Nitrogen as a carrier gas for regime control in focused electron beam induced deposition

Abstract

The synthesis of ferromagnetic nanostructures has received great attention over the past few years. These structures are usually manufactured by lithographic structuring of a substrate, blanket deposition of the desired magnetic material and a subsequent lift-off process [1,2]. As a successful alternative to this multi-step procedure, focused electron beam induced deposition (FEBID) allows the mask-and resist-less nanofabrication of planar and three dimensional (3D) structures [3]. In FEBID, the focused electron beam (FEB) of a scanning electron microscope (SEM) locally supplies the energy needed to activate the precursor and induce a local chemical vapour deposition process. The direct-write nature of FEBID enables high flexibility in the (three dimensional) design of the deposited objects, avoiding complex and time-consuming multi-step lithography processes [4,5]. This makes FEBID an excellent candidate for research and prototyping applications, such as circuit editing or the design and fabrication of various nanosystems, e.g., in sensing applications as well as data-storage and processing [6][7][8]. In FEBID a variety of precursors containing magnetic elements is available [3,5]. High purity magnetic materials based on Fe and Co were already synthesized by FEBID using carbonyl (CO) based precursors, for their application in magnetic sensing and logic technologies [8,9]. The choice of these chemicals is driven by the relatively "clean" decomposition path and their high volatility [3]. It has been shown [3, 10, 11] that precursor flow as well as the FEB current are important factors effecting chemical and geometric properties of the deposit. To further enhance the growth rate using CO-based substances, a sufficiently high precursor flux is necessary [12]. For this reason the whole gas injection system (GIS) is often heated up in order to increase the vapour pressure and thereby precursor flux to the deposition area [13]. However, temperature gradients along the delivery system may lead to undesirable re-condensation or deposition of precursor molecules Abstract: This work reports on focused electron beam induced deposition (FEBID) using a custom built gas injection system (GIS) equipped with nitrogen as a gas carrier. We have deposited cobalt from Co 2 (CO) 8 , which is usually achieved by a heated GIS. In contrast to a heated GIS, our strategy allows avoiding problems caused by eventual temperature gradients along the GIS. Moreover, the use of the gas carrier enables a high control over process conditions and consequently the properties of the synthesized nanostructures. Chemical composition and growth rate are investigated by energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM), respectively. We demonstrate that the N 2 flux is strongly affecting the deposit growth rate without the need of heating the precursor in order to increase its vapour pressure. Particularly, AFM volume estimation of the deposited structures showed that increasing the nitrogen resulted in an enhanced deposition ...

Review of magnetic nanostructures grown by focused electron beam induced deposition (FEBID)

“…In that situation, even for low beam currents such as 21 pA (allowing lateral resolution of 30 nm)Co content greater than 90% is found(60). Similarly, Wachter et al have reported the advantage of Co growth at the crossover between the precursor-limited and electron-limited regimes(82). Summarizing, thermal effects are not necessary to achieve high Co content as thought in the first studies, which makes possible to obtain simultaneously high Co content and lateral resolution.…”

Atomistic simulation of the FEBID-driven growth of iron-based nanostructures

“…According to those experiments, the deposited volume increases linearly at low electron current (below approx. 0.5 nA), and the linear growth slows down at higher currents, indicating a transition from the ELR to the PLR [28]. At the same time, a linear increase in the deposit's volume with beam current (indicative of the ELR) has been observed in another FEBID experiment [29] for much higher beam currents up to 22 nA.…”

“…The electron-limited and precursor-limited FEBID regimes have been studied theoretically by means of the continuum (diffusion-reaction) models [14,26,27]. Experimentally, these regimes have been identified by measuring the volume variation of the deposits as a function of beam current [28]. According to those experiments, the deposited volume increases linearly at low electron current (below approx.…”

Focused-Electron-Beam Engineering of 3D Magnetic Nanowires

“…It is worth noting that for higher beam currents, this transition occurs at higher working pressures, i.e., higher precursor gas fluxes. Thus, the growth rate is determined by the amount of gas molecules delivered (increasing with ΔP), which is known as the precursor-limited regime [ 52 ]. Consequently, the nanowires (or segments of nanowire) grown in the linear regime present a high growth rate, expressed in terms of nanowire’s length per unit of time, while in the radial regime, nanowires grow more slowly.…”