The concept of on-chip double-resonant-tunneling-diode (RTD) patch-antenna oscillator has the virtues of compactness, simplicity, high isolation from the external circuitry, and increased output power. Relying on this concept, we demonstrate an order of magnitude increase in the output power compared to previous reports on patch-antenna RTD oscillators: 10 μW at the fundamental frequency of 525 GHz and 70 μW at 330 GHz. Estimates show that significantly higher frequencies and powers are achievable with this type of oscillator. Only optical lithography has been used in the fabrication process of the oscillators.

Mapping charged chemical groups at the solid–liquid interface is important in many areas, ranging from colloidal systems to biomolecular interactions. However, classical methods to measure surface charges either lack spatial resolution orlike Kelvin-probe force microscopy (KPFM)cannot be applied in aqueous solutions because a DC bias voltage is used. Here, we show that using AC Kelvin probe force microscopy (AC-KPFM), in which the DC bias is replaced with an AC voltage of sufficiently high frequency, the surface potential of spatially fixated, charged surface groups can be mapped in aqueous solution. We demonstrate this with micropatterned, functionalized alkanethiol layers which expose ionized amino- and carboxy-groups. These groups are representative of the charged groups of most biomolecules such as proteins. By adjusting the pH of the solution, the charge of the groups was reversibly altered, demonstrating the electrostatic nature of the measured signal. The influence of the electric double layer (EDL) on the measurement is discussed, and we, furthermore, show how charged, micropatterned layers can be used to spatially direct the deposition of nanoparticles of opposite charge.

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