FMT4302504_Aula_SPM-STM

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03 de novembro 
Técnicas de Caracterização de Materiais – 4302504 
 
 
2º Semestre de 2016 
 
Instituto de Física 
Universidade de São Paulo 
 
 
 
Professores: Antonio Domingues dos Santos 
 Manfredo H. Tabacniks 
 
 
Caracterização dos Materiais 
Energia / 
Momento 
Matéria 
 
Propriedade 
a ser 
caracterizada 
 
Interação 
matéria-
matéria, 
(ou 
radiação-
matéria) 
Detectam-
se forças 
ou corrente 
elétrica (ou 
intensidade 
luminosa) 
Energia / 
Momento 
Matéria 
•Microscopias de Sonda Local 
 (SPM) 
Nature Nanotechnology, 1 (2006) 3 
+ 
Caracterização dos Materiais SPM 
Interação Ponta-Amostra 
Microscópio de tunelamento 
eletrônico (STM) 
Caracterização dos Materiais 
SPM 
Interação Ponta-Amostra 
Microscópio de tunelamento 
eletrônico (STM) 
Caracterização dos Materiais 
SPM 
Interação Ponta-Amostra 
Microscópio de tunelamento 
eletrônico (STM) 
Caracterização dos Materiais 
SPM 
Interação Ponta-Amostra 
Microscópio de tunelamento 
eletrônico (STM) 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Corrente Constante 
 
The tunnel currents registered in the course 
of the measurement are sufficiently small - up 
to 0.03 nA (with a special STM head - up to 
0.01 nA), so it is possible to investigate also 
low conductivity surfaces, in particular 
biological objects. 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/constant-current-mode 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Altura Constante 
 
In Constant Height mode (CHM) of operation the 
scanner of STM moves the tip only in plane, so that 
current between the tip and the sample surface 
visualizes the sample relief. Because in this mode 
the adjusting of the surface height is not needed a 
higher scan speed can be obtained. CHM can only 
be applied if the sample surface is very flat, because 
surface corrugations higher than 5-10 A will cause 
the tip to crash. The weak feedback is still present to 
maintain a constant average tip-sample distance. As 
the information on the surface structure is obtained 
via the current, a direct gauging of height 
differences is no longer possible.. 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/constant-height-mode 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Altura de Barreira 
 
The LBH image is obtained by measuring point by 
point the logarithmic change in the tunneling current 
with respect to the change in the gap separation, 
that is, the slope of log I vs. z. In the LBH 
measurement, the tip-sample distance is modulated 
sinusoidally by an additional AC voltage applied to 
the feedback signal for the z-axis piezodevice 
attached to the tip. The modulation period is chosen 
to be much shorter than the time constant of the 
feedback loop in the STM. 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/barrier-height-imaging 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Densidade de Estados 
 
LDOS determining can also help to distinguish 
chemical nature of the surface atoms. LDOS 
acquisition is provided simultaneously with the STM 
images obtaining. During scanning the Bias Voltage 
is modulated on the value dU, the modulation period 
is chosen to be much shorter than the time constant 
of the feedback loop in the STM. 
 
Suitable modulation of tunnel current dI is 
measured, divided by dU and presented as LDOS 
image. On Example the topography and LDOS image 
of HOPG sample are presented. 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/density-of-states-imaging 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Espectroscopia I(z) 
 
The I(z) Spectroscopy is related to LBH 
spectroscopy and can be used for providing an 
information about the z-dependence of the 
microscopic work function of the surface. Next 
important use of the I(z) Spectroscopy is concerned 
with for testing of the STM tip quality. 
The tunneling current IT in STM exponentially decays 
with the tip-sample separation z . 
 
In the I(z) Spectroscopy, we measure the tunnel 
current versus tip-sample separation at each pixel of 
an STM image. For Uav = 1 eV, 2k = 1.025 A
-1eV-1. 
 
Sharp I(z) dependence helps in determining of tip 
quality. As is empirically established if tunnel 
current IT drop to one-half with Z < 3 A the tip is 
considered to be very good, if with Z < 10 A, then 
using this tip it is possible to have an atomic 
resolution on HOPG. If this takes place with Z > 20 A 
this tip should not be used and must be replaced. 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/iz-spectroscopy 
Caracterização dos Materiais 
SPM 
Modos de Operação 
Microscópio de tunelamento 
eletrônico (STM) 
Modo de Espectroscopia I(V) ou CITS 
 
In I(V) Spectroscopy (or Current Imaging Tunneling 
Spectroscopy, CITS) a normal topographic image is 
acquired at fixed Io and Vo. At each point in the 
image feedback loop is interrupted and the bias 
voltage is set to a series of voltages Vi and the 
tunneling current Ii is recorded. The voltage is then 
returned to Vo and the feedback loop is turned back 
on. Each I-V spectra can be acquired in a few 
milliseconds so there is no appreciable drift in the 
tip position. 
 
