Giant Grain Research Articles

Giant Grain Growth of 2,5-Di(2-thienyl)-1H-pyrrole Crystal Films: Kinetic Analysis of Self-Crystallization from Its Supercooled Liquid in Vacuum Deposition

Self-crystallization of 2,5-di(2-thienyl)-1H-pyrrole (DTP) from its supercooled liquid in vacuum deposition was demonstrated. In situ infrared absorption spectroscopy and polarizing microscope observation techniques were employed to investigate the kinetic effect of three kinds of substrates whose surfaces were differently treated on the phase transformation during deposition. Essentially, irrespective of the kind of substrates, the crystallization was found to proceed in a steady-state manner, where the supercooled liquid could be regarded as an intermediate whose amount was kept almost constant during the deposition. After stopping the deposition, the supercooled liquid underwent further phase transformation to complete the crystallization, which process could be well understood with the Avrami model. Giant grain growth of DTP crystal films was found on a substrate, which was uniformly covered with a thin ionic liquid layer, and their crystallinity was much improved.

Enhanced Strength and Hardness of AS41 Magnesium Alloy Fabricated by Selective Laser Melting

AS41 magnesium alloy possesses outstanding performance features such as light weight, high strength to toughness ratio and excellent heat resistance due to the addition of Si element, while traditional casting methods are prone to inducing large grain size and coarse Mg2Si phase. In this study, we first reported utilizing the selective laser melting (SLM) technique, fabricating AS41 samples and exploring the effect of laser energy densities on the metallurgical quality by characterizing and investigating the microstructure and mechanical properties. Results showed that the optimal laser energy density range was 60 to 100 J/mm3. Average grain size of only 2.9 μm was obtained with weak texture strength of 1.65 in {0001} orientation. Meanwhile, many dispersed secondary β-Mg17Al12 and Mg2Si phases were distributed inside the α-Mg matrix. It was confirmed that the SLM process introduced more grain recrystallization, inducing giant high-angle grain boundaries (HAGBs) and hindering the movement of dislocations, therefore forming dislocation strengthening while achieving grain refinement strengthening. Finally, three times the ultimate tensile strength of 313.7 MPa and higher microhardness of 96.4 HV than those of the as-cast state were obtained, verifying that the combined effect of grain refinement, solid solution strengthening and precipitation strengthening was responsible for the increased strength. This work provides new insight and a new approach to preparing AS41 magnesium alloy.

Thermal-Radiation-Driven Ultrafast Crystallization of Perovskite Films Under Heavy Humidity for Efficient Inverted Solar Cells.

Fabricating perovskite solar cells (PSCs) in air is conducive to low-cost commercial production; nevertheless, it is rather difficult to achieve comparable device performance as that in an inert atmosphere because of the poor moisture toleration of perovskite materials. Here, the perovskite crystallization process is systematically studied using two-step sequential solution deposition in an inert atmosphere (glovebox) and air. It is found that moisture can stabilize solvation intermediates and prevent their conversion into perovskite crystals. To address this issue, thermal radiation is used to accelerate perovskite crystallization for integrated perovskite films within 10s in air. The as-formed perovskite films are compact, highly oriented with giant grain size, superior photoelectric properties, and low trap density. When the films are applied to PSC devices, a champion power conversion efficiency (PCE) of 20.8% is obtained, one of the best results for air-processed inverted PSCs under high relative humidity (60±10%). This work substantially assists understanding and modulation to perovskite crystallization kinetics under heavy humidity. Also, the ultrafast conversion strategy by thermal radiationprovides unprecedented opportunities to manufacture high-quality perovskite films for low-temperature, eco-friendly, and air-processed efficient inverted PSCs.

