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AFM characterization of AlGaAs/AlAs distributed Bragg reflectors
Published in A G Cullis, J L Hutchison, Microscopy of Semiconducting Materials 2001, 2018
A Klein, M Zorn, U Zeimer, R Schneider, A Oster, M Weyers
For AFM measurement the VCSEL structure was prepared by a combination of mechanical and chemical treatment. The samples were grinded and polished using diamond lapping film with 0.1 μm grain size at a bevelled angle of 0.3°. As a result, the 50 nm thick layers were spread to 10 μm at the surface of the bevelled sample. To remove the surface damage and to uncover the AlGaAs interfaces the sample surface was etched with HF 7,5 %. The AlAs layers were removed and the AlGaAs layers remained because the etch rate for AlAs is almost an order of magi’:‘ude higher than that for the AlGaAs layers. After chemical treatment the layer stack reveals a terraced surface. The free surface at each step is given by the AlGaAs interface. All step surfaces were prepared under the same chemical conditions. Thus, it was possible to measure the RMS value for roughness evaluated over a 10 μm × 10 μm field in all cases in various depths within the structure. This permits a study of development of the surface roughness of the whole VCSEL structure. The atomic force microscope images were obtained using a Digital Instrument Nanoecope II AFM operated in tapping mode.
Ultrathick Boron Carbide Coatings for Nuclear Fusion Targets
Published in Fusion Science and Technology, 2023
Swanee J. Shin, Leonardus B. Bayu Aji, Alison M. Engwall, John H. Bae, Gregory V. Taylor, Paul B. Mirkarimi, Chantel Aracne-Ruddle, Jack Nguyen, Casey W. N. Kong, Sergei O. Kucheyev
Since both surface polishing and substrate etching steps are common in the fabrication of ICF ablators, samples deposited in two representative runs C and D (with high- and low-density B4C targets, respectively) were selected to study mechanical polishing of the film surface and chemical etching of the Si substrate. We investigated two different approaches to substrate etching: (1) an ~26-h soak in 44% KOH at 65°C and (2) a 1-min soak in a 2.5:1 (volumetric) mix of 50% HF and 70% HNO3 aqueous solutions at room temperature. Mechanical polishing was performed in the following three 10-min stages: (1) 25-μm diamond particle water-based slurry on a 9-μm diamond lapping film, (2) a 9-μm diamond lapping film in water, and (3) a 3-μm diamond lapping film in water. Each stage was repeated two to three times as necessary. Surface roughness was evaluated by interferometric imaging between each step.