Atomic Depth Distribution Research Articles

Study of Mos Structures Using Nuclear Analytical Methods

The atomic concentrations and depth distribution of elements in MOS (metal oxide semiconductor) structures have been investigated using two nuclear analytical methods: Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection (ERD). The elements with atomic masses in range from hydrogen up to copper were identified. Their depth profiles show that a MOS structure consists from metal (Al) layer, silicon oxide layer and a silicon substrate. The heavy elements Cu, Ti were found at near-surface area of one sample with low concentrations. The transitional area between the silicon substrate and the oxide layer as well as between the metal and oxide layers was noticed. The obtained results provide valuable information about MOS structures and concurrently demonstrate possibilities of both RBS and ERD methods in material analysis.

Transition from alloying layer growth to island growth of Sn on a Ga-covered Si [formula omitted] surface

Atomic depth distribution and growth modes of Sn on an Si(1 1 1)-√3×√3-Ga(1 ML) surface at room temperature were studied after each monolayer deposition of Sn by using reflection high-energy electron diffraction (RHEED) and characteristic X-ray spectroscopy measurements as functions of the glancing angle θ g of the incident electron beam. Intermixing between Sn and Ga occurred after deposition of one monolayer (ML) of Sn, resulting in the formation of a flat film of Ga–Sn alloy. Above a critical Sn coverage of about 1 ML, the growth mode changed significantly. That is, the alloying between Sn and Ga was suppressed, and additional Sn grew into islands on the Sn–Ga alloy.

Atomic depth distribution analysis and growth dynamics of metals on metal-covered Si(111) surfaces studied by incident-angle-dependent RHEED-TRAXS (total-reflection-angle x-ray spectroscopy)

During observation of reflection high-energy electron diffraction, characteristic x-rays are emitted from surfaces. The intensities of these x-rays change with change in the incident glancing angle (θg) of the primary electron beam, since density distribution of electrons near the surface changes with change in θg. By analyzing θg dependence of x-ray intensities, the depth distribution of elements near the surface can be determined without destruction of the surface. Resolution of depth in this method is one monolayer at the uppermost layers. By using this method, various growth motions of elements, such as substitution, alloying and floating were observed during growth of metals on metal-covered Si(111) surfaces. Morphology and growth modes of metals were significantly altered by preadsorption of other metals, and sometimes very flat metal films that would be applicable for fabrication of future electronic nano devices were obtained. In this review, the method for analysis of depth distribution of elements and growth modes of metals (Au, Ag, Ga, In and Sn) on an Si(111) surface precovered by another metal are described. [DOI: 10.1380/ejssnt.2003.91]

Transition from overlayer growth to alloying growth of Ga on Si(111)-alpha-(sqrt[3]xsqrt[3])-Au.

Atomic depth distribution and growth modes of Ga on an Si(111)-alpha-(sqrt[3]xsqrt[3])-Au surface at room temperature were studied after each monolayer deposition of Ga via reflection high-energy electron diffraction and characteristic x-ray spectroscopy measurements as functions of glancing angle theta(g) of the incident electron beam. One monolayer of Ga grew on the Au layer, and the sqrt[3]xsqrt[3] periodicity was conserved below the Ga overlayer. Above a critical Ga coverage of about one monolayer, this growth mode drastically changed; i.e., Au atoms dissociated from the sqrt[3]xsqrt[3] structure and Ga grew into islands of Ga-Au alloy.

Surfactant-mediated growth of an ordered flat film of an intrinsic liquid metal on a semiconductor surface: Ga onSi(111)−4×1−In

The morphology and atomic depth distribution of Ga films grown on $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7$ and $\ensuremath{-}4\ifmmode\times\else\texttimes\fi{}1\ensuremath{-}\mathrm{In}$ surfaces at room temperature were studied by using reflection high-energy electron diffraction and characteristic x-ray measurements as functions of glancing angle ${\ensuremath{\theta}}_{g}$ of the incident electron beam. Ga grew into liquid droplets on the $\mathrm{Si}(111)\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}7$ surface, as it does on many other semiconductors. On the other hand, on the $4\ifmmode\times\else\texttimes\fi{}1\ensuremath{-}\mathrm{In}$ surface, Ga grew into an ordered flat film and In floated to the uppermost layer during the growth process of Ga. The resultant top In layer and Ga-Si interface had $\sqrt{3}/2\ifmmode\times\else\texttimes\fi{}\sqrt{3}/2$ and $5\ifmmode\times\else\texttimes\fi{}5$ periodicities, respectively.

