From 357568e1fb77afed9dfa203e62da237bf7ce51b3 Mon Sep 17 00:00:00 2001 From: Blaise Thompson Date: Mon, 9 Apr 2018 00:24:18 -0500 Subject: 2018-04-09 00:24 --- PbSe_global_analysis/methods.tex | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) create mode 100644 PbSe_global_analysis/methods.tex (limited to 'PbSe_global_analysis/methods.tex') diff --git a/PbSe_global_analysis/methods.tex b/PbSe_global_analysis/methods.tex new file mode 100644 index 0000000..a62d590 --- /dev/null +++ b/PbSe_global_analysis/methods.tex @@ -0,0 +1,38 @@ +Quantum dot samples used in this study were synthesized using the hot injection method.\cite{Wehrenberg2002} +Samples were kept in a glovebox after synthesis and exposure to visible and UV light was minimized. +These conditions preserved the dots for several months. +Two samples, Batch A and Batch B, are presented in this study, in an effort to show the robustness of the results. +Properties of their optical characterization are shown in Table \ref{tab:QD_abs}. +The 1S band of Batch A is broader than Batch B, an effect which is usually attributed to a wider size distribution and therefore greater inhomogeneous broadening. + +\begin{table}[] + \centering + \caption{Batch Parameters extracted from absorption spectra. $\langle d \rangle$: average QD diameter, as inferred by the 1S transition energy. } + \label{tab:QD_abs} + \begin{tabular}{l|cc} + & A & B \\ + \hline + $ \omega_{10} \left( \text{cm}^{-1} \right)$ & 7570 & 6620 \\ + $ \text{FWHM} \left(\text{cm}^{-1}\right) $ & 780 & 540 \\ + $ \langle d \rangle \left(\text{nm}\right)$ & 4 & 4.8 \\ + $ \sigma_0 \left( \times 10^{16} \text{cm}^2 \right)$ & 1.7 & 2.9 + \end{tabular} +\end{table} + +The experimental system for the TG experiment has been previously explained.\cite{Kohler2014,Czech2015} +Briefly, two independently tunable OPAs are used to make pulses $E_1$ and $E_2$ with colors $\omega_1$ and $\omega_2$. +The third beam, $E_{2^\prime}$, is split off from $E_2$. The TG experiment utilized here uses temporally overlapped $E_2$ and $E_{2^\prime}$. +Previous ultrafast TG work has characterized the delay of $E_1$ as $\tau_{21}=\tau_2-\tau_1$; to connect the experimental space with the TA measurements, we will report the population delay time between the probe and the pump as $T(=-\tau_{21})$. +Pulse timing is controlled by a motorized stage that adjusts the arrival time of $E_1$ relative to $E_2$ and $E_{2^\prime}$. + +All three beams are focused onto the sample in a BOXCARS geometry and the direction $\vec{k}_1-\vec{k}_2+\vec{k}_{2^\prime}$ is isolated and sent to a monochromator to isolate the $\omega_1$ frequency with $\sim 120 \text{cm}^{-1}$ detection bandwidth. +The signal, $N_{\text{TG}}$, was detected with an InSb photodiode. Reflective neutral density filters (Inconel) limit the pulse fluence to avoid multi-photon absorption. +To control for frequency-dependent changes in pulse arrival time due to the OPAs and the neutral density, a calibration table was established to assign a correct zero delay for each color combination (see supporting information for more details). + +The TA experiments were designed to minimally change the TG experimental conditions. +The $E_{2^\prime}$ beam was blocked and signal in the $\vec{k}_1$ direction was measured. +$E_2$ was chopped and the differential signal and the average signal were measured to define $T_0$ and $T$ needed to compute $\Delta A$. +Just as in TG experiments, the excitation frequencies were scanned while the monochromator was locked at $\omega_m=\omega_1$. +% DK: perhaps leave this part out +%Finally, fluence studies resonant with the 1S band were performed to test for indications of intensity-dependent relaxation. +%These studies showed no indication of accelerated Auger recombination rates (see supporting info). -- cgit v1.2.3