Electron-Induced Decomposition of Different Silver(I) Complexes: Implications for the Design of Precursors for Focused Electron Beam Induced Deposition

New palladium(II) β-ketoesterates for focused electron beam induced deposition: synthesis, structures, and characterization

We report the synthesis and characterization of new palladium(II) β-ketoesterate complexes [Pd(CH3COCHCO2R)2] with alkyl substituents R = tBu, iPr, Et. These compounds can have potential use in focused electron beam induced deposition (FEBID), which is a direct write method for the growth of structures at the nanoscale. However, it is still a major challenge to obtain deposits with a high metal content, and new precursor molecules are needed to overcome this. Single crystal X-ray diffraction, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and density-functional theory calculations were used to confirm the compounds' composition and structure. Using thermal analysis and sublimation experiments, we investigate their thermal stability and volatility. These studies show that the palladium complexes sublimate over the range 348-353 K under 10-2 mbar pressure. The electron-induced decomposition of the complex molecules in the gas phase and their thin layers on silicon substrates were analysed using electron impact mass spectrometry (EI MS) and microscopy studies (SEM/EDX). They confirm that the precursor electron-induced fragmentation depends on the molecular structure. The obtained results reveal that [Pd(CH3COCHCO2tBu)2] with cis-positioned tert-butyl groups may be a promising FEBID precursor, and we carried out preliminary deposition experiments using this compound.

Area-Selective Chemical Vapor Deposition of Gold by Electron Beam Seeding

Chemical vapor deposition (CVD) is an established method for producing high-purity thin films, but it typically necessitates the pre- and post-processing using a mask to produce structures. This study presents a novel maskless patterning technique that enables area-selective CVD of gold. A focused electron beam is used to decompose the metal-organic precursor Au(acac)Me2 locally, thereby creating an autocatalytically active seed layer for subsequent CVD with the same precursor. The procedure can be included in the same CVD process without the need for clean room lithographic processing. Moreover, it operates at low temperatures of 80 °C, over 200 K lower than standard CVD temperatures for this precursor, reducing thermal load on the specimen. Given that electron beam seeding operates on any even moderately conductive surface, the process does not constrain device design. This is demonstrated by the example of vertical nanostructures with high aspect ratios of ≈40:1 and more. Written using a focused electron beam and the same precursor, these nanopillars exhibit catalytically active nuclei on their surface. Furthermore, by using the onset of the autocatalytic CVD growth, for the first time the local temperature increase caused by the writing of nanostructures with an electron beam can be precisely determined.

Ligand Size and Carbon-Chain Length Study of Silver Carboxylates in Focused Electron-Beam-Induced Deposition

Gas-assisted focused electron-beam-induced deposition is a versatile tool for the direct writing of complex-shaped nanostructures with unprecedented shape fidelity and resolution. While the technique is well-established for various materials, the direct electron beam writing of silver is still in its infancy. Here, we examine and compare five different silver carboxylates, three perfluorinated: [Ag₂(µ-O₂CCF₃)₂], [Ag₂(µ-O₂CC₂F₅)₂], and [Ag₂(µ-O₂CC₃F₇)₂], and two containing branched substituents: [Ag₂(µ-O₂CCMe₂Et)₂] and [Ag₂(µ-O₂C^tBu)₂], as potential precursors for focused electron-beam-induced deposition. All of the compounds show high sensitivity to electron dissociation and efficient dissociation of Ag-O bonds. The as-deposited materials have silver contents from 42 at.% to above 70 at.% and are composed of silver nano-crystals with impurities of carbon and fluorine between them. Precursors with the shortest carbon-fluorine chain ligands yield the highest silver contents. In addition, the deposited silver content depends on the balance of electron-induced ligand co-deposition and ligand desorption. For all of the tested compounds, low electron flux was related to high silver content. Our findings demonstrate that silver carboxylates constitute a promising group of precursors for gas-assisted focused electron beam writing of high silver content materials.

Liquid injection field desorption/ionization as a powerful tool to characterize volatile, labile, and reactive metal-organic complexes

Electron ionization mass spectrometry (EI-MS) is often used to characterize volatile and thermally stable organometallic complexes relevant for chemical vapor deposition (CVD) processes. However, this method has limitations for thermally unstable and labile organometallic complexes. In this context, EI-MS is not the preferred method of choice for characterizing such compounds. With three different representative organometallic complexes based on the transition metals yttrium, iridium, and silver, relevant as precursors for CVD of different materials, the significance of liquid injection field desorption/ionization mass spectrometry (LIFDI-MS) as an important precursor characterization tool is exemplified. The precursors are not only reactive toward ambient air, but also thermally labile especially in the case of iridium and silver complexes. As a promising alternative, LIFDI-MS is used to overcome the limitations of EI-MS. For the first time, these complexes were successfully analyzed using LIFDI-MS. The comparison between EI-MS and LIFDI-MS highlights that LIFDI-MS is superior for the mass spectrometric analysis of sensitive and labile complexes. In terms of precursor characterization, LIFDI-MS can be fully exploited to gain valuable insights into the decomposition mechanisms and identifying the nuclearity of organometallic precursors used for CVD applications.

In Situ Time-of-Flight Mass Spectrometry of Ionic Fragments Induced by Focused Electron Beam Irradiation: Investigation of Electron Driven Surface Chemistry inside an SEM under High Vacuum

Recent developments in nanoprinting using focused electron beams have created a need to develop analysis methods for the products of electron-induced fragmentation of different metalorganic compounds. The original approach used here is termed focused-electron-beam-induced mass spectrometry (FEBiMS). FEBiMS enables the investigation of the fragmentation of electron-sensitive materials during irradiation within the typical primary electron beam energy range of a scanning electron microscope (0.5 to 30 keV) and high vacuum range. The method combines a typical scanning electron microscope with an ion-extractor-coupled mass spectrometer setup collecting the charged fragments generated by the focused electron beam when impinging on the substrate material. The FEBiMS of fragments obtained during 10 keV electron irradiation of grains of silver and copper carboxylates and shows that the carboxylate ligand dissociates into many smaller volatile fragments. Furthermore, in situ FEBiMS was performed on carbonyls of ruthenium (solid) and during electron-beam-induced deposition, using tungsten carbonyl (inserted via a gas injection system). Loss of carbonyl ligands was identified as the main channel of dissociation for electron irradiation of these carbonyl compounds. The presented results clearly indicate that FEBiMS analysis can be expanded to organic, inorganic, and metal organic materials used in resist lithography, ice (cryo-)lithography, and focused-electron-beam-induced deposition and becomes, thus, a valuable versatile analysis tool to study both fundamental and process parameters in these nanotechnology fields.