Bioengineering single crystal growth

Biomineralization is a "bottom-up" synthesis process that results in the formation of inorganic/organic nanocomposites with unrivaled control over structure, superior mechanical properties, adaptive response, and the capability of self-repair. While de novo design of such highly optimized materials may still be out of reach, engineering of the biosynthetic machinery may offer an alternative route to design advanced materials. Herein, we present an approach using micro-contact-printed lectins for patterning sea urchin embryo primary mesenchyme cells (PMCs) in vitro. We demonstrate not only that PMCs cultured on these substrates show attachment to wheat germ agglutinin and concanavalin A patterns but, more importantly, that the deposition and elongation of calcite spicules occurs cooperatively by multiple cells and in alignment with the printed pattern. This allows us to control the placement and orientation of smooth, cylindrical calcite single crystals where the crystallographic c-direction is parallel to the cylinder axis and the underlying line pattern.     

Adaptive nematic liquid crystal lens array with resistive layer

ABSTRACT

We propose an adaptive nematic liquid crystal (LC) lens array using a dielectric layer with low dielectric constant as resistive layer. With the resistive layer and periodic-arranged iridium tin oxide (ITO) electrodes, the vertical electric field across the LC layer varies linearly over the lens aperture is obtained in the voltage-on state. As a result, a centrosymmetric gradient refractive index profile within the LC layer is generated, which causes the focusing behaviour. As a result of the optimisation, a thin cell gap which greatly reduces the switching time of the LC lens array can be achieved in our design. The main advantages of the proposed LC lens array are in the comparatively low operating voltage, the flat substrate surface, the simple electrodes, and the uniform LC cell gap. The simulation results show that the focal length of the LC lens array can be tuned continuously from infinity to 3.99 mm by changing the applied voltage.     

Scanning-induced growth on single crystal calcite with an atomic force microscope

We report observations of localized growth on the (1014) surface of single-crystal CaCO3 in supersaturated solutions while scanning with the tip of an atomic force microscope (AFM). At low contact forces, AFM scanning strongly enhances deposition along preexisting steps. This enhancement increases rapidly with increasing solution supersaturation, and is capable of filling in multilayer etch pits to produce defect-free surfaces at the resolution of the AFM. Attempts to achieve similar deposition rates in the absence of scanning require high supersaturations that produce three-dimensional crystal nuclei, which are important defects. Localized deposition produced by drawing the AFM tip back and forth across step edges can produce monolayer deposits extending well over a micron from the scanned area. These tip-induced deposits provide convincing evidence for the importance of ledge diffusion in calcite crystal growth.     

ZSM-5单晶生长的研究

本文研究了DEA(二乙醇胺)-Na2O-SiO2-Al2O3-H2O体系中由晶种水热生长的ZSM-5单晶形貌和线性生长速度. 晶体外部晶面为轴面(100)、(010)及坡面(101)、(011). 在互相贯穿连生的各单晶之间, 其对称轴互成倾角. 在160-220℃范围内, 晶体线性生长速度保持恒定. 观察到单晶生长的诱导期. 由线性生长速度与温度的关系计算了生长活化能. 研究了反应物组成对晶面法线生长速度的影响、母液成分变化, 并分析了晶体的化学成分. 按晶体生长的基本原理及ZSM-5结构, 构想了实际上可能存在的ZSM-5单晶的面结构, 并估算了不同晶面上生长位的密度及其分布. 从面结构及沸石生长基元角度讨论了单晶生长机理的DEA的作用, 支持了生长基元为高聚态硅(铝)阴离子团的假设.     

Coalescence of nanobranches: a new growth mechanism for single crystal nanobelts

We report a fundamentally new growth mechanism for single crystalline nanobelts, namely, the growth and coalescence of nanobranches. The growth process of the nanobelts includes four typical steps such as nucleation and growth of the stem, nucleation and growth of the nanobranches at the expense of the stem, widening and geometrical coalescence of the nanobranches, and finally having nanobelts with perfect structure. The unique widening growth process of the nanobranches is apparently driven by the lattice distortion within the surface area of the stem. The continuous geometrical coalescence between the neighboring branches leads to the formation of the beltlike structures.     

A microchip to analyze single crystal growth and size-controllability

A microfluidic device to control single crystallization on the micron scale has been developed. The salt solution was stored in the nano-volume gaps between the arrays of protrudent circular plots in the microchip. The mixed organic solvent was injected into the chip as the counter diffusion phase for crystallization forming. This device provides a liquid-liquid interface through which only one phase flows while the other stays at the fixed plot. Therefore, it is possible to control the position of crystallization on the fixed plot. We can control the size and the uniformity of single crystals from 5 to 50 μm in length by adjusting the relative factors, such as interface lifetime, breeds of the mix-organic solvents and injecting velocities. The longer interface lifetime and lower organic solvent injecting velocities can bring up larger and more asymmetric crystals, which nearly shows the same trend compared with the macroscopic crystallization. Finally, the effect of the surfactant on the crystallization in the micro-device was studied. By adding the surfactant into the liquid-liquid interface, smaller sizes of crystals can be obtained without changing the crystal configuration. Supported by the National Natural Science Foundation of China (Grant No. 20775042) and the National Basic Research Program of China (Grant No. 2007CB714507)     

