J. J. Hren

Electron emission from diamond coated silicon field emitters

Polycrystalline diamond thin films have been formed on single crystal silicon field emitters using bias‐enhanced nucleation in a microwave plasma chemical vapor deposition system. A diamond nucleation density greater than 1010/cm2 with small grain sizes (<25 nm) was achieved on the surfaces of silicon emitters with nanometer scale curvature. Field emission from these diamond coated silicon emitters exhibited significant enhancement compared to the pure Si emitters both in total emission current and stability. Using a Fowler–Nordheim analysis a very large effective emitting area of nearly 10−11 cm2 was obtained from the diamond coated Si emitters compared to that of uncoated Si emitters (10−16 cm2). This area was found to be comparable to the entire tip surface area.

Field emission from silicon and molybdenum tips coated with diamond powder by dielectrophoresis

Thin diamond layers have been formed on molybdenum and single‐crystal silicon field emitters using a dielectrophoresis coating method from a suspension of diamond powder in a nonconducting fluid. Transmission and scanning electron microscopy observation revealed a significant amount of diamond on the tips. The average thickness of the deposited diamond layer depended on the applied bias and the immersion time. Field emission from these diamond‐coated emitters exhibited significant enhancement compared to the pure emitters.

Field emission characteristics of diamond coated silicon field emitters

Single crystal silicon field emitters have been modified by surface deposition of diamond using bias‐enhanced microwave plasma chemical vapor deposition. Polycrystalline diamond with a high nucleation density (1010/cm2) and small grain size (<20 nm) was achieved on silicon field emitters. Field emission from these diamond coated emitters exhibited significant enhancement both in total emission current and stability compared to pure silicon emitters. A large effective emitting area comparable to the tip surface area was obtained from a Fowler–Nordheim analysis. The effective work function of the polycrystalline diamond coated emitter surface was found to be larger than that of a pure silicon emitter surface.

Energy distribution of field emitted electrons from diamond coated molybdenum tips

Field emission energy distribution (FEED) measurements were performed on Mo and diamond coated Mo tips under ultrahigh vacuum conditions to investigate the origin of field emitted electrons. Mo emitters were prepared by electrochemical etching and were subsequently coated with diamond powder by a dielectrophoretic procedure. Field emission energy spectra were taken on the same samples before and after diamond coating. In vacuo thermal annealing of coated samples was essential to obtain stable field emission. FEED data indicated that the field emission current originated from the diamond/vacuum interface, and that electrons were emitted from the conduction band minimum of diamond.

Field emission from diamond coated molybdenum field emitters

Diamond deposition onto single Mo field emitters was accomplished by two methods: microwave plasma chemical vapor deposition and a dielectrophoresis of diamond powder. Observation by transmission electron microscopy and scanning electron microscopy revealed a significant amount of deposition at the tips. The field emission characteristics were measured before and after diamond deposition on the same emitters. Field emission from diamond coated emitters yielded significant increases in emission current and lower Fowler–Nordheim slopes. We discuss a possible mechanism to explain current enhancement that depends primarily upon the Mo‐diamond interface.

“Standardization” of field emission measurements

Interest in field emission and field emission devices has been renewed in the last 5 yr. This increase has been due to work on several new materials systems, which have shown promising field emission (FE) behavior. In turn, this interest gives impetus to the search for new FE sources. In order to move the technology ahead at a faster pace, there is a need for common ground rules and a “standardization” of the data reported so that it can be compared directly in a meaningful way and thereby accelerate the development process. In this article key factors affecting the FE data will be discussed and several parameters are suggested to initiate the process of developing a set of “standardized” FE parameters. A correct, or at least consistent, determination of characteristics such as work function, emission area, and field enhancement form the basis for developing a framework to make meaningful comparisons between different sets of data.

Characterization of ultra-shallow p/sup +/-n junction diodes fabricated by 500-eV boron-ion implantation

Ultrashallow gated diodes have been fabricated using 500-eV boron-ion implantation into both Ge-preamorphized and crystalline silicon substrates. Junction depths following rapid thermal annealing (RTA) for 10 s at either 950 degrees C or 1050 degrees C were determined to be 60 and 80 nm, respectively. These are reportedly the shallowest junctions formed via ion implantation. Consideration of several parameters, e.g. reduced B/sup +/ channeling, increased activation, and reduced junction leakage current, lead to the selection of 15 keV as the optimal Ge preamorphization energy. Transmission electron microscope results indicated that an 850 degrees C/10-s RTA was sufficient to remove the majority of bulk defects resulting from the Ge implant. Resulting reverse leakage currents were as low as 1 nA/cm/sup 2/ for the 60-nm junctions and diode ideality factors for crystalline and preamorphized substrates ranged from 1.02 to 1.12. Even at RTA temperatures as low as 850 degrees C, the leakage current was only 11 nA/cm/sup 2/. The final junction depths were found to be approximately the same for both preamorphized and nonpreamorphized samples after annealing at 950 degrees C and 1050 degrees C. However, the preamorphized sample exhibited significantly improved dopant activation. >

Diamond coated Si and Mo field emitters: diamond thickness effect

Abstract Individual silicon and molybdenum field emitters were coated with synthetic high-pressure diamond particles by dielectrophoresis. A comparison of the field emission characteristics before and after coating showed significant shifts of the I - V curves depending on the thickness of the coatings. A model of emission through the diamond layer is proposed that depends primarily upon tunneling through the Schottky barrier into diamond, while assuming a negligible barrier to emission from the diamond surface into vacuum. This model yields a value of the “effective” work function in agreement with experimental measurements.

Electron emission from diamond nanoparticles on metal tips

Single-crystalline diamond nanoparticles (∼5 nm in scale) have been deposited onto molybdenum needles (with radii <100 nm), and their effects on field emission behavior were measured. Combined transmission electron microscopy observations, field emission measurements, and diamond depositions allowed for direct comparison of the effects of various amounts of nanodiamond coating on the field emission properties of a coated metal field emitter. In the limit, field emission from a single isolated diamond nanoparticle is compared here with that from an uncoated metal emitter and from a coating comprised of several layers of nanoparticles.

Modification of Si field emitter surfaces by chemical conversion to SiC

Silicon field emitters have been modified by coating with a thin SiC film through a chemical conversion process. Silicon carbide was formed on Si emitter surfaces by reacting with ethylene gas at temperatures between 850 and 950 °C using pressures as high as 5×10−3 Torr. The thickness of the coatings ranged from 2 to 500 nm, determined by a combination of reaction time, pressure, and temperature. Stable emission currents above 10 μA were measured from individual SiC coated emitters.