טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMoshe Tordjman
SubjectElectron Field Emission from Ultra Nano Crystalline Diamond
DepartmentDepartment of Physics
Supervisor Professor Emeritus Kalish Rafael


Abstract

Diamond is a unique material with outstanding physical and chemical properties. Among these, its surface exhibits a negative electron affinity when hydrogen terminated and when further exposed to humidity (H2O), transfer doping (TD) takes place leading to a two dimensional surface conductivity . These make diamond a material of choice for the study and application of electron emission processes.

  In this work we study the field emission of UNCD films which exhibit uncommon electron emission properties showing an extremely sharp turn on of the electron emission at a particular applied electric field and a reproducible hysteresis of the emission current.

  The samples are thin films of a high density of diamond nano grains (5-20nm) surrounded by tetrahedral amorphous carbon (ta-C) grown on quartz. The experimental results of Electron Field Emission (FE) from the UNCD sample with surface contact carried out under UHV show abrupt successive jumps followed by plateaux in the FE current. The FE current is sustained, when the field is reduced even at fields lower than the turn on field, when the voltage is ramped down. These FE data are repeatable, reversible and show a consistent hysteresis from the same emission spot. The temperature dependence of this phenomenon has been studied and found to change when the water layer is removed by heating.

  The unusual behavior found here is explained as being the result of the properties of the UNCD material, namely the effect of surface treatment (hydrogenation and exposure to air) of the outermost nano-grains and the composite structure of the UNCD layer namely being composed of diamond grains that are embedded in ta-C. The jumps and hysteresis in the FE and their dependence on the water layer presence are explained to be due to charge transfer between the nano diamond grains and the surrounding nano ta-C layers that can be modeled as being a heterostructure through which electrons are transferred to the emission sites.

  The novel observation of this work reveals a new outstanding phenomenon in the FE domain never reported before. These observations may find new technological applications.