Crystal Length Research Articles

Reappraising Crystallization Kinetics with Overgrowth Chronometry: an in Situ Study of Olivine Growth Velocities

Abstract We investigated the early stages of olivine crystal growth via in situ seeded experiments in a single plagioclase-hosted melt inclusion, using a heating stage microscope. Each experiment was subjected to a cooling ramp of 7800°C/h followed by an isothermal dwell at 19°C, 38°C, 57°C, 77°C, 96°C or 129°C of undercooling. The seeds (6–16 μm in diameter Ø) grew into large crystals (Ø 80–169 μm) in 3 to 30 min through the symmetrical development of tabular, skeletal, and dendritic overgrowths as the undercooling of the system increased. Time-resolved image processing and incremental measurements of the overgrowth thicknesses indicate up to three stages of crystal growth: an acceleration stage, a linear (constant growth rate) stage, and a deceleration stage. At the isotherm, the growth velocities reach a stable maximum that in all experiments corresponds to the period of linear growth. The highest linear values are measured at the $\left\{101\right\}$ interfaces, from 2.1 × 10−8 m/s at 19°C of undercooling to 4.8 × 10−7 m/s at 129°C of undercooling. Crystal growth is slower at other interfaces, in the ranges 1.9–7.6 × 10−8 m/s and 4.5 × 10−9 – 7.6 × 10−8 m/s for the $\left\{100\right\}$ and $\left\{001\right\}$ forms, respectively. Growth in the $<010>$ dimension appears limited to less than 2.4 × 10−8 m/s at 129°C of undercooling. We constrain the uncertainty on these growth velocities, which includes the environmental conditions (± 8.6°C on the nominal undercooling) and the measurements of crystal lengths (underestimated by <16% at most fast interfaces). A systematic and comprehensive review of 19 pre-existing datasets indicates that our linear growth velocities are faster than most growth rates determined at comparable undercoolings. Growth rates determined as half crystal lengths divided by total time are intrinsically low estimates of the true maximum, linear growth velocities, because the total time includes periods of slower or non-growth, and measured crystal dimensions are subject to projection foreshortening or truncation. These errors can lead to values that are several times to several orders of magnitude lower than the true maximum growth rates. This study completes and refines previously published data on the crystallization kinetics of olivine, highlighting the sensitivity of growth rates to specific environmental conditions and measurement methods. We emphasize the importance of symmetrical growth and true maximum growth velocities for interpreting olivine growth histories.

Theoretical Study of Self-Heating-Induced Thermal Stress Effects on Quantum Transport in p-Type Ultrathin Body-FinFET by Multiphysics Simulation

Self-heating of the device will intensify the thermo-mechanical effects, leading to an increase in thermal stress. Currently, most of the research focuses on strain engineering of the device by intentionally introducing mechanical stress. However, how thermal stress affects the performance of nanoscale transistors remains unclear. Thus, in this manuscript, a comprehensive coupled Multiphysics simulation is performed to investigate the self-heating induced thermal stress effects on quantum transport in the p-type ultrathin body (UTB)-FinFET. The quantum transport equation with consideration of thermal stress effects by the strain term in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{k}\cdot \textit{p}$</tex-math> </inline-formula> Hamiltonian, heat conduction equation, and equilibrium equations of solid mechanics are solved self-consistently. Then, the impacts of self-heating-induced thermal stress on hole effective mass, hole average velocity, and current density of the FinFETs with different crystal orientation configurations and channel lengths are compared and analyzed. The simulation results show that thermal stress can decrease or increase the ON-state current depending on the crystal orientation configuration. Further analysis of the band structure obtained from the Hamiltonian shows that thermal stress can change the material properties such as the hole effective mass of the top subband, thus leading to the variations of device characteristics.

