Abstract

We demonstrate that polycrystalline multialkali Na₂KSb(Cs,Sb) photocathodes with negative effective electron affinity have mean transverse energies at room temperature about a factor of 2 lower than those of monocrystalline p-GaAs(Cs,O) photocathodes. The low MTE values arise from electron refraction at the interface between a small effective mass in Na₂KSb and free-electron mass in vacuum. At the NEA state, up to half of the photoelectrons are emitted in a narrow-angle cone with fractional MTE of 9 meV at room temperature. After annealing that changes the effective affinity from negative to positive, the Na₂KSb(Cs,Sb) photocathode reaches a record low subthermal total MTE of 18 meV at room temperature while retaining QE of about 10⁻².

Abstract

We demonstrate that polycrystalline multialkali Na₂KSb(Cs,Sb) photocathodes with negative effective electron affinity have mean transverse energies at room temperature about a factor of 2 lower than those of monocrystalline p-GaAs(Cs,O) photocathodes. The low MTE values arise from electron refraction at the interface between a small effective mass in Na₂KSb and free-electron mass in vacuum. At the NEA state, up to half of the photoelectrons are emitted in a narrow-angle cone with fractional MTE of 9 meV at room temperature. After annealing that changes the effective affinity from negative to positive, the Na₂KSb(Cs,Sb) photocathode reaches a record low subthermal total MTE of 18 meV at room temperature while retaining QE of about 10⁻².

Abstract

We demonstrate that polycrystalline multialkali Na₂KSb(Cs,Sb) photocathodes with negative effective electron affinity have mean transverse energies at room temperature about a factor of 2 lower than those of monocrystalline p-GaAs(Cs,O) photocathodes. The low MTE values arise from electron refraction at the interface between a small effective mass in Na₂KSb and free-electron mass in vacuum. At the NEA state, up to half of the photoelectrons are emitted in a narrow-angle cone with fractional MTE of 9 meV at room temperature. After annealing that changes the effective affinity from negative to positive, the Na₂KSb(Cs,Sb) photocathode reaches a record low subthermal total MTE of 18 meV at room temperature while retaining QE of about 10⁻².

Abstract

We demonstrate that polycrystalline multialkali Na₂KSb(Cs,Sb) photocathodes with negative effective electron affinity have mean transverse energies at room temperature about a factor of 2 lower than those of monocrystalline p-GaAs(Cs,O) photocathodes. The low MTE values arise from electron refraction at the interface between a small effective mass in Na₂KSb and free-electron mass in vacuum. At the NEA state, up to half of the photoelectrons are emitted in a narrow-angle cone with fractional MTE of 9 meV at room temperature. After annealing that changes the effective affinity from negative to positive, the Na₂KSb(Cs,Sb) photocathode reaches a record low subthermal total MTE of 18 meV at room temperature while retaining QE of about 10⁻².