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138 results on '"Ludwig, Karl F."'

1. Coherent X-ray Spectroscopy Elucidates Nanoscale Dynamics of Plasma-Enhanced Thin-Film Growth

Author

Myint, Peco, Woodward, Jeffrey M., Wang, Chenyu, Zhang, Xiaozhi, Wiegart, Lutz, Fluerasu, Andrei, Headrick, Randall L., Eddy, Jr., Charles R., and Ludwig, Karl F.

Subjects
Condensed Matter - Materials Science
Abstract

Sophisticated thin film growth techniques increasingly rely on the addition of a plasma component to open or widen a processing window, particularly at low temperatures. However, the addition of the plasma into the growth environment also complicates the surface dynamical evolution. Taking advantage of continued increases in accelerator-based X-ray source brilliance, this real-time study uses X-ray Photon Correlation Spectroscopy (XPCS) to elucidate the nanoscale surface dynamics during Plasma-Enhanced Atomic Layer Deposition (PE-ALD) of an epitaxial indium nitride film. XPCS examines the evolution of the coherent X-ray scattering speckle pattern, which is a fingerprint of the unique sample microstructure at each moment in time. In PE-ALD, ultrathin films are synthesized from repeated cycles of alternating self-limited surface reactions induced by temporally-separated pulses of material precursor and plasma reactant, allowing the influence of each on the evolving morphology to be examined. During the heteroepitaxial 3D growth examined here, sudden changes in surface structure during initial film growth, consistent with numerous overlapping stress-relief events, are observed. When the film becomes continuous, the nanoscale surface morphology abruptly becomes long-lived with correlation time spanning the period of the experiment. Throughout the growth experiment, there is a consistent repeating pattern of correlations associated with the cyclic growth process, which is modeled as transitions between different surface states. The plasma exposure does not simply freeze in a structure that is then built upon in subsequent cycles, but rather there is considerable surface evolution during all phases of the growth cycle., Comment: 25 pages, 8 figures

Published
2023

2. Local step-flow dynamics in thin film growth with desorption

Author

Zhang, Xiaozhi, Ulbrandt, Jeffrey G., Myint, Peco, Fluerasu, Andrei, Wiegart, Lutz, Zhang, Yugang, Nelson, Christie, Ludwig, Karl F., and Headrick, Randall L.

Subjects
Condensed Matter - Materials Science
Abstract

Desorption of deposited species plays a role in determining the evolution of surface morphology during crystal growth when the desorption time constant is short compared to the time to diffuse to a defect site, step edge or kink. However, experiments to directly test the predictions of these effects are lacking. Novel techniques such as \emph{in-situ} coherent X-ray scattering can provide significant new information. Herein we present X-ray Photon Correlation Spectroscopy (XPCS) measurements during diindenoperylene (DIP) vapor deposition on thermally oxidized silicon surfaces. DIP forms a nearly complete two-dimensional first layer over the range of temperatures studied (40 - 120 $^{\circ}$C), followed by mounded growth during subsequent deposition. Local step flow within mounds was observed, and we find that there was a terrace-length-dependent behavior of the step edge dynamics. This led to unstable growth with rapid roughening ($\beta>0.5$) and deviation from a symmetric error-function-like height profile. At high temperatures, the grooves between the mounds tend to close up leading to nearly flat polycrystalline films. Numerical analysis based on a 1 + 1 dimensional model suggests that terrace-length dependent desorption of deposited ad-molecules is an essential cause of the step dynamics, and it influences the morphology evolution., Comment: 21 pages, 9 figures, and one table

Published
2023

3. Early Stage Growth of Amorphous Thin Film: Average Kinetics, Nanoscale Dynamics and Pressure Dependence

Author

Wang, Chenyu, Ludwig, Karl F., Wagenbach, Christa, Rainville, Meliha G., Narayanan, Suresh, Zhou, Hua, Ulbrandt, Jeffrey G., and Headrick, Randall L.

Subjects
Condensed Matter - Materials Science
Abstract

We used the Coherent Grazing Incidence Small Angle X-Ray Scattering (Co-GISAXS) technique to study the average kinetics and nanoscale dynamics during early-stage a-WSi$_2$ sputter deposition. The kinetic and dynamic properties are examined as a function of pressure, which is known to be a critical factor in determining final surface roughness. Surface growth kinetics and dynamics are characterized by time parameters extracted from the height-height structure factor and correlation functions. The roughness at a given length scale reaches a maximum before relaxing down to a steady state. The lateral length scale dependence and pressure dependence are then compared among measured kinetics and dynamics time parameters. Surfaces grown at lower pressures are smoother, leading to longer correlation times. The time to reach a dynamic steady state and a kinetic steady state show contrasting pressure dependence. A dynamic steady state is reached earlier than the kinetic steady state at high pressure. A more random deposition direction and lower kinetic energy at higher pressures can explain these phenomena, along with the hypothesis that larger nanoclusters form in vapor before arriving at the surface. A continuum model is applied to simulate the overall behavior with mixed success., Comment: 13 pages, 17 figures

