Solution-grown Single Crystals Research Articles

Reproducible high-quality perovskite single crystals by flux-regulated crystallization with a feedback loop

Controlling the linear growth rate, a critical factor that determines crystal quality, has been a challenge in solution-grown single crystals due to complex crystallization kinetics influenced by multiple parameters. Here we introduce a flux-regulated crystallization (FRC) method to directly monitor and feedback-control the linear growth rate, circumventing the need to control individual growth conditions. When applied to metal halide perovskites, the FRC maintains a stable linear growth rate for over 40 h in synthesizing CH3NH3PbBr3 and CsPbBr3 single crystals, achieving outstanding crystallinity (quantified by a full width at half-maximum of 15.3 arcsec in the X-ray rocking curve) in a centimetre-scale single crystal. The FRC is a reliable platform for synthesizing high-quality crystals essential for commercialization and systematically exploring crystallization conditions, maintaining a key parameter—the linear growth rate—constant, which enables a comprehensive understanding of the impact of other influencing factors.

Scanning Photocurrent Microscopy in Single Crystal Multidimensional Hybrid Lead Bromide Perovskites.

We investigated solution-grown single crystals of multidimensional 2D-3D hybrid lead bromide perovskites using spatially resolved photocurrent and photoluminescence. Scanning photocurrent microscopy (SPCM) measurements where the electrodes consisted of a dip probe contact and a back contact. The crystals revealed significant differences between 3D and multidimensional 2D-3D perovskites under biased detection, not only in terms of photocarrier decay length values but also in the spatial dynamics across the crystal. In general, the photocurrent maps indicate that the closer the border proximity, the shorter the effective decay length, thus suggesting a determinant role of the border recombination centers in monocrystalline samples. In this case, multidimensional 2D-3D perovskites exhibited a simple fitting model consisting of a single exponential, while 3D perovskites demonstrated two distinct charge carrier migration dynamics within the crystal: fast and slow. Although the first one matches that of the 2D-3D perovskite, the long decay of the 3D sample exhibits a value two orders of magnitude larger. This difference could be attributed to the presence of interlayer screening and a larger exciton binding energy of the multidimensional 2D-3D perovskites with respect to their 3D counterparts.

Uniaxial compression of [001]-oriented CaFe2As2 single crystals:the effects of microstructure and temperature on superelasticity Part I: Experimental observations

Micropillar compression experiments on [001]-oriented CaFe2As2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit of over 10%. The collapsed tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. In this study, therefore, we investigated how the microstructure and temperature affect the superelasticity of [001]-oriented CaFe2As2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe2As2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe2As2 under uni-axial compression.

Uniaxial Compression of [001]-Oriented CaFe 2As 2 Single Crystals: The Effects of Microstructure and Temperature on the Superelasticity, Part I: Experimental Observations

Micropillar compression experiments on [001]-oriented CaFe 2 As 2 single crystals have recently revealed the existence of superelasticity with a remarkably high elastic limit over 10%. The collapsed tetragonal phase transition, which is a uni-axial contraction process in which As-As bonds are formed across an intervening Ca-plane, is the main mechanism of superelasticity. Usually, superelasticity and the related structural transitions are affected strongly by both the microstructure and the temperature. In this study, therefore, we investigated how the microstructure and temperature affect the superelasticity of [001]-oriented CaFe 2 As 2 micropillars cut from solution-grown single crystals, by performing a combination of in-situ cryogenic micromechanical testing and transmission electron microscopy studies. Our results show that the microstructure of CaFe 2 As 2 is influenced strongly by the crystal growth conditions and by subsequent heat treatment. The presence of Ca and As vacancies and FeAs nanoprecipitates affect the mechanical behavior significantly. In addition, the onset stress for the collapsed tetragonal transition decreases gradually as the temperature decreases. These experimental results are discussed primarily in terms of the formation of As-As bonds, which is the essential feature of this mechanism for superelasticity. Our research outcomes provide a more fundamental understanding of the superelasticity exhibited by CaFe 2 As 2 under uni-axial compression.

Quantifying the Chain Folding in Polymer Single Crystals by Single-Molecule Force Spectroscopy.

