Total Growth Time Research Articles

Observation of nonthermal electrons further acceleration and long-lasting associated with magnetic reconnection and turbulence bursting in tokamak plasma

Abstract Vital to magnetized plasma performance, the acceleration of nonthermal electrons significantly influences the current drive of radio frequency (RF) waves in plasma. In EAST, we observed nonthermal electrons initially <215 keV in energy, being locally accelerated to 600 keV within 100 milliseconds, which corresponds to the total growth time of the magnetic island. Surprisingly, these fast electrons (FE) lasted for 1.4 seconds, several times longer than the estimated relaxation time of 0.26 seconds, and exceeded 1/10 of the discharge length. Turbulence generation at island’s X point is attributed to the unexpected confinement and repopulation of FEs. This phenomenon may have positive implications for the steady-state long pulse H mode operation in EAST, especially regarding non-inductive current sustainment. For future RF electron heating-dominant devices, the mechanisms elucidated in this study have immediate implications for optimizing RF current drive efficiency.

A Kinetic Model for Oxide–Carbonitride Inclusion Heterogeneous Nucleation and Precipitation during Superalloy Solidification

Complex oxide–carbonitrides (MgO-Ti(CN), Al2O3-Ti(CN), and MgO·Al2O3-Ti(CN)) are the most common non-metallic inclusions presented in cast and wrought superalloys. In this work, a coupled kinetics model was proposed to predict the complex oxide–carbonitride inclusion’s precipitation behavior during the solidification of superalloys. This model takes into account thermodynamics, micro-segregation, heterogeneous nucleation in the inter-dendritic liquid, and growth controlled by the diffusion of solute elements and kinetics of interfacial reaction. The results demonstrated that both the cooling rate and nitrogen content take significant effects on the final size of complex oxide–carbonitride inclusions, as the former controls the total growth time and the latter determines the initial precipitation temperature. In comparison, the particle size of primary oxides shows a negligible impact on the final size of complex inclusions. The practice of an industrial vacuum arc remelting confirmed that the inclusion size variation predicted by the present model is reasonably consistent with the experimental results.

Lu–Hf Geochronology on Single Garnets in a Micaschist from the North Qilian Orogenic Belt

The acquisition of the timing and duration of metamorphic mineral growth is the key to understanding the evolution of metamorphic belts. Garnet Lu–Hf geochronology is becoming increasingly powerful in this aspect. It is believed that garnet Lu–Hf radiometric systems are preserved during low-temperature metamorphism. However, this hypothesis has not been systematically tested. To examine the Lu–Hf systematics of garnets during low-temperature metamorphism, we conducted radiometric dating on individual garnet crystals of different sizes from a single micaschist in the North Qilian orogenic belt. The garnet Lu–Hf dates correlate well with the grain sizes and their core Mn concentrations. The positive correlation between the ages and grain sizes suggests that grain size is a proxy for preserving garnet nucleation and growth history. Small grains nucleated and grew later than large crystals. The Lu–Hf date of the individual garnet crystals faithfully recorded the total growth time span. The date difference of ~16 Myr is the minimum duration of the total garnet growth. The age discrepancy between the micaschist and the eclogite indicates they may not have experienced the same subduction and exhumation in the North Qilian orogenic belt.

Rapid growth of a 24 mm2 scale hexagonal boron nitride crystal in Ni–Cr solution

A 24 mm2 exfoliated hBN film is achieved within a total growth time of 49.17 hours. A signal-to-noise ratio of 2 orders of magnitude is reported for a metal–semiconductor–metal type photodetector based on hBN.

Correlations among morphology, composition, and photoelectrochemical water splitting properties of InGaN nanorods grown by molecular beam epitaxy

The mechanism underlying the effect of growth condition on the morphology evolution of InGaN nanorods (NRs) has been systematically investigated. The increased Ga flux enhances both the axial and the radial growth at the growth stage. However, the changed Ga flux influences not only the growth but also the nucleation of InGaN NRs. At the nucleation stage, the increased Ga flux shortens the delay time for NR formation, and prolongs the growth stage for a fixed total growth time. Those two aspects result in the increase of NR diameter and height with the supplied Ga flux. In addition, the continuous nucleation is ended much earlier due to the accelerated saturation of substrate area with the increased Ga flux, resulting in a decreased final NR density. In addition to the morphology evolution with the Ga flux, the composition characteristic of InGaN NRs has been also studied. The In distribution of InGaN NRs depends critically on the NR diameter along the NR growth direction, and the NRs show a morphology-dependent In incorporation. Interestingly, the InGaN NRs discussed here show a radial Stark effect induced by the pinned Fermi level. The radial Stark effect shifts the absorption edge of the InGaN NRs toward longer wavelengths, makes the InGaN NRs attractive for photoelectrochemical water splitting applications. The photoelectrochemical measurements present a significant increase in the photocurrent with the increased total surface area of the InGaN NRs, which is due to the enhanced light absorption effects and the enlarged interfacial area of the semiconductor/electrolyte.