Published
2021

6. Atomic layer deposition-based tuning of the pore size in mesoporous thin films studied by in situ grazing incidence small angle x-ray scattering

Author

Dendooven, Jolien, Devloo-Casier, Kilian, Ide, Matthias, Grandfield, Kathryn, Kurttepeli, Mert, Ludwig, Karl F., Bals, Sara, Van Der Voort, Pascal, and Detavernier, Christophe

Subjects
Condensed Matter - Materials Science
Abstract

Atomic layer deposition (ALD) enables the conformal coating of porous materials, making the technique suitable for pore size tuning at the atomic level, e.g., for applications in catalysis, gas separation and sensing. It is, however, not straightforward to obtain information about the conformality of ALD coatings deposited in pores with diameters in the low mesoporous regime (< 10 nm). In this work, it is demonstrated that in situ synchrotron based grazing incidence small angle x-ray scattering (GISAXS) can provide valuable information on the change in density and internal surface area during ALD of TiO2 in a porous titania film with small mesopores (3-8 nm). The results are shown to be in good agreement with in situ x-ray fluorescence data representing the evolution of the amount of Ti atoms deposited in the porous film. Analysis of both data sets indicates that the minimum pore diameter that can be achieved by ALD is determined by the size of the Ti-precursor molecule.

Published
2015
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8. Influence of plasma species on the early-stage growth kinetics of epitaxial InN grown by plasma-enhanced atomic layer deposition

Author

Woodward, Jeffrey M., primary, Rosenberg, Samantha G., additional, Boris, David R., additional, Johnson, Michael J., additional, Walton, Scott G., additional, Johnson, Scooter D., additional, Robinson, Zachary R., additional, Nepal, Neeraj, additional, Ludwig, Karl F., additional, Hite, Jennifer K., additional, and Eddy, Charles R., additional

Published
2022
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15. (Invited) A Surface Science Toolbox for Understanding Atomic Layer Epitaxy

Author

Eddy, Charles R., primary, Rosenberg, Samantha G, additional, Woodward, Jeffrey Michael, additional, Anderson, Virginia R, additional, Johnson, Scooter D., additional, Ludwig, Karl F, additional, Wagenbach, Christa, additional, Kozen, Alex C, additional, Walton, Scott G, additional, Boris, David R., additional, and Nepal, Neeraj, additional

Published
2019
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18. Influence of temperature on atomic layer epitaxial growth of indium nitride assessed with in situ grazing incidence small-angle x-ray scattering

Author

Woodward, Jeffrey M., primary, Rosenberg, Samantha G., additional, Kozen, Alexander C., additional, Nepal, Neeraj, additional, Johnson, Scooter D., additional, Wagenbach, Christa, additional, Rowley, Andrew H., additional, Robinson, Zachary R., additional, Joress, Howie, additional, Ludwig, Karl F., additional, and Eddy, Charles R., additional

Published
2019
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19. In situ studies of low temperature atomic level processing of GaN surfaces for atomic layer epitaxial growth

Author

Rosenberg, Samantha G., primary, Wagenbach, Christa, additional, Anderson, Virginia R., additional, Johnson, Scooter D., additional, Nepal, Neeraj, additional, Kozen, Alexander C., additional, Woodward, Jeffrey M., additional, Robinson, Zachary R., additional, Munger, Max, additional, Joress, Howie, additional, Ludwig, Karl F., additional, and Eddy, Charles R., additional

Published
2019
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20. Understanding the effect of nitrogen plasma exposure on plasma assisted atomic layer epitaxy of InN monitored by real time grazing incidence small angle x-ray scattering

Author

Nepal, Neeraj, primary, Anderson, Virginia R., additional, Johnson, Scooter D., additional, Downey, Brian P., additional, Meyer, David J., additional, Robinson, Zachary R., additional, Woodward, Jeffrey M., additional, Ludwig, Karl F., additional, and Eddy, Charles R., additional

Published
2019
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21. Low temperature surface preparation of GaN substrates for atomic layer epitaxial growth: Assessment of ex situ preparations

Author

Rosenberg, Samantha G., primary, Pennachio, Daniel J., additional, Wagenbach, Christa, additional, Johnson, Scooter D., additional, Nepal, Neeraj, additional, Kozen, Alexander C., additional, Woodward, Jeffrey M., additional, Robinson, Zachary, additional, Joress, Howie, additional, Ludwig, Karl F., additional, Palmstrøm, Chris J., additional, and Eddy, Charles R., additional

Published
2019
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25. Real-time studies of gallium adsorption and desorption kinetics on sapphire (0001) by grazing incidence small-angle x-ray scattering and x-ray fluorescence.

