Elongated Islands Research Articles

Nodulo-Ulcerative Plaque Over the Vertex of Scalp.

A 45-year-old man presented with a 12-year-old swelling in the vertex region of his scalp that had gradually grown in size for the last few years. Pus discharge and minor pain had been present for the previous 10 days. Patient had received treatment with oral and topical antibiotics. There was no history of preceding trauma, nevoid lesions, or associated comorbidities. Cutaneous examination revealed a hard non-tender fixed plaque of 3 cm × 2 cm size over vertex area of scalp with central ulceration and yellowish white discharge. It was separated from surrounding skin with a sharp demarcation [Figure 1]. There was no regional lymphadenopathy.Figure 1: Single hard, non-tender fixed plaque of 3 cm × 2 cm size over vertex area of scalpSkin biopsy from the lesion revealed an epithelial neoplasm in the dermis reaching up to the base and both lateral margins without any connection with the epidermis [Figure 2]. Upper dermis and mid-dermis showed numerous dilated keratin cysts and orthokeratotic corneocytes [Figure 2]. Mid- and lower dermis showed numerous small rounded and elongated tumor islands made up of basaloid cells without too much atypia with ductal structures or differentiation at their center and surrounded by dense fibroblastic stroma. Some of these ducts were elongated and dilated but were lined by cuboidal basaloid cells without any signs of apocrine differentiation [Figure 3].Figure 2: An epithelial neoplasm in the dermis reaching up to the base and both lateral margins but showing no connection with surface epidermis (H & E 40x)Figure 3: In the mid-dermis and lower dermis, the neoplasm shows numerous keratin cysts, many of which are dilated and show orthokeratotic corneocytes, majority of the tumor islands are small and rounded, while others are small irregular and surrounded by dense fibroblastic stroma, numerous rounded and elongated tumor islands made up of basaloid cells without too much atypia (H&E 100x)What is the diagnosis? Answer Microcystic adnexal carcinoma. Discussion Microcystic adnexal carcinoma (MAC) is a rare, slow-growing but locally aggressive malignant neoplasm with low mortality rate and it rarely metastasizes.[1] It arises from pluripotent keratinocytes and shows characteristic pilar and eccrine differentiation.[1] It was first described in 1982 by Goldstein et al. as a distinct clinicopathologic entity.[2] It is reported mainly in adults between 55 and 60 years of age with a slight female preponderance. Clinically, it presents as a solitary asymptomatic plaque or nodule most commonly on the head and neck areas. Occasionally, patients may present with pain, itching, burning sensation, numbness, and tingling as a result of perineural invasion by the tumor.[2] Immunosuppression, UV radiation exposure, and radiotherapy are the predisposing factors.[2] MAC is commonly misdiagnosed as desmoplastic trichoepithelioma (DT), syringoma, morpheaform basal cell carcinoma (mbcc), and desmoplastic squamous cell carcinoma (SCC) on histopathology.[3] It is often difficult to clinically distinguish MAC from other skin-colored growths on the head and neck including BCC. Histopathologically, the presence of ductal structures helps to differentiate MAC from DT, whereas the presence of calcification, prominent horn cysts, and single-file strand formation differentiates MAC from syringoma. Among all these tumors, perineural and subcutaneous involvement is characteristic feature of MAC on histopathology. MAC is also characterized by presence of normal tissue between epidermis and dermis.[4] Immunohistochemical markers that help to distinguish MAC from morpheaform BCC and SCC include cytokeratin 15 (CK15), carcinoembryonic antigen (CEA), and BerEP4 [Table 1].[5]Table 1: Immunohistochemical markers to distinguish MAC from morpheaform BCC and SCCThe most definitive treatment for MAC is complete surgical excision. Mohs micrographic surgery (MMS) is the preferred option as it is associated with low recurrence rate.[6] MAC has a high recurrence rate that ranges from 15% to 60% depending on the treatment option used. Recurrence may occur many years following the excision; hence, long-term follow-up is mandatory. Other treatment options include wide local excision, adjuvant or definitive radiotherapy, and chemotherapy.[7] Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

