Mostafa Moonir Shawrav
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Direct writing of gold nanostructures with an electron beam: On the way to pure nanostructures by combining optimized deposition with oxygen-plasma treatment
Peer-reviewed JournalAbstract
This work introduces an additive direct-write nanofabrication technique for producing extremely conductive gold nanostructures from a commercial metalorganic precursor. Gold content of 91 atomic % (at. %) was achieved by using water as an oxidative enhancer during direct-write deposition. A model was developed based on the deposition rate and the chemical composition, and it explains the surface processes that lead to the increases in gold purity and deposition yield. Co-injection of an oxidative enhancer enabled Focused Electron Beam Induced Deposition (FEBID)—a maskless, resistless deposition method for three dimensional (3D) nanostructures—to directly yield pure gold in a single process step, without post-deposition purification. Gold nanowires displayed resistivity down to 8.8 μΩ cm. This is the highest conductivity achieved so far from FEBID and it opens the possibility of applications in nanoelectronics, such as direct-write contacts to nanomaterials. The increased gold deposition yield and the ultralow carbon level will facilitate future applications such as the fabrication of 3D nanostructures in nanoplasmonics and biomolecule immobilization.
Keywords
- Atomic Layer Deposition (ALD)
- FEBID
- gold
- MOS Capacitor
- capacitance-voltage characteristics
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 Co2(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 N2 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 rate. The wide range of achievable precursor fluxes allowed to clearly distinguish between precursor- and electron-limited regime. With the carrier-based GIS an optimized deposition procedure with regards to the desired deposition regime has been enabled.
Keywords
- FEBID
- carrier gas
- cobalt
- dicobalt octacarbonyl
- gas injection system
- GIS
- SEM
- nitrogen
- electron limited regime
- precursor limited regime
Abstract
Focused electron beam induced deposition (FEBID) is a novel direct-writing technique to produce noble metal nanostructures. In this work, FEBID has been employed for the first time to fabricate metal-oxide-semiconductor capacitors (MOSCAPs). Experimental parameters such as precursor temperature, substrate temperature and the (de)focus of the electron beam have been optimized to deposit electrode structures of a relatively large area within a short timeframe. Using FEBID, gold electrodes have been deposited on top of an atomic layer deposited (ALD) dielectric aluminum oxide layer. Chemical composition of the produced structures has been studied using energy dispersive X-ray spectroscopy (EDX). Current–voltage (I–V) measurements have confirmed the conductivity of FEBID gold nanowires (NWs). Measured capacitance–voltage (C–V) characteristics of FEBID-fabricated MOSCAP prototypes resemble the typical C–V characteristics of conventionally fabricated MOSCAPs, thus confirming the functionality of our FEBID devices.
Keywords
- Atomic Layer Deposition (ALD)
- FEBID
- gold
- MOS Capacitor
- capacitance-voltage characteristics
Abstract
The capability to control matter down to the nanoscale level in combination with the novel magnetic properties of nanomaterials have attracted increasing attention in the last few decades due to their applications in magnetic sensing, hard disc data storage and logic devices. Therefore, many efforts have been devoted to the implementation of both nanofabrication methods as well as characterization of magnetic nanoelements. In this study, Fe-based nanostructures have been synthesized on Si(100) by focused electron beam induced deposition (FEBID) utilizing iron pentacarbonyl as precursor. The so obtained nanostructures exhibit a remarkably high iron content (Fe > 80 at.%), expected to give rise to a ferromagnetic behaviour. For that reason, magnetic force microscopy (MFM) analyses were performed on the obtained FEBID Fe nanostructures. Moreover, object oriented micromagnetic framework (OOMMF) magnetic simulations have been executed to study the influence of the geometry on the magnetic properties of iron single-domain nanowires.
Keywords
- FEBID
- iron pentacarbonyl
- magnetic nanostructures
- MFM
Abstract
Among various multi-metal combinations, Au-Fe nanoalloys are envisaged as prospective materials for data storage applications. Here we report on the first successful achievement of Au-Fe nanoalloys using focused electron beam-induced deposition (FEBID), exploiting the possibility of directly writing nanostructures at nanometer resolution. Gaseous organometallic precursors are injected simultaneously into the deposition chamber to co-deposit Fe and Au within the same nanostructure. Fabricated nanostructures show a spatially uniform elemental ratio of iron to gold that can be tailored by experimental conditions.
Keywords
- FEBID
- Gold
- Iron
- Multi-material
- Nanoalloys
Abstract
Magnetic materials synthesized on the nanometer-scale level are essential for several applications, such as spintronics and magnetologic. As a successful nanofabrication approach, focused electron beam-induced deposition (FEBID) stands out as a direct-write technique. FEBID uses an electron beam to locally induce a CVD process, avoiding the use of masks and resists. In this work, Fe–based nanostructures are synthesized on Si(100) by FEBID, starting from iron pentacarbonyl. A systematic variation of FEBID parameters is performed, to study their influence on the geometry and composition of the deposit. Based on the results, specific deposition conditions are suggested for magneto-logic applications and fabrication of large structures.
