Channeling-RBS

Figura 3 Crystal channeled RBS spectra from Si samples implanted with 10, and...

One of the most fascinating applications of channeling RBS is the study of lattice locations of impurity atoms. By measuring the angular dependence of the back-scattering yield of the impurity and host atoms around three independent channeling axes it is possible to calculate the position of the impurity. Details can be found elsewhere [3.122]. 

The Rutherford back scattering/channeling (RBS/C) technique offers an unrivalled tool for a quantitative analysis of the amount of disorder created by ion irradiation. To measure the extent of the damage accumulation process, a commonly accepted parameter is the peak value of the... 

In addition to elemental compositional information, RBS also can be used to study the structure of single-crystal samples. When a sample is channeled, the rows of atoms in the lattice are aligned parallel to the incident He ion beam. The bombard-... 

Ion Beam Handbook for Material Analysis. (J. W. Mayer and E. Rimini, eds.) Academic Press, New York, 1977. This book provides useful tabular and graphic data for RBS, channeling, PIXE, and NRA. 

As in RBS analysis, ERS can provide information on the atomic concentration of hydrogen as a function of depth (measured in atoms/cm ). This is derived from the height Aobs°f ERS spectrum (counts per channel), at energies corresponding to particular depths within the sample (see Figure 3c). For a sample consisting of H and another material X, with composition the spectrum height... 

Fig. 3.49. RBS spectra from GaAs implanted with Si (120 keV, 5 x lO cm before and after annealing at 950 °C. The uppermost spectrum is taken in a random direction, the others are in the channeling direction [3.127],...

Fig. 3.50. RBS spectra of buried (5 -FeSi2 (full line) and /J-FeSi2 (dotted line) layers taken in a random direction. The <111 > channeling spectrum (circles) refers to the /J-FeSi2 layer [3.130],...

RBS and channeling are extremely useful for characterization of epitaxial layers. An example is the analysis of a Sii-j Gejc/Si strained layer superlattice [3.131]. Four pairs of layers, each approximately 40 nm thick, were grown by MBE on a <100> Si substrate. Because of the lattice mismatch between Sii-jcGe c (x a 0.2) and Si, the Sii-j Ge c layers are strained. Figure 3.51 shows RBS spectra obtained in random and channeling directions. The four pairs of layers are clearly seen in both the Ge and Si... 

Li+ (0.77) < Na+ (1.0) < K+ (1.48) < Rb+ (1.55) < Cs+ (1.56). While indeed the order is the same, the significant point is that the range of discrimination has been expanded by almost an order of magnitude. The concern then becomes the mechanism whereby the Gramicidin channel effects this enhancement of selectivity. An important source of selectivity that must be considered is the relative solvation energy of water... 

Fig. 12A, has a 10° libration. This gives a channel size which would be optimal for an ionic radius between that of Rb+ and Cs+. Therefore enhanced discrimination is not expected between Rb+ and Cs+, but the energy required to librate further inward to make contact with smaller ions in the series can be expected to enhance selectivity between these ions. Work is currently in progress to calculate the change in channel energy as a function of libration angle or of the equivalent, the effective channel radius S6). The implications of a peptide libration mechanism for enhancing ion selectivity can also be pursued experimentally as outlined below. 

If the value of rB,oNB Ts, (D -c 1) the integral characteristics for the circular channels, the rectangular channels with four and three heated walls, respectively,... 

Depolarization of the synaptosomes with Ca-free media containing lOOmM K increased 86Rb efflux (figure 1, open squares) two kinetically and pharmacologically distinct K conductances could be discerned. Between 1 and 4 seconds, Rb efflux was linear and was 2.2 to 2.4%/sec (component "S"). Extrapolation of Rb efflux to the ordinate ("zero time") exposed an additional, rapid component of 86Rb efflux (component "T"). Component T reflects a distinct K channel that, unlike component S, appeared to inactivate in less than 1 second (Bartschat and Blaustein 1985a). 

Channelling effects can provide two types of information in RBS experiments. If a detector is adjusted to have an energy window corresponding to a chosen atomic species, a specimen tilt-through over a channelled direction brings information on the perfection of crystallinity of the target and also on the lattice location of dopants or impurities. The yields vs. tilt-through curve has a minimum in the channelled direction, and the smaller this minimum yield, the more perfect is the crystal. 

To start with a relatively simple case, Rb[Cd Ag(CN)2 3] (from RbCl, AgN03, Cd(N03)2, and NaCN in H20) is discussed. In its structure (P312, Z = 1), Cd and the rod-like N-coordinating NC—Ag—CN units create three independent, interpenetrating, 3-D frameworks Cd (symmetry 32 —Z)3) has trigonally distorted octahedral coordination (r(Cd—N) 232.4 pm). Rb occupies one of two types of trigonal channels.218... 

It has been known for some years that gramicidin forms transmembrane ion channels in lipid bilayers and biological membranes and that these channels are assembled from two molecules of the polypeptide 213). The channels are permeable specifically to small monovalent cations [such as H+, Na+, K+, Rb+, Cs+, Tl+, NH4+, CHjNHj, but not (CH3)2NH2+J and small neutral molecules (such as water, but not urea). They do not allow passage of anions or multivalent cations 21 n. 

Striibing C, Krapininsky G, Krapivinsky L, Clapham DE 2001 TRPC1 and TRPC5 form a novel cation channel in mammalian brain. Neuron 29 645-655 Trepakova ES, Csutora P, Hunton DL, Marchase RB, Cohen RA, Bolotina VM 2000 Calcium influx factor directly activates store-operated cation channels in vascular smooth muscle cells. J Biol Chem 275 26158-26163... 

Figure 4.15 Schematic representation of RBS. Top the incident ions are directed such that they either scatter back from surface atoms or channel deeply into the crystal. Middle the ions scatter back from target atoms throughout the outer micrometers and suffer inelastic losses, causing the energy of the backscattered ions to tail to zero. Bottom scattering from the heavy outer layer gives a sharp peak separated from the spectrum of the substrate as in the middle diagram.

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