Showing 1–15 of 15 results for author: Hsiao, C

Electrothermal control of spin-reorientation transition in Co/Fe_3GaTe_2 heterostructures

Authors: Po-Wei Chen, Ming-Hsien Hsu, Cheng-Ying Hsiao, Ming-Yang Ho, Masahiro Haze, Yan-Ru Chu, Yu-Cheng Shao, Po-Chun Chang, Chen-Yu Ou, Ruei Chen, Ko-Fan Chen, Chung-Ting Ke, Chao-Hung Du, Yukio Hasegawa, Wen-Chin Lin, .

Abstract: Electrical control of magnetic anisotropy in van der Waals (vdWs) magnets is a key step toward reconfigurable two-dimensional spintronics, yet how a conventional metallic ferromagnet competes with a van der Waals magnet across a direct interface has remained largely unexplored. Here we demonstrate reversible thermal and electrothermal control of a spin-reorientation transition in Co/Fe_3GaTe_2 (FG… ▽ More Electrical control of magnetic anisotropy in van der Waals (vdWs) magnets is a key step toward reconfigurable two-dimensional spintronics, yet how a conventional metallic ferromagnet competes with a van der Waals magnet across a direct interface has remained largely unexplored. Here we demonstrate reversible thermal and electrothermal control of a spin-reorientation transition in Co/Fe_3GaTe_2 (FGaT) heterostructures. As Joule heating weakens the FGaT anisotropy, the heterostructure switches from an out-of-plane- to an in-plane-dominated state at a reorientation temperature of approximately 311 K, well below the Curie temperature, consistent with an exchange-mediated anisotropy competition between the Co overlayer and FGaT. An electrically driven device shows a closely matching loop evolution within an 80-100 mW power window, reversibly over five measurement cycles, consistent with an electrothermal origin. In a Co-free FGaT device, Kerr microscopy traces the switching to a power-tunable domain nucleation barrier and demonstrates power-thresholded, field-assisted magnetization reversal at a threshold near 15 mW. These results demonstrate electrothermal anisotropy competition as a route to heat-assisted and device-level control of vdWs magnetism. △ Less

Submitted 17 July, 2026; originally announced July 2026.

Epitaxial MgSnN2 on 4H-SiC (0001): An Earth-Abundant Nitride for Green Optoelectronics and Photovoltaics

Authors: D. Gogova, D. Tran, V. Stanishev, D. Shafizadeh, C. -L. Hsiao, M. Kim, B. Pécz, A. Kovács, K. Frey, A. Sulyok, N. K. Singh, A. Le Febvrier, P. Eklund, V. Darakchieva

Abstract: Group II-IV nitrides have recently emerged as a novel class of semiconductors composed of earth-abundant elements. Owing to their tunable bandgaps, comparable to those of III-nitrides, these materials are attractive candidates for replacing expensive Ga-based alloys in photovoltaics and green-gap optoelectronics. In this work, epitaxial growth of MgSnN2 layers on 4H-SiC(0001) substrates by direct… ▽ More Group II-IV nitrides have recently emerged as a novel class of semiconductors composed of earth-abundant elements. Owing to their tunable bandgaps, comparable to those of III-nitrides, these materials are attractive candidates for replacing expensive Ga-based alloys in photovoltaics and green-gap optoelectronics. In this work, epitaxial growth of MgSnN2 layers on 4H-SiC(0001) substrates by direct current magnetron sputtering is demonstrated. Mg and Sn metal targets have been co-sputtered in nitrogen-containing atmosphere at growth temperatures up to 500 °C. X-ray diffraction and cross-sectional transmission electron microscopy confirm the MgSnN2 layers grow epitaxially in a wurtzite crystal structure, exhibiting the epitaxial relationships with the substrate: MgSnN2 [0001]//4H-SiC [0001] and MgSnN2 [10-10]//4H-SiC[10-10]. Improved crystalline quality is observed for higher deposition temperatures and near-stoichiometric composition, as evidenced by the narrowing of rocking curve linewidths. Optical characterization reveals high absorption coefficients (1e5 cm-1) in the visible spectrum, comparable to that of GaAs, highlighting the suitability of MgSnN2 for photovoltaic applications. A photoluminescence emission band at ~2.4 eV is detected, highly desirable for optoelectronic devices operating in the challenging green spectral region. These results establish MgSnN2 as an earth-abundant, environmentally friendly material, structurally compatible with III-nitrides, with potential for cost-efficient components in sustainable optoelectronics and photovoltaics. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Electronic and optical properties of core-shell InAlN nanorods: a comparative study via LDA, LDA-1/2, mBJ and $G_0W_0$ methods

