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Highly conductive and pure gold nanostructures grown by electron beam induced deposition

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ABSTRACT

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.

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TEM EDX investigations.(a) HAADF STEM image of the assisted FEBID gold structure. The image reveals a mass contrast among the germanium substrate, the FEBID gold deposit, the sputtered chrome layer, and the applied FEBID platinum layer. The grey area between the chrome layer and Ge is halo deposition from secondary electrons. (b) TEM EDX spectrum of water-assisted FEBID gold structure. (c) TEM EDX line scan along the z-axis of the deposition (marked with a red line in a). (d) TEM EDX quantification results.
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f2: TEM EDX investigations.(a) HAADF STEM image of the assisted FEBID gold structure. The image reveals a mass contrast among the germanium substrate, the FEBID gold deposit, the sputtered chrome layer, and the applied FEBID platinum layer. The grey area between the chrome layer and Ge is halo deposition from secondary electrons. (b) TEM EDX spectrum of water-assisted FEBID gold structure. (c) TEM EDX line scan along the z-axis of the deposition (marked with a red line in a). (d) TEM EDX quantification results.

Mentions: To confirm the SEM findings, extensive TEM analysis was conducted on the water-assisted FEBID Au nanostructures. As test structures, square shape FEBID-Au nanostructures were deposited on a Ge substrate, using the parameter set mentioned in the method section. The TEM lamella of this FEBID-Au nanostructure was prepared by FIB milling. Prior to FIB milling, a capping layer of chromium was sputtered on the deposit with a nominal thickness of 150 nm. This layer shielded the gold deposit from ion and (even more importantly) electron irradiation during the focused ion beam processing of the cross section. Hence, electron beam-induced curing is effectively excluded, and the Monte Carlo simulation shown in Supplement 2a,b confirms that 5 keV primary electron beam energy cannot penetrate the 150 nm thick protective chrome layer. In addition, prior to FIB processing, a protective platinum layer was also deposited using FEBID. In the bright field TEM image presented in Supplement 2c, all four different layers of Ge, FEBID gold, sputtered chrome layer, and a FEBID Pt layer can be clearly distinguished The selected area diffraction (SAED) shown in Supplement 2d was obtained from an area approximately 100 nm around the centre of the Au-FEBID deposit. The SAED shows that the first diffraction ring is located 4.19 nm−1 from the un-diffracted spot in the reciprocal space; this corresponds to a distance of 0.238 nm for the 111 gold plane. This defined diffraction ring confirms that the deposited gold has polycrystalline behaviour. A High-Angle Annular Dark-Field (HAADF) scanning transmission electron microscopy (STEM) image obtained of the FEBID-Au is shown in Fig. 2a. The top layer corresponds to homogeneous FEBID platinum, appearing dimmer relative to the deposited gold structure. The gold deposit shows small dark spots due to the coalescing carbon clusters entrapped in the gold. The halo deposition around the primary deposit shows the typical EBID gold crystallites embedded in a carbonaceous matrix404950. The sputtered chrome layer appears to be darker than the heavier gold and platinum deposits. The grey area between the protective chrome layer and Ge substrate is a halo deposition from secondary electrons. The location of the grey layer, its decreasing thickness from the scan area to the outside are the typical characteristics of a halo deposition in FEBID process. This halo can be removed by post-deposition Ar+ milling9.


Highly conductive and pure gold nanostructures grown by electron beam induced deposition
TEM EDX investigations.(a) HAADF STEM image of the assisted FEBID gold structure. The image reveals a mass contrast among the germanium substrate, the FEBID gold deposit, the sputtered chrome layer, and the applied FEBID platinum layer. The grey area between the chrome layer and Ge is halo deposition from secondary electrons. (b) TEM EDX spectrum of water-assisted FEBID gold structure. (c) TEM EDX line scan along the z-axis of the deposition (marked with a red line in a). (d) TEM EDX quantification results.
© Copyright Policy - open-access
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f2: TEM EDX investigations.(a) HAADF STEM image of the assisted FEBID gold structure. The image reveals a mass contrast among the germanium substrate, the FEBID gold deposit, the sputtered chrome layer, and the applied FEBID platinum layer. The grey area between the chrome layer and Ge is halo deposition from secondary electrons. (b) TEM EDX spectrum of water-assisted FEBID gold structure. (c) TEM EDX line scan along the z-axis of the deposition (marked with a red line in a). (d) TEM EDX quantification results.
Mentions: To confirm the SEM findings, extensive TEM analysis was conducted on the water-assisted FEBID Au nanostructures. As test structures, square shape FEBID-Au nanostructures were deposited on a Ge substrate, using the parameter set mentioned in the method section. The TEM lamella of this FEBID-Au nanostructure was prepared by FIB milling. Prior to FIB milling, a capping layer of chromium was sputtered on the deposit with a nominal thickness of 150 nm. This layer shielded the gold deposit from ion and (even more importantly) electron irradiation during the focused ion beam processing of the cross section. Hence, electron beam-induced curing is effectively excluded, and the Monte Carlo simulation shown in Supplement 2a,b confirms that 5 keV primary electron beam energy cannot penetrate the 150 nm thick protective chrome layer. In addition, prior to FIB processing, a protective platinum layer was also deposited using FEBID. In the bright field TEM image presented in Supplement 2c, all four different layers of Ge, FEBID gold, sputtered chrome layer, and a FEBID Pt layer can be clearly distinguished The selected area diffraction (SAED) shown in Supplement 2d was obtained from an area approximately 100 nm around the centre of the Au-FEBID deposit. The SAED shows that the first diffraction ring is located 4.19 nm−1 from the un-diffracted spot in the reciprocal space; this corresponds to a distance of 0.238 nm for the 111 gold plane. This defined diffraction ring confirms that the deposited gold has polycrystalline behaviour. A High-Angle Annular Dark-Field (HAADF) scanning transmission electron microscopy (STEM) image obtained of the FEBID-Au is shown in Fig. 2a. The top layer corresponds to homogeneous FEBID platinum, appearing dimmer relative to the deposited gold structure. The gold deposit shows small dark spots due to the coalescing carbon clusters entrapped in the gold. The halo deposition around the primary deposit shows the typical EBID gold crystallites embedded in a carbonaceous matrix404950. The sputtered chrome layer appears to be darker than the heavier gold and platinum deposits. The grey area between the protective chrome layer and Ge substrate is a halo deposition from secondary electrons. The location of the grey layer, its decreasing thickness from the scan area to the outside are the typical characteristics of a halo deposition in FEBID process. This halo can be removed by post-deposition Ar+ milling9.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus