalidomide disaster!) and a noodle soup of chiral DNA emerged (Figure 3).

Method for making a single-step etch mask for 3D monolithic nanostructures

Current nanostructure fabrication by etching is usually limited to planar structures as they are defined by a planar mask. The realization of three-dimensional (3D) nanostructures by etching requires technologies beyond planar masks. We present a method for fabricating a 3D mask that allows one to etch three-dimensional monolithic nanostructures using only CMOS-compatible processes. The mask is written in a hard-mask layer that is deposited on two adjacent inclined surfaces of a Si wafer. By projecting in a single step two different 2D patterns within one 3D mask on the two inclined surfaces, the mutual alignment between the patterns is ensured. Thereby after the mask pattern is defined, the etching of deep pores in two oblique directions yields a three-dimensional structure in Si. As a proof of concept we demonstrate 3D mask fabrication for three-dimensional diamond-like photonic band gap crystals in silicon. The fabricated crystals reveal a broad stop gap in optical reflectivity measurements. We propose how 3D nanostructures with five different Bravais lattices can be realized, namely cubic, tetragonal, orthorhombic, monoclinic and hexagonal, and demonstrate a mask for a 3D hexagonal crystal. We also demonstrate the mask for a diamond-structure crystal with a 3D array of cavities. In general, the 2D patterns on the different surfaces can be completely independently structured and still be in perfect mutual alignment. Indeed, we observe an alignment accuracy of better than 3.0 nm between the 2D mask patterns on the inclined surfaces, which permits one to etch well-defined monolithic 3D nanostructures.

Optical characterization of Ga-doped ZnS micro- and nanostructures

An evaporation–deposition method has been employed to grow wurtzite Ga-doped ZnS micro- and nanostructures with different morphologies. The main structures obtained are pyramids, diamond-like crystals, plates, pencil-like and triangular cross-section wires. The influence of Ga doping has been studied by cathodoluminescence, photoluminescence and Raman spectroscopy. The luminescence behaviour is found to depend on the growth conditions and dopant incorporation. In pyramids and diamonds, the dopant incorporation produces a blue-shift of the defect-related emission, associated with the apparition of a 3.0 eV band related to Ga defects. For plates, pencil-like and triangular wires the major changes seem to be associated to the kind and polarity of the face under study, rather than to the Ga content in the precursor.

Design of a three-dimensional photonic band gap cavity in a diamondlike inverse woodpile photonic crystal

We theoretically investigate the design of cavities in a three-dimensional (3D) inverse woodpile photonic crystal. This class of cubic diamondlike crystals has a very broad photonic band gap and consists of two perpendicular arrays of pores with a rectangular structure. The point defect that acts as a cavity is centered on the intersection of two intersecting perpendicular pores with a radius that differs from the ones in the bulk of the crystal. We have performed supercell band structure calculations with up to $5\ifmmode\times\else\texttimes\fi{}5\ifmmode\times\else\texttimes\fi{}5$ unit cells. We find that up to five isolated and dispersionless bands appear within the 3D photonic band gap. For each isolated band, the electric-field energy is localized in a volume centered on the point defect, hence the point defect acts as a 3D photonic band gap cavity. The mode volume of the cavities resonances is as small as 0.8 ${\ensuremath{\lambda}}^{3}$ (resonance wavelength cubed), indicating a strong confinement of the light. By varying the radius of the defect pores we found that only donorlike resonances appear for smaller defect radius, whereas no acceptorlike resonances appear for greater defect radius. From a 3D plot of the distribution of the electric-field energy density we conclude that peaks of energy are found in sharp edges situated at the point defect, similar to how electrons collect at such features. This is different from what is observed for cavities in noninverted woodpile structures. Since inverse woodpile crystals can be fabricated from silicon by CMOS-compatible means, we project that single cavities and even cavity arrays can be realized, for wavelength ranges compatible with telecommunication windows in the near infrared.

Fabrication of diamond-like carbon-based two-dimensional photonic crystals

In this paper, we discuss the development of a process for fabricating diamond-like carbon (DLC)-based two-dimensional photonic crystals with a wider electronic bandgap and better thermostability than silicon (Si), which is used widely in nanophotonics. In the developed process, the DLC film was deposited on an Si substrate by RF plasma chemical vapor deposition, and the refractive index of the film could be changed from 1.8 to 1.95 by varying the RF power. We also theoretically show that a wide photonic bandgap can be obtained with these DLC-based photonic crystals, even though they have a low refractive index compared to pure diamond. Finally, we develop a process for fabricating DLC-based photonic crystal structures by using electron-beam lithography and inductively coupled plasma (ICP) etching techniques.

When and Why Like-Sized, Oppositely Charged Particles Assemble into Diamond-like Crystals

Like-sized, oppositely charged nanoparticles are known to assemble into large crystals with diamond-like (ZnS) ordering, in sharp contrast to analogous molecular ions and micrometer-scale colloids, which invariably favor more closely packed structures (NaCl or CsCl). Here, we show that these experimental observations can be understood as a consequence of ionic screening and the slight asymmetry in surface charge present on the assembling particles. With this asymmetry taken into account, free-energy calculations predict that the diamond-like ZnS lattice is more favorable than other 1:1 ionic structures, namely, NaCl or CsCl, when the Debye screening length is considerably larger than the particle size. A thermodynamic model describes how the presence of neutralizing counterions within the interstitial regions of the crystal acts to bias the formation of low-volume-fraction structures. The results provide general insights into the self-assembly of non-close-packed structures via electrostatic interactions.

Grounds for the application of fractional-order diffusion equations in channeling theory using the Langevin approach

Transverse-energy distribution densities in the case of ultrarelativistic proton channeling in the (100) planes of diamond-like crystals have been numerically calculated within the framework of the Langevin approach. Based on the self-similarity principle, the subdiffusion character of the motion under consideration has been established, which can be regarded as grounds for using fractional-order diffusion equations to adequately describe channeling and dechanneling processes mathematically.

Dispersion of optical and acoustic phonons in diamond and germanium crystals

The dispersion laws of the optical and acoustic branches in diamond-like crystals have been derived using idealized models of crystal lattices. Two types of analytical expressions have been proposed, whose parameters can be derived from inelastic neutron scattering experiments and the properties of acoustic waves. The calculation results are in satisfactory agreement with experimental data for the crystallographic directions [100], [110], and [111]. The group velocities of optical and acoustic phonons have been determined, and expressions for the effective mass of optical phonons have been derived.

Continuum strain-gradient elasticity from discrete valence force field model for diamond-like crystals

In this paper using polynomial approximation of the dispersion relations near the center of the first Brillouin zone, we construct a continuum model with internal length scale starting from the discrete valence force field model. As a consequence, and in agreement with a recent result by Maranganti and Sharma, we obtain an explicit estimate of the internal lengths which is ≃0.1A.