Scanning Tunneling Spectroscopy Sensitive to Layer Structure of BSCCO

Scanning tunneling microscopy images and scanning tunneling spectroscopy characteristics were measured at 4.2 K in liquid helium bath on the cleaved in air a-b surface of Bi$\text{}_{2}$Sr$\text{}_{2}$CaCu$\text{}_{2}$O$\text{}_{8}$ (BSCCO-2212). Electronic densities of states and superconductivity parameters Δ and Γ evaluated from dI/dV characteristics depend on tip-sample distance s: with shortening of the distance s superconducting gap structure becomes more distinct, i.e. Δ increases and Γ decreases. We explain this phenomenon as a non-vacuum tunneling, where for longer s tunneling electrons reach only the surface contamination layer on non-metallic BiO top-surface layer, whereas for shorter s tunneling electrons penetrate also deeper lying CuO layers reflecting their superconducting properties. The dependence of Δ on s is evaluated. This result allows to understand better the non-vacuum scanning tunneling microscopy imaging: by adjusting properly the tip-sample distance one can select suitable local density of states contributing dominantly to the scanning tunneling microscopy images taken on BSCCO

Magnetic Force Microscopy Study of Zn1−xCoxOZn_{1-x}Co_{x}O Nanowires Grown by Rapid Thermal Evaporation

In this work we studied domain structure of $Zn_{1-x}Co_{x}O$ nanowires which are single arms of tetrapode crystals. The as-grown material exhibits hysteretic behavior even at room temperature as revealed by SQUID mesurements. In order to get insight into the magnetic properties of individual tetrapodes they were dismembered into nanowires of nanometric diameters, deposited on a flat substrate and imaged by magnetic force microscopy. A magnetic interaction between the magnetic force microscopy probe and single nanowires has been detected which confirms that nanometric volume of the material possesses a magnetic moment. The magnetic force microscopy contrast is attractively independent of the tip magnetization direction which indicates that shape anisotropy of nanowires is not strong enough to prevent occurrence of tip-induced magnetic field disturbance

Atomic Force Microscopy Study of a Voltage Effect on CdZnTe Crystal Dimensions

In this work we studied the influence of an external electric voltage on spatial dimensions of CdZnTe mixed crystals. In order to get an absolute magnitude of the sample thickness and to gain insight to the changes of lateral dimension, in quasi-bulk 3 μm thick CdZnTe layers grown by molecular beam epitaxy square craters were formed by ion sputtering in a secondary ion mass spectrometer. The vertical and lateral dimensions of the craters were studied by the atomic force microscopy. The atomic force microscopy measurement revealed that the thickness of the CdZnTe layer increases in a result of applying a single voltage pulse to the sample surface and decreases reversibly after applying reversely biased voltage. The voltage triggering was high enough to switch the conductivity state of the sample i.e., the effect of thickness change is accompanied by the effect of conductivity switching. The thickness change is significant, reaching several percents of the entire layer thickness

Fabrication and Ferroelectric Properties of BiFeO₃/BaTiO₃ Heterostructures

We report on preparation and electrical characterization of the epitaxial BaTiO₃ (BTO), BiFeO₃ (BFO) thin films and BFO/BTO bi- and multilayers, grown on (001) SrTiO₃ (STO) and $(LaAlO_3)_{0.3}(Sr_2TaAlO_6)_{0.7}$ (LSAT) substrates. The ferroelectric properties were characterized using the electric force microscopy method to image and switch the electric domains. This fabrication process opens the routes towards wide study of magnetoelectric effect in complex oxide heterostructures

Atomic Force Microscopy Study of a Voltage Effect on CdZnTe Crystal Dimensions

In this work we studied the influence of an external electric voltage on spatial dimensions of CdZnTe mixed crystals. In order to get an absolute magnitude of the sample thickness and to gain insight to the changes of lateral dimension, in quasi-bulk 3 μm thick CdZnTe layers grown by molecular beam epitaxy square craters were formed by ion sputtering in a secondary ion mass spectrometer. The vertical and lateral dimensions of the craters were studied by the atomic force microscopy. The atomic force microscopy measurement revealed that the thickness of the CdZnTe layer increases in a result of applying a single voltage pulse to the sample surface and decreases reversibly after applying reversely biased voltage. The voltage triggering was high enough to switch the conductivity state of the sample i.e., the effect of thickness change is accompanied by the effect of conductivity switching. The thickness change is significant, reaching several percents of the entire layer thickness

Optimization of the Superconducting Properties of Laser Ablated YBa2Cu3O7−δYBa_2Cu_3O_{7-δ} Films on CeO2CeO_2-Buffered Sapphire

We use pulsed laser deposition to grow $YBa_2Cu_3O_{7-δ}$ (YBCO) superconducting films for microwave applications. The films are grown on R-cut sapphire substrates, with $CeO_2$ buffer layers, which are re-crystallized at high temperature prior to YBCO growth. Using the atomic force microscopy (AFM) and X-ray diffractometry we determine the optimal temperature for recrystallization (1000°C) and the optimal buffer layer thickness (30 nm). The properties of YBCO films of various thickness, grown on the optimized $CeO_2$ buffer layers, are studied using several methods, including AFM, magnetooptical imaging, and transport experiments. The YBCO film roughness is found to increase with the increasing film thickness, but the magnetic flux penetration in the superconducting state remains homogeneous. The superconducting parameters (the critical temperature and the critical current density) are somewhat lower than the similar parameters for YBCO films deposited on mono-crystalline substrates

Topographical, Magnetic and Optical Studies of (II,Mn)VI Quantum Structures Grown on (Ga,Mn)As

We report on an overgrowth of quantum structures consisting of diluted magnetic semiconductor CdMnTe quantum wells with non-magnetic barriers made of CdMgTe or ZnTe on ferromagnetic MnAs and GaMnAs films by molecular beam epitaxy. Atomic force microscopy images of the quantum structures grown on MnAs demonstrated the existence of two types of regions on the surface: protruded islands with micrometric sizes, surrounded by areas of small-scale roughness. Magnetic force microscopy study of these samples revealed a magnetic domain structure only on the above mentioned islands. The (II,Mn)VI quantum wells grown on GaMnAs films exhibited relatively smooth surface, but no magnetic force microscopy signal was measurable either before or after magnetizing the sample. In the luminescence spectra of all our quantum structures the emission attributed to CdMnTe quantum wells was observed. The influence of magnetization on the luminescence line position was investigated

Topographical, Magnetic and Optical Studies of (II,Mn)VI Quantum Structures Grown on (Ga,Mn)As

We report on an overgrowth of quantum structures consisting of diluted magnetic semiconductor CdMnTe quantum wells with non-magnetic barriers made of CdMgTe or ZnTe on ferromagnetic MnAs and GaMnAs films by molecular beam epitaxy. Atomic force microscopy images of the quantum structures grown on MnAs demonstrated the existence of two types of regions on the surface: protruded islands with micrometric sizes, surrounded by areas of small-scale roughness. Magnetic force microscopy study of these samples revealed a magnetic domain structure only on the above mentioned islands. The (II,Mn)VI quantum wells grown on GaMnAs films exhibited relatively smooth surface, but no magnetic force microscopy signal was measurable either before or after magnetizing the sample. In the luminescence spectra of all our quantum structures the emission attributed to CdMnTe quantum wells was observed. The influence of magnetization on the luminescence line position was investigated