hopg_ds

HOPG

Highly Oriented Pyrolitic Graphite (HOPG) for SPM applications

For obtaining critical Z resolution, atomic resolution, atomic smooth substrate for customer’s objects, and conductive samples for STM.

It’s a type of pure, highly laminar graphite used as an atomic-scale calibration standard for atomic force microscopy and scanning tunneling microscopy.

Such HOPG properties as atomic plane surface and good conductivity make it the best material for STM calibration and the excellent substrate for different samples. HOPG is a material that consists of many atomic layers of carbon highly oriented among each other. HOPG is manufactured at the temperature of 3273K and remains stable at the temperatures up to 2000°C in the inert environment. The parallelism of atomic layers is characterized by “mosaic spread angle”. The less this angle the higher the quality of HOPG is.

$22.00$414.00

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Specifications

ZYA Quality ZYB Quality ZYD Quality ZYH Quality
Working Side Single Sided, Double Sided
Top Working Layer Mosaic Spread 0.3-0.5 degree 0.6-1.0 degree 1.3-2.1 degree 2-5 degree
Available Sizes, mm3 7×7, 10×10 7×7, 10×10 10×10 7×7, 10×10
Available Thickness of working layer3 0.6mm (0.4-0.7)
1.0 mm (0.8-1.8)
1.5mm
2.0mm
0.6mm (0.4-0.7)
1.0 mm (0.8-1.8)
1.5mm
2.0mm
1.5mm
2.0mm
0.6mm (0.4-0.7)
1.0 mm (0.8-1.8)
1.5mm
2.0mm
Base Layer ~1 mm (not specified mosaic spread quality)
Double-sided HOPG can be used from both sides and its properties are not changed in depth.
For single-sided pieces, the non-working side is matte, glare-less and can’t be cleaved. The number of working side cleavages of single-sided pieces is limited in comparison with double sided substrate. The properties for single-sided pieces are changed in depth.
HOPG crystals are widely used as substrates in STM (Scanning Tunneling Microscopy). The most distinguishing features of HOPG which enable this application are a very smooth surface and electro conductivity.
HOPG has a layered structure which makes sample preparation very simple. By pressing a double-stick tape to a HOPG piece and peeling it off, one gets a fresh conductive surface which is very smooth. This surface can be examined in STM or serve as a substrate for other materials under investigation.
HOPG itself is an interesting object for STM investigations. One can measure the surface roughness, microscopic surface features, arrangement of the carbon atoms on the HOPG surface, etc. Besides, HOPG images at the atomic level can be used for calibrating STM for high-resolution imaging. 
Instructions

To clean and smooth the graphite sample, do the following:

  1. Stick a piece of the adhesive tape (slightly wider than the sample) on the surface of the graphite sample.
  2. Smooth it out to remove air bubbles.
  3. With an abrupt movement remove the adhesive tape together with the top layer of graphite. The molecular layers of graphite have a spalling angle in relation to the surface layer, at which the layers are easily removed. Therefore the smoothness of the surface will depend on the direction, in which you remove a layer. Find the best direction to obtain the smoothest surface and remember (or mark) it, to use it later for cleaning the surface of pyrolitic graphite samples.

Additional Information

HOPG Substrate Materials for Scanning Tunneling Microscopy and Atomic Force Microscopy

Introduction
HOPG, is a relatively new form of high purity carbon and provides microscopists with a renewable and smooth surface. Unlike mica, HOPG is completely non-polar, and for samples where elemental analysis will also be done, it provides a background with only carbon in the elemental signature. The extreme smoothness of HOPG gives results in a featureless background, except at atomic levels of resolution.

Lamellar structure
Graphite in general and HOPG in particular are described as consisting of a lamellar structure, like mica and other layered materials that are composed of stacked planes. All of these examples of lamellar structures have much stronger forces within the lateral planes than between the planes, thus explaining the characteristic cleaving properties of all of these materials.

Some interesting information about HOPG

Cleaving Properties– HOPG because of its layered structure cleaves almost like mica. The usual approach is to take a piece of tape, press it onto the flat surface, pull it off and the tape invariably takes with is a thin layer of HOPG. This freshly cleaved surface is what is used as sample substrate material. How many cleavings per sample? This is not easy to answer, but per a 2 mm thick block of the best grades (ZYA), it is reported that one can get 20-40 cleavings. We do not guarantee a fixed number of cleavings. For the lower level grades the number of cleavings per 2 mm thickness will be less, but again just how much less we can not predict with accuracy.