CARACTERIZAÇÃO HIDROLÓGICA DOS SISTEMAS LACUSTRES DO ARQUIPÉLAGO DE ANAVILHANAS COM BASE EM SENSORIAMENTO REMOTO

Este estudo caracterizou os sistemas lacustres do Arquipélago de Anavilhanas e avaliou a variação espacial da superfície de água em condições próximas as médias fluviométricas interanuais para cada período, utilizando imagens do Landsat 08 e dados fluviométricos do Rio Negro. A variação sazonal observada para todo o arquipélago foi na ordem de 10%. Para os sistemas lacustres e áreas de “águas mortas” foi de 17%. Para 447 lagos identificados, 46% possuem conexão com os canais do arquipélago durante o período de águas baixas e 54% ficam isolados neste período. Foram apontados três domínios para o Arquipélago. No domínio A (montante) o rio é relativamente estreito e as ilhas e lagos são menores. No domínio B (centro) o rio é relativamente mais largo e as ilhas e lagos são de grandes extensões. No domínio C (jusante) o rio apresenta largura semelhante ao domínio A e as ilhas estreitas, alongadas e sinuosas com lagos alongados e abertos. O domínio C apresentou menor variação sazonal e um maior número de lagos conectados, o que pode estar associado às características geomorfológicas e as condições hidráulicas dadas pela influência do barramento hidráulico do Rio Solimões.

Shape of Ni-containing nanoislands grown on an Ag-terminated Ge(111) surface

By using scanning tunneling microscopy we found that Ni-containing islands grown on an Ag/Ge(111)-√3 × √3 surface adopt hexagonal (isotropic) shapes when the size is smaller than the critical value ~12.7 nm. Above this critical size islands either grow with no change in shape or become elongated (anisotropic). The shape transformation in the latter case indicates that even on an isotropic surface the influence of surface stress anisotropy on the island growth is significant. Besides, we compared the thermo-evolutions of the Ni-containing islands grown on the multiphase Ag/Ge(111) and the single Ag/Ge(111)-√3 × √3 surfaces and found that the formation of hexagonal and elongated islands is a common feature. This observation made us conclude that the surface stress anisotropy also exerts an impact on the island shape on an inhomogeneous surface.

Near-equilibrium growth from borophene edges on silver.

Two-dimensional boron, borophene, was realized in recent experiments but still lacks an adequate growth theory for guiding its controlled synthesis. Combining ab initio calculations and experimental characterization, we study edges and growth kinetics of borophene on Ag(111). In equilibrium, the borophene edges are distinctly reconstructed with exceptionally low energies, in contrast to those of other two-dimensional materials. Away from equilibrium, sequential docking of boron feeding species to the reconstructed edges tends to extend the given lattice out of numerous polymorphic structures. Furthermore, each edge can grow via multiple energy pathways of atomic row assembly due to variable boron-boron coordination. These pathways reveal different degrees of anisotropic growth kinetics, shaping borophene into diverse elongated hexagonal islands in agreement with experimental observations in terms of morphology as well as edge orientation and periodicity. These results further suggest that ultrathin borophene ribbons can be grown at low temperature and low boron chemical potential.

From patch to channel scale: The evolution of emergent vegetation in a channel

Computational fluid dynamics was used to study the evolution of small patches of vegetation into a vegetated landscape in a channel. The growth of new vegetation occurred in regions where the flow velocity was reduced below a threshold value defined as a fraction of the channel-average velocity (U0). Two threshold values, or limiting velocity values (LV), were used: LV = 0.5 and 0.7. Two initial blockage factors (percentage vegetation coverage of the channel) were considered, 3% and 0.3%, chosen to represent cases with and without, respectively, hydrodynamic interaction between the initial patches. The simulation illustrated both positive feedbacks between flow and vegetation, which enhanced vegetation expansion, and negative feedbacks, which led to patch erosion and limited patch growth. The most rapid expansion of the vegetated area occurred during the initial simulation steps, when the flow blockage due to vegetation was small. A higher velocity threshold (higher LV) produced more rapid initial growth and a higher final coverage of vegetation. The patches evolved to one or a few elongated islands extending along the channel.