Authors: Ronaldo Rodrigues Pela, Ching-Lien Hsiao, Lars Hultman, Jens Birch, Gueorgui Kostov Gueorguiev

Abstract: Currently, self-induced InAlN core-shell nanorods enjoy an advanced stage of accumulation of experimental data from their growth and characterization as well as a comprehensive understanding of their formation mechanism by the ab initio modeling based on Synthetic Growth Concept. However, their electronic and optical properties, on which most of their foreseen applications are expected to depend,… ▽ More Currently, self-induced InAlN core-shell nanorods enjoy an advanced stage of accumulation of experimental data from their growth and characterization as well as a comprehensive understanding of their formation mechanism by the ab initio modeling based on Synthetic Growth Concept. However, their electronic and optical properties, on which most of their foreseen applications are expected to depend, have not been investigated comprehensively. $G_0W_0$ is currently regarded as a gold-standard methodology with quasi-particle corrections to calculate electronic properties of materials in general. It is also the starting point for higher-order methods that study excitonic effects, such as those based on the Bethe-Salpeter equation. One major drawback of $G_0W_0$, however, is its computational cost, much higher than density-functional theory (DFT). Therefore, in many applications, it is highly desirable to answer the question of how well approaches based on DFT, such as e. g. LDA, LDA-1/2, and mBJ, can approximately reproduce $G_0W_0$ results with respect to the electronic and optical properties. Thus, the purpose of the present paper is to investigate how the DFT-based methodologies LDA, LDA-1/2, and mBJ can be used as tools to approximate $G_0W_0$ in studies of the electronic and optical properties of scaled down models of core-shell InAlN nanorods. For these systems, we observed that band gaps, density of states, dielectric functions, refractive indexes, absorption and reflectance coefficients are reasonably well described by LDA-1/2 and mBJ when compared to $G_0W_0$, however, at a much more favorable computational cost. △ Less

Submitted 26 September, 2023; originally announced September 2023.

Comments: The following article has been submitted to The Journal of Chemical Physics. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals/

Journal ref: Phys. Chem. Chem. Phys. 26, 7504-7514 (2024)

Network physics of attractive colloidal gels: Resilience, Rigidity, and Phase Diagram

Authors: Mohammad Nabizadeh, Farzaneh Nasirian, Xinzhi Li, Yug Saraswat, Rony Waheibi, Lilian C. Hsiao, Dapeng Bi, Babak Ravandi, Safa Jamali

Abstract: Attractive colloidal gels exhibit solid-like behavior at vanishingly small fractions of solids, owing to ramified space-spanning networks that form due to particle-particle interactions. These networks give the gel its rigidity, and as the attraction between the particles grows, so does the elasticity of the colloidal network formed. The emergence of this rigidity can be described through a mean f… ▽ More Attractive colloidal gels exhibit solid-like behavior at vanishingly small fractions of solids, owing to ramified space-spanning networks that form due to particle-particle interactions. These networks give the gel its rigidity, and as the attraction between the particles grows, so does the elasticity of the colloidal network formed. The emergence of this rigidity can be described through a mean field approach; nonetheless, fundamental understanding of how rigidity varies in gels of different attraction strengths is lacking. Moreover, recovering an accurate gelation phase diagram based on the system's variables have been an extremely challenging task. Understanding the nature of these fractal clusters, and how rigidity emerges from their connections is key to controlling and designing gels with desirable properties. Here, we employ well-established concepts of network science to interrogate and characterize the network of colloidal gels. We construct a particle-level network, having all the spatial coordinates of colloids with different attraction levels, and also identify polydisperse rigid fractal clusters using a Gaussian Mixture Model, to form a coarse-grained cluster network that distinctly shows main physical features of the colloidal gels. A simple mass-spring model then is used to recover quantitatively the elasticity of colloidal gels from these cluster networks. Interrogating the resilience of these gel networks show that the elasticity of a gel (a dynamic property) is directly correlated to its cluster network's resilience (a static measure). Finally, we use the resilience investigations to devise [and experimentally validate] a fully resolved phase diagram for colloidal gelation, with a clear solid-liquid phase boundary using a single volume fraction of particles well beyond this phase boundary. △ Less

Submitted 30 January, 2023; originally announced January 2023.

