Superconducting quantum interference devices (SQUIDs) can be used to detect weak magnetic fields and have traditionally been the most sensitive magnetometers available. However, because of their relatively large effective size (on the order of 1 mu m)(1-4), the devices have so far been unable to achieve the level of sensitivity required to detect the field generated by the spin magnetic moment (mu(B)) of a single electron(5,6). Here we show that nanoscale SQUIDs with diameters as small as 46 nm can be fabricated on the apex of a sharp tip. The nano-SQUIDs have an extremely low flux noise of 50 n Phi(0) Hz(-1/2) and a spin sensitivity of down to 0.38 mu(B) Hz(-1/2), which is almost two orders of magnitude better than previous devices(2,3,7,8). They can also operate over a wide range of magnetic fields, providing a sensitivity of 0.6 mu(B) Hz(-1/2) at 1 T. The unique geometry of our nano-SQUIDs makes them well suited to scanning probe microscopy, and we use the devices to image vortices in a type II superconductor, spaced 120 nm apart, and to record magnetic fields due to alternating currents down to 50 nT.

We report the synthesis of silver-decanethiolate (AgSC10) lamellar crystals. Nanometer-sized Ag clusters grown on inert substrates react with decanethiol vapor to form multi-layer AgSC10 lamellar crystals with both layer-by-layer and in-plane ordering. The crystals have strong (010) texture with the layers parallel to the substrates. The synthesis method allows for a precise control of the number of layers. The thickness of the lamellae can be manipulated and systematically reduced to a single layer by decreasing the amount of Ag and lowering the annealing temperature. The single-layer AgSC10 lamellae are two-dimensional crystals and have uniform thickness and in-plane ordering. These samples were characterized with nanocalorimetry, atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), and Rutherford backscattering spectroscopy (RBS).

Thin film based nanocalorimetry is a powerful tool to investigate nanosystems from a thermal point of view. However, nanocalorimetry is usually limited to amorphous or polycrystalline samples. Here we present a device that allows carrying out experiments on monocrystalline silicon. The monocrystalline silicon layer consists of the device layer from a silicon-on-insulator wafer and lies on a low-stress freestanding silicon nitride membrane. We applied a number of characterization techniques to determine the purity and quality of the silicon layer. All these techniques showed that the silicon surface is as pure as a standard silicon wafer and that it is susceptible to standard surface cleaning procedures. Additionally, we present a numerical model of the nanocalorimeter, which highlights that the silicon layer acts as a thermal plate thereby significantly improving thermal uniformity. This nanocalorimeter constitutes a promising device for the study of single-crystal Si surface processes and opens up an exciting new field of research in surface science. (C) 2010 Elsevier B.V. All rights reserved.

The annealing of damage generated by low-energy ion implantation in polycrystalline silicon (poly-Si) and amorphous silicon (a-Si) is compared. The rate of heat release between implantation temperature and 350-500 degrees C for Si implanted in both materials and for different ions implanted in poly-Si shows a very similar shape, namely, a featureless signal that is characteristic of a series of processes continuously distributed in terms of activation energy. Nanocalorimetry signals differ only by their amplitude, a smaller amount of heat being released after light ion implantation compared to heavier ones for the same nominal number of displaced atoms. This shows the importance of dynamic annealing of the damage generated by light ions. A smaller amount of heat is released by implanted poly-Si compared to a-Si, underlining the effect of the surrounding crystal on the dynamic annealing and the relaxation of the defects. Damage accumulation after 30-keV Si implantation is also characterized by Raman scattering and reflectometry, featuring a similar trend in a-Si, poly-Si, and monocrystalline silicon (c-Si) with a saturation around 4 Si/nm(2). Considering these results together with other recent experiments in c-Si and molecular dynamic simulations, it is concluded that the damage generated by low-energy ion implantation that survives dynamic annealing is structurally very similar if not identical in both crystalline and amorphous silicon, giving rise to the same kind of processes during a thermal anneal. However, the damage peak obtained by channeling saturates only above 10 Si/nm(2). This suggests that between 4 and 10 Si/nm(2), further damage occurs by structural transformation without the addition of more stored energy.

Nanocalorimetry revealed that the annealing kinetics of ion-implanted defects in polycrystalline Si is independent of ion fluence and implantation energy. Ion implantation of 30 keV Si-, 15 keV Si-, and 15 keV C- was performed at fluences ranging from 6 x 10(11) to 1 X 10(15) atoms/cm(2), followed by temperature scans between 30 and 450 degreesC. The rate of heat release has the same shape for all fluences, featuring no peaks but rather a smooth, continuously increasing signal. This suggests that the heat release is dominated by the annealing of highly disordered zones generated by each implantation cascade. Such annealing depends primarily on the details of the damage zone-crystal interface kinetics, and not on the point defect concentration. (C) 2005 American Institute of Physics.

Nanocalorimetry of ion-implanted damage annealing in polycrystalline Si is presented. Si was implanted at 30 keV. Temperature scans were performed between room temperature and 350 degrees C at heating rates between 48 and 144 kK/s for a fluence of 1 x 10(13) Si/cm(2), and between room temperature and 540 degrees C at beam fluxes of 11 and 44 nA/cm(2) with a fluence of 2 x 10(13) Si/cm(2). The heat release shows no features, but rather a broad increase with temperature which is characteristic of a series of processes continuously distributed in terms of activation energy. Higher heating rates shift the signal towards higher temperatures and decrease its amplitude, which is typical for thermally activated processes. Lower beam flux implants translate into smaller heat release. This is partly attributed to shorter implantation times at higher fluxes, which leave less time for dynamic annealing, but could also be due to the higher impact rate in the environment of previously generated disordered zones. Such impact generates damage that may stabilize disordered zones, which would have enough time to undergo dynamic annealing at lower fluxes. (c) 2005 Elsevier B.V. All rights reserved.

The structural relaxation of amorphous silicon, created by ion implantation, was investigated by in situ differential scanning nanocalorimetry. Nanocalorimetry provided the possibility to measure the heat released by relaxation during annealing, for a wide range of implantation fluences and beginning at cryogenic temperatures. Ion implantation was first carried out for fluences between 10(-5) and 0.8 displacements per atom (DPA) at 133 K and 297 K, and then for temperatures ranging from 118 K to 463 K for fluences of 0.0185 and 0.37 DPA. A heat release saturation occurred above 0.1 DPA, and was found to depend on implantation temperature. The saturation level was extrapolated to 0 K, leading to an estimate of 28 +/- 3 kJ/mol for the maximum enthalpy that can be stored in a-Si, relative to crystalline Si.

In situ observations of thermal processes involving nJ energies are impractical, if not impossible, with conventional differential scanning calorimetry (DSC), but the nanometric scale of recently developed nanocalorimetry systems should make such observations possible. Nanocalorimetry is based on membrane calorimeters made using nanofabrication technologies. Here we present initial results of an in situ investigation of damage dynamics in amorphous silicon (a-Si). A thin film of a-Si was deposited on the calorimeter membrane and implanted with low-energy Si ions. One-time heat releases were measured for doses ranging from 10(12) to 10(14) ion cm(-2). Subsequent calorimetry scans showed no difference with the baselines, indicating that the damage remaining is stable over the temperature of operation. The measurements were taken immediately after ion implantation in the same environment and were repeated. For doses of 10(12) ion cm(-2) and less, the signal intensity was below the sensitivity limit. A saturation of the total heat released was observed. This saturation was correlated with previous DSC measurements and attributed to the relaxation of ion beam implanted a-Si. (C) 2003 Elsevier B.V. All rights reserved.