Raman Spectroscopy of Optical Transitions and Vibrational Energies of ∼1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes

Spencer, Joseph H.; Nesbitt, John M.; Trewhitt, Harrison; Kashtiban, Reza J.; Bell, Gavin R.; Ivanov, V. Yu.; Faulques, Eric; Sloan, Jeremy; Smith, David C.

doi:10.1021/nn5023632

Cited by 41 publications

(48 citation statements)

References 49 publications

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“…15 The samples were then fully characterised using HRTEM to ensure that no extraneous HgTe remained and determine the atomic structure of the filling structures. 15,16 Inspection of more than 100 SWCNTs from the supplied sample by HRTEM revealed that the significant majority (~85%) fall within a limited diameter range of 1.2-1.6nm and that more than 50% of these SWCNTs were observed with filling. All of the nanotubes observed with filling within this diameter range were found to correspond to the novel tubular form of HgTe.…”

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Coherence lifetime broadened optical transitions in a 2 atom diameter HgTe nanowire: a temperature dependent resonance Raman study

et al. 2016

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This paper presents the results of measurements of the temperature dependence of resonance Raman scattering from 2 atom diameter HgTe nanowires embedded in the central pore of single walled carbon nanotubes, over the temperature range 4-295K and excitation photon energies in the range 1.65 to 1.90 eV. The spectra are analysed to extract the temperature dependence of the phonon energies and linewidths and the central energy, linewidth and peak scattering strength of the optical resonances. The temperature dependence of the peak scattering strength is explained by a model in which the resonance broadening is dominated by coherence lifetime broadening, allowing us to determine the coherence lifetime of the underlying optical transition: 9fs at 295K and 18fs at 50K. The results are comparable with similar results on carbon nanotubes which suggests that the optical transitions responsible for the Raman resonances are excitonic.

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Coherence lifetime broadened optical transitions in a 2 atom diameter HgTe nanowire: a temperature dependent resonance Raman study

et al. 2016

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“…The images throughout Figure 1A-F, depict low dimensional, confined HgTe extreme nanowires, with a diameter of ~1 nm, whose microstructure corresponds to the form discussed in ref 14 . Representative images of bundles and discrete tubes are presented in Figure 1D.…”

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confidence: 56%

“…The final key indicator that specific Raman features are associated with nanowires rather than nanoparticles or lumps of the parent material is a characteristic polarization dependence like that shown in Figure 3. As discussed in more detail in reference 14 the Raman scattering from an ensemble of randomly oriented 1D systems is preferentially polarized in the same direction as the exciting laser light with a contrast ratio of 3:1 and thus shows the characteristic figure of eight shape present in the optimum results shown in Figure 3. It is important to test that preferred emission direction rotates with the excitation polarization, as shown in Figure 3, as polarized Raman due to other mechanisms is not uncommon.…”

Section: Representative Resultsmentioning

confidence: 91%

“…The detailed attribution and interpretation of the HgTe Raman spectra are set out in reference 14 . It should be noted that strong multiple phonon Raman is a common feature of II-IV materials, such as HgTe, and not necessarily a feature of all extreme nanowire samples.…”

Section: Representative Resultsmentioning

confidence: 99%

“…It should be noted that strong multiple phonon Raman is a common feature of II-IV materials, such as HgTe, and not necessarily a feature of all extreme nanowire samples. In addition to the nanowire features the Raman spectra also contain one carbon nanotube Raman feature; predominantly due to a Radial Breathing Mode observed at 168 cm -1 whose resonant energy of 1.67 eV 14 is clearly different from the resonance energies of the filling Raman features (Figure 4). The host tube Raman features can be clearly identified from Raman spectra of the pure nanotubes used for filling.…”

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confidence: 99%

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Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

Smith

Spencer

Sloan

et al. 2016

JoVE

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This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

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Extreme Nanowires: The Smallest Crystals in the Smallest Nanotubes

Sloan¹,

Kashtiban²,

Marks³

et al. 2016

European Microscopy Congress 2016: Proceedings

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A logical extension to fabrication of monolayer 2D materials such as graphene is creation of ‘Extreme Nanowires’ (i.e. Fig. 1), down to a single atom column in width.[1,2] In this limit, crystals have fundamentally different physical characteristics and properties.[3‐5] We and others have created atomically regulated nanowires by confining them within the smallest diameter carbon nanotubes (i.e. either single walled carbon nanotubes (SWNTs) or double walled carbon nanotubes (DWNTs)), and are investigating their structural and electronic properties. These materials also provide an ultimate benchmark for testing the most sensitive characterisation methodologies which, when corroborated with suitable theory, will provide new data on physics at the most fundamental length scale accessible to nanomaterials fabrication. The most powerful investigative tools for structural investigation are aberraton‐corrected Transmission Electron Microscopy (ac‐TEM) and Scanning Transmission Electron Microscopy (ac‐STEM) and, here, we describe the application of these methods to a variety of Extreme Nanowire systems. One of the most crucial aspects of the role of electron microscopy in our investigation is the 2D and 3D elucidation of the structure of quasi‐ or true 1D nanowires formed in SWNTs as these form the primary source of information for density functional theory (DFT) and other ab initio theoretical approaches to both structure and properties elucidation. When combined with real physical measurements, this combined approach becomes even more powerful as we can start to piece together how the fundamental physics of a crystalline nanowire changes once we constrain its width down to one or two atoms in cross section. For example we recently record Raman Spectra from 2x2 atom thick HgTe nanowires embedded within 1.2‐1.4 nm SWNTs[4] and found that we are able to model the Raman‐measured lattice phonons of this system based on a simple structural model previously determined from two pairs of Exit Wave Reconstruction images which we also used to make DFT predictions about the altered electronic structure of this system which is predicted to change from a ‐0.3 eV semi‐metal to a ~1.2 eV band gap semiconductor.[3] Following on from the exciting recent work of Senga et al.[2] who imaged the first true 1D crystals of CsI in DWNTs we are now modeling single atomic chain coils of tellurium formed within narrow SWNTs (Fig. 2).[6]

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Raman Spectroscopy of Optical Transitions and Vibrational Energies of ∼1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes

Cited by 41 publications

References 49 publications

Coherence lifetime broadened optical transitions in a 2 atom diameter HgTe nanowire: a temperature dependent resonance Raman study

Coherence lifetime broadened optical transitions in a 2 atom diameter HgTe nanowire: a temperature dependent resonance Raman study

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

Extreme Nanowires: The Smallest Crystals in the Smallest Nanotubes

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