Growth Regime Research Articles

Ar transport and blister growth kinetics in titania-doped germania-based optical coatings

Blistering is a phenomenon sometimes observed in sputtered-deposited thin films but seldom investigated in detail. Here, we consider the case of titania-doped germania (TGO)/silica multilayers deposited by ion beam sputtering. TGO is a candidate as high refractive index material in the Bragg mirrors for the next iteration of gravitational waves detectors. It needs to be annealed at 600 ∘C for 100 h in order to reach the desired relaxation state. However under some growth conditions, in 52-layer TGO/silica stacks, blistering occurs upon annealing at a temperature near 500 ∘C, which corresponds to the temperature where Ar desorbs from TGO. In order to better understand the blistering phenomenon, we measure the Ar transport in single layers of TGO and silica. In the case of < 1 µm-thick TGO layers, the Ar desorption is mainly limited by detrapping. The transport model also correctly predicts the evolution of the total amount of Ar in a 8.5 µm stack of TGO and silica layers annealed at 450 ∘C, but in that case, the process is mainly limited by diffusion. Since Ar diffusion is an order of magnitude slower in TGO compared to silica, we observe a correspondingly strong accumulation of Ar in TGO. The Ar transport model is used to explain some regimes of the blisters growth, and we find indications that Ar accumulation is a driver for their growth in general, but the blisters nucleation remains a complex phenomenon influenced by several other factors including stress, substrate roughness, and impurities.

Simulations of non-integer upconversion in resonant six-wave scattering

Resonant upconversion through a sixth order relativistic nonlinearity resulting in a unique resonance was recently proposed [Malkin and Fisch, Phys. Rev. E 108, 045208 (2023)]. The high order resonance is a unique non-integer multiple of a driving pump frequency resulting in a frequency upshift by a factor of ≈3.73. We demonstrate the presence, unique requirements, and growth of this mode numerically. Through tuning waves to high amplitude, in a mildly underdense plasma, the six-photon process may grow more than other non-resonant but lower order processes. The growth of the high frequency mode remains below the nonlinear growth regime. However, extending current numerical results to more strongly coupled resonances with longer pulse propagation distances suggests a pathway to significant upconversion.

Autonomous Synthesis of Thin Film Materials with Pulsed Laser Deposition Enabled by In Situ Spectroscopy and Automation.

Autonomous systems that combine synthesis, characterization, and artificial intelligence can greatly accelerate the discovery and optimization of materials, however platforms for growth of macroscale thin films by physical vapor deposition techniques have lagged far behind others. Here this study demonstrates autonomous synthesis by pulsed laser deposition (PLD), a highly versatile synthesis technique, in the growth of ultrathin WSe2 films. By combing the automation of PLD synthesis and in situ diagnostic feedback with a high-throughput methodology, this study demonstrates a workflow and platform which uses Gaussian process regression and Bayesian optimization to autonomously identify growth regimes for WSe2 films based on Raman spectral criteria by efficiently sampling 0.25% of the chosen 4D parameter space. With throughputs at least 10x faster than traditional PLD workflows, this platform and workflow enables the accelerated discovery and autonomous optimization of the vast number of materials that can be synthesized by PLD.

Diffraction-based approach for real-time monitoring of nanosecond direct laser interference patterning structure formation on stainless steel

Direct Laser Interference Patterning (DLIP) stands out as a versatile and cost-effective method for functionalizing material surfaces at high throughputs. Monitoring the dynamics of the structure formation can lead to a deeper understanding of the interplay between the main factors governing the process and ultimately to optimize the final texture. Here, the formation of gratings on stainless steel by DLIP with ns-pulses is studied using a diffraction-based approach, which measures the time-resolved reflectivity (TRR) of the sample. Measurements are performed for single pulses across different laser fluences. The melting dynamics are analyzed and compared with numerical results. By correlating the recorded signals with the structure depths, growth rates of 11 nm/ns and 57 nm/ns were estimated for fluences of 1.9 J/cm2 and 5.3 J/cm2, respectively. Furthermore, two growth regimes are identified. In the fast growth phase, the melting time increased from 73 to 380 ns for fluences of 1.9 J/cm2 and 5.9 J/cm2, respectively, showing a good agreement with the performed thermal simulations.

