Direct observation of negative electron affinity in hydrogen-terminated diamond surfaces

Takeuchi, Daisuke; Kato, Hiromitsu; Ri, Gum-Chol; Yamada, Takatoshi; Vinod, Purayath Robert; Hwang, D. S.; Nebel, Christoph E.; Okushi, Hideyo; Yamasaki, Satoshi

doi:10.1063/1.1900925

Cited by 152 publications

(107 citation statements)

References 15 publications

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“…As an example, direct vacuum electron emission has been established from forward-biased diamond-based pin diodes; these devices could be employed in very high voltage (>10 kV) switches or TWT cathode designs (Figure 17). [49,255] Interest in using UWBG semiconductors for electron emission can be traced to early measurements of efficient electron emission from diamond surfaces stimulated by above-bandgap light. [256] The measurements were related to a negative electron affinity (NEA) of the hydrogen-terminated surface, and could be described by theoretical analysis of the dipole due to the CH bonding.…”

Section: Vacuum Electronicsmentioning

confidence: 99%

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Tsao

Chowdhury

Hollis

et al. 2017

Adv Elect Materials

1,051

463

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Section: Vacuum Electronicsmentioning

confidence: 99%

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Tsao

Chowdhury

Hollis

et al. 2017

Adv Elect Materials

1,051

463

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“…The surfaces of diamond exhibit one of the most relevant properties for electron emission applications in the nature of its electron affinity that can shift to negative values under certain surface terminations, most readily prepared utilizing a hydrogen passivation process (see Figure 3) (Pickett, 1994;Takeuchi et al, 2005).…”

Section: Properties Of Diamond As Wide Band-gap Semiconductormentioning

confidence: 99%

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Koeck

Nemanich

2017

Front. Mech. Eng.

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Thermionic energy conversion, a process that allows direct transformation of thermal to electrical energy, presents a means of efficient electrical power generation as the hot and cold side of the corresponding heat engine are separated by a vacuum gap. Conversion efficiencies approaching those of the Carnot cycle are possible if material parameters of the active elements at the converter, i.e., electron emitter or cathode and collector or anode, are optimized for operation in the desired temperature range. These parameters can be defined through the law of Richardson-Dushman that quantifies the ability of a material to release an electron current at a certain temperature as a function of the emission barrier or work function and the emission or Richardson constant. Engineering materials to defined parameter values presents the key challenge in constructing practical thermionic converters. The elevated temperature regime of operation presents a constraint that eliminates most semiconductors and identifies diamond, a wide band-gap semiconductor, as a suitable thermionic material through its unique material properties. For its surface, a configuration can be established, the negative electron affinity, that shifts the vacuum level below the conduction band minimum eliminating the surface barrier for electron emission. In addition, its ability to accept impurities as donor states allows materials engineering to control the work function and the emission constant. Singlecrystal diamond electrodes with nitrogen levels at 1.7 eV and phosphorus levels at 0.6 eV were prepared by plasma-enhanced chemical vapor deposition where the work function was controlled from 2.88 to 0.67 eV, one of the lowest thermionic work functions reported. This work function range was achieved through control of the doping concentration where a relation to the amount of band bending emerged. Upward band bending that contributed to the work function was attributed to surface states where lower doped homoepitaxial films exhibited a surface state density of ∼3 × 10 11 cm −2 . With these optimized doped diamond electrodes, highly efficient thermionic converters are feasible with a Schottky barrier at the diamond collector contact mitigated through operation at elevated temperatures.

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“…However, the O-termination is not suitable for electroanalysis because of its low electron transfer rate [28][29][30] and high surface pollution derived from its hydrophilicity. In contrast, H-terminated BDD electrodes are suitable especially to electroanalysis because its low surface energy and a negative electron affinity [31][32][33] that can increase the rate of interface charge transfer, 28,34 thereby improving the sensitivity and detection limit of heavy metal ions analysis. Therefore, a BDD electrode with H-terminated surface should be a preferred electrode used for an electroanalysis.…”

mentioning

confidence: 99%

Investigation on Electrochemically Cathodic Polarization of Boron-Doped Diamond Electrodes and Its Influence on Lead Ions Analysis

Jiang

Liú

Jiang³

et al. 2014

J. Electrochem. Soc.

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The purpose of this paper is to further understand the dependence of the electrochemical activity of a boron-doped diamond (BDD) film electrode on its surface boron doping concentration and the pretreatment applied to its surface. An electrochemically cathodic polarization (−3 V vs. SCE) with a varying polarization duration (5-50 min) was carried separately out to three types of BDDs with a boron doping level of 700, 2500, 8000 ppm in 0.5 M H 2 SO 4 solution. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to evaluate surface activity of the BDDs with and without cathodic polarizations by using 1.0 mM Fe(CN) 6 3−/4− . Moreover, the surface activity of the polarized BDD electrodes was examined further by using anodic stripping voltammetry to detect a series of known concentrations of Pb 2+ . Our results indicated that the applied cathodic polarization significantly improved the surface activity of the as-received BDD, and exhibited more active effect on the surface of a higher boron doping level BDD compared to a lower boron doping level BDD, thereby improving the ability of the polarized BDDs to detect trace Pb(II) in aqueous solutions by anodic stripping voltammetry. Boron-doped diamond (BDD) electrodes not only exhibit similar chemical-stability to that obtained in graphite and glassy carbon electrodes, but also possess a rather wide electrochemical window (>3 V) and very low background current. Thus, it can be a promising replacement for dropping mercury electrode and classic other electrodes used in electrochemical sensors, 1 electrochemical synthesis, 2 electrooxidization decomposition of pollutants, 3 and electroanalysis. BDD is characterized by p-type semiconductor 5-9 and its electrochemical property is dependent strongly on boron doping level, 10 purity of the diamond, crystal orientation of grain 11 and the kind of atom/group bonded chemically to carbon atoms on the surface of diamond. Generally, the electrochemical property of BDD electrodes is primarily determined by the terminal type of the carbon atoms on the surface. The surface termination of an as-deposited BDD electrode is H-termination, 9,12-15 but the H-terminal surface is also converted to a O-terminated surface as it is exposed to air, 8 or an aqueous solution containing strong oxidizers, or subjected to an electrochemically anodic treatment. [16][17][18][19][20] The change in surface carbon atom termination alters undoubtedly the kinetics of redox reactions occurring on the BDD surface due to a distinct difference in electronic structure and surface energy between H-terminated and O-terminated surface. [21][22][23] Therefore, in order to make full use of the merits of BDD electrodes, it is important to make the type of surface carbon termination of a BDD electrode match up with application purposes.The O-termination surface of a BDD presents high surface energy and positive electron affinity, 22,24-26 thereby favoring hydroxyl radicals ( · OH) formation during anodic oxidation.27 Thus, this feature has be...

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Direct observation of negative electron affinity in hydrogen-terminated diamond surfaces

Cited by 152 publications

References 15 publications

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Ultrawide‐Bandgap Semiconductors: Research Opportunities and Challenges

Advances in Thermionic Energy Conversion through Single-Crystal n-Type Diamond

Investigation on Electrochemically Cathodic Polarization of Boron-Doped Diamond Electrodes and Its Influence on Lead Ions Analysis

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