Appl Surf Sci 2013, 270:301–306. 19. Hovis J, Greenlief HR: Preparation of clean and atomically flat germanium (001) surfaces. Surf Sci 1999, 440:L815-L819. 10.1016/S0039-6028(99)00866-3CrossRef 20. Klesse WM, Scappucci G, Capellini G, Simmons MY: Preparation of the Ge(001) surface towards fabrication of atomic-scale germanium devices. Nanotechnology 2011, 22:145604. 10.1088/0957-4484/22/14/145604CrossRef 21. Van
Nostrand J, Chey J, Hasan MA, Cahill D, Greene JE: Surface morphology during multilayer epitaxial growth of Ge(001). Phys Rev Lett 1995, 74:1127–1130. 10.1103/PhysRevLett.74.1127CrossRef 22. Shin B, Leonard J, McCamy J, Aziz M: Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and CHIR-99021 molecular weight molecular-beam epitaxy. Appl Phys Lett 2005, 87:181916. 10.1063/1.2108115CrossRef 23. Akazawa H: Hydrogen induced roughening and smoothing in surface morphology during synchrotron-radiation-excited GeH4-source homoepitaxy on Ge(001). J Appl Phys 2006, 99:103505. 10.1063/1.2194232CrossRef 24. Picco A, Bonera E, Grilli E, Guzzi M, Giarola M, Mariotto G, Chrastina D, Isella
G: Raman efficiency in SiGe alloys. Phys Rev B 2010, 82:115317.CrossRef 25. Mooney PM, Dacol FH, Tsang JC, Chu JO: Raman scattering analysis of relaxed Ge x Si 1-x alloy layers. Appl Phys Lett 1993, 62:2069–2071. 10.1063/1.109481CrossRef Selleckchem Torin 1 26. Sgarlata A, Persichetti L, Balzarotti A: Semiconductor quantum dots: the model case of the Ge/Si system. In Surface and Interface Science. Volume 4. Edited by: Wandelt K. Wiley: WEINHEIM (Germany): WILEY-VCH Verlag GmbH & Co; 2014:863. 27. Pezzoli F, Bonera E, Grilli E, Guzzi M, Sanguinetti S, Chrastina D, Isella G, von Känel H, Wintersberger E, Stangl J: Raman spectroscopy determination of composition and strain in Si1-xGex/SiSi1-xGex/Si heterostructures. Mater Sci Semicond Process 2008, 11:279–284. 10.1016/j.mssp.2008.09.012CrossRef 28. Scopece D, Beck M: Epilayer thickness and strain dependence of Ge(113) surface energies. Phys Rev B 2013, 87:155310.CrossRef 29. Migas DB, Cereda S, Montalenti F, Miglio
else L: Electronic and elastic contributions in the enhanced stability of Ge(105) under compressive strain. Surf Sci 2004, 556:121–128. 10.1016/j.susc.2004.03.023CrossRef Competing interests The authors declare that they have no competing interests. Authors’ contributions LP conceived of the study and carried out its design, realization, and coordination during all the different stages; he also drafted the manuscript. AS and SM participated in the sample growth and morphological characterization. MN carried out the SEM, TEM, and Raman measurements. VC participated in the sample growth and characterization. MF, NM, and AB participated in the design and coordination of the study and helped to draft the manuscript. All authors read and approved the final manuscript.