Temperature-dependent epitaxial evolution of carbon-free corundumα-Ga2O3 on sapphire

Abstract Unintentionally doped carbon impurities from organometallic precursors are primary sources of carrier compensation and mobility degradation in wide bandgap semiconductors, leading to lowered performance of power devices. To address this challenge, carbon-free α-Ga2O3 single crystalline thin-films were heteroepitaxially grown on sapphire substrates by using gallium inorganic precursors through mist chemical vapor deposition technique. Determined through temperature dependence of growth rates, three distinct growth regimes are identified: the surface reaction limited regime below 480°C, the mid-temperature mass-transport limited regime (480-530 °C) and the high temperature limited regime related to desorption or phase transition. With an optimized around 530 °C, the densities of screw and edge dislocations are reduced to 7.17×10^6 and 7.60×10^9 cm-2, respectively. Notably, carbon incorporation was eliminated in the α-Ga2O3 grown by inorganic GaCl3, as evidenced by the absence of carbon-related vibrational bands in Raman scattering analysis, while crystalline quality was comparable to that grown with organometallic precursors. The high solubility of GaCl3 in water is expected to enable the rapid growth of high-purity α-Ga2O3 with improved electronic performances. Keywords: ultrawide bandgap semiconductor, chemical vapor deposition, impurity contamination.

Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation

Abstract Current operational considerations require steam turbines to operate in a more flexible way, with more frequent and faster start-up and an increasing part-load operation. For very low mass flowrates, the interaction of highly separated flow with the high-speed rotor blades causes windage flow. This type of flow is characterized by increased temperature and highly unsteady flow, which forms vortex structures that rotate at a fraction of the rotor speed. If their magnitude is sufficiently high and the frequency is close to the blade eigenfrequency, non-synchronous vibration (NSV) can be induced. In this paper, low-flow turbine operation is investigated using a three-stage turbine rig that features an instrumentation concept focused on capturing aerodynamic and aeroelastic phenomena. Extensive steady probe, unsteady pressure, and tip-timing measurements are utilized. The experimental scope covers a wide range of operating points in terms of rotational speed and mass flowrates. Low-flow regimes are detected by a reversal in torque and increase in temperature. Unsteady measurements during transient operation identified large-scale vortical flow structures rotating along the circumference, so-called rotating instabilities (RIs). The onset, growth, and breakdown regimes of RI are characterized for different low-flow conditions. The quantitative characteristics of RI with regard to nodal diameter and rotational speed are derived by a cross-correlation of multiple unsteady sensors. The blade vibration measurements show a moderate structural response from unsteady aerodynamic excitation, indicating no significant NSV occurring in the present experimental setup. Later in the study, an acoustic excitation system has been applied to trigger a locked-in NSV without interrupting the coherent flow structures. From that, significant blade response has been observed, revealing a high degree of mistuning and damping of the rotor blading.

Highly-doped MBE-grown GaP nanowires: Synthesis, electrical study and modeling

Efficient doping of semiconductor nanowires remains a major challenge towards the commercialization of nanowire-based devices. In this work we investigate the growth regimes and electrical properties of MBE-grown p- and n-type gallium phosphide nanowires doped with Be and Si, respectively. Electrical conductivity of individual nanowires is quantitatively studied via atomic force microscopy supported with numerical analysis. Based on conductivity measurements, we provide growth strategies for achieving the doping level up to ND=5⋅1018 cm-3 and NA=2⋅1019 cm-3 for GaP:Si and GaP:Be nanowires respectively, which is high enough for technological applications.

