November 05, 2018

crikey!

So... I was looking to start a blog and realised this one still existed from 2007, relating to undergraduate research.


September 08, 2007

more power Igor

The cold cathode ion gun needs a magnetic field which is provided by the big electromagnet surrounding the gun cylinder. Normally the power supply is a fixed 24V (or 20V) from one of the control boxes.

However, by winding up the electromagnet power a bit higher it's possible to achieve significantly higher ion flux rates (> 5 micro amps / cm2) at around 1 keV energy. The new 30V PSU works well.


August 17, 2007

Progress….

During the past few weeks, I have been running various simulations using the many layer Hydrodynamic and Boltzmann-Mermin dielectric functions, observing how changing the plasmon lifetime affects the model. Effect of changing Tau upon the 100 layer BM model with E0 = 6eV

Effect of changing tau upon the 100 layer Hydrodynamic model with E0 = 6eV

Aditionally, simulations have been performed to observe how the 100 layer models compare with each other at different energies

model vs model plot with tau = 30 fs

Model vs model plot with tau = 60 fs

The next stage of the project is to introduce a prameterised description of the plasmon lifetime. The first parameterisation is a simple exponential decay to the surface, involveing a decay length, a bulk plasmon lifetime and a surface plasmon lifetime.  


July 29, 2007

Sunday Supplement

Sunday machine status:

A.  MADGEneto - P(XPS) = 1.9E-10, P(BFG) = 8.0E-10

    P(FEC) = 1.4E-7 mbar... excellent Friday afternoon spannerwork!!!

B.  Magnusson - P(Side) = 9E-10mbar, P(Main) = 5E-10

    P(FEC) = 1.8E-8 mbar, added a bit of liquid N2

    Pd acetate cell temperature 101 deg C, filament 1.11 V and 2.5A

C.  Robb`s evaporator - Pirani 1.1E-1 mbar, Penning 3.5E-6 mbar

    Pd acetate still room temp., no change of appearance (still Co-op Hot curry powder)

mmmm... curry...


July 12, 2007

LEED images of GaAs (100)–S

The sample was prepared with the same procedures described earlier, i.e. passivation of sample surface. It was annealed at about 350 C overnight. The sample was then deposited Pd Acetate for an hour with the temperature 118-125 C. It is stored in a big container with nitrogen and ready for XPS, Mass Spec, SEM and EDX.

Energy = 183.3

01

Energy = 271.4

02

Energy = 272.1

03

Energy = 302.6

07


July 08, 2007

Nanostructuring InP (100)

An InP sample with the (100) plane exposed was prepared. The sample was attached to a sample plate using eutectic and Indium as a binding gent. It was then cleaned using acetone, DI water and drying with Nitrogen gas.

The surface was cleaned in situ in an ultra high vacuum (UHV) using the IBA process. It was first annealed overnight at temperature 340 deg C. LEED was carried out on the sample to test for purity of the surface. 3 spots were observed as opposed to the 4 expected, suggesting a slightly amorphous surface.

To clean the surface further, it was ion bombarded with Ar+ ions at a grazing angle with energy 1.8keV and a flux J=0.61µAcm-2, then flash annealed to 400 deg C. LEED experiments now showed 4 faint dots on the phosphorous screen. Another ion bombardment and flash anneal was used to clean it further, to no avail.

The InP (100) surface was then ion bombarded with 2.4keV Ar+ ions. A voltage of 26mV was detected on a plate just behind the sample plate. Using the equation

J = V/(RA) cm-2, V voltage, R resistance, A surface area of a test aperature.

a flux of J = 0.46µAcm-2 was obtained. Over a period of an hour, this equates to 1.04 x1016 ions, a relatively small dose.

Experiments on InP (100) carried out by Tan and Wee suggest that lower energies and large fluxes give optinal organisation in nanostructures [S. K. Tan and A. T. S. Wee, Self-Organised Nanodot Formation of InP(100), J. Vac. Sci. Techno, B24 (2006), 1444-1448]. However, a problem arises in that flux and energy are interdependent, so higher energies are needed for larger beam fluxes. Tan and Wee quote a flux of Ar+ ions between 5-20µAcm-2 at energies of 1keV. After 30 minutes, they obtained a dose of 2.62µAcm-2. These are considerably larger doses than that obtained in the Magnusson set up and at lower energies. Clearly a more stable ion gun would produce better beam doses.

(for some reason all images taken with AFM show just a blank screen when i tried transferring them from my USB stick :S)

First week

During the first week I spent most of my time trying to get acquainted with  the various codes I will be working with/modifying. These include various Fortran 90 codes designed to  implement first the Hydrodynamic and more recently the Boltzmann-Mermin dielectric functions in order to simulate electron energy losses. I also had a look at some Matlab codes used to calculate the space charge distribution by solving Poisson's equation using numerical integration. Running the Fortran code using the collisional Boltzmann dielectric function (ie with a complex omega) produces the graph below, with a pronounced plasmon loss peak.

EELS using Boltzmann dielectric function with collisional damping


July 06, 2007

Pd Acetate Arrival Rate

Using the equation: r = 3.51E+22 x P / (T x M)^0.5

Can work out the arrival rate of the molecule

Where T = Temperature in K, P = Pressure in torr, M = molecular weight (g/mol)

The following plot was Pd Acetate arrival rate and was calculated by the equation described above

Pd Acetate arrival rate

Reference: Modern Techniques of Surface Science, 2nd ed. 


July 05, 2007

Lab notes Week 5

Week 5

Obtained XPS spectra and learned how to interpret the spectra.

Learned how to use XPSPeak 4.0 and used the software to obtain peak areas.

But the area needs to be normalised by the normalisation factor:

Area/(Atomic Senstivity Factors x Scans x Dwell)

The following peaks have been assigned:

Pd (3d5/2) High Binding Energy (HBE): 342.1 Low Binding Energy (LBE): 333 Area (A): 6712.57 [XPS2]

As (2p3/2) HBE: 1361 LBE: 1350 A: 28721.36 [XPS4]

Ga (3d) HBE: 28.6 LBE: 23 A: 4504.161 [XPS5]

S (2p) HBE: 171 LBE: 161 A: 18270.02 [XPS5]

C (1s) HBE: 295 LBE: 285 A: 1851.9 [XPS1]

O (1s) HBE: 543 LBE: 530.9 A: 3014 [XPS3]


XPS of Pd Acetate on GaAs

Scans 2.0 Dwell 0.25 

XPS1

Scans 50.0 Dwell 0.10 

XPS2

Scans 5.0 Dwell 0.25 

XPS3

Scans 5.0 Dwell 0.25

XPS4

Scans 3.0 Dwell 0.1 

XPS5


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