Nitrogen doping of tetrahedral amorphous carbon films: Scanning tunneling spectroscopy

Abstract

Amorphous nitrogenated carbon films with nitrogen atomic concentration between 12% and 29% were deposited using a filtered cathodic vacuum arc and a Kaufman-type ion source. The surface topography of the samples has been investigated by scanning tunneling microscopy in ultrahigh vacuum, showing that the roughness of the film surface decreases with nitrogen concentration. Scanning tunneling spectroscopy is employed to understand the role of nitrogen in the change of the surface microstructure and electronic structure near the Fermi level. The tunneling current (I) -bias voltage (V) curve is flat at low bias regions indicating a finite gap for the sample with low ͑12%͒ nitrogen concentration. An increase of tunneling current and its nonlinearity along with the decrease of energy gap occurs in the samples with increase of N concentration. The observed surface density of states ͓(dI/dV)/(I/V)͔ has been fitted as a square-root function of bias voltage. An improvement of the quality of these fits in the films with the increase of nitrogen concentration suggests that a depletion of defect density of states near the Fermi level (E F ) takes place. These analyses could be attributed to the modification of the structure of amorphous carbon by a large concentration of nitrogen.

Effects of Sulfur Concentration on the Electron Field Emission Properties of Nanocrystalline Carbon Thin Films

“…The reduction in E. with sulfur concentration is plotted in Figure 4, which provides an inverse correlation between E, and sulfur concentration within the range of our study. Similar observations have also been found for nitrogen-doped amorphous carbon materials [20][21][22][23][24] and metal-oxide-semiconductor (MOS) structures by several authors [27][28][29].…”

“…While morphology on sulfur addition: (A and C) 2.0% the film grown with 100 ppm is quite CH 4 , no sulfur is incorporated in chamber, (B and D) similar to intrinsic material (n-C), one 2.0 % CH 4 , 500 ppm H 2 S. All of these samples are grown at substrate temperature of 900 TC. [22][23][24]. Figure 3.…”

Morphological, structural and electrical characterization of nanostructured vanadium–tin mixed oxide thin films

“…5(b)), so it is evident that in inert atmosphere the D component appear at 1.18 eV above the Fermi energy level and disappear when oxygen is adsorbed onto film surface. In addition we have estimated the energy gap determining the edges of the bands from the parabolic fitting of the normalized conductance intersecting the line with 0 tunnelling current [26]. The results are summarized in Table 2.…”

Electron field emission from nitrogen and sulfur-doped diamond-like carbon films deposited by simple electrochemical route

“…Unlike diamond, some forms of DLC can be doped n-type by the addition of nitrogen or phosphorous, and this increases their electron emission at low turn-on fields by raising their Fermi level and lowering the work function of the material. Recently, a great deal of interest arose from the experimental and theoretical findings that sulfur is a donor dopant in microcrystalline diamond [8], and it has the potential to enhance the electron field emission properties of carbon films by providing electrons close to the conduction band [9]. There are several reports on N doping to DLC films deposited by a variety of techniques, such as plasma enhanced chemical vapour deposition [10], filtered cathodic vacuum arc [11] etc., to enhance the emission current density at lower turnon fields than undoped DLC.…”