High-Power Acoustic-Optical Q-Switched 1.83 µm Tm-Doped Bulk Laser

We report on a high-power acoustic-optical (AO) Q-switched Tm:YLF laser operating at ~1.83 μm by controlling the transmittance of the output coupler. Under the continuous-wave (CW) operation, the maximum output power of 13 W is achieved, and the slope efficiency is up to 32.7%. With a YAG etalon inserted into the cavity, the linewidth is compressed below 0.5 nm with a maximum output power of 12.2 W. In the Q-switched state, the maximum pulsed output power of 10.32 W is achieved with a pulse duration of 150 ns when the repetition rate is 15 kHz. And the maximum pulsed energy of 1.13 mJ is generated with a duration of 131 ns at 5 kHz. As far as we know, this is the highest output power reported for the CW and pulsed 1.83 μm laser. In addition, the relationship between the output wavelength and crystal length is theoretically analyzed, which shows that increasing the loss of 1880 nm is the key to high-power 1.83 μm laser output.

Electromagnetic bandgaps of fixed-length Thue-Morse plasma/dielectric/superconductor photonic band multilayers

ABSTRACT In this work, we study the electromagnetic bandgaps and passbands of some fixed-length Thue-Morse plasma/dielectric/superconductor photonic band multilayers. we consider vanadium (V) as a low-temperature superconductor and investigate the effect of the refractive index of the dielectric, the length of the photonic crystal length, the number of layers, plasma density, and the temperature of the superconductor on the transmission spectrum of the photonic crystal. In the second part, we consider copper oxide calcium barium mercury as a high-temperature superconductor, and similar to the first part, we examine the effect of the mentioned factors on the transmission spectrum. Finally, we investigate the high and low-temperature superconductivities by comparing and examining the above-mentioned parameters for these structures in a fixed-length configuration.

Growth of ferroelectric lithium niobate-tantalate LiNb(1-x)TaxO3 crystals

Congruent and stoichiometric ferroelectric lithium niobate-tantalate crystals LiNb(1-x)TaxO3 of different compositions were grown by the Czochralski method. The stoichiometric crystals were grown using the top seeded solution growth method using LiWO4, which increases the Li content in the melt and in the grown crystal. Also, the use of a solvent can significantly reduce the temperature of the melt. The composition of the crystals was studied by inductively coupled plasma mass spectrometry using laser ablation, which allow studying the change in the composition of the grown crystals along the length and diameter. It is demonstrated that the content of Ta in the crystals exceeds the content of Ta in the initial charge, i.e., in the process of crystal growth, the melt becomes depleted in Ta. It is shown that the Ta content decreases along the crystal length due to the decrease in the Ta content in the melt. In the LiNb0.88Ta0.12O3 crystals, the piezoelectric moduli d22 and d33, and the velocities of bulk and surface acoustic waves were measured. The values of piezoelectric moduli and acoustic wave velocities are shown to occupy an intermediate position between LiNbO3 and LiTaO3 crystals.

Secondary Phase CeO2 Precipitates in Ce,Er-Doped Na0.5La0.5MoO4 Single Crystals Grown by Czochralski Method

Analytical scanning and transmission electron microscopy were used to study the microstructure of Ce,Er-doped Na0.5La0.5MoO4 laser crystals. Crystals were grown by the Czochralski method from the melts with a nominal composition of Na0.5La0.5−xCexEr0.005MoO4, where x = 0.125 and 0.15, then annealed at 700 and 1000 °C in the oxidizing atmosphere. We found the secondary phase precipitation of Ce2O3 oxide in as-grown crystals, while after high-temperature annealing the CeO2 precipitated crystals are always observed. Impurity ions Ce3+ occupy the La sites, and approximately 20% of the nominal Ce content is involved in the formation of Ce oxide secondary phase precipitates. The length of CeO2 precipitated crystals ranged between 100 nm and 550 nm (average length was 200 nm) and their width was 30–70 nm. The mechanism of CeO2 formation is discussed. The orientation relationships of Na0.5La0.5−xCexEr0.005MoO4/CeO2, the degree of coherence of the interface, and the preferential directions of their growth in the matrix were established. CeO2 crystals precipitated in the matrix cause light scattering with a wavelength comparable to the size of the precipitates and lead to deterioration of optical transparency of the material.

