KAWAKUBO Takashi

NAKANE Hideaki

English

中根,  英章

NAKANE, Hideaki

ナカネ, ヒデアキ

KAWAKUBO, Takashi

川久保, 貴史

Muroran-IT Academic Resource Archive

電子源の仕事関数その他（別言語等）のタイトルPossibility of the Schottky emitter with lowwork function surface著者 NAKANE Hideaki, KAWAKUBO Takashijournal orpublication title真空ナノエレクトロニクスシンポジウム予稿集volume 16year 2019URL http://hdl.handle.net/10258/000101262019/11/71電子源の仕事関数Possibility of the Schottky emitter with low work function surfaceHideaki NAKANEMuroran Institute of TechnologyTakashi KAWAKUBONational Institute of Technology, Kagawa College2018/3/1   第16回真空ナノエレクトロニクスシンポジウム電界放射電流密度と陰極表面の仕事関数との関係 23/2)(7)(226 Α/cm1083.6exp1054.1  FtFSI yyφφ V/cmVF β  /cm151rβI : emission current [A]      S : emission area [cm2]      F : field strength [V/cm]f ：work function [eV]      β: cathode structure constant[1/cm]     V : voltage [V]r : tip radius [cm]Cathode tip○Fowler-Nordheim Ex.Background (1)熱電子電流密度と陰極表面の仕事関数との関係○Richardson Ex.ூௌ= AT 2exp(-f/kT) [A/cmଶ]2019/11/72Background (2)ZrO/W(100) Schottky emitter・Work function of W(100) bare surface is 4.6 eV.・But it can be reduced to 2.7 eV by heating it in oxygen ambient with slight layer of Zr. ・The lower the value of the work function is, the more electrons are emitted from the emitter. Our goal was to make lower work function emitter than ZrO/W(100).In this research,We measured the work function of W(100) modified by group Ⅲ, Ⅳ metal oxideby using 1. FEM (field emission microscope)2. Retarding method3. PEEM (photoemission electron microscope) We have tried to study the reducing work function mechanism andto search materials better than Zr oxide.Purpose 2019/11/731. Selection of materials for emitter modification (1) 1.1 Mechanism of reducing work functionP=(Eo-Ex)(Ro+Rx)Eo: Electro-negativity for oxygenEx: Electro-negativity for the metalRo: Ionic radius for oxygenRx: Ionic radius for the metal•Electric dipoles on a metal surface are believed to reduce the work function remarkably. •The dipole moment has a tight relation to the P value which is defined as followings:Pair Electro-negativity(Pauling)Ionic radius(nm) P valueSc -O 1.36 0.075 0.442Y -O 1.22 0.090 0.511La -O 1.10 0.103 0.564Ce -O 1.12 0.087 0.517Pr -O 1.13 0.099 0.547Nd -O 1.14 0.098 0.543Sm -O 1.17 0.096 0.531Tb -O 1.10 0.092 0.539Er -O 1.24 0.089 0.499Yb -O 1.10 0.087 0.495Lu -O 1.27 0.086 0.486Th -O 1.30 0.094 0.492Ti -O 1.54 0.086 0.429Zr -O 1.33 0.072 0.439Hf -O 1.30 0.071 0.447Table 1  P value1. Selection of materials for emitter modification (3) LanthanoidActinoidGroup ⅢGroup Ⅳ2019/11/741.2 Periodic table and selected materials1. Selection of materials for emitter modification (2) LanthanoidActinoid2. Method of work function measurement (1) 2.1 FEM (1) ○ The emitter fabrication1. <100>  or <110> directed tungsten wire is spot welded  to vertex of a heating loop.2. The sample is electro-chemically cleaned.3. The sample is electro-chemically sharpened. 4. Small quantity of metallic oxide powder is put on the shaft.Ceramic baseV-shaped tungsten heating loopTungsten needleMetallic oxide powderThe emitter sample2019/11/752. Method of work function measurement (2) 2.1 FEM (2) ○FEM procedure1. The sample was put on the ultrahighvacuum chamber at 10-7 Pa. 2. The sample was heated at 1200 to 2700 K for several minutes.3. When high voltage was applied betweenthe sample emitter and the anode), the emission pattern from the sample was projected on the phosphor screen.4.  