Characterization of Ag–In–S films with AFM

AFM is a powerful technique for analyzing thin films and coatings, and it can provide useful information that is crucial to the performance of a material or process. AFM assesses nanoscale functionality, including electrical, magnetic, and mechanical characteristics, by quantifying 3D roughness and texture with unprecedented spatial resolution.

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Thin films and coatings are used in everything from food storage to photovoltaics. They are made from a wide range of materials and by a variety of procedures, including deposition, self-assembly, and sol-gel techniques.

The technique of generating and bonding thin films to a substrate material is known as thin film deposition. Coatings can be made of a variety of materials, including metals, oxides, and compounds.

Thin film coatings also have a variety of characteristics that can be used to modify or improve substrate performance. Some are transparent, others are very rugged and scratch resistant, while still others improve or reduce electrical or signal transmission conductivity.

Role of AFM in thin film characterization

Achieving sub-nanometer to micrometer resolutions in the characterization of these films is essential. Moreover, the ability to test many functional characteristics at the same time at these scales has become an essential part of thin film engineering for certain applications.

In creating, optimizing, and monitoring thin-film growth processes, as well as streamlining design pathways to achieve desired functional attributes, atomic force microscopy (AFM) offers crucial insights.

Characterization of Ag–In–S films with AFM

In a study from the journal Materials Today: Reviews, thermal evaporation from a Knudsen cell has been used to create Ag–In–S ternary films with a variety of different compositions. It was found by AFM analysis of the films produced that they are smooth and homogeneous, with an average surface roughness ranging from 4–5 nanometers for stoichiometric AgInS2 to about 11 nanometers for highly Ag-deficient films.

The structure, composition and characteristics of films are known to be influenced by the production technique, component ratio and subsequent heat treatment. The chemical composition of AgInS2 films formed by thermal evaporation is known to correlate well with the ratio of charged components, unlike other preparation methods.

XRD measurements reveal that the films are amorphous, containing visible silver crystallite inclusions in the stoichiometric films as well as less Ag deficient, respectively.

The Raman spectra of the prepared amorphous films show a strong correlation with that of AgInS2 polycrystals and Ag–In–S nanocrystals, indicating that silver is integrated into the structure of the amorphous film for all film compositions and that only a part of the Ag atoms is contained inside Ag crystallites revealed by XRD measurements.

Results of Ag-In-S with AFM topography

Images of Ag–In–S films with varying component ratios taken with an AFM topography probe reveal that the surfaces of the created films are rather homogeneous. The surface roughness of AgInS2 films made by spray pyrolysis, thermal silver diffusion in In2S3 buffer layers and electrodeposition was found to be significantly higher than that of AgInS2 films prepared by other methods.

It was discovered that the appearance of many crystalline phases can be explained by the presence of smoother surfaces after annealing.

As shown by the Raman spectra of Ag–In–S films with varying component ratios, the main features discovered are relatively similar in all samples. The maxima are significantly larger than those of crystalline AgInS2 or AgIn5S8characteristic of amorphous materials.

Advances in this research

Considering the existence of a crystalline phase of Ag in the films generated by XRD, it was essential to determine whether the amorphous phase included a significant amount of silver or if all the silver precipitated in nanocrystalline form.

Raman spectroscopy should be used to solve this problem. At the current count, no Raman investigation of Ag–In–S amorphous materials has been published before. Neither bulk single crystals of AgInS2 nor Raman data are present in the literature. As a new advance in this research, the researchers propose an unpolarized spectrum of a polycrystalline AgInS2 sample recorded under identical experimental circumstances for comparison purposes.

The Raman spectra of the amorphous films show a strong correlation with those of the polycrystals of AgInS2 and the nanocrystals of Ag–In–S, confirming the presence of all the elements in the composition of the amorphous films, whereas only a fraction of the atoms of ‘Ag is contained in Ag crystallites, as indicated by radiographic data. The amorphous structure of films generated with inclusions of silver crystallites for stoichiometric and less Ag-deficient films is shown by XRD studies.

References and further reading

Azhniuk, Y., et al. (2022). Characterization of Ag–In–S films prepared by thermal evaporation. Materials Today: Acts.

Asylum research. (2022). AFM for thin films and coatings. Oxford Instrument Cluster.

Bishop, C. (2015). Process diagnostics and coating characteristics. Vacuum Deposition on Canvas, Films and Sheets (Third Edition). Pages 85-128.

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