A method for in-situ determination of the surface characteristics of conductive targets under vacuum, comprising the steps of: a) generating a low-pressure plasma in front of the surface of the target b) applying a voltage to the surface of the target c) orientating at least one light-sensitive detector at an angle θ relative to the perpendicular of the surface of the target d) measuring the intensity of the light emitted by the electrically neutral atoms generated by conversion from the ions which are accelerated out of the low-pressure plasma by the applied voltage towards the surface of the target and subsequently reflected thereon, and which thus exchange suitable charges with the surface to reach electrical neutrality e) measuring spectral lines from the Balmer series of the atoms reflected by the surface of the target, and Doppler shifts of these spectral lines to establish a value curve, comprising the wavelengths and the intensity of the light associated with each wavelength, which, as a result of Doppler shifts, comprises a blue-shifted wavelength range with smaller wavelengths than the wavelength λ 0 of the light emitted by atoms stationary relative to the detector, and such, comprising a red-shifted range with wavelengths greater than λ 0 f) determining the velocity v of the atoms which emit light of a wavelength λ from the value curve according to v = λ λ − λ 0 ⋅ c, where c denotes the speed of light, and therefrom, the respective kinetic energy E of the atoms according to E = 1 2 m 1 v 2, where m 1 denotes the respective mass of the reflected atoms g) determining the energy value E max as the smallest energy determined from the measured wavelengths, from which all values of the intensity of the value curve are greater than or equal to the intensity values of the base line of the detector signal h) establishing the mass m 2 of the atoms of the surface using the formula: E max = m 2 2 − m 1 2 sin 2 θ 1 / 2 − m 1 ⋅ cos θ m 1 + m 2 2 ⋅ E 0, where E 0 denotes the respective kinetic energy of the ions when impinging on the surface, which is equal to the absolute value of the applied voltage, and θ denotes the angle relative to the normal vector of the surface of the target or to the perpendicular of the surface of the target. a) generating a low-pressure plasma in front of the surface of the target b) applying a voltage to the surface of the target c) orientating at least one light-sensitive detector at an angle θ relative to the perpendicular of the surface of the target d) measuring the intensity of the light emitted by the electrically neutral atoms generated by conversion from the ions which are accelerated out of the low-pressure plasma by the applied voltage towards the surface of the target and subsequently reflected thereon, and which thus exchange suitable charges with the surface to reach electrical neutrality e) measuring spectral lines from the Balmer series of the atoms reflected by the surface of the target, and Doppler shifts of these spectral lines to establish a value curve, comprising the wavelengths and the intensity of the light associated with each wavelength, which, as a result of Doppler shifts, comprises a blue-shifted wavelength range with smaller wavelengths than the wavelength λ 0 of the light emitted by atoms stationary relative to the detector, and such, comprising a red-shifted range with wavelengths greater than λ 0 f) determining the velocity v of the atoms which emit light of a wavelength λ from the value curve according to v = λ λ − λ 0 ⋅ c, where c denotes the speed of light, and therefrom, the respective kinetic energy E of the atoms according to E = 1 2 m 1 v 2, where m 1 denotes the respective mass of the reflected atoms g) determining the energy value E max as the smallest energy determined from the measured wavelengths, from which all values of the intensity of the value curve are greater than or equal to the intensity values of the base line of the detector signal h) establishing the mass m 2 of the atoms of the surface using the formula: E max = m 2 2 − m 1 2 sin 2 θ 1 / 2 − m 1 ⋅ cos θ m 1 + m 2 2 ⋅ E 0, where E 0 denotes the respective kinetic energy of the ions when impinging on the surface, which is equal to the absolute value of the applied voltage, and θ denotes the angle relative to the normal vector of the surface of the target or to the perpendicular of the surface of the target.