Kinetic-energy induced smoothening and delay of epitaxial breakdown in pulsed-laser deposition
TL;DR: In this paper, the effect of kinetic energy of depositing species from flux pulsing during pulsed-laser deposition (PLD) on surface morphology evolution of Ge(001) homoepitaxy at low temperature was isolated.
Abstract: We have isolated the effect of kinetic energy of depositing species from the effect of flux pulsing during pulsed-laser deposition (PLD) on surface morphology evolution of Ge(001) homoepitaxy at low temperature $(100\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$. Using a dual molecular beam epitaxy (MBE) PLD chamber, we compare morphology evolution from three different growth methods under identical experimental conditions except for the differing nature of the depositing flux: (a) PLD with average kinetic energy $300\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ (PLD-KE); (b) PLD with suppressed kinetic energy comparable to thermal evaporation energy (PLD-TH); and (c) MBE. The thicknesses at which epitaxial breakdown occurs are ranked in the order $\mathrm{PLD}\text{\ensuremath{-}}\mathrm{KE}g\mathrm{MBE}g\mathrm{PLD}\text{\ensuremath{-}}\mathrm{TH}$; additionally, the surface is smoother in PLD-KE than in MBE. The surface roughness of the films grown by PLD-TH cannot be compared due to the early epitaxial breakdown. These results demonstrate convincingly that kinetic energy is more important than flux pulsing in the enhancement of epitaxial growth, i.e., the reduction in roughness and the delay of epitaxial breakdown.
Figures (3)
Fig. 4. (a) RHEED specular intensity variations during PLD-KE with 1 Hz (dashed line) and 2 Hz (solid line) of repetition rate while keeping instantaneous flux the same in both cases. Time axes are adjusted such that intensity minima and maxima for both cases are aligned at the same positions on abscissa. (b) First 20 seconds of RHEED intensity variation of PLD-KE with 1 Hz from (a). Modulations from individual laser pulses are visible. 
Fig. 2. (Color online) AFM images of films grown at 100 °C by (a) MBE, (b) PLD-KE, and (c) PLD-TH, and (d) RHEED pattern taken from surface shown in (c). Scan size and vertical scale of (a) – (c) are 0.25 x 0.25 μm2 and 5 nm, respectively. Thickness of films in (a) – (c) is shown in the left bottom corner of each image. 
Table I. Epitaxial thickness of PLD-KE, PLD-TH, and MBE at 100 °C and 150 °C. In the case of PLD-KE, the thickest samples – 270 nm at 100 °C and 410 nm at 150 °C – are still fully epitaxial.
Citations
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TL;DR: Detailed growth kinetics results are discussed, which illustrate that 'true' layer-by-layer (LBL) growth can only be approached, not fully met, even though many characterization techniques reveal interfaces with unexpected sharpness.
Abstract: Pulsed-laser deposition (PLD) is one of the most promising techniques for the formation of complex-oxide heterostructures, superlattices, and well controlled interfaces. The first part of this paper presents a review of several useful modifications of the process, including methods inspired by combinatorial approaches. We then discuss detailed growth kinetics results, which illustrate that 'true' layer-by-layer (LBL) growth can only be approached, not fully met, even though many characterization techniques reveal interfaces with unexpected sharpness. Time-resolved surface x-ray diffraction measurements show that crystallization and the majority of interlayer mass transport occur on timescales that are comparable to those of the plume/substrate interaction, providing direct experimental evidence that a growth regime exists in which non-thermal processes dominate PLD. This understanding shows how kinetic growth manipulation can bring PLD closer to ideal LBL than any other growth method available today.
245 citations
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TL;DR: In this article, a comparison of growth morphology evolution for pulsed laser deposition and thermal deposition in the same dual-use chamber under identical thermal, background, and surface preparation conditions, and varying the kinetic energy by varying the laser fluence or using an inert background gas was made.
Abstract: This paper reviews our recent studies of the fundamentals of growth morphology evolution in Pulsed Laser Deposition in two prototypical growth modes: metal-on-insulator island growth and semiconductor homoepitaxy. By comparing morphology evolution for pulsed laser deposition and thermal deposition in the same dual-use chamber under identical thermal, background, and surface preparation conditions, and varying the kinetic energy by varying the laser fluence or using an inert background gas, we have isolated the effect of kinetic energy from that of flux pulsing in determining the differences between morphology evolution in these growth methods. In each growth mode analytical growth models and Kinetic Monte Carlo simulations for thermal deposition, modified to include kinetic energy effects, are successful at explaining much of what we observe experimentally.