This procedure generates a complete current image 
Ii(x,y) at each voltage Vi in addition to the 
topographic image z(x,y)|VoIo. 
CITS data can be used to calculate a current 
difference image DIVi,Vj(x,y) where Vi and Vj bracket a 
particular surface state, producing an atomic 
resolved, real space image of a surface state. 
 
This technique, for example can be used in UHV to 
image filled ad-atom states or the dangling bond 
states for silicon reconstructions. 
 
G. Binnig and H. Rohrer: Surf. Sci. 126 (1983) 236. 
Rep. Prog. Phys. 55, 1165-1240 (1992). 
Ver o movie em 
http://www.ntmdt.com/spm-principles/view/iv-spectroscopy 
• Microscopia de tunelamento eletrônico 
Microscópio de tunelamento 
eletrônico (STM) 
Onda evanescente 
• Microscopia de tunelamento eletrônico 
Microscópio de tunelamento 
eletrônico (STM) 
• Microscopia de tunelamento eletrônico 
exemplos 
• Microscopia de tunelamento eletrônico 
exemplos 
• Microscopia de tunelamento eletrônico 
exemplos 
• Microscopia de tunelamento eletrônico 
exemplos 
• Microscopia de tunelamento eletrônico 
Exemplos de processos 
• Resolução e superresolução ótica 
O critério de Rayleigh estabelece para um microscópio ótico tradicional a 
resolução: 
 
0,61
sin
x
n


 
onde, λ é o comprimento de onda da radiação, n é o 
índice de refração do meio e θ é a semi-largura 
angular definida pela abertura da lente objetiva. 
 Considerando –se que o módulo do vetor de onda é 
dado por: 
 
2 /k n  
Sendo a variação da componente x do momento dada 
por: 
 
2 sin (2 / )xp n    
Assim, o critério de Rayleigh se assemelha ao Princípio da 
Incerteza: 
xx p h  
Como, para uma onda homogênea, todas as suas componentes 
de k serão inferiores ou iguais a n2π/λ. 
Consequentemente, a resolução espacial em cada componente 
fica limitada ao critério de Rayleigh. 
• Resolução esuperresolução ótica 
Mas, se tivermos a componente z da onda com carater evanescente, o 
valor da componente de k nesta direção será imaginário. 
Assim, podemos escrever que: 
Com 
 
 
22 2 2 2 /x y zk k k n    
e 
 
O que permite uma melhor resolução lateral !!! 
(comparativamente ao que seria obtido com uma 
onda plana de mesmo comprimento de onda) 
2 0zk 
 
22 2 2 /x yk k n   
Portanto, Δpx e Δpy ↑ 
 e Δx e Δy ↓ 
 
Onda evanescente 
• Princípio da incerteza de Heisenberg 
Como o critério de Rayleigh e o Princípio da incerteza de Heisenberg são 
formalmente semelhantes, esperamos o mesmo comportamento para a 
resolução de imagens construídas com elétrons. 
Se os elétrons forem descritos por uma onda com uma 
componente evanescente, teremos uma resolução lateral 
melhor do que se trabalharmos com uma onda plana. 
Esta condição é exatamente atendida na situação de 
tunelamento eletrônico. 
Onda evanescente 
Comprimento de onda para partículas 
Não relativístico 
 
Relativístico: 
 
 
 
Microscopia Eletrônica de Varredura e de Transmissão 
Comprimento de onda para radiação eletromagnética 
Desde 10-14 m (raios ) até ~km (rádiofrequência) 
/hc E 
/h p 
0 0/ 2 (1 / 2 )h m K K E  
E (eV) λ (nm) 
1x106 0,00122 
1x104 0,0122 
1x102 0,122 
1 1,22 STM 
Caracterização dos Materiais SPM 
Accuracy and Calibration 
 
