Electron Emission Due to Exciton Breakup from Negative Electron Affinity Diamond

Bandis, C.; Pate, Bradford B.

doi:10.1103/physrevlett.74.777

Cited by 115 publications

(80 citation statements)

References 15 publications

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“…Bandis et al energies than for the fully hydrogen-terminated surface. Generally we have done the plasma treat- [32] have analyzed this constraint for the diamond (111) surface and found that x must be less than ments for more than 1 h, always resulting in uniform terminated surfaces [17]. Agreement between −4.55 eV in order to satisfy the energy and k || -conservation.…”

Section: Resultsmentioning

confidence: 99%

NEA peak of the differently terminated and oriented diamond surfaces

et al. 1999

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The negative electron affinity (NEA) peak of differently terminated and oriented diamond surfaces is investigated by means of ultraviolet photoemission spectroscopy. Electron emission measurements in the range below the conduction band minimum (CBM ) up to the vacuum level E vac permit the quantitative calculation of the upper limit of the NEA value. The inelastic scattering at the surface to the vacuum interface and the emission of electrons from the unoccupied surface states, situated in the band gap, are the mechanisms responsible for explaining this below CBM emission. All the H-terminated diamond surfaces present NEA. However, the characteristic NEA peak observed in the spectra is only detected for the (100)-(2×1):H surface and to a lesser extent for the (110)-(1×1):H surface, while it is absent for the (111)-(1×1):H surface because of the k || -conservation in the photoemission process.

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Section: Resultsmentioning

confidence: 99%

NEA peak of the differently terminated and oriented diamond surfaces

et al. 1999

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“…However, no information about NEA emission was acquired. A PES study on H:C[111] [6,8] using an incoherent light source with photon energies between 5 and 6 eV suggested a mechanism of phonon assisted exciton desorption, though the relation between emission from the [111] and [100] surfaces is unclear.The present ARPES experiments were performed at beamline U13UB of the National Synchrotron Light Source. Synchrotron (SR) based photoemission was carried out at 16 eV photon energy.…”

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confidence: 99%

“…Under low energy laser excitation this process occurs in the bulk of the sample. Because the CBM lies at a large absolute value of k || in the first Brillouin zone [16], very low energy emission of electrons from the sample surface, from the CBM, is kinematically inhibited [12] [6]. Direct emission of valence band electrons at low k || is suppressed by the absence of a well defined free electron final state.…”

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confidence: 99%

Properties of Hydrogen Terminated Diamond as a Photocathode

et al. 2011

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Electron emission from the negative electron affinity (NEA) surface of hydrogen terminated, boron doped diamond in the [100] orientation is investigated using angle resolved photoemission spectroscopy (ARPES). ARPES measurements using 16 eV synchrotron and 6 eV laser light are compared and found to show a catastrophic failure of the sudden approximation. While the high energy photoemission is found to yield little information regarding the NEA, low energy laser ARPES reveals for the first time that the NEA results from a novel Franck-Condon mechanism coupling electrons in the conduction band to the vacuum. The result opens the door to development of a new class of NEA electron emitters based on this effect.The electron affinity of a semiconductor surface is defined as χ ≡ E vac − E CBM where E vac is the "binding energy" of the vacuum level and E CBM is that of the conduction band minimum. Semiconductors for which the electron affinity is negative, meaning that E vac lies within the band gap, are prized for their unique potential as advanced electron emitters [1]. This is because a negative electron affinity (NEA) surface generally leads to very efficient emission of electrons into the vacuum. The emitted beams also often possess characteristics such as narrow energy spread and low emittance that are highly desirable for use in devices such as electron microscopes, photoinjectors for free electron lasers and the recently demonstrated diamond electron amplifier [2]. Most NEA surfaces are difficult to prepare and maintain, usually requiring the deposition of alkali metals on a specially prepared surface and which exhibit a subsequently short operational lifetime. The [100] surface of hydrogen terminated diamond (H:C[100]) has proven to be a remarkable exception. A χ on the order of -1 eV is repeatedly obtainable by a simple annealing procedure and the surface is robust against exposure to air and other contaminants. H:C[100] achieves this feat through the combination of its large band gap E g = 5.5 eV and robust H terminated surface, stable up to 800 o C, that drives E vac into the band gap.Interest in diamond has been recently rekindled due to the increasing availability of economically viable, devicequality, synthetic crystals as well as the obvious advantages of functionalizing a material possessing such exceptional thermal, electrical and mechanical properties. It is therefore remarkable that no agreed upon mechanism for NEA emission from H:C[100] has been established. In the following Letter we present angle resolved photoemission spectroscopy (ARPES) measurements showing how H:C[100] attains a useful NEA surface by means of strong electron-optical phonon (e-ph) coupling and a breakdown of the sudden approximation. This mechanism is potentially germane to not only NEA emission but also to a range of recently demonstrated diamond based devices [2][3][4].The vast majority of PES experiments performed on H:C[100] have been carried out using photon energies well in excess of E g ([5, 6] for example). A notable e...