Magnetic properties and structure of low temperature phase MnBi with island structure

The magnetic properties of the low temperature phase (LTP) MnBi thin films of islands structure are discussed. The LTP MnBi islands are formed onto silica substrates after the multilayers Bi(3.2nm)/Mn(2nm)x N are deposited and then annealed at 450C for 0.5hr, where N is the number of the repetition of a pair of Mn and Bi layer. Those islands are found to be of the LTP MnBi, with the c-axis orientation along the normal to the sample plane for N=10 ∼ 40. Their size vary from place to place, but are averagely of about a few hundred nm in height and a few μm in width for N from 10 to 40. For N=200, the elongated islands are formed densely, with the length of about a few tens of μm. The coverage of those islands increases with N. The temperature dependence of saturation magnetization Ms is qualitatively similar to that for bulk, though the absolute values for Ms are smaller by 20%. The magnetic anisotropy constants of Ku1 and Ku2 are evaluated for the samples with N=10 ∼ 40, where Ku1 and Ku2 are the magnetic anisotropy constants corresponding to the second and fourth power term in the uniaxial magnetic anisotropy energy expression. It is found that the Ku1 increases with T monotonously, reaching to about 1x107 erg/cc at 400K. On the other hand, the Ku2 remains nearly zero for temperatures below 300K, and then becomes negative, reaching to about 7 x 106 erg/cc at 400K. This is the first to report of the temperature dependence of Ku1 and Ku2 in the LTP MnBi of an island structure. It is also noted that the decrease of Ku for a temperature range beyond around 450 K is possibly due to the decrease of the Ku2 component, as demonstrated in the present study.

Controlling In-Plane Isotropic and Anisotropic Orientation of Organic Semiconductor Molecules on Ionic Fluoride Dielectrics

α-Sexithiophene (6T) ultrathin films have been grown on CaF2(111)/Si(111) planar surfaces and on CaF2(110)/Si(001) ridged surfaces by molecular beam epitaxy. The growth mode has been studied by means of atomic force microscopy (AFM), photoemission, and near edge X-ray absorption fine structure (NEXAFS). AFM reveals a substantial difference in the film morphology on the two substrates: on CaF2(111) large islands with flat terraces form with no in-plane preferential growth direction; on CaF2(110) narrow and elongated islands develop following the substrate corrugation. Photoemission and X-ray absorption at Ca L2,3 and F K edges indicate that the interaction with the substrate is negligible. Near-edge X-ray absorption (NEXAFS) flanked by DFT calculations of the angular-resolved absorption cross section of 6T at the carbon K-edge reveal that the molecules on both substrates have their long axis vertically oriented with respect to the substrate plane. In addition, in-plane anisotropy of the molecular orientati...

Fe on W(001) from continuous films to nanoparticles: Growth and magnetic domain structure

The evolution of the structural and magnetic properties of Fe films during growth on the W(001) surface have been studied with low energy electron diffraction, real-time low energy electron microscopy, and quasi-real-time, spin-polarized low energy electron microscopy in the absence of a magnetic field (virgin state). Depending on the growth temperature, different growth modes are observed: growth of atomically rough and highly strained (10.4% tensile) pseudomorphic films at room temperature, kinetically limited layer-by-layer growth (quasi--Frank-van der Merwe growth mode) of smooth pseudomorphic films up to 4 monolayers at around 500 K and growth of fully relaxed three-dimensional Fe islands on top of a thermodynamically stable 2-monolayer-thick wetting layer (Stranski-Krastanov growth mode) at and above 700 K. Around 500 K, layered growth is terminated by partial (2 monolayers) dewetting of the metastable Fe film and formation of thin, partially relaxed, elongated islands on a thermodynamically stable 2 monolayer film. Ferromagnetic order is first detected during growth at room temperature at 2.35 monolayer Fe film thickness. The magnetization is in-plane with a thickness-dependent direction, rotating from the substrate $\ensuremath{\langle}110\ensuremath{\rangle}$ directions at 3 monolayers toward the $\ensuremath{\langle}100\ensuremath{\rangle}$ directions at 4 monolayers and back again toward the $\ensuremath{\langle}110\ensuremath{\rangle}$ directions at about 8 monolayers. The in-plane spin reorientation that occurs at room temperature is accompanied by significant changes of the magnetic domain structure. In the Frank-van der Merwe growth regime, large magnetic domains are observed in metastable 3 and 4 monolayer films. The isolated three-dimensional Fe islands that form in the Stranski-Krastanov regime have vortex, quasi-single domain ($C$ state), or single magnetic domain structures, depending on their size and shape. The detailed results that are obtained with high thickness, lateral and azimuthal angular resolution with spin-polarized low energy electron microscopy are compared with earlier laterally averaging and laterally resolving magnetic studies, and discrepancies are explained.