After low work function surface is formed, total emission current is measured.Experimental setup2. Method of work function measurement (3) 2.1 FEM (3) 23/2)(7)(226 Α/cm1083.6exp1054.1  FtFSI yyφφ V/cmVF β  /cm151rβI : emission current [A]      S : emission area [cm2]      F : field strength [V/cm]φ: work function [eV]      β: cathode structure constant[1/cm]     V : voltage [V]r : tip radius [cm]   φββφ 262/372 1054.1ln11083.6ln SVVICathode tip○Fowler-Nordheim Plot2019/11/763. Experimental results (1) 3.1 FEM (1)A field emission pattern from before treated Sc-oxide/W emitter.A field emission pattern from after treated Sc-oxide/W emitter.・The emission pattern is changed to a two-fold symmetry with two bright spots after heating. ・The work function of Sc-oxide/W(100) sample was estimatedby using F-N plot. ○Sc – oxide /W emitterF-N Plot of Sc-oxide/W emitterThe slope = -25689The radius of the Sc-oxide/W emitterThe radius r=0.167 μm・The work function estimated from the slope of F-N plot and the radius of the sample. ・The work function was 2.7 eV.3. Experimental results (3) 3.1 FEM (3)○Sc – oxide /W emitter2019/11/77F-N Plot of Y-oxide/W emitterThe slope = −3.2 × 10ସThe radius of the Sc-oxide/W emitterThe radius r=0.2 μm・The work function estimated from the slope of F-N plot and the radius of the sample. ・The work function was 2.8 eV.3. Experimental results (2) 3.1 FEM (2)○Y – oxide /W emitter3. Experimental results (4) 3.1 FEM (4)Pair Electro-negativity(Pauling)Ionic radius(nm) P valueWork function (eV)FEM Retarding PEEMSc -O 1.36 0.075 0.442 2.7Y -O 1.22 0.090 0.511 2.0～3.1La -O 1.10 0.103 0.564 2.5, 2.9～3.3Ce -O 1.12 0.087 0.517 2.9～3.1Pr -O 1.13 0.099 0.547 2.5Nd -O 1.14 0.098 0.543 2.5Sm -O 1.17 0.096 0.531 3.4Tb -O 1.10 0.092 0.539 ×Er -O 1.24 0.089 0.499 2.4Yb -O 1.10 0.087 0.495Lu -O 1.27 0.086 0.486 2.6Th -O 1.30 0.094 0.492 2.7Ti -O 1.54 0.086 0.429 4.57Zr -O 1.33 0.072 0.439 2.7～2.9Hf -O 1.30 0.071 0.447Group ⅢGroup ⅣTable 2  Work function (FEM)2019/11/782. Method of work function measurement (4) 2.2 Retarding method (1)8 mm(100)0.3 mm(a) Experimental setup(b) Experimental sample （W(100) single crystalline disk）(a) (b)1. The first electron beam is hit the sample.2. The electrons in the sample is exited and shot as secondary electrons.3. The electron is collected at the collectorand analyzed by the lock-in amplifier and PC.2. Method of work function measurement (5) 2.2 Retarding method (2)2019/11/792. Method of work function measurement (6) 2.2 Retarding method (3)1. To clean the surface of the W(100) single crystalline disk sample, the sample is heated at 2200 K for 30 seconds in an ultra high vacuum chamber at 10-7 Pa. 2. Metal was deposited at several monolayers onto the W(100) sample in an ultra high vacuum chamber at 10-7 Pa. 3. The sample was heated at 1100 K for 5 minutes in oxygen ambient at 10-5 Pa, resulting in producing metallic oxide on the W(100) sample. Metal O21) 2) 3)4) 5)Electron beam Secondary  electronMeasure the work function2. Method of work function measurement (7) 2.2 Retarding method (4)4. After evacuating the oxygen, the sample is heated for 10 seconds in an ultrahigh vacuum at 10-7 Pa. The heating temperature is raised from 1100 K to 2200 K at an interval of 100 K. 5. The work function of the sample is measured just