Limits...
Coherent magnetic semiconductor nanodot arrays.

Wang Y, Xiu F, Wang Y, Zou J, Beyermann WP, Zhou Y, Wang KL - Nanoscale Res Lett (2011)

Bottom Line: In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors.Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility.The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Materials Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, St Lucia Campus, Brisbane QLD 4072, Australia. y.wang4@uq.edu.au.

ABSTRACT
In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

No MeSH data available.


Related in: MedlinePlus

High resolution transmission electron microscopy results (HRTEM) of the MnGe nanodots. (a) A high-magnification TEM image showing several aligned MnGe nanodots. (b) The HRTEM images of the MnGe nanodots (the selected area in (a)) showing a perfect diamond structure as the Ge matrix. (c, d) Bragg filterings of ± (111) (c) and ± () (d) reflections, respectively; where no dislocation or distortion was observed. The dark contrast of the nanodots indicates the existence of significant strain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211181&req=5

Figure 3: High resolution transmission electron microscopy results (HRTEM) of the MnGe nanodots. (a) A high-magnification TEM image showing several aligned MnGe nanodots. (b) The HRTEM images of the MnGe nanodots (the selected area in (a)) showing a perfect diamond structure as the Ge matrix. (c, d) Bragg filterings of ± (111) (c) and ± () (d) reflections, respectively; where no dislocation or distortion was observed. The dark contrast of the nanodots indicates the existence of significant strain.

Mentions: Practically, we employed a concept of stacked MnGe nanodots by alternatively growing MnGe and Ge layers with designated thicknesses (nominal 3-nm-thick MnGe and 11-nm-thick Ge), as shown in Figure 1a. It is well known that Mn doping in Ge induces compressive strain because of its larger atomic size [29], assuming that no lattice defects are generated during the doping process, i.e., lattice coherence. Mn-rich MnGe nanodots induced by the spinodal decomposition should be strained if the lattice coherence between the nanodots and the matrix remains. Once the strained nanodots are developed, a thin Ge spacer layer, subsequently deposited with an optimized thickness, will retain the perfect lattice coherence with the underneath nanodots. This enables the existing nanodots to exert strain on the Ge spacer layer and produce "strained spots", which, in turn, become preferred nucleation sites for successive nanodots. Eventually, multilayered and vertically aligned MnGe nanodot arrays can be produced, similar to the scenarios of stacked InAs/GaAs [27,28] and Ge/Si [30] quantum dots. Indeed, by employing this innovative approach, we achieved the growth of coherent self-assembled MnGe nanodot arrays with an estimated density of 1011 cm-2 to approximately 1012 cm-2 within each MnGe layer, as schematically demonstrated in Figure 1b. In this study, ten periods of MnGe nanodots were epitaxially grown on Ge (100) and GaAs (100) substrates by a Perkin-Elmer solid source molecular beam epitaxy (MBE) system. A detailed description of growth method and parameters are presented in the Methods part (also refer to Figure S1 in Additional file 1). TEM and energy dispersive spectroscopy (EDS) in the STEM mode were performed to understand the nanostructures and compositional variations of the resulting thin films. Figure 2a and 2c are typical plane-view and cross-sectional TEM images and show the general morphology of the MnGe nanostructures, viewed along the <100> and <011> directions, respectively. A high-density of dark nanodots can be clearly seen in both cases. Based on the magnified cross-sectional image shown in Figure 2d, the nanodot arrays are clearly observed with ten stacks along the growth direction although not perfectly vertical (see Figure S2 in Additional file 1 for more images). In order to determine the composition of the dark dots, EDS analyses in the STEM mode were carried out and typical plane-view and cross-sectional STEM images are shown in Figure 2b and 2e, respectively. Figure 2f is the EDS result taken from a typical dot and shows clearly the Mn and Ge peaks. Figure 2g and 2h present EDS line scans using the Mn K peak for the dots marked by G and H in Figure 2b and 2e, respectively, indicating high concentrations of Mn inside the dots. Taking all these comprehensive TEM results into account, it is concluded that the nanodots are Mn-rich when compared with the surrounding matrix. Figure 3a shows a high magnification TEM image taken from a thin area, where several aligned MnGe nanodots can be evidently observed. The distance between two vertically adjacent nanodots (along the growth direction) is measured to be 14 ± 1 nm, well matched with the designed period of a 11-nm-thick Ge spacer layer and a 3-nm-thick MnGe layer. It should be noted that these nanodots are uniform in size with an elliptical shape (a dimension of 5.5 ± 0.5 nm and 8 ± 0.3 nm in the horizontal and vertical directions, respectively), as demonstrated in Figure 3a. Since the nominal thickness of the MnGe layer (3 nm) is far less than the dot vertical dimension (8 nm), it suggests that, during the growth of the MnGe thin film, Mn not only diffuses laterally (to form dots), but also migrates vertically into the adjacent Ge spacer layers, primarily in the proximity of the dot regions, resulting in ellipse-shaped nanodots.


Coherent magnetic semiconductor nanodot arrays.

