PURPOSE: To count free electrons with a sensitivity that is larger than that of a normal device by at least approximately three digits by converting an electron flow that passes through the sample of an electrical conductor and is measured to a free electron. CONSTITUTION: A chip 1 that is connected to a voltage source 18 for giving a known voltage U1 via a sample conductor 17 where current us measured us formed so that the tip is sharp near the limit, opposes a particle detector such as an electron multiplication part 4, and is arranged in a straight line with an opening 2 of an electrode 3. The chip 1 may be constituted, for example, by extremely sharp and pointed whiskers of tungsten that are terminated with only one atom at the tip. The tip 1, the electrode 3, and the electron multiplication part 4 are positioned inside the container 5 in ultra-high vacuum and the elements are connected to an electrical circuit outside the vacuum container 5 through proper holes 6, 7, and 8. Then, electrons that are discharged from the chip 1, are amplified by the electron amplification part 4, and are counted by an electronic counter 13 give the measured value of current that passes through a sample.
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