Positron annihilation study of cavities in black Au films

Abstract

Abstract. Defects in a black Au film were studied using variable energy positron annihilation spectroscopy. Black Au films exhibit porous morphology similar to cauliflower. This type of structure enhances the optical absorption due to a multiple reflections in the micro-cavities. A nanostructured black Au film was compared with conventional smooth Au films with high reflectivity. The black Au film exhibited a remarkably enhanced S-parameter in sub-surface region. This is caused by a narrow para-Positronium contribution to the annihilation peak. IntroductionLight absorbers are needed in optical applications for preventing crosstalk between optical connections and for thermal light-emitting sources. A complete absorption of light from the visible into the infrared spectral region over the whole range of incident angles remains still a challenge [1]. This goal could be achieved in nanostructured metal surfaces containing a broad size distribution of cavities that sustain localized optical excitations [2]. Metals evaporated in the presence of a gas with pressure of about 100 Pa deposit as porous layers called black metals [3]. Their porous structure with percolated microcavities leads to high absorbance in the visible to infrared spectral region. Black metals, in particular black Au, are therefore highly suitable as absorbers [4]. The surface morphology and the structure of cavities in sub-surface region are crucial for performance of black metals absorbers. In the present work variable energy positron annihilation spectroscopy (VEPAS) was employed for characterization of cavities in black Au film. Microstructures of black Au and a conventional smooth Au film were compared. Note that a conventional smooth Au films have been already studied by VEPAS in Ref. [5].

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

“…Generally, black metals are considered to be stable up to 300 °C. [ 5 ] Several metals, such as silver, [ 6 ] gold, [ 7,8 ] platinum, [ 9 ] tungsten, [ 10 ] titanium, [ 11 ] palladium, [ 12 ] and aluminum, [ 13,14 ] are known to be fabricated in the form of black metals. Black aluminum (Black Al) is a metal that has good thermal stability and at the same time is inexpensive to produce.…”

“…[3,4] Such coatings must have good thermal stability, namely they must retain their porous structure and, consequently, heatabsorbing properties at elevated temperatures. Generally, black metals are considered to be stable up to 300 C. [5] Several metals, such as silver, [6] gold, [7,8] platinum, [9] tungsten, [10] titanium, [11] palladium, [12] and aluminum, [13,14] are known to be fabricated in the form of black metals. Black aluminum (Black Al) is a metal that has good thermal stability and at the same time is inexpensive to produce.…”

Positronium Formation in Nanostructured Metals

“…3. The S(E) curve for a well annealed (1000 [13] is plotted in the figure as well. The S parameter values were always normalized to the bulk parameter value S 0 for the well annealed Au reference.…”

Microstructure and Nanoscopic Porosity in Black Pd Films

“…Use of BMs in gas sensor applications profits from their extraordinary large surface area, e.g., 60 m 2 /g for black Pd [5]. BM films of various elements are deposited usually by thermal evaporation in carefully adjusted low pressure (∼ 100 Pa) of N 2 gas [7,8]. It has been reported that BMs can be prepared also by magnetron sputtering in Ar with small amount of N 2 [6][7][8][9][10].…”

“…BM films of various elements are deposited usually by thermal evaporation in carefully adjusted low pressure (∼ 100 Pa) of N 2 gas [7,8]. It has been reported that BMs can be prepared also by magnetron sputtering in Ar with small amount of N 2 [6][7][8][9][10]. In the growth of metallic films in PVD systems contamination from residual atmosphere should be considered [11].…”