Keywords
- FEBID
- Iron
- Magnetism
- Nanowires
Abstract
Three-dimensional gold (Au) nanostructures offer promise in nanoplasmonics, biomedical applications, electrochemical sensing and as contacts for carbon-based electronics. Direct-write techniques such as focused-electron-beam-induced deposition (FEBID) can provide such precisely patterned nanostructures. Unfortunately, FEBID Au traditionally suffers from a high nonmetallic content and cannot meet the purity requirements for these applications. Here we report exceptionally pure pristine FEBID Au nanostructures comprising submicrometer−large monocrystalline Au sections. On the basis of high-resolution transmission electron microscopy results and Monte Carlo simulations of electron trajectories in the deposited nanostructures, we propose a curing mechanism that elucidates the observed phenomena. The in situ focused-electron-beam-induced curing mechanism was supported by postdeposition ex situ curing and, in combination with oxygen plasma cleaning, is utilized as a straightforward purification method for planar FEBID structures. This work paves the way for the application of FEBID Au nanostructures in a new generation of biosensors and plasmonic nanodevices.
Keywords
- FEBIC
- FEBID
- gold nanostructure
- nanopillar
- nanowire
- oxygen plasma cleaning
- purity
Abstract
During the last decades, focused electron beam induced deposition (FEBID) has become a successful approach for direct-write fabrication of nanodevices. Such a deposition technique relies on the precursor supply to the sample surface which is typically accomplished by a gas injection system using a tube-shaped injector nozzle. This precursor injection strategy implies a position-dependent concentration gradient on the surface, which affects the geometry and chemistry of the final nanodeposit. Although simulations already proposed the local distribution of nozzle-borne gas molecules impinging on the surface, this isolated step in the FEBID process has never been experimentally measured yet. This work experimentally investigates the local distribution of impinging gas molecules on the sample plane, isolating the direct impingement component from surface diffusion or precursor depletion by deposition. The experimental setup used in this work maps and quantifies the local impinging rate of argon gas over the sample plane. This setup simulates the identical conditions for a precursor molecule during FEBID. Argon gas was locally collected with a sniffer tube, which is directly connected to a residual gas analyzer for quantification. The measured distribution of impinging gas molecules showed a strong position dependence. Indeed, a 300-µm shift of the deposition area to a position further away from the impingement center spot resulted in a 50 % decrease in the precursor impinging rate on the surface area. With the same parameters, the precursor distribution was also simulated by a Monte Carlo software by Friedli and Utke and showed a good correlation between the empirical and the simulated precursor distribution. The results hereby presented underline the importance of controlling the local precursor flux conditions in order to obtain reproducible and comparable deposition results in FEBID.
Keywords
- FEBID
- gas flux distribution
- precursor flux
- gas injection
- nozzle geometry
Abstract
Three-dimensional gold (Au) nanostructures offer promise in nanoplasmonics, biomedical applications, electrochemical sensing and as contacts for carbon-based electronics. Direct-write techniques such as focused-electron-beam-induced deposition (FEBID) can provide such precisely patterned nanostructures. Unfortunately, FEBID Au traditionally suffers from a high nonmetallic content and cannot meet the purity requirements for these applications. Here we report exceptionally pure pristine FEBID Au nanostructures comprising submicrometer−large monocrystalline Au sections. On the basis of high-resolution transmission electron microscopy results and Monte Carlo simulations of electron trajectories in the deposited nanostructures, we propose a curing mechanism that elucidates the observed phenomena. The in situ focused-electron-beam-induced curing mechanism was supported by postdeposition ex situ curing and, in combination with oxygen plasma cleaning, is utilized as a straightforward purification method for planar FEBID structures. This work paves the way for the application of FEBID Au nanostructures in a new generation of biosensors and plasmonic nanodevices.
Keywords
- FEBIC
- FEBID
- gold nanostructure
- nanopillar
- nanowire
- oxygen plasma cleaning
- purity
Abstract
Focused electron beam induced etching (FEBIE) with chlorine as etching agent has been used to geometrically shape and to electrically modify semiconductor nanodevices. Selected sections of monocrystalline nanowires were modified directly without the requirement for a photomask or a resist layer. FEBIE as a subtractive nanofabrication technology allows to locally etch active semiconductor devices made of Si or Ge. In this work, chlorine is used as the etchant gas to thin germanium channel structures fabricated by standard photolithography. For effective material removal a sufficiently high electron influence is essential to avoid the pitfalls of this method. Topography and conductivity of FEBIE-modified structures prior and after the etching process was studied by AFM and by electrical I–V characteristics. The presented work demonstrates the potential of Cl-based FEBIE for device prototyping and electrical trimming of future Ge-based nanodevices.
Keywords
- Focused electron beam induced etching (FEBIE)
- Germanium
- Chlorine