W. Scholz

Multipurpose sensor tips for scanning near‐field microscopy

The reproducible micromachining of hollow metal tips on Si cantilevers and their applicability to scanning probe microscopy techniques are described. Provided with apertures below 130 nm and hollow pyramidal tips proved to be highly suited probes for scanning near‐field optical microscopy (SNOM). First results of combined SFM/SNOM measurements together with scanning electron microscopy (SEM) photographs of the new sensors are presented. The SNOM images show a resolution of about 100 nm demonstrating the usefulness of these probes.

Fabrication of integrated diamond cantilevers with tips for SPM applications

Abstract The fabrication of diamond cantilevers with diamond tips integrated on silicon wafers for scanning probe microscopy (SPM) applications is reported. Hot filament CVD diamond deposition and standard techniques of silicon micro-machining are employed. The deposition of well-developed tips depends critically on the pretreatment applied to enhance nucleation density. With an optimized process, well-shaped tips with a radius of curvature in the order of 30 nm are obtained. According to micro-Raman investigations they consist of high quality diamond. Another critical step is the definition of the cantilever area. It can be solved by proper process design. Preliminary performance tests show the cantilevers to possess high resonance frequencies.

FABRICATION OF SMALL DIAMOND TIPS FOR SCANNING PROBE MICROSCOPY APPLICATION

A process for the fabrication of diamond cantilevers integrated on a silicon wafer is presented. At one end the cantilevers possess a tip with a small radius of curvature thus allowing their use in scanning probe microscopy applications. The influence of various procedures to enhance diamond nucleation of the properties of the tips is investigated. Ultrasonic pretreatment with 1 μm diamond paste and subsequent hot-filament chemical-vapor deposition turned out to yield the best results. Micro-Raman measurements show the tips to consist of stress-free diamond up to their very apex.

Novel micromachined cantilever sensors for scanning near-field optical microscopy*

The reproducible micromachining of hollow metal tips on Si cantilevers and their applicability to scanning near‐field optical microscopy (SNOM) is described. This sensor is fabricated using semiconductor compatible technologies. A hollow metal pyramid is employed as an optical aperture sensor for SNOM and simultaneously as a force sensor for scanning force microscopy applications. Apertures down to 120 nm were realized. To confirm the feasibility of the sensor we present measurements on microstructured chromium films as well as on hot filament chemical vapour deposition grown (111) diamond membranes. The SNOM images show a resolution of about 100 nm, demonstrating the usefulness of these probes.

Fabrication of monolithic diamond probes for scanning probe microscopy applications

A process relying on the molding technique for the fabrication of diamond cantilevers with diamond tips integrated on silicon wafers for scanning probe microscopy applications is described. Either hot filament or microwave CVD diamond deposition and standard techniques of silicon micro-machining are employed. The deposition of well- developed tips depends critically on the pretreatment applied to enhance nucleation density; abrasive treatment with diamond powder as well as the bias-enhanced nucleation turned out to be successful. With optimized processes, well- shaped tips with a radius of curvature in the order of 30 nm can be obtained. They consist of high quality diamond according to micro-Raman spectroscopy. The definition of the cantilever area is another critical step which can be solved by proper process design. The fabrication of conductive tips/cantilevers is possible by boron doping. Finally, first performance tests of the diamond tips and cantilevers are presented.

Micromachined probes for high-frequency scanning force microscopy and scanning thermal microscopy

The spatial and time resolved characterization of electronic devices by scanning probe microscopy demands the fabrication of proximal probes with well defined properties. To fulfill these requirements micromachining is the most appropriate technique, as it allows probe fabrication in a batch process with highest reproducibility. In this paper we describe the development of electrical and thermal near-field probes which can be employed for high frequency scanning force microscopy (HFSFM) and scanning thermal microscopy (SThM) respectively. Both probes have been completely fabricated in a micromachining batch process based on an almost identical technological design. For electrical imaging by HFSFM a coplanar wave guide probe was developed. The probes wave guide properties have been characterized by network analysis. A novel thermal probe consisting of a Schottky diode at the tip of a silicon cantilever was developed for SThM. Preliminary results on electrical and thermal characterization will be presented.

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InP-based two-section distributed Bragg reflector lasers employing surface defined lateral gratings, which are compatible with low-cost nanoimprint technology, were fabricated. A newly developed inductively coupled plasma reactive ion etching process was utilized for obtaining large aspect ratios and good device performance. The lasers operate in a single mode up to 50°C under continuous-wave conditions. A modulation bandwidth of about 10 GHz was obtained for 0.9-mm-long devices.

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A combined SNOM/SFM aperture probe is presented which is based on a conventional scanning force microscopy cantilever. Probe fabrication was performed in a batch process which allows to get reproducible mechanical and optical properties. For SNOM applications a tip is integrated at the very end of the cantilever which consists of a hollow metal pyramid with a miniaturized aperture of about 60 nm. To select the appropriate tip material the transmissivity of different metals were investigated in the visible range. The SNOM/SFM probes were characterized both mechanically and optically, e.g. the transmission of apertures is measured as a function of their size. To determined the lateral resolution in the optical transmission mode measurements on test samples are shown. Additionally, a novel probe design is introduced where the geometry of the single aperture tip is altered to obtain a double aperture tip.

m Two-Section DBR Lasers Based on Surface Defined Gratings for High-Speed Telecommunication

To combine low-cost fabrication and high-speed data communication like 100 GBit/s, multi-section DBR lasers are developed with nanoimprint compatible surface defined gratings. This laser design has the potential to enhance the modulation bandwidth by exciting a higher order optical mode, the so-called photon-photon resonance (PPR). ICP-RIE etching was used to transfer the e-beam exposed surface pattern in one step into the semiconductor. High aspect ratios of > 1:15, vertical trenches with a width of about 140 nm and an etch depth of > 2 μm were obtained for the lateral gratings. Three-section DBR lasers are fabricated on an MOVPE grown 1.5 μm InP laser material exhibiting CW threshold currents of 94 mA for a 0.9 mm long device. A side mode suppression ratio of > 50 dB could be achieved demonstrating a high enough coupling strength of the lateral gratings. The influence of different operation conditions (currents, temperature) and dependence on the grating period on threshold current and emission wavelength are studied and will be discussed in this paper. First high frequency measurements in operation conditions without PPR enhancement show a - 3dB bandwidth of about 15 GHz.