Tunable Nanosynthesis of Composite Materials by Electron‐Impact Reaction

Abstract

Nanoscale electron-induced reactions being triggered by a finely focused electron beam in modern scanning electron microscopes are commonly used to pattern surfaces of thin films of irradiation sensitive material. Classical polymer and inorganic resist films allow precise masks to be defined for further deposition or etching process steps in the semiconductor industry. [1] A new, promising approach employs new film materials, among which are self-assembled monolayers of biphenyl, passivated gold nanoclusters, Langmuir-Blodgett films, or liquid precursors. The exposure of these films to electrons directly results in membranes, electrical wires, plasmonic structures, or conducting dots with nanoscale dimensions. [2] A very promising approach to electron-impact nanosynthesis is to replace the solid or liquid film and use a physisorbed monolayer that is continuously refreshed by injected volatile molecules. [3] The process can be compared to local chemical vapor deposition; however, the decomposition is due to electron-impact dissociation rather than thermal dissociation, thus keeping the reaction confined to the size of the electron beam and the active electron interaction volume. It has been proven to be a very innovative concept for direct, local, three-dimensional, and minimally invasive nanosynthesis of future photonic, [4] electronic, [5] and mechanical [6] nanodevice materials as well as for site-specific patterning of catalyst for individual carbon nanotube growth [7] and atomic layer deposition. [8] For nanoscale deposition, a focused electron beam is usually scanned over surface-adsorbed metal containing compounds that are volatile at room temperature. Electron-impact dissociation of such adsorbates by both the primary beam electrons (with keV energy) and the emitted secondary electrons (with eV energy) results in metalcontaining deposits and volatile reaction products, the latter being removed by the vacuum system. Advantageously, the same principle allows nanoscale removal of material. For example, physisorbed water on carbon surfaces dissociates under electron impact to produce highly reactive species that react to volatile carbon compounds, thus etching a nanosized hole in the substrate when a stationary focused electron beam is used. [9] Injected molecules used for electron-impact nanosynthesis so far comprise various metal-ligand compounds that contain carbon-, phosphorous-, or halogen-based ligands as well as organic compounds. [3] With the recent development of gas injection systems that allow the admission of two or more gases to the substrate surface, the nanosynthesis of binary metal alloys [10] or metal-(carbon) matrix deposits with outperforming properties [5c,e] can be envisaged. In contrast to classical vapor deposition exploiting co-evaporation, the deposit will be locally confined and the composition will depend not only on the ratios of molecule flow adsorption but also on the electron-impact dissociation efficiency of each individual molecule, giving a further degree of freedom to t...

Unveiling the optical properties of a metamaterial synthesized by electron-beam-induced deposition

“…This tendency implies that the EBID composite behaves more and more dielectric for thicker deposits. This observation is consistent with a chemisorption of the gold-containing precursor molecules onto the sample surface together with possibly decreasing vapor pressure over the long deposition times [21,26]. As mentioned, the concave shape of the pads implies a masstransport-limited deposition regime [24] in which excess electrons start to dissociate residual gases mainly hydrocarbons present in the vacuum chamber.…”

“…For long deposition time, this effect becomes particularly important if the precursor vapor pressure decreases with time. Thus, the carbon content of the deposits rises along with the deposition time and with the deposit thickness [26]. As a consequence, properties of the EBID composite can be tuned by the density of the gold inclusions, from strongly dielectric to slightly metallic optical behavior.…”

Purified and Crystalline Three-Dimensional Electron-Beam-Induced Deposits: The Successful Case of Cobalt for High-Performance Magnetic Nanowires

“…Even though the smart tuning of the growth parameters (primary beam voltage and current, base pressure, precursor flux, dwell time, etc.) enables the growth of relatively-highly-metallic deposits 18,[21][22][23][24] , in many cases the as-grown metallic content is remarkably low. For example, Pt deposits grown by FEBID with the standard precursor (CH3)3Pt(CpCH3) only contain 18% of Pt, in the form of 3 nm small grains, the rest being C and O 25 .…”

Chemical Vapor Deposition Kinetics and Localized Growth Regimes in Combinatorial Experiments

“…[2,3] On the other hand, interest in the growth of nanostructures [5][6][7][8] or the position-controlled growth of nanowires and carbon nanotubes [7] has driven efforts toward the area-selective decomposition of precursor molecules on the surface using either energy beams (electron, [5,9] ion, [6] or laser [7] beam) or selective optothermal heating of metallic nanostructures on the surface due to plasmonic effects. [8] The nano-tunability [9] and potential for low-temperature growth of nanostructures over flexible substrates [7,10] are among the key drivers to follow selective-area CVD. Despite the large amount of research on the above-mentioned topics there is a lack of fundamental understanding of the CVD process relating to the establishment of which conditions are optimal for either of the above-mentioned applications.…”