Self-organization of nanostructures on the n-GaN(0001) surface in the Cs and Ba adsorption

A regular self-organized 2D nanostructure of a new type of nanocombs has been created in situ in an ultrahigh vacuum on the n-GaN(0001) surface. The nanostructure is formed as a result of multilayer adsorptions of Cs and Ba. The structure is highly regular in the microrange, arranged in the form of combs 60–70 nm in diameter with a wall height of about 7 nm. It has been revealed that the nanostructure has a quasi-metallic conduction, a low work function of about 1.4 eV, and a high quantum yield of photoemission under light excitation in the GaN transparency region. A self-organization model is proposed, which implies the formation of a surface 2D longperiod incommensurate phase interacting with the superstructure of the Cs⁺ and Ba²⁺ ion clusters with allowance for the polaron compensation on the GaN surface.     

Electronic Structure of an Ultrathin Molybdenum Oxide Film

Physics of the Solid State - The electronic structure of an ultra-thin molybdenum oxide film obtained by oxidation of molybdenum at an oxygen pressure of 1 Torr and the effect of adsorption of...     

Surface states and accumulation nanolayer induced by Ba and Cs adsorption on the n-GaN(0 0 0 1) surface

The Ba and Cs adsorption on the n-GaN(0 0 0 1) surface has been studied in situ by the threshold photoemission spectroscopy using s- and p-polarized light excitation. Two surface bands induced by Ba (Cs) adsorption are revealed in surface photoemission spectra below the Fermi level. The surface-Fermi level position is found to be changed from significantly below the conduction band minimum (CBM) at clean n-GaN surface to high above the CBM at Ba, Cs/n-GaN interfaces, with the transition from depletion to electron accumulation occurring at low coverages. Photoemission from the accumulation nanolayer is found to excite by visible light in the transparency region of GaN. Appearance of an oscillation structure in threshold photoemission spectra of the Ba, Cs/n-GaN interfaces with existing the accumulation layer is found to originate from Fabry–Perot interference in the transparency region of GaN.     

Accumulation nanolayer and surface states of ultrathin Cs,Ba/<Emphasis Type="Italic">n</Emphasis>-GaN interfaces

It is found that Cs and Ba ultrathin coatings induce formation of a charge accumulation layer (2D electron channel) on the n-GaN(0001) surface. Photoemission of conduction electrons from the accumulation layer under excitation by light in the range of GaN transparency is revealed. It is established that the depth of the potential well of the accumulation layer can be deliberately controlled.     

Charge accumulation nanolayer: A 2D electronic channel in Cs/n-InGaN ultrathin interfaces

This paper reports on the formation of a 2D electronic channel, i.e., a charge accumulation layer on the n-InGaN(0001) surface observed under adsorption of submonolayer Cs coatings. It is found that photoemission from the accumulation layer is excited by light in the InGaN transparency region. It is established that the potential well depth and the density of electronic states in the accumulation layer can be controlled by properly varying the Cs coverage. It is shown that the accumulation layer exhibits quantum-well effects. The photoemission matrix element is calculated, and the energy parameters of the accumulation layer are obtained. An oscillatory structure originating from the Fabry-Perot interference is revealed in the spectra of photoemission from the accumulation layer.     

Model of periodic superstructure formation induced by mobile defects on a semiconductor surface

A model for forming a periodic superstructure on a semiconductor surface with mobile defects is proposed. It is shown that a self-organized system of such defects could lead to considerable modulation of incommensurate phase parameters in near-surface layers under the conditions of defect interaction with an incommensurate displacement wave. This type of defect system could induce a substantial energy decrease for the incommensurate phase and its additional stabilization on the one hand, and an increase in modulation amplitude that might be accompanied by a soliton-like nonsinusoidal incommensurate displacement wave on the other. The model allows us to explain the experimental results regarding the periodic superstructure discovered by G.V. Benemanskaya et al. on the surface of a GaN semiconductor. In particular, the model enables us to explain the nature of such superstructures based on the self-organization of mobile neutral triad-type defects, composed of negatively charged (3−) vacancies of the host lattice centers of Ga³⁺ and surface impurity ions of Cs⁺ and Ba²⁺, under conditions of triad interaction with an incommensurate displacement wave.     

Electronic structure of a Ba/<Emphasis Type="Italic">n</Emphasis>-AlGaN(0001) interface and the formation of a degenerate 2D electron gas

The electronic structure of ultrathin Ba/n-AlGaN(0001) interfaces has been investigated in situ in an ultra-high vacuum by the ultraviolet photoelectron spectroscopy method. The photoemission spectra from the n-AlGaN valence band and the spectra of the core levels Ga 3d, Al 2p, and Ba 4d have been studied under synchrotron excitation with photon energies of 60–400 eV. The modification of the spectra in the process of the formation of the Ba/n-AlGaN interface in the mode of the Ba submonolayer coverages has been revealed. It has been found that a decrease in the intensity in some spectral regions of the valence band is attributed to the interaction of the surface states of the AlGaN substrate with the Ba adatoms. It has been revealed that the interface formation results in the appearance of a new photoemission peak of the quasimetallic character at the Fermi level in the AlGaN bandgap. It has been established that the peak is due to the formation of the degenerate electron gas in the accumulation nanolayer induced by adsorption near the n-AlGaN surface.     

Photoelectron spectroscopy of electronic surface structure of the Cs/GaN and Cs/InN interfaces

The electronic structure of the epitaxial GaN, InN nanolayers, and the ultrathin Cs/GaN and Cs/InN interfaces was investigated under ultrahigh vacuum at various Cs coverages. The experiment was carried out using synchrotron-based photoelectron spectroscopy. The photoemission spectra of the valence band and the In 4d, N 2s, Ga 3d, and Cs 4d semicore levels were studied as a function of Cs coverages. It was found that the Cs adsorption in the submonolayer coverage region causes substantial changes in the spectra due to charge transfer between the Cs adlayer and surface Ga or In atoms. The strong interaction of the dangling bonds of Ga or In with Cs adatoms effectively increases the Ga or In valency.     

Aromatic-Like Carbon Nanostructures Created on the Vicinal SiC Surfaces

Physics of the Solid State - Electronic structure of the ultrathin Cs, Ba/SiC(111)-4°, 8° interfaces have been studied in situ in an ultrahigh vacuum using synchrotron-based photoelectron...     

Electronic Structure of Molybdenum Oxidized in Air

Physics of the Solid State - The electronic structure of a clean molybdenum surface oxidized in air and upon sodium Na adsorption at submonolayer coating have been studied by photoelectron...