The Role of Diffusion in Step Flow Growth

The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles ranging from 0° to 8° by using the atmospheric pressure meta–organic chemical vapor deposition (APMOCVD) technique. Morphology analysis revealed that the formation of the ZnO films on vicinal surfaces with small off-axis angles (1.4°–3.5°) follows the mixed growth mode: from one side, ZnO nucleation still occurs on wide (0001) terraces, but from another side, step-flow growth becomes more apparent with the off-cut angle increasing. We show for the first time that the off-cut angle of 8° provides conditions for step-flow growth of ZnO, resulting in highly improved growth morphology, respectively structural quality. Temperature-dependent photoluminescence (PL) measurements showed a strong dependence of the excitonic emission on the off-cut angle. The dependences of peak parameters for bound exciton and free exciton emissions on temperature were analyzed. The present results provide a correlation between the structural and optical properties of ZnO on vicinal surfaces and can be utilized for controllable ZnO heteroepitaxy on SiC toward device-quality ZnO epitaxial layers with potential applications in nano-optoelectronics.

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Key Influencers in Public Diplomacy 2.0: A Country-Based Social Network Analysis

Social Media + Society ◽

10.1177/2056305120981053 ◽

2021 ◽

Vol 7 (1) ◽

pp. 205630512098105

Author(s):

Diana Ingenhoff ◽

Giada Calamai ◽

Efe Sevin

Keyword(s):

New Media ◽

Public Diplomacy ◽

Qualitative Content Analysis ◽

Dominant Role ◽

Opinion Leaders ◽

Centrality Measures ◽

Political Actors ◽

Step Flow ◽

Twitter Users

This article presents a study of Twitter-based communication in order to identify key influencers and to assess the role of their communication in shaping country images. The analysis is based on a 2-month dataset comprised of all tweets including hashtags of the three countries selected for this study: Austria, Switzerland, and the Netherlands. Following a two-step flow model of communication, we initially identified the influential Twitter users in all three countries based on their centrality measures. Subsequently, we carried out a qualitative content analysis of tweets posted by these influential users. Finally, we assessed the similarities and differences across the three country cases. This article offers new insights into public diplomacy 2.0 activities by discussing influence within the context of country images and demonstrating how opinion leaders can play a more dominant role than states or other political actors in creating and disseminating content related to country image. The findings also provide practical insights in the production of a country’s image and its representation on new media platforms.

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Growth of (Zn)CdSe quantum structures on vicinal GaAs(001) substrates: step flow growth versus strain effects

Journal of Crystal Growth ◽

10.1016/s0022-0248(00)00162-7 ◽

2000 ◽

Vol 214-215 ◽

pp. 606-609 ◽

Cited By ~ 5

Author(s):

T Passow ◽

H Heinke ◽

D Kayser ◽

K Leonardi ◽

D Hommel

Keyword(s):

Quantum Structures ◽

Strain Effects ◽

Step Flow ◽

Step Flow Growth ◽

Versus Strain

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Development of Cross-Hatch Morphology During Growth of Lattice Mismatched Layers

MRS Proceedings ◽

10.1557/proc-673-p5.2 ◽

2001 ◽

Vol 673 ◽

Author(s):

A. Maxwell Andrews ◽

J.S. Speck ◽

A.E. Romanov ◽

M. Bobeth ◽

W. Pompe

Keyword(s):

Misfit Dislocation ◽

Film Growth ◽

Strain Relaxation ◽

Dislocation Generation ◽

Force Microscopy ◽

Step Flow ◽

Atomic Force ◽

Subsequent Step ◽

Step Flow Growth ◽

Lateral Scale

ABSTRACTAn approach is developed for understanding the cross-hatch morphology in lattice mismatched heteroepitaxial film growth. It is demonstrated that both strain relaxation associated with misfit dislocation formation and subsequent step elimination (e.g. by step-flow growth) are responsible for the appearance of nanoscopic surface height undulations (0.1-10 nm) on a mesoscopic (∼100 nm) lateral scale. The results of Monte Carlo simulations for dislocation- assisted strain relaxation and subsequent film growth predict the development of cross-hatch patterns with a characteristic surface undulation magnitude ∼50 Å in an approximately 70% strain relaxed In0.25Ga0.75As layers. The model is supported by atomic force microscopy (AFM) observations of cross-hatch morphology in the same composition samples grown well beyond the critical thickness for misfit dislocation generation.

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