Giant Grain Growth in (K,Na)NbO3 Ceramics

In this manuscript, an interesting phenomenon is reported. It has been reported that the growth of single crystals is observed in donor-doped (K,Na)NbO3 (KNN)-based ceramics. It is very interesting that the growth happens without the addition of a seed. The growth of huge grains (single crystal, approximately 30 mm,) occurs due to the abnormal grain growth (AGG) in KNN-based ceramics. In the AGG compositions, moreover, the seed plates can be synthesized by not topochemical reaction but simple molten salt synthesis (SMSS) which is a simple-and-cheap process. They can be a good candidate for the seeds at reactive templated grain growth (RTGG) or templated grain growth (TGG) process.

Preliminary study on quality and storability of giant hybrid rice grain

Grain quality is one of the key targets for rice breeding. Two-meter-high giant rice, Xiangju-1, is a new high-quality restorer line of hybrid rice. Here, the grain quality and storability of three varieties Jufeng 5 (JF5), Jufeng 6 (JF6), and Jufeng 8 (JF8) were studied. The grain sizes of three giant hybrid rice varieties (JFs) were larger than that of the control rice Jingliangyou 1212 (1212). With respect to nutritional value, the three JFs varieties had similar protein content (~8%) but much higher fat content (>0.8%) than 1212. In addition, JF6 had better storability than JF8 when assessed by controlled deterioration treatment (CDT). RNA-seq analysis revealed that the heatmaps of differentially expressed genes in JF6 and JF8 were similar after 20 days of CDT when compared with 0 days. Of particular interest were the different mRNA levels of several genes related to the pathways of DNA damage response and abscisic acid biosynthesis in JF6 and JF8 after 20 days of CDT. Taken together, the data suggested that JF6 had better grain quality and storability than the other hybrid varieties, and several candidate genes for seed storability were identified.

Intra-grain polarized infrared spectroscopy realized in domain-engineered Zn2GeO4 ceramics

Intra-grain infrared spectroscopy was carried out on a domain-engineered ceramic with abnormally large grains. The model system used was a polycrystalline Zn2GeO4 ceramic sample, with a rhombohedral R3¯ crystal structure and giant grain microstructure (50–350 μm). The micro-infrared spectra unveiled preferential crystal orientations for the different grains. Polarized spectra revealed well-defined crystallographic domains inside the ceramic grains. Appropriate crystallographic planes for full assignment of the infrared modes were found by polarized infrared light. This allowed the first realization of a polarization-resolved symmetry assignment of an as-grown ceramic material. A sound description of the polar phonon features of rhombohedral Zn2GeO4 is then presented. Also, an infrared spectroscopic mapping of the crystallographic domains inside the ceramic grains is demonstrated.

Scalable methods for ultra-smooth platinum in nanoscale devices

Ultra-smooth metal structures are increasingly important in nanoscale device applications, from photonics to molecular electronics and 2D material growth. We describe three methods for achieving ultra-smooth platinum: patterned template stripping, chemical mechanical polishing and giant grain growth. Specifically, we demonstrate 1) the first use of spin-on glass as an adhesive for the transfer of a patterned platinum film via template stripping, enabling the film to be exposed to harsher solvents and at higher temperatures; 2) an updated CMP process for platinum with slurry materials that are currently available; 3) a giant grain growth process on a 4″ quartz substrate that uses a thinner Pt film than previously reported. Overall, root mean squared film roughness was decreased from ~14 Å for as-deposited platinum to <4 Å, while improving on scalability and compatibility subsequent processing of pre-existing techniques.

Oxygen-induced giant grain growth in Ag films

Thin film crystallites typically exhibit normal or abnormal growth with maximum grain size limited by energetic and geometric constraints. Although epitaxial methods have been used to produce large single crystal regions, they impose limitations that preclude some compelling applications. The generation of giant grain thin film materials has broad implications for fundamental property analysis and applications. This work details the production of giant grains in Ag films (2.5 μm-thick), ranging in size from ≈50 μm to 1 mm, on silicon nitride films upon silicon substrates. The presence of oxygen during film deposition plays a critical role in controlling grain size and orientation.

