Jiří David v diplomové práci zpočátku rozvíjel téma původně zahájené v práci bakalářské. Brzy přešel na mírně odlišný materiálový systém a podařilo se mu experimentálně získat vynikající výsledky, jež budou v brzké době publikovány. Student prokázal vysokou míru samostatnosti při práci v laboratoři. Zároveň velmi oceňuji schopnost interpretovat provedená měření, zejména komplexní difrakční obrazce. Jirka kriticky pracoval s literaturou, přicházel s vlastními hypotézami, práci si systematicky plánoval a díky tomu se mu podařilo získat ucelený obraz studovaného systému a zároveň tak splnit všechny navržené cíle diplomové práce. Prvotní texty nebyly příliš dobré, ale student na nich postupně zapracoval a diplomová práce tak důstojně představuje množství experimentů, které byly provedeny, včetně krtického posouzení autorem.

This Master thesis is a well-designed and executed original scientific work on the preparation and characterization of two-dimensional (2D) epitaxial layers on metal substrates under ultra-high vacuum (UHV) conditions. The results from this thesis shed light on the growth mechanisms and chemical and structural properties of blue phosphorene on Ag(111) and Cu(111). The author also probes into the preparation and characterization of graphene/blue phosphorene heterostructures. These materials are at the forefront of current fundamental and applied research as key candidates for next-generation electronics.

In the Introduction (Úvod), the student presents a compelling argument about the current prospects of 2D materials in research and actual application, and the drawbacks and challenges that hinder their use. The aims of the thesis are also well-portrayed.

The Phosphorene (Fosforen) chapter is a comprehensive and exhaustive description of the key elements to be considered before embarking in the actual experimental work: structural properties of phosphorene allotropes, structural and chemical properties of potential substrates and theoretical predictions, precursors for epitaxial growth, review on existing literature, and the properties and growth mechanisms of heterostructures. The student shows a proper understanding of the substrate properties to be considered when producing 2D materials (structure, lattice parameter and magnitude of the chemical interaction with the 2D layer). The literature review depicts the state-of-the-art of phosphorene growth on metallic substrates and the current limitations which this thesis aims to push forward. In particular, blue phosphorene on Ag(111), which theoretically should be the best candidate for epitaxial growth, is limited to only small domains on the surface, whereas the growth of blue phosphorene on Cu(111) is limited by the strong chemical interaction between Cu and P.

The Experimental part (Experimentální část) deals with the actual research conducted for this thesis. The student provides a description of the UHV cluster at CEITEC BUT in Brno, the Ag(111) and Cu(111) preparation process, and the device for P deposition and P source (GaP). Only a very brief description of the Low-energy electron microscope (LEEM) and the X-ray photoelectron spectroscope (XPS) is included, but this is well-justified since this master thesis is a continuation of the student’s bachelor thesis, where a more-detailed description is shown.

The research on the growth of blue phosphorene on Ag(111) is focused on optimizing the preparation conditions. Here, the student investigates the structural quality of blue phosphorene domains when P is deposited on a cold vs hot substrate, and the effect of post-deposition annealing temperature vs duration. Higher temperature annealing after P deposition on Ag(111) at RT yields a clear Moiré diffraction pattern. The student points out the existence of hexagonal overlayer structure, albeit no large domains were obtained. The student proposes investigating different P sources for higher quality blue phosphorene on Ag(111).

The growth of blue phosphorene on Cu(111) is shown to occur in a remarkably different fashion than on Ag(111). The student identifies a Cu phosphide layer by means of LEED, XPS and scanning tunneling microscopy (STM)  that forms for a P coverage <0.75 ML. This phosphide layer is shown to preclude the formation of blue phosphorene, which grows upon further P deposition. A LEED and STM Moiré pattern consistent with a blue phosphorene overlayer is identified. Longer P deposition results in the formation of two dissimilar 3D structures: triangular islands and ‘rice-like’ structures. These are tentatively identified as multiple blue phosphorene layers and amorphous P structures, respectively. Last, the student initiated the investigation of graphene growth on Cu(111) as a buffer layer to reduce the interaction between Cu and P for high quality blue phosphorene growth. This part proved to be challenging given the time limitations, but the existence of two different Moiré structures encourages further research.

The author of this master thesis demonstrates a high-level understanding of how to tackle a scientific investigation. He shows excellent scientific skills when motivating the current work and preparing the literature review. As a note of caution, the quality of some figures reproduced from the literature is below recommended and appear slightly pixelated. The author clearly acknowledges the abundant literature on the topic at hand and what is needed to build on it and provide further key knowledge. The results presented here are well-described, compared to existing literature, and interpreted. Appropriate credit is given to the colleagues that conducted complementary measurements, which demonstrates that the author understands the collaborative nature of science. The description of the procedures for P deposition and blue phosphorene growth are detailed enough to ensure reproducibility. The author acknowledges the extent of his results and points towards proper ways that could improve it or where further research could be beneficial.

Overall, I rate this master thesis as very successful and recommend it for approval. The author shows high potential for an academic career, should he decide to pursue a PhD program. Topics for thesis defence:

1. 1) The author mentions that the stability of free-standing blue phosphorene is similar to that of black phospherene, and that blue phosphorene can only been synthesized in UHV. Why does that occur? Also, are there examples of black phosphorene monolayer grown in UHV on a substrate?
2. 2) The author states that phosphorene is not stable in air. What happens to it when exposed to air? What are the current approaches to protect it from air exposure?
3. 3) The author shows that a Cu phosphide layer forms for a certain range of P deposition on Cu(111). What is the nature of this phosphide layer (stoichiometry, structure…)? Is it a unique species or are there different phases or alloys that can form at different conditions (% of P, temperature…).
4. 4) The Moiré spots of blue phosphorene on Ag(111) appear ´elongated´ in figure 23a) and 23d). However, single sharp spots are visible in figure 26b) for blue phosphorene on Cu(111). What does this mean?
5. 5) What is the ratio of the P 2p 1/2 and 3/2 components and spin-orbit splitting found in your fittings? Is it consistent with the values from the literature?