Atomic depth distribution and growth modes of Sn on Si(1 1 1)–4×1-In and α-√3×√3-Au surfaces at room temperature

Atomic depth distribution and growth modes of Sn on 4×1-In and α-√3×√3-Au surfaces were studied at room temperature by using reflection high-energy electron diffraction and characteristic X-ray spectroscopy measurements as functions of glancing angle θ g of the incident electron beam. In the growth of Sn on an α-√3×√3-Au surface, partial alloying between Au and Sn occurred after deposition of 1 ML of Sn. During further deposition of Sn, alloying between Au and Sn became more significant. During growth of Sn on a 4×1-In surface, alloying between Sn and In occurred, and a part of In segregated to the upper parts of the film.

Atomic Depth Distribution Analysis of In and Ga on Si(111) during Epitaxial Growth and New Surfactant-Mediated Epitaxy

Atomic depth distribution and growth modes of In and Ga on a Si(111) surface were studied by a method using reflection high-energy electron diffraction (RHEED) and total reflection angle X-ray spectroscopy (TRAXS). Indium was deposited on a Si(111)-√3×√3-Ga(1 ML) surface at room temperature. After 2 ML and 6 ML of In deposition, the peak positions and the shapes were similar in the glancing angle dependence of GaK emission. By the analysis of these measurements, the growth mode was concluded to be as follows. First, two layers of In grew on the Ga layer in an ordinary growth mode. After the third layer, however, In grew under the third Ga layer, resulting in a layer structure of (In2Ga)Inm (m=1,2,3 ...). On other Ga-covered Si(111) surfaces, In grew in an ordinary growth mode.

Atomic depth distribution analysis of Ag and Au on Si(111) during epitaxial growth by total reflection angle X-ray spectroscopy

When an electron beam is incident upon a surface, the electron trajectories near the surface in the sample change drastically depending upon the change in glancing angle θ g. The X-ray emission from surface atoms changes markedly depending on their atomic depth distribution. Thus, by measuring the θ g dependence of the X-ray emission, the composition in depth direction near the surface can be estimated. This method is very sensitive and a depth resolution better than 1 ML can be attained. By applying this method, it was found that when Ag was deposited on a Si(111)-α-√3 × √3-Au structure at room temperature, Ag grew on Au in the normal fashion; on the other hand, when 1 ML of Au was deposited on a Si(111)-√3 × √3-Ag structure at room temperature, the sites of Ag and Au atoms exchanged with each other and Ag atoms moved to the topmost layer of the surface. At further Au deposition, Au atoms moved continuously below the Ag layer, resulting in a condition as if Ag atoms were floating. These are new epitaxial growth modes, wherein the former should be called the “substitution atom growth mode” and the latter the “floating atom growth mode”. These phenomena were confirmed also by UHV-SEM observation. The results are further explained by Monte Carlo electron trajectory simulation.

Atomic depth distribution analysis of Ag and Au on Si(111) during epitaxial growth by total reflection angle X-ray spectroscopy

Atomic depth distribution analysis of Ag and Au on Si(111) during epitaxial growth by total reflection angle X-ray spectroscopy

Ion beam mixing of La(OH)3/Cu bilayers

The evolution of atomic composition, atomic depth distribution, and structural states of La(OH)3/Cu bilayers prepared by electron gun evaporation and submitted to ion beam irradiation is described. Chemical reactivity of La with O and H is evidenced in the initially deposited La/Cu bilayer, despite the fact that the pure La layer is coated with a thick Cu layer. Ion beam mixing with energetic Au ions, at 300 K and 700 K, results in breaking down the La–O–H bonds, while Cu atoms are knocked into the layer. There is a depth redistribution of the different atomic species, with formation of nonidentified phases.