61 citations
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TL;DR: In this paper, the authors studied the pulsed laser deposition of homoepitaxial SrTiO3 thin films in different deposition regimes in order to elucidate the possibility to promote two-dimensional growth by increasing the kinetic energy of the oncoming particles.
Abstract: We studied the pulsed laser deposition of homoepitaxial SrTiO3 thin films in different deposition regimes in order to elucidate the possibility to promote two-dimensional growth by increasing the kinetic energy of the oncoming particles. The kinetic energy of the oncoming species is determined by exploiting plume diagnostics techniques and the resulting nucleation and growth processes are analysed by reflection high-energy electron diffraction and atomic force microscopy. We could show that although the kinetic energy of the oncoming species varies to a great extent, the diffusion process is mostly influenced by the stoichiometry. Under stoichiometric conditions, obtained only in a limited window of process parameters, the adatoms on the surface have the highest diffusivity, thus promoting a step-flow growth mode. Under nonstoichiometric conditions, both Sr- and Ti-rich, the diffusivity is strongly reduced. This results in a transition from a two-dimensional to a three-dimensional growth under Sr-rich conditions. Conversely, in the Ti-rich case, obtained at high laser fluence, the two-dimensional growth sustains until the end of the growth process. We attribute this to the high island density available at high laser fluence which facilitates the diffusion of adatoms to step edges despite of their reduced diffusion length.
56 citations
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TL;DR: In this paper, Nanosecond pulsed laser deposition (PLD) has been used to grow nanoparticle films of Au on Si and sapphire substrates, and the equivalent solid density thickness was measured with a quartz crystal monitor and the ion flux was measured using a time-of-flight Langmuir probe.
Abstract: Nanosecond pulsed laser deposition (PLD) has been used to grow nanoparticle films of Au on Si and sapphire substrates. The equivalent solid density thickness was measured with a quartz crystal monitor and the ion flux was measured with a time-of-flight Langmuir probe. The ion signal yields the ion energy distribution. The angular distribution of deposited material and the ablated mass per pulse were also measured. These values are incorporated into an isentropic plasma expansion model for a better description of the expansion of the ablated material. Atomic force microscopy and UV/vis optical spectroscopy were used to characterise the films. Atomic force microscopy shows that in the equivalent thickness range 0.5–5 nm the deposited material is nanostructured and the surface coverage increases with increasing equivalent thickness. The optical absorption spectra show the expected surface plasmon resonance, which shifts to longer wavelengths and increases in magnitude as the equivalent thickness is increased.
46 citations
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TL;DR: In this paper, the formation and evolution process of self-assembled InGaAs quantum dot molecules (QDMs) is studied in terms of configuration, volume, and types of QDMs.
Abstract: The formation and evolution process of self-assembled InGaAs quantum dot molecules (QDMs) are studied in terms of configuration, volume, and types of QDMs. QDMs are formed around self-assembled GaAs nanoscale island induced by adapting a hybrid growth approach combining droplet homoepitaxy and Stranski–Krastanov mode. In distinction from our previous results [Lee et al., Appl. Phys. Lett. 89, 202101 (2006)], hexa-QDMs are fabricated without the formation of background QDs, which can be due to a combinational effects of enhanced intermixing of Ga and In atoms, enhanced surface diffusion (high mobility) of adatoms, and higher In desorption rate due to the higher thermal energy provided during the fabrication of QDMs. In addition, a detailed evolution mechanism from bi-QDMs (two QDs per each GaAs island) to hexa-QDMs (six QDs per island) is proposed based on atom diffusion, material transfer, and equilibrium dimension (saturation) of QDs. Under a fixed InAs coverage, depending on postannealing process after ...
27 citations
References
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01 Jan 1994
TL;DR: Pulsed laser deposition of high-temperature superconducting thin films for active and passive device applications is discussed in this article, with a focus on the commercial scale-up of Pulsed Laser Deposition.
