Electron emission from ferroelectrics (FEE) is an unconventional electron emission effect. Methods of FEE excitation are quite different compared to classic electron emission from solids. Two kinds of FEE have been observed, “weak” and “strong.” “Weak” electron emission (current density 10−12–10−7 A/cm2) occurs from polar surfaces of ferroelectric materials in the ferroelectric phase only. A source of the electric field for “weak” FEE excitation is an uncompensated charge, generated by a deviation of macroscopic spontaneous polarization from its equilibrium state under a pyroelectric effect, piezoelectric effect, or polarization switching. The FEE is a tunneling emission current which screens uncompensated polarization charges. It is shown that the FEE is an effective tool for direct domain imaging and studies of electronic properties of ferroelectrics. “Strong” FEE, which is 10–12 orders of magnitude higher than “weak” FEE, achieves 100 A/cm2 and is plasma-assisted electron emission. Two modes of the sur...

Electron emission from ferroelectrics

Manipulating and dispensing liquids on the micrometre- and nanoscale is important in biotechnology and combinatorial chemistry, and also for patterning inorganic, organic and biological inks. Several methods for dispensing liquids exist, but many require complicated electrodes and high-voltage circuits. Here, we show a simple way to draw attolitre liquid droplets from one or multiple sessile drops or liquid film reservoirs using a pyroelectrohydrodynamic dispenser. Local pyroelectric forces, which are activated by scanning a hot tip or an infrared laser beam over a lithium niobate substrate, draw liquid droplets from the reservoir below the substrate, and deposit them on the underside of the lithium niobate substrate. The shooting direction is altered by moving the hot tip or laser to form various patterns at different angles and locations. Our system does not require electrodes, nozzles or circuits, and is expected to have many applications in biochemical assays and various transport and mixing processes.

Dispensing nano-pico droplets and liquid patterning by pyroelectrodynamic shooting

Many methods of reproducing nuclear fusion — the process that powers the Sun — at the table-top scale have been tried, but failed to convince. Remember ‘cold fusion’? More recently, fusion linked to sonoluminescence is still controversial. Now comes a claim from the labs of the University of California at Los Angeles of unequivocal evidence of nuclear fusion in a simple room-temperature experiment. They report that gently heating a pyroelectric crystal — material that becomes charged when heated — causes ionization of a surrounding deuterium gas. The ions bombard a deuterated solid target with such energy that a large neutron signal is detected, a hallmark of deuterium fusion. Though not a viable power source, ‘crystal fusion’ may find application as a generator of neutrons for imaging technology. While progress in fusion research continues with magnetic1 and inertial2 confinement, alternative approaches—such as Coulomb explosions of deuterium clusters3 and ultrafast laser–plasma interactions4—also provide insight into basic processes and technological applications. However, attempts to produce fusion in a room temperature solid-state setting, including ‘cold’ fusion5 and ‘bubble’ fusion6, have met with deep scepticism7. Here we report that gently heating a pyroelectric crystal in a deuterated atmosphere can generate fusion under desktop conditions. The electrostatic field of the crystal is used to generate and accelerate a deuteron beam (> 100 keV and >4 nA), which, upon striking a deuterated target, produces a neutron flux over 400 times the background level. The presence of neutrons from the reaction D + D → 3He (820 keV) + n (2.45 MeV) within the target is confirmed by pulse shape analysis and proton recoil spectroscopy. As further evidence for this fusion reaction, we use a novel time-of-flight technique to demonstrate the delayed coincidence between the outgoing α-particle and the neutron. Although the reported fusion is not useful in the power-producing sense, we anticipate that the system will find application as a simple palm-sized neutron generator.

Observation of nuclear fusion driven by a pyroelectric crystal

Fundamental aspects of energy dissipation in friction.

Proximity‐imaging techniques are used to observe thermally stimulated field emission (TSFE) from single‐domain and multidomain single crystals of LiNbO3. Experimental results are reported and the mechanism responsible for this emission is discussed.

Thermally stimulated field emission from pyroelectric LiNbO3

Using Channeltron‐type detectors and magnetic discrimination techniques, it has been shown that electrons, positive and negative ions, and photons are all emitted spontaneously while oxide‐covered metals such as Al and Ni are being deformed in a tensile mode in a vacuum of approximately 10−10 Torr in total darkness. For dense anodically grown Al2O3 films of a given thickness on high‐purity Al substrates, the emission yields of all charged particles and photons are found to exhibit identically the same strain dependence. The same applies to compact thermally grown NiO films on Ni. It is concluded from these and other observations that the entire emission spectrum is generated simultaneously as a result of the formation and propagation of cracks in the oxide film during the deformation process. The shortcomings of previously proposed models for this type of triboinduced emission are pointed out, and some alternative suggestions regarding the emission mechanism are offered.

Spontaneous emission of charged particles and photons during tensile deformation of oxide‐covered metals under ultrahigh‐vacuum conditions

An apparatus is described for the investigation of chemically stimulated, photostimulated and tribostimulated exoelectron emission. Emphasis was placed on tribostimulated emission from uniaxially deformed oxide-covered metals (aluminium, titanium and nickel). Experiments were performed in either ultra-high vacuum or a controlled atmosphere using single-particle counting techniques. The emission of positive and negative ions as well as of photons during the propagation of fracture cracks in the oxide is reported for the first time.

https://iopscience.iop.org/article/10.1088/0022-3735/10/10/025/pdf

Measurement of tribo-emission from oxide-covered metals

A simple exoelectron emission microscope is described, first images obtained from BeOceramic are reported, and potential applications of the device in surface characterization of a wide variety of solids are discussed.

B. Rosenblum

Papers

Thermally stimulated field emission from pyroelectric LiNbO3

Spontaneous emission of charged particles and photons during tensile deformation of oxide‐covered metals under ultrahigh‐vacuum conditions

Measurement of tribo-emission from oxide-covered metals

Imaging of surfaces with the exoelectron microscope