H. K. Wickramasinghe

Kelvin probe force microscopy

Measurements of the contact potential difference between different materials have been performed for the first time using scanning force microscopy. The instrument has a high resolution for both the contact potential difference (better than 0.1 mV) and the lateral dimension (<50 nm) and allows the simultaneous imaging of topography and contact potential difference. Images of gold, platinum, and palladium surfaces, taken in air, show a large contrast in the contact potential difference and demonstrate the basic concept.

Atomic force microscope-force mapping and profiling on a sub 100-Å scale

A modified version of the atomic force microscope is introduced that enables a precise measurement of the force between a tip and a sample over a tip‐sample distance range of 30–150 A. As an application, the force signal is used to maintain the tip‐sample spacing constant, so that profiling can be achieved with a spatial resolution of 50 A. A second scheme allows the simultaneous measurement of force and surface profile; this scheme has been used to obtain material‐dependent information from surfaces of electronic materials.

Magnetic imaging by ‘‘force microscopy’’ with 1000 Å resolution

We describe a new method for imaging magnetic fields with 1000 A resolution. The technique is based on using a force microscope to measure the magnetic force between a magnetized tip and the scanned surface. The method shows promise for the high‐resolution mapping of both static and dynamic magnetic fields.

High‐resolution magnetic imaging of domains in TbFe by force microscopy

High‐resolution images of domains written in a magnetic thin film have been obtained for the first time using force microscopy. The sample consisted of 500‐A‐thick Tb19Fe81 with magnetization of 109 emu/cm3. Micron‐sized magnetic domains were thermomagnetically written in the sample using a focused laser beam. Domain images were obtained by observing the magnetic interaction of the sample with a small vibrating magnetized iron tip. Typical observed force gradients were in the range 0.8×10−4–6×10−4 N/m and the forces were in the range 10−12–10−11 N. The spatial resolution of the technique was on the order of 1000 A. This was sufficient resolution to see irregularities in those laser written marks which were recorded using low bias field.

Lateral dopant profiling with 200 nm resolution by scanning capacitance microscopy

Measurement of dopant density in silicon with lateral resolution on the 200 nm scale has been demonstrated with a near‐field capacitance technique. The technique is based upon the measurement of local capacitance between a 100 nm tip and a semiconducting surface. Lateral dopant imaging is achieved by the measurement of the voltage‐dependent capacitance between tip and sample due to the depletion of carriers in the semiconductor, as the tip is scanned laterally over the surface. Measurements of dopant density have been demonstrated over a dopant range of 1015–1020 cm−3. Capacitance‐voltage measurements have been made on a submicrometer scale.

Scanning probe microscopy of thermal conductivity and subsurface properties

The past six years has seen a tremendous growth in scanned probe microscopies of various sorts. In this letter, we add a new capability to this family−mapping of thermal conductivity variations on a nanometer scale. We show how our new probe technique can be used to measure thermal conductivity of conductors and thin insulating films deposited on top of conductors. Our results also demonstrate for the first time, the capability of the technique to image subsurface details of samples. As the thermal conductivities of different materials can vary by over three orders of magnitude, we suggest this as an important new contrast mechanism for studying materials on the nanometer scale.

Scanning thermal profiler

Apparatus is provided for investigating surface structures irrespective of the materials involved. A fine scanning tip is heated to a steady state temperature at a location remote from the structure to be investigated. Thereupon, the scanning tip is moved to a position proximate to, but spaced from the structure. At the proximate position, the temperature variation from the steady state temperature is detected. The scanning tip is scanned across the surface sturcture with the aforesaid temperature variation maintained constant. Piezo electric drivers move the scanning tip both transversely of, and parallel to, the surface structure. Feedback control assures the proper transverse positioning of the scanning tip and voltages thereby generated replicate the surface structure to be investigated.

Optical data storage read out at 256 Gbits/in.2

A new form of read out for high density read-only memory is presented whereby a data density of 400 bits/μm2, corresponding to 256 Gbits/in.2, can be accessed at data rates in the tens of MHz range. The technique is based on detecting the modulation in light scattering from a sharp scattering object due to the dipole-dipole coupling between the probe and surface being scanned using a sensitive homodyne interferometer. Theoretical considerations indicate that data densities in the 100 Tbits/in.2 range could be accessed at data rates of 100 MHz using this technology.

Lateral dopant profiling in semiconductors by force microscopy using capacitive detection

Recently, high‐resolution mapping of dopant concentration has been demonstrated with the scanning capacitance microscope (SCM). Here, we demonstrate that a similar measurement can be made with the atomic force microscope using the previously demonstrated capacitive force sensing mode. By applying appropriate bias to the force tip, depletion‐induced capacitive variation is mapped over regions of varying dopant density. This method has a predicted sensitivity comparable to the SCM, and in addition allows imaging of trapped charge, as well as an independent measurement of the surface topography. Results of first‐order model calculations are presented which give estimates as to the limits in sensitivity and resolution of this method

Scattering spectroscopy of molecules at nanometer resolution

A new form of optical spectroscopy is demonstrated whereby the local scattering from the interaction between a nanometer size probe tip and a sample is measured as a function of wavelength. We show images of viruses and molecules at molecular spatial resolution and demonstrate how the image contrast varies with wavelength. To first approximation, the contrast as a function of wavelength varies in the same way as the local polarizability of the sample