The properties of two dimensional (2D) materials depend strongly on the chemical and electrochemical activity of their surfaces. MXene, one of the most recent additions to 2D materials, shows great promise as an energy storage material. In the present investigation, the chemical and structural properties of individual Ti 3 C 2 MXene sheets with associated surface groups are investigated at the atomic level by aberration corrected STEM-EELS. The MXene sheets are shown to exhibit a non-uniform coverage of O-based surface groups which locally affect the chemistry. Additionally, native point defects which are proposed to affect the local surface chemistry, such as oxidized titanium adatoms (TiO x ), are identified and found to be mobile. * To whom correspondence should be addressed † Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden The latter originate from the MAX phases, consisting of a transition metal (M), an Agroup (A) element and C or N (X). 4 The significance of the MAX phases stems from their laminated structure, where M n+1 X n sheets are interleaved with atomically thin A layers. 5,6The M-X bonds consist of a mixture of covalent, metallic, and ionic bonds 6 making MXene exceptionally strong and hence appealing for new applications. 6-8MXenes are synthesized from the MAX phases by removal of A-layers through chemical etching, resulting in stand-alone 2D sheets. 5,6,8,9 is crucial to advance the understanding of MXenes. Here, we investigate the structural properties of single, double and multiple sheets of Ti 3 C 2 T x with attached surface groups by atomic-resolution scanning transmission electron microscopy (STEM). The elemental and chemical properties were further investigated by electron energy loss spectroscopy spectrum imaging (EELS SI). Through these methods we identify the atomic structure of the MXene sheets as well as intrinsic defects, surface and edge terminations by the partial coverage of surface groups. We also report on the mobility and migration of intrinsic defects and surface groups.Ti 3 C 2 T x powder was produced from Ti 3 AlC 2 which was prepared by ball-milling Ti 2 AlC (> 92 wt%, 3-ONE-2, Voorhees, NJ) and TiC (99 %, Johnson Matthey Electronic, NY) powders in a 1:1 molar ratio for 24 h using zirconia balls. The mixture was annealed at 1350• C for 2 h in argon. The sintered compact was converted to a powder by milling. Ti 3 C 2 MXene powder was prepared by immersing 2.5 g of < 400 mesh Ti 3 AlC 2 powder in 1 M of NH 4 HF 2 (Sigma Aldrich, USA) solution for 5 days. After treatment the suspension was washed several times using deionized water and centrifuged to separate the settled powder from the supernatant. The settled powders were removed from vials using ethanol and dried at room temperature. TEM samples were prepared by crushing the powder in a mortar and 3 dispersing the powder on a holey carbon Cu TEM-grid, followed by immediately insertion into the TEM.Characterization was performed using the Linköping double corrected FE...

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A new method for preparing morphology gradients in electrochemically etched porous silicon layers is presented. The idea is to etch on the back side of the anode and thus utilize an inhomogeneous electrical field to control the pore size along a surface. The etching procedure resulted in a complex gradient in pore size, porosity, and porous layer thickness, which was studied by spectroscopic ellipsometry and scanning electron microscopy. The gradients are of interest, e.g., for biomaterials research, biosensor applications, and for basic studies of adsorption of organic molecules, like proteins. In order to investigate the potential of the gradient surfaces for protein adsorption studies, these were exposed to human serum albumin, and a gradient in the amount of adsorbed protein was observed.

Backside etching has been utilized to produce gradients of pore size and layer thickness in porous silicon. Human serum albumin (HSA) was adsorbed on such gradients at two different pH values: 4.9, the pI of HSA, and 7.4, the physiological pH. The samples were investigated by scanning electron microscopy, spectroscopic ellipsometry, and autoradiography. The results show that the protein adsorbed displays a gradient along with the pore size and the thickness gradient. The higher the current density used during etching, the more sway-back shaped curves were seen for the protein adsorption pattern, independent of pH. When 50 mA/cm 2 current density was used during etching, the quota between the maximal intensity value and the plateau value seen after adsorption of the HSA increased for pH 7.4.