The dust mass in z &amp;gt; 6 normal star-forming galaxies

Abstract We interpret recent ALMA observations of z &amp;gt; 6 normal star-forming galaxies by means of a seminumerical method, which couples the output of a cosmological hydrodynamical simulation with a chemical evolution model which accounts for the contribution to dust enrichment from supernovae, asymptotic giant branch stars and grain growth in the interstellar medium. We find that while stellar sources dominate the dust mass of small galaxies, the higher level of metal enrichment experienced by galaxies with Mstar &amp;gt; 109 M⊙ allows efficient grain growth, which provides the dominant contribution to the dust mass. Even assuming maximally efficient supernova dust production, the observed dust mass of the z = 7.5 galaxy A1689-zD1 requires very efficient grain growth. This, in turn, implies that in this galaxy the average density of the cold and dense gas, where grain growth occurs, is comparable to that inferred from observations of quasar (QSO) host galaxies at similar redshifts. Although plausible, the upper limits on the dust continuum emission of galaxies at 6.5 &amp;lt; z &amp;lt; 7.5 show that these conditions must not apply to the bulk of the high-redshift galaxy population.

Giant secondary grain growth in Cu films on sapphire

Single crystal metal films on insulating substrates are attractive for microelectronics and other applications, but they are difficult to achieve on macroscopic length scales. The conventional approach to obtaining such films is epitaxial growth at high temperature using slow deposition in ultrahigh vacuum conditions. Here we describe a different approach that is both simpler to implement and produces superior results: sputter deposition at modest temperatures followed by annealing to induce secondary grain growth. We show that polycrystalline as-deposited Cu on α-Al2O3(0001) can be transformed into Cu(111) with centimeter-sized grains. Employing optical microscopy, x-ray diffraction, and electron backscatter diffraction to characterize the films before and after annealing, we find a particular as-deposited grain structure that promotes the growth of giant grains upon annealing. To demonstrate one potential application of such films, we grow graphene by chemical vapor deposition on wafers of annealed Cu and obtain epitaxial graphene grains of 0.2 mm diameter.

Giant magnetoimpedance and grain boundary effect in La0.75Ba0.25MnO3 sol–gel manganite

The La0.75Ba0.25MnO3 sol–gel manganite shows a typical dc low field magnetoresistance (LFMR) effect at low temperature. Besides the sharp resistance peak representing the metal–insulator transition around Curie temperature, another broad peak associated with the effect of grain boundaries could be observed around 260K. At low frequencies, such double peaks in ac resistance also occur. With increasing ac frequency, skin effect gradually enhances, the peak associated with the grain boundaries becomes less pronounced. At 0.5MHz, beside the peak of ac magnetoresistance ΔR/R0 at Curie temperature, the ac ΔR/R0 increases with decreasing temperature, since the ac resistance is strongly dependant on dc resistivity at low frequency. With increasing ac frequency, the peak of ac ΔR/R0 at Curie temperature becomes weak and almost disappears, as the ac ΔR/R0 strongly depends upon variation of magnetic-permeabilities at high frequencies. The magnetoreactance originates mainly from the change of permeability induced by the field. At 300K, the value of magnetoimpedance ΔZ/Z0 for La0.75Ba0.25MnO3 sol–gel polycrystalline sample can reach −49% at f=4MHz under a very small field of 500Oe.

THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from lsim1 to 10 M JUP, and accretion rates ranging from lsim10-11 to 10-7.7 M \odot yr-1. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.

Magnetotransport Properties of Co-Au Granular Alloys

A series of Cox-Au1-x granular alloys was grown using pulsed-current electrodeposition on polyimide substrates. The relationship between the giant magnetoresistance effect, saturation magnetization, and grain size was examined as the deposition current density and annealing temperatures were changed. A maximum magnetoresistance (MR) ratio of 4.5 % was obtained. The magnetization and ferromagnetic grain size of the as-deposited and annealed alloy films were examined against the deposition current density. The saturation magnetization decreased as the composition of Au was increased for both the alloys deposited at the current densities of 1 and 5 mA/cm2. The total magnetic moment further decreased on annealing. The grain size is found to be highly influenced by both the deposition current density and temperature. A low temperature magnetization measurement suggested that the ferromagnetic grain size decreases with increase in current densities. For the annealed samples, the ferromagnetic grain sizes were found to be dispersed in the Au matrix with different diameters. The decrease in magnetic moments with annealing is correlated with the grain size of the Co and its distribution in the gold matrix. The MR ratio increased with the increase in the deposition current density as a result of the formation of smaller grain size at higher deposition current densities.

