This article reviews the progress of atomic force microscopy in ultrahigh vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows us to image surfaces of conductors and insulators in vacuum with atomic resolution. The most widely used technique for atomic-resolution force microscopy in vacuum is frequency-modulation atomic force microscopy (FM-AFM). This technique, as well as other dynamic methods, is explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened our theoretical understanding of frequency-modulation atomic force microscopy. Consequently spatial resolution and ease of use have been increased dramatically. Vacuum atomic force microscopy opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.

https://hep.physics.utoronto.ca/WilliamTrischuk/courses/phy189/AFM_revmodphys.pdf

Advances in atomic force microscopy

Biomolecular motors such as F 1 –adenosine triphosphate synthase (F 1 -ATPase) and myosin are similar in size, and they generate forces compatible with currently producible nanoengineered structures. We have engineered individual biomolecular motors and nanoscale inorganic systems, and we describe their integration in a hybrid nanomechanical device powered by a biomolecular motor. The device consisted of three components: an engineered substrate, an F 1 -ATPase biomolecular motor, and fabricated nanopropellers. Rotation of the nanopropeller was initiated with 2 mM adenosine triphosphate and inhibited by sodium azide.

https://science.sciencemag.org/content/sci/290/5496/1555.full.pdf

Powering an Inorganic Nanodevice with a Biomolecular Motor

Field emission (FE) is based on the physical phenomenon of quantum tunneling, in which electrons are injected from the surface of materials into vacuum under the influence of an applied electric field. A variety of field emission cold cathode materials have been developed to date. In this review, we shall focus on several kinds of novel cold cathode materials that have been developed in the past decade. These include materials for microfabricated field-emitter arrays, diamond and related films, carbon nanotubes, other quasi one-dimensional nanomaterials and printable composite materials. In addition, cold cathode materials have a wide range of applications such as in flat panel displays, high-power vacuum electronic devices, microwave-generation devices, vacuum microelectronic devices and vacuum nanoelectronic devices. Applications are in consumer goods, military industries and also space technology. A comprehensive overview of the various applications is presented. Recently, recognizing the strong possibility that vacuum nanoelectronic devices using quasi one-dimensional nanomaterials, such as carbon nanotubes may emit electrons with driving voltages comparable to that of a solid-state device, there is a growing interest in novel applications of such devices. With such exciting opportunities, there is now a flurry of activities to explore applications far beyond those considered for the conventional hot cathodes that operate on thermionic emission. We shall discuss the details of a number of fascinating potential applications.

Novel cold cathode materials and applications

In this review/tutorial paper, we cover the history, physics, and current status of vacuum microelectronic devices. First we overview the performance requirements of vacuum microelectronic devices necessary for them to replace, or fill voids left by, solid state devices. Next we discuss the physical characteristics of micro-field-emission sources important to device applications. These characteristics include fundamental features, such as current-voltage data and noise, in addition to engineering considerations, such as life expectancy and procedures for tube assembly. We conclude with a review of a wide variety of demonstrated and proposed devices based on vacuum microelectronic principles, including electron guns, microwave tubes, and flat-panel displays. >

Vacuum microelectronic devices

Substrate preparation for reliable imaging of DNA molecules with the scanning force microscope.

Electron emitters in vacuum microelectronic devices need sharp tips in order to permit electron emission at moderate voltages A method has been found for preparing uniform silicon tips with a radius of curvature less than 1 nm These tips are formed by oxidation of 5‐μm‐high silicon cones through exploitation of a known oxidation inhibition of silicon at regions of high curvature

Formation of silicon tips with <1 nm radius

Field emission current was measured from arrays of wet chemically etched silicon cold-cathode diodes. Two types of cathode tips were measured both as-etched and after sharpening by low-temperature oxidation. The field enhancement increase resulting from tip sharpening is less than expected from simulation. The currents measured follow a Fowler-Nordheim characteristic and are temperature insensitive from 130 to 360 K. Turn-on voltage is near 4 V, a value much less than measured from most other field emission sources. With a 920-nm anode-cathode spacing, a minimum 0.2- mu A current per cathode was found. Telegraph noise of about 1% at 20 V was observed. These sharpened silicon tips are a viable cold cathode for vacuum microelectronics and other electron device applications. >

Structure and electrical characteristics of silicon field emission microelectronic devices

Gated silicon field emission cathodes have been fabricated by the self-aligned lift-off method. The addition of a gold gate not only simplifies processing, but also facilitates easy packaging and allows the placement of many devices on a single chip. Currents have been measured on 2500 tip arrays which follow Fowler-Nordheim characteristics over several decades. Field emission from these arrays begins at less than 20 V. Low frequency noise measurements exhibit spectral power density indices from 1.18 to 1.55. Single tip and small array devices are being characterized.

Low voltage silicon field emitters with gold gates

The spectral response and outgassing characteristics of the three new, low-voltage phosphors combustion synthesized and electrophoretically deposited for application in field-emission flatpanel displays, are presented. The phosphors, forming a candidate Red-Blue-Green (RGB) triplet are YAG:Eu, YAG:Tb and Y2SiO5:Ce. These cathodoluminescent materials are tested with electron-beam excitation at currents up to 50 x03BC;A within the 200-2000V (eg. "low-voltage") and 3000-8000V (eg. "medium voltage") ranges. The spectral coordinates, as compared with industrially-manufactured P22 phosphors in low voltage operation, are reasonable; however, there is considerable difference in the green coordinates, and the red and green materials show significant satellite intensities. Phosphor outgassing, as a function of time, is measured by a residual gas analyzer at fixed 50 gA beam current in the low-voltage range. We find that after two hours of excitation, levels of outgassed CO, CO2 and H2 stabilize to low values.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400198422

J.T. Trujillo

Papers

Formation of silicon tips with <1 nm radius

Structure and electrical characteristics of silicon field emission microelectronic devices

Low voltage silicon field emitters with gold gates

Characterization of Y2SiO5:Ce, YAG:Tb AND YAG:Eu RGB Phosphor Triplet for Field Emission Display Application