Abstract: Partial table of contents: History and Fundamentals of Pulsed Laser Deposition (J. Cheung). Diagnostics and Characteristics of Laser--Produced Plasmas (D. Geohegan). Particulates Generated by Pulsed Laser Ablation (L.--C. Chen). Angular Distribution of Ablated Material (K. Saenger). Film Nucleation and Film Growth in Pulsed Laser Deposition of Ceramics (J. Horwitz & J. Sprague). Processes Characteristics and Film Properties in Pulsed Laser Plasma Deposition (S. Metev). Commercial Scale--Up of Pulsed Laser Deposition (J. Greer). Pulsed Laser Deposition: Future Trends (T. Venkatesan). Comparison of Vacuum Deposition Techniques (G. Hubler). Pulsed Laser Deposition of High--Temperature Superconducting Thin Films for Active and Passive Device Applications (R. Muenchausen & X. Wu). Pulsed Laser Deposition of Metals (J. Kools). Appendix. References. Index.
3,227 citations
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TL;DR: In this article, the authors outline the fundamental physics involved and go on to discuss recent experimental findings of pulsed laser deposition, as an alternative to chemical vapor deposition or molecular beam epitaxy.
Abstract: Photons have many advantages for vaporizing condensed systems, and laser vaporization sources have a flexibility not available with other methods. These sources are applied to making thin films in the well-known technique of pulsed laser deposition (PLD). The vaporized material may be further processed through a pulsed secondary gas, lending the source additional degrees of freedom. Such pulsed-gas sources have long been exploited for fundamental studies, and they are very promising for film deposition, as an alternative to chemical vapor deposition or molecular beam epitaxy. The authors outline the fundamental physics involved and go on to discuss recent experimental findings.
682 citations
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TL;DR: In this paper, the magnetoresistance peak occurs around the Curie point, whereas for x = 0.5 the onset of magnetoreduction is somewhat below and increases monotonically as.
Abstract: Manganites of the series , with x = 0, 0.1, 0.3, 0.5, 0.7 and 1.0, have been characterized in ceramic form and thin films have been prepared by pulsed laser deposition. Characterization techniques included x-ray diffraction, conductivity and magnetoresistance, magnetization and susceptibility, optical spectroscopy and the Faraday effect. Both the films and ceramics exhibit a maximum low-temperature conductivity at which is coexistent with ferromagnetic order. The negative magnetoresistance effect is qualitatively different for the x = 0.3 and x = 0.5 compositions. For x = 0.3 the magnetoresistance peak occurs around the Curie point, whereas for x = 0.5 the onset of magnetoresistance is somewhat below and increases monotonically as . The applied field appears to modify the magnetic order (on the scale of the spin diffusion length) down to the lowest temperatures for x = 0.5, but for x = 0.3 the ferromagnetic order is essentially complete and collinear below the Curie point.
393 citations
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TL;DR: In this article, the dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation of c-Si into 1-10 Torr He and Ar gases are revealed by imaging laser-induced photoluminescence and Rayleigh-scattered light from gas-suspended 1−10 nm SiOx particles.
Abstract: The dynamics of nanoparticle formation, transport, and deposition by pulsed laser ablation of c-Si into 1–10 Torr He and Ar gases are revealed by imaging laser-induced photoluminescence and Rayleigh-scattered light from gas-suspended 1–10 nm SiOx particles. Two sets of dynamic phenomena are presented for times up to 15 s after KrF-laser ablation. Ablation of Si into heavier Ar results in a uniform, stationary plume of nanoparticles, while Si ablation into lighter He results in a turbulent ring of particles which propagates forward at 10 m/s. Nanoparticles unambiguously formed in the gas phase were collected on transmission electron microscope grids for Z-contrast imaging and electron energy loss spectroscopy analysis. The effects of gas flow on nanoparticle formation, photoluminescence, and collection are described.
309 citations
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TL;DR: In this article, the basic principles of nanoparticle synthesis by conventional pulsed laser ablation are described and the theoretical development and analysis of the experimental results are given for condensation, expansion and properties of silicon nanoclusters.
Abstract: We describe the basic principles of nanoparticle synthesis by conventional pulsed laser ablation. The generalization of the Zeldovich and Raizer theory of condensation has been performed for inhomogeneous laser-induced plume where the rates of nucleation as well as the condensation times are different for different parts of the plume. The theoretical development and analysis of the experimental results are given for condensation, expansion and properties of silicon nanoclusters.
183 citations