Template‐Assisted Large‐Scale Ordered Arrays of ZnO Pillars for Optical and Piezoelectric Applications

Fan, Hong Jin; Lee, Woo; Hauschild, Robert; Alexe, Marin; Rhun, G. Le; Scholz, Roland; Dadgar, A.; Nielsch, Kornelius; Kalt, H.; Krost, A.; Zacharias, Margit; Gösele, U.

doi:10.1002/smll.200500331

Cited by 219 publications

(184 citation statements)

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“…In general, previous reports have observed high quality ZnO nanowire array growth on sputtered seed layers [26][27][28] but array quality is inconsistent for nanowires grown on spincoated seed layers [29,30]. Nanowire array engineering for PV device, piezoelectric [31] and field-emitter [32] applications will require quantitative study of the effect of processing conditions on array properties, specifically on branching (multiple nanowires growing from a single template hole) and on nanowire alignment. Here, we focus on controlling the branching and alignment of ZnO nanowire arrays fabricated by electron-beam lithography (EBL) and hydrothermal synthesis at the length scales that are relevant for nanowire-based QD PV devices.…”

Section: Introductionmentioning

confidence: 99%

Control of zinc oxide nanowire array properties with electron-beam lithography templating for photovoltaic applications

et al. 2015

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Hydrothermally synthesized zinc oxide nanowire arrays have been used as nanostructured acceptors in emerging photovoltaic (PV) devices. The nanoscale dimensions of such arrays allow for enhanced charge extraction from PV active layers, but the device performance critically depends on the nanowire array pitch and alignment. In this study, we templated hydrothermally-grown ZnO nanowire arrays via high-resolution electron-beam-lithography defined masks, achieving the dual requirements of high-resolution patterning at a pitch of several hundred nanometers, while maintaining hole sizes small enough to control nanowire array morphology. We investigated several process conditions, including the effect of annealing sputtered and spincoated ZnO seed layers on nanowire growth, to optimize array property metrics -branching from individual template holes and off-normal alignment. We found that decreasing template hole size decreased branching prevalence but also reduced alignment. Annealing seed layers typically improved alignment, and sputtered seed layers yielded nanowire arrays superior to spincoated seed layers. We show that these effects arose from variation in the size of the template holes relative to the ZnO grain size in the seed layer.The quantitative control of branching and alignment of the nanowire array that is achieved in this study will open new paths toward engineering more efficient electrodes to increase photocurrent in nanostructured PVs. This control is also applicable to inorganic nanowire growth in general, nanomechanical generators, nanowire transistors, and surface-energy engineering.2

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Section: Introductionmentioning

confidence: 99%

Control of zinc oxide nanowire array properties with electron-beam lithography templating for photovoltaic applications

et al. 2015

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“…The effective piezoelectric coefficient of individual (0001) surface dominated ZnO nanobelts measured by piezoresponse force microscopy was found to be much larger than the value for bulk wurtzite ZnO [21]. In contrast, Fan et al showed that the piezoelectric coefficient for ZnO nanopillar with the diameter about 300 nm is smaller than the bulk values [22]. They suggested that the reduced electromechanical response might be due to structural defects in the pillars [22].…”

mentioning

confidence: 96%

“…In contrast, Fan et al showed that the piezoelectric coefficient for ZnO nanopillar with the diameter about 300 nm is smaller than the bulk values [22]. They suggested that the reduced electromechanical response might be due to structural defects in the pillars [22]. Whether the electromechanical coupling is enhanced or depressed in defect-free ZnO nanowires is not clear.…”

