Simultaneous measurement of nanoprobe indentation pressure and photoluminescence of quantum dots

Kazunari Ozasa 1,3Mizuo MAEDA 1Masahiko HARA 1Masane OHASHI 2Yuan-Hua LIANG 2Yoshio ARAI 2

1. Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-Shi, Saitama 351-0198, Japan
2. Saitama University, 255 Shimo-ookubo, Sakuraku, Saitama 338-8570, Japan
3. CREST-JST, 3-1-6-5 Shibuya, Tokyo 150-0002, Japan


Nanoprobe indentation onto the surfaces of solid materials can produce a very high pressure (strain) more than 20-80 GPa for the nm-scale areas. When the nanoprobe is made from an optical fiber, the optical properties such as photoluminescence (PL) or reflectance of the samples under a high pressure can be measured with nm-scale resolutions. However, simultaneous measurements of high pressure and optical properties are generally difficult for nanoprobe indentations, since the indentation force is too small for direct measurements.

We have succeeded to measure simultaneously the nanoprobe indentation-force (pressure) and the PL of InGaAs/GaAs quantum dots (QDs) at low temperatures (down to 10K), by employing a small resistance-bridge load-cell. Indentation force as low as 200 uN can be measured, which corresponds to approximately 62 GPa at the sample surface. The PL of InGaAs/GaAs QDs was measured through the 1μm aperture at the apex of the optical-fiber-nanoprobe, indented onto the surface within the elastic limits. The strain-enhanced fine PL peaks originating from single QDs were observed reproducibly, only when a certain range of GPa pressures were produced by the nanoprobe indentation. Blue shifts of fine peaks were observed with the PL enhancement, suggesting that the strain effects are responsible for the PL enhancement.

By the model calculation of nanoprobe indentation with elastic deformation theory and strain Hamiltonian, we figured out the strain distribution and energy-level shifts, and found that the potential minimum for light holes is formed in GaAs beneath the nanprobe, which causes the PL enhancement through hole accumulation into the QDs. Since the simultaneous measurement of indentation force and PL peaks enable us to analyze the nanoprobe-induced strain (pressure) distribution, it contributes much to the application of nanprobe-modulation spectroscopy, where we can measure the nm-scale optical properties of the samples.

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Presentation: oral at E-MRS Fall Meeting 2005, Symposium I, by Kazunari Ozasa
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-27 02:59
Revised:   2009-06-07 00:44
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