Formation of giant crystalline grain via delayed growth process driven by organic molecular anisotropy

The growth of (001)-oriented pentacene (${\text{C}}_{22}{\text{H}}_{14}$, Pn) thin films on silicon surfaces has been extensively studied to elucidate the role of molecular anisotropy in nucleation and island evolution in organic film growth. In situ real-time low-energy electron microscopy studies of growth of Pn revealed a delayed, low-density nucleation that could be related to the difference in the orientation of this anisotropic molecule in its diffusing state and in the crystalline film. In contrast to the growth of Pn on self-assembled monolayers or ${\text{SiO}}_{2}$, we observed a delayed nucleation and formation of extraordinarily large grains (in submillimeter scale) on semiconducting $\ensuremath{\alpha}\sqrt{3}\text{-Bi-Si}(111)$ and on semimetallic Bi(0001)/Si(111) with a continuation in film growth after stopping Pn deposition. The delayed and very low-density nucleation and continuing growth after stopping deposition could be explained by a incorporation-limited growth processes resulted from a large energy barrier for Pn nucleation in standing-up orientation, as the molecule needs to reorient itself from a lying-down, diffusing state in order to build into the crystalline film.

(K,Na,Li)NbO3系材料の巨大粒子成長と圧電特性

(K,Na,Li)NbO3系材料の巨大粒子成長と圧電特性

Grain Boundary and Size Effect on the Dielectric, Infrared and Raman Response of SrTiO3 Nanograin Ceramics

The recently revealed giant grain size effect on dielectric properties in undoped SrTiO 3 ceramics (J. Petzelt et al., J. Phys.: Condens. Matter 19 , 196222 (2007) and references therein), was extended to smaller grains of 80 nm mean grain size. Like for previously studied ceramics with larger grain size, in addition to dielectric permittivity also the infrared and Raman responses were studied and discussed. It was shown that the reduced effective permittivity is fully accounted for by the infrared soft mode behaviour and, similar to single crystals and other ceramics studied, no dielectric dispersion appears below the THz frequency range. The rather universal (independent of the grain size and sintering process) double dead layer structure was proposed to be responsible for the observed changes in the infrared and Raman spectra, allowing the grain core to keep the single crystal dielectric function. The outer dead layer shell (obviously charged due to an oxygen deficit) is very thin (∼ 1 nm) having frequency and temperature independent low permittivity (∼ 10) and is responsible for the static permittivity suppression. The inner layer of only slightly distorted perovskite structure is polar with local polarization normal to grain boundaries gradually decreasing towards the grain centre. This polarization and/or the thickness of the polar layers, which compensate the charged grain boundaries, appear to increase on decreasing temperature, particularly below the structural phase transition. Its nature is still not fully understood. In agreement with our previous suggestions, from the Raman data it can be also concluded that in the low-temperature tetragonal phase of all SrTiO 3 ceramics, the local tetragonal axes tend perpendicular to the grain boundaries and the tetragonality is strongly reduced compared to single crystals.

Inside Front Cover: Perfect Bi4Ti3O12 Single‐Crystal Films via Flux‐Mediated Epitaxy (Adv. Funct. Mater. 4/2006)

