Efficient Drilling of Amorphous Alloy Foils Using Low-Energy Long Pulses of a Nd:YAG Laser

Laser drilling of amorphous alloy foils was conducted using low-energy long-pulses (LP) generated using a Nd:YAG laser. Results showed that LP can drill an amorphous alloy foil more efficiently than a nanosecond pulse (NSP) can: an LP at 1 mJ can open a through-hole on an amorphous alloy foil with 25 mm thickness although single shot NSP at 20 mJ formed a crater with ca. 3 mm depth. From these findings, we infer that the markedly higher drilling efficiency of a low-energy LP than that of NSP is attributable to 1) lower plasma generation by LP than by NSP, and 2) repeated irradiation of the target material by multiple sub-pulses in an LP. Results also demonstrate that low-energy LP drilling is applicable to various metal foils and that the drilling efficiency depends on the metal species.

Computer-aided design of graphene and 2D materials synthesis via magnetic inductive heating of eleven transition metals

We performed numerical simulations to determine the effect of the most influential operating parameters on the performance of radio frequency (RF) induction heating system in which RF magnetic fields inductively heat metal foils to grow graphene. Thermal efficiency of the system depends on the geometry as well as on the material electrical conductivity and skin depth. The process is simulated under specific graphene and 2D materials growth conditions using finite elements software in order to predict transient temperature and magnetic field distribution during standard graphene and 2D materials growth conditions. The proposed model considers different coil Helmholtz-like geometries and eleven metal foils including Ag, Au, Cu, Ni, Co, Pd, Pt, Rh, Ir, Mo and W. In each case, an optimal window of process variables ensuring a temperature range of 1035–1084 °C or 700–750 °C suitable for graphene and MoS2 growth respectively was found. Temperature gradient calculated from the simulated profiles between the edge and the center of the substrate showed a thermal uniformity of less than ~2% for coinage metals like Au, Ag and Cu and up to 7% for Pd. Model validation was performed for graphene growth on copper. Due to its limited heat conductivity, good heating uniformity was obtained. As a consequence, full coverage of monolayer graphene on copper with few defects and grain domain size of ~2 µm is obtained. Substrate temperature reached ~ 1035 ° C from ambient after only ~90 s, in excellent agreement with model predictions. This allows for improved process efficiency in terms of fast, localized, homogeneous and precise heating with energy saving. Due to these advantages, inductive heating has great potential for large scale and rapid manufacturing of graphene and 2D materials.

The same chemical state of carbon gives rise to two peaks in X-ray photoelectron spectroscopy

Chemical state analysis in X-ray photoelectron spectroscopy (XPS) relies on assigning well-defined binding energy values to core level electrons originating from atoms in particular bonding configurations. Here, we present direct evidence for the violation of this paradigm. It is shown that the C 1s peak due to C–C/C–H bonded atoms from adventitious carbon (AdC) layers accumulating on Al and Au foils splits into two distinctly different contributions, as a result of vacuum level alignment at the AdC/foil interface. The phenomenon is observed while simultaneously recording the spectrum from two metal foils in electric contact with each other. This finding exposes fundamental problems with the reliability of reported XPS data as C 1s peak of AdC is routinely used for binding energy scale referencing. The use of adventitious carbon in XPS should thus be discontinued as it leads to nonsense results. Consequently, ISO and ASTM charge referencing guides need to be rewritten.