Polarization-Sensitive Photodetector Based on High Crystallinity Quasi-1D BiSeI Nanowires Synthesized via Chemical Vapor Deposition.

Bismuth chalcohalides (BiSeI and BiSI), a class of superior light absorbers, have recently garnered great attention owing to their promise in constructing next-generation optoelectronic devices. However, to date, the photodetection application of bismuth chalcohalides is still limited due to the challenge in controllable preparation. Herein, the synthesis of large-scale quasi-1D BiSeI nanowires via chemical vapor deposition growth is reported. By precisely tuning the growth temperature and the Se supply, it can effectively control the growth thermodynamics and kinetics of BiSeI crystal, and thus achieve high purity quasi-1D BiSeI nanowires with high crystal quality, uniform diameter, and tunable domain length. Theory and optical characterizations of the quasi-1D BiSeI nanowires reveal an indirect bandgap of 1.57eV with prominent optical linear dichroism. As a result, the quasi-1D BiSeI nanowire-based photodetector demonstrates a broadband photoresponse (400-800nm) with high responsivity of 5880mAW-1 , fast response speed of 0.11ms and superior air stability. More importantly, the photodetector displays strong polarization sensitivity (anisotropic ratio = 1.77) under the 532nm light irradiation. This work will provide important guides to the synthesis of other quais-1D metal chalcohalides and shed light on their potential in constructing novel multifunctional optoelectronic devices.

Investigation of Doping Processes to Achieve Highly Doped Czochralski Germanium Ingots

Highly doped germanium (HD-Ge) is a promising material for mid-infrared detectors, bio-sensors, and other devices. Bulk crystals with a doping concentration higher than 1018 cm−3 would be desirable for such device fabrication technologies. Hence, an effective method needs to be developed to dope germanium (Ge) ingots in the Czochralski (Cz) growth process. In this study, a total of 5 ingots were grown by the Cz technique: two undoped Ge ingots as a reference and three doped ingots with 1018, 1019 , and 1020 atoms/cm3 respectively. To obtain a uniform p-type doping concentration along the crystal, co-doping of boron-gallium (B-Ga) via the Ge feed material was also attempted. Both B and Ga are p-type dopants, but with a large difference in their segregation behavior (contrary segregation profile) in Ge, and hence it is expected that the incorporation of dopants in the crystal would be uniform along the crystal length. The distribution of the dopants followed the Scheil-predicted profile. The etch pit density maps of the grown crystals showed an average dislocation density in the order of 105 cm−2. No increase in the overall etch pit count was observed with increasing dopant concentration in the crystal. The grown highly doped Ge crystals have a good structural quality as confirmed by x-ray diffraction rocking curve measurements.

Separating radial and azimuthal polarizations of circular Airy vortex beam via uniaxial crystal.

Since Ciattoni A. et al. found that a particular circularly polarized beam propagating along the optical axis in a uniaxial crystal can generate a vortex with a reversed circular polarization, numerous studies of spin-orbit coupling in this polarization conversion process have been carried out. In this paper, from another perspective rather than the circular polarization conversion, for the first time we find that radial- and azimuthal-polarization components will be separated and finally focus on two separated focus points when circular Airy vortex beams propagate in a uniaxial crystal. Both the separation of the radial- and azimuthal-polarization components in positive and negative uniaxial crystals are investigated, and the physical mechanism of this phenomenon is explained in details. Moreover, the influences of the crystal length and birefringence on the separation of the radial- and azimuthal-polarization components are also discussed. Our results could offer deeper understanding of the propagation of light beam in uniaxial crystal and facilitate the flexible applications of circular Airy vortex beams.