Island characteristics within wetlands influence waterbird nest success and abundance

ABSTRACTCoastal waterbird populations are threatened by habitat loss and degradation from urban and agricultural development and forecasted sea level rise associated with climate change. Remaining wetlands often must be managed to ensure that waterbird habitat needs, and other ecosystem functions, are met. For many waterbirds, the availability of island nesting habitat is important for conserving breeding populations. We used linear mixed models to investigate the influence of pond and island landscape characteristics on nest abundance and nest success of American avocets (Recurvirostra americana), black‐necked stilts (Himantopus mexicanus), and Forster's terns (Sterna forsteri) in San Francisco Bay, California, USA, based on a 9‐year dataset that included >9,000 nests. Nest abundance and nest success were greatest within ponds and on individual islands located either <1 km or >4 km from San Francisco Bay. Further, nest abundance was greater within ponds with relatively few islands, and on linear‐shaped, highly elongated islands compared to more rounded islands. Nest success was greater on islands located away from the nearest surrounding pond levee. Compared to more rounded islands, linear islands contained more near‐water habitat preferred by many nesting waterbirds. Islands located away from pond levees may provide greater protection from terrestrial egg and chick predators. Our results indicate that creating and maintaining a few, relatively small, highly elongated and narrow islands away from mainland levees, in as many wetland ponds as possible would be effective at providing waterbirds with preferred nesting habitat. © 2016 The Wildlife Society.

The creation of microscopic surface structures by interfacial diffusion of Au and Ag on Ag(110): A XPS and STM study

Experiments on single crystal Au/Ag alloy surfaces may provide insight into the physical and chemical phenomena that determine the reactivity of complex alloy surfaces such as nanoporous gold or bimetallic nanoparticles. In this study, we report the highly unexpected observation that as soon as interfacial diffusion is feasible (400K) thin gold films drastically restructure Ag(110) surfaces on the micrometer scale and create regular islands in a pattern which resembles the result of a sputter-etching process; bulk diffusion plays apparently no role during this phenomenon. Scanning tunneling microscopy (STM) reveals that the deposition of monolayer quantities of gold on the surface creates elongated islands, typically with a length of 1000nm, a width of ~50nm, and a height of ~30 lattice planes. The islands are predominantly elongated along the [1–10] direction and have a mutual distance of about 50nm. Approximately, one monolayer of gold causes the relocation of ~11ML of material. The islands are thermally unstable as further heating between 450K and 600K reduces the island structure significantly. The ‘etching’ of gold into the Ag(110) bulk material and the associated island formation can be rationalized with a simple kinetic model involving the diffusion of surface atoms only, illustrated with Monte Carlo simulations. A kinetic interpretation is also supported by the fact that those structures diminish after further annealing to higher temperatures. The observed large-scale reorganization underlines that even seemingly simple and well-defined surfaces may evolve in complex ways and that massive restructuring of surfaces can occur at temperatures well below the onset of bulk diffusion.

Effects of Ga-induced reconstructed surfaces and atomic steps on the morphology of GaSb islands on Si(1 0 0)

The effects of the Ga-induced reconstructed surface and atomic step type on the shape and morphology of GaSb islands on a Si(100) surface were studied using ultrahigh-vacuum scanning tunneling microscopy and atomic force microscopy. Though both anisotropic elongated islands and isotropic islands were formed on clean Si and Ga/Si(100)-2×3 substrates, isotropic islands were dominantly formed on Ga/Si(100)-2×2 substrates at 300°C. The density and size of GaSb islands on 2×2-Ga at 300°C were estimated to be 4.9×1010cm−2 and 29.1nm, respectively. The difference in the GaSb island shapes could be caused by the terrace and step of the substrate surface being changed by step rearrangement due to the deposition of Ga atoms at high temperatures. Above 350°C, the density and size of islands decreased to 2.7×109cm−2 and increased to 62.0nm, respectively. In the initial growth stage, scanning tunneling microscopy results revealed that a Sb/Si(100)-2×1 reconstructed surface was formed above 350°C. The large islands were assumed to aggregate from the surface diffusion of each atom because the Sb-terminated Si surface is inactive against Ga and Sb atoms. The type of the reconstructed surface is also suggested to affect the density and size of the islands.

