ABSTRACT Understanding charge transport in networks of 2D crystals is essential for developing reliable applications such as chemiresistors or electromagnetic shields. For this purpose, intra‐ and inter‐flake contributions to the network resistance must be disentangled. MXenes such as Ti 3 C 2 T x , are prime examples of 2D crystals often employed as thin networks of interconnected flakes for functional devices. While a significant number of studies focused on transport in individual MXene flakes, inter‐flake transport remains scarcely explored. Here, we demonstrate that charge transport in multi‐flake conductive paths of Ti 3 C 2 T x is dominated by interflake junctions and provide quantitative estimates of junction resistances. Scanning probe measurements reveal that in a MXene multi‐flake conductive path, individual flakes behave as isopotential domains, since the voltage drop is localized precisely at inter‐flake junctions. The chemiresistive response to humidity is further investigated at the single flake, multi‐flake and flake network scale, evidencing the crucial impact of junctions on sensing kinetics. These findings underline the dominant role of inter‐flake junctions in MXene charge transport and sensing capabilities.

Silver nanowire (AgNW) networks are in the spotlight as flexible transparent electrodes (TEs) thanks to their combination of high optical transmittance, low electrical resistance, and excellent flexibility. As such network is formed from a multitude of interwoven AgNW, a postdeposition treatment is needed to get the best electrical conductivity from each interconnect. Traditionally, thermal annealing above 200 °C enhances AgNW junction contacts but restricts compatibility with heat-sensitive substrates such as polymers and perovskites, common in flexible electronics and solar cells. The present study explores the potential of capillary-force-induced cold-welding, an already reported low-temperature alternative operating at or below 100 °C. Better insight into the morphological and electrical properties of cold-welded AgNWs is essential for their large-scale integration as flexible and stable TEs in devices. In this work, the effective welding of AgNW junctions is directly demonstrated by in situ and nanoscale transport measurements. The junction resistance is drastically reduced while preserving both optical transparency and nanowire morphology at significantly lower temperatures than those used with conventional treatments such as thermal annealing. These results strengthen cold welding as a promising approach for overcoming the challenges of AgNW network integration in flexible electronics.

In the broader context of the electronics industry, the development of new on-wafer characterization techniques and instruments is imperative for precise validation of circuits designed for high-frequency (HF) applications. Advancing the miniaturization of HF devices necessitates addressing new metrological challenges related to dimensional and electrical characterization. To tackle these challenges, a new fully automated and robotic on-wafer probe station was conceived and constructed from scratch. The measurement probes and the chuck hosting the DUT are mounted on SmarAct® piezoelectric nano-positioners. Integration of a Keysight® Streamline vector network analyzer into the station offers a compact solution close to the probes, reducing non-systematic errors arising from environmental variations. This work is centered on the mechanical aspects necessary for achieving exemplary fine control of probe movements, which are essential for future system automation.

Increasing quantum confinement in semiconductor quantum dot (QD) systems is essential to perform robust simulations of many-body physics. By combining molecular beam epitaxy and lithographic techniques, we developed an approach consisting of a twofold selective area growth to build QD chains. Starting from 15 nm-thick and 65 nm-wide in-plane In0.53Ga0.47As nanowires on InP substrates, linear arrays of In0.53Ga0.47As QDs were grown on top, with tunable lengths and separations. Kelvin probe force microscopy performed at room temperature revealed a change of quantum confinement in chains with decreasing QD sizes, which was further emphasized by the spectral shift of quantum levels resolved in the conduction band with low temperature scanning tunneling spectroscopy. This approach, which allows the controlled formation of 25 nm-thick QDs with a minimum length and separation of 30 nm and 22 nm respectively, is suitable for the construction of scalable fermionic quantum lattices.

This article describes an approach to making highly stable copper nanowire networks on any type of substrates. These nanostructured materials are highly sought after for, among other applications, the development of next-generation flexible electronics. Their high susceptibility to oxidation in air currently limits their use in the real world. Here, we develop a multistep chemical method to fabricate transparent electrodes (TEs) using Cu-based bimetallic NW networks on various substrates at room temperature. First, we synthesized homogeneous core@shell copper@nickel (Cu@Ni) NWs using a one-pot colloidal approach. After their deposition on a substrate, we exploited the exothermic nature of the reaction between the Ni oxide and hydrazine to eliminate the naturally formed metal oxide moieties and interlock the NW junctions of the network. Electrical measurements, at the single junction level, indicate that the exothermic reaction induces a reduction of resistance by up to 4 orders of magnitude. On a macroscopic scale, the resulting Cu-based NW networks feature an optical transmittance of 80% in the visible region and a sheet resistance of 10 Omega/sq with a record stability of over 2 years. This process offers a simple and efficient strategy for fabricating cost-effective, long-life electronic devices, as illustrated by a proof-of-concept integrating an optimized Cu@Ni-based TE as a flexible transparent heater.