Constrained economic policy in Italy’s dual-hybrid economy

ABSTRACT This article examines recent developments in Italy’s economic and fiscal policymaking. It does so by contextualising the 2023 changes in the Italian National Recovery and Resilience Plan (NRRP) within three broader aspects which have characterised the Italian political economy: (1) the country’s conservative fiscal trajectory inside the monetary union (EMU); (2) the expansionary economic policies pursued in the face of both the pandemic and energy crises; (3) the peculiar characteristics of Italy’s ‘dual-hybrid economy’. The article posits that, since the EMU, Italy has continuously run primary budget surpluses higher than its EMU peers. Only since Covid-19, and with the relaxation of EMU constraints, has Italy’s fiscal stance turned expansionary. This has allowed space for various socioeconomic policies to partially shield households and firms from the crises’ fallout. However, with a return to fiscal conservatism, the NRRP now represents the only game in town to try and address Italy’s dual hybridity characterised by weak state capacity and supply-side institutional inconsistencies as well as two diametrically opposed regional growth regimes in the North and the South.

Phase-Centric MOCVD Enabled Synthetic Approaches for Wafer-Scale 2D Tin Selenides.

Following an initial nucleation stage at the flake level, atomically thin film growth of a van der Waals material is promoted by ultrafast lateral growth and prohibited vertical growth. To produce these highly anisotropic films, synthetic or post-synthetic modifications are required, or even a combination of both, to ensure large-area, pure-phase, and low-temperature deposition. A set of synthetic strategies is hereby presented to selectively produce wafer-scale tin selenides, SnSex (both x=1 and 2), in the 2D forms. The 2D-SnSe2 films with tuneable thicknesses are directly grown via metal-organic chemical vapor deposition (MOCVD) at 200°C, and they exhibit outstanding crystallinities and phase homogeneities and consistent film thickness across the entire wafer. This is enabled by excellent control of the volatile metal-organic precursors and decoupled dual-temperature regimes for high-temperature ligand cracking and low-temperature growth. In contrast, SnSe, which intrinsically inhibited from 2D growth, is indirectly prepared by a thermally driven phase transition of an as-grown 2D-SnSe2 film with all the benefits of the MOCVD technique. It is accompanied by the electronic n-type to p-type crossover at the wafer scale. These tailor-made synthetic routes will accelerate the low-thermal-budget production of multiphase 2D materials in a reliable and scalable fashion.

Between export-led growth and administrative Keynesianism: Italy’s two-tiered growth regime

ABSTRACT Comparative political economy scholarship struggles to categorise Italy’s model of capitalism between a mixed-market economy and a hybrid, stagnant economic system. To enhance our understanding of the Italian political economy, this article employs the analytical framework of growth regimes to study Italy’s regional economic systems. Our analysis indicates that Italy can hardly be defined as a ‘national growth regime’ due to the presence of two diametrically opposed regional growth regimes: Northern regions conform to a manufacturing-based, export-led growth regime supported by competitiveness-enhancing territorial institutions; southern regions conform to a particular variety of the consumption-led growth regime, that is, an administrative Keynesianism regime, which we theorise to typify a regime where growth and employment are systematically dependent on the state’s role of employer of last resort, the state’s consumption-enhancing social policies and economic forbearance of labour and corporate tax regulations. The article suggests that studying regional growth regimes is desirable when marked internal diversity in economic outcomes or productive structures exists across regions within (generally larger) countries, and when subnational governments have powers to develop major own institutions/policies in support of regional growth regimes.

Macroeconomic policy regimes and demand and growth regimes in emerging market economies: the case of Argentina

Demand and growth regimes (DGR) and macroeconomic policy regimes (MPR) frameworks have assumed prominence within the post-Keynesian literature. However, most studies based on these conceptual frameworks have focused on developed economies. The main contribution of this paper is to provide a post-Keynesian analysis of the DGR and MPR of an emerging capitalist economy, Argentina, in the period between 2002 and 2019. By providing a novel periodization of the Argentine macroeconomic development, the results show a more precise characterization of the latter, thus allowing a better understanding of economic policy and its results in terms of aggregate demand and growth. In particular, it is possible to observe the MPR and DGR transition between 2002 and 2015, as well as an abrupt change after 2016.

In search of a growth model for Italy: the failed attempt of an export-led recovery strategy?