A geometric multigrid solver for the free-surface equation in environmental models featuring irregular coastlines

A recently developed multigrid method (Botto, 2013), based on the concept of volume fraction, has been tested for the inversion of the Helmholz-type equation for the free surface in the environmental public domain code COHERENS. The volume fraction concept is particularly interesting for coarse grid cells that are agglomerated from both dry and wet fine grid cells at irregular coastlines. At these locations, modifying the prolongation operator and the coarse grid discretization, using the volume fraction, results in better convergence. However, as convergence deteriorates in the case of small, elongated islands that tend to disappear by the multigrid coarsening procedure, a correction is proposed, yielding good convergence rates, irrespective of the presence of small or large islands. The method is tested extensively for the inversion of the academic Poisson equation. Larger test cases, solving the Helmholz-type equation, prove the applicability for real-life applications of environmental flows.

Homoepitaxial electrodeposition on reconstructed and unreconstructed Au(100): An in-situ STM study

Abstract A study of homoepitaxial electrodeposition on reconstructed and unreconstructed Au(100) surfaces is presented. The growth behavior has been investigated by in-situ scanning tunneling microscopy for Au(100) in contact with 0.1 M H2SO4 + 5 μM K[AuCl4]. It is shown that the initial surface structure is decisive for the emerging Au structures, giving rise to clearly different surface morphologies for electro-crystallization of Au on the unreconstructed and on the reconstructed Au(100) surface. A layer-by-layer growth is observed at more positive potentials for unreconstructed Au(100). The electrodeposition proceeds initially by the formation of Au islands followed by island coalescence due to the high mobility of surface atoms. Monatomic recessed stripes are formed as a result of the coalescence of deposited Au islands. At more negative potentials, the growth of Au proceeds strongly anisotropic on the reconstructed surface by the formation of reconstructed elongated islands.

Formation of Ni-driven nano-sized structures on Ag/Ge(111)-√3 × √3 surface: STM study

The formation of nano-sized structures upon room temperature (RT) deposition of small amounts of Ni (~0.1 ml) onto an Ag/Ge(111)-√3 × √3 surface was investigated by scanning tunnelling microscopy. The RT behaviour was dominated by the formation of Ni clusters, which did not interact chemically with the surface. The images as obtained after annealing within the temperature range between 100oC and 500oC corresponded to the formation of clusters as well as triangular, elongated and hexagonal-shaped nano-sized islands. Annealing above 550oC resulted in the transformation of the √3 × √3 phase into a c(2 × 8) phase. This process was accompanied by the thermal decomposition of the majority of the islands, except the hexagonal-shaped ones. The latter remained on the surface in an unaltered form upon annealing even at 800oC. We propose that the hexagonal-islands are made of Ni and Ge compounds rather than pure Ni atoms.

Comparative analysis of pyramidal and wedge-like quantum dots formation kinetics in Ge/Si(001) system

In this work complex mathematical model for calculation of dependencies on growth conditions of parameters of self-organized quantum dots (QDs) of Ge on Si grown by the method of molecular beam epitaxy (MBE) is described. Calculations on pyramidal and elongated islands formation energies in Ge/Si(001) system with respect to surface energy, elastic strains relaxation and attraction of atoms to substrate decreasing are done. On the basis of well-known model based on generalization of classical nucleation theory it is shown that wedge-like clusters form later than pyramidal but begin to dominate in the QDs massive on the later stages of growth. Conclusions from the described theory correspond to the experimental observations.

Nickel-containing nano-sized islands grown on Ge(111)-c(2 × 8) and Ag/Ge(111)-(√3 × √3) surfaces.

The formation of nano-islands on both a Ge(111)-c(2 × 8) surface and an Ag/Ge(111)-(√3 × √3) surface evaporated with 0.1 ML Ni was investigated by scanning tunneling microscopy (STM). We have noticed that at temperatures lower than 670 K, the reaction between Ni and the individual substrate surfaces proceeds to form different structures: flat-topped islands with a 2√7 × 2√7 or a 3 × 3 reconstruction on the Ni/Ge(111)-c(2 × 8) surface vs. islands with a 7 × 7 reconstruction on the Ni/Ag/Ge(111)-(√3 × √3) surface. From this we have inferred that within a temperature range between room temperature and 670 K, the intermediate Ag layer retards mixing between Ni and Ge atoms. As a result, the grown islands are composed of pure Ni atoms. Within a temperature range from 670 to 770 K, most islands produced on the Ag/Ge(111)-(√3 × √3) surface are identical with those formed on the Ni/Ge(111)-c(2 × 8) surface, suggesting that above 670 K, Ni atoms are likely to bind with Ge atoms. However, an essential difference between STM images of the surfaces under study exists in the appearance of large elongated islands on the Ni/Ag/Ge(111)-(√3 × √3) surface. The formation of the latter is explained in terms of a difference in energy for Ni diffusion on the Ge(111)-c(2 × 8) and Ag/Ge(111)-(√3 × √3) surfaces.