Jamming Distance Dictates Colloidal Shear Thickening

Authors: Shravan Pradeep, Mohamad Nabizadeh, Alan R. Jacob, Safa Jamali, Lilian C. Hsiao

Abstract: We report experimental and computational observations of dynamic contact networks for colloidal suspensions undergoing shear thickening. The dense suspensions are comprised of sterically stabilized poly(methyl methacrylate) hard sphere colloids that are spherically symmetric and have varied surface roughness. Confocal rheometry and dissipative particle dynamics simulations show that the shear thic… ▽ More We report experimental and computational observations of dynamic contact networks for colloidal suspensions undergoing shear thickening. The dense suspensions are comprised of sterically stabilized poly(methyl methacrylate) hard sphere colloids that are spherically symmetric and have varied surface roughness. Confocal rheometry and dissipative particle dynamics simulations show that the shear thickening strength scales exponentially with the scaled deficit contact number and the scaled jamming distance. Rough colloids, which experience additional tangential and rolling constraints, require an average of 1.5 - 2 fewer particle contacts as compared to smooth colloids, in order to generate the same shear thickening strength. This is because the surface roughness enhances geometric friction in a way that the rough colloids do not experience a large change in the free volume near the jamming point. In contrast, smooth colloids must undergo significant reduction in the free volume to support an equivalent shear stress. The available free volume for different colloid roughness is related to the deficiency from the maximum number of nearest neighbors at jamming under shear. Our results further suggest that the force per contact is different for particles with different morphologies. △ Less

Submitted 3 June, 2021; v1 submitted 3 July, 2020; originally announced July 2020.

Journal ref: Phys. Rev. Lett. 127, 158002 (2021)

Influence of the growth interface shape on the defect characteristics in the facet region of 4H-SiC single crystals

Authors: Matthias Arzig, Michael Salamon, Ta Ching Hsiao, Norman Uhlmann, Peter J. Wellmann

Abstract: Two 75mm 4H-SiC single crystals are grown by the physical vapor transport (PVT) technique, using different insulation materials. The insulation material of higher thermal conductivity led to an increased radial temperature gradient. The evolution of the growth front was monitored using the in-situ computed tomography (CT). A slightly bent growth interface and a bigger facet are formed during the g… ▽ More Two 75mm 4H-SiC single crystals are grown by the physical vapor transport (PVT) technique, using different insulation materials. The insulation material of higher thermal conductivity led to an increased radial temperature gradient. The evolution of the growth front was monitored using the in-situ computed tomography (CT). A slightly bent growth interface and a bigger facet are formed during the growth applying a lower radial temperature gradient while a smaller facet and steeper crystal flanks are formed in the case of the larger radial temperature gradient. Micropipes are deflected laterally by large surface steps on the steep crystal flanks and a reduction of threading edge dislocations by 60% is revealed by KOH defect etching. △ Less

Submitted 13 December, 2019; originally announced December 2019.

Comments: Preprint, crystal growth, Conference, ICCGE-19

Lubricated friction of textured soft substrates

Authors: Yunhu Peng, Christopher M. Serfass, Catherine N. Hill, Lilian C. Hsiao

Abstract: The understanding of sliding friction for wet, patterned surfaces from first principles is challenging. While emerging applications have sought design principles from biology, a general framework is lacking because soft interfaces experience a multiphysics coupling between solid deformation and fluid dissipation. We investigate the elastohydrodynamic sliding of >50 patterned sliding pairs comprisi… ▽ More The understanding of sliding friction for wet, patterned surfaces from first principles is challenging. While emerging applications have sought design principles from biology, a general framework is lacking because soft interfaces experience a multiphysics coupling between solid deformation and fluid dissipation. We investigate the elastohydrodynamic sliding of >50 patterned sliding pairs comprising elastomers, thermosets, and hydrogels, and discover that texturing induces a critical transition in the macroscopic friction coefficient. This critical friction scales universally, without any fitting parameters, with the reduced elastic modulus and the pattern geometry. To capture the frictional dissipation, we separate the flow curve into two regimes and account for the contributions of shear and normal forces applied by the fluid on the patterns. Our model combines Reynolds' equations and elastic deformation to provide physical insights that allow engineering of the elastohydrodynamic friction in a class of soft tribopairs using pattern geometry, material elasticity, and fluid properties. △ Less