Chain folding is a motif of polymer crystallization, which is essential for determining the crystallization kinetics. However, the experimental quantification of the chain folding remains a challenge because of limited instrumental resolution. Here, we quantify chain folding in solution-grown single crystals by using atomic force microscopy (AFM)-based single-molecule force spectroscopy. The fingerprint spectrum of force-induced chain motion allows us to decipher the adjacent and nonadjacent re-entry folding with spatial resolution of subnanometers. The average fractions of adjacent re-entry folds ⟨f⟩ are in the range 91-95% for polycaprolactone, poly-l-lactic acid, and polyamide 66, which is higher than the values determined by other classical technologies. The established single-molecule method is applicable to a broad range of crystalline polymer systems with different chain conformations or compositions.

Crystalline and pseudo-crystalline phases of polyacrylonitrile from molecular dynamics: Implications for carbon fiber precursors

The molecular structure of spun polyacrylonitrile (PAN) fibers used in the production of carbon fibers (CFs) is known to critically affect the microstructure and, consequently, the properties of the final fiber. We use molecular dynamics (MD) simulations to predict the molecular structure of the crystalline regions of spun PAN. We characterized how tacticity and the arrangement of torsional angles along the backbone affect packing of the chains and lattice parameters. Most configurations, regardless of tacticity, loose periodicity along the chain axis during relaxation resulting in pseudo-crystalline structures. Simulated X-ray diffraction (XRD) patterns of these pseudo-crystalline structures show excellent agreement with recent experimental measurements and reveal that intermolecular spacing decreases as backbone trans/gauche ratio increases corresponding to different experimental conditions. Stability and stiffness also increase as backbone trans/gauche ratio increases. A syndiotactic system with planar zig-zag configuration results in crystalline order along the c axis; this more ordered structure has the lowest potential energy and highest stiffness of all structures studied. The predicted XRD pattern differs significantly from those of the pseudo-crystalline structures but, interestingly, it matches the multi-peak fingerprint reported experimentally in solution-grown single crystals of PAN. The simulations shed light into long-standing discrepancies in XRD patters of PAN precursors.

RETRACTED ARTICLE: A focus on the features of polyaniline nanofibres prepared via developing the single crystals of their block copolymers with poly(ethylene glycol)

Poly(ethylene glycol) (PEG)–polyaniline (PANI) diblock and triblock copolymers were synthesized via copolymerization of aniline with amine-terminated PEG by interfacial polymerization using sulphuric acid as dopant and ammonium peroxydisulfate (APS) as well as potassium hydrogen diiodate (PHD) as oxidants. The PHD-based synthesized PANI nanorods possessed longer lengths, narrower diameter distribution and higher conductivity. The electroactivity of synthesized copolymers was characterized using ultraviolet–visible (UV–Vis) spectrometry, cyclic voltammetry (CV) and resistivity measurement. Even in the presence of dielectric PEG blocks, the synthesized block copolymers had a conductivity around 3 S $$\hbox {cm}^{-1}$$ . In a further step, the solution-grown single crystals were prepared to investigate the general features of grafted PANI nanorods using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Based on AFM and SAXS analyses, the bimodal gel permeation chromatography (GPC) traces obtained from the block copolymers were originated from the diameter distribution of nanofibres, not from the dispersity of their lengths and molecular weights.

Defect structures in solution-grown single crystals of the intermetallic compound Ag3Sn

The compound Ag3Sn adopts the ordered orthorhombic D0a Cu3Ti-type structure. It exhibits an unusual low yield stress and high ductility for an intermetallic compound, but the reasons for these effects are not clear. Here, we report an electron microscopy study on the defects present in solution-grown Ag3Sn single crystals that have deformed during the decanting and subsequent handling processes. It is found that the crystals contain two types of lenticular deformation twins: {011}-type and {211}-type. These twins interpenetrate with no evidence of cracking at the intersections. The crystals also contain high densities of dislocations including long straight dipoles with b = ± [010] and shorter curved segments and loops with b = [ $$ 10\bar{2} $$ ] and [001]. It is inferred that the dipoles are artifacts of specimen preparation that climb in from the cross-sectional sample surfaces, whereas the shorter segments are deformation debris. If a combination of twinning and dislocation glide of the types observed here were to form concurrently during general deformation of Ag3Sn, then they could provide the necessary number of independent deformation modes to accommodate an arbitrary plastic strain, which might help to explain the unusual ductility of this compound.

