Tunable room-temperature single-photon emission at telecom wavelengths from sp 3 defects in carbon nanotubes

Transcription

1 In the format provided by the authors and unedited. Tunable room-temperature single-photon emission at telecom wavelengths from sp 3 defects in carbon nanotubes Xiaowei He 1, Nicolai F. Hartmann 1, Xuedan Ma 1, Younghee Kim 1, Rachelle Ihly 2, Jeffrey L. Blackburn 2, Weilu Gao 3, Junichiro Kono 3, Yohei Yomogida 4, Atsushi Hirano 5, Takeshi Tanaka 5, Hiromichi Kataura 5, Han Htoon 1, *, Stephen K. Doorn 1, * 1 Center for Integrated Nanotechnologies, Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A. 2 Chemical and Materials Science Center, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401, U.S.A. 3 Department of Electrical and Computer Engineering, Rice University, Houston, TX 77005, U.S.A. SUPPLEMENTARY INFORMATION DOI: /NPHOTON Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo , Japan. 5 Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki , Japan NATURE PHOTONICS Macmillan Publishers Limited, part of Springer Nature. All rights reserved.

2 a b Figure S1. (a) Room-T ensemble PL spectra of Cl 2 -Dz and MeO-Dz functionalized (6,5) (black and green trace, top), (7,5) (blue trace, middle), and (10,3) (red trace, bottom) SWCNTs in aqueous 1% DOC suspensions. Standard exciton (E 11 ) and defect-state (E 11 * and E 11 * - ) emission peaks are labeled. (b) Statistics of PL spectra for individual nanotubes in comparison to ensemble spectrum. An average spectrum (black trace) obtained as the sum of room-t PL spectra recorded from 30 individual 3,5-dichlorobenzene-functionalized (6,5) SWCNTs is compared to the solution ensemble PL spectrum for the source sample (overlaid in red).

3 S2. Synthetic tunability of aryl-diazonium dopants: spectra and reactivity. Beyond the enhanced PL stability and reaction control afforded by use of aryl diazonium functionalization, these agents also provide synthetic tunability over reactivity and defect-state emission wavelengths. 1 In addition to incorporation of 3,5-dichlorobenzenediazonium (Cl 2 -Dz) at defect sites, we have used 4-methoxybenzendiazonium (MeO-Dz) as a dopant. The more Figure S2. Representative room temperature PL spectra of single (6,5) SWCNT functionalized by MeO-Dz (a) and Cl 2 -Dz (b). All spectra are from DOC-wrapped SWCNT. Emission peaks appearing near 1000 nm are due to (6,5) E 11 exciton emission, while longer wavelengths originate from the aryl sp 3 defect states.

4 electron withdrawing nature of Cl 2 -Dz provides greater reactivity in comparison to MeO-Dz. The increased reactivity is an important factor in the dip-doping of the PFO-bpy-wrapped nanotubes (see Methods), in that we found MeO-Dz to be insufficiently reactive to functionalize the PFO-bpy-wrapped nanotubes. Furthermore, by choosing Cl 2 -Dz as a dopant, SPE crossing 1.3 µm is successfully realized on PFO-bpy-wrapped (6,5) nanotubes (see Fig. S2), which cannot be achieved with MeO-Dz or by simple oxygen doping. 2,3 In ensemble level spectra, variation of the aryl group functionality can tune defect-state emission wavelengths over 10s of mev. 1 In addition to the primary defect-state emission feature (E 11 *) occurring ~ mev to lower energy from E 11, (see Fig. S1a), an additional feature occurring mev lower can occur (E 11 * - ). This feature can thus extend the wavelength range over which a given dopant introduces emitting states. We note that the SPE behavior of MeO-Dz functionalized nanotubes are found to be similar to those of the Cl 2 -Dz examples (see below, Section S5), demonstrating the generality of this type of functionalization for obtaining single photon emission (SPE). Shown in Fig. S2 are typical PL spectra of individual (6,5) SWCNT functionalized by these two aryl diazonium species. 70% of the PL spectra (out of 60 nanotubes checked for each dopant) show single defect-state emission peaks. SPE is observed only for individual SWCNT displaying a single defect-state emission peak (see also main text Fig. 3a). The peak position and intensity can vary from tube-to-tube. While E 11 exciton emission is centered at 1000 nm, the defect-state peaks are red-shifted and distributed over a broad wavelength range. The reddest extension of the wavelength range is different for the two dopants. For MeO-Dz functionalized (6,5) SWCNT, the longest wavelength we observe is around 1290 nm, while it is ~1310 nm for Cl 2 -Dz functionalized (6,5) SWCNT.