Submitted 13 September, 2019; originally announced September 2019.

Elasticity of colloidal gels: structural heterogeneity, foppy modes, and rigidity

Authors: D. Zeb Rocklin, Lilian C. Hsiao, Megan Szakasits, Michael J. Solomon, Xiaoming Mao

Abstract: Rheological measurements of model colloidal gels reveal that large variations in the shear moduli as colloidal volume-fraction changes are not reflected by simple structural parameters such as the coordination number, which remains almost a constant. We resolve this apparent contradiction by conducting a normal mode analysis of experimentally measured bond networks of the gels. We find that struct… ▽ More Rheological measurements of model colloidal gels reveal that large variations in the shear moduli as colloidal volume-fraction changes are not reflected by simple structural parameters such as the coordination number, which remains almost a constant. We resolve this apparent contradiction by conducting a normal mode analysis of experimentally measured bond networks of the gels. We find that structural heterogeneity of the gels, which leads to floppy modes and a nonaffine-affine crossover as frequency increases, evolves as a function of the volume fraction and is key to understand the frequency dependent elasticity. Without any free parameters, we achieve good qualitative agreement with the measured mechanical response. Furthermore, we achieve universal collapse of the shear moduli through a phenomenological spring-dashpot model that accounts for the interplay between fluid viscosity, particle dissipation, and contributions from the affine and non-affine network deformation. △ Less

Submitted 4 August, 2018; originally announced August 2018.

Comments: 7 pages, 4 figures

A rheological state diagram for rough colloids in shear flow

Authors: Lilian C. Hsiao, Safa Jamali, Daniel J. Beltran-Villegas, Emmanouil Glynos, Peter F. Green, Ronald G. Larson, Michael J. Solomon

Abstract: The flow of dense suspensions, glasses, and granular materials is heavily influenced by frictional interactions between constituent particles. However, neither hydrodynamics nor friction has successfully explained the full range of flow phenomena in concentrated suspensions. Particles with asperities represent a case in point. Lubrication hydrodynamics fail to completely capture two key rheologica… ▽ More The flow of dense suspensions, glasses, and granular materials is heavily influenced by frictional interactions between constituent particles. However, neither hydrodynamics nor friction has successfully explained the full range of flow phenomena in concentrated suspensions. Particles with asperities represent a case in point. Lubrication hydrodynamics fail to completely capture two key rheological properties - namely, that the viscosity increases drastically and the first normal stress difference can switch signs as volume fraction increases. Yet, simulations that account for interparticle friction are also unable to fully predict these properties. Furthermore, experiments show that rheological behavior can vary depending on particle roughness and deformability. We seek to resolve these apparent contradictions by systematically tuning the roughness of model colloids, investigating their viscosity and first normal stress differences under steady shear, and finally generating a rheological state diagram that demonstrates how surface roughness influences the transition between shear thickening and dilatancy. Our simulations, which are in good agreement with the experiments, suggest that friction between rough particles is significant. In addition, we find that roughness progressively lowers the critical conditions required for the onset of shear thickening and dilatancy. Our results thus provides a major contribution in the field of suspension rheology with broad relevance to granular and particulate materials. For instance, particle geometry can be tuned to increase the efficacy of materials that turn solid-like on the application of stimuli. On the other hand, engineers who work with concentrated slurries can now use images of the constituent particles to estimate optimal flow processing conditions. △ Less

Submitted 28 October, 2016; originally announced October 2016.