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“…Diamond films are also candidate field emission materials ( E M ) due to diamond's high thermal conductivity and low surface work function. 3 The large thermal conductivity of diamond enables the cathode to draw large currents and dissipate the heat generated by these currents. Although the high thermal conductivity and low work function are compelling reasons for using diamond as a field emission material, probably the most often invoked reason for pursuing diamond as a FEM is the negative electron affinity (NEA) property of specially-prepared diamond surfaces .495 Despite many of its material properties, there are few practical diamond devices (with the exception of particle detectors) available which exploit the electronic properties of diamond because of several limitations in diamond growth.…”

Section: Introduction Cmentioning

confidence: 99%

The chemistry of halogens on diamond: effects on growth and electron emission

Hsu¹,

Pan²,

Brown³

1997

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Portions of this ABSTRACTThe feasibility of diamond growth using halogenated precursors was studied in several diamond growth reactors. In a conventional microwave plasma reactor, diamond growth using the following gas mixtures was studied: CF4/H,, CH4/H,, CH,F/H,, and CH,Cl/H,. Both' the diamond growth measurements (film growth rate, film quality, etc.) and in-situ near-surface gas composition measurements demonstrated ineffective transport of halogen radicals to the diamond surface during the growth process. In order to transport radical halogen species to the diamond surface during growth, a flow-tube reactor was constructed which minimized gas phase reactions. In addition, the flow-tube reactor enabled pulsed gas transport to the diamond surface by fast-acting valves. Molecular beam mass spectroscopy was used to find conditions which resulted in atomic hydrogen and/or atomic fluorine transport to the growing diamond surface. Although such conditions were found, they required very low pressures (.5 Torr and below); these low pressures produce radical fluxes which are too low to sustain a reasonable diamond growth rate. Due to the limitations of both the conventional plasma reactor and the flow-tube reactor, the sequential reactor at Stanford University was modified to add a halogen-growth step to the conventional atomic hydrogerdatomic carbon diamond growth cycle. Since the atomic fluorine, atomic hydrogen, and atomic carbon environments are independent in the sequential reactor, the effect of fluorine on diamond growth could be studied independently of gas phase reactions. Although the diamond growth rate was increased by the use of fluorine (compared to growth without fluorine under similar conditions), the film quality was seen to deteriorate as well as the substrate surface. Moreover, materials incompatibilities with fluorine significantly limited the use of fluorine in this reactor.A diamond growth model incorporating both gas phase and surface reactions was developed for the halocarbon system concurrent with the film growth efforts. In this experiments done to understand fluorine interaction with diamond surfaces. In addition, fluorine modification of diamond surfaces after growth is used to prepare cesiated-diamond cathodes which have field emission characteristics that are both air stable and thermally stable (200°C).

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Electron Emission Due to Exciton Breakup from Negative Electron Affinity Diamond

Cited by 115 publications

References 15 publications

NEA peak of the differently terminated and oriented diamond surfaces

NEA peak of the differently terminated and oriented diamond surfaces

Properties of Hydrogen Terminated Diamond as a Photocathode

The chemistry of halogens on diamond: effects on growth and electron emission

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