Switchable Assembly of Ultra Narrow CdS Nanowires and Nanorods

Acharya, Somobrata; Patla, Israel; Kost, Joseph; Efrima, Shlomo; Golan, Yuval

doi:10.1021/ja062404i

Cited by 79 publications

(77 citation statements)

References 19 publications

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“…The polarization perpendicular to the long axis of the ordered rods is in contrast to the polarization behavior observed previously for InP wires, [1] WZ CdS nanorods and wires, [13] WZ CdSe nanorods; [7,14,15] and several other semiconductor nanoparticles, which all appear to exhibit strong polarization along the major axis of the wires/rods. However, a mixed behavior in polarization has been reported for CdSe quantum dots as a result of the presence of an optical "dark axis".…”

contrasting

confidence: 99%

“…It is important to emphasize that, using the same experimental setup, we have measured parallel polarization for WZ CdS nanorods and nanowires that were similarly suspended in toluene. [13] Hence, the results reported here for WZ ZnSe are unlikely to be attributable to artifacts related to the experimental measurement system. Practical application of devices based on 1D nanoparticles requires intrinsic large-scale production of ordered assemblies.…”

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confidence: 67%

“…It appears that this stringlike ordering is associated with the c-axis of the noncentrosymmetric WZ structure being oriented along the major axis of the rods (and eventually of the strings). [10][11][12][13] WZ ZnSe is intrinsically anisotropic and has a unique c-axis, along which closely packed layers of Zn and Se are alternately stacked. Thus, along this direction the crystal will always be terminated with a Zn 2+ plane at one end and a Se 2-plane at the other, implying a chemical bipolarity.…”

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Polarization Properties and Switchable Assembly of Ultranarrow ZnSe Nanorods

et al. 2007

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Size-and shape-dependent optical properties of 1D semiconductor nanoparticles and their 2D or 3D assembly holds great promise in nanoscale optoelectronics. [1,2] The 1D nanoparticles are intrinsically asymmetric, suggesting unique structures, assembly, and properties. Assembly into collective structures with well-defined orientation of the particles could display a variety of interesting properties, whereas in a large assembly of asymmetric nanoparticles, random orientations of individual nanoparticles may inhibit the inherent properties of the collective behavior. An external field can be used to overcome energy barriers underpinning the random orientation in order to achieve a system revealing the inherent properties of the individual nanoparticles. The crystallographic phase of 1D nanoparticles has considerable importance in determining the inherent polarization properties that underlie their assembly. Zinc selenide, an important wide-bandgap (2.7 eV) material with a broad range of potential applications, [3,4] can exist in the hexagonal (wurtzite, WZ) or the cubic (sphalerite, zinc blende, ZB) phase (crystal structure). Recently, we reported uniform ZnSe nanorods and nanowires of ultranarrow width (1.3 nm), and their assembly into highly ordered 2D arrays with ultrahigh junction densities of ca. 6610 4 lm 2 . [5,6] In this Communication, we relate the crystallographic phase and shape to the optical polarization properties upon application of an electric field to a large-scale nanorod assembly (microstrings). We demonstrate that changes in the crystallographic phase, from WZ to ZB, are accompanied by a sharp transition in the polarization-dependent optical properties of the nanorods. Interestingly, while all previously reported works suggested optically active 1D semiconductors to be polarized along their long (c-)axis, [1,7,8] we notably show perpendicular polarization behavior in fluorescence emission when 1.3 nm wide WZ nanorods are aligned by an electric field into centimeter-long microstrings. Synthesis of shape-and phase-controlled nanorods was carried out by addition of relatively innocuous zinc acetate and selenourea precursors to controlled ratios of liganding solvents of octadecylamine (ODA) and trioctylphosphine oxide (TOPO) in the temperature range 140-220°C.[5,9] Nanoparticle shape (aspect ratio) and size could be changed from spherical to elongated particles by increasing the molar ratio of ODA in the mixed solvent.[9]Transmission electron microscopy (TEM) images of highly ordered rods prepared in pure ODA and random rods prepared in a 2:3 TOPO/ODA solvent are shown in Figure 1a and b, respectively. Notably, the width and length of the ordered rods are 1.3 and 4.5 nm, respectively, while the dimensions of random rods are significantly larger, ca. 4 nm wide and 15-40 nm long. Energy dispersive spectroscopy (EDS) analysis confirmed the 1:1 atomic ratio of Zn to Se, as expected for a stoichiometric ZnSe crystal (see Fig. S1 in the Supporting Information). The powder X-ray diffraction (XRD) patterns ...

