Go to page

Bibliographic Metadata

Restriction-Information
 The document is publicly available on the WWW.
Links
Abstract (English)

In this work, various carbon, metallic and semiconductor nanostructures were fabricated within collaborations and systematically investigated for potential field emission (FE) cathode applications.

Various carbon-based cathodes were obtained by different chemical vapour deposition methods. Single-walled carbon nanotube (CNT) networks grown on n-Si substrates at ~150°C showed well-homogeneous FE with ~10⁴ emitting sites/cm² at low onset field Eon (1nA) ~2.5 V/μm. During the local measurements ∅ 150 μm sites yielded stable currents up to 0.2 mA. Integral measurements of the whole cathodes revealed fairly homogeneous FE resulting in at least 10 mA/cm². Arrays of entangled CNT bundles of ~2 μm height, 2-3 μm patch and 100, 10 and 5 μm pitch were grown on n-Si wafers with trimetallic Mo/Al/Ni layers. Highly efficient and well-aligned FE at Eon (1nA) ~15 V/μm was obtained from CNT arrays with a pitch of 100 μm, however, the highest current up to 0.5 mA at 400 V was achieved from a spot of 150 μm for cathodes with a pitch of 5 μm. Integral measurements of the whole cathodes showed fairly homogeneous FE at currents up to 4.4 A/cm². CNT columns of ∅=250 μm and different height (h = 70 or 350 μm) forming quadratic arrays with a pitch of 650 μm showed fairly aligned and efficient FE at comparatively low Eon (1nA) ~2 V/μm. Maximum current values up to 600 μA at 15 V/μm were achieved independently of the column height. The FE triode tests of single CNT columns yielded anode-cathode current ratio up to 97 % at a gate (anode) voltage of 247 (2500) V. Structuring of carbon nanowall (CNW) films was successfully performed with a laser for the optimization of their FE properties. Such cathodes exhibited fairly aligned and efficient FE at Eon (1nA) = 10-20 V/μm. Local FE measurements of selected CNW patches revealed maximum current values up to ~100 μA.

Mechanically stable and randomly distributed copper nanocones (Cu-NCs) were fabricated by ion-track template method. Depending on the process parameters, Cu-NCs of ~28 μm length, ~3 μm base, with different ~60-300 nm tip radius and number density were fabricated. The cathode with high number density of Cu-NCs (10⁷ cm-2) yielded stable currents up to 280 μA at 100 V/μm from an emission spot of 30 μm. In contrast, the cathodes with a triangular patch array (∅ 150 μm, 320 μm pitch) of less Cu-NCs (10⁵ cm-2) provided fairly homogeneous and well-aligned FE of all Cu-NC patches at much reduced Eon (1nA) <10 V/μm and demonstrated an average current of 30 μA/patch at 32 V/μm. The FE performance of the Cu-NC cathode was improved by a thin Au coating resulting in an average current of 151 μA at 50 V/μm. Integral FE measurements on the whole Cu-NC cathode showed fairly homogeneous FE at 8 A/cm².

Silicon technology is the most suitable for fabrication of highly-uniform arrays of bare p- and n-type Si tips. Rather homogeneous and well-aligned FE from all tips and stable currents up to ~0.1 (0.6) μA for p-(n-) type tips were achieved. In comparison, Au-coated n-type Si tips showed improved FE uniformity and at least 5 times higher current values (i.e. ~3 μA/tip), at ~30% higher extraction field though. P-Si tips showed a current saturation region of about 10 nA. In this region, emitters provide the highest current stability (<5%) and an optical current switching ratio of ~2.5.

Potential applications of the described above materials are discussed.

Stats