Note: all the information here are work of imagination, only for the purpose of an exercise.

Project: Write a paper about a specific topic

INTRODUCTION.

Ultrawide band gap material has been studied for its applications in fields like opto-electronics and high-power electronics because of its peculiarity of an energy gap with a very high value. Among these, X has acquired more interest due to its energy gap around 5,3 eV (that is tunable using its metastable or stable phases) and its Belinga figure of merit superior to the common material used until now (reference 1). However, there is an open problem in the scientific literature: how to stabilize good metastable phases. In fact, they are possible to obtain only in a specific range of growth parameters, and until now, it has not possible to achieve the right values. The situation in the state of the art is that the stable phase is within a few nanometres of the metastable phase (reference 2).

Researcher X suggested that tuning the temperature and precursor ratio could help to achieve the purpose, but it is not enough to obtain pure metastable X (reference 3). Other groups (reference 4,5) paid more attention to the pre-treatment of the samples. This helped to improve the quality of the film, but was not enough to delete the stable phase from the sample.

The idea presented in this work is to change the focus of the research on the different Growth technique, to find the best one for the metastable phase. To do that, we developed different samples using Y, K, J, and from the comparison, we obtained the best solution for this problem.

METHOD.

The preparation required 10 samples for each growth technique ( names of techniques with their characteristics). The precursors used are B and A, arranged with different ratios. The range of temperatures used was in the range of […], with a pressure in the chamber of … . The ratio of precursor was varied in the range of […], and the growth was performed for 1h in total for each sample, obtaining different thickness [….]nm, which differed from the different growth rate and diffusion process on the substrate (Xy).

After the preparation of the samples with Y, K, J, each films were charachterized by XRD using instrument T with these characteristics…., and with SEM (name of instrument with characteristics) or AFM (name of instrument with characteristics). The purpose of this analysis was to show the presence or absence of different X phases or the only presence or absence of metastable phase.

RESULTS.

Before the analysis, the samples were prepared using the method suggested by (reference 5), which results the best one, obtaining films with mixed phases of high quality. That procedure suggested washing the substrate (Xy) with alcohol and propanol in a sonication bath. After that, leave them to air dry, without other manipulation of the substrate.

To answer the question if there is a better growth technique to obtain pure metastable phase, we proceed with the same conditions and same characterisation for every 10 samples of each growth technique.

As we can see from the XRD graph, Figure 1, all the samples grown with Y show some peaks of the stable phase, with a few peaks related to the metastable one. Also some sample growth with K has the presence of stable phase, but there are also some other (grown at different temperature) that don’t present the typical peaks of the stable X. Finally, only the samples obtained with J show only the presence of the metastable phase for all T and all thickness.

Figure 1

From the SEM and AFM images, we can see the differences in morphology. As it is clear from Figure 2, the samples grown with Y have the worst morphology in comparison to the other techniques. The presence of defects is visible, and the roughness is around …. nm. The samples grown with J have low density of defects and a roughness with a value around … nm. That is a good smoothness, but some sample grown with K in the temperature range of [..] has better values of roughness, which in the best situation is .. nm.

Figure 2.

DISCUSSION.

As it was explained in the section before, the best technique to avoid the stable phase for all the growth conditions studied is J, but if we want to focus also on the quality of the film, J can give a good smoothness, but the best one for a pure phase of X is obtained with K at certain temperature conditions.

The phase selection can be explained by the fact that J has a more controlled growth chamber, and the possibility to use a High vacuum chamber gives the opportunity to avoid interferences from the outside ambient. But the morphology is due to how the particles of X are attached to the substrate Xy, and this is controlled by temperature (which is crucial for the diffusion) and the precursor ratio. In fact, we can select the same ratio for all the techniques, but the real quantity that arrives on the substrate depends on the machine structure. K has a more direct voyage of transport of the precursors, and this can be an explanation for the difference in the smoothness.

This is a new discovery in the state of the art. No one was able to compare all three different techniques using the same parameters. Until now, only Y and J were used (references 4 and 6), but we are the first ones to analyse the situation using also K. This paper can open the door to new studies that will imply the optimization of the films and the preparation of devices based on the metastable phase, which permits tuning the energy gap value.

However, limitations such as the impossibility of controlling the real ratio on the substrate in the growth chamber, the results give us valuable information, and this was not a problem in the final comparison of the samples.

Taken together, this offers a novel perspective on the film's growth of X and the results show that to obtain a film with only a metastable phase with a very high quality, the best growth technique is J, but with the limitations of use only a sharp range of temperature […]°C.

ACKNOWLEDGMENT.

This project was kindly funded by G and co.
We want to tank all the people who worked with us for this project: names and association.

REFERENCES

-reference 1

-reference 2

-reference 3

-reference 4

reference 5

reference 6

Sabrina Corbellini

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