We analyse Italy’s growth pattern from 2001 to 2019 using the demand and growth regime categories proposed in the post-Keynesian tradition and recently adopted in the comparative political economy (CPE) literature. We argue that after the Global Financial and Economic Crisis (GFEC), Italy followed an export-led recovery strategy. In this respect, Germany’s growth model emerged as the successful model to follow. In the dominant view, Germany’s economic success since the mid-2000s was attributed to a series of painful but necessary economic reforms. The success of Germany’s export-led mercantilist regime became particularly attractive to Italy given the similar export-oriented manufacturing industry. However, Italy has followed the ‘wrong’ German model based on wage compression and restrictive budget policies while the ‘true’ German model is based on non-price competitiveness factors.

Incomplete monolayer regime and mixed regime of nanowire growth

Incomplete monolayer regime and mixed regime of nanowire growth

Deciphering Clues Regarding Magma Composition Encoded in Quartz‐Hosted Embayments and Melt Inclusions Through Direct Numerical Simulations

AbstractCrystal‐hosted melt embayments and melt inclusions partially record magmatic processes at depth, but it is not always obvious how to interpret this record. One impediment is our incomplete understanding of how embayments and melt inclusions form. In this study, we investigate the formation mechanism of embayments and melt inclusions during quartz growth to quantify the relationship between the compositions of the entrapped and average melt. We study the growth of embayments and inclusions through direct numerical simulations that couple the growth of a crystal surface with the evolution of the concentrations of incompatible components in the surrounding melt. We find that H2O is more enriched in the interior of defects on crystal surface compared to the exterior. The resultant lower disequilibrium in the defect interior causes lower growth rate than in the exterior, elongating the defect into an embayment. If crystal growth stops, the composition in the embayment equilibrates with the average melt within days to months. If crystal growth continues until the embayment neck closes, a melt inclusion forms. The melt entrapped by both embayments and melt inclusions is enriched in incompatible components, such as H2O and CO2. In addition to inclusion size, the enrichment of incompatible components in melt inclusions also depends on component diffusivity and the crystal growth regime. High‐diffusivity components like H2O have similar enrichment levels in all scenarios, while lower‐diffusivity components like CO2 are more enriched in melt inclusions with smaller sizes or formed in continuous crystal growth.

Prolonged pattern coarsening in ion irradiated swinging Si substrates

Low energy ion beams are regarded as an effective means to spatio-temporally pattern a wide variety of surfaces that exhibit intriguing motifs. In this work, an unconventional technique of surface patterning has been demonstrated by studying the topographical evolution of a Si(100) surface in the presence of azimuthal sample swinging (Δϕ=20∘) under 500 eV Ar+irradiation with a polar incidence angle of 67°. A prolonged wavelength coarsening is also noticed for the swinging sample. Ripple anticoarsening is observed for static sample at high fluences. The linear and nonlinear growth regimes are found to bear a direct consequence of this unconventional geometry. Furthermore, two-dimensional slope distributions of the surface morphologies clearly indicate reduced asymmetries in the surface structures. The present geometry brings in an additional factor of differential exposure and redeposition effects in addition to the near-surface mass redistribution, the former being inconceivable in the static configuration. This study establishes the role of this unconventional yet simple method to precisely modify and control surface asymmetries and influence regime shifts.

Economic growth, current account dynamics, and growth regimes in the Baltic states

ABSTRACT This article considers the growth performance of the Baltic states from the mid-1990s to 2021. Economic growth was rapid before the global financial crisis but slowed markedly after the crisis. Panel data estimations using seemingly unrelated regressions suggest that the dynamics of the current account balance are important for short and medium-term growth in the Baltic states but that there is a break signifying a change of short-term growth regime around the time of the global financial crisis. Before the crisis, rapid growth was supported by domestic demand that was made possible by large current account deficits. After the crisis, economic growth was supported by external demand reflected in improvements in current account balances. The shift in the short-term economic growth regime after the global financial crisis has brought lower rates of economic growth but also reduced financial vulnerability.

