F. Frost, R. Fechner, B. Ziberi, J. Völlner, D. Flamm, A. Schindler
J. Phys. Condens. Matter 21 (2009) 224026
https://doi.org/10.1088/0953-8984/21/22/224026

Ion beam erosion can be used as a process for achieving surface smoothing at microscopic length scales and for the preparation of ultrasmooth surfaces, as an alternative to nanostructuring of various surfaces via self-organization. This requires that in the evolution of the surface topography different relaxation mechanisms dominate over the roughening,and smoothing of initially rough surfaces can occur. This contribution focuses on the basic mechanisms as well as potential applications of surface smoothing using low energy ion beams.

Y. Li, H. Takino, F. Frost
Opt. Express 25 (2017) 7828-7838
https://doi.org/10.1364/OE.25.007828

The effectiveness of ion beam planarization (IBP) to reduce surface roughness of diamond turned NiP surfaces was investigated. It is found that the combined process of spray-coating and ion-beam planarization can effectively reduce the surface roughness of diamond turned NiP.  The final surface roughness after ion beam planarization is 30%~40% of the original roughness, irrespective of spatial wavelength and depth of turning marks. Extending planarization time does not alter surface quality after photoresist is etched away. These results show that the IBP is applicable to roughness minimization of diamond turned surfaces.

A. Finzel, G. Dornberg, S. Görsch, M. Mitzschke, J. Bauer, F. Frost
EPJ Web. Conf. EOS Optical Technologies 215 (2019) 03004
https://doi.org/10.1051/epjconf/201921503004

A new approach for the realization of depth reference samples is presented. By a combination of photolithography, reactive ion beam etching, surface planarization with photoresists and a subsequent coating with non-transparent materials, defined sinusoidal surface profiles are generated which can be used as depth references for the comparison and calibration of different surface profile measurements. The smallest realized surface amplitudes are in the range of less than 0.1 nm.

D. Chen, G. Yang, J. Li, D. Hirsch, Y. Liu, F. Frost, Y. Hong
Appl. Phys. Lett. 113 (2018 ) 033102
https://doi.org/10.1063/1.5039565

The morphology evolution of self-organized nanopatterns induced during Ar+ ion bombardment (IB) with Mo co-deposition on fused silica (SiO2) surfaces at different incidence angles and fluences was investigated by using atomic force microscopy and transmission electron microscopy. For pure IB at incidence angles from 30° to 70°, SiO2 surfaces evolve from being flat, via ripples, to direction-transversed ripples. In contrast, at the same ion fluence and incidence angles, the simultaneous Mo co-deposition leads to significant terraced structures with significantly enhanced roughness and wavelength. Our observations show that the concurrent Mo co-deposition during IB can reduce the critical incidence angle and the fluence level of terrace formation. Owing to the guidance of the IB-induced morphology, at incidence angles where a well-ordered ripple-mode can be generated, well-ordered terrace morphology is more likely to be formed.

A. Finzel, F. Koch, G. Dornberg, D. Lehr, F. Frost, T. Glaser
Opt. Eng. 58 (2019) 092614
https://doi.org/10.1117/1.OE.58.9.092614

Reflection losses due to refractive index mismatch limit the obtainable diffraction efficiencies for transmission gratings in the highly dispersive regime, i.e., with period to wavelength ratios smaller than 0.7. The design and fabrication of such gratings with high-diffraction efficiencies (≥94%, Littrow configuration) will be discussed with an emphasis on process strategies to control the profiles in the reactive ion beam etching step. Experimental results from the manufacturing of monolithic fused silica pulse compression gratings with 3000 L∕mm optimized for a center wavelength of 519 nm will be presented. The influence of different etching parameters such as etch gas mixture, ion incidence angle, and acceleration voltage of the ion source on profile depth, side-wall angle, duty cycle, and ultimately diffraction efficiencies will be discussed.