Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers

Rueckriem K, Grotheer S, Vieker H, et al. Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers. BEILSTEIN JOURNAL OF NANOTECHNOLOGY. 2016;7:852-861.Copper(II) oxalate grown on carboxy-terminated self-assembled monolayers (SAM) using a step-by-step approach was used as precursor for the electron-induced synthesis of surface-supported copper nanoparticles. The precursor material was deposited by dipping the surfaces alternately in ethanolic solutions of copper(II) acetate and oxalic acid with intermediate thorough rinsing steps. The deposition of copper(II) oxalate and the efficient electron-induced removal of the oxalate ions was monitored by reflection absorption infrared spectroscopy (RAIRS). Helium ion microscopy (HIM) reveals the formation of spherical nanoparticles with well-defined size and X-ray photoelectron spectroscopy (XPS) confirms their metallic nature. Continued irradiation after depletion of oxalate does not lead to further particle growth giving evidence that nanoparticle formation is primarily controlled by the available amount of precursor

Electron-Induced Radiolysis of Astrochemically Relevant Ammonia Ices

We elucidate mechanisms of electron-induced radiolysis in cosmic (interstellar, planetary, and cometary) ice analogs of ammonia (NH3), likely the most abundant nitrogen-containing compound in the interstellar medium (ISM). Astrochemical processes were simulated under ultrahigh vacuum conditions by high-energy (1 keV) and low-energy (7 eV) electron-irradiation of nanoscale thin films of ammonia deposited on cryogenically cooled metal substrates. Irradiated films were analyzed by temperature-programmed desorption (TPD). Experiments with ammonia isotopologues provide convincing evidence for the electron-induced formation of hydrazine (N2H4) and diazene (N2H2) from condensed NH3. To understand the dynamics of ammonia radiolysis, the dependence of hydrazine and diazene yields on incident electron energy, electron flux, electron fluence, film thickness, and ice temperature were investigated. Radiolysis yield measurements versus (1) irradiation time and (2) film thickness are semiquantitatively consistent with a reaction mechanism that involves a bimolecular step for the formation of hydrazine and diazene from the dimerization of amidogen (NH2) and imine (NH) radicals, respectively. The apparent decrease in radiolysis yield of hydrazine and diazene with decreasing electron flux at constant fluence may be due to the competing desorption of these radicals at 90 K under low incident electron flux conditions. The production of hydrazine at electron energies as low as 7 eV and an ice temperature of 22 K is consistent with condensed phase radiolysis being mediated by low-energy secondary electrons produced by the interaction of high-energy radiation with matter. These results provide a basis from which we can begin to understand the mechanisms by which ammonia can form more complex species in cosmic ices

Formation of 2-propanol in condensed molecular films of acetaldehyde following electron impact ionisation-induced proton transfer

Experimental studies on thin condensed layers of acetaldehyde have previously revealed that electron exposure at an energy above the ionisation threshold leads to formation of 2-propanol. However, the mechanism of this reaction remained unclear. Therefore, a computational approach is used to explore the electron-induced reactions of acetaldehyde yielding 2-propanol. Starting from hydrogen-bonded dimers of acetaldehyde we show that the initial ionisation event triggers proton transfer between the two acetaldehyde moieties resulting in a hydrogen-bonded complex of a [OCCH3] radical and a protonated acetaldehyde cation. Given an excess energy of up to 0.75 eV and a favourable arrangement, a methyl radical released upon dissociation of the CC bond within the [OCCH3] radical can migrate to the carbonyl carbon of the protonated acetaldehyde cation. This produces a 2-propanol radical cation and CO. Neutral 2-propanol is then obtained by recombination with a second electron. A mechanism involving ionisation-driven proton transfer is thus proposed as pathway to the formation of 2-propanol during electron exposure of condensed layers of acetaldehyde

Towards Improved Humidity Sensing Nanomaterials via Combined Electron and NH3 Treatment of Carbon-Rich FEBID Deposits

Focused Electron Beam Induced Deposition (FEBID) is a unique tool to produce nanoscale materials. The resulting deposits can be used, for instance, as humidity or strain sensors. The humidity sensing concept relies on the fact that FEBID using organometallic precursors often yields deposits which consist of metal nanoparticles embedded in a carbonaceous matrix. The electrical conductivity of such materials is altered in the presence of polar molecules such as water. Herein, we provide evidence that the interaction with water can be enhanced by incorporating nitrogen in the deposit through post-deposition electron irradiation in presence of ammonia (NH3). This opens the perspective to improve and tune the properties of humidity sensors fabricated by FEBID. As a proof-of-concept experiment, we have prepared carbonaceous deposits by electron irradiation of adsorbed layers of three different precursors, namely, the aliphatic hydrocarbon n-pentane, a simple alkene (2-methyl-2-butene), and the potential Ru FEBID precursor bis(ethylcyclopentadienyl)ruthenium(II). In a subsequent processing step, we incorporated C-N bonds in the deposit by electron irradiation of adsorbed NH3. To test the resulting material with respect to its potential humidity sensing capabilities, we condensed sub-monolayer quantities of water (H2O) on the deposit and evaluated their thermal desorption behavior. The results confirm that the desorption temperature of H2O decisively depends on the degree of N incorporation into the carbonaceous residue which, in turn, depends on the chemical nature of the precursor used for deposition of the carbonaceous layer. We thus anticipate that the sensitivity of a FEBID-based humidity sensor can be tuned by a precisely timed post-deposition electron and NH3 processing step

