Quantitative analysis of backscattered‐electron contrast in scanning electron microscopy

Backscattered-electron scanning electron microscopy (BSE-SEM) imaging is a valuable technique for materials characterisation because it provides information about the homogeneity of the material in the analysed specimen and is therefore an important technique in modern electron microscopy. However, the information contained in BSE-SEM images is up to now rarely quantitatively evaluated. The main challenge of quantitative BSE-SEM imaging is to relate the measured BSE intensity to the backscattering coefficient η and the (average) atomic number Z to derive chemical information from the BSE-SEM image. We propose a quantitative BSE-SEM method, which is based on the comparison of Monte–Carlo (MC) simulated and measured BSE intensities acquired from wedge-shaped electron-transparent specimens with known thickness profile. The new method also includes measures to improve and validate the agreement of the MC simulations with experimental data. Two different challenging samples (ZnS/Zn(O$_x$S$_{1–x}$)/ZnO/Si-multilayer and PTB7/PC$_{71}$BM-multilayer systems) are quantitatively analysed, which demonstrates the validity of the proposed method and emphasises the importance of realistic MC simulations for quantitative BSE-SEM analysis. Moreover, MC simulations can be used to optimise the imaging parameters (electron energy, detection-angle range) in advance to avoid tedious experimental trial and error optimisation. Under optimised imaging conditions pre-determined by MC simulations, the BSE-SEM technique is capable of distinguishing materials with small composition differences

Correlative Raman imaging and scanning electron microscopy: The role of single Ga islands in surface-enhanced Raman spectroscopy of graphene

Surface-enhanced Raman spectroscopy (SERS) is a perspective nondestructive analytic technique enabling the detection of individual nanoobjects, even single molecules. In this paper, we have studied the morphology of Ga islands deposited on chemical vapor deposition graphene by ultrahigh vacuum evaporation and local optical response of this system by the correlative Raman imaging and scanning electron microscopy (RISE). Contrary to the previous papers, where only an integral Raman response from the whole ununiformed Ga nanoparticles (NPs) ensembles on graphene was investigated, the RISE technique has enabled us to detect graphene Raman peaks enhanced by single Ga islands and particularly to correlate the Raman signal with the shape and size of these single particles. In this way and by a support of numerical simulations, we have proved a plasmonic nature of the Raman signal enhancement related to localized surface plasmon resonances. It has been found that this enhancement is island-size-dependent and shows a maximum for medium-sized Ga islands. A reasonable agreement between the simulations of the plasmon enhancement of electric fields in the vicinity of Ga islands and the experimental intensities of corresponding Raman peaks proved the plasmonic origin of the observed effect known as SERS. © 2022 American Chemical Society.European Commission, EC: 71020004, 810626; Grantová Agentura České Republiky, GA ČRCzech Science FoundationGrant Agency of the Czech Republic [20-28573S]; European Commission (H2020-Twininning project)European Commission [810626.SINNCE, M-ERA NET HYSUCAP/TACR-TH71020004]; *BUT*.specific research [*FSI-S-20-648*5]; Ministry of Education, Youth and Sports of the Czech Republic (CzechNanoLab Research Infrastructure) [LM2018110

The deposition of Ga and GaN nanostructures with metal core

The presented thesis deals with preparation of GaN nanocrystals with a metal core. In the theoretical part of the thesis GaN with its properties and applications is introduced. Further, some of the preparation methods of GaN are presented, mainly focusing on MBE growth. Deposition of metal NPs from colloidal solution and the state of the art approaches to enhance luminescence of GaN based structures is discussed. The experimental part follows three steps of preparation of GaN crystals with the Ag core. In the first step the Ag NPs are deposited on the Si(111) substrate. In the second step the Ga deposition process is optimized and in the third step the deposited Ga is transformed into GaN. After the Ga deposition the samples were analyzed by SEM/EDX and SAM/AES. The properties of prepared GaN crystals with the Ag core were studied by XPS, photoluminescence and Raman spectroscopy

Preparation of graphene layers by MBE

This bachelor's thesis deals with growth of graphene by molecular beam epitaxy (MBE). The theoretical section explains the preperation, properties, and detection methods of the material graphene, and the MBE method of graphene preparation is discussed in detail. In the experimental section, optimization of the sublimation carbon source and its properties are shown. Further experiments dealing with the preparation of graphene on Cu and Ge substrates are also described. The presence of graphene structures is proven by Raman spectroscopy