Journal ref: Phys. Rev. Lett. 119, 158001 (2017)

Out-of-plane spin polarization of edge currents in Chern insulator with Rashba spin-orbit interaction

Authors: Tsung-Wei Chen, Chin-Lun Hsiao, Chong-Der Hu

Abstract: We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at site-I and -II atoms and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increase… ▽ More We investigate the change in the non-zero Chern number and out-of-plane spin polarization of the edge currents in a honeycomb lattice with the Haldane-Rashba interaction. This interaction breaks the time-reversal symmetry due to the Haldane phase caused by a current loop at site-I and -II atoms and also accounts for the Rashba-type spin-orbit interaction. The Rashba spin-orbit interaction increases the number of Dirac points and the band-touching phenomenon can be generated by tuning the on-site potential in the non-zero Haldane phase. By using the Pontryagin winding number and numerical Berry curvature methods, we find that the Chern number pattern is $\{+2, -1, 0\}$ and $\{-2, +1, 0\}$ for the positive and negative Haldane phase, respectively. A non-zero Chern number is called a Chern-insulating phase. We discovered that changes in both the Haldane phase and on-site potential leads to a change in the orientation of the bulk spin polarization of site-I and site-II atoms. Interestingly, in a ribbon with a zigzag edge, which naturally has site-I atoms at one outer edge and site-II atoms at the opposite outer edge, the spin polarization of the edge states approximately obeys the properties of bulk spin polarization regardless of the change in the Chern number. In addition, even when the Chern number changes from $+2$ to $-1$ (or $-2$ to $+1$), by tuning the strength of the on-site potential, the sign of the spin polarization of the edge states persists. This approximate bulk-edge correspondence of the spin polarization in the Haldane-Rashba system would play an important role in spintronics, because it enables us to control the orientation of the spin polarization in a single Chern-insulating phase. △ Less

Submitted 3 May, 2016; originally announced May 2016.

Comments: 10 pages, 7 figures

Journal ref: J. Phys.: Condens. Matter 28 (2016) 275801

A model colloidal gel for coordinated measurements of force, structure, and rheology

Authors: Lilian C. Hsiao, Kathryn A. Whitaker, Michael J. Solomon, Eric M. Furst

Abstract: We introduce a model gel system in which colloidal forces, structure, and rheology are measured by balancing the requirements of rheological and microscopy techniques with those of optical tweezers. Sterically stabilized poly(methyl methacrylate) (PMMA) colloids are suspended in cyclohexane (CH) and cyclohexyl bromide (CHB) with dilute polystyrene serving as a depletion agent. A solvent comprising… ▽ More We introduce a model gel system in which colloidal forces, structure, and rheology are measured by balancing the requirements of rheological and microscopy techniques with those of optical tweezers. Sterically stabilized poly(methyl methacrylate) (PMMA) colloids are suspended in cyclohexane (CH) and cyclohexyl bromide (CHB) with dilute polystyrene serving as a depletion agent. A solvent comprising of 37% weight fraction CH provides sufficient refractive index contrast to enable optical trapping, while maintaining good confocal imaging quality and minimal sedimentation effects on the bulk rheology. At this condition, and at a depletant concentration c = 8.64 mg/mL (c/c* = 0.81), results from optical trapping show that 50% of bonds rupture at 3.3 pN. The linear strain-dependent elastic modulus of the corresponding gel (volume fraction = 0.20) is G' = 1.8 Pa, and the mean contact number of the particles in the gel structure is 5.4. These structural and rheological parameters are similar to colloidal gels that are weakly aggregating and cluster-like. Thus, the model gel yields a concomitant characterization of the interparticle forces, microstructure, and bulk rheology in a single experimental system, thereby introducing the simultaneous comparison of these experimental measures to models and simulations. △ Less

Submitted 30 December, 2013; originally announced January 2014.

Experimental Studies of Low-field Landau Quantization in Two-dimensional Electron Systems in GaAs/AlGaAs Heterostructures

Authors: Jing-Han Chen, D. R. Hang, C. F. Huang, Tsai-Yu Huang, Jyun-Ying Lin, S. H. Lo, J. C. Hsiao, Ming-Gu Lin, M. Y. Simmons, D. A. Ritchie, C. -T. Liang

Abstract: By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems, we study the low-field Landau quantization when the thermal damping is reduced with decreasing the temperature. Magneto-oscillations following Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results sho… ▽ More By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems, we study the low-field Landau quantization when the thermal damping is reduced with decreasing the temperature. Magneto-oscillations following Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results show the importance of the positive magneto-resistance to the extension of SdH formula under the damping induced by the disorder. △ Less

Submitted 29 October, 2006; originally announced October 2006.