Evaluation of numerical simulation of constitutional supercooling during heavily Boron-Doped silicon crystal growth using Cz method

Using the Czochralski (Cz) method, it has been established that heavily doped silicon (Si) single crystals with impurities such as boron (B) can negatively impact the quality of grown crystals due to morphological instabilities such as cellular growth caused by constitutional supercooling for doping higher than 1 × 1019 cm−3. To produce high-quality heavily doped Si single crystals, constitutional supercooling must be prevented during growth. In this study, we used a three-dimensional numerical simulation to predict constitutional supercooling during the growth of heavily B-doped Cz-Si single crystals, considering the transport of B in the melt and the segregation effect. We compared the numerically predicted constitutional supercooling region with experimental data to assess its accuracy and found that the cellular growth region observed in the experiment was in good agreement with the region of constitutional supercooling predicted by the simulation. Moreover, we considered the effects of different pulling rates and crystal lengths during the growth process on constitutional supercooling, and the limitations of numerical modelling.

Monte Carlo Simulation to Test the Effectiveness of Crystal Detector Length for PHITS-Based PET Modality

PET (Positron-emission tomography) is used to determine physiological and metabolic functions in the body. Monte Carlo simulation is an important part of PET imaging, and the Particle Heavy Ion Transport code System (PHITS) is a simulation platform that can be used to perform Monte Carlo simulations. This study uses a Monte Carlo simulation based on PHITS to determine the range of gamma absorption with an energy of 511 keV in a scintillation detector crystal material. The gamma absorption range determines the effective crystal length in the PET modality. The simulation process is carried out by shooting Gamma at various types of materials, which are the materials used in PET scintillation crystals. The materials used in this simulation are NaI (Sodium Iodide), BaF2 (Barium Florida), BGO (Bismuth Germanate), and GSO (Gadolinium Oxyorthosilicate), considering their atomic number and crystal density. The crystal material is capable of absorbing gamma radiation with an energy of 511 keV with detailed crystal lengths for each NaI crystal of 0.26 cm; 0.25 cm BaF2 crystals; 0.1cm BGO crystals; and 0.18 cm GSO crystals. The crystal length from this simulation is smaller than the commercially available crystal length (range 1-3 cm). Based on the crystal length data, the most effective crystal for absorbing gamma radiation is the BGO crystal.

Theoretical Study on Nonreciprocity for Third-Harmonic Generation Process in Nonlinear Photonic Crystals

Based on the nonlinear coupled wave equations, the nonreciprocal response of the third-harmonic generation process has been theoretically investigated in nonlinear photonic crystals with a defect embedded. The simulation results have shown that complete nonreciprocity for third-harmonic generation can be achieved under specific conditions, and the arbitrary nonreciprocal response can be realized by adjusting the structure parameters, including the crystal length, the defect position and the defect width. These findings hold great potential for implementing practical nonlinear optical isolating devices.

Importance of crystal length on the stability of a picosecond supercontinuum generated in undoped YAG

In this paper, we present the stability characteristics of a supercontinuum (SC) generated in a 60 mm, 100 mm, and 130 mm long undoped yttrium aluminum garnet (YAG) crystal pumped by a Yb thin-disk regenerative amplifier. The 1.2 ps pulses with a central wavelength of 1030 nm and repetition rate of 89 kHz are loosely focused (NA = 0.0031) into the crystal in order to prevent laser-induced damage and to increase the energy stability of the generated SC. Out of the tested crystal lengths, the optimal is experimentally determined to be 130 mm. The energy contained in the blueshifted side, which has a 530 nm spectral cutoff, is 71 nJ and exhibits average power stability of 0.4% RMS, which is 2.5× better than the stability of the pump beam.