5 Figure S3. Defect-state PL intensity saturation behavior. Single-tube defect-state emission intensity is shown as a function of pump power for an example individual (6,5) SWCNT emitting at 1240 nm. Data is for pulsed excitation at 854 nm. PL saturation onset occurs at ~1.5 µw in this case. The orange region highlights the typical incident power range over which g (2) and intensity time-trace data is obtained (1.5-2 µw).

6 S4. The determination of g 2 (0) Our g (2) (0) values are determined as the ratio of the center-peak area normalized to the side peaks at times >330ns, as shown in Fig. S4-1. Performing this ratio at long times avoids underevaluation of g (2) (0) when taking the ratio at short times at which minor photon bunching is found for early-time side peaks, which decays to an average uniform value at long times (> 330 ns). Fig. S4-2 shows the full g (2) traces of Fig. 2 of the main text. Figure S4-1. (a) Full g (2) trace of DOC wrapped (6,5) tubes doped by Cl 2 -Daz and emitting at ~1.25 µm. (b) a magnification of the central part of (a) around t =0, and g (2) (0) is indicated by the black curve at the zero delay time.

7 Figure S4-2. (a-c) Full g (2) traces of Fig.2b, f, and j in the main text, respectively. As suggested by single-tube PL studies at cryogenic temperatures, 4 the short-time bunching signatures demonstrated in Figs. S4-1 and S4-2 likely arise from blinking and spectral wandering that occur on short timescales. Such behavior may arise from local charging induced by perturbation of the electrostatic environment caused by the aryl defects. While this effect is minimized for the aryl defects in comparison to that introduced by oxygen functionalization (see main text), it is still present to some degree. 5 The decay time of the bunching behavior illustrated in Fig. S4 reflects the timescale of the PL fluctuations: tens of nanoseconds.

8 S5. Additional optical data sets at different defect-state emission wavelengths under pulsed excitation. Photon-correlation measurements were peformend in the wavelength range from 1.14 to 1.55 µm on three species of CNTs ((6,5), (7,5), (10,3)), using Cl 2 -Dz and MeO-Dz as dopants, at room-t and ambient condition. For (10,3) samples, because of the low combined collection and detection efficiency of the microscope and detector system at wavelengths around 1.5 µm (see Supplementary Section S7), some g (2) (0) measurements were done at 220K (for emission wavelengths of µm) to get sufficiently high signal for these longest emission wavelengths. At both room temperature and 220K, high single-photon purities are obtained, as shown in Fig. S5t and S5x. Figure S5. (Continued below.)

9 Figure S5. Additional representative PL spectra ( a, e, i, m, q, u) (likely band origin of the defect-state emission is labeled, based on relative position with respect to the E 11 * and E 11 * - positions shown in Fig. S1a), PL time traces with corresponding σσ QQQQ σσ SSSS values (b, f, j, n, r, v),

10 PL decay curves (c, g, k, o, s, w) and g (2) traces (d, h, l, p, t, x) of individual tubes with defectstate emission at different wavelength. All the time traces were fitted with Gaussian functions (red curves). All the lifetime curves were fitted with double exponential functions (black curves) in a reconvolution mode and the values of lifetime are highlighted. Instrument response function is also shown in (c) (gray curve). S6. g (2) (t) measurement under continuous wave excitation. Photon correlation measurements were performed on Cl 2 -Dz-functionalized (6,5) SWCNT with CW excitation at 5 µw of incident power. Under continuous wave (CW) excitation, the emission rate is normally larger than that under pulsed excitation at comparable excitation power. As shown in Fig. S6, stable and high emission rates (~ 15 khz) and complete photonantibunching (g (2) (0) ~0) are obtained at room temperature. Figure S6. (a) Defect-state PL spectrum, (b) PL time trace and (c) photon antibunching properties of a DOC-wrapped Cl 2 -Dz-functionalized (6,5) SWCNT under CW excitation (854 nm) at room temperature.