Non-dissipative internal optical filtering with solution-grown perovskite single crystals for full-colour imaging

Herein we demonstrate that solution-grown single crystals of semiconducting methylammonium lead halide perovskites (MAPbX3, where MA=CH3NH3+, X=Cl−, Br− and Br/I−) can be used as semiconductor absorbers for full-colour imaging. A one-pixel photodetector prototype was constructed by stacking three layers of blue-, green- and red-sensitive MAPbCl3, MAPbBr3 and MAPb(Br/I)3 crystals, respectively. The prototype detector was demonstrated to recognize and faithfully reproduce coloured images by recombination of the signals from each individual colour channel. This layered structure concept, besides imparting a two- to three-fold reduction in the number of required pixels, also offers several other advantages over conventional technologies: three times more efficient light utilization (and thus higher sensitivity) than common Bayer scheme devices based on dissipative optical filters, colour moiré suppression and no need for de-mosaic image processing. In addition, the direct band gap structure of perovskites results in optical absorption that is several orders of magnitude greater than silicon. This opens a promising avenue towards the reduction of pixel-size in next-generation devices as compared with conventional silicon-based technologies.

Detection of gamma photons using solution-grown single crystals of hybrid lead halide perovskites

Cheap and sensitive gamma-ray detectors are desired for defence, medical and research applications. Solid-state gamma-radiation detectors made from solution-grown perovskites have now been demonstrated for multiple practical applications.

Spatially resolved micro-photoluminescence imaging of porphyrin single crystals

We describe the collection of both time-resolved and steady-state micro-photoluminescence data from solution-grown single crystals of 5,15-bis(4-carbomethoxyphenyl)porphyrin (BCM2PP). Linking molecular orientation and structure with excited-state dynamics is crucial for engineering efficient organic solar cells, light-emitting diodes, and related molecular electronics. Photoluminescence features of single porphyrin crystals were imaged using a laser scanning confocal microscope equipped with time-correlated single photon counting (TCSPC). We show enhanced exciton lifetimes (τs1=2.6ns) and stronger steady-state emission in crystalline BCM2PP samples relative to semicrystalline thin films (τs1=1.8ns).

Highly-emissive solution-grown furan/phenylene co-oligomer single crystals

Solution-grown single crystals of furan/phenylene co-oligomer combine efficient charge transport properties and high fluorescence efficiency.

Thermolability, enzymatic degradation and aminolysis of solution-grown single crystals of novel poly(ethylene succinate-co-5mol% trimethylene succinate)s

Solution-grown single crystals of poly(ethylene succinate-co-trimethylene succinate)s (PETSA) were hydrolyzed by polyhydroxybutyrate (PHB) depolymerase from Ralstonia pickettii T1. Enzymatic degradation proceeded from the edges of the lamellar crystals, yielding serrated contours and small crystal fragments. On the other hand, single PETSA crystals were aminolyzed in 20 % aqueous methylamine solution to remove the folded chain regions, and enzymatically degraded using PHB depolymerase to remove poly(trimethylene succinate)—PTSA—components at the surfaces of single aminolyzed crystals. It was found that a small amount of PTSA component could be incorporated into the poly(ethylene succinate)—PESA—mother crystal lattice irrespective of the PTSA content.

Vickers microhardness studies on solution-grown single crystals of potassium boro-succinate

The semiorganic crystals of potassium boro-succinate (KBS) were grown by slow evaporation method. KBS crystallizes in monoclinic system which was confirmed by powder XRD analysis. Vickers microhardness study has been carried out over a load range of 25-100 g. The Vickers hardness numbers (Hv) of the material increases as the load increases so the material is suitable for device fabrication. The Meyer index 'n' is estimated to be greater than 1.6, the crystal system belongs to the soft material category. The elastic stiffness coefficient, c11, has also been calculated using Wooster's empirical relation from the hardness data. The fracture toughness values 'Kc', determined from measurements of crack lengths, were estimated to be 0.15166 MN/m3/2. The brittleness indices 'Bi' were estimated as 276 m−1/2.