Raman spectroscopy is well-suited for the characterization of semiconductor materials. However, due the weakness of the Raman signal, the studies of thin semiconductor layers in complex environments, such as ultrahigh vacuum, are rather scarce. Here, we have designed a Raman apparatus based on the use of a fiber optic probe, with a lens collecting the backscattered light directly inserted in ultrahigh vacuum. The solution has been tested for the preparation of III-V semiconductor surfaces, which requires the recovery of their atomic reconstruction. The surfaces were either protected with a thin As amorphous layer or covered with a native oxide prior to their treatment. The analysis of the Raman spectra, which was correlated with the study of the surfaces with low temperature scanning tunneling microscopy at the end of the cleaning process, shows the high potential of Raman spectroscopy for monitoring the cleanliness of III-V semiconductor heterostructures in situ.

We demonstrate a high electron conductivity (>102 S/cm and up to 103 S/cm) of tungsten suboxide W18O52.4−52.9 (or equivalently WO2.91−2.94) nanotubes (2–3 nm in diameter, ∼μm long). The conductivity is measured in the temperature range of 120–300 K by a four-probe scanning tunneling microscope in ultrahigh vacuum. The nanotubes are synthesized by a low-temperature and low-cost solvothermal method. They self-assemble in bundles of hundreds of nanotubes forming nanowires (∼μm long, few tens nm wide). We observe a large anisotropy of the conductivity with a ratio (longitudinal conductivity/perpendicular conductivity) of ∼105. A large fraction of them (∼65%–95%) shows a metallic-like, thermal activation-less electron transport behavior. Few of them, with a lower conductivity from 10 to 102 S/cm, display a variable range hopping behavior. In this latter case, a hopping barrier energy of ∼0.24 eV is inferred in agreement with the calculated energy level of the oxygen vacancy below the conduction band. This result is in agreement with a relative average concentration of oxygen vacancies of ∼3%, for which a semiconductor-to-metal transition was theoretically predicted. These tungsten suboxide nanostructures are prone to a wide range of applications in nanoelectronics.

Precise and repeatable radiofrequency (RF) measurements call for innovative characterization techniques. In particular, the use of nanorobotics for on-wafer measurements is a viable solution to address RF characterization with enhanced alignment accuracy. In this work, we present the development of a nanorobotics and automatic on-wafer probing station designed and realized for GSG on-wafer millimetre-wave measurements.

Physics-based models of the Li-ion battery are promising to decipher and quantify the electrode limitations, thereby providing valuable insights for choosing the optimal electrode design for a specific application. However, to obtain relevant results from the models, a reliable set of input parameters is required. This work presents a combined experimental/modeling approach relying on the Newman pseudo-2D model for a complete characterization of a set of LiNi0.5Mn0.3Co0.2O2 electrodes. Intrinsic properties of the active materials are determined and validated using low-loading electrodes having negligible porous-electrode limitations. Then, high-energy-density electrode properties are characterized using appropriate experimental methods, which are widely reported in the literature. In the second part of this series of papers, parameters obtained from this part serve as input parameters in the Newman pseudo-2D model as well as in its extension in order to simulate the rate capability during discharge of the aforementioned set of high-energy-density electrodes. List of symbols a i m i 2 / m PE 3 interfacial surface area of phase i c s , surf mol m − 3 concentration at the surface of the AM particle c s , max mol m − 3 maximum concentration of intercalated Li in AM particle c s mol m − 3 solid-phase Li concentration within the AM particle c ¯ s mol m − 3 local volume-averaged solid Li concentration of AM phase within the PA c mol m − 3 salt concentration in a binary electrolyte d 50 μ m median diameter of AM particles D m 2 s − 1 bulk diffusion coefficient of the liquid phase D s m 2 s − 1 diffusion coefficient of Li in the AM particles F C mol − 1 Faraday’s constant i coexisting phase presented in the PE i n 0 A m − 2 exchange current density i Li 0 A m − 2 exchange current density at the Li foil I app A / m CC 2 discharge current density j n mol / m AM 2 · s pore-wall flux across the sandwich k 0 mol m 2 · s · mol m − 3 1.5 − 1 reaction rate constant of the AM k 0 , Li mol m 2 · s · mol m − 3 0.5 − 1 reaction rate constant of Li foil L el μ m PE thickness L sep μ m separator thickness Q th Ah kg − 1 electrode theoretical capacity R J mol · K − 1 ideal gas constant r μ m radial dimension along the AM particle T K absolute temperature t s time t + 0 transference number of Li+ in the electrolyte with respect to the solvent velocity U V equilibrium potential of the AM Δ V V voltage drop between the two inner contacts in the μ4-probe experiment x μ m dimension across the sandwich x 0 initial stoichiometry Greek Symbols α thermodynamic factor β charge transfer coefficient ε m elyte 3 / m PE 3 PE porosity ε sep m elyte 3 / m sep 3 separator porosity κ eff S m − 1 effective ionic conductivity of the liquid phase ρ el g cm − 3 electrode density σ eff S m − 1 effective electronic conductivity of the solid phase of the electrode τ Br tortuosity factor by Bruggeman τ e electrode tortuosity factor τ sep tortuosity factor of the separator Φ 1 , Li V electric potential at Li foil Φ i V electric potential of phase i