Author

Wang, Yiyi, Özcan, Ahmet S., Ludwig, Karl F., and Bhattacharyya, Anirban

Subjects
X-ray scattering, SEPARATION (Technology), SURFACE chemistry, PHYSICAL & theoretical chemistry, ANALYTICAL chemistry
Abstract

Gallium adsorption and desorption on c-plane sapphire has been studied by real-time grazing incidence small-angle x-ray scattering and x-ray fluorescence as a function of substrate temperature (680–740 °C) and Ga flux. The x-ray techniques monitor the surface morphology evolution and amount of Ga on the surface. During deposition, nanodroplets of liquid Ga are observed to form on the surface and coarsen. The growth of droplet size during continuous deposition follows dynamical scaling, in agreement with expectations from theory and simulations which include deposition-induced droplet coalescence. However, observation of continued droplet distance scale coarsening during desorption points to the necessity of including further physical processes in the modeling. The desorption rate at different substrate temperatures gives the activation energy of Ga desorption as 2.7 eV, comparable to measured activation energies for desorption from Ga droplets on other substrates and to the Ga heat of vaporization. [ABSTRACT FROM AUTHOR]

Published
2008
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26. Transition behavior of surface morphology evolution of Si(100) during low-energy normal-incidence Ar+ ion bombardment.

Author

Ozaydin, Gozde, Ludwig, Karl F., Zhou, Hua, Zhou, Lan, and Headrick, Randall L.

Subjects
*ION bombardment, *SILICON research, *THIN films, *SURFACES (Technology), *DIFFUSION processes
Abstract

The temperature dependence of the surface morphology evolution during 1000 eV Ar+ ion bombardment of Si(100) surfaces at normal incidence is studied in real time. At room temperature the surface is amorphized by the ion bombardment but remains smooth. Calculations suggest this may be due to ion impact induced lateral mass redistribution. However, at the fluxes used here, surface roughening occurs above 400 °C, and in the range of 400 °C to 500 °C a transition region from amorphous to crystalline surface is observed. Above 500 °C, the surface remains crystalline and the growing corrugations exhibit dynamic scaling with power law growth in amplitude and characteristic length scale. This behavior is characteristic of instabilities driven by surface diffusion processes. [ABSTRACT FROM AUTHOR]

Published
2008
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27. Real-time x-ray studies of gallium nitride nanodot formation by droplet heteroepitaxy.

Author

Wang, Yiyi, Özcan, Ahmet S., Sanborn, Christopher, Ludwig, Karl F., Bhattacharyya, Anirban, Chandrasekaran, Ramya, Moustakas, Theodore D., Zhou, Lin, and Smith, David J.

Subjects
GALLIUM nitride, NANOSTRUCTURED materials, ELECTRON-hole droplets, EPITAXY, NITROGEN plasmas, X-ray diffraction, ATOMIC force microscopy
Abstract

Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between the GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710 °C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620 °C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of ∼ three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620 °C, but no such layer was observed for the substrate temperature of 710 °C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface. [ABSTRACT FROM AUTHOR]

Published
2007
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28. Real-time x-ray studies of gallium adsorption and desorption.

Author

Özcan, Ahmet S., Wang, Yiyi, Ozaydin, Gozde, Ludwig, Karl F., Bhattacharyya, Anirban, Moustakas, Theodore D., and Siddons, D. Peter

Subjects
GALLIUM nitride, ADSORPTION (Chemistry), ELECTRON-stimulated desorption, OPTOELECTRONICS, MOLECULAR beam epitaxy, SAPPHIRES, SMALL-angle X-ray scattering
Abstract

Real-time grazing-incidence small-angle x-ray scattering has been employed to study the adsorption and desorption of Ga on c-plane sapphire and Ga-polar GaN surfaces. Formation of self-organized liquid Ga nanodroplets has been observed on sapphire during Ga exposure from an effusion cell at high flux. Subsequent to the Ga deposition, the nanodroplets were nitridated in situ by a nitrogen plasma source, which converted the droplets into GaN nanodots. In addition to the droplet studies, at lower Ga flux, the adsorption and desorption of Ga have been studied in the predroplet regime. For identical processing conditions, significantly different Ga adsorption/desorption rates were observed on sapphire and GaN surfaces. [ABSTRACT FROM AUTHOR]

Published
2006
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29. Real-time studies of gallium adsorption and desorption kinetics on sapphire (0001) by grazing incidence small-angle x-ray scattering and x-ray

Author

Yiyi Wang, Ozcan, Ahmet S., Ludwig, Karl F., and Bhattacharyya, Anirban

Subjects
Gallium -- Spectra, Gallium -- Optical properties, Sapphires -- Optical properties, Physics
Abstract

A real-time grazing incidence small-angle x-ray scattering and x-ray fluorescence as a function of substrate temperature and Ga flux was employed to study the gallium adsorption and desorption on c-plane sapphire. The results provide insight into the surface morphology evolution.

Published
2008

31. Plasma-assisted atomic layer epitaxial growth of aluminum nitride studied with real time grazing angle small angle x-ray scattering

Author

Anderson, Virginia R., primary, Nepal, Neeraj, additional, Johnson, Scooter D., additional, Robinson, Zachary R., additional, Nath, Anindya, additional, Kozen, Alexander C., additional, Qadri, Syed B., additional, DeMasi, Alexander, additional, Hite, Jennifer K., additional, Ludwig, Karl F., additional, and Eddy, Charles R., additional

Published
2017
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33. Axiotaxy of CoSi2 thin films on Si(100) substrates and the effects of Ti alloying

Author

Ozcan, Ahmet S., Ludwig, Karl F., Jr., Detavernier, Christophe, Lavoie, Christian, and Jordan-Sweat, Jean L.

Subjects
Dielectric films -- Research, Thin films -- Research, Titanium compounds -- Research, Titanium compounds -- Optical properties, Silicon compounds -- Research, Silicon compounds -- Optical properties, Physics
Abstract

The texture of CoSi2 films on Si(001) substrates is examined using synchrotron based high-resolution pole figure analysis. It is found that axiotaxy, a recognized type of texture, which was observed in NiSi thin films on Si(001), is also occurring in CoSi2 layers.

Published
2004

34. Co-GISAXS as a New Technique to Investigate Surface Growth Dynamics

Author

Rainville, Meliha G., Hoskin, Christa, Ulbrandt, Jeffrey G., Narayanan, Suresh, Sandy, Alec R., Zhou, Hua, Headrick, Randall L., and Ludwig, Karl F.

Subjects
Condensed Matter - Materials Science, Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

Detailed quantitative measurement of surface dynamics during thin film growth is a major experimental challenge. Here X-ray Photon Correlation Spectroscopy with coherent hard X-rays is used in a Grazing-Incidence Small-Angle X-ray Scattering (i.e. Co-GISAXS) geometry as a new tool to investigate nanoscale surface dynamics during sputter deposition of a-Si and a-WSi$_2$ thin films. For both films, kinetic roughening during surface growth reaches a dynamic steady state at late times in which the intensity autocorrelation function $g_2$(q,t) becomes stationary. The $g_2$(q,t) functions exhibit compressed exponential behavior at all wavenumbers studied. The overall dynamics are complex, but the most surface sensitive sections of the structure factor and correlation time exhibit power law behaviors consistent with dynamical scaling., 32 pages, 12 figures

Published
2015

35. Using coherent X-rays to directly measure the propagation velocity of defects during thin film deposition

Author

Ulbrandt, Jeffrey G., Rainville, Meliha G., Hoskin, Christa, Narayanan, Suresh, Sandy, Alec R., Zhou, Hua, Ludwig, Karl F., and Headrick, Randall L.

Subjects
Condensed Matter - Materials Science, Materials Science (cond-mat.mtrl-sci), FOS: Physical sciences
Abstract

The properties of artificially grown thin films are often strongly affected by the dynamic relationship between surface growth processes and subsurface structure. Coherent mixing of X-ray signals promises to provide an approach to better understand such processes. Here, we demonstrate the continuously variable mixing of surface and bulk scattering signals during real-time studies of sputter deposition of a-Si and a-WiS2 films by controlling the X-ray penetration and escape depths in coherent grazing incidence small angle X-ray scattering (Co-GISAXS). Under conditions where the X-ray signal comes from both the growth surface and the thin film bulk, oscillations in temporal correlations arise from coherent interference between scattering from stationary bulk features and from the advancing surface. We also observe evidence that elongated bulk features propagate upward at the same velocity as the surface. Additionally, a highly surface sensitive mode is demonstrated that can access the surface dynamics independently of the subsurface structure., Revised version. 5 figures, 27 pages

Published
2015

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