Fast and Controllable Electric‐Field‐Assisted Reactive Deposited Stable and Annealing‐Free Perovskite toward Applicable High‐Performance Solar Cells

Recently, organic–inorganic hybrid perovskite materials have drawn great attention for their outstanding performance in high‐efficiency solar cells. Successful synthesis has been realized either in solution‐based chemical deposition or vapor deposition. However, conflicts have never ceased among quality control, growth rate, process complexity, and instrument requirement, which have limited their development toward real applications. In this work, the first electrochemical fabrication of perovskite toward high‐efficiency and scalable perovskite solar cells (PSCs) is established. The morphology and crystallization of the CH3NH3PbI3 film can be effectively controlled by simply modulating a few physical parameters. A detailed study on its optoelectronic properties reveals significantly improved film quality and interfacial conditions. Aided by this, the total process does not require standard annealing, which greatly reduces the total growth time from hours to minutes. Up to now, an efficiency of 15.65% has been achieved in planar PSCs under 1 sun AM 1.5 condition, with small hysteresis and efficiency loss under longtime exposure to air. Moreover, high efficiency (10.45%) can be easily attained for large cells (2 cm2). This result will hopefully facilitate research for applicable high‐efficiency PSCs and other multicomponent materials as well.

Improved control over spontaneously formed GaN nanowires in molecular beam epitaxy using a two-step growth process

We investigate the influence of modified growth conditions during the spontaneous formation of GaN nanowires (NWs) on Si(111) in plasma-assisted molecular beam epitaxy. We find that a two-step growth approach, where the substrate temperature is increased during the nucleation stage, is an efficient method to gain control over the area coverage, average diameter, and coalescence degree of GaN NW ensembles. Furthermore, we also demonstrate that the growth conditions employed during the incubation time that precedes nanowire nucleation do not influence the properties of the final nanowire ensemble. Therefore, when growing GaN NWs at elevated temperatures or with low Ga/N ratios, the total growth time can be reduced significantly by using more favorable growth conditions for nanowire nucleation during the incubation time.

Active galactic nuclei flicker: an observational estimate of the duration of black hole growth phases of ∼105yr

We present an observational constraint for the typical active galactic nucleus (AGN) phase lifetime. The argument is based on the time lag between an AGN central engine switching on and becoming visible in X-rays, and the time the AGN then requires to photoionize a large fraction of the host galaxy. Based on the typical light travel time across massive galaxies, and the observed fraction of X-ray selected AGN without AGN-photoionized narrow lines, we estimate that the AGN phase typically lasts 10 5 years. This lifetime is short compared to the total growth time of 10 7 10 9 years estimated from e.g. the Soltan argument and implies

Optimizing the Vacuum Growth of Epitaxial Graphene on 6H-SiC

Multilayer epitaxial graphene has been grown on the Si-face of 6H-SiC on-axis commercial substrates under high vacuum conditions and at growth temperatures up to 1900 °C, utilizing the standard sublimation growth technique and a modified SiC rapid thermal annealing system which allows for excellent control of heating and cooling ramp rates. The peak growth temperature and total growth time during the graphene growth step, along with the temperature of the initial substrate etch step, were all systematically varied in order to ascertain their effect on the formation of epitaxial graphene films on the SiC surface. Modifying the substrate etch temperature was found to have a significant impact on the morphology of the SiC substrate, with a uniform step structure only developing across the surface within a narrow temperature band. Furthermore, changing the values of the peak temperature or the growth time during the growth step were both shown to have a large effect on the resultant materials properties of the graphene films.