Comments: 9 pages, 3 figures

Journal ref: J. Korean Phys. Soc. 50, 776 (2007).

From semiclassical transport to quantum Hall effect under low-field Landau quantization

Authors: D. R. Hang, C. F. Huang, Y. W. Zhang, H. D. Yeh, J. C. Hsiao, H. L. Pang

Abstract: The crossover from the semiclassical transport to quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the S… ▽ More The crossover from the semiclassical transport to quantum Hall effect is studied by examining a two-dimensional electron system in an AlGaAs/GaAs heterostructure. By probing the magneto-oscillations, it is shown that the semiclassical Shubnikov-de Haas (SdH) formulation can be valid even when the minima of the longitudinal resistivity approach zero. The extension of the applicable range of the SdH theory could be due to the damping effects resulting from disorder and temperature. Moreover, we observed plateau-plateau transition like behavior with such an extension. From our study, it is important to include the positive magnetoresistance to refine the SdH theory. △ Less

Submitted 17 August, 2006; originally announced August 2006.

Comments: 11 pages, 5 figures

Journal ref: Solid State Communications 141, 17 (2007).

Characterizations of strain and defect free GaN nanorods on Si(111) substrates

Authors: H. W. Seo, Q. Y. Chen, M. N. Iliev, W. K. Chu, L. W. Tu, C. L. Hsiao, James K. Meen

Abstract: GaN-nanorods grown on Si(111) substrates are found strain- and defect-free as characterized by micro Raman spectroscopy, secondary electron (SE) and cathode-luminescence (CL) imaging. The matrix supporting the nanorods bears the brunt of all strains, strain-relaxations, and defect generations, giving the nanorods an ideal environment to grow to perfection. Photo-excitations by the Raman laser so… ▽ More GaN-nanorods grown on Si(111) substrates are found strain- and defect-free as characterized by micro Raman spectroscopy, secondary electron (SE) and cathode-luminescence (CL) imaging. The matrix supporting the nanorods bears the brunt of all strains, strain-relaxations, and defect generations, giving the nanorods an ideal environment to grow to perfection. Photo-excitations by the Raman laser source and electron irradiation during CL imaging lead to an increase of non-equilibrium electrons, suggesting an effective approach to photo-emitting or field emitting device applications. The nanorods, largely isolated from but perfectly aligned with the sustaining matrix, are grown in excellent epitaxy with the Si substrates. △ Less

Submitted 8 March, 2005; originally announced March 2005.

Epitaxial GaN Nanorods via Catalytic Capillary Condensation

Authors: H. W. Seo, Q. Y. Chen, L. W. Tu, C. L. Hsiao, M. N. Iliev, W. K. Chu

Abstract: Intrinsic catalytic process by capillary condensation of Ga-atoms into nanotrenches, formed among impinging islands during the wurzite-GaN thin film deposition, is shown to be an effective path to growing GaN nanorods without metal catalysts. The nano-capillary brings within it a huge imbalance in equilibrium partial pressure of Ga relative to the growth ambient. GaN nanorods thus always grow ou… ▽ More Intrinsic catalytic process by capillary condensation of Ga-atoms into nanotrenches, formed among impinging islands during the wurzite-GaN thin film deposition, is shown to be an effective path to growing GaN nanorods without metal catalysts. The nano-capillary brings within it a huge imbalance in equilibrium partial pressure of Ga relative to the growth ambient. GaN nanorods thus always grow out of a holding nanotrench and conform to the boundaries of surrounding islands. The nanorods are epitaxially orientated with <0001>GaN // <111>Si and <2110>GaN // <110>Si similar to the matrix. Concaved geometry is essential and is a condition that limits the axial dimension of the nanorods protruding above the base (matrix) material region. Revelation of the growth mechanism in the current context suggests that fabrication of nano quantum structures with controlled patterns is enabling for any attainable dimensions △ Less

Submitted 8 March, 2005; originally announced March 2005.