Chemistry for electron-induced nanofabrication

ImPhys/Charged Particle Optic

Cisplatin as a Potential Platinum Focused Electron Beam Induced Deposition Precursor: NH3 Ligands Enhance the Electron-Induced Removal of Chlorine

Rohdenburg M, Martinovic P, Ahlenhoff K, et al. Cisplatin as a Potential Platinum Focused Electron Beam Induced Deposition Precursor: NH3 Ligands Enhance the Electron-Induced Removal of Chlorine. The Journal of Physical Chemistry C. 2019;123(35):21774-21787.Nanostructures fabricated by focused electron beam induced deposition (FEBID) often have low deposit purities that can be traced back to incomplete precursor decomposition. Among others, removal of halide ligands is particularly slow under electron irradiation. Herein, we report on the electron-induced decomposition of cisplatin (cis-Pt(NH3)(2)Cl-2), a potential precursor for Pt deposition. Cisplatin samples were irradiated with electrons, and the resulting compositional and chemical changes were monitored by surface analysis tools. The results reveal that electron exposure yields nearly pure Pt deposits, and the ligands are transformed into the gas-phase species N-2, NH3, and HCl. Also, surface-bound NHx (x < 3) species were identified that can act as reducing agents. Production of such reactive intermediates and N-2 implies that the electron-induced decomposition of the NH3 ligands releases atomic hydrogen, a species known to efficiently remove surface Cl via HCl formation. Furthermore, proton transfer from NH3 to Cl- triggered by ionization is deduced from the formation of NH4+ and proposed as a second reaction pathway producing HCl. Overall, this leads to rapid loss of the Cl ligands. We thus provide evidence that NH3 is favorable either as a ligand in FEBID precursors or as a postdeposition purification agent for halide-contaminated FEBID deposits

Low energy electron induced reactions in fluorinated acetamide – probing negative ions and neutral stable counterparts

Electron impact to trifluoroacetamide (CF3CONH2, TFAA) in the energy range 0–12 eV leads to a variety of negative fragment ions which are formed via dissociative electron attachment (DEA). The underlying reactions range from single bond cleavages to remarkably complex reactions that lead to loss of the neutral units HF, H2O and HNCO as deduced from their directly observed ionic counterparts (M – H2O)−, (M – HF)− and (M – HNCO)−. Also formed are the pseudo-halogen ions CN− and OCN−. All these reactions proceed dominantly via a resonance located near 1 eV, i.e., electrons at subexcitation energies trigger reactions involving multiple bond cleavages. The electron induced generation of the neutral molecules HF, H2O and HNCO in condensed TFAA films is probed by temperature controlled thermal desorption spectrometry (TDS) which can be viewed as a complementary techniques to gas-phase experiments in DEA to directly probe the neutral counterparts

Electron-induced chemistry of surface-grown coordination polymers with different linker anions

Ahlenhoff K, Koch S, Emmrich D, Dalpke R, Gölzhäuser A, Swiderek P. Electron-induced chemistry of surface-grown coordination polymers with different linker anions. Physical Chemistry Chemical Physics. 2019;21(5):2351-2364.Electron beam processing of surface-grown coordination polymers is a versatile approach to the fabrication of nanoscale surface structures. Depending on their molecular components, these materials can be converted into pure metallic particles or they can be activated to become a template for the spatially selective decomposition of suitable gaseous precursor molecules and subsequent autocatalytic growth of deposits. However, insight into the fundamental electron-induced chemistry for such processes has been scarce so far. Therefore, we investigated the electron-induced reactions of three self-assembled copper-containing materials, namely, copper(ii) oxalate, copper(ii) squarate, and copper(ii) 1,3,5-benzenetricarboxylate (HKUST-1) which were grown on the surface of self-assembled monolayers of mercaptoundecanoic acid in a layer-by-layer approach from copper(ii) acetate and various linker molecules. Changes incurred to these materials during electron irradiation were monitored by four complementary techniques. Reflection absorption infrared spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS) were used to identify the chemical species that are formed upon electron exposure. The temporal evolution of electron-stimulated desorption (ESD) of neutral volatile fragments was monitored to reveal the kinetics governing the decomposition of the different materials. Furthermore, the morphology was investigated by helium ion microscopy (HIM). A detailed analysis of the results for the different linker molecules provides new insights into the electron-induced chemistry of such surface-grown layers