Growth of multicrystalline Si ingots using noncontact crucible method for reduction of stress

Stress control is necessary when preparing high-quality multicrystalline Si ingots using crucibles because crystal defects such as dislocations are mainly generated by stress in the ingots. Conventional crystal growth methods using crucibles cannot control the stress caused by expansion due to the solidification of the Si melt. We proposed a noncontact crucible method using conventional crucibles that reduces the stress in Si multicrystalline ingots. In this method, nucleation occurs on the surface of a Si melt using seed crystals, and crystals grow inside the Si melt without touching the crucible walls. Then, the ingots continue to grow while being slowly pulled upward to ensure that the crystal growth remains in the low-temperature region. The diameter and solidification ratio of the ingots can be controlled by reducing the melt temperature in the low-temperature region and by varying the product of the temperature reduction from the melting point of Si and the total growth time, respectively. A Si ingot with a diameter of 21cm and a solidification ratio of 83% was obtained in a crucible with a diameter of 30cm. We have confirmed that ingot growth in a crucible is feasible, during which the ingot does not come in contact with the crucible walls.

Knots' rings in different development phases for larch plantations.

Based on the knot analysis data of 95 sample trees in 19 sample plots, the number of rings of knots in different development phases was analyzed for larch(Larix gmelinii) plantations with different ages, stand densities and sites. The results showed: The knots of larch plantation produced perceptible rings during normal growth. The number of perceptible rings ranged from 1 to 36, with an average of 10.9. The relationship between perceptible rings and length of knots was positive linear. It is common that the knots of larch plantation had missing rings, the number of missing rings was from 0 to 19(mean value is 3.44). The missing rings increased with knots length increasing. During this period the branches made no contribution to the growth of trees, so this was the right time for artificial pruning. The time of knots between death and occlusion was 12 years on average, which was about 51% of their total growth time. The loose knots produced during this period would be a great impact on the quality of wood.

Indium Interruption Growth법으로 성장한 InAs 양자점의 광학적 특성

분자선 에피택시 (molecular beam epitaxy: MBE)를 이용하여 GaAs (100) 기판에 Indium interruption growth법으로 성장한 InAs 양자점 (quantum dots: QDs)의 광학적 특성을 photoluminescence (PL)와 time-resolved PL (TRPL) 실험을 이용하여 분석하였다. In interruption growth법은 InAs 양자점 성장 동안 As 공급은 계속 유지하면서 셔터 (shutter)를 이용해서 In 공급을 조절하는 방법이다. 본 연구에서는 In을 1초 동안 공급하고 셔터를 0초 , 9초, 19초, 29초, 또는 39초 동안 닫아 In 공급을 차단하였으며, 공급과 차단 과정을 각 30회 반복하여 양자점을 성장하였다. In interruption 시간을 0초에서 19초까지 증가하였을 때 PL 피크는 1096 ㎚에서 1198 ㎚로 적색편이 (~100 ㎚)하고 PL 세기는 증가하였으나, 19초에서 39초까지 증가하였을 때 PL 스펙트럼의 변화는 없고 PL 세기는 감소하였다. 모든 양자점의 PL 소멸시간 (decay time)은 약 1 ㎱로 바닥상태 (ground state) PL 피크에서 가장 길게 나타났다. In interruption 시간이 19초인 시료가 가장 좋은 PL 특성과 가장 짧은 운반자 소멸시간을 나타내었다. PL 특성의 향상은 In interruption 시간동안 일정한 양의 In 원자들의 분리와 이동이 증가한 것으로 설명될 수 있다. 이러한 결과로부터 In interruption 법을 이용하여 InAs 양자점의 크기, 균일도, 조밀도 등을 조절하여 원하는 파장대의 양자점을 성장할 수 있음을 알 수 있다.

In situ monitoring and control of multicomponent gas-phase streams for growth of GaN via MOCVD

A monitoring method based on ultraviolet absorption spectroscopy (UVAS) coupled with a multivariate analysis technique was developed to measure the partial pressure of several metalorganic reactant species and the hydride commonly used for III–V nitride growth. Trimethylaluminum, triethylgallium, dimethylethylamine alane and ammonia are all shown to absorb strongly in the UV with highly overlapping spectra. It was found that a single absorption spectrum can be decomposed to obtain accurate predictions of pure component partial pressures in a multicomponent stream. This method was used to monitor and control the gas-phase concentrations for the multicomponent mixture of triethylgallium and ammonia diluted in nitrogen, which is used to grow GaN thin films via MOCVD. There was a 5% average error for the predicted partial pressure of TEGa in the range 245–700 mTorr and a 2% average error for the predicted partial pressure of NH 3 in the range 15–35 Torr. A detection limit of 10 mTorr and 1 Torr were measured for TEGa and NH 3, respectively. For simple feedback control and using this method as a measurement device, settling times of 1 min for TEGa and 30 s for NH 3 to reach within 2% of the desired partial pressure have been obtained. Control tests included both setpoint tracking and gas-phase disturbance rejection. These settling times were found to be no greater than 1 40 of the total growth time for a commonly grown GaN thin film.

