Combining AFM with XPS to Analyze Graphene Oxide Membranes

Graphene oxide (GO)

Graphene oxide (GO) is a two-dimensional nano-material consisting of a graphene monolayer highly functionalized with oxygen-containing chemical groups. Of late, GO have evinced great interest because of their excellent physiochemical properties that can be used for many applications.

Scalable, relatively easy, and cost-effective methods are available to convert GO sheets into a graphene-like material known as reduced GO (rGO). GO has become an important element in producing industrial-scale graphene-like materials.

Dr. Angel Perez del Pinho works in the Instituto de Ciencia de Materiales de Barcelona (ICMAB), Spain, and specializes in the transformation of materials through laser processing. Recently, he and his fellow researchers published the findings on the conductivity of such processed GO materials.

GO has some interesting functional properties such as being dispersible in water and being biocompatible. Its optical band gap and electrical conductivity can be tailored by modifying its oxidation degree. Whilst GO does not conduct electricity, rGO is more conductive and behaves as a p-type semiconductor. rGO and GO have large potential for use in various electrochemical applications, such as photocatalysts.

Laser processing is emerging as a promising technique for scalable fabrication of rGO-based devices. Recently, Perez’s group employed nanosecond pulsed ultraviolet laser radiation to GO membranes in gaseous and liquid ammonia-rich environments. When the structure and composition of the resultant materials were analyzed, it was shown that there were substantial differences in the chemical composition and morphology of samples produced under analogous laser conditions in these two different environments.

Results and Further Analysis

When samples are irradiated in gaseous conditions, they undergo a significant deoxygenation process, a small amount of nitrogen species incorporation into the rGO structure, and a considerable amount of morphological modification. The resulting material is highly conductive whereas the analogous treatment in liquid brings about only a little reduction in electrical resistance.

SPM-based electric characterization was performed to further study the conductivity. The resulting series of spectra processed in MountainsMap® demonstrated the distinct electrical properties of each sample (Figure 1).

Measurements using scanning probe microscopy showed laser-induced structural defects, appearing as tiny filament-like features, in the gaseous environment sample. The multilayer feature in MountainsMap® (Figure 2) was used to create three-dimensional topography-resistance maps. These maps confirmed that the filament-like structures mostly show higher resistance at their topmost sites (crests).

MountainsMap®, An All-in-One Solution for Multiple Types of Analysis

As with other research projects, various types of instruments were employed to characterize samples in this study (scanning electron microscopy, atomic force microscopy, resistance measurement instrument, X-ray photoelectron spectroscopy). MountainsMap® software offers multiple instrument compatibility, and can deal with various scientific analysis procedures. Two examples are given below.

Math Functions (Operator)

Math functions can be applied to data employing MountainsMap®.

In this study, the math function abs(A)-13 is applied to a series of spectra in order to convert the raw signal into electrical resistivity.

This allows asymmetric resistance to be observed in the non-irradiated GO membrane (in blue).

The irradiated samples (liquid conditions in gold, gaseous conditions in red) show symmetric behavior and demonstrate the ohmic nature of the material.

Figure 1.

Build Multilayer Surface (Operator) + 3D View (Study)

Superimposition of the two layers shows a high correspondence between resistance-related structural defects and topography in the GO sample irradiated in gaseous conditions.

Figure 2. Superimposition of the two layers shows a high correspondence between resistance-related structural defects and topography in the GO sample irradiated in gaseous conditions.

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