Advanced optical materials: tellurium nanowires -- one dimensional van der Waals force material with strong nonlinear optical response and anisotropy
As a single element semiconductor with excellent piezoelectric thermoelectric photoelectric properties
tellurium (TE) is widely used in energy optoelectronic devices. Recent studies have also shown that tellurium has attractive topological properties such as transition from ordinary semiconductors to strong topological insulators the existence of multiple wail nodes near its Fermi level. On the other h because tellurium is formed by relatively weak van der Waals interaction between its one-dimensional helical chains one-dimensional two-dimensional tellurium nanomaterials with quantum confinement effect can be synthesized to obtain some more interesting electronic optical mechanical properties. For example when the thickness of tellurium thin film is reduced to nanometer level n-type p-type high carrier mobility can be achieved simultaneously with the value as high as thouss of cm2v-1s-1; this also makes it a unique material system to realize quantum transport under quantum confinement realize quantum Hall effect. Although the optical properties of tellurium nanomaterials such as optical absorption optical radiation Raman scattering have been studied the nonlinear optical effects of tellurium nanomaterials are rarely reported. So can the unique electronic transport properties of te nanomaterials provide attractive nonlinear optical responses can these responses further exp the functions of devices?
Gan Xuetao School of physical science technology Northwest University of technology China his collaborators have carried out systematic research on the second third harmonic generation of tellurium nanowires prepared by chemical vapor deposition. The experimental results reveal that te nanowires have strong unique anisotropic nonlinear optical response. There are one-dimensional spiral chains of tellurium atoms in the crystal structure of
there is only relatively weak van der Waals force between these spiral chains. There are lone pair electrons around the tellurium helix chain which makes it easy for the electric field of external pump light to induce Dipole Oscillation in tellurium nanowires. When the pump light power is high it shows strong nonlinear optical response. In the experiment we compare tellurium nanowires with III-V II-VI compound semiconductor nanowires such as zinc oxide indium phosphide aluminum gallium arsenic. The results show that the secondary tertiary harmonics of te nanowires are 2-3 orders of magnitude higher than those in III-V or II-VI nanowires. The second-order nonlinear coefficient of te nanowires is 1.25 × 104 PM / V which is four orders of magnitude higher than that of ZnO nanowires. Generally speaking because the diameter of nanowires is only 100 nm the interaction distance between nanowires light is short so the nonlinear effect of nanowires needs to be realized by pulsed laser with high peak power which needs to consider the complex problem of pulse synchronization. Due to the extremely high second-order nonlinear effect of te nanowires the second harmonic generation of te nanowires can be pumped by CW laser the problem of pulse synchronization in pulsed laser is avoided which makes it possible to realize the neutralization process of te nanowires. On the other h
are also due to the fact that tellurium nanowires are composed of helix chains of tellurium atoms arranged in parallel the second harmonic wave shows double symmetry. It only responds to the pump light whose polarization direction is perpendicular to the nanowires but has no response to the pump light whose polarization direction is parallel to the nanowires. The second harmonic polarization dependence of other nanowires (such as ZnO GaAs LiNbO3 etc.) is just the opposite. The polarization dependence of the third harmonic generation of te nanowires shows a distorted quadruple symmetry that is the two lobes perpendicular to the long axis of the nanowires are perfectly symmetrical while there is an octave twist angle along the long axis of the nanowires showing strong anisotropy. The strong anisotropic nonlinear optical response of
tellurium nanowires makes it possible to realize high efficiency polarization selective nanoscale wavelength converters all-optical switches electro-optic modulators other devices.
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