after every flash heating.2019/11/7103. Experimental results (4) 3.2 Retarding method (1)○Y – oxide /W(100)2.5 eV2.2 eV・ The lowest work function of the sample is measured just after flash heating at 1900 K.4.6 eV3. Experimental results (5) 3.2 Retarding method (2)Pair Electro-negativity(Pauling)Ionic radius(nm) P valueWork function (eV)FEM Retarding PEEMSc -O 1.36 0.075 0.442 2.7Y -O 1.22 0.090 0.511 2.0～3.1 2.2La -O 1.10 0.103 0.564 2.5, 2.9～3.3Ce -O 1.12 0.087 0.517 2.9～3.1Pr -O 1.13 0.099 0.547 2.5 2.7, 3.6Nd -O 1.14 0.098 0.543 2.5Sm -O 1.17 0.096 0.531 3.4Tb -O 1.10 0.092 0.539 ×Er -O 1.24 0.089 0.499 2.4Yb -O 1.10 0.087 0.495Lu -O 1.27 0.086 0.486 2.6Th -O 1.30 0.094 0.492 2.7Ti -O 1.54 0.086 0.429 4.57Zr -O 1.33 0.072 0.439 2.7～2.9Hf -O 1.30 0.071 0.447Group ⅢGroup ⅣTable 3  Work function (Retarding method)2019/11/7112. Method of work function measurement (8) 2.3 PEEM (1)Experimental setupThe light is irradiated by the sample.The photoelectrons is amplified by MCP,and projected on the screen.The image is captured by the CCD camera,and analyzed by the PC.The wavelength of the light is selected by the interference filter.1.  Metallic oxide powder was put on the W(100) single crystal surface, after the sample was introduced in an ultrahigh vacuum chamber at 10-7 Pa. 2. The sample was flash heated at 2100 K, afterward the sample was irradiated by a selected wave length light with the interference filter. The photoemission pattern was obtained by PEEM system. 3. The work function of the sample was estimated by using with Fowler plot that was produced from the brightness of the photoemission pattern.It is possible to estimate the intrinsic work function, because the work function is essentially defined by photoelectric effect.2. Method of work function measurement (9) 2.3 PEEM (2)2019/11/712ekTshiftfFowler plot from experimental results.= 2.5 eVMaterial constanth: Planck's constantk: Boltzmann's constante: elementary electron chargef: frequency of wavelengthT: sample temperature (absolute value)Jp: emission currentWork functionTheoretical curve as f=0 eVThe measured plotsThe work function is estimated from horizontal shift.3. Experimental results (6) 3.3 PEEM (1)○Nd – oxide /W(100)Pair Electro-negativity(Pauling)Ionic radius(nm) P valueWork function (eV)FEM Retarding PEEMSc -O 1.36 0.075 0.442 2.7 2.5Y -O 1.22 0.090 0.511 2.0～3.1 2.2 2.7～2.8La -O 1.10 0.103 0.564 2.5, 2.9～3.3 2.87～2.90Ce -O 1.12 0.087 0.517 2.9～3.1 2.44～2.50Pr -O 1.13 0.099 0.547 2.5 2.7, 3.6 3.11～3.14Nd -O 1.14 0.098 0.543 2.5 2.47Sm -O 1.17 0.096 0.531 3.4 3.34Tb -O 1.10 0.092 0.539 ×Er -O 1.24 0.089 0.499 2.4 2.65Yb -O 1.10 0.087 0.495 3.68Lu -O 1.27 0.086 0.486 2.6 2.52～2.56Th -O 1.30 0.094 0.492 2.7Ti -O 1.54 0.086 0.429 4.57Zr -O 1.33 0.072 0.439 2.7～2.9Hf -O 1.30 0.071 0.447 2.84～2.90Group ⅢGroup ⅣTable 4 Work function (PEEM)3. Experimental results (7) 3.3 PEEM (2)2019/11/713・The work function of the tungsten surface is successfully reduced modified by group Ⅲ and Ⅳ metallic oxide. 4. Summary3. Experimental results (9) 1999Emission microscope for a field emitter array.2019/11/7142019/11/71520022019/11/716

Possibility of the Schottky emitter with low work function surface

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Possibility of the Schottky emitter with low work function surface

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