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confidence: 67%

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Polarization Properties and Switchable Assembly of Ultranarrow ZnSe Nanorods

et al. 2007

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“…On the other hand, elongated anisotropic nanomaterials possessing an inherent permanent dipole moment respond dramatically in an applied field, facilitating alignment along the direction of the field. [15,16] Anisotropic nanomaterials of proper dimensions coupled locally with the LC director field in a favorable energetic configuration should enhance long-range ordering and device performance. Additionally, the optical properties of the nanocrystals can be tuned by varying the size and shape of the nanocrystals, a feature which is useful for generating a range of spectral behaviors.…”

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confidence: 99%

Nanorod‐Driven Orientational Control of Liquid Crystal for Polarization‐Tailored Electro‐Optic Devices

et al. 2009

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Liquid-crystal display (LCD) devices are indispensable elements of modern life because of the ubiquity of their applications from wristwatch to personal-computer displays. Control over the longrange orientational order of the liquid crystal (LC) is critical for obtaining superior optical switching and display-device performance. [1][2][3][4][5][6][7] However, control of long-range alignment of LCs remains challenging because of the formation of unaligned dislocation regions, which is detrimental to LC device performance. Long-range alignment has been attempted by a variety of methods, including using alignment layers, modification of the LC cells, or using the interaction between nanosized aggregates of LC molecules. [7][8][9][10] Dispersion of nanoparticles as active-matrix components in LCs has been investigated to achieve long-range alignment, large scale orientation manipulation, and for faster switching speeds of LC devices. [10][11][12][13][14] However, incorporation of nanomaterials into an LC matrix gives rise to topological defects, due to deformations of the director field about the surface of the colloid species, breaking the continuous symmetry of the blend. [6,10,[12][13][14] For incorporation of nanomaterials in an LC matrix, the proper selection of size, shape, and crystallographic phase of the nanomaterials is critical for enhancing the performance of the blend. For example, spherical particles or centrosymmetric materials are less responsive to external fields, and tend to not form long-range ordered structures. On the other hand, elongated anisotropic nanomaterials possessing an inherent permanent dipole moment respond dramatically in an applied field, facilitating alignment along the direction of the field. [15,16] Anisotropic nanomaterials of proper dimensions coupled locally with the LC director field in a favorable energetic configuration should enhance long-range ordering and device performance. Additionally, the optical properties of the nanocrystals can be tuned by varying the size and shape of the nanocrystals, a feature which is useful for generating a range of spectral behaviors. [17,18] Anisotropic nanomaterials with ''parallel'' optical polarization axes have been used in attempts to control the state of polarization and viewing angle of LCs. [17][18][19] However, the parallel polarization axis coincides with the LC orientational order, thus restraining the viewing angle and contrast ratios to be tailored over wide angles. Moreover, the larger size of these materials limits device performance, requiring, in particular, higher operating voltages. Here, we show that dispersion of ultranarrow ZnS nanorods encapsulated by a fluid-like soft organic layer in the nematic LC ZLI-4792 results in a novel softmatter-type blend, with previously unachieved and robust electrooptic properties. The ultrasmall nanorods possess a strong inherent dipole moment, and show excellent miscibility in the LC host, forming well-organized locally aligned arrays. This local ordering affects significantly the glo...

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“…The measured PL ratio, ρ, is around 0.80-0.85 indicating very good polarization anisotropy for CdS nanowires. The highest polarization ratio observed previously for CdS nanowires is only 0.78 (Acharya, Patla, Kost, Efrima, & Golan, 2006;Robert et al, 2014. These nanowire arrays can be used as optical switches as a result of their polarization anisotropy properties.…”

Section: Resultsmentioning

confidence: 77%

Photoluminescence Characterization of Cadmium Sulphide (CdS) Nanowires for Polarization Studies

Poduri

Dutta²,

Stroscio³

2017

APR

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In this paper, the polarizing properties for CdS nanowire arrays were explored for their potential use in the design of nanowire based polarizers and optical switches. These free standing cadmium sulphide (CdS) nanowires were grown in anodized aluminum oxide (AAO) template via dc electrodeposition. Raman and photoluminescence (PL) measurements were investigated for parallel and perpendicular polarization with two orientations of the sample having light propagating parallel to the nanowire axis in one orientation and light propagating perpendicular to the nanowire axis in other orientation. Polarization-sensitive measurements show strong polarization anisotropy in the photoluminescence (PL) intensity measurements observed in parallel and perpendicular orientation to the long axis of a nanowire. The measured PL ratio, ρ, for parallel to perpendicular orientation was around 0.80-0.85 which shows strong polarization anisotropy for the grown CdS nanowires. Strong peaks of A1 (TO) at 235 cm of the CdS nanowires were seen with different polarizations for Raman spectral studies. These polarization studies show that these dc electrodeposited grown CdS nanowire arrays are well suited for uses in polarization-based nanoscale devices such as in optical switches, and high performance photodetectors.

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Switchable Assembly of Ultra Narrow CdS Nanowires and Nanorods

Cited by 79 publications

References 19 publications

Polarization Properties and Switchable Assembly of Ultranarrow ZnSe Nanorods

Polarization Properties and Switchable Assembly of Ultranarrow ZnSe Nanorods

Nanorod‐Driven Orientational Control of Liquid Crystal for Polarization‐Tailored Electro‐Optic Devices

Photoluminescence Characterization of Cadmium Sulphide (CdS) Nanowires for Polarization Studies

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