The deposition of Ga and GaN nanostructures with metal core

Tato diplomová práce se zabývá přípravou GaN nanokrystalů s kovovým jádrem. V teoretické části této práce je představen materiál GaN se svými vlastnostmi a aplikacemi. Dále jsou uvedeny některé metody přípravy GaN, přičemž metoda MBE je popsána podrobněji. Dále je popsána depozice kovových nanočástic z koloidního roztoku a nejnovější metody zesílení luminiscence GaN struktur. Experimentální část je rozdělena na tři části odpovídající postupu přípravy GaN krystalů s Ag jádrem. V prvním kroku jsou Ag nanočástice naneseny na Si(111) substrát. Ve druhém kroku je optimalizován proces depozice Ga a v posledním kroku je nadeponované Ga transformováno na GaN. Po depozici Ga byly vzorky analyzovány pomocí SEM/EDX a SAM/AES. Vlastnosti připravených GaN krystalů s Ag jádrem byly studovány metodou XPS, fotoluminiscenční spektroskopií a Ramanovou spektroskopií.The presented thesis deals with preparation of GaN nanocrystals with a metal core. In the theoretical part of the thesis GaN with its properties and applications is introduced. Further, some of the preparation methods of GaN are presented, mainly focusing on MBE growth. Deposition of metal NPs from colloidal solution and the state of the art approaches to enhance luminescence of GaN based structures is discussed. The experimental part follows three steps of preparation of GaN crystals with the Ag core. In the first step the Ag NPs are deposited on the Si(111) substrate. In the second step the Ga deposition process is optimized and in the third step the deposited Ga is transformed into GaN. After the Ga deposition the samples were analyzed by SEM/EDX and SAM/AES. The properties of prepared GaN crystals with the Ag core were studied by XPS, photoluminescence and Raman spectroscopy.

Low temperature 2D GaN growth on Si(111) 7 x 7 assisted by hyperthermal nitrogen ions

As the characteristic dimensions of modern top-down devices are getting smaller, such devices reach their operational limits imposed by quantum mechanics. Thus, two-dimensional (2D) structures appear to be one of the best solutions to meet the ultimate challenges of modern optoelectronic and spintronic applications. The representative of III-V semiconductors, gallium nitride (GaN), is a great candidate for UV and high-power applications at a nanoscale level. We propose a new way of fabrication of 2D GaN on the Si(111) 7 x 7 surface using post-nitridation of Ga droplets by hyperthermal (E = 50 eV) nitrogen ions at low substrate temperatures (T < 220 degrees C). The deposition of Ga droplets and their post-nitridation are carried out using an effusion cell and a special atom/ion beam source developed by our group, respectively. This low-temperature droplet epitaxy (LTDE) approach provides well-defined ultra-high vacuum growth conditions during the whole fabrication process resulting in unique 2D GaN nanostructures. A sharp interface between the GaN nanostructures and the silicon substrate together with a suitable elemental composition of nanostructures was confirmed by TEM. In addition, SEM, X-ray photoelectron spectroscopy (XPS), AFM and Auger microanalysis were successful in enabling a detailed characterization of the fabricated GaN nanostructures

Low temperature 2D GaN growth on Si(111) 7 x 7 assisted by hyperthermal nitrogen ions

As the characteristic dimensions of modern top-down devices are getting smaller, such devices reach their operational limits imposed by quantum mechanics. Thus, two-dimensional (2D) structures appear to be one of the best solutions to meet the ultimate challenges of modern optoelectronic and spintronic applications. The representative of III-V semiconductors, gallium nitride (GaN), is a great candidate for UV and high-power applications at a nanoscale level. We propose a new way of fabrication of 2D GaN on the Si(111) 7 x 7 surface using post-nitridation of Ga droplets by hyperthermal (E = 50 eV) nitrogen ions at low substrate temperatures (T < 220 degrees C). The deposition of Ga droplets and their post-nitridation are carried out using an effusion cell and a special atom/ion beam source developed by our group, respectively. This low-temperature droplet epitaxy (LTDE) approach provides well-defined ultra-high vacuum growth conditions during the whole fabrication process resulting in unique 2D GaN nanostructures. A sharp interface between the GaN nanostructures and the silicon substrate together with a suitable elemental composition of nanostructures was confirmed by TEM. In addition, SEM, X-ray photoelectron spectroscopy (XPS), AFM and Auger microanalysis were successful in enabling a detailed characterization of the fabricated GaN nanostructures.Czech Science Foundation [20-28573S]; Ministry of Education, Youth and Sports of the Czech Republic (CzechNanoLab Research Infrastructure) [LM2018110]; European Commission [810626 - SINNCE, TH71020004]; BUT [FSI-S-20-6485]European Commission, EC: 71020004, 810626; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: LM2018110; Grantová Agentura České Republiky, GA ČR: 20-28573S; Vysoké Učení Technické v Brně, BUT: FSI-S-20-648