Proximity effects in free-standing EBID structures

Abstract

Proximity effects causing thickening and bending of closely spaced, free-standing pillars grown by electron-beam-induced deposition are investigated. It is shown that growth of a new pillar induces deposition of a layer of additional material on the side of already grown pillars facing the new pillar. We present experimental results which suggest that the bending of pillars is caused by shrinkage of the newly formed layer on exposure to the primary electron beam.

On the Principles of Tweaking Nanostructure Fabrication via Focused Electron Beam Induced Processing Combined with Catalytic Growth Processes

“…[33] This aspect is interesting because it reflects a delicate chemical sensitivity of the EBISA process depending on the actual choice of one of the two precursors, which are otherwise apparently similar. Furthermore, the probed deposit sites fabricated from Co(CO) 3 NO contain no carbon, but a similar elemental composition compared to previous reports of FEBIP experiments with the same precursor, [33,40,41] i.e., about 50 at% Co and varying contents of O and N. We cannot conclude about the exact chemical nature of the deposits, however, a Co oxidation state higher than zero is likely, as it was reported for similar systems as well, e.g., for EBID and autocatalytic growth with Co(CO) 3 NO on Si 3 N 4 -membranes [33] and thermal decomposition of Co 2 (CO) 8 on titanate nanowires. [42] The formation of carbon-free deposits from Co(CO) 3 NO on amorphous carbon was recently also reported in a UHV study by Rosenberg et al [43] They observe the formation of (CO) x OCoN (x = 1-2) upon 500 eV electron irradiation of an adsorbed Co(CO) 3 NO layer at a substrate temperature of −168 °C.…”

“…The extent of the deposit is usually larger than the beam spot size due to the contribution of backscattered, secondary and forward scattered electrons. [7][8][9][10][11][12] Consequently, an increase in primary electron (PE) dose leads to more deposited material when the deposition occurs in the electron limited regime. [1] The vast amount of available precursor compounds is a distinct advantage of the technique; however, precise control over the chemical composition of the deposit is a major challenge.…”

“…Metal contents ranging from <10 at% (e.g., Pt from C 5 H 5 Pt(CH 3 ) 3 , Mo from Mo(CO) 6 [13] ) up to >90 at% (e.g., Fe from Fe(CO) 5 , [14] Co from Co 2 (CO) 8 , [15] Au from (CH 3 ) 2 (C 5 H 7 O 2 )Au [16] ) have been reported (see also ref. [17]), with impurities including precursor and residual gas fragments, the most common ones being carbon and oxygen.…”

“…This leads to a chemical modification of the irradiated surface sites such that they become catalytically active toward the decomposition of a subsequently dosed precursor, resulting in the formation of a deposit. EBISA has already been found to work with a variety of precursor/substrate combinations: Fe(CO) 5 on SiO x [12,[19][20][21] and TiO 2 (110) [22] in ultrahigh vacuum (UHV), where the active sites have been identified as oxygen vacancies due to electron beam stimulated desorption (ESD) of oxygen; further examples are Fe(CO) 5 on thin porphyrin layers on Ag(111) in UHV, [23] and Co 2 (CO) 8 on SiO 2 in HV. [24] It has also been shown that a self-assembled monolayer (SAM) can be activated by an electron beam for site…”

“…For lithographic parameters, see Table S1 in the Supporting Information. 3 NO is a suitable precursor for the method, in addition to the precursors Fe(CO) 5 and Co 2 (CO) 8 that have already been shown to work. [19,24] Even a substrate that lacks a suitable e-beam activation mechanism, i.e., Si(111) 7 × 7, can be used for EBISA by precovering it, e.g., with 2HTPP and activating the thin organic layer.…”