Instrumental Factors. The performance of a scanning probe instrument is limited by a number of factors. One of these is the 
resolution of the mechanical components used to move the tip and measure its position. The sharpness and stability of the probe tip 
determine the area of contact and the reproducibility of imaging. Obviously, environmental vibrations must be controlled to a high 
degree. In addition, most positioners depend on piezoelectric drive, which is subject to problems of non-linearity and to overshoot 
during rapid movements. The major manufacturers of SPM equipment have made substantial improvements in mechanical and 
electronic design. These improvements and advanced electronic calibration routines result in measurements that are more linear and 
accurate than the early models. Mark VanLandingham (University of Delaware) has published a discussion of instrumental 
uncertainties on the Web. (http://www.me.udel.edu/~vanlandi/MTpaper.html) 
 
Accurately nanofabricated gratings are the basis for two and three-dimensional calibrations. Such calibration gratings and calibration 
software are commercially available. 
Probe-Related Image Distortions. At very high magnifications and high-relief sample surfaces, the mode of imaging and the geometry 
of the probe tip can influence the scanned image. Knowledge of the probe geometry then becomes important for interpretation of 
the image. 
 
To image individual atoms and molecules it is necessary for the tip-surface interaction to depend only on the nearest atom(s) of the 
tip. This occurs in scanning tunneling microscopy because the tunneling current passes only through the nearest atom of the 
tip. Tunneling current falls off very steeply with distance from the surface. In atomic force microscopy the tip-surface interaction 
forces fall off less steeply with distance. Thus an AFM probe responds to the average force of interaction for a number of tip atoms, 
depending on the sharpness of the tip. An AFM image does not show individual atoms, but rather an averaged surface. For ordered 
surfaces this will reflect the average unit cell. 
 
Probe Deconvolution (Image Restoration). Imaging very sharp vertical surfaces (surfaces with high relief) is also influenced by the 
sharpness of the tip. Only a tip with sufficient sharpness can properly image a given z-gradient. Some gradients will be steeper or 
sharper than any tip can be expected to image without artifact. False images are generated that reflect the self-image of the tip 
surface, rather than the object surface. Mathematical methods of tip deconvolution can be employed for image restoration. The 
effectiveness of these methods will depend on the specific characteristics of the sample and the probe tip. 
(http://www.mobot.org/jwcross/spm/Deconvolution.htm) 
http://www.me.udel.edu/~vanlandi/MTpaper.html
http://www.me.udel.edu/~vanlandi/MTpaper.html
http://www.mobot.org/jwcross/spm/spm-manufacturers.htm
http://www.mobot.org/jwcross/spm/spm-manufacturers.htm
http://www.mobot.org/jwcross/spm/spm-manufacturers.htm
Developments Industry Events 
1981 STM invented at IBM-Zurich by 
Binnig and Rohrer. 
 
1982 
First atomic resolution 
demonstrated by Binnig on Si(7x7) 
 
1984 First Near-field Optical Microscope 
is invented 
 Omicron is founded 
1985 Binnig, Gerber, and Quate develop 
the first AFM 
 
1986 Binnig and Rohrer share half the 
Nobel Prize in physics for the 
invention of the STM 
 
1987 
First Atomic resolution with the 
AFM demonstrated by T. Albrecht 
at Stanford 
Noncontact AFM introduced 
MFM invented 
 Digital Instruments is founded by 
Univ. of California - Santa Barbara 
researchers. 
1988 First commercial AFM available 
 
Park Scientific is founded by Stanford 
researchers 
1989 
 
Topometrix is founded 
 
Burleigh Instruments offers SPM 
systems 
1991 
 Microfabricated AFM probes are 
first introduced 
 
 
 First AFM probe company founded, 
Nanoprobe (later renamed 
Nanosensors) 
 
1992 Piezolevers are first introduced 
Shear-force detection type NSOM/SNOM 
first introduced 
 Quesant is founded 
1993 TappingMode® is first introduced. 
 
Molecular Imaging is founded by Arizona 
State Univ. researchers. 
1994 TappingMode® in fluids is first 
introduced 
 
1995 Nanonics is founded 
1996 MACMode® is introduced 
1997 
 
ThermoSpectra acquires Park Scientific 
WITec founded by Universität Ulm 
researchers 
Nanosurf founded by Universität Basel 
researchers 
Park Scientific Instruments Asia Founded 
(later renamed Park Systems) 
1998 
 
Veeco Instruments acquires Digital 
Instruments 
1999 
 
Asylum Research founded by former Digital 
Instruments employees 
JPK founded 
2001 
 
Veeco acquires ThermoMicroscopes, 
renaming it TM Microscopes. 
2002 
 
 Digital Instruments and TM Microscopes 
merged with Veeco Metrology Group. 
Nanoscience Instruments Founded 
2005 Agilent acquires Molecular Imaging Corp. 
2006 Ambios acquires Quesant Instrument Corp.