The knowledge of the band alignment in semiconductor heterostructures is crucial, as it governs carrier confinement with many impacts on the performances of devices. By controlling the direction of the current flow in in-plane In0.53Ga0.47As/InP heterostructure nanowires, either horizontally along the nanowires or vertically into the InP substrate with low temperature multiple-probe tunneling spectroscopy, a direct measurement of the band offsets at the buried In0.53Ga0.47As/InP heterointerface is performed. Despite the unavoidable processing steps involved in selective area epitaxy, conduction and valence band offsets of 0.21 ± 0.01 and 0.40 ± 0.01 eV are, respectively, found, indicating the formation of an interface with a quality comparable to two-dimensional In0.53Ga0.47As/InP heterostructures.

Oriented attachment of colloidal quantum dots allows the growth of two-dimensional crystals by design, which could have striking electronic properties upon progress on manipulating their conductivity. Here, we explore the origin of doping in square and epitaxially fused PbSe quantum dot superlattices with low-temperature scanning tunneling microscopy and spectroscopy. Probing the density of states of numerous individual quantum dots reveals an electronic coupling between the hole ground states of the quantum dots. Moreover, a small amount of quantum dots shows a reproducible deep level in the band gap, which is not caused by structural defects in the connections but arises from unpassivated sites at the {111} facets. Based on semiconductor statistics, these distinct defective quantum dots, randomly distributed in the superlattice, trap electrons, releasing a concentration of free holes, which is intimately related to the interdot electronic coupling. They act as acceptor quantum dots in the host quantum dot lattice, mimicking the role of dopant atoms in a semiconductor crystal.

Micro-batteries are attractive miniaturized energy devices for new Internet of Things applications, but the lack of understanding of their degradation process during cycling hinders improving their performance. Here focused ion beam (FIB)-lamella from LiMn1.5 Ni0.5 O4 (LMNO) thin-film cathode is in situ cycled in a liquid electrolyte inside an electrochemical transmission electron microscope (TEM) holder to analyze structural and morphology changes upon (de)lithiation processes. A high-quality electrical connection between the platinum (Pt) current collector of FIB-lamella and the microchip's Pt working electrode is established, as confirmed by local two-probe conductivity measurements. In situ cyclic voltammetry (CV) experiments show two redox activities at 4.41 and 4.58/4.54 V corresponding to the Ni2+/3+ and Ni3+/4+ couples, respectively. (S)TEM investigations of the cycled thin-film reveal formation of voids and cracks, loss of contact with current collector, and presence of organic decomposition products. The 4D STEM ASTAR technique highlights the emergence of an amorphization process and a decrease in average grain size from 20 to 10 nm in the in situ cycled electrode. The present findings, obtained for the first time through the liquid electrochemical TEM study, provide several insights explaining the capacity fade of the LMNO thin-film cathode typically observed upon cycling in a conventional liquid electrolyte.

Germanane is a two-dimensional material consisting of stacks of atomically thin germanium sheets. It’s easy and low-cost synthesis holds promise for the development of atomic-scale devices. However, to become an electronic-grade material, high-quality layered crystals with good chemical purity and stability are needed. To this end, we studied the electrical transport of annealed methyl-terminated germanane microcrystallites in both high vacuum and ultrahigh vacuum. Scanning electron microscopy of crystallites revealed two types of behavior which arise from the difference in the crystallite chemistry. While some crystallites are hydrated and oxidized, preventing the formation of good electrical contact, the four-point resistance of oxygen-free crystallites was measured with multiple tips scanning tunneling microscopy, yielding a bulk transport with resistivity smaller than 1 Ω·cm. When normalized by the crystallite thickness, the resistance compares well with the resistance of hydrogen-passivated germanane flakes found in the literature. Along with the high purity of the crystallites, a thermal stability of the resistance at 280 °C makes methyl-terminated germanane suitable for complementary metal oxide semiconductor back-end-of-line processes.