AbstractFlux‐mediated epitaxy has been developed for ferroelectric Bi4Ti3O12 single‐crystal film growth, as shown on the inside cover. The key point is the selection of an appropriate flux material. A combinatorial high‐throughput screening technique reported by Matsumoto and co‐workers on p. 485 has led to the successful discovery of the novel flux composition, Bi–Cu–O, for Bi4Ti3O12 single‐crystal film growth. This flux‐mediated epitaxy is not limited to oxide epitaxy, but is also widely applicable to various promising materials for the realization of non‐Si‐based electronics, such as nitrides, carbides, and halides.Excellent crystallinity of material films and atomic control of their surface/interface, sufficient for the realization of their optimal physical properties, are technological premises for modern functional‐device applications. Bi4Ti3O12 and related compounds attract much interest as highly insulating, ferroelectric materials for use in ferroelectric random‐access memories. However, it has been difficult thus far for Bi4Ti3O12 films to satisfy such requirements when formed using vapor‐phase epitaxy, owing to the high volatility of Bi in a vacuum. Here, we demonstrate that flux‐mediated epitaxy is one of the most promising and widely applicable concepts to overcome this inevitable problem. The key point of this process is the appropriate selection of a multi‐component flux system. A combinatorial approach has led to the successful discovery of the novel flux composition of Bi–Cu–O for Bi4Ti3O12 single‐crystal film growth. The perfect single‐crystal nature of the stoichiometric Bi4Ti3O12 film formed has been verified through its giant grain size and electric properties, equivalent to those of bulk single crystals. This demonstration has broad implications, opening up the possibility of preparing stoichiometric single‐crystal oxide films via vapor‐phase epitaxy, even if volatile constituents are required.

Perfect Bi4Ti3O12 Single‐Crystal Films via Flux‐Mediated Epitaxy

AbstractExcellent crystallinity of material films and atomic control of their surface/interface, sufficient for the realization of their optimal physical properties, are technological premises for modern functional‐device applications. Bi4Ti3O12 and related compounds attract much interest as highly insulating, ferroelectric materials for use in ferroelectric random‐access memories. However, it has been difficult thus far for Bi4Ti3O12 films to satisfy such requirements when formed using vapor‐phase epitaxy, owing to the high volatility of Bi in a vacuum. Here, we demonstrate that flux‐mediated epitaxy is one of the most promising and widely applicable concepts to overcome this inevitable problem. The key point of this process is the appropriate selection of a multi‐component flux system. A combinatorial approach has led to the successful discovery of the novel flux composition of Bi–Cu–O for Bi4Ti3O12 single‐crystal film growth. The perfect single‐crystal nature of the stoichiometric Bi4Ti3O12 film formed has been verified through its giant grain size and electric properties, equivalent to those of bulk single crystals. This demonstration has broad implications, opening up the possibility of preparing stoichiometric single‐crystal oxide films via vapor‐phase epitaxy, even if volatile constituents are required.

Location control of giant silicon grains using organic lenses

We studied the location control of a giant grain of polycrystalline silicon produced by Ni-mediated crystallization of amorphous silicon (a-Si) using a cap layer. An organic lens made of acryl was used for the focusing of light for the seed formation and subsequent crystallization. A single grain 62μm in diameter was made using an 80-μm-square SiNx cap layer on the a-Si. The position of a thin-film transistor (TFT) on a grain can be controlled, so that a single grain TFT can be fabricated at a predetermined position without use of the laser annealing technique.

Response of three annual weeds to corn population density and nitrogen fertilization timing

Abstract The limited understanding of soil nitrogen (N) effects on crop yield loss to weeds prevents the refinement of integrated weed management to consider soil fertility. A 3-yr field experiment compared ammonium nitrate applications before corn emergence (PRE N) or in late June (POST N) on the growth of giant foxtail, velvetleaf, common waterhemp, and grain corn. The N responses were studied in corn population densities of 5.4 and 7.9 plants m−2 to understand how crop density might influence N effects on yield loss. In late June of each year, leaf areas were 25% (corn), 64% (velvetleaf), and 41% (giant foxtail) lower with POST N than with PRE N. Common waterhemp leaf area in late June was unaffected by N timing. Corn population density did not affect weed shoot dry weights evaluated in late June. Corn and velvetleaf heights in late July were up to 19 and 48% lower, respectively, with POST N compared with PRE N. Common waterhemp and giant foxtail heights in late July were unaffected by N timing. Corn y...