Basal Plane Image– In an atomic resolution scanning tunneling microscope image of the graphite structure of HOPG, there are two possible images. The image normally obtained looks like a close packed array; in this array each atom is surrounded by six nearest neighbors. The distance between any two of these atoms is 0.246 nm. Under ideal conditions, particularly if the probe tip is truly a single atom, you will see the “chicken wire” structure that shows the hexagonal rings that are the true structure of graphite; the center to center atomic distance in this image is 0.1415 nm. This distance in either case is an atomic property of carbon and it does not depend on the grade of graphite. The image shown here is the close packed array and that is the image obtained form the basal plane of HOPG under most circumstances.

Flatness/Roughness– The HOPG has a structure of polycrystals, the size of which varies, the maximum being 10 mm for the highest quality. The freshly cleaved surface consists of atomic steps, 0.2-0.3 nm and steps of several or dozens of atomic layers. The higher the quality, the less the roughness of the surface, and the smaller the number of such steps on a freshly cleaved surface.

Mosaic spread– This term is a measure of just how highly ordered is the HOPG. The lower the mosaic spread, the more highly ordered is the HOPG, resulting in a cleaved surface that exhibits virtually no steps. Lower mosaic spreads are also associated with higher prices. However, since the lower mosaic spread material is more “cleavable”, one usually realizes more “cleavings” from the more expensive material, so the increased cost is a bit less than it might first appear.

Columnar structure:
The structure is strictly columnar, that is, the columns run vertically within the flat slab of the material. The grain boundaries can be seen on the lateral surfaces. The mosaic spread is the angle of deviation of the grain’s boundary from this perpendicular axis (of the columnar structure).

Calibration in z direction:
The hills and valleys on a cleaved HOPG surface are not calibrated as to their height. However, the crystallographic planes do have a definite structure and the height of a single step is 0.34 nm. Reference: L. Pauling, The Nature of the Chemical Bond, p. 235, 3rd. Edition 1960.

You may find steps randomly as a result of the cleavage process. An alternative method is to create etch pits by oxidizing the surface in an oven in air.

High Purity– All HOPG grades have comparable purities and impurity levels are on the order of 10 ppm ash or better.

Thermal conductivity:
Because of the anisotropic nature of HOPG, the thermal conductivity is different in different directions. It is 1800Wt/C° along the basal plane, and 8-10Wt/C° in the direction perpendicular to the basal plane. Thermal conductivity is high for any type of HOPG. Heat transfer HOPG has the same thermal conductivity as other HOPG samples, but is cheaper. The thermal conductivity seems to be independent of HOPG grade.

Density of HOPG:
The density for all three grades is 2.27 g/cm-3.

Measurement side:
X-ray diffraction is done on only one of the two sides of each HOPG plate and the value obtained is the value reported. The two sides are not exactly the same, and there can be a slight asymmetry through the cross-section of each plate. When the HOPG is manufactured, one side ends up relatively flat looking and the other size somewhat “bubbly”. Believe it or not, the tightest mosaic spread is the side that is “bubbly”. The opposite side will be either the same mosaic spread or slightly less tight. The packaging is made so, that there is a tape on that “opposite” side so that there could never be any question as to which side is which.



Details Price QTY
GRHS/0.6-7mm
Material Quality:
Working Side:
Piece Thickness: 0.6mm
Piece Size:
$22.00
GRAS/0.6-7mm
Material Quality:
Working Side:
Piece Thickness: 0.6mm
Piece Size:
$106.00
GRBS/1.0-7mm
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$64.00
GRHS/1.0-7mm
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$37.00
GRBS/0.6-7mm
Material Quality:
Working Side:
Piece Thickness: 0.6mm
Piece Size:
$38.00
GRAS/1.0-7mm
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$176.00
GRDS_DS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$88.00
GRDS_DS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$106.00
GRDS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$39.00
GRDS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$47.00
GRDS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$58.00
GRBS_DS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$121.00
GRBS_DS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$154.00
GRBS_DS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$183.00
GRBS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$96.00
GRBS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$111.00
GRAS_DS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$275.00
GRAS_DS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$352.00
GRAS_DS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$414.00
GRHS_DS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$60.00
GRHS_DS/1.5
Material Quality:
Working Side:
Piece Thickness: 1.5mm
Piece Size:
$75.00
GRHS_DS/2.0
Material Quality:
Working Side:
Piece Thickness: 2.0mm
Piece Size:
$86.00
GRDS_DS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$70.00
GRBS/1.0
Material Quality:
Working Side:
Piece Thickness: 1.0mm
Piece Size:
$71.00