Plasma‐assisted self‐formation of nanotip arrays on the surface of Cu(In,Ga)Se₂ thin films

Abstract

In this paper, we report on the phenomenon of nanostructure self‐formation on the surface of Cu(In,Ga)Se2 (CIGS) thin films during inductively coupled argon plasma treatment with its duration varied from 10 to 120 s. The initial films were grown on glass substrates using the selenization technique. During the CIGS film surface treatment in the high‐density low‐pressure radio‐frequency inductively coupled argon plasma there took place a formation of arrays of uniform vertical nanostructures, which shape with increasing processing duration changed from nanocones to nanorods and back to nanocones. A model of the nanotip plasma‐assisted self‐formation associated with the implementation of micromasking and vapor–liquid–solid mechanisms involving metallic In‐Ga (In‐Ga‐Cu) liquid alloy droplets is proposed.

Surface nanostructuring of CuIn1−xGaxSe2films using argon plasma treatment

“…As a result of such a complex mechanism, there is no simple linear dependence of the average nanostructure height on the sputtering rate of film composition. The proposed model of the plasma-assisted self-formation of the nanostructure arrays showed its validity for the analysis of the experimental results on the dynamics of the nanostructure growth for the treatment duration in the range of 10-120 s [15]. Also of note, the plasma treatment approach allows the growth of CIGS nanostructures without long-lasting and high temperature catalyst preparation operations, which are usually related to the epitaxial VLS growth of the copper indium diselenide (5 h, 700 °C) [22].…”

“…The fact that the arrays of uniform vertical nanostructures appear steadily for all the studied samples is a consequence of a successful combination of metals (Cu, In, Ga) in the CIGS films, for which alloys have low melting points and therefore provide the formation of homogeneous liquid droplets already at the initial stages of the plasma treatment (with incubation time less than 10 s [15]). A rather narrow interval of the nanostructure density for all the investigated samples is due to the total number of metal atoms (In+Ga+Cu) in different samples being approximately the same.…”

“…First, they serve as micromasks and lead to the nanocone arrays' formation during plasma treatment. On the other hand, they also serve as liquid catalyst droplets for the vapour-liquidsolid (VLS) mechanism growth [15,[20][21][22] underneath them with the sputtered CIGS elements from the vapour phase, which results in the formation of vertical nanostructures. The competition of these two simultaneous mechanisms explains both the conical and the cylindrical shapes of the nanostructures.…”

“…For these discharge parameters, the ion-flux density was 7.5 mA cm −2 . The plasma treatment duration was 60 s, which was selected considering that during the CIGS plasma treatment in the range of 10-180 s [15] the interchanging processes of nucleation, growth and subsequent merger of nanostructures are characterized by the stable formation of vertical nanorod arrays with the most developed surface area for the 60 s duration.…”

Plasma-assisted surface nanostructuring of epitaxial Pb1−x Sn x Te (0 ≤ x ≤ 1) films

“…However, the reported 'bottom-up' nanostructure formation methods are high-temperature and expensive, and a search for more economically viable and accessible approaches to the Pb 1−x Sn x Te nanostructuring actively continues. In a series of our recent papers [5][6][7][8][9], we have proposed a new 'top-down' approach to the surface nanostructuring using inductively coupled argon plasma treatment, which we have applied to a wide range of chalcogenide materials, allowing the fabrication, among others, of the PbTe nanowires on Si substrate [7] and of the vertical cylindrical CuIn 1−x Ga x Se 2 nanostructures [8]. Previously, we have already started the experimental work aimed to carry over this approach to the Pb 1−x Sn x Te material, which resulted in successful nanostructuring for polycrystalline Pb 1−x Sn x Te films [10], and we have started the studies of the singlecrystal epitaxial Pb 1−x Sn x Te films with the investigations of their sputtering rates [11].…”