The FFT method from HREM images, on the other hand, provides LRO parameters in a small selected microscopic area, and therefore, it enables microscopic fluctuations of LRO parameters to be examined. Ordering maps from geometric ATM/ATR inhibitor clinical trial phase algorithm HRTEM images allow us to extract information on compositional variations and/or the state of deformation of the nanostructures by comparing the actual positions of the unit cells in the image with a reference lattice using such techniques as the peak pairs algorithm or geometric phase analysis [23, 24]. Even though these programs are mainly applied

to the analysis of the deformation present in the nanostructures, they can be used to perform other types of studies such as the spatial location of different phases and grains [25]. We follow a similar procedure here in order to obtain a spatial map of the distribution of the ordering. The procedure used for calculating the phase image, the Bragg filtered image and numerical moiré image using the GPA are as described by Hÿtch and co-workers [24, 26]. Briefly, the method consists of constructing a differential phase Selleckchem Aloxistatin map for a given Bragg region with respect to a reference lattice. In our case, we build numerical moiré images at position r, M(r), by superimposing the real lattice with a reciprocal lattice vector smaller than the average lattice where M is a magnification constant as [25, 27]: where g r is the

reference lattice in reciprocal space and u(r) is the displacement of the atomic column position from its nominal Astemizole position. Following this procedure, two translational moiré images (we used M = 1) are obtained using g r as the reference position of each (111) spot in the FFT pattern and a Bragg mask that includes the collinear ½(111) spot associated with the ordering arrangement. The final RGB multilayer reconstructed image is formed from the two inverse FFT (iFFT) images

of these selected masks. The spatial localization of ordering in each of the 111 planes is represented in the sets of red and green fringes. In order to improve visualization, a null matrix blue layer is used as background. The red and green fringes in this resultant image are consistent with the presence of ordering where the moiré spacing is proportional to 1/(g − gr). Results Photoluminescence In order to evaluate the optical emission efficiency, RT-PL measurements were carried out on both samples (Figure 1). Sample S100 showed a bimodal spectrum, with an emission peak at 1,108 nm and a distinct low wavelength shoulder feature at 980 nm. The main peak has a full width at half maximum (FWHM) of 79 meV. However, S25 showed only a single peak centred at 1,057 nm with a FWHM of 75 meV. The PL intensities were nominally identical to within the experimental error. Figure 1 Room-temperature PL spectra of MBE-grown GaAsBi layers. S25 (dashed) and S100 (solid) lines.