946/1030 nm Dual-Wavelength Laguerre-Gaussian (LG01) Mode Vortex Laser Based on Intracavity Cascade Pumped Resonator

In this paper, the 946/1030 nm dual-wavelength LG01 mode vortex laser is obtained by applying the intracavity cascade pumped structure and annular-beam end-pumped method, an innovative and pioneering exploration of the transverse mode of the dual-wavelength laser. First, we demonstrate the oscillation characteristic theoretical model of the dual-wavelength LG01 mode laser, considering the reabsorption effect. Then the length of the laser crystal and the transmittance of the output mirror are simulated and analyzed, respectively, related to the oscillation characteristics of the 946 and 1030 nm LG01 mode vortex lasers. Finally, a 946/1030 nm LG01 mode vortex laser with the same handedness is successfully achieved in our experiment. With 20 W of annular-beam pump power, the output power of 946 and 1030 nm LG01 mode vortex lasers is 0.404 and 0.510 W, the slope efficiency is 3.6% and 6.2%, and the total optical-optical conversion efficiency is 4.6%. At the maximum output power, the fluctuations of output power within 1 h are 4.02% and 4.23%, and the beam quality factors M2 are 2.32 and 2.27, respectively, for 946 and 1030 nm LG01 mode vortex lasers. The wavefront phase exp(iϕ) of the 946/1030 nm dual-wavelength is also proved by the self-interference method.

Simultaneous Improvements in Efficiency and Stability of Organic Solar Cells via a Symmetric‐Asymmetric Dual‐Acceptor Strategy

AbstractSimultaneously achieving improvements in power conversion efficiency (PCE) and stability is the main task of the current development stage of organic solar cells (OSCs). This work reports a symmetry–asymmetry dual‐acceptor (SADA) strategy to construct ternary devices, which is found to be feasible for increasing both the PCE and the operational lifetime of OSCs. In this contribution, the symmetric acceptor L8‐BO and the asymmetric acceptor BTP‐S9 are blended in equal proportions with polymer donor PM6 for the consideration of absorption spectrum complementarity and cascade energetic alignment. In addition, the features of crystallinity and miscibility of the dual‐acceptor deliver optimized morphology lead to a high PCE of 18.84%. In addition, the asymmetric acceptor BTP‐S9 with a larger dipole moment shows tighter molecular stacking and longer crystal correlation length, which favor intrinsic molecular photostability, and further consolidate the operational lifetime of OSCs when coordinated with L8‐BO. This work demonstrates the efficacy of the SADA strategy for constructing efficient and stable OSCs.

High open-circuit voltage in single-crystalline n-type SnS/MoO3 photovoltaics

It has been recently reported that n-type single crystalline SnS exhibits a large band bending (∼1 eV) at the interface with MoO3, which is a large work function material. In this study, we applied this interface to solar cells for the first time and evaluated its photovoltaic properties. The highest VOC achieved was 437 mV. Although this value is the highest ever recorded for SnS solar cells, it was lower than the expected value of 700–800 mV. The highest power conversion efficiency (PCE) was 4.4%. Based on an analysis of the device parameters, we propose methods for improving the device performance, including VOC, the short-circuit current, and PCE. The carrier-collection length of the n-type SnS single crystals was estimated to be ∼200 nm based on the external quantum efficiency measurements. Therefore, this study demonstrates that the VOC of SnS solar cells can be improved by fabricating a junction with MoO3 thin films.

Effect of water-cooled jacket on the oxygen transport during the Czochralski silicon crystal growth process

Nowadays, the water-cooled jacket is widely used in the large industrial Czochralski (Cz) furnace to enhance the pulling rate of the monocrystalline silicon crystal for solar cells. It is an efficient tool to increase productivity and reduce the production cost of the photovoltaic industry. However, the water-cooled jacket would affect the oxygen concentration of the grown silicon crystals. In this study, a two-dimensional numerical model was used to investigate the influence of the water-cooled jacket on the heat and oxygen transport in the silicon melt during the crystal growth process. The results demonstrate that the water-cooled jacket significantly enhances the heat loss from the melt-crystal and melt-gas interfaces, resulting in a larger temperature difference and stronger buoyancy convection in the melt, compared to the case without water-cooled jacket. The strong buoyancy convection causes the higher turbulent viscosity in the melt. Consequently, the oxygen transport in the melt is strengthened. By using the water-cooled jacket, the oxygen concentration in the grown crystals was increased by about 2.6 ppma at the crystal length of 400 mm. The simulation results agree reasonably with the experimental data.

