STM Sample Requirements, Preparation, Artifacts and Experiment Planning

A successful scanning tunneling microscopy experiment begins before the first scan. Sample conductivity, surface preparation, electrical contact, tip condition, vibration, drift, and operating setpoints determine whether the tunneling junction is stable and whether an image can be interpreted. This practical guide focuses on STM sample requirements, preparation, mode selection, artifacts, and experiment planning.

For the full explanation of quantum tunneling, instrument components, imaging modes, and spectroscopy, start with the comprehensive STM guide.

Can your sample be measured by STM?

• A continuous conductive path is required from the scanned surface to the instrument ground or bias connection.

• Conductors and many semiconductors are suitable; thick insulating layers usually prevent stable tunneling.

• Surface roughness must fit the scanner z range and approach safety margin.

• The surface must be mechanically stable and firmly mounted.

• Contamination, native oxide, adsorbed water, residue, or loose particles can destabilize the current.

• The required resolution determines how clean, flat, vibration-free, and thermally stable the experiment must be.

Sample preparation checklist

• Define the material, doping or conductivity, surface orientation, coating, and expected oxide or contamination.

• Choose cleaning or preparation methods compatible with the material and required environment.

• Create a reliable electrical contact without placing conductive paint, clips, or wire bonds in the scan path.

• Mount the sample flat and rigidly within the holder’s thickness and lateral-size limits.

• Avoid sharp protrusions that can crash the tip during approach or scanning.

• For air-sensitive surfaces, plan glovebox, vacuum transfer, inert gas, or in-situ preparation before choosing the instrument.

Choosing constant-current or constant-height mode

Use constant-current mode when

• The surface has moderate height variation.

• You want feedback-controlled tracking and lower crash risk.

• Scan speed can be traded for stable following of topography.

Use constant-height mode when

• The surface is sufficiently flat and the approach is well characterized.

• Faster acquisition or direct current contrast is required.

• The increased crash risk is acceptable and the instrument is stable.

Setpoint current and bias determine the tunneling conditions. Changing them can change contrast because STM responds to electronic structure as well as geometric height.

Planning STM spectroscopy

• Define bias range, current limit, sweep direction, dwell time, averaging, and whether feedback is disabled during the sweep.

• Choose positions from a stable image and record topography, current, and spectroscopy together.

• Check repeatability with multiple sweeps and locations.

• Account for preamplifier range, bandwidth, junction stability, and tip changes.

• Avoid overinterpreting differential-conductance data without suitable calibration and an electronic model.

Common STM artifacts and troubleshooting

• Double or repeated features: possible multi-apex tip; condition or replace the tip and rescan.

• Streaks or sudden contrast changes: tip change, contamination, feedback instability, or a loose sample.

• Wavy lines: mechanical vibration, acoustic coupling, electrical interference, or thermal drift.

• Flattened or distorted features: feedback gains or scan speed are poorly matched.

• No tunneling current: verify conductivity, contact, bias, preamplifier range, tip integrity, and approach.

• Frequent crashes: reduce roughness, improve navigation, check z range, slow approach, and confirm sample mounting.

• Image changes with scan direction: investigate drift, feedback lag, creep, or tip–sample interaction.

Information to provide when selecting an STM

• Sample material, conductivity, dimensions, roughness, and preparation method.

• Required scan area and expected feature height.

• Ambient, controlled gas, liquid, vacuum, or low-temperature environment.

• Constant-current, constant-height, current–voltage, or current–distance needs.

• Current range, bias range, noise target, and acquisition speed.

• Coarse positioning, optical navigation, vibration isolation, enclosure, and installation constraints.

• Training, automation, export, analysis, and integration requirements.

ezSTM planning notes

The current ezSTM page lists constant-current and constant-height imaging, current–voltage and current–distance spectroscopy, Pt/Ir tips, ultrasonic-motor approach, up to 5 mm XY coarse positioning, and a maximum sample thickness of 15 mm. It lists two current and scanner ranges without clear configuration labels, so these should be confirmed in the quotation.

View ezSTM.

STM is one member of the larger scanning probe microscopy family. Compare STM with AFM, MFM, KPFM, conductive AFM and other options in the SPM technique-selection hub.

Frequently asked questions

Can STM measure an oxidized metal surface?

It depends on oxide thickness, conductivity, defects, and contact. A sufficiently insulating oxide can prevent stable current even when the underlying metal is conductive.

How flat must an STM sample be?

It must fit within the scanner z range and approach margin. Atomic-resolution targets usually require much flatter and cleaner surfaces than routine nanoscale imaging.

How should the sample be grounded?

Use a low-resistance, mechanically stable connection compatible with the bias convention and preamplifier. Keep contact materials outside the scan path.

Why does an STM image change with bias?

Bias selects different electronic states that contribute to tunneling, so contrast can change even when physical topography is unchanged.

Request an STM experiment review

Send the sample material, conductivity, size, roughness, preparation, scan and spectroscopy requirements, environment, and installation constraints. An NMI engineer can review feasibility and prepare a configuration-specific quotation.