We describe the design of a low temperature scanning Hall probe microscope (SHPM) for a dilution refrigerator system. A detachable SHPM head with 25.4 mm OD and 200 mm length is integrated at the end of the mixing chamber base plate of the dilution refrigerator insert (Oxford Instruments, Kelvinox MX-400) by means of a dedicated docking station. It is also possible to use this detachable SHPM head with a variable temperature insert (VTI) for 2 K-300 K operations. A microfabricated 1μm size Hall sensor (GaAs/AlGaAs) with integrated scanning tunneling microscopy tip was used for magnetic imaging. The field sensitivity of the Hall sensor was better than 1 mG/√Hz at 1 kHz bandwidth at 4 K. Both the domain structure and topography of LiHoF4, which is a transverse-field Ising model ferromagnet which orders below TC = 1.53 K, were imaged simultaneously below 40 mK.

Few layer graphene is attractive due to its extraordinary electronic and optical properties, which are strongly influenced by the orientation between the layers called as stacking sequence. It is challenging to synthesize high quality large size single or multi layer graphene crystals on the metal catalyst using chemical vapor deposition technique. The present work is about synthesis of few layer graphene grains on platinum foil using ambient pressure chemical together vapor deposition technique. The main focus is how the different grains coalesced and maintain the stacking sequence. Different characterization techniques are used to analyze the grains when they are in the process of merging to make a bigger grain. Scanning electron microscopy clearly shows different stacking sequences and merging of different nucleation sites of different grains. Interestingly, different stacking sequences are observed during the process of coalescence of grains. Raman spectroscopy gives accurate information about the number of layers and their stacking sequence. We observed Bernal AB and twisted layer stacking in the grains when they were combining together to grow into a bigger size. The full width at half maximum (FWHM) value of 2D Raman peaks appeared in the range of 52–69 cm−1 which shows an increase from the value of single layer graphene (30.18 cm−1) and identifies Bernal stacking in grains. For twisted stacking FWHM values lie in the range of 19–32 cm−1.

We describe the design of a wide temperature range (300 mK-300 K) atomic force microscope/magnetic force microscope with a self-aligned fibre-cantilever mechanism. An alignment chip with alignment groves and a special mechanical design are used to eliminate tedious and time consuming fibre-cantilever alignment procedure for the entire temperature range. A low noise, Michelson fibre interferometer was integrated into the system for measuring deflection of the cantilever. The spectral noise density of the system was measured to be ∼12 fm/√Hz at 4.2 K at 3 mW incident optical power. Abrikosov vortices in BSCCO(2212) single crystal sample and a high density hard disk sample were imaged at 10 nm resolution to demonstrate the performance of the system.

Submitted for the MAR12 Meeting of The American Physical Society mK-Scanning Probe Microscope(mK-SPM) operating in a Cryogen-Free Dilution Refrigerator at 20mK MUNIR DEDE, Nanomagnetics Instruments Ltd. Suite 290 266 Banbury Road OX2 7DL. Oxford, UK, OZGUR KARCI, Hacettepe University, Dept. of Nanotechnology and Nanomedicine, Beytepe, 06800, Ankara, Turkey, CHRIS SNELLING, Oxford Instruments plc Tubney Woods, Abingdon, Oxon OX13 5QX, UK, AHMET ORAL, Sabanci University, Faculty of Science and Engineering, Orhanli Tuzla, 34956, Istanbul, Turkey — Dramatic increase in liquid helium price limits the usage of cryogenic equipment. Dry cryogen-free dilution refrigerators(DR) systems are promising platforms to run mK-Scanning Probe Microscopes(mK-SPM) systems with a number of operating modes: STM, AFM, MFM, EFM, SSRM, PFM, etc. We present the design of a mK-Scanning Probe Microscope (mK-SPM) operating in a cryogen-free DR. An Oxford Instrument cryogen-free DR(Triton DR200) with 200uW cooling power and 7mK base temperature is used for the experiments. A 1W Pulse Tube cryocooler is integrated into the DR. After wiring and attaching the microscope we achieved 20mK base temperature. Piezo driven Stick slip coarse approach mechanism is used to bring the sample in to close proximity of the sample. In these initial results we deliberately did not take any precautions to isolate the pumping lines, attached to the DR and the DR itself. The turbomolecular pump was attached directly to the top plate of the DR. We first tested our mK-SPM in Scanning Tunnelling Microscope (STM) mode as it is the most sensitive of the SPM techniques. An image, using a gold coated 6μm period calibration grating at 20mK, obtained under these rudimentary conditions. Munir Dede Nanomagnetics Instruments Ltd. Suite 290 266 Banbury Road OX2 7DL. Oxford, UK Date submitted: 13 Dec 2011 Electronic form version 1.4