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-O2CtBu)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.

Thermally Stable Nanotwins: New Heights for Cu Mechanics.

Nanocrystalline and nanotwinned materials achieve exceptional strengths through small grain sizes. Due to large areas of crystal interfaces, they are highly susceptible to grain growth and creep deformation, even at ambient temperatures. Here, ultrahigh strength nanotwinned copper microstructures have been stabilized against high temperature exposure while largely retaining electrical conductivity. By incorporating less than 1 vol% insoluble tungsten nanoparticles by a novel hybrid deposition method, both the ease of formation and the high temperature stability of nanotwins are dramatically enhanced up to at least 400 °C. By avoiding grain coarsening, improved high temperature creep properties arise as the coherent twin boundaries are poor diffusion paths, while some size-based nanotwin strengthening is retained. Such microstructures hold promise for more robust microchip interconnects and stronger electric motor components.

Elemental Characterization of Al Nanoparticles Buried under a Cu Thin Film: TOF-SIMS vs STEM/EDX.

In this work, we present a comprehensive comparison of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy (STEM/EDX), which are currently the most powerful elemental characterization techniques in the nano- and microscale. The potential and limitations of these methods are verified using a novel dedicated model sample consisting of Al nanoparticles buried under a 50 nm thick Cu thin film. The sample design based on the low concentration of nanoparticles allowed us to demonstrate the capability of TOF-SIMS to spatially resolve individual tens of nanometer large nanoparticles under ultrahigh vacuum (UHV) as well as high vacuum (HV) conditions. This is a remarkable achievement especially taking into account the very small quantities of the investigated Al content. Moreover, the imposed restriction on the Al nanoparticle location, i.e., only on the sample substrate, enabled us to prove that the measured Al signal represents the real distribution of Al nanoparticles and does not originate from the artifacts induced by the surface topology. The provided comparison of TOF-SIMS and STEM/EDX characteristics delivers guidelines for choosing the most optimal method for efficient characterization of nano-objects.

Flexible ε-Fe2O3-Terephthalate Thin-Film Magnets through ALD/MLD.

Pliable and lightweight thin-film magnets performing at room temperature are indispensable ingredients of the next-generation flexible electronics. However, conventional inorganic magnets based on f-block metals are rigid and heavy, whereas the emerging organic/molecular magnets are inferior regarding their magnetic characteristics. Here we fuse the best features of the two worlds, by tailoring ε-Fe2O3-terephthalate superlattice thin films with inbuilt flexibility due to the thin organic layers intimately embedded within the ferrimagnetic ε-Fe2O3 matrix; these films are also sustainable as they do not contain rare heavy metals. The films are grown with sub-nanometer-scale accuracy from gaseous precursors using the atomic/molecular layer deposition (ALD/MLD) technique. Tensile tests confirm the expected increased flexibility with increasing organic content reaching a 3-fold decrease in critical bending radius (2.4 ± 0.3 mm) as compared to ε-Fe2O3 thin film (7.7 ± 0.3 mm). Most remarkably, these hybrid ε-Fe2O3-terephthalate films do not compromise the exceptional intrinsic magnetic characteristics of the ε-Fe2O3 phase, in particular the ultrahigh coercive force (∼2 kOe) even at room temperature.

3D Imaging of Nanoparticles in an Inorganic Matrix Using TOF-SIMS Validated with STEM and EDX.

Imaging nano-objects in complex systems such as nanocomposites using time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a challenging task. Due to a very small amount of the material and a matrix effect, the number of generated secondary ions can be insufficient to represent a 3D elemental distribution despite being detected in a mass spectrum. Therefore, a model sample consisting of a ZrCuAg matrix with embedded Al nanoparticles is designed. A high mass difference between the light Al and heavy matrix components limits mass interference. The chemical structure measurements using a pulsed 60 keV Bi32+ beam or a continuous 30 keV Ga+ beam reveals distinct Al signal segregation. This can indicate a spatially resolved detection of single 10s of nanometer large particles and/or their agglomerates for the first time. However, TOF-SIMS images of 50 nm or smaller objects do not necessarily represent their exact size and shape but can rather be their convolutions with the primary ion beam shape. Therefore, the size of nanoparticles (25-64 nm) was measured using scanning transmission electron microscopy. Our studies prove the capability of TOF-SIMS to image chemical structure of nanohybrids which is expected to help building new functional materials and optimize their properties.