Thermal Stability of Black Aluminum Films and Growth of Aluminum Nanowires from Mechanical Defects on the Film Surface during Annealing

Abstract

The thermal stability of black aluminum (Black Al) films deposited on unheated fused silica substrates by pulsed DC magnetron sputtering is investigated. The deposited films have porous moth‐eye morphology and a relatively soft surface that can be easily damaged mechanically. Photothermally stimulated exoelectron emission (PTSE) spectra of the films have emission peaks at 180 and 300 °C, which can be associated with processes of aluminum recrystallization occurring at these temperatures. The total emitted charge of PTSE decreases according to a power law with each subsequent heating, indicating that the most pronounced structural changes on the film surface occur during its first annealing. The shape of the mechanically intact pores of the films does not change after heating. However, spiral‐shaped aluminum nanowires grow from scratches and abrasions on the film surface already after heating up to 200 °C due to the stress‐induced migration of aluminum atoms. When scratches are deliberately applied to the surface of an already annealed film, the nanowires do not grow when the film is reheated. The results of this study show that mechanically intact as‐deposited Black Al films are thermally stable up to temperatures of at least 400 °C.

Surface Enhancement Using Black Coatings for Sensor Applications

“…SEM images from the B-Al layer and B-Au layer deposited on the surfaces of the QCM sensor are presented in Figure 2 , which shows the surface of the B-Al and B-Au layers; Figure 3 presents cross-section images of both layers. Both surface morphologies reveal similar structures of cauliflowers similar to those reported in the literature [ 34 , 36 , 37 ]. The two main differences are the size of the grains and the layer densities, which are smaller for B-Au than the B-Al.…”

“…Especially highly porous aluminum has attracted great interest in recent years [ 26 , 27 ]. Several metals, such as gold, platinum, tungsten, copper, titanium, palladium, or aluminum, were examined to obtain a black or colored coating [ 13 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. Recently, surface desorption processes have been reported on thin layers of black aluminum [ 35 ].…”

Defect‐Induced Effects in Nanomaterials

“…The growth of Al nanowires from mechanical defects on the black Al film surface is reported by M. Romanova et al [8] Spiralshaped Al nanowires grow from scratches and abrasions on the film surface already after heating up to 200 °C due to the stress-induced migration of aluminium atoms.…”

A Porous Nanostructured ZnO Layer for Ultraviolet Sensing with Quartz Crystal Microbalance Technique

“…When realizing a sensing layer/QCM-based sensor, a trade-off must be found: high porosity of the sensitive layer means a larger adsorbing area and thus a larger sensitivity; nevertheless, too high porosity of the sensitive layer usually leads to its weak adhesion to the substrate, which, if QCM plate is used as a substrate, may ultimately affect the stability and reliability of resonant “sensitive layer/QSM”-based devices due to destruction and delaminating of the sensitive layer [ 27 , 32 , 33 ].…”