Room temperature visible (683-713 nm) all-AlGaAs vertical-cavity surface-emitting lasers (VCSELs)

Visible emitting all-AlGaAs vertical-cavity surface-emitting lasers (VCSELs) have been produced by metal organic vapor phase epitaxy (MOVPE) using ultra-high purity source reagents. Lasing was obtained at wavelengths in the range 683-713 nm using four 45 /spl Aring/ Al/sub 0.18/Ga/sub 0.82/As quantum wells in the active region. At room temperature, a minimum threshold current density of 3.8 kA.cm/sup -2/ was measured for a wavelength of 692 nm; this is the lowest value for an all-AlGaAs vertical-cavity laser operating at this wavelength. Growth of the epitaxial mirrors at 5.2 μm/h/sup -1/ results in a total growth time of only two and a half hours.

Stick-Slip Motion in Boundary Lubrication

Using dynamical analysis for a pin-on-disk sliding system and the consideration of meniscus formation at the sliding interface, a wide range of experimental observations on stick-slip motion can be explained. It is shown that when the initial growth rate of the static friction force is larger than about half the product of the substrate speed and the spring constant, slick-slip motion occurs in that sliding system. The critical substrate speed or the critical spring constant, above which stick-slip motion ceases, can thus be determined. It is also shown that the saturation substrate speed, below which stick-slip motion retains its maximum stick-slip amplitude, is inversely proportional to the total growth time of the static friction force. The maximum stick-slip amplitude is proportional to the final difference between the static and kinetic friction force. For a thicker surface liquid-film, the initial growth rate and the final static friction force are larger but the total growth time is shorter, result...

Microstructural studies of CdTe and InSb films grown by molecular beam epitaxy

Epitaxial thin films of CdTe (1–5 μm) have been grown directly onto (001) InSb substrates or onto intermediate buffer layers of InSb (0.25–0.5 μm) by molecular beam expitaxy. Cross-sectional transmission electron microscopy and high-resolution transmission electron microscopy have been used to characterize the film and interfacial microstructures. Inferences about film quality were also compared with single-crystal x-ray rocking curve data and agreed well. Resulting microstructural features were correlated with various experimental growth parameters and substrate cleaning procedures. Results show that near-perfect CdTe films can be grown on InSb substrates, but film quality is critically dependent upon substrate cleaning. Other factors observed to influence defect formation in the films include growth rate, total growth time, or a change in growth rate during film growth. Extended defects which form include twins, line dislocations, or looplike defects. Lattice imaging has demonstrated the lattice matching across the InSb film/InSb substrate interface, despite the formation of In precipitates during the heat cleaning procedure.

Plastic creep flow effects in the diffusive cavitation of grain boundaries

We analyze the growth of cavities along grain interfaces by the combined processes of grain boundary diffusion and plastic dislocation creep in the adjoining grains. It is shown that the coupling between the processes can be expressed in terms of a parameter L, which has the dimensions of length and which is a function of material properties, temperature and applied stress; L decreases with increasing temperature and stress and has, e.g., values in the range of 0.25 to 25 μm for various pure metals when stressed to 10 −3 × shear modulus at 0.5 T m . The contribution of dislocation creep to the cavity growth rate is shown to be negligible when L is comparable to or larger than the cavity spacing, but significant interactions occur, leading to growth rates very much in excess of those predicted on the basis of boundary diffusion alone, when L is comparable to or smaller than the cavity size. The coupling occurs because extensive dislocation creep allows local accommodation of matter diffused into the grain boundary from the cavity walls. The cavity growth rate is analyzed by formulating a new variational principle that governs combined processes of grain boundary diffusion and non-linear viscous creep, and by implementing this principle through the finite-element method to obtain numerical solutions. Results for the cavity growth rate are presented for a wide range of ratios of L to cavity spacing, and of cavity radius to spacing. Also, results are presented for the total growth time of cavities from an initial size to final coalescence.

Simplified vapor growth of arsenic single crystals

Large, strain free single crystals of α-arsenic were grown by the vapor phase technique. The method uses a simplified thermal profile and an easy to construct clear fused silica growth ampoule. Total growth time is approximately 3 days. Growth conditions and physical equipment descriptions are reported.