CAlogbook

= Welcome to Chris's logbook! = Two very good Images of a surface of Octanethiol on Au(111) 6-28-11AI toc 6-28-11AJ 7-24-11AM These images show in a detailed manner how the Octanethiol arranges itself on the surface of the gold. It arranges in rows of about four or five chains of Octanethiol and forms different sets of these five chains at a different angle from the others. My research, from the beginning of Summer 2011 until the end of Summer 2012, was based on the use of gold coated with Octanethiol.The goal of my research was to take scans of the surface of the gold coated with Octanethiol and when the scan would show a detailed enough surface, I would shoot the gold surface with a blue-violet laser (405 nm). Afterwards, I would re-scan the same area, or at least try to. To avoid the thermal expansion of the gold to the tip of the STM, we created a sample holder which houses a piezoelectric stack on top of it. By increasing or decreasing the voltage charged into the piezoelectric stack by a set of fifteen 9 volt batteries, I could increase or decrease the length of the piezoelectric stack by a few microns. This allowed me to scan with the piezoelectric stack charged with a certain voltage, then bring the voltage down to a low level so as to minimize movement of the sample holder and to increase the chances of scanning the same area. Over the last year, our results with this laser-based system have been few and far between. The summer of 2012 was devoted mostly to developing a new system which could heat the gold and still allow us to scan the same area afterwards. After many experiments with different sample holders and methods of heating, we finally developed a stable system. Our current system utilizes a resistor to heat the surface of the gold. The resistor is placed directly on top of the gold and clamped to the gold by the sample holder's clips. Then, the tip of the STM can scan through the hole that is supposed to be used to bolt the resistor down. There are two wires connected to the resistor which lead out of the box that houses the STM. The STM that we use now is also different from that of last year. It is more isolated from noise and generally works better. The two wires are soldered on the other end to banana plugs which can be plugged in to a power source. The power source is plugged into a wall outlet. The wall outlet has the electric potential to deliver 12 Volts. The power system regulates it to 5 Volts and, after that, it is connected in series with a rheostat which then goes to the resistor inside the STM. The rheostat allows for variable currents which can increase the rate at which we apply heat. Lower currents produce lower temperatures and higher currents produce higher temperatures. Typically after taking an image worth heating, I will retract the tip with the computer 15 steps. This allows for a decent amount of thermal expansion but also allows us to scan the same region afterwards. Once retracted, the heat is applied, usually between 3 and 10 seconds. Any time longer than 10 seconds usually results in a tip crash or a frying of the sample. We have had a great deal of success in being able to take before and after images of the same regions. Beginning with the 2012 school year, I have started to use gold samples coated with C-60 (Buckminsterfullerine), or more commonly known as Buckyballs This image shows the resistor clamped on top of the gold by the sample holder clips. The pink objects on the right are crimp connectors, which electrically connects the leads on the resistor to the wires that go to the power system. The crimp connectors are more durable than a comparable soldering joint, The tip is able to scan through the bolt hole pictured above. This image shows the sample holder in position inside the box. This is a picture of the electronics which control the functions of the STM. The first column from the left controls the X-slope and X-offset. The second column from the left controls the Y-slope and Y-offset. The third column controls the Z-offset. This is useful for preventing drift. The fourth column controls the gain applied to the system and the knob on the bottom of it controls the A/D gain. The fifth column controls the voltage bias and the fifth column controls the time/line of the scan. This box houses the power system which puts out variable currents through the rheostat. From this view, we see the connection to the wall outlet. Also, there is an on/off switch and a fuse to prevent the system from applying too much current. This image shows the two spots where the wires from the resistor are plugged in. The white is the hot wire and the red is the ground wire. The knob in this picture is what controls the amount of resistance in the rheostat. In this picture it is placed at lowest resistance to allow for the largest amount of heat in the shortest amount of time. . = Summer Research 2011 = =Junior Year(2011-2012)= = Summer Research 2012 = =Senior Year(2012-2013)=