mentioning

confidence: 98%

Piezoelectricity in ZnO nanowires: A first-principles study

Xiang¹,

Yang²,

Hou³

et al. 2006

Applied Physics Letters

187

126

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Hexagonal [0001] nonpassivated ZnO nanowires are studied with density functional calculations. The band gap and Young's modulus in nanowires which are larger than those in bulk ZnO increase along with the decrease of the radius of nanowires. We find ZnO nanowires have larger effective piezoelectric constant than bulk ZnO due to their free boundary. In addition, the effective piezoelectric constant in small ZnO nanowires doesn't depend monotonously on the radius due to two competitive effects: elongation of the nanowires and increase of the ratio of surface atoms. Although many studies on ZnO nanowires have been conducted, there are some important issues remained to be addressed. First, the mechanical properties, especially the Young's modulus of ZnO nanowires are on debate in the literature [16,17,18,19,20]. For instance, Chen et al. [16] showed that the Young' modulus of ZnO nanowire with diameters smaller than about 120 nm is significantly higher than that of bulk ZnO. However, the elastic modulus of vertically aligned [0001] ZnO nanowires with an average diameter of 45 nm measured by atomic force microscopy was found to be far smaller than that of bulk ZnO[17]. The second issue is about the electromechanical coupling in ZnO nanowires. The effective piezoelectric coefficient of individual (0001) surface dominated ZnO nanobelts measured by piezoresponse force microscopy was found to be much larger than the value for bulk wurtzite ZnO [21]. In contrast, Fan et al. showed that the piezoelectric coefficient for ZnO nanopillar with the diameter about 300 nm is smaller than the bulk values [22]. They suggested that the reduced electromechanical response might be due to structural defects in the pillars [22]. Whether the electromechanical coupling is enhanced or depressed in defect-free ZnO nanowires is not clear. Thirdly, although it is well known that the quantum confinement effect will decrease the band gap of passivated nanowires, the question that how the dangling bond in bare ZnO nanowires affects the band gap remains open. The fundamental study on these issues is crucial for developing future applications of ZnO nanowires.In this letter, we have studied the electronic, mechanical, and piezoelectric properties of [0001] ZnO nanowires using first-principles methods for the first time. We find that the band gap increases along with the decrease of the radius of ZnO nanowires due to the radial confinement. The Young's modulus of nanowires is larger than bulk ZnO, in agreement with the experimental results of Chen et al. [16]. The effective piezoelectric constant in ZnO nanowires is larger than that of bulk ZnO due to the free boundary of nanowires. Moreover, the effective piezoelectric constant in small ZnO nanowires doesn't depend monotonously on the radius due to two competitive effects.Our calculations are performed using the SIESTA package[23], a standard Kohn-Sham density-functional program using norm-conserving pseudopotentials and numerical atomic orbitals as basis sets. The local density approximation (LD...

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“…[4][5][6] Experimental observations exhibit that, as the diameter of nanowires decreases, the Young's modulus of GaN and Si nanowires decreases, 7,8 while the Young's modulus of ZnO nanowires increases. 9 Theoretical simulations, including first principle calculations 10,11 and molecular dynamics ͑MD͒ simulations, [12][13][14][15][16][17] show that when the nanowire transverse dimension ͑or the diameter͒ decreases, Young's moduli of ͓100͔ Si, 10,11 ͓111͔ 2H-SiC, 12 ͓100͔ Ni, 13 ͓100͔ W, 14 …”

Section: Introductionmentioning

confidence: 99%

Size-dependent surface stress, surface stiffness, and Young’s modulus of hexagonal prism [111] β-SiC nanowires

Zhang

Luo

Chan

2008

Journal of Applied Physics

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The present work studies the size-dependent surface stress, surface stiffness, and Young's modulus of a prism crystalline nanowire, which is theoretically treated to be composed of a hypothetical nanowire phase, a true two-dimensional geometric surface phase, and a true one-dimensional geometric edge phase. The hypothetical nanowire phase could be elastically deformed due to relaxation of a free-standing nanowire, without any applied load, with respect to its bulk counterpart. The initially deformed nanowire phase is taken as reference in the present work in the determination of excess surface and edge energies. The theoretical results indicate that the edge phase causes the nominal specific surface energy, surface stress, and surface stiffness to be size dependent, and the surface phase and the edge phase make the nominal Young's modulus size dependent. The edge and surface effects are more significant as the cross-sectional area of a nanowire becomes smaller. Molecular dynamics simulations on hexagonal prism ͓111͔ ␤-SiC nanowires were conducted and the results verified the theoretical approach and illustrated the intrinsic mechanism of the size-dependent surface properties and Young's modulus of nanowires. The theoretical analysis and methodology are universal when the continuum concepts of surface energy, surface stress, and Young's modulus are used to characterize mechanical properties of nanowires.

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Template‐Assisted Large‐Scale Ordered Arrays of ZnO Pillars for Optical and Piezoelectric Applications

Cited by 219 publications

References 40 publications

Control of zinc oxide nanowire array properties with electron-beam lithography templating for photovoltaic applications

Control of zinc oxide nanowire array properties with electron-beam lithography templating for photovoltaic applications

Piezoelectricity in ZnO nanowires: A first-principles study

Size-dependent surface stress, surface stiffness, and Young’s modulus of hexagonal prism [111] β-SiC nanowires

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