Near-field Scanning Optical Microscope and Nanoprobe in controlled atmosphere

Near-field Scanning Optical Microscopy (NSOM, or SNOM) is an advanced optical technique suitable for imaging and performing optical spectroscopy beyond the diffraction limit. It is ideal for exploring materials, optoelectronic devices and biological systems with nanoscale resolution.

State of the art aperture-type NSOM setups comprise a piezo-scanner mounting cantilevers or tapered optical fibers with apertures 5-10 times smaller than a wavelength of the light used, and a superimposed optical microscope to drive light through the tip (see Figure below). Many NSOM's, including ours, can also mount standard Atomic Force Microscope (AFM) tips.

Our Witec AlphaSNOM 300 instrument combines a suite of capabilities including:

> Confocal optical microscope imaging (reflection, transmission and fluorescence)

> Topographic imaging (i.e. AFM) in contact, non-contact and intermittent-contact

> NSOM imaging (reflection, transmission, collection and photoluminescence)

> Electrical scans, interfacing a probe station for semiconductor device testing

> Surface potential measurements.

Uniquely, our NSOM system is being modified for handling samples and operating in a controlled atmosphere glove-box (argon or nitrogen). Optical and electronic devices can be prepared in-situ and electrically contacted through the tip. Tips tailored for such specific applications are prepared at the Western Nanofabrication Facility.

Electron Spin Resonance - Electronic Paramagnetic Resonance (ESR, or EPR)

Paramagnetism can be defined as the physical phenomenon leading to the generation of weak magnetic moments from singly-occupied electronic states in solids and molecules under the application of an external magnetic field. Paramagnetic electrons in semiconductors are typically situated near defects or impurities. Defect comtrol in many (nano)materials of common use in electronics have been attained using ESR, a powerful technique capable of detecting paramagnetic centers. Two components are at the basis of any ESR tool (see Figure below):

> A DC magnetic field B, that causes the splitting of singly-occupied electron energy levels into sublevels corresponding to parallel and antiparallel spin orientations, and

> An AC field at a frequency v, which induces optical transitions between these sub-levels. Our Jeol JES-FA200 ESR system operates in the microwave X-band (v~9.5GHz)

Since the integrated intensity of the signal is proportional to the spin density, and since ESR is highly specific to unpaired electrons, this technique is able to recognize and quantify very small concentrations of paramagnetic "defects" in solids.

Laboratory equipment

Nanodevice fabrication

In addition to these instruments from our group, my students are actively using the equipment available at the Nanofabrication Facility existing within our Department.