One-dimensional lateral growth of epitaxial islands on focused ion beam patterned substrates

Lateral growth of highly elongated SiGe islands in one dimension has been achieved by ex-situ substrate patterning using a focused ion beam (FIB) to create an array of surface grooves in the Si substrate. Growth of Si0.7Ge0.3 on this template results in preferential formation of strain-relieving islands next to the edges of the grooves under kinetically limited growth conditions. The length of the nanowire-like islands is limited only by the length of the patterned trench. Occasional bridging across the groove is also observed due to non-uniformity of the underlying topography and the strong preference for the formation of four-fold island structures in this system. The success of this method is dependent upon the initial Si buffer layer thickness and on the orientation of the grooves, which must be parallel to the crystallographic 〈110〉 directions. These results demonstrate that important crystallographic as well as kinetic factors must be considered for controlling the lateral growth of nanostructures on patterned substrates.

Emergent magnetic monopoles, disorder, and avalanches in artificial kagome spin ice (invited)

We study artificial spin ice with isolated elongated nanoscale islands arranged in a kagome lattice and solely interacting via long range dipolar fields. The artificial kagome spin ice displays a phenomenology similar to the microscopic pyrochlore system, where excitations at sub-Kelvin temperatures consist of emergent monopole quasiparticles that are connected via a solenoidal flux line, a classical and observable version of the Dirac string. We show that magnetization reversal in kagome spin ice is fundamentally different from the nucleation and extensive domain growth scenario expected for a generic 2D system. Here, the magnetization reverses in a strictly 1D fashion: After nucleation, a monopole-antimonopole dissociates along a 1D path, leaving a (Dirac) string of islands with reversed magnetization in its wake. Since the 2D artificial spin ice spontaneously decays into a 1D subsystem, magnetization reversal in kagome spin ice provides an example of dimensional reduction via frustration.

THE EFFECTS OF PLASMA BETA AND ANISOTROPY INSTABILITIES ON THE DYNAMICS OF RECONNECTING MAGNETIC FIELDS IN THE HELIOSHEATH

The plasma {\beta} (the ratio of the plasma pressure to the magnetic pressure) of a system can have a large effect on its dynamics as high {\beta} enhances the effects of pressure anisotropies. We investigate the effects of {\beta} in a system of stacked current sheets that break up into magnetic islands due to magnetic reconnection. We find significant differences between {\beta} < 1 and {\beta} > 1. At low {\beta} growing magnetic islands are modestly elongated and become round as contraction releases magnetic stress and reduces magnetic energy. At high {\beta} the increase of the parallel pressure in contracting islands causes saturation of modestly elongated islands as island cores approach the marginal firehose condition. Only highly elongated islands reach finite size. The kinking associated with the Weibel and firehose instabilities prevents full contraction of these islands, leading to a final state of highly elongated islands in which further reconnection is suppressed. The results are directly relevant to reconnection in the sectored region of the heliosheath and possibly to saturation mechanisms of the magnetorotational instability in accretion flows.

Mismatch relaxation by stacking fault formation of AlN islands in AlGaN/GaN structures on m-plane GaN substrates

We study the mismatch relaxation of 2-5 nm thin elongated AlN islands formed during growth of AlGaN on bulk m-plane GaN by molecular beam epitaxy. The relaxation of these m-plane AlN layers is anisotropic and occurs through the introduction of stacking faults in [0001] planes during island coalescence, while no relaxation is observed along the perpendicular [112¯0] direction. This anisotropy in the mismatch relaxation and the formation of stacking faults in the AlN islands are explained by the growth mode of the AlN platelets and their coalescence along the [0001] direction.