From sponge to dot arrays on (100) Ge by increasing the energy of ion impacts

Abstract

Ge surfaces of up to 780 K temperature have been irradiated at normal incidence with up to 10 17 Bi þ ions cm À2 having kinetic energies from 10 to 30 keV. The resulting surface morphologies have been studied by scanning electron microscopy. While at room temperature the impacts of highenergy Bi þ ions result in porous networks, at elevated irradiation temperatures hexagonally ordered dot arrays are formed, whereas after a further temperature increase the surface becomes smooth. The comprehensive experimental studies have been summarized in a phase diagram of surface morphologies in the ion energy versus substrate temperature plane. In this phase diagram, the onset of dot formation with increasing substrate temperature has been consistently modeled by nanomelting of the collision cascade volume of ion impacts, thereby taking into account the thermodynamic parameters of amorphous Ge (melt temperature, heat of fusion, and heat capacity) as well as the energy density deposited in the cascade volume as predicted by established simulation programs.

Continuum modeling of particle redeposition during ion-beam erosion

“…The resulting aspect ratios are in the same order as the experiments on binary compounds [6][7][8][9][10][11] and Ge irradiated by Bi-(cluster)-ions [12][13][14][15][16][17]. Additionally, the negative sign of κ is compatible with the physical interpretation of this parameter.…”

“…While the first experiments can be dated back to 1962 [5], a new impetus was given in 1999, when Facsko et al discovered the self-organized formation of hexagonally arranged nanodot structures on semiconductor surfaces by lowenergy ion-beam erosion at normal incidence [6]. Since then, numerous experiments have been carried out which can essentially be categorized into three groups: (i) lowenergy erosion of III-V semiconductor compounds [6][7][8][9][10][11]; (ii) erosion of Ge with heavy ions or ion clusters [12][13][14][15][16][17] and (iii) low-energy erosion of Si with additional metal co-deposition [18][19][20][21].…”

Continuum modeling of particle redeposition during ion-beam erosion

“…The remaining defects dissolve for longer simulation times and the surface converges to a perfect hexagonal arrangement. Besides the qualitative similarity of the resulting pattern in comparison with experimentally observed dot morphologies, we can also notice a quantitative agreement: the aspect ratio has a value of = 0.76 (A = 6.62 and L = 8.74) and is therefore comparable to the dot morphologies found on binary compounds [6][7][8][9][10][11] and by irradiation with heavy Bi-(cluster)-ions [12][13][14][15][16][17]. Since we had to use the same scales forĥ and x in (46), the aspect ratio is a characteristic quantity of the model equation (47), which cannot be adjusted by rescaling the height or the lateral extent.…”

The origin of conductivity in ion-irradiated diamond-like carbon – Phase transformation and atomic ordering

“…Furthermore, any heat conduction into the surrounding matrix is not considered but note that heat conduction is small in amorphous systems in general [23]. Nevertheless, good results were obtained in other works [37,38] with such an approach for the deposited energy density. The values of DT should emphasize that the ion-induced transient temperature rise increases drastically with the ion mass.…”