11 S7. Data collection efficiency and quantum efficiency. We measured the photon collection efficiency of our microscope system in order to estimate the quantum efficiency of the SWCNT single-photon emitters. While operating our excitation laser at 900 nm, it was coupled into the system and focused on a gold substrate through the microscope objective. The laser beam was reflected by the substrate (with reflective losses being near-zero) and passed through exactly the same collection light path as experienced by the sample PL emission (note that the original long pass filter used to block the excitation beam was removed for this measurement). The laser power was measured at the substrate and before the detector, with the ratio giving a collection efficiency around 0.2%, including losses from the microscope objective, beam splitter, mirrors and fiber coupling. Accounting for a detector efficiency of ~ 25%, we arrive at a combined collection and detection efficiency of ~ 0.05%. Given the measured count rate under pulsed excitation of ~ 6 khz for a PFO-bpy wrapped (6,5) tube, a corrected emission rate is obtained of around 12 MHz. Taking into account the laser repetition rate of 89 MHz, the quantum efficiency for single photon emission is then estimated as ~13.4% We also estimate a quantum efficiency for defect-state emission under CW excitation for PFO-bpy-wrapped (6,5) nanotubes emitting around 1300 nm. Defect-state emission intensity observed under varying CW excitation powers is shown in Fig. S7. A count rate of ~120 khz is observed in the saturation region. Using our determined photon collection/detection efficiency of 0.05%, we arrive at a corrected emission rate of 200 MHz. As a conservative estimate, using our longest measured emission lifetime of ~ 0.6 ns, the quantum efficiency for single photon emission is then estimated as ~ 11.9%, which is consistent with the result obtained for pulsed excitation. Figure S7. PL emission saturation measurement of PFO-bpy wrapped (6,5) single tubes under CW excitation at room temperature.

12 S8. Substrate effects on functionalized and unfunctionalized (6,5) SWCNT PL spectra. Unfunctionalized (6,5) SWCNTs, and those functionalized by 3,5-dichlorobenzene diazonium (Cl 2 -Dz), were deposited from aqueous 1% DOC suspensions onto bare glass substrates and those coated with a thin layer of polystyrene (PS) (~160nm), with equivalent deposition volumes onto each substrate. Wide-field photoluminescence (PL) images and ensemble spectra are then compared (Fig. S8). Spectra are obtained by performing wide-field excitation while collecting all PL from the illuminated area into our spectrometer system. Images and spectra of functionalized SWCNT on the glass coverslip show significantly lower PL intensities than those deposited on the polystyrene-coated substrates. Figure S8. Wide field image (middle, top-to-bottom, with image area of 50 X 50 µm) and ensemble PL spectrum (bottom) of unfunctionalized (6,5) SWCNT on glass cover slip (a), wide field images and ensemble PL spectra of Cl 2 -Dz functionalized (6,5) SWCNT on glass cover slip (b) and on polystyrene (c).

13 S9. Defect-state emission linewidth distributions for DOC and PFO-bpy-wrapped (6,5) SWCNT. Emission peak linewidths are weakly sensitive to the SWCNT wrapping environment at room temperature, with PFO-bpy-wrapped (6,5) samples having slightly narrower linewidths compared to DOC wrapped ones at room temperature. Shown in Fig. S9 are histograms of observed defect-state emission linewidths (for emission peaks between 1.1 to 1.3 µm), obtained from fifty DOC and PFO-bpy wrapped (6,5) SWCNT, each functionalized with Cl 2 -Dz. Average linewidths are 33 mev (DOC wrapping) and 29 mev (PFO-bpy wrapping). Figure S9. Histograms of defect-state emission linewidths for 50 individual Cl2-Dz functionalized (6, 5) SWCNT wrapped by DOC (a) and PFO-bpy (b). Supplementary References 1. Piao, Y.; Meany, B.; Powell, L. R.; Valley, N.; Kwon, H.; Schatz, G. C.; Wang, Y. Brightening of carbon nanotube photoluminescence through the incorporation of sp 3 defects. Nature Chem. 5, (2013). 2. Ma, X.; Hartmann, N. F.; Baldwin, J. K. S.; Doorn, S. K.; Htoon, H. Room-temperature single-photon generation from solitary dopants of carbon nanotubes. Nature Nanotech. 10, (2015). 3. Ma, X.; Adamska, L.; Yamaguchi, H.; Yalcin, S. E.; Tretiak, S.; Doorn, S. K.; Htoon, H. Electronic structure and chemical nature of oxygen dopant states in carbon nanotubes. ACS Nano 8, (2014). 4. Walden-Newman, W.; Sarpkaya, I. & Strauf, S. Quantum light signatures and nanosecond spectral diffusion from cavity-embedded carbon nanotubes. Nano Lett. 12, (2012). 5. Hartmann, N. F.; Yalcin, S. E.; Adamska, L.; Hároz, E. H.; Ma, X.; Tretiak, S.; Htoon, H. & Doorn, S. K. Photoluminescence imaging of solitary dopant sites in covalently doped singlewall carbon nanotubes. Nanoscale 7, (2015).