Nascent lateral habits of solution crystallization of poly(ethylene glycol)-block-polystyrene diblock copolymers

Some special habits of dilute solution-grown single crystals were introduced by means of atomic force microscopy (AFM) and transmission electron microscopy (TEM) equipped with electron diffraction (ED). Well-defined block copolymers of poly(ethylene glycol)-block-polystyrene (PEG-b-PS) having predetermined molecular weight and narrow molecular weight distribution (1.06–1.08) were synthesized by atom transfer radical polymerization (ATRP). The single crystals of PEG-b-PS copolymers were grown in a mixed solvent comprised of chlorobenzene/octane and separately in amyl acetate, both using a self-seeding technique. We were capable to develop various growth fronts that resulted from different growth rates through infinitesimal temperature fluctuations. Elevated crystallization temperatures and a higher ratio of molecular weight of PS to that of PEG intensified the curvatures. The corresponding overall, crystalline, and amorphous thickness of a given single crystal, either in square and truncated shapes or with concave and convex lateral sides, had high consistency with each other.

Quantum Beats in Crystalline Tetracene Delayed Fluorescence Due to Triplet Pair Coherences Produced by Direct Singlet Fission

A detailed analysis of the oscillations seen in the delayed fluorescence of crystalline tetracene is presented in order to study the mechanism of singlet fission. Three quantum beat frequencies of 1.06 ± 0.05, 1.82 ± 0.05, and 2.92 ± 0.06 GHz are resolved, which are damped on a time scale of 20 ns. The effects of sample morphology, excitation wavelength, and temperature are examined. A density matrix model for singlet fission is developed that quantitatively describes the frequencies, amplitudes, and damping of the oscillations. The model assumes a direct coupling of the initially excited singlet exciton to the triplet pair manifold. There is no electronic coherence between the singlet and triplet pair states, but the rapid singlet decay time of ∼200 ps in solution-grown single crystals provides the impulsive population transfer necessary to create a coherent superposition of three zero-field triplet pair states |xx>, |yy>, and |zz> with overall singlet character. This superposition of the three states gives rise to the three quantum beat frequencies seen in the experiment. Damping of the quantum beats results from both population exchange between triplet and singlet manifolds and pure dephasing between the triplet pair states. By lowering the temperature and slowing the SF rate, the visibility of the oscillations decreases. There is no evidence of magnetic dipole-dipole coupling between the product triplets. Our model provides good overall agreement with the data, supporting the conclusion that singlet fission in tetracene proceeds through the "direct" mechanism without strong electronic coupling between the singlet and triplet pair states.

Deformation of Confined Poly(ethylene oxide) in Multilayer Films

The effect of confinement on the deformation behavior of poly(ethylene oxide) (PEO) was studied using melt processed coextruded poly(ethylene-co-acrylic acid) (EAA) and PEO multilayer films with varying PEO layer thicknesses from 3600 to 25 nm. The deformation mechanism was found to shift as layer thickness was decreased between 510 and 125 nm, from typical axial alignment of the crystalline fraction, as seen in bulk materials, to nonuniform micronecking mechanisms found in solution-grown single crystals. This change was evaluated via tensile testing, wide-angle X-ray diffraction (WAXD), atomic force microscopy (AFM), and differential scanning calorimetry (DSC). With the commercially relevant method of melt coextrusion, we were able to overcome the limitations to the testing of solution-grown single crystals, and the artifacts that occur from their handling, and bridged the gap in knowledge between thick bulk materials and thin single crystals.

Magnetic properties ofRFe2Zn20andRCo2Zn20(R=Y,Nd,Sm,Gd–Lu)