Size effects in fatigue crack growth in confined volumes: A microbending case study on nanocrystalline nickel

Mechanical size effects are a well known phenomenon when the sample volume is reduced or the characteristic length of the microstructure is changed. While size effects in micropillar compression (smaller is stronger) or due to grain refinement (Hall-Petch) are well understood, this is less so in fracture mechanics. Given this lack of knowledge, the main question addressed in this work is: What happens to the fatigue crack growth properties when extrinsic size effects play a role? To answer this question, nanocrystalline nickel cantilevers, ranging in width from 5 to ▪, were subjected to fatigue crack growth. The crack growth rates and stress intensity factors were calculated and the Paris exponent in the stable crack growth regime was determined. It was found that the results scatter more strongly for the smaller cantilevers compared to the larger cantilevers. Results are interpreted in terms of plastic zone size and ligament size which are found to be critical for small cantilevers.

The influence of the mass transport regime on laser chemical vapor deposited carbon fibers

Laser Chemical Vapor Deposition (LCVD) is a process through which fibers are additively deposited by the dissociation and deposition of a precursor gas into the solid phase under a translating laser focal point. In the hyperbaric pressure conditions, LCVD has two identified reaction regimes. The first being limited by surface reaction kinetics (SRK) and the second being limited by mass transport (MT). This article examines the effects of mass transport (MT) limitations on carbon fiber growth using either ethane (C2H6) or ethylene (C2H4). Both hydrocarbon precursors reveal a growth rate reduction when transitioning from SRK-to-MT to meet the no-slip condition in fluid dynamics. This transition correlates to a fiber microstructure change from a core shell morphology with a graphitic structure (SRK) to a nodular morphology with an amorphous structure (MT). The fiber fracture stress is generally found to be higher in the MT than SRK regime because of the reduction of easily cleaved graphitic planes in the MT fibers. Collectively, these results demonstrate the importance of the MT limited growth regime and how fiber characteristics can be manipulated when grown in this regime.

Colloidal Multi-Dot Nanorods.

Colloidal nanorod heterostructures consisting of multiple quantum dots within a nanorod (n-DNRs, where n is the number of quantum dots within a nanorod) are synthesized with alternating segments of CdSe "dot" and CdS "rod" via solution heteroepitaxy. The reaction temperature, time dependent ripening, and asymmetry of the wurtzite lattice and the resulting anisotropy of surface ligand steric hindrance are exploited to vary the morphology of the growing quantum dot segments. The alternating CdSe and CdS growth steps can be easily repeated to increment the dot number in unidirectional or bidirectional growth regimes. As an initial exploration of electron occupation effects on their optical properties, asymmetric 2-DNRs consisting of two dots of different lengths and diameters are synthesized and are shown to exhibit a change in color and an unusual photoluminescence quantum yield increase upon photochemical doping.

Microstructural influences on simultaneous strength and fatigue crack resistance in advanced high-strength steels

In this study, we investigate the relation between microstructure and fatigue crack propagation mechanisms in three commercial hot-rolled thick-plate advanced high-strength steels (AHSSs), namely 800CP, 700MC, and 700MCPlus, and compare them with a conventional high-strength low-alloy (HSLA) steel, 500MC, commonly used in heavy-duty vehicle chassis production. Tensile testing, and fatigue crack growth rate (FCGR) assessments have been conducted, and mechanisms controlling the performance of these steels are comprehensively examined through microstructure characterization before and after fatigue testing. Notably, FCGR results reveal that, despite having the highest yield strength among the investigated steels, 700MCPlus exhibits the slowest FCGR in both near-threshold and stable crack growth regimes. This improved fatigue crack propagation resistance of 700MCPlus in terms of its threshold stress intensity factor range (ΔKth) is attributed to its unique texture, which restricts slip activity, and the presence of martensite at grain boundaries, contributing to fatigue crack deflection. This martensite-induced crack deflection becomes more significant in the stable crack growth regime, where fatigue crack primarily propagates intergranularly as the stress intensity factor range (ΔK) increases. These mechanistic findings offer new design possibilities for AHSSs, combining excellent strength and fatigue performance.