A scanning microwave microscope (SMM) for spatially resolved capacitance measurements in the attofarad-to-femtofarad regime is presented. The system is based on the combination of an atomic force ...microscope (AFM) and a performance network analyzer (PNA). For the determination of absolute capacitance values from PNA reflection amplitudes, a calibration sample of conductive gold pads of various sizes on a SiO(2) staircase structure was used. The thickness of the dielectric SiO(2) staircase ranged from 10 to 200 nm. The quantitative capacitance values determined from the PNA reflection amplitude were compared to control measurements using an external capacitance bridge. Depending on the area of the gold top electrode and the SiO(2) step height, the corresponding capacitance values, as measured with the SMM, ranged from 0.1 to 22 fF at a noise level of ~2 aF and a relative accuracy of 20%. The sample capacitance could be modeled to a good degree as idealized parallel plates with the SiO(2) dielectric sandwiched in between. The cantilever/sample stray capacitance was measured by lifting the tip away from the surface. By bringing the AFM tip into direct contact with the SiO(2) staircase structure, the electrical footprint of the tip was determined, resulting in an effective tip radius of ~60 nm and a tip-sample capacitance of ~20 aF at the smallest dielectric thickness.
We present a novel approach to develop and process a microelectrode integrated in a standard AFM tip. The presented fabrication process allows the integration of an electroactive area at an exactly ...defined distance above of the end of a scanning probe tip and the subsequent remodeling and sharpening of the original AFM tip using a focused ion beam (FIB) technique (See ref for patent information). Thus, the functionality of scanning electrochemical microscopy (SECM) can be integrated into any standard atomic force microscope (AFM). With the demonstrated approach, a precisely defined and constant distance between the microelectrode and the sample surface can be obtained, alternatively to the indirect determination of this distance usually applied in SECM experiments. Hence, a complete separation of the topographical information and the electrochemical signal is possible. The presented technique is a significant step toward electrochemical imaging with submicrometer electrodes as demonstrated by the development of the first integrated frame submicroelectrode.
In this paper, we adapt the transfer matrix method to calculate the current-voltage curves of type-II GaAsSb/InGaAs resonant tunneling diodes on which a huge Rashba splitting of the current ...resonances has been reported recently. It is shown that, in transverse magnetic fields, the k sub() distribution of tunneling electrons is shifted to higher values. Through this process, a significant asymmetry is induced in the tunneling structure, which finally leads to a strong enhancement of the Rashba effect. Further, we find that the Rashba effect is extremely sensitive to the electric fields produced by the band discontinuities at the heterostructure interfaces and to the spin-orbit coupling constants in the respective materials. Using a one-band model for the spin-orbit coupling constant, the effects of temperature and local electric fields on the Rashba parameter are also investigated. From our findings, we conclude that spin-splitting effects and large spin-orbit interactions should be quite dominant in any narrow-gap type-II heterostructure, and not only in the GaAsSb/InGaAs material system.
► Comparative XPS analysis of the chemical stability of La2O3 and GeO2 Ge surface passivation during ALD of ZrO2. ► Comparative electrical characterization of La2O3 and GeO2 Ge surface passivations ...in MOS capacitors. ► Decomposition of the 1.5nm thick initial GeO2 interface layer during ALD of 6.5nm ZrO2 indicated by TEM and XPS. ► Changing of the Ge oxidation states during ALD of ZrO2 on interfacial GeO2 indicated by XPS. ► Detection of zirconia germanate inside the ZrO2 matrix by XPS independently from surface passivation.
La2O3 grown by atomic layer deposition (ALD) and thermally grown GeO2 are used to establish effective electrical surface passivations on n-type (100)-Ge substrates for high-k ZrO2 dielectrics, grown by ALD at 250°C substrate temperature. The electrical characterization of MOS capacitors indicates an impact of the Ge-surface passivation on the interfacial trap density and the frequency dependent capacitance in the inversion regime. Lower interface trap densities can be obtained for GeO2 based passivation even though a chemical decomposition of the oxidation states occur during the ALD of ZrO2. As a consequence the formation of a ZrGeOx compound inside the ZrO2 matrix and a decline of the interfacial GeO2 are observed. The La2O3 passivation provides a stable amorphous lanthanum germanate phase at the Ge interface but also traces of Zr germanate are indicated by X-ray-Photoelectron-Spectroscopy and Transmission-Electron-Microscopy.
In most atomic force microscopes (AFMs), the motion of the tip is detected by the deflection of a laser beam shining onto the cantilever. AFM applications such as scanning capacitance spectroscopy or ...photocurrent spectroscopy, however, are severely disturbed by the intense stray light of the AFM laser. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. The versatility of this feedback method is demonstrated by measuring tip-force dependent Schottky barrier heights on GaAs samples.
We have investigated the impact of shrinking feature sizes on the sputter efficiency of focused ion beams on crystalline silicon. On the basis of this analysis, we have demonstrated the main ...competitive mechanisms determining the complex response of silicon. Low-dose irradiation with a 50-keV Ga beam in the range from 10 ions/cm to 10 ions/cm produced pronounced swelling of the silicon due to amorphization. Higher doses led to material removal with an efficiency of about 2.5 atoms/ion. A sputter yield promoting the self-focusing effect combined with the sputter rate increase at oblique angles, and an opposing dose-deficiency effect, determined the complex characteristics of nanoscale trench milling. Shrinking critical dimensions led to higher sputter yields, attributable to self-focusing effects of incident ions becoming dominant at aspect ratios in the region of unity. At aspect ratios beyond unity, re-deposition was the dominant effect.
In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with ...weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAsInAs heterostructures.