Magnetization, resistivity, and specific heat measurements were performed on solution-grown single crystals of $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ and $R{\text{Co}}_{2}{\text{Zn}}_{20}$ $(R=\text{Y},\text{Nd},\text{Sm},\text{Gd-Lu})$. Whereas ${\text{LuCo}}_{2}{\text{Zn}}_{20}$ and ${\text{YCo}}_{2}{\text{Zn}}_{20}$ manifest unremarkable metallic behavior, ${\text{LuFe}}_{2}{\text{Zn}}_{20}$ and ${\text{YFe}}_{2}{\text{Zn}}_{20}$ display behaviors such as characteristic of nearly ferromagnetic Fermi liquids. When the well-defined $4f$ local moments $({\text{Gd}}^{3+}{\text{-Tm}}^{3+})$ are embedded into this strongly polarizable host, they manifest enhanced ferromagnetic ordering and the values of ${T}_{\text{C}}$ for $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ $(R=\text{Gd-Tm})$ scale with the de Gennes factor. In addition, data on the $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ compounds indicate a small crystal electric field (CEF) effect compared with the interaction energy scale. On the other hand, the local moment bearing members of $R{\text{Co}}_{2}{\text{Zn}}_{20}$ $(R=\text{Nd},\text{Sm},\text{Gd-Tm})$ manifest weak magnetic interactions and the magnetic properties for $R=\text{Dy-Tm}$ members are strongly influenced by the CEF effect on the $R$ ions. The magnetic anisotropy and specific heat data for the Co series were used to determine the CEF coefficient of $R$ ion with its cubic point symmetry. These CEF coefficients, determined for the Co series, are consistent with the magnetic anisotropy and specific heat data for the Fe series, which indicates similar CEF effects for the Fe and Co series. Such analysis, combined with specific heat and resistivity data, indicates that for $R=\text{Tb-Ho}$, the CEF splitting scale is smaller than their ${T}_{\text{C}}$ values, whereas for ${\text{ErFe}}_{2}{\text{Zn}}_{20}$ and ${\text{TmFe}}_{2}{\text{Zn}}_{20}$ the $4f$ electrons lose part of their full Hund's rule ground state degeneracy above ${T}_{\text{C}}$. ${\text{YbFe}}_{2}{\text{Zn}}_{20}$ and ${\text{YbCo}}_{2}{\text{Zn}}_{20}$ manifest typical but distinct heavy fermion behaviors associated with different Kondo temperatures.

Three-dimensional Anisotropic Electronic Properties of Solution Grown Organic Single Crystals Measured by Space-Charge Limited Current (SCLC)

AbstractOrganic single crystals offer the interesting and unique opportunity to investigate the intrinsic electrical behaviour of organic materials, excluding hopping phenomena due to grain boundaries and structural imperfections. Their structural asymmetry permits also to investigate the correlation between their three-dimensional order and their charge transport characteristics. Here we report on millimeter-sized, solution-grown organic single crystals, based on 4-hydroxycyanobenzene (4HCB), which exhibit three-dimensional anisotropic electrical properties along the three crystallographic axes a, b (constituting the main crystal flat face) and c (the crystal thickness), measured over several different samples. The carrier mobility was determined by means of space charge limited current (SCLC) and air-gap field effect transistors fabricated with 4HCB single crystals and the measured value well correlate with the structural packing anisotropy of the molecular crystal. A differential analysis of SCLC curves allowed to determine the distribution and the concentration of the dominant electrically active density of states within the gap.

Variation of the magnetic ordering inGdT2Zn20(T=Fe, Ru, Os, Co, Rh and Ir) and its correlation with the electronic structure of isostructuralYT2Zn20

Magnetization, resistivity, and specific heat measurements were performed on solution-grown single crystals of six $\text{Gd}{T}_{2}{\text{Zn}}_{20}$ ($T=\text{Fe}$, Ru, Os, Co, Rh, and Ir) compounds, as well as on their Y analogs. For the Gd compounds, the Fe column members manifest a ferromagnetic (FM) ground state (with an enhanced Curie temperature ${T}_{C}$ for $T=\text{Fe}$ and Ru), whereas the Co column members manifest an antiferromagnetic (AFM) ground state. Thermodynamic measurements on $\text{Y}{T}_{2}{\text{Zn}}_{20}$ revealed that the enhanced ${T}_{C}$ for ${\text{GdFe}}_{2}{\text{Zn}}_{20}$ and ${\text{GdRu}}_{2}{\text{Zn}}_{20}$ can be understood within the framework of Heisenberg moments embedded in a nearly ferromagnetic Fermi liquid. Furthermore, electronic structure calculations indicate that this significant enhancement is due to a large transition metal partial density of states at the Fermi level that places these compounds close to the Stoner FM criterion. The change from FM to AFM ordering (between the Fe and Co column materials) is associated with the filling of electronic states with two additional electrons/f.u. The degree of this sensitivity is addressed by the studies of the pseudoternary compounds $\text{Gd}{({\text{Fe}}_{x}{\text{Co}}_{1\ensuremath{-}x})}_{2}{\text{Zn}}_{20}$ and $\text{Y}{({\text{Fe}}_{x}{\text{Co}}_{1\ensuremath{-}x})}_{2}{\text{Zn}}_{20}$, which clearly reveal the effect of $3d$-band filling on their magnetic properties.