Applications of resistive heating in gas chromatography: A review

Gas chromatography is widely applied to separate, identify, and quantify components of samples in a timely manner. Increasing demand for analytical throughput, instrument portability, environmental sustainability, and more economical analysis necessitates the development of new gas chromatography instrumentation. The applications of resistive column heating technologies have been espoused for nearly thirty years and resistively heated gas chromatography has been commercially available for the last ten years. Despite this lengthy period of existence, resistively heated gas chromatography has not been universally adopted. This low rate of adoption may be partially ascribed to the saturation of the market with older convection oven technology, coupled with other analytical challenges such as sampling, injection, detection and data processing occupying research. This article assesses the advantages and applications of resistive heating in gas chromatography and discusses practical considerations associated with adoption of this technology.     

Platinum additive impacts on vapor-liquid-solid growth chemical interface for high-quality SiC single crystal films

Pt additive to Si-based flux in the vapor-liquid-solid (VLS) process for 4H–SiC epitaxial films has been successful in suppressing the step bunching as well as in promoting the step-flow growth mode at growth temperatures much lower than 2000 °C, as evidenced by in situ laser microscope observation of a model solution growth chemical interface. As a result, the SiC film surface became remarkably flat, exhibiting well-regulated step-and-terrace structures with narrow terrace widths and straight step lines; the polytype of 4H–SiC was much more stabilized in the grown SiC films even at a growth temperature of 1250 °C. Furthermore, there is little concern about incorporation of Pt atoms as an impurity into the grown SiC films so that their Schottky junction properties are almost as excellent as those of 4H–SiC single crystals.     

Structure and growth of single crystal SiP2 using flux method

A new orthorhombic phase of silicon diphosphide has been grown in Sn flux by using Gd as a mineralizer. It is a needle-like crystal and its structure has been determined through single crystal X-ray diffraction and elemental analysis. It crystallizes in the orthorhombic space group Pnma (No. 62, Z = 8) with cell parameters: a = 10.0908(19) Å, b = 3.4388(6) Å and c = 13.998(3) Å and the final R value is 0.0294. It has a layered structure that is closely related to the Pbam phase of SiP₂. Its optical band gap is 1.45 eV and it decomposes at 1002 K.     

Epitaxial single crystal surface patterning and study of physical and chemical environmental effects on crystal growth

For designing the responsive polymer brushes, and tuning the local and chemical surface responses to the external stimuli, the epitaxial single crystals were patterned by combination of bared surfaces of poly(ethylene glycol) (PEG) substrate, polymer homo-brushes constructed from poly(ethylene glycol)-b-polystyrene (PEG-b-PS) as well as poly(ethylene glycol)-b-poly(methyl methacrylate) (PEG-b-PMMA), and PEG-b-PS/PEG-b-PMMA mixed-brush channels. To achieve this target, various single crystals and epitaxial structures grown from dilute solutions through self-seeding approach were utilized as seeds to fabricate the next channels. The characteristics and morphologies of different channels were detectable by atomic force microscopy (AFM). The influence of chemical (solvent quality and interaction of substrate with different brushes) and physical (presence of brushes from another type in their vicinity) environments on crystallization was studied. Due to the effect of chemical environment, the PS brushes hampered the growth of PEG crystals at M _n ^PS?=?10,000 g/mol. However, the PMMA brushes allowed PEG crystals to grow completely at M _n ^PMMA =13,100 g/mol, and indicated their hindrance at higher molecular weights (here, M _n ^PMMA?=?17,100 g/mol). It was feasible to neutralize the mentioned hindrance through fabricating the channels with brushes having the highest hindrance (M _n ^PS?=?14,800 g/mol and M _n ^PMMA?=?17,100 g/mol), and altering the physical environment from homo- to mixed-brush morphology. The characteristics (thickness, tethering density, and domain size) of developed channels from a certain material, in all arrangements and in various channels were in good agreement with those of corresponding non-epitaxial single crystals grown under the same conditions.     

Video-tape observation of the crystal growth and morphology of colloidal single crystals

Crystal growth and morphology of colloidal crystals of silica spheres (81.2 nm in diameter) are observed directly on a video-tape camera. Crystal growth from the round-shaped, small single crystals to the angular-shaped ones is clear. It is observable that the single crystals are packed densely and separated from each other with the grain boundaries. The morphology of colloidal crystals is quite similar to that of typical crystals such as metals, proteins, and ice.     

Investigating interfacial parameters with platinum single crystal electrodes

The concepts of total and free charge of platinum single crystal electrodes are revised in this paper, together with the associated concepts of potential of zero total and free charge. Total charges can be measured from CO displacement method. Results on solution of different pH are described. A novel buffer composition is used to attain pH values close to neutrality while avoiding interferences from anion adsorption processes. Stress is made on the fact that free charges are not accessible through electrochemical measurement for systems at equilibrium since adsorption processes (hydrogen and hydroxyl) interfere with free charge determination. Still, a model is described that allows, under some assumptions, extract free charge values and the corresponding potential of zero free charge for Pt(111) electrodes. On the other hand, fast measurement outside equilibrium can separate free charges from adsorption processes based on their different time constant. In this way, the laser induced temperature jump experiment allows determination of the potential of maximum entropy, a magnitude that is intimately related with the potential of zero free charge. Values of the potential of maximum entropy as a function of pH are given for the different basal planes of platinum.     

Improvement of Nd:GGG crystal growth process under dynamic atmosphere composition

In this paper, the temperature dependency of the required oxygen on the quality of Nd:GGG crystal during the growth process has been investigated. Based on the thermodynamic analysis, the oxygen partial pressure in the surrounding vapor phase should be as low as possible through heating the raw material at lower temperatures to prevent the oxidation of iridium to IrO₂ (s). In order to eliminate the volatilization of Ga₂O₃, the oxygen was charged into the gas atmosphere (N₂) near the Nd:GGG melting point. Powder X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) were employed to characterize the crystal quality under different growth atmosphere. The experimental results confirm the validity of thermodynamic calculations. It was predicted that charging the required oxygen at about 1950 K could reduce the iridium loss rate to about 36%. Consequently, it would be expected to acquire more favorable Nd:GGG crystals with quite improved properties by applying the accurate growth conditions.     

Synthesis of polycrystalline materials of SrWO4 and growth of its single crystal

The polycrystalline materials of SrWO₄ were synthesized by means of a solid phase reaction with analytical purity SrCO₃ and WO₃ at high temperature. The transparent SrWO₄ single crystal with dimension of ϕ 22 mm×40 mm has been successfully grown along a-axis by Czochralski method. X-ray powder diffraction results show that the as-grown SrWO₄ single crystal belongs to tetragonal system and I4₁/a space group. The measured density of SrWO₄ is 6.439 g·cm⁻³ by buoyancy method. The effective segregation coefficients of W and Sr elements in SrWO₄ single crystal are close to 1 by the X-ray fluorescence method. __________ Translated from Journal of Shandong University (Natural Science), 2005, 40(4) (in Chinese)     

The growth of single crystal silver wires at the nitrobenzene|water interface

Single crystal silver wires can be grown at the nitrobenzene|water interface when silver ions dissolved in the aqueous phase are reduced by decamethyl ferrocene dissolved in the nitrobenzene phase. The successful growth of these wires depends on a number of experimental conditions, most prominently on the concentration ratio of reactants, nucleation rates, shape of formed nuclei, and wettability of nuclei. The size-time dependence can be modeled on the basis of microelectrode behavior of the silver nuclei and wire. AFM, SEM, light microscopy and single crystal X-ray diffraction has been applied to study the morphology of the silver nuclei and wires.     

Nucleation and growth phenomena in nanosized electrochemical systems for resistive switching memories

The impact of the electrochemical nucleation on the switching kinetics in many nanoscaled redox-based resistive switching memories is critically discussed. In the case of the atomic switch, the system is site invariant and the nucleation process is strictly localized below the STM tip. Using RbAg₄I₅ solid electrolyte, nucleation was found to be rate limiting. The electrochemical metallization memory cells (gapless type atomic switch) operate at conditions closer to the conventional nucleation. They introduce additional difficulties for interpretation of the experimental results due to formation of hillocks, of surface oxide barrier films, induction of strain, and the influence of the high electric field. In valence change memories, the nucleation seems to be less important because of the higher applied voltages. The results are discussed in the context of the atomistic theory of electrochemical nucleation. We believe that re-analysis of the experimental data for many systems will reveal that the nucleation is limiting the switching time.     

Fast temperature programming on a stainless-steel narrow-bore capillary column by direct resistive heating for fast gas chromatography

A direct resistive-heating fast temperature programming device for fast gas chromatography was designed and evaluated. A stainless-steel (SS) capillary column acted both as a separation column and as a heating element. A fast temperature controller with the deviation derivative proportional-integral-derivative (DDPID) control algorithm, which was suitable for ramp control using ramp-to-setpoint function, was used to facilitate the fast pulse heating. The SS resistive-heating column can generate linear temperature ramps up to 10 degrees C/s and can re-equilibrium from 250 degrees C down to 50 degrees C within 30s. With n-alkanes as the test analytes, the relative standard deviations (RSDs) of retention time were between 0.19 and 0.59% and the RSDs of their peak areas were less than 4% for all but one. The results indicated that this technique could be used for both qualitative and quantitative analysis. Phenolic and nitroaromatic compounds were also analyzed by using the SS resistive-heated system. The combination of a short narrow-bore SS column and rapid heating rates provides sufficient separation efficiency for relatively simple mixtures at drastically reduced analysis time. The total analysis time including equilibration time was less than 2 min for all test mixtures in this study.