Sonochemically Synthesized Quantum Nanocrystals of Cubic CuInS₂: Evidence for Multifractal Surface Morphology, Size-Dependent Structure, and Particle Size Distribution

Abstract

Advanced techniques for analysis of XRD patterns and optical absorption spectra were employed to derive in-depth physical insights into the structure and properties of quantum nanocrystals of the cubic modification of CuInS 2 synthesized by a sonochemical route. Three-dimensional assemblies of the synthesized nanocrystals deposited as thin films exhibit multifractal surface morphology, with the multifractal singularity spectral widths being far above the monofractal limit. The widths of the multifractal spectra indicate that films grown by the conventional chemical method are structurally richer and at the same time characterized by higher complexity of the surface than those grown under sonochemical conditions, while the values of the Holder exponent corresponding to their maxima are rather close. In both cases, the multifractal spectra are right-skewed, with a positive asymmetry parameter a s and domination of high fractal exponents. The right-skewness is more pronounced in the case of sonochemically deposited films. Lacunarity in the chemically deposited samples is smaller than in the sonochemically deposited ones, regardless of the particular scale on which the comparison is carried out, indicating a higher homogeneity and, in parallel, higher translational invariance in the former case. Somewhat larger heterogeneity and wider distribution of gap sizes in the sonochemically deposited samples are attributed to acoustic streaming phenomena that take place within the ultrasonically irradiated reactor under heterogeneous sonochemical conditions. The average particle size as well as the size distribution and the degree of structural disorder can be controlled by an appropriate control of the reactor content and its exposure to ultrasonic irradiation in the course of deposition process. This, in turn, allows appropriate tuning of the material's band gap energy, which is physically based on both intradot size-quantization effects and the interdot charge carrier coupling phenomena. Considering the substantial relevance of the title material in optoelectronics and solar cell technology, the physically based design of the material's properties demonstrated in the present study can open certain new directions in the development of solar cells based on inorganic semiconductor systems.

Molecular-Level Insight into Semiconductor Nanocrystal Surfaces

“…Notably, SAXS provides indirect insight into the local environments at NC surfaces. The applications of these tools to study NCs have recently been reviewed in detail. − The insight provided by X-ray techniquesinto both the underlying inorganic crystal structure and the local environments of surface atomsis critical to developing a molecular-level understanding of NC surface structure. , While PXRD is typically available on university campuses, methods such as XAFS often require collaborations at specialized research institutes that have the necessary instrumentation and access to a synchrotron source, making them less commonly used despite their potential for high-value insight. In comparison to PXRD, XAFS, and SAXS, small-angle neutron scattering ( SANS ) has been less frequently utilized for probing the surface structure of NCs; however, SANS has the capability to analyze the inorganic lattice, surface capping ligands, and surrounding solvent simultaneously. ,− While incredibly useful for studying NC surface chemistry with atomic-level detail and high spatial resolution, limited access to neutron scattering diffractometers has likely impeded the incorporation of SANS as a widespread technique …”

“…64−68 The insight provided by X-ray techniquesinto both the underlying inorganic crystal structure and the local environments of surface atomsis critical to developing a molecular-level understanding of NC surface structure. 69,70 While PXRD is typically available on university campuses, methods such as XAFS often require collaborations at specialized research institutes that have the necessary instrumentation and access to a synchrotron source, making them less commonly used despite their potential for high-value insight. In comparison to PXRD, XAFS, and SAXS, small-angle neutron scattering (SANS) has been less frequently utilized for probing the surface structure of NCs; however, SANS has the capability to analyze the inorganic lattice, surface capping ligands, and surrounding solvent simultaneously.…”

From Self-Affine Ag to Mounded Ag@Ag2O Core–Shell Nanoplasmonic Surfaces By Sonochemistry

“…In contrast with the other cases that have been studied by our group so far, ,, in the current study, sonication of the reaction system creates NPs with a larger average size deposited in thin-film form. Under most circumstances, such observation could mean that the collision of the highly energized NPs as a consequence of the shockwaves and microjets, generated under heterogeneous sonochemistry conditions, exhibit collisions in which the released energy can lead to local overheating and sequential melting of the NPs, resulting in their agglomeration and hence larger crystal size.…”

“…In contrast with the other cases that have been studied by our group so far, 22,23,27 in the current study, sonication of the reaction system creates NPs with a larger average size system fundamentally changes the reaction mechanism, leading to growth of the Ag@Ag 2 O core−shell NPs. Therefore, we here deal with a sonochemically supported growth of the oxide shell surrounding the initially grown Ag NPs.…”

Morphology Controlled Synthesis of Composition Related Plasmonic CuCdS Alloy Nanocrystals

“…Cu-based ternary semiconductor nanocrystals are of great scientific interest for applications in solar cells (Rivest et al, 2011 ), light-emitting devices (LEDs) (Yoon et al, 2019 ; Li et al, 2020 ), biological imaging (Meng et al, 2017 ), photo-catalytic (Zhao et al, 2016 ), photoelectric detectors because of their low-toxicity, tunable band gaps, and high absorption coefficients (Pejova et al, 2020 ). Especially, ternary nanocrystals based on Cu 1.94 S, with localized surface plasmon resonance due to the large number of copper vacancies, have been widely demonstrated for photoelectrochemical water reduction and solar cells due to their high concentration of free charge carriers (Liu et al, 2017 ; Bai et al, 2020 ; Bera et al, 2020 ; Zhu et al, 2020 ).…”