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Single self-assembled InAs quantum dots embedded in a In0.12Ga0.88As quantum well and emitting in the near infrared have been optically investigated. The dependence on the excitation power of the single quantum dot photoluminescence has been used to identify the emission of the biexciton complex. The biexciton binding energy, which has been measured for a dozen dots, increases with increasing exciton transition energy for the dot sizes investigated in the present work, as a consequence of stronger confinement in a smaller quantum dot. The obtained data is compared with experimental results available in the literature for InAs quantum dots. [ABSTRACT FROM AUTHOR]

The frequency response of an atomic force microscope silicon cantilever located in a vacuum cryostat chamber was investigated. The resonance frequency and the peak width were extracted by a Lorentzian fit of the resonance curves for different sample temperatures (15–310 K). Frequency shifts significantly less than one could expect from known temperature dependencies of Young’s modulus and the density of silicon were found. The estimations described in this article show that the temperature of a silicon cantilever is mainly defined by the temperature of its holder, mainly due to the thermal conductivity of silicon. Thermal radiation emission plays a minor role in cooling the cantilever. Furthermore, heat transport through tip-sample contact, as well as contact with the environmental gas, could be neglected. [ABSTRACT FROM AUTHOR]

We present an interferometric displacement sensor based on a folded low-finesse Fabry-Perot cavity. The fiber-optic sensor uses a quadrature detection scheme based on the wavelength modulation of a DFB laser. This enables measuring position changes over a range of 1 m for velocities up to 2 m/s. The sensor is well suited to work in extreme environments such as ultrahigh vacuum, cryogenic temperatures, or high magnetic fields and supports multichannel applications. The interferometer achieves a repeatability of 0.44  nm(3σ) at a working distance of 20 mm, a resolution of 1 pm, and an accuracy of 1 nm.

A combined system for far- and near-field optical spectroscopy consisting of a compact scanning near-field optical microscope and a dedicated spectrometer was realized. The set-up allows the optical investigation of samples at temperatures from 10 to 300 K. The sample positioning range is as large as 5 x 5 x 5 mm3 and the spatial resolution is in the range of 1.5 micro m in the far-field optical microscopy mode at low temperatures. In the scanning near-field optical microscope mode the resolution is defined by the microfabricated cantilever probe, which is placed in the focus of a double-mirror objective. The tip-to-sample distance in the scanning near-field optical microscope is controlled by a beam deflection system in dynamic scanning force microscopy mode. After a description of the apparatus, scanning force topography images of self-assembled InAs quantum dots on a GaAs substrate with a density of less than one dot per square micrometre are shown, followed by the first spectroscopic investigations of such a sample. The presented results demonstrate the potential of the system.