Optical Recrystallization of Nanocrystalline Silicon Ribbons

The Silicon on Dust Substrate (SDS) is a gas-to-wafer process that produces multicrystalline silicon ribbons directly from gaseous feedstock (silane), avoiding the standard industry steps of polysilicon deposition, crystal growth, and wafering. The SDS technique consists of three main steps: (i) micrometric-sized silicon powder production by grinding silicon chunks; (ii) chemical vapor deposition (CVD) of silicon over this silicon powder substrate; and (iii) zone-melting recrystallization (ZMR) of the nanocrystalline pre-ribbon obtained in the CVD step. Several samples were produced by this technique. During CVD, mechanically self-sustained nanocrystalline pre-ribbons were grown over silicon powder substrates, with growth rates in the order of 50 µm/min. The ZMR process performance is substantially impacted by the pre-ribbon physical characteristics. The best and largest recrystallizations were achieved on pre-ribbons grown over powder substrates with smaller particle sizes, which also have lower substrate powder incorporation ratios. Multicrystalline silicon ribbons with crystalline areas as large as 2 × 4 cm2 were successfully produced. These areas have visible columnar crystal growth with crystal lengths up to 1 cm. The SDS ribbons’ measured resistivity confirmed the high powder content of the resulting material. The ability to produce solar cells on SDS multicrystalline silicon ribbons was demonstrated.

Effects of laser energy density on morphology features and microstructures of the single molten track in selective laser melting

Single molten track (SMT) is the basic unit of the selective laser melting (SLM) process, of which the morphology features and microstructures have great significance on the molding quality. In this study, the effects of laser energy density (LED) on characteristics of SMT were studied with 316 L stainless steel processing by SLM. The results indicate that an optimized range of LED was between 200 and 500 J/mm3, which was the best for SLM process of 316 L leading to beautiful SMT appearance such as continuous uniform water-ridge-like surface, good contour straightness, smooth edges, little adhesive powder, and high densification. The microstructures of the SMT molten pool are mainly composed of equiaxed cellular and columnar dendrites. As the LED decreased, the cellular became smaller and disappeared, while the length and width of columnar crystals even gradually increased. The size of the cellular varies between 0.43 and 1.70 μm with the LEDs increase. The relationship between SMT characteristics and LED found in this work can be readily used to optimize SMT and control the microstructures in situ, and the laser energy density range that the work has identified will simplify most of the guess work in additive manufacturing.

General solution of phase mismatched second harmonic conversion efficiency in periodically poled nonlinear medium

In this work we provide for the first time a novel and more accurate second harmonic generation (SHG) conversion efficiency equation for periodically poled nonlinear medium. We believe the equation derived in this work is more useful than equations reported in previous works which are limited because it is considering the case of either nondepleted pump regime or perfect phase matching. The equation derived in this work tackles the general case: depleted pump regime and phase mismatching which makes it important for theoretical – experimental study. We used MgO:PPLN crystal as an example to illustrate SHG conversion efficiency as function of crystal length, laser power density, crystal temperature and beam divergence. We included fundamental and second harmonic waves reflection at entrance and exit surfaces respectively and performed numerical solution using fifth-order Runge-Kutta method. The numerical results show excellent match with analytical results obtained from the derived formula. We compared our theoretical results with experimental results reported in the literature and the comparison shows a good match. Finally, we performed a comparison between depleted and nondepleted pump regime. The results show a difference of 20% between two efficiencies making nondepleted efficiency equation, which used in many theoretical – experimental comparisons, not accurate at high power densities.