Near-Field Microwave Microscopy: Subsurface Imaging for In Situ Characterization

The centuries-old field of microscopy has revolutionized and is now indispensable in the natural sciences, medicine, and many branches of technology. New techniques and approaches used for visualizing small objects and measuring their physical or chemical properties and their structures are in demand and constantly being developed. In the suite of modern microscopy techniques, nondestructive methods are especially important. One of the challenging tasks of microscopic imaging, independent of the employed physical principle, is the imaging of nanoscale objects in situ and in operando, in the medium of their natural existence or operation. These are cases when an object of interest is in some sort of interaction with its surrounding medium and its form and operation are either based on or fundamentally dependent upon this interaction. Examples of this include integrated circuits, living objects such as biological cells in water-based solutions, and electrochemical devices such as parts of rechargeable batteries or the electrolytic cells in electrolytes. Breaking its interaction with the environment or changing the environment leads to the disappearance of the object or alters the object so that, in its altered state, the key information relevant to its in vivo or in operando state is lost. Therefore, microscopy should be performed nondestructively, in situ.