Wang Y, Xiu F, Wang Y, Zou J, Beyermann WP, Zhou Y, Wang KL - Nanoscale Res Lett (2011)

High resolution transmission electron microscopy results (HRTEM) of the MnGe nanodots. (a) A high-magnification TEM image showing several aligned MnGe nanodots. (b) The HRTEM images of the MnGe nanodots (the selected area in (a)) showing a perfect diamond structure as the Ge matrix. (c, d) Bragg filterings of ± (111) (c) and ± () (d) reflections, respectively; where no dislocation or distortion was observed. The dark contrast of the nanodots indicates the existence of significant strain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211181&req=5

Figure 3: High resolution transmission electron microscopy results (HRTEM) of the MnGe nanodots. (a) A high-magnification TEM image showing several aligned MnGe nanodots. (b) The HRTEM images of the MnGe nanodots (the selected area in (a)) showing a perfect diamond structure as the Ge matrix. (c, d) Bragg filterings of ± (111) (c) and ± () (d) reflections, respectively; where no dislocation or distortion was observed. The dark contrast of the nanodots indicates the existence of significant strain.
Mentions: Practically, we employed a concept of stacked MnGe nanodots by alternatively growing MnGe and Ge layers with designated thicknesses (nominal 3-nm-thick MnGe and 11-nm-thick Ge), as shown in Figure 1a. It is well known that Mn doping in Ge induces compressive strain because of its larger atomic size [29], assuming that no lattice defects are generated during the doping process, i.e., lattice coherence. Mn-rich MnGe nanodots induced by the spinodal decomposition should be strained if the lattice coherence between the nanodots and the matrix remains. Once the strained nanodots are developed, a thin Ge spacer layer, subsequently deposited with an optimized thickness, will retain the perfect lattice coherence with the underneath nanodots. This enables the existing nanodots to exert strain on the Ge spacer layer and produce "strained spots", which, in turn, become preferred nucleation sites for successive nanodots. Eventually, multilayered and vertically aligned MnGe nanodot arrays can be produced, similar to the scenarios of stacked InAs/GaAs [27,28] and Ge/Si [30] quantum dots. Indeed, by employing this innovative approach, we achieved the growth of coherent self-assembled MnGe nanodot arrays with an estimated density of 1011 cm-2 to approximately 1012 cm-2 within each MnGe layer, as schematically demonstrated in Figure 1b. In this study, ten periods of MnGe nanodots were epitaxially grown on Ge (100) and GaAs (100) substrates by a Perkin-Elmer solid source molecular beam epitaxy (MBE) system. A detailed description of growth method and parameters are presented in the Methods part (also refer to Figure S1 in Additional file 1). TEM and energy dispersive spectroscopy (EDS) in the STEM mode were performed to understand the nanostructures and compositional variations of the resulting thin films. Figure 2a and 2c are typical plane-view and cross-sectional TEM images and show the general morphology of the MnGe nanostructures, viewed along the <100> and <011> directions, respectively. A high-density of dark nanodots can be clearly seen in both cases. Based on the magnified cross-sectional image shown in Figure 2d, the nanodot arrays are clearly observed with ten stacks along the growth direction although not perfectly vertical (see Figure S2 in Additional file 1 for more images). In order to determine the composition of the dark dots, EDS analyses in the STEM mode were carried out and typical plane-view and cross-sectional STEM images are shown in Figure 2b and 2e, respectively. Figure 2f is the EDS result taken from a typical dot and shows clearly the Mn and Ge peaks. Figure 2g and 2h present EDS line scans using the Mn K peak for the dots marked by G and H in Figure 2b and 2e, respectively, indicating high concentrations of Mn inside the dots. Taking all these comprehensive TEM results into account, it is concluded that the nanodots are Mn-rich when compared with the surrounding matrix. Figure 3a shows a high magnification TEM image taken from a thin area, where several aligned MnGe nanodots can be evidently observed. The distance between two vertically adjacent nanodots (along the growth direction) is measured to be 14 ± 1 nm, well matched with the designed period of a 11-nm-thick Ge spacer layer and a 3-nm-thick MnGe layer. It should be noted that these nanodots are uniform in size with an elliptical shape (a dimension of 5.5 ± 0.5 nm and 8 ± 0.3 nm in the horizontal and vertical directions, respectively), as demonstrated in Figure 3a. Since the nominal thickness of the MnGe layer (3 nm) is far less than the dot vertical dimension (8 nm), it suggests that, during the growth of the MnGe thin film, Mn not only diffuses laterally (to form dots), but also migrates vertically into the adjacent Ge spacer layers, primarily in the proximity of the dot regions, resulting in ellipse-shaped nanodots.

Bottom Line: In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors.Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility.The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

View Article: PubMed Central - HTML - PubMed

Affiliation: Materials Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, St Lucia Campus, Brisbane QLD 4072, Australia. y.wang4@uq.edu.au.

ABSTRACT
In searching appropriate candidates of magnetic semiconductors compatible with mainstream Si technology for future spintronic devices, extensive attention has been focused on Mn-doped Ge magnetic semiconductors. Up to now, lack of reliable methods to obtain high-quality MnGe nanostructures with a desired shape and a good controllability has been a barrier to make these materials practically applicable for spintronic devices. Here, we report, for the first time, an innovative growth approach to produce self-assembled and coherent magnetic MnGe nanodot arrays with an excellent reproducibility. Magnetotransport experiments reveal that the nanodot arrays possess giant magneto-resistance associated with geometrical effects. The discovery of the MnGe nanodot arrays paves the way towards next-generation high-density magnetic memories and spintronic devices with low-power dissipation.

No MeSH data available.


Related in: MedlinePlus