No abstract

Spot laser melting of monocrystalline silicon leads to characteristic surface structures that are defined by a peak and a quasi-periodic ripple structure. The structures are created by a 50–100 μs pulsed infrared fiber laser and are approximately 30–100 μm in size. We present an analytical model explaining the creation of the peak by the density anomaly of silicon. Additionally, we show that the quasi-periodic ripple structure stems from a frozen capillary wave, which allows us to determine the resolidification velocity from the ripple radii. For a structure of molten radius Rmelt=41.5μm, we determine a resolidification velocity vre=56.6±9.2cm/s. A numerical model for the same structure yields vre=49.2cm/s, which agrees with the value determined from the ripple pattern. The capillary wave is excited in the melt pool due to thermocapillary convection.

Laser processing of monocrystalline silicon has become an important tool for a wide range of applications. Here, we use microsecond spot laser melting as a model experiment to investigate the generation of crystal defects and residual stress. Using Micro-Raman spectroscopy, defect etching, and transmission electron microscopy, we find no dislocations in the recrystallized volume for cooling rates exceeding |dT/dt|=2×107 K/s, and the samples remain free of residual stress. For cooling rates less than |dT/dt|=2×107 K/s, however, the experiments show a sharp transition to a defective microstructure that is rich in dislocations and residual stress. Moreover, transmission electron microscopy indicates dislocation loops, stacking-fault tetrahedra, and voids within the recrystallized volume, thereby indicating supersaturation of intrinsic point defects during recrystallization. Complementing photoluminescence spectroscopy indicates even three regimes with decreasing cooling rate. Spectra of regime 1 do not contain any defect related spectral lines. In regime 2, spectral lines appear related to point defect clusters. In regime 3, the spectral lines related to point defect clusters vanish, but dislocation-related ones appear. We propose a quantitative model explaining the transition from dislocation-free to dislocation-rich recrystallization by means of the interaction between intrinsic point defects and dislocations.

The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adpr.202200045.

We report on the spectral analysis and the local measurement of intensity correlations of microwave fields using ultra cold quantum gases. The fluctuations of the electromagnetic field induce spin flips in a magnetically trapped quantum gas and generate a multi-mode atomlaser. The output of the atomlaser is measured with high temporal resolution on the single atom level, from which the spectrum and intensity correlations of the generating microwave field are reconstructed. We give a theoretical description of the atomlaser output and its correlations in response to resonant microwave fields and verify the model with measurements on an atom chip. The measurement technique is applicable for the local analysis of classical and quantum noise of electromagnetic fields, for example on chips, in the vicinity of quantum electronic circuits. [5], are well characterized by the electron counting statistics and the corresponding field noise. This becomes especially important, as novel materials such as artificial honeycomb crystals [6] predict quantum effects in the electron transport even at room temperature, due to the formation of topological protected states [7]. Such quantum transport phenomena might be measured by means of a recently proposed quantum galvanometer [8], in which the low frequency current noise of a nano-device is coherently coupled to an atomic quantum gas and analyzed via state selective single atom detection.Here, we demonstrate the basic operation of the quantum galvanometer and extend it to quantum correlation measurements. Using a Bose-Einstein condensate, we coherently probe artificial, low frequency magnetic field fluctuations (noise) by shifting them electronically into the microwave (mw) regime, close to an atomic resonance. These fluctuations, generate a multi-mode atomlaser, with an output directly connected to the original field fluctuations. Using a sensitive detector, we analyze this output on the single atom level and show, how the power spectral density and the intensity correlations of the microwave field can be reconstructed. We give a theoretical description for the output of the multi-mode atomlaser, including decoherence effects.Experimental setup: The experiment is illustrated in Fig. 1a. Using an atom-chip based cold atom apparatus[9], we prepare Bose-Einstein condensates and thermal ensembles of 87 Rb atoms in the 5S 1/2 , F = 2, m F = 2 ground state. The atoms are magnetically trapped in a harmonic configuration with trap frequencies ω (x,y,z) = 2π × (85, 70, 16)Hz and offset field B z,off ≈ 0.93G. If this cloud is exposed to resonant microwave radiation, spin flips to the anti-trapped 5S 1/2 , F = 1, m F = 1 state occur. Here, we irradiate microwaves of various spectra to demonstrate the measurement of noise spectra and correlations. In particular, we apply amplitude modulation to a microwave carrier at ω c ≈ 2π × 6.834GHz with a variable function A (t) in the kHz regime. Here, A(t) mimics the low frequency field noise, which in the quantum galvanometer case is intrinsically (...