Sub-10 nanometer lithography is opening a new area for beyond-CMOS devices. Regarding to single nano-digit manufacturing we have established a new maskless patterning scheme by using field-emission, current controlled Scanning Probe Lithography (cc-SPL) in order to create optical nanodevices in thin silicon-on-insulator (SOI) substrates. This work aims to manufacture split ring resonators into calixarene resist by using SPL, while plasma etching at cryogenic temperatures is applied for an efficient pattern transfer into the underlying Si layer. Such electromagnetic resonators take the form of a ring with a narrow gap, whose 2D array was the first left-handed material tailored to demonstrate the so-called left-hand behavior of the wave propagation. It is shown that the resonance frequency can be tuned with the feature size of the resonator, and the resonance frequency can be shifted further into near infrared or even visible light regions.
Cost-effective generation of single-digit nano-lithographic features could be the way by which novel nanoelectronic devices, as single electron transistors combined with sophisticated CMOS integrated circuits, can be obtained. The capabilities of Field-Emission Scanning Probe Lithography (FE-SPL) and reactive ion etching (RIE) at cryogenic temperature open up a route to overcome the fundamental size limitations in nanofabrication. FE-SPL employs Fowler-Nordheim electron emission from the tip of a scanning probe in ambient conditions. The energy of the emitted electrons (<100 eV) is close to the lithographically relevant chemical excitations of the resist, thus strongly reducing proximity effects. The use of active, i.e. self-sensing and self-actuated, cantilevers as probes for FE-SPL leads to several promising performance benefits. These include: (1) Closed-loop lithography including pre-imaging, overlay alignment, exposure, and post-imaging for feature inspection; (2) Sub-5-nm lithographic resolution with sub-nm line edge roughness; (3) High overlay alignment accuracy; (4) Relatively low costs of ownership, since no vacuum is needed, and ease-of-use. Thus, FE-SPL is a promising tool for rapid nanoscale prototyping and fabrication of high resolution nanoimprint lithography templates. To demonstrate its capabilities we applied FE-SPL and RIE to fabricate single electron transistors (SET) targeted to operate at room temperature. Electrical characterization of these SET confirmed that the smallest functional structures had a diameter of only 1.8 nanometers. Devices at single digit nano-dimensions contain only a few dopant atoms and thus, these might be used to store and process quantum information by employing the states of individual atoms.
Measurement of composition of mixtures at high pressures is important in many applications such as supercritical drying of aerogels, high-pressure sterilization and synthesis of nanostructured materials. The frequency response of uncoated microcantilevers immersed in ethanol-CO2 mixtures with compositions ranging from 0.85 to 4 weight % of ethanol in ethanol-CO2 were measured at a temperature of 318 K and pressure range of 10 MPa to 22 MPa. The resonant frequencies and Q-factors were found to decrease with the increasing weight % of ethanol in the mixture. The data indicate that the composition of a mixture can be measured by measuring the resonant frequency of the cantilever in the mixture after obtaining a calibration curve by measuring resonant frequencies of mixtures with known composition. The sensitivity of the technique which is defined as the ratio of resonant frequency shift to the change in fluid mixture was investigated. An analytical expression for sensitivity was derived using Sader’s model. The sensitivity was found to be a complex function of density and viscosity of the mixture as well as the length, density and width of the cantilever. Using the density and viscosity data in the literature for ethanol-CO2 mixtures with various compositions, the sensitivity of the cantilevers were calculated at each pressure and temperature. The results indicate that the minimum composition that can be measured with the current setup is between 480 ppm and 980 in the pressure range of 10 MPa to 22 MPa by using a 150 µm long cantilever and between 600 and 1450 ppm by using 200 µm long cantilever.
Acknowledgment: - This project has received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 685648.
Next-generation electronic and optical devices demand high-resolution patterning techniques and high-throughput fabrication. Thereby Field-Emission Scanning Probe Lithography (FE-SPL) is a direct writing method that provides high resolution, excellent overlay alignment accuracy and high fidelity nanopatterns. As a demonstration of the patterning technology, single-electron transistors as well as split ring electromagnetic resonators are fabricated